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Philadelphia Weekend Weather and Storm Forecasts

Glenn F. Schreiber DMD and Glenn Schreiber is theweatherguy writing about Philadelphia Weather [radar] [surface map] [disclaimer]

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Glenn F Schreiber
aka "theweatherguy"

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Tue, 23 Feb 2010
Winter 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

[/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.

The weatherguy.net home page has been visited times since October 2003.

theweatherguy's website
		Philadelphia Weekend Weather and Storm Forecasts
Glenn F. Schreiber DMD and Glenn Schreiber is theweatherguy writing about Philadelphia Weather [radar] [surface map] [disclaimer]
	About this blog theweatherguy's website, "Thoughts and comments on Philadelphia Weather and Daily Life." Glenn F Schreiber aka "theweatherguy" Photos Weather Definitions Copy link for RSS feed Links These are a few of my favorite links. National Weather Service Official Forecasts Meteorology Glossary Archives Weather Archives: 13: Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 12: Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 11: Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 10: Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 09: Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 08: Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 07: Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 06: Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec 05: Apr May Jun July Aug Sept Oct Nov Dec Commentary: Miscellaneous Find	Tue, 23 Feb 2010 Winter 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 [/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. The weatherguy.net home page has been visited times since October 2003.