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Miscellaneous
Wed, 24 Feb 2010
Winter 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
[/weather/feb10] permanent link
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
[/weather/feb10] permanent link
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.
Like these forecasts?? Click on a Yahoo text ad and increase my ratings! Thanks!
posted: Feb 24 2010 at 9:50 pm
[/weather/feb10] permanent link
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.
Like these forecasts?? Click on a Yahoo text ad and increase my ratings! Thanks!
posted: Feb 24 2010 at 11:11 am
[/weather/feb10] permanent link
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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