Snowy Saturday Potential
Saturday's storm continues to refine in focus and based on the midday model trends the verdict is still out on just how much snow will fall for Philadelphia. You have two computer models who want to give Philadelphia snow. Unfortunately, both computer forecast models have been about as accurate as forecasting snowfall amounts in the two to three day range as thinking one can go anywhere near the speed limit on the Blue Route during rush hour.
The NAM and GFS computer models are lathering Philadelphia with varying amounts of snowfall from south to north for Saturday's event, with more to the north of the city and next to nothing south of 295 and Route 70 in New Jersey. Their tracks are farther to the south and indicate a slightly more flat system, one that will not dig out as deep a trough in its wake. This would be a good thing for a couple of reasons. One, a shallower trough means no corresponding ridge to the east of the low. This keeps the storm on a flatter trajectory and prevents it from bending left (north) as quickly. If it bombs out too quick, you get a track like the EURO.
The other big difference between these systems is timing. The EURO and NAM are in some agreement about this being a slower system, arriving during the afternoon and evening hours and continuing through a good part of Saturday night. The GFS has been holding steady to a Saturday AM arrival with overrunning precipitation followed by the low moving off the coast during the early evening hours. Timing is still a good ways off amongst the computer forecasts but past performance this winter indicates the GFS is usually better on timing details so my thinking is that precipitation arrives west of the city during the mid-morning hours and at the coast around midday.
What ultimately falls? In this "thread the needle" storm, with Philadelphia being the eye of the needle, the EURO track gives us snow to rain as warmer air draws into the system as it lifts past us. The GFS and NAM, which are south of us, bring more snow to the region down to around I-295, with some showers and a period of rain to the south of Philadelphia. In the GFS/NAM forecast, the farther north one is the greater the chances for snowfall...even in the Philadelphia suburbs.
One of the concerns with the storm is the possible influx of warmer air aloft that could change precipitation over to rain and/or sleet, especially close to Philadelphia. With the track running just south of Philadelphia any slight nudge north would bring this changeover line farther north.
As of now, the thinking is that the greatest snowfall accumulations will be along I-80 and north. It should be an all snow event across those areas, with several inches of snow possible. They stand a good chance of getting the golden snow shovel and getting the most snow from this event. The Lehigh Valley, Central Jersey, Philadelphia's northern burbs, and Central Pennsylvania may see a little bit less snowfall and could run the risk of a changeover to rain or sleet. If that changeover does not take place, snowfall totals could reach upwards of five inches. This area has a pretty high margin of error right now simply because of the differences in computer forecast tracks. If the EURO track is correct these areas could see 2-3" of snow before changing over to rain as a "best case scenario" -- one that the snow-starved may not like.
Farther south, across Philadelphia a couple of inches of snow is possible before things possibly change to rain. If the low takes the EURO track it will be a short burst of snow before the changeover whereas the GFS could bring a little bit more.
Needless to say, this is a close call again and a wide variety of snowfall amounts are possible with this event, with the best chances to see the most snow being to the north of the city.
I'll have another update tomorrow morning.
The NAM and GFS computer models are lathering Philadelphia with varying amounts of snowfall from south to north for Saturday's event, with more to the north of the city and next to nothing south of 295 and Route 70 in New Jersey. Their tracks are farther to the south and indicate a slightly more flat system, one that will not dig out as deep a trough in its wake. This would be a good thing for a couple of reasons. One, a shallower trough means no corresponding ridge to the east of the low. This keeps the storm on a flatter trajectory and prevents it from bending left (north) as quickly. If it bombs out too quick, you get a track like the EURO.
The other big difference between these systems is timing. The EURO and NAM are in some agreement about this being a slower system, arriving during the afternoon and evening hours and continuing through a good part of Saturday night. The GFS has been holding steady to a Saturday AM arrival with overrunning precipitation followed by the low moving off the coast during the early evening hours. Timing is still a good ways off amongst the computer forecasts but past performance this winter indicates the GFS is usually better on timing details so my thinking is that precipitation arrives west of the city during the mid-morning hours and at the coast around midday.What ultimately falls? In this "thread the needle" storm, with Philadelphia being the eye of the needle, the EURO track gives us snow to rain as warmer air draws into the system as it lifts past us. The GFS and NAM, which are south of us, bring more snow to the region down to around I-295, with some showers and a period of rain to the south of Philadelphia. In the GFS/NAM forecast, the farther north one is the greater the chances for snowfall...even in the Philadelphia suburbs.
One of the concerns with the storm is the possible influx of warmer air aloft that could change precipitation over to rain and/or sleet, especially close to Philadelphia. With the track running just south of Philadelphia any slight nudge north would bring this changeover line farther north.
As of now, the thinking is that the greatest snowfall accumulations will be along I-80 and north. It should be an all snow event across those areas, with several inches of snow possible. They stand a good chance of getting the golden snow shovel and getting the most snow from this event. The Lehigh Valley, Central Jersey, Philadelphia's northern burbs, and Central Pennsylvania may see a little bit less snowfall and could run the risk of a changeover to rain or sleet. If that changeover does not take place, snowfall totals could reach upwards of five inches. This area has a pretty high margin of error right now simply because of the differences in computer forecast tracks. If the EURO track is correct these areas could see 2-3" of snow before changing over to rain as a "best case scenario" -- one that the snow-starved may not like.
Farther south, across Philadelphia a couple of inches of snow is possible before things possibly change to rain. If the low takes the EURO track it will be a short burst of snow before the changeover whereas the GFS could bring a little bit more.Needless to say, this is a close call again and a wide variety of snowfall amounts are possible with this event, with the best chances to see the most snow being to the north of the city.
I'll have another update tomorrow morning.
Tags:
