February 14, 2003
1:15PM Update in red
By the looks of the radar and new data rolling in, it is becoming clearer that the snow slated for tonight and Saturday will be very minor, a primer for a potentially crippling snowstorm for the area between Sunday and Tuesday AM. Lowering accumulations through Saturday PM down to 1-3" with some isolated 4 or even 5" totals expecially South and West of the city.
Guidance at 12Z Friday went gung ho in redeveloping low pressure off the NC coastline and traking it closer to the coast and farther North than prior runs. This does not mean PHL falls into the heaviest snow bands, but the liklihood of a significant, perhaps crippling snowstorm is quickly becoming increasingly apparent by the minute. FOr now, will stick with the chance of more snow Sunday and Monday with additional signficant accumulation likely (4"+). Snow could be on the heavy side if the storm develops quickly enough and hugs the coastline, as it is beginnning to appear. Another brief update late tonight and hopefully another before work on Saturday.
As if the wintry blast of cold temperatures was not bad enough, parts of the Mid-Atlantic and Northeastern United States will also see plowable snowfall during the Friday night - Tuesday time frame, perhaps measured in feet. As in last night's discussion, it is quite obvious from the headache that I had all day, that some forecasters are in for a tough time over the next 24-120 hour time frame. While confidence in the forecast is still high through Saturday, all bets are off from Sunday morning through Tuesday in regards to a second storm (actually a re-energizing of the same storm that will be responsible for overspreading snows Friday night and on into Saturday).
Clouds increase during the day on Friday with highs in the low to mid 30s. The setup will be a classic setup for overunning snows with a very strong area of high pressure building over the Great Lakes and into the Northeast with strong low pressure coming out of the Rockies. Snow will begin around midnight Friday and will become moderate rather quickly after initial light snow. Lows Friday night around 27. Accumulation near 2-4" by daybreak. Snow will begin to lighten by midmorning and will taper off by 1:00PM. Snow may mix with sleet for a period before ending. A chance for flurries or snow showers still exists during the afternoon. High temperature Saturday near freezing. Total accumulations by Saturday 7:00PM will be within the 3-6" range for the Philadelphia Area. There may be an isolated 7" total or two especially South and West of the city.
The storm system responsible for the nasty weather will be a storm system moving out of the Rockies and across the Central Plains then into the lower Mississippi Valley during the day on Friday. As the upper low runs into ridging in the Southeast, it will ultimately begin to slow it's progression. Meanwhile, a massive dome of Arctic high pressure will be building in towards the Great Lakes and into the Northeast late Friday and into Saturday. Not only will this area of high pressure lock in the cold air, it will also play a critical role in determining just how far North any disturbances might travel. It is quickly becoming a concern that while the piece of upper energy slows over the Southeast US, another disturbance racing across the Canadian border may dig far enough South to phase the two systems later in the weekend.
In essence, the surface area of low pressure should stall or slow to a crawl in the Southeast due in part to two blocking highs, one over the Northeast and another off the Southeast Coast in the form of an upper level ridge. When the snow stops here on Saturday, this does not mean that the storm system is gone and has pulled away. Quite the contrary actually. At that point Saturday afternoon, the storm is being forced to go around the bottom of the massive arctic high and redevelop on the other side of the high and the Appalachians, near the NC coastline. Again, appears to be a classic setup for something big, but the fly in still in the ointment so-to-speak with regards to the final details.
Guidance has been all over the place recently and this can be attributed perhaps to a pattern change on the horizon. Regardless, guidance is paying the price in the short run by spitting out various, what appears to be crazy, solutions at times. However, in the past 12 hours, it has become cleared that we are headed towards some sort of solution that the GGEM had for a few days, as well as the EC and Ukmet. As the storm system is forced to redevelop along the NC coast on Sunday, it will spread heavy snow back Northward. The question right now is just where the heaviest snow band will set up. At the moment, it appears hat area will be South of the Mason Dixon line, into Northern Virginia and parts of central MD. While all of this is going on at the surface, at upper levels, the energy is closing off and basically stalling the storm. But wait, this is not eveything!!
As a second shortwave comes racing Southeastward out of Canada and into the Plains early on Monday, it may phase with the closed vortmax at 500mb in the Southeast and help to hold low pressure back towards the coast for a bit longer.
Ok, so what does this spell in layman's terms for us? Simply put, the increasing liklihood of a very memorable snow event in parts of the Mid-Atlantic and Northeast with the *potential* for our area to get in on the action. While it may actually appear there are two separate storms (and we could argue all day whether or not this is true), I believe there will really be just one main entity that will travel across the Central Plains and into the Mississippi Valley on Saturday then will redevelop off the NC coastline on Sunday and head Northeast on Monday. There will be a very sharp cutoff between heavy snow and light or even no snow with this storm.
So, snow starting Friday around midnight and continuing through the night with moderate snow until mid-morning. Snow tapers to snow showers by 1:00PM and could mix with or turn to sleet before ending. Chance for flurries during the afternoon. Total accumulation by 7:00PM of 3-6" around PHL. Cloudy Saturday night with chance for a flurry. Confidence to this point above average.
Snow redeveloping during the morning on Sunday and becoming moderate at times in the afternoon and night. Additional accumulation of 2-4" by daybreak Monday. Snow tapering to light snow and snow showers the remainder of the day on Monday and Monday night as the storm pulls away. An additional 1-2" possible Monday afternoon and night. Total snowfall forecast bwetween Friday PM and Tuesday AM of 6-12".
This is going to be a very close call between who sees the heaviest band of snow and who sees virtually nothing. One of the cons of the strong high pressure to the North is that it could force the system farther South and off the coast with little snows Sunday-Tuesday. However, a jog to the North and West and we fall in the heaviest snow band. In case you are curious as to what type of snow may fall in the heaviest band of snow, totals would be somewhere in the 1-2 feet range of additional snow from Sunday-Tuesday. Again, I am taking the middle road, almost the 'off the coast' road for now as this seems most logical, though some reliable guidance is telling me otherwise.
Confidence through Saturday PM is high with snow accumulation around 3-6" for the Philly area. Confidence turns lower after Sunday morning as a very moisture laden storm may come quite close to giving us heavy snow. Thinking an additional 3-6" of snow Sunday-Tuesday AM. Another run of guidance should pin things down for the second half of the weekend. Sorry for the confusing update. There is alot of information to look over tonight. Another brief update Friday night with better details of the Sun-Tues "event". Take care!
S.B.
