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Miscellaneous
Sat, 27 Feb 2010
Philadelphia Weekend Weather Forecast- Sat AM
The low pressure system that brought us the snow continues to rotate disturbances around its circulation center. These areas of moisture and vorticity may cause snow flurries and showers today and Sunday.
Sat 12/27: Considerable cloudiness, some breaks of sun. Snow showers likely. High 37.
Sun 12/28 Mostly cloudy, chance of snow showers. High 40.
Solar Climate Discussion (Updated 2/6): This past July and August (see post here) (and here), I suggested that this winter would be unusually cold due to a prolonged lull in solar activity. The sun is beginning to come out of a solar minimum, and there has finally been the long expected increase in solar activity signaling the real beginning of Solar Cycle 24. There are several sunspot areas, but the solar flux still hasn't taken off. It's still early in the cycle.
Total Solar Irradiance continues to be about 1 watt/m2 lower than it was during the peak of the last solar cycle, Solar Cycle 23, in April 2000.
As of early February, it looks like the solar cycle is providing the predicted colder than normal temperatures and the El Nino is providing the potent moisture rich southern jet stream. Continue to expect colder than normal temperatures into the spring.
posted: Feb 27 2010 at 7:55 am
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Fri, 26 Feb 2010Winter Weather Update- Fri 7:30 AM
The stacked upper/lower low pressure system remains near Long Island, rotating snow into our area. The storm will weaken as a result of becoming occluded (warm and cold sectors of the storm have rotated onto themselves). The experimental High Resolution Rapid Refresh model shows steady snows tapering after 12 PM today in Philadelphia, somewhat later to the south. Total accumulation likely to be 4-7 inches, depending upon where you measure it. High winds will continue through mid-afternoon and then reduce to moderate winds for tonight into tomorrow.
Circulation around this low will continue, occasionally rotating snow showers/flurries through our area through later today and even into Saturday.
Regular Philly Weekend Weather will return later today.
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posted: Feb 26 2010 at 7:42 am
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Thu, 25 Feb 2010Winter Weather Update- Thu 10:30 PM
No change with latest NAM data. 0.42 inches water to fall as snow before 1 PM Fri. High winds and below freezing temps. Snow showers linger into the afternoon and evening. The drive in the morning will be a challenge.
posted: Feb 25 2010 at 10:39 pm
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Winter Weather Update- Thurs 7 PM
Just a quick update:
No surprise that there hasn't been the sort of accumulations that were talked about at this time yesterday. Solar Insolation and warmer temps kept snow from accumulating. The news is saying "the real storm is just starting". True in terms of the cold and wind. GFS and NAM data have about 0.40 inches water falling as snow tonight into Friday morning, then tapering to snow showers during the afternoon. Likely accumulations will be 4-7 inches, although there is still uncertainty with the QPF value of 0.40 inches.
The big issue will be the high winds and ice. Power outages are likely. I'll update later this evening, about 9:40 PM
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posted: Feb 25 2010 at 6:57 pm
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Winter Weather Update- Thurs 7 AM
I'm beginning to think that the NAM model (with lesser snow amounts) and a lull in snow activity in the afternoon (as the main low stacks up in northern NJ) is going to be the better of the two models. The experimental High Resolution Rapid Refresh model supports this lull in snowfall during the afternoon.
In addition to the uncertainties of maximum precipitation, it appears that the thermal profiles of this storm may keep warmer temps at the surface. So while it will fall as snow, accumulations on roadways will be less than grassy surfaces. Still not able to give a final accumulation prediction; it will depend on whether you're measuring things on the driveway or the grass. But I'm leaning towards 4-7 inches and less on roads by Friday morning. Still a guess.
The biggest predictable problem with this storm will be the winds affecting trees with some heavy snow on branches. Winds pick up tonight. Trees may come down. Ice will be a problem early Friday morning.
So for today, heavy snow this morning, but driving will be doable. Snow tapers this afternoon, then picks up again this evening. The amount of snow this evening is still uncertain. It will be a difficult commute Friday morning.
Here's the issues with this storm which prevent a clear-cut forecast:
1. Model disparity- GFS and NAM are different.
2. Temperatures are going to be close to or above freezing. While the precip will fall as snow, it will be wet snow or may mix with sleet and rain. Trying to predict accumulations will be a guess at best.
3. "Insolation" (Solar infrared transmitted through the clouds) becomes an issue at this time of year. The sun is higher in the horizon and there's more thermal effects during the day on roads. This means that accumulations on grassy areas are often much larger than dark asphalt that absorbs heat. Road conditions during daylight hours are often better than expected.
4. The storm involves an upper closed low and a blocked jet flow. The models have significant trouble with locating areas of maximum precipitation with closed lows.
With these points in mind, here's what's expected to happen:
Deep low pressure system is expected to develop over NYC/ Northern NJ on Thursday. The low will be developing as a result of interaction between an upper low and a surface low. This system to undergo "explosive cyclogenesis" and retrograde (move from east to west) as the two lows become vertically stacked and the upper trough becomes negatively tilted. The models have been consistent with this developing feature. With closed lows, the distribution of precipitation is extremely difficult to pinpoint. It appears that the thermal profile of this storm (too warm at surface) will also be an issue.
This storm has more "known unknowns" and "unknown unknowns" than any recent storm. Expect interesting (and unpleasant) weather, high winds later. Bad commuting conditions Friday morning.
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posted: Feb 25 2010 at 7:09 am
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Wed, 24 Feb 2010Winter Weather Update- Wed 11:30 PM
Updates later today.
One more thing. The model output statistics (MOS) have temps above freezing at the surface for much of Thurs. Its possible that there will be much melting on roadways decreasing snow totals.
posted: Feb 24 2010 at 11:36 pm
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Winter Weather Update- Wed 10:45 PM
The GFS model early product data has became available.
The GFS model is consistent with itself, predicting fairly heavy snow starting before daybreak and continuing through Thursday night, tapering to snow showers on Friday. The GFS cranks out almost 1.30 inches of water, falling as wet snow. The GFS differs considerably with the NAM; the NAM has much lighter precip during Thursday, with a lull in the afternoon. Which is right?
Probably the GFS model, but maybe that neither model is correct. Unlike past storms, the models are likely not able to accurately capture the three dimensional structure of this sort of storm. This storm is a different animal. While the official range of about 6-12 inches for PHL is entirely reasonable, (higher amounts north), it could be much less and it could be much more. This storm could last longer into Friday. The most impressive aspect of this storm will be the winds, affecting power lines. Lack of confidence in snow totals with this forecast remains for the reasons below--.
1. The NAM and GFS differ.
2. There has been little model run consistency over the past few days between them.
3. Temperatures are going to be close to freezing. While the precip will fall as snow, it will be wet snow or may mix with sleet and rain. Trying to predict accumulations will be a guess at best.
4. "Insolation" (Solar infrared transmitted through the clouds) becomes an issue at this time of year. The sun is higher in the horizon and there's more thermal effects during the day on roads. This means that accumulations on grassy areas are often much larger than dark asphalt that absorbs heat. Road conditions during daylight hours are often better than expected.
5. The storm involves an upper closed low and a blocked jet flow. The models have significant trouble with locating areas of maximum precipitation with closed lows.
With these points in mind, here's what's expected to happen:
Deep low pressure system is expected to develop over NYC/ Northern NJ on Thursday. The low will be developing as a result of interaction between an upper low and a surface low. This system to undergo "explosive cyclogenesis" and retrograde (move from east to west) as the two lows become vertically stacked and the upper trough becomes negatively tilted. The models have been consistent with this developing feature. With closed lows, the distribution of precipitation is extremely difficult to pinpoint.
This storm has more "known unknowns" and "unknown unknowns" than any recent storm. I'm not even going to try to predict snow totals with this one. Expect interesting (and unpleasant) weather, high winds, on Thursday into Friday.
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posted: Feb 24 2010 at 10:53 pm
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Winter Weather Update- Wed 9:30 PM
The NAM model became available.
The NAM model still differs from the GFS model of earlier this afternoon. The NAM has light snow in the morning on Thursday, starting before daybreak, a lull in activity in the afternoon and more snow Thursday night. The GFS did not show the dry-slot lull in the afternoon; in fact, the GFS has much heavier snow in the morning and afternoon, through Thursday night. Both have the precip essentially ending during Friday morning with just light snow showers.
These differences do not surprise me. Unlike past storms, the models will likely not be able to accurately capture the three dimensional structure of this storm. This storm is a different animal. While the official range of about 6-12 inches for PHL is entirely reasonable, (much more north), it could be much less and it could be much more. Anyone making a prediction of amounts is guess here. This storm could last longer into Friday. Lack of confidence with this forecast remains for the reasons below.
An update again about 10:45 PM
The most important thing to get across is that this particular weather event is going to be the most difficult to predict of all the past storms. Here's the uncertainties:
1. The models aren't accurately capturing the short term. The NAM and GFS differ.
2. There has been little model run consistency over the past few days.
3. Temperatures are going to be close to freezing. While the precip will fall as snow, it will be wet snow or may mix with sleet and rain. Trying to predict accumulations will be a guess at best.
4. "Insolation" (Solar infrared transmitted through the clouds) becomes an issue at this time of year. The sun is higher in the horizon and there's more thermal effects during the day on roads. This means that accumulations on grassy areas are often much larger than dark asphalt that absorbs heat. Road conditions during daylight hours are often better than expected.
5. The storm involves an upper closed low and a blocked jet flow. The models have significant trouble with locating areas of maximum precipitation with closed lows.
With these points in mind, here's what's expected to happen:
Deep low pressure system is expected to develop over NYC/ Northern NJ on Thursday. The low will be developing as a result of interaction between an upper low and a surface low. This system to undergo "explosive cyclogenesis" and retrograde (move from east to west) as the two lows become vertically stacked and the upper trough becomes negatively tilted. The models have been consistent with this developing feature. With closed lows, the distribution of precipitation is extremely difficult to pinpoint.
This storm has more "known unknowns" and "unknown unknowns" than any recent storm. I'm not even going to try to predict snow totals with this one. Expect interesting (and unpleasant) weather, high winds, on Thursday into Friday.
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posted: Feb 24 2010 at 9:50 pm
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Winter Weather Update- Wed 11 AM
The new NAM and GFS models have become available. None of the uncertainties and unknowns that I wrote of in earlier posts about the this storm have changed. There remain differences in the NAM and GFS models.
Here are the current trends:
The precipitation starts during the early morning hours (before daybreak) on Thursday. The precipitation will be all snow, but early on, it may be a very wet snow, since temps are expected to be about 32. About 2-3 of inches is likely by rush hour Thursday morning. According to the GFS, the snow continues all the way through Thursday and Thursday night into Fri morning, taping about 7 AM on Friday. The GFS cranks out about 1.5 inches water. If this were a past storm, we'd be talking about 10-20 inches snow. High winds, wet grounds with snow may result in significant power outages.
The most important thing to get across is that this particular weather event is going to be the most difficult to predict of all the past storms. This forecast could be a bust. Here's the uncertainties:
1. The models aren't accurately capturing the short term. The NAM and GFS differ.
2. There has been little model run consistency over the past few days.
3. Temperatures are going to be close to freezing. While the precip will fall as snow, it will be wet snow or may mix with sleet and rain. Trying to predict accumulations will be a guess at best.
4. "Insolation" (Solar infrared transmitted through the clouds) becomes an issue at this time of year. The sun is higher in the horizon and there's more thermal effects during the day on roads. This means that accumulations on grassy areas are often much larger than dark asphalt that absorbs heat. Road conditions during daylight hours are often better than expected.
5. The storm involves an upper closed low and a blocked jet flow. The models have significant trouble with locating areas of maximum precipitation with closed lows.
With these points in mind, here's what's expected to happen:
Deep low pressure system is expected to develop over NYC/ Northern NJ on Thursday. The low will be developing as a result of interaction between an upper low and a surface low. This system to undergo "explosive cyclogenesis" and retrograde (move from east to west) as the two lows become vertically stacked and the upper trough becomes negatively tilted. The models have been consistent with this developing feature but exact location has been inconsistent.
This storm has more "known unknowns" and "unknown unknowns" than any recent storm. I'm not even going to try to predict snow totals with this one. Expect interesting (and unpleasant) weather, high winds, on Thursday into Friday.
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posted: Feb 24 2010 at 11:11 am
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Tue, 23 Feb 2010Winter Weather Update- Tues 9 PM
An unusual and interesting weather system continues to evolve for us on Thursday into Friday.
The most important thing to get across with this discussion is that this particular weather event is going to be the most difficult to predict of all the past storms. Here's why:
1. The models haven't accurately captured the amount of rain today; When the models aren't capturing the short term forecast, there is less confidence in the longer term.
2. The placement of the developing low continues to change significantly from model run to model run. The low is expected to now form even closer to Philadelphia than was previously expected.
3. Temperatures are going to be close to freezing. While the precip will fall as snow, it will be wet snow or may mix with sleet and rain. Trying to predict accumulations will be a guess at best.
4. Insolation (Solar infrared transmitted through the clouds) becomes an issue at this time of year. The sun is higher in the horizon and there's more thermal effects during the day on roads. This means that accumulations on grassy areas are often much larger than dark asphalt that absorbs heat.
5. The storm involves the interaction of an upper closed low and a blocked jet flow. The models have trouble with specifics of this sort of pattern.
With these points in mind, here's what's expected to happen:
Deep low pressure system is expected to develop over NYC/ Northern NJ on Thursday. The low will be developing as a result of interaction between an upper low and a surface low. This system to undergo "explosive cyclogenesis" and retrograde (move from east to west) as the two lows become vertically stacked and the upper trough becomes negatively tilted. The models have been consistent with this developing feature but exact location has been inconsistent.
Here are the current trends:
The low seems to be forming closer to us than previously expected. There is more deformation of the jet stream, bringing in warmer air on the east side of the storm. The GFS model is cranking out over an inch of water. The NAM has been also cranking out about an inch of water. It seems we may wake up to several inches of wet snow on Thursday morning. Significantly more accumulation is possible during the day.
This storm has more "known unknowns" and "unknown unknowns" than any recent storm. I'm not even going to try to predict snow totals with this one. Expect interesting (and unpleasant) weather on Thursday into Friday.
posted: Feb 23 2010 at 9:01 pm
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Mon, 22 Feb 2010Philadelphia Weather Outlook- Mon PM
The GFS model is showing snow for late Thursday into Friday morning. This is an unusual system and exact amounts are very uncertain. See my earlier note below:
A very interesting weather week, as a deep low pressure system is expected to develop over New England on Thursday through Saturday. An interaction between an upper low and a surface low will cause this system to undergo explosive cyclogenesis and retrograde from east to west as the two lows become vertically stacked and the upper trough becomes negatively tilted. The models have been consistent with this developing feature but exact location remains unclear.
As a result, very cold temperatures will return to our area. Very windy conditions will also develop during the same period. Depending on how far south and west this storm retrogrades and how large it becomes, we will either have snow showers or accumulating snow. Stay tuned.
Solar Climate Discussion (Updated 2/6): This past July and August (see post here) (and here), I suggested that this winter would be unusually cold due to a prolonged lull in solar activity. The sun is beginning to come out of a solar minimum, and there has finally been the long expected increase in solar activity signaling the real beginning of Solar Cycle 24. There are several sunspot areas, but the solar flux still hasn't taken off. It's still early in the cycle.
Total Solar Irradiance continues to be about 1 watt/m2 lower than it was during the peak of the last solar cycle, Solar Cycle 23, in April 2000.
As of early February, it looks like the solar cycle is providing the predicted colder than normal temperatures and the El Nino is providing the potent moisture rich southern jet stream. Continue to expect colder than normal temperatures into the spring.
posted: Feb 22 2010 at 7:30 pm
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Philadelphia Weather Outlook- Mon AM
A very interesting weather week, as a deep low pressure system is expected to develop over New England on Thursday through Saturday. An interaction between an upper low and a surface low will cause this system to undergo explosive cyclogenesis and retrograde from east to west as the two lows become vertically stacked and the upper trough becomes negatively tilted. The models have been consistent with this developing feature but exact location remains unclear.
As a result, very cold temperatures will return to our area. Very windy conditions will also develop during the same period. Depending on how far south and west this storm retrogrades and how large it becomes, we will either have snow showers or accumulating snow. Stay tuned.
Solar Climate Discussion (Updated 2/6): This past July and August (see post here) (and here), I suggested that this winter would be unusually cold due to a prolonged lull in solar activity. The sun is beginning to come out of a solar minimum, and there has finally been the long expected increase in solar activity signaling the real beginning of Solar Cycle 24. There are several sunspot areas, but the solar flux still hasn't taken off. It's still early in the cycle.
Total Solar Irradiance continues to be about 1 watt/m2 lower than it was during the peak of the last solar cycle, Solar Cycle 23, in April 2000.
As of early February, it looks like the solar cycle is providing the predicted colder than normal temperatures and the El Nino is providing the potent moisture rich southern jet stream. Continue to expect colder than normal temperatures into the spring.
posted: Feb 22 2010 at 7:45 am
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Sun, 21 Feb 2010Winter Weather Update- Sun PM
The NAM model has come in line with the GFS model for an all rain event for Monday night into Tuesday. This is more than fine, since we've had more than enough snow!
A large low pressure system winds up along the NE coastline Thursday into Friday, bringing very cold temps to our area and areas south. Right now, it looks like the low will be too far north to bring us much in the way of snow, but stay tuned.
Solar Climate Discussion (Updated 2/6): This past July and August (see post) (see post), I suggested that this winter would be unusually cold due to a prolonged lull in solar activity. The sun is beginning to come out of a solar minimum, and there has finally been the long expected increase in solar activity signaling the real beginning of Solar Cycle 24. There are several sunspot areas, but the solar flux still hasn't taken off. It's still early in the cycle.
Total Solar Irradiance continues to be about 1 watt/m2 lower than it was during the peak of the last solar cycle, Solar Cycle 23, in April 2000.
As of early February, it looks like the solar cycle is providing the predicted colder than normal temperatures and the El Nino is providing the potent moisture rich southern jet stream. Continue to expect colder than normal temperatures into the spring.
posted: Feb 21 2010 at 2:50 pm
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Sat, 20 Feb 2010Winter Weather Update- Sat PM
I've been watching models for the next weather event Monday into Tuesday. The GFS has been much warmer than the NAM, and it has been predicting rain.
The latest NAM model data has become available. It has rain, starting about 6 PM Monday night, but mixing with and changing to snow during the night time hours. Some wet snow accumulation is possible by Tuesday morning, about 1-3 inches, possibly more north and west.
Again, the GFS has been warmer and predicting an all-rain event, but stay tuned. The NAM did fairly well with the last storm.
posted: Feb 20 2010 at 9:40 pm
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Fri, 19 Feb 2010Philly Winter Weather Outlook- Fri PM
The the upper trough associated with a large dome of cold high pressure that has been with us since the end of January will maintain its hold through the weekend. High temps will be in the low 40s, the normal high is 45, yet it will feel warm relative to the past cold. An upper air disturbance will cause some cloudiness on Saturday.
The low pressure system expected to affect us on Monday into Monday night will likely be a rain event during the daytime hours, perhaps mixing with some wet snow during the night time hours. A more interesting pattern is suggested by the GFS model for later in the week, where another deep storm will wind up along the northeast US. A blocking pattern and closed low may result in a rain-->snow storm the end of the week. Too early to be sure, but it looks interesting.
Sat 2/20: Considerable cloudiness. High 40
Sun 2/21: Partly cloudy/sunny and cold. High 42.
Solar Climate Discussion (Updated 2/6): This past summer (see post), I suggested that this upcoming winter would be unusually cold due to a prolonged lull in solar activity. The sun is beginning to come out of a solar minimum, and there has finally been the long expected increase in solar activity signaling the real beginning of Solar Cycle 24. There are several sunspot areas, but the solar flux still hasn't taken off. It's still early in the cycle.
Total Solar Irradiance continues to be about 1 watt/m2 lower than it was during the peak of the last solar cycle, Solar Cycle 23, in April 2000.
As of early February, it looks like the solar cycle is providing the predicted colder than normal temperatures and the El Nino is providing the potent moisture rich southern jet stream. Continue to expect colder than normal temperatures into the spring.
posted: Feb 19 2010 at 7:31 pm
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Wed, 17 Feb 2010Philly Winter Weather Outlook- Wed AM
The large dome of cold high pressure that has been with us since the end of January will maintain its hold through the next week. While temps will get near 40, it's still below the average high of 45.
Sat 2/20: Sunny and cold. High 40
Sun 2/21: Partly cloudy/sunny and cold. High 41.
Solar Climate Discussion (Updated 2/6): This past summer (see post), I suggested that this upcoming winter would be unusually cold due to a prolonged lull in solar activity. The sun is beginning to come out of a solar minimum, and there has finally been the long expected increase in solar activity signaling the real beginning of Solar Cycle 24. There are several sunspot areas, but the solar flux still hasn't taken off. It's still early in the cycle.
Total Solar Irradiance continues to be about 1 watt/m2 lower than it was during the peak of the last solar cycle, Solar Cycle 23, in April 2000.
As of early February, it looks like the solar cycle is providing the predicted colder than normal temperatures and the El Nino is providing the potent moisture rich southern jet stream. Continue to expect colder than normal temperatures into the spring.
posted: Feb 17 2010 at 7:14 am
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Sun, 14 Feb 2010Winter Weather Update- Sun 2PM
Another low pressure system is expected to affect us Monday evening into early Tuesday. Latest GFS data has light snow starting after 7 PM, mixing with rain and then back to snow. Total QPF is about 0.45 inches water, but a warm tongue of air is expected to move in about 5000 feet and a brief change to rain is expected. Total accumulations will be about 2-4 inches with the lower amount most likely.
posted: Feb 14 2010 at 4:46 pm
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Fri, 12 Feb 2010Winter Weather Update- Fri 5 PM
So where are the updates? We lost our electrical power/heat during the storm Wednesday and been trying to catch up ever since. Hasn't been fun. You'd think I would be enjoying this, but I've had enough of this winter!
Just took a quick peek at the numbers for Monday's snow. Current QPF values are up to 0.59 inches water or about 6-9 inches. Should start late afternoon Monday with the heaviest snow during the evening hours. Hard to believe from an Alberta clipper, but this has been an unusual winter. The very cold weather was expected for this winter. Whether we would have much snow depended on other factors. The El Nino and the Solar Cycle minimum has provided all the ingredients.
I'll be returning to the Weekend Weather forecast shortly. Stay tuned.
posted: Feb 12 2010 at 5:10 pm
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Wed, 10 Feb 2010Winter Weather Update- Wed 11 AM
Latest GFS data still showing similar temps and QPF values as the NAM (0.90 inches water falling between 7 AM and 7PM)
The heaviest precipitation is supposed to occur before 1PM, so things gotta get going real soon if we're going to approach the amounts forecast by the models.
Temperatures at PHL airport have finally dropped to 32 and at NE PHL airport, it's 31 and at Wings Field, Blue Bell, it's still above freezing at 32.5.
The fact that so much precipitation this morning has fallen as sleet/freezing rain will significantly impact the snow totals. We may only get 5-7 more inches of snow before ending.
Getting the snow totals correct today is going to take as much luck as skill. And, as always will depend on where you're located. Assuming 5-7 more inches, I'm going to go with a total of 12-16 inches for PHL total. Whatever does fall will be heavy to shovel! Stay warm
posted: Feb 10 2010 at 11:11 am
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Winter Weather Update- Wed 9:15 AM
Again, the changeover to sleet wasn't predicted by either the GFS or NAM. Temperatures at 800-900 mb height were 1 degree above freezing instead of the predicted 0 C. The NAM did well with the QPF values, but not the temperatures.
Latest NAM data still showing about 0.90 inches water left to fall before ending about 6PM. The NAM drops the temperatures during the morning so that things should change back to snow. If temps cool down as expected, we can expect another 10 inches of snow, ending about 6 PM
I'll update when the GFS model comes out about 10:45.
posted: Feb 10 2010 at 9:37 am
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Winter Weather Update- Wed 8 AM
Temperatures at 5000 ft are warmer than predicted by any model. That's why we have freezing rain. Temps should fall again. But confidence in this forecast is currently not high.
I'll update when the GFS model comes out about 10:45.
posted: Feb 10 2010 at 8:29 am
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Tue, 09 Feb 2010Winter Weather Update- Tues 10:50 PM
The GFS model data just became available-- Total QPF is about 1.58 inches water. The GFS has the precip ending about 6-7 PM on Wednesday, earlier than the NAM.
So there are differences between the GFS model and the NAM model. The NAM is has 2.2 inches water and somewhat warmer. Both models have the temperatures at or just below freezing at the surface at or just below freezing up until 7000 feet. Most of the precipitation from the airport and north/west will be snow.
In past storms where there are model differences, the average of the two works well. So my updated total (with a low 1-10 or 1-12 snow ratio) is about 16-22 inches of heavy snow. I think my earlier forecast of much more, based exclusively on the NAM model, isn't going fly.
posted: Feb 09 2010 at 10:49 pm
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Winter Weather Update- Tues 9:30 PM
Correction: The NAM data was available early tonight. QPF values have increased to 2.2 inches water, which translates into 24-32 inches of heavy snow. The new NAM prolongs the snow into Wednesday evening.
I'll update when the GFS model comes out about 10:45.
posted: Feb 09 2010 at 9:37 pm
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Winter Weather Update- Tues PM
This morning's and afternoon NAM and GFS models have not changed appreciably from last night. Basically about 1.2 inches water. What is of interest is that temperatures are a little higher than previously predicted which may reduce snow totals. The snow will be denser and heavier to shovel.
I'll update when the new models come out about 10:45.
posted: Feb 09 2010 at 9:14 pm
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Winter Weather Update- Tues 7 AM
Last evening's models along with the 1 AM rerun of the NAM and GFS have come together on very similar forecasts of about 1.20 inches of water (QPF) falling as snow from Tuesday evening into very early Wednesday evening. Interestingly, the WRF (Weather Research Forecast model) has 1.96 inches water falling as snow, suggesting the possibility of a bigger storm.
While I had described some uncertainties about this storm last night, I'd have to say that with so much model consistency and continuity, this snow storm is a high confidence event. Temperatures for this storm will be closer to freezing, so the ratio of snow to water may be on the lower range of 10:1 or 12:1. That means a heavier snow to shovel than the last one. With current QPF values, a 12-24 inch snowfall is what we'll receive, with 15-18 inches most likely.
By the way, the heaviest snow will be falling before daybreak tomorrow and during the morning hours.
I'll be at work during the next model output later this morning, but I'll try to use my iPhone to update the website if expected snow totals change significantly.
posted: Feb 09 2010 at 7:07 am
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Mon, 08 Feb 2010Winter Weather Update- Mon PM [3]
Latest GFS data just became available. It is remarkably similar to the NAM. At daybreak on Wednesday, there will be about 6+ inches; by the end of the storm, about 12 -15 inches.
All of the uncertainties discussed in my previous discussion still apply.
Updates tonorrow.
posted: Feb 08 2010 at 11:00 pm
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Winter Weather Update- Mon PM
A complex low pressure system, the result of secondary low development off the of coast, will evolve from Tuesday evening through Wednesday evening. Differences in placement of the upper low pressure, along with exact speed of development and position of the secondary surface low, will make exact prediction of snow amounts this time around more complicated.
There is a general consensus that anywhere from 0.90-1.65 inches of water will fall in the general area as snow, but exact location of the moisture convergence may be difficult to pin down, with several models showing that a dry slot may occur over Philadelphia during the morning of Wednesday, with much of the heavy snow falling to our west and south. Additionally, temperatures will vary during the storm, so the ratio of snow to rain will be changing during the storm.
I agree with current official forecasts that anywhere from 8-18 inches snow may fall from Tuesday evening through early Wednesday evening. That's a much larger range than I ususually predict, but I think there's more uncertainty about specifics with this storm than the recent past storms.
Tonight's models will shed more light on this forecast. The NAM model output becomes available about 9:30 PM and the GFS model output becomes available about 10:50 PM
posted: Feb 08 2010 at 7:57 pm
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Sun, 07 Feb 2010Philadelphia Week Weather Forecast- Sun PM
The persistant northern jet stream winter trough has built following the exit of our snowstorm yesterday. Cold high pressure will control our weather on Monday and some of Tuesday.
The El-Nino enhanced southern jet is fueling another disturbance that is crossing the country. This area is expected to redevelop as a coastal low near the Delmarva Tuesday night and Wednesday. The GFS model has been consistent in predicting another significant snowfall for Tuesday night into Wednesday. Incredibly, the current QPF predictions for PHL airport is over 1 inch water, or another 12+ inch snowfall by the end of Wednesday! The NAM and NOGAPS model support this storm development, with lower QPF values. Stay tuned!
Solar Climate Discussion (Updated 2/6): This past summer (see post), I suggested that this upcoming winter would be unusually cold due to a prolonged lull in solar activity. The sun is beginning to come out of a solar minimum, and there has finally been the long expected increase in solar activity signaling the real beginning of Solar Cycle 24. There are several sunspot areas, but the solar flux still hasn't taken off. It's still early in the cycle.
Total Solar Irradiance continues to be about 1 watt/m2 lower than it was during the peak of the last solar cycle, Solar Cycle 23, in April 2000.
As of early February, it looks like the solar cycle is providing the predicted colder than normal temperatures and the El Nino is providing the potent moisture rich southern jet stream. Continue to expect colder than normal temperatures into the spring.
posted: Feb 07 2010 at 5:00 pm
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Sat, 06 Feb 2010Philly Winter Weather Forecast- Sat PM
The snow is over in most areas. Philadelphia Airport recorded 28.5 inches of snow, but most areas had only around 20.
Things calm down for Sunday, but it will be cold!
Incredibly, the GFS model is predicting another big storm for Tuesday night through Wednesday. Current estimates, based on GFS QPF values, is over a foot! Stay tuned.
Sun 2/7: Mostly sunny, breezy and cold. High 29.
Solar Climate Discussion (Updated 2/6): This past summer (see post), I suggested that this upcoming winter would be unusually cold due to a prolonged lull in solar activity. The sun is beginning to come out of a solar minimum, and there has finally been the long expected increase in solar activity signaling the real beginning of Solar Cycle 24. There are several sunspot areas, but the solar flux still hasn't taken off. It's still early in the cycle.
Total Solar Irradiance continues to be about 1 watt/m2 lower than it was during the peak of the last solar cycle, Solar Cycle 23, in April 2000.
As of early February, it looks like the solar cycle is providing the predicted colder than normal temperatures and the El Nino is providing the potent moisture rich southern jet stream. Continue to expect colder than normal temperatures into the spring.
posted: Feb 06 2010 at 6:05 pm
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Winter Weather Update- Sat 10:45AM
The latest GFS data now available- very similar to the NAM model with 0.42 inches water falling over the 12 hours (from 7AM to 7PM). Several more inches of snow likely before ending about 5-6PM.
As mentioned earlier, the band of maximum moisture convergence is right over Philadelphia and continues to tip and rotate with PHL as the axis of rotation. We're in the heaviest snow band and this may enhance snow totals beyond what the resolution of the models have been predicting.
With the current amounts and the banding that's occuring over Philadelphia, I'm increasing total snow totals in Philadelphia and immediate suburbs from to 20-30 inches. (Last night I was predicting 15-22 inches)
Updates if needed.
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posted: Feb 06 2010 at 10:43 am
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Disclaimer: I am not a meteorologist and provide this information as a hobby and for entertainment (mostly my own :-) . While attempts are made to predict the weather as best as I can, use at your own risk! I am NOT responsible for any direct or indirect consequential injury/damages due to your use of these forecasts. Always check the NWS Official Forecast for your final plans.
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