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Mon, 21 Dec 2009
Philadelphia Weekend Weather- Mon 12/21
The weather over the next week or so will have to go on without me. Much of the time I'll be without internet access.
(Looking at the long range outlook, there's a rainstorm in the forecast for Xmas. The longer range GFS has shows a storm, rain/snow, before New Years Eve. More details when I can update this site.)
On the solar front, the sun has picked up dramatically in activity. Several sunspot areas visible with the solar flux approaching 90. This is the highest it's been in about 2 years. The cold climate effects of the extended solar minimum will likely continue through this winter, despite the recent increase in activity and the clear beginning of Solar Cycle 24.
posted: Dec 21 2009 at 9:35 pm
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Sat, 19 Dec 2009Philly Winter Storm Update- Sat 6:45 PM
This afternoon's NAM and GFS model output continues to show at least 4-5 additional inches of snow falling for Philadelphia after 7 PM tonight. Less north and west. Most of the snow will be over after midnight.
Areas in Camden, Gloucester, Salem and Cape May counties and continued to get the highest snow rates and the totals there may easily exceed 25 inches.
The mostly likely amount is still 18 inches in Philadelphia and I'm moving back to my range earlier today of 14-25 inches.
posted: Dec 19 2009 at 6:49 pm
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Philly Winter Storm Update- Sat 1:30 PM
Snow amounts and rates vary quite a bit across our area. The cut off for the highest amounts appears to be near Center City; areas in much of northern Montgomery county and much of Bucks county have been receiving much lighter amounts. Even in Wyndmoor/Chestnut Hill, the snows haven't been as heavy as areas from Center City and south and east. In fact, at this rate, I won't have 18 inches at my home.
It appears that the heaviest snows in our area will be Delaware county, Southern Philadelphia County and areas just across the river in Camden, Gloucester, Salem and Cape May Counties. This is based on the experimental High Resolution Rapid Refresh Model output.
The mostly likely amount is still 18 inches with ranges of 14-20 inches. The heaviest snow will mostly likely fall during the late afternoon.
posted: Dec 19 2009 at 1:42 pm
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Philly Winter Storm Update- Sat 11 AM
The latest GFS data from this morning's model run just became available.
GFS Total QPF values near 1.40 inches water.
Assuming a 15:1 ratio (based on cold temps) , I'm staying my current estimate of 18 inches by Sunday morning. I'm lowering the range to 14-20 inches of snow for Philadelphia and immediate suburbs, less further northwest and west.
Significant banding of snow is occurring based on radar (and anticipated by models). Areas of south Philadephia and Delaware county are getting much more snow than areas around Chestnut Hill and NE Philadelphia.
posted: Dec 19 2009 at 11:04 am
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Philly Winter Storm Update- Sat 9:30 AM
The latest NAM data from this morning's model run just became available.
NAM Total QPF values near 1.80 inches water. Assuming a 15:1 ratio (based on cold temps) , I'm staying my current estimate of 18 inches by Sunday morning, with a range of 14-25 inches of snow for Philadelphia and immediate suburbs, less further northwest and west.
The new GFS model data will be available about 10:40 AM. Will update at that time.
posted: Dec 19 2009 at 9:24 am
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Philly Winter Storm Update- Sat 9 AM
The 1 AM run of the GFS and NAM models continue with high QPF values; GFS has about 2 inches water equivalent and NAM has well over 2 inches water equivalent.
Sounds like Accuweather and the NWS just caught up to my forecast :-)
I'm staying my current estimate of 18 inches by Sunday morning, with a range of 14-25 inches of snow for Philadelphia and immediate suburbs, less further northwest and west. Frankly, the upper range is certainly a possibility and I'm being conservative with my upper limit of 25 inches. With a high snow to water ratio and QPF values closer to the NAM model, we could exceed 30 inches.
posted: Dec 19 2009 at 9:06 am
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Fri, 18 Dec 2009Philly Winter Storm Update- Fri 10:45 PM
Latest GFS model data available. QPF values are now similar to the NAM and are close to 2 inches water equivalent.
My current estimate is 18 inches, with a range of 14-25 inches of snow for Philadelphia and imediate suburbs, less further northwest and west.
posted: Dec 18 2009 at 10:51 pm
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Philly Winter Storm Update- Fri 9:30 PM
Latest NAM model data available. QPF values are still close to 2 inches water equivalent. Frankly, I'm being conservative when i say it's very possible to have 12-24 inches of snow by Sunday morning.
My current estimate is 18 inches, with a range of 12-24 inches of snow for Philadelphia and imediate suburbs, less further northwest and west.
Next GFS data about 10:45 PM. I'll update again.
posted: Dec 18 2009 at 9:30 pm
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Philly Winter Storm Update- Fri 4 PM
Latest models are more consistent about amounts, although the GFS is somewhat less active than the NAM. The GFS qpf values are about 1 inch or water or 10-12 inches of snow. The NAM continues to crank out over 2 inches water equivalent or, over 2 feet of snow.
My current estimate is 16 inches, with a range of 10-20 inches of snow for Philadelphia and immediate suburbs, less further northwest and west.
Next NAM model runs become available at 9:40 PM and GFS data about 10:55 PM. I'll undate again later.
posted: Dec 18 2009 at 3:58 pm
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Philly Winter Snow Update- Fri AM 5:50
Exact snow amounts for the upcoming storm are impossible to call at this time. The model range has been anywhere from 3-5 inches to 2 feet, with each model being inconsistent with their own successive model runs. Last night's GFS went from 3-6 inches to possibly more than 12 inches (in Philly). Last night's NAM went from 2 feet of snow to 4-5 inches with the later model run.
Here's what we know: it will be all snow. It will start before daybreak Saturday and last into the evening. Amounts are likely to be significant. Areas to the south and east will have more snow than far north and west. Updates later today.
posted: Dec 18 2009 at 5:56 am
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Thu, 17 Dec 2009Snow Update
The latest GFS model has much less precipitation than the NAM model. The GFS model has as much as 6 inches of snow, compared to the NAM model which has over 2 feet of snow. Final amounts of snow will likely be an average of the two.
posted: Dec 17 2009 at 11:06 pm
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Philly Snow Update- Thurs 10 PM
Looking at the latest NAM FOUS data, over 2 inches water equivalent of snow will fall Saturday through Saturday night. This is turning into the possibility of a major snow storm for Philadelphia. At the temps, this translates into over 24 inches. This is impressive. You heard it here first. Way too early to get hyped, but I'd make sure your snow blower works.
posted: Dec 17 2009 at 9:59 pm
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Snow Update- Thurs 9:50 PM
Latest NAM has heavy snow for Saturday through Sat night. Approximately 1 foot of snow possible, according to NAM. GFS model data available later.
posted: Dec 17 2009 at 9:52 pm
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Philly Winter Weather Outlook- Thur PM
The GFS, NAM and NOGAPS models are similar this evening, although there has been a bit of flip-flop around the amount of snow falling and the timing.
The latest models have the snow starting much earlier, now on Saturday before daybreak. While the morning GFS had backed off from the 3-5 inches of snow, the 1 PM run of the GFS again shows 2-5 inches of snow for Philadelphia, with LESS north and west of the city. The NAM has 1-3 inches during the same time frame. Areas to our south and east, in southern NJ and DE may have several inches more.
Right now, Philadelphia is right on the northern border of the expected precipitation shield. Usually the models are fairly good at determining the northern extent, but this storm track and intensification has moved north and west considerably since earlier in the week, (where it was expected to entirely miss us).
Stay tuned. This is depicted by the GFS as a fairly deep low, and any further movement north and west could raise snow totals.
Sat 12/19: Snow beginning before daybreak, light through the day with occasional pauses. Current estimate is 3-5 inches by late Saturday night for the area for PHL airport gridpoint, less north and west.
Sun 12/20 (tentative) Slow clearing, some sun by afternoon, windy and cold. High 34.
Since this past summer (see post), I've postulated that this upcoming winter would be unusually cold due to a lull in solar activity. The sun remains at a prolonged minimum sunspot activity. Total solar irradiance is about 1 watt/m2 lower than it was during the peak of the last solar cycle in April 2000. Read my most recent Fall-Winter Climate prediction here.
posted: Dec 17 2009 at 7:47 pm
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Philly Winter Weather Outlook- Thur AM
Last night' NAM and NOGAPS is looking a bit more like the GFS for Saturday night's snow, although the GFS has heavier snow (5 inches or more) due to greater intensification of the low along the NJ coast and a slightly closer track. Areas in NJ may have heavier amounts than in PHL and northern and western PHL suburbs may have just a dusting or much less snow. Details still developing.
Sat 12/19: Becoming cloudy by afternoon. Cold. High 35. Snow develops late afternoon into the evening with amounts possible of 5 + inches.
Sun 12/20 (tentative) Slow clearing, some sun by afternoon, windy and cold. High 34.
Since this past summer (see post), I've postulated that this upcoming winter would be unusually cold due to a lull in solar activity. The sun remains at a prolonged minimum sunspot activity. Total solar irradiance is about 1 watt/m2 lower than it was during the peak of the last solar cycle in April 2000. Read my most recent Fall-Winter Climate prediction here.
posted: Dec 17 2009 at 6:34 am
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Wed, 16 Dec 2009Philadelphia Weekend Weather Outlook- Wed PM
Cold air and an upper trough will be with us through the weekend.
This afternoon's GFS model has low pressure staying close to the coast, giving us snow late Saturday night and Sunday morning. HOWEVER, the NOGAPS model and the DGEX model (an extended version of the NAM) keeps the precip to our south and east.
(During the last snowy event two weekends ago, the NOGAPS and DGEX/NAM were also together, while the GFS had the snow missing us. The DGEX turned out to be correct last time around. So the GFS is again an outlier. We'll see which model verifies.
Sat 12/19: Becoming cloudy by afternoon. Cold. High 35. Possible snow at night if the GFS is correct; the snow misses us if the DGEX and NOGAPS are correct.
Sun 12/20 (tentative) Clearing windy and cold. High 34.
Since this past summer (see post), I've postulated that this upcoming winter would be unusually cold due to a lull in solar activity. The sun remains at a prolonged minimum sunspot activity. Total solar irradiance is about 1 watt/m2 lower than it was during the peak of the last solar cycle in April 2000. Read my most recent Fall-Winter Climate prediction here.
posted: Dec 16 2009 at 8:11 pm
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Fri, 11 Dec 2009Philadelphia Weekend Weather Forecast- Fri PM
Cold air will be with us for much of Saturday. The upper air trough over us relaxes rapidly on Saturday night, as warm, moist air moves in with a disturbance from the south. Temperatures will be above freezing by the time the precip arrives during the morning on Sunday.
Sat 12/12: Sunny and very cold. High 37.
Sun 12/13 Cloudy with light rain in the morning, possibly mixed with some sleet at the start, quickly changing to all rain. (Some brief icy conditions are possible north early on. ) Rain during the afternoon and early evening. High 43
Since this past summer (see post), I've postulated that this upcoming winter would be unusually cold due to a lull in solar activity. The sun remains at a prolonged minimum sunspot activity. Total solar irradiance is about 1 watt/m2 lower than it was during the peak of the last solar cycle in April 2000. Read my most recent Fall-Winter Climate prediction here.
posted: Dec 11 2009 at 2:15 pm
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Thu, 10 Dec 2009Philadelphia Weekend Weather Forecast- Thur AM
Cold air will be brought in for the balance of the week as low pressure departs into Canada.
A deep upper trough will provide fair, cold weather for Saturday. Warm air will move up from the south on Sunday, causing a cloudy day and some sleet changing to rain. There may be some icy conditions north, as surface temperatures initially remain near freezing. Rain may be heavy in the afternoon.
Sat 12/12: Sunny and very cold. High 37.
Sun 12/13 Cloudy with sleet mixed with some snow by late morning, quickly changing to all rain. No accumulation. Some icy conditions possible north before things warm up by mid day. Rain may be heavy. High 38.
Since this past summer, I've postulated that this upcoming winter would be unusually cold due to a lull in solar activity. The sun remains at a prolonged minimum sunspot activity. Total solar irradiance is about 1 watt/m2 lower than it was during the peak of the last solar cycle in April 2000. Read my most recent Fall-Winter Climate prediction here.
posted: Dec 10 2009 at 8:19 am
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Wed, 09 Dec 2009Philadelphia Week Weather Outlook- Wed AM
The very deep and intensifing low pressure system over the Great Lakes will move away later today, and cold air will be brought in for the balance of the week.
A deep upper trough will provide fair, cold weather for Satuday. Warm air will move up from the south on Sunday, causing clouds and some sleet changing to rain. The DGEX and GFS models differ- the GFS has the precip starting during the morning on Sunday.
Sat 12/12: Sunny and cold. High 37.
Sun 12/13 Cloudy with rain by late morning, possibly beginning as sleet, if the precip starts early enough. High 38.
Since this past summer, I've postulated that this upcoming winter would be unusually cold due to a lull in solar activity. The sun remains at a prolonged minimum sunspot activity. Total solar irradiance is about 1 watt/m2 lower than it was during the peak of the last solar cycle in April 2000. Read my most recent Fall-Winter Climate prediction here.
posted: Dec 09 2009 at 7:44 am
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Mon, 07 Dec 2009Philadelphia Week Weather Outlook- Snow Again?
An interesting week weatherwise, as low pressure undergoes deep cyclogenesis as it tracks west of us towards the Great Lakes on Wednesday. As the storm deepens and wraps up, heavy rains on Wednesday will be replaced with high winds and cold temperatures brought in on the flow around the low.
Thursday will be a transitional day, with Friday and much of Saturday in cold high pressure. There will be no doubt we are in December.
Most interesting, the long range GFS and DGEX show another approaching low late Saturday into Sunday morning. The DGEX is currently predicting snow (2-4 inches) for early Sunday morning Way too early to take this too literally, but I will keep an eye on it.
One thing interesting from the snow of this past weekend- the NAM showed itself to be a serious contender for winter prediction. The NAM-WRF was updated this past April and again over the summer. It appears that significant improvements may have made with this model.
Since the summer, I've postulated that this upcoming winter would be unusually cold. The sun remains at a prolonged minimum in activity. Total solar irradiance is about 1 watt/m2 lower than it was during the peak of the last solar cycle in April 2000. Read my most recent Fall-Winter Climate prediction here.
posted: Dec 07 2009 at 8:01 pm
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Sat, 05 Dec 2009Philly Winter Weather Update- Sat eve
The 1 PM NAM model reverted back to a colder scenario, which can be appreciated by looking out of the window. Temps are still above freezing, but the precipitation rate is high, so dynamic cooling is allowing accumulation of snow. Temps are 34 degrees here and are not expected to fall to freezing until after 2AM.
A heavier band of snow is poised to move through in the next hour. Based on the the latest NAM and current conditions, I'll have to return to my earlier forecast for 2-3 inches snow. It looks like Sunday will be colder than previously thought.
This was an interesting meteorological event for several reasons-- it's one of the few times in recent memory that the NAM model did consistently better than the GFS model. It also suggests that the trend for a record cold and maybe snowy winter may hold. Read my most recent Fall-Winter Climate prediction here.
Sun 12/6 Mostly sunny, breezy and cold. High 37.
posted: Dec 05 2009 at 6:58 pm
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Philly Winter Weather Update- Sat AM
Last night's GFS and NAM model continue the trend of warmer surface temps, with temperatures slightly above freezing (in Philadelphia) for most of the time that precipitation will be falling. (Doesn't sink to below 32 until morning hours.)
Except for some dynamic cooling during the peak precip time of late afternoon, the warm ground temps will reduce chances of accumulating snow in PHL and immediate surrounding suburbs.
The latest GFS LAMPS forecast has the changeover to snow in the upper atmosphere occurring now about 8 PM in Philadelphia, not the afternoon. The NAM FOUS data has the upper atmosphere cold enough to support snow about 4-6 PM.
So expect little more than a coating at most when all is said and done.
I'll update later this morning is things change.
posted: Dec 05 2009 at 8:58 am
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Fri, 04 Dec 2009Winter Weather Update- Fri Eve
Latest NAM model is a bit warmer at rhe surface, keeping snow during the evening period to a slushy inch at most.
posted: Dec 04 2009 at 9:46 pm
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Winter Weather Update- Fri Afternoon
The GFS forecast has come into agreement with the NAM model for moderate precipitation, beginning during the mid morning Saturday, and continuing into Saturday evening. The precipitation will be RAIN for most of the day, however, about 4 PM, the rain will mix with wet snow and a changeover to all snow is expected by 5 or 6 PM. That said, the NAM MOS and GFS MOS (Model Output Statistics) have the high temp about 38 and falling to near or above freezing for the afternoon and evening, which would prevent accumulation. The NAM FOUS data (numerical data I find useful during these sort of events) has temps that are colder, nearer to freezing.
With the NAM cranking out so much precipitation, it is possible that 2-3 inches of snow will accumulate during the early evening hours on, 4-6 inches north and west.
Sat 12/5: Cloudy with rain beginning about 9 AM, changing and mixing with wet snow during the afternoon and some accumulating snow by late afternoon. No accumulation at first, but accumulations possible by late afternoon. Accumulations will depend on surface temps. 2-3 inches possible, more W and NW of the city.
Sun 12/6 Mostly sunny, breezy and cold. High 42.
Read my most recent Fall-Winter Climate prediction here.
Follow me on Twitter as theweatherguy for on-the-fly weather updates and observations.
posted: Dec 04 2009 at 3:00 pm
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Philadelphia Weekend Weather Forecast- Fri AM
There remain major differences in the GFS and NAM models for Saturday afternoon.
The NAM is wetter and somewhat milder, the GFS is drier and colder, with the storm being suppressed to our east by cold air.
The differences remain on the order of a factor of 10 in the amount of precipitation! So expect some snow during the afternoon on Saturday, but confidence in predicting amounts is poor. This is compllicated by surface temperatures that won't be near freezing until late afternoon, so predicting actual accumulation is even more complex.
I generally prefer the GFS model (light snow, not accumulating much) but with last Thursday night's rains, the NAM ( which is predicting 1-3 inches for Saturday) was more accurate about amounts. So it's feeling like a betting parlour with this forecast. Maybe a blend of 1 inch by mid evening will be the reality?
Sat 12/5: Cloudy and cold with rain by afternoon, possibly starting earlier, then mixing with and changing to snow before ending early evening. Above freezing temperatures may not allow much accumulation during the afternoon, so there are many unknowns, both about the temperatures and the High 39, decreasing during the day.
Sun 12/6 Mostly sunny, breezy and cold. High 44.
Read my most recent Fall-Winter Climate prediction here.
Follow me on Twitter as theweatherguy for on-the-fly weather updates and observations.
posted: Dec 04 2009 at 6:10 am
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Thu, 03 Dec 2009Winter Weather Update- Thurs Eve Latest GFS model not yet available, but earlier GFS was much less impressive with the snow. Stay tuned.
Latest NAM model is wetter and colder. Still has rain late morning Sat, but has a changeover to snow by late afternoon and now suggests 1-2 inches.
posted: Dec 03 2009 at 10:27 pm
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Philadelphia Weekend Weather Forecast- Thurs PM
Things have already changed from my previous outlook and there are differences in the models, with the GFS differing from the NOGAPS and NAM.
It now apprears that the atmosphere will be warmer and more moist early Saturday, according to the NAM and NOGAPS. The NAM is showing rain for Saturday morning. The GFS is colder and suppresses the moisture to the south and east until later in the afternoon. So which one is correct? The GFS is generally better than the NAM, although the NAM more correctly handled the heavy rain yesterday.
I'm going to hedge and go with a blend.
Sat 12/5: Cloudy and cold with rain by afternoon, possiby starting earlier. A few wet snow flakes possible in the evening. High 45
Sun 12/6 Mostly sunny, breezy and cold. High 44.
Read my most recent Fall-Winter Climate prediction here.
Follow me on Twitter as theweatherguy for on-the-fly weather updates and observations.
posted: Dec 03 2009 at 5:23 pm
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Wed, 02 Dec 2009Philadelphia Weekend Weather Outlook- Wed PM The GFS model from this morning has the coastal storm for Saturday staying further to our east, missing us. So the expectation of snow is currently dashed. Saturday will be cloudy but dry. Stay tuned for any changes.
A deep low pressure system will wind up over us tonight (Wed) and move away on Thursday.
Cold air will move in Thursday through Friday, giving us a first taste of winter.
posted: Dec 02 2009 at 1:10 pm
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Tue, 01 Dec 2009Philadelphia Weekend Weather Outlook- Tues PM
As mentioned yesterday, the computer models are looking more and more winterlike.
The latest GFS model has a changed the forecast for the upcoming week/weekend-- it shows a deeper and broader upper trough developing during the week, with heavy rain and windy conditions for late Wednesday into Thursday. Colder air moves in later Thursday through Friday, as the winds subside.
Once the cold air moves in on Friday, the latest GFS has a fast moving low developing and moving up the coast on Saturday, possibly giving us some wet snow late Saturday. Surface temperatures will likely be too warm for accumulation, but some light wet snow or snow mixed with light rain is still a possible for Saturday afternoon into early evening. Areas to the south and east of Philadelphia will likely have more precipitation but temps might be a bit warmer.
With ongoing changes in the computer models, we'll have to wait to see the final track of this coastal low.. Expect a cold weekend, certainly colder than it has been since the end of last winter.
Read my most recent Fall-Winter Climate prediction here.
Follow me on Twitter as theweatherguy for on-the-fly weather updates and observations.
posted: Dec 01 2009 at 9:32 pm
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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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