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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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Mon, 12 Feb 2007
Storm Update- GFS Model - Mon Late PM Update
Here's the GFS data just becoming available. Some differences between the GFS and NAM-WRF. Most of my regular readers know I prefer the GFS model over the NAM.
Here is the latest:
The GFS has more snow Tuesday afternoon than the NAM or its previous runs....it cranks out .028 inches water (2-3 inches snow) BEFORE evening Tuesday. Temperatures rise in the upper atmosphere earlier in the evening, with mixing with sleet occuring between 7-10 PM Tuesday.
Freezing rain starting after midnight, but it has temperatures very warm at the surface by daybreak on Wednesday, so freezing rain should be mostly rain early morning. Very heavy rain before daybreak (0.89 inches water)
HEAVY rain (1.33 inches water) during the morning on Wednesday with high winds. Flooding conditions possible. Temperatures drop rapidly early afternoon Wednesday with rain becoming snow again. Possible 1-2 inches snow late Wednesday afternoon. Windy. Things freeze over late Wednesday afternoon. Bitter cold Wednesday night.
Wow, what a roller coaster! Gonna be interesting! Updates tomorrow morning.

posted: Feb 12 2007 at 10:54 pm

[/weather/feb07] permanent link

Light Snow then Sleet Ice and HEAVY Rain - Mon PM Update
Not much has changed since this morning. The upper atmosphere is going to be too warm for snow a short time after is starts Tues eve and the difficulties with this storm will depend on whether the ground warms above freezing.
The raw FOUS data from the tonight's NAM-WRF just became available. Here's the scoop and the trends-
The NAM shows only a light dusting (0.04 inches water) before 7PM Tuesday. That's a light dusting of snow. The drive home shouldn't be too bad Tuesday evening
By midnight, we have about 2 or so inches of snow on the ground, but it will change over to sleet and freezing rain, as the upper atmosphere becomes too warm to support snow just after midnight. Ground temperatures are expected to be below freezing, so sleet and rain will freeze, especially north and west of city. A significant accumulation of ice is possible before daybreak on Wednesday IF the models are correct about the temperatures on the ground.
By 7AM Wednesday, temperatures should move above freezing in Philadelphia, although areas north and west may remain below freezing. HEAVY rain (0.80" water) is predicted to fall in the morning on Wednesday. Depending upon temperatures, it could be a terrible ice storm or just rain storm at that time. Any snow that fell will disappear or become slush with that much rain. If temps remain below freezing in the northern and western suburbs, serious travel problems will result Wednesday morning.
The NAM suggests a brief period of snow again late Wednesday as temperatures rapidly drop late afternoon. This light snow at the end, with pooling water and slush will freeze Wednesday night becoming a different sort of ice problem late Wednesday night and Thursday morning.
The GFS model has been similar to the WRF-NAM with this storm. Its new data won't be available for another hour.
Here's what I'm noticing: The temperatures being predicted by the NAM for right now seem too cold for what the current observations actually are. Perhaps the temperatures when the rain falls late Tuesday night will also be warmer than predicted? That would make things a lot better around here. I'll update tomorrow morning.

posted: Feb 12 2007 at 9:56 pm

[/weather/feb07] permanent link

An Ice Storm instead of a Snow storm? - Monday AM Update
The models continue with a change to sleet and rain about midnight Tuesday night. The big issue near Philadelphia will not be the snow-rain line but rather the surface temperatures allowing icing conditions in many areas, both in Philadelphia and especially north and west.
The latest models has some light snow and flurries during the day on Tuesday, not amounting to much. First real snow of about 1 inch will be around drive time Tuesday late afternoon. Snow will become heavier during the evening hours maybe accumulating another 2-3 inches, but will change to sleet and freezing rain both in the city and to our immediate north and west.
Heavy rain will be falling early Wednesday morning in most areas around Philadelphia and immediate suburbs. Whether it will continue to freeze on the ground is the concern in this storm
The big question will be the temperature of the ground/surface. Cold air trapped at the surface from weeks of cold temperatures may allow a significant ice storm to occur in our area before temps rise above freezing later Wednesday morning. This ground freezing potential will occur both in Philadelphia and especially north and west. Above freezing temps should occur in Philadephia by daybreak on Wednesday, but areas north and west may continue to have prolonged icing conditions. Getting above freezing temps in these areas may be delayed.
Again right now, the real concern is an ice storm instead of a snow storm. Predicting exact amounts of snow on the ground at the end completely misses the point.

posted: Feb 12 2007 at 7:28 am

[/weather/feb07] 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	Mon, 12 Feb 2007 Storm Update- GFS Model - Mon Late PM Update Here's the GFS data just becoming available. Some differences between the GFS and NAM-WRF. Most of my regular readers know I prefer the GFS model over the NAM. Here is the latest: The GFS has more snow Tuesday afternoon than the NAM or its previous runs....it cranks out .028 inches water (2-3 inches snow) BEFORE evening Tuesday. Temperatures rise in the upper atmosphere earlier in the evening, with mixing with sleet occuring between 7-10 PM Tuesday. Freezing rain starting after midnight, but it has temperatures very warm at the surface by daybreak on Wednesday, so freezing rain should be mostly rain early morning. Very heavy rain before daybreak (0.89 inches water) HEAVY rain (1.33 inches water) during the morning on Wednesday with high winds. Flooding conditions possible. Temperatures drop rapidly early afternoon Wednesday with rain becoming snow again. Possible 1-2 inches snow late Wednesday afternoon. Windy. Things freeze over late Wednesday afternoon. Bitter cold Wednesday night. Wow, what a roller coaster! Gonna be interesting! Updates tomorrow morning. posted: Feb 12 2007 at 10:54 pm [/weather/feb07] permanent link Light Snow then Sleet Ice and HEAVY Rain - Mon PM Update Not much has changed since this morning. The upper atmosphere is going to be too warm for snow a short time after is starts Tues eve and the difficulties with this storm will depend on whether the ground warms above freezing. The raw FOUS data from the tonight's NAM-WRF just became available. Here's the scoop and the trends- The NAM shows only a light dusting (0.04 inches water) before 7PM Tuesday. That's a light dusting of snow. The drive home shouldn't be too bad Tuesday evening By midnight, we have about 2 or so inches of snow on the ground, but it will change over to sleet and freezing rain, as the upper atmosphere becomes too warm to support snow just after midnight. Ground temperatures are expected to be below freezing, so sleet and rain will freeze, especially north and west of city. A significant accumulation of ice is possible before daybreak on Wednesday IF the models are correct about the temperatures on the ground. By 7AM Wednesday, temperatures should move above freezing in Philadelphia, although areas north and west may remain below freezing. HEAVY rain (0.80" water) is predicted to fall in the morning on Wednesday. Depending upon temperatures, it could be a terrible ice storm or just rain storm at that time. Any snow that fell will disappear or become slush with that much rain. If temps remain below freezing in the northern and western suburbs, serious travel problems will result Wednesday morning. The NAM suggests a brief period of snow again late Wednesday as temperatures rapidly drop late afternoon. This light snow at the end, with pooling water and slush will freeze Wednesday night becoming a different sort of ice problem late Wednesday night and Thursday morning. The GFS model has been similar to the WRF-NAM with this storm. Its new data won't be available for another hour. Here's what I'm noticing: The temperatures being predicted by the NAM for right now seem too cold for what the current observations actually are. Perhaps the temperatures when the rain falls late Tuesday night will also be warmer than predicted? That would make things a lot better around here. I'll update tomorrow morning. posted: Feb 12 2007 at 9:56 pm [/weather/feb07] permanent link An Ice Storm instead of a Snow storm? - Monday AM Update The models continue with a change to sleet and rain about midnight Tuesday night. The big issue near Philadelphia will not be the snow-rain line but rather the surface temperatures allowing icing conditions in many areas, both in Philadelphia and especially north and west. The latest models has some light snow and flurries during the day on Tuesday, not amounting to much. First real snow of about 1 inch will be around drive time Tuesday late afternoon. Snow will become heavier during the evening hours maybe accumulating another 2-3 inches, but will change to sleet and freezing rain both in the city and to our immediate north and west. Heavy rain will be falling early Wednesday morning in most areas around Philadelphia and immediate suburbs. Whether it will continue to freeze on the ground is the concern in this storm The big question will be the temperature of the ground/surface. Cold air trapped at the surface from weeks of cold temperatures may allow a significant ice storm to occur in our area before temps rise above freezing later Wednesday morning. This ground freezing potential will occur both in Philadelphia and especially north and west. Above freezing temps should occur in Philadephia by daybreak on Wednesday, but areas north and west may continue to have prolonged icing conditions. Getting above freezing temps in these areas may be delayed. Again right now, the real concern is an ice storm instead of a snow storm. Predicting exact amounts of snow on the ground at the end completely misses the point. posted: Feb 12 2007 at 7:28 am [/weather/feb07] 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.