February 13, 2003
Bitterly cold weather has fallen upon us again with nearly the coldest nighttime lows of the season the next few nights and the chance for more wintry weather over the weekend. Looks like highs stay in the low to mid 20s on Thursday under mostly sunny skies with diminishing winds, especially near evening. The main event, so-to-speak, potentially awaits us for the holiday weekend and early next week.
As most regulars here may or may not be aware of, as I hinted for the Christmas Storm this year in my winter outlook back in October, I also have been sold on an 'event' near Valentine's Day for quite some time. My thinking is that when we are in weather patterns as persistent(and favorable for storminess and arctic outbreaks) as we have seen this winter, we usually have a storm that comes in when the days really start getting longer (Feb 14ish) that sort of sets the tone for the beginning of the end to the season. Anyway, as crazy as that thinking was/is, it has worked, and looks to come through again this weekend with a very complex and wild string of weather events.
Clouds will increase on Friday in typical pre-winter storm fashion with high stratus covering the sun and clouds lowering as the day goes on. This, coupled with temperatures in the upper 20s to around freezing, will feel like winter weather is slowly approaching the area. Well, winter weather wont be *returning* per se since the bitterly cold temperature readings haven't left and cannot exactly be written off as springlike :-) However, there will be a return of moisture to the cold air via warm air advection or overunning snows overspreading the region Friday night. Confidence is high up through this point with the odds still out for what may or may not transpire from early Saturday through the President's Day holiday on Monday.
The culprit for the inclement weather will be a storm system coming out of the Rockies that will head Eastward and throw(advect) warm Gulf moisture overtop of the dome of very cold air in the Northeast. As this system heads East, the warm front associated with it will be stretched from West to East and will actually become stationary as the warm and cold air fight for positioning in the Middle Atlantic. This is where things get tricky, as if they weren't already.
A wave or two of low pressure may develop and try to ride up and along this front. As daybreaks on Saturday, and southerly winds try to erode the cold air, temperatures aloft could warm to above freezing and leave the door open for what could be a very messy day on Saturday. With a very strong CAD signal (Cold Air Damming as clockwise winds around high pressure to the North funnel in cold air that lays low and wedges itself against the Appalachian Mountains), chances are that precipitation will stay frozen in one form or another. Snow could change to sleet or freezing rain during the day on Saturday and will likely be off-and-on in nature. However, at this time, it appears that as another impulse rides along the stationary front, it could end as snow Saturday night. While all this is going on, the main piece of upper energy associated with the original system that pulled out of the Rockies, is sitting somewhere the Tennesse Valley Saturday afternoon.
I will not dwell too much on the next time frame(Sunday morning-Tuesday morning) for now though as any changes in the short run will affect the forecast beyond Saturday. However, there are signs from a few pieces of guidance, that another shortwave at upper levels will race out of Canada and will try to interact with the initial shortwave(located over the Tennessee Valley on Saturday). In short, it will depend how far South the Northern energy digs when it comes out of Canada on Saturday afternoon as to what will transpire post-Saturday night. If the shortwave dives South and combines with the initial s/w located in the Tenn. Valley on Saturday, it would cause the upper low to close off and create a monster of a snowstorm somwhere in the Middle Atlantic on Sunday and Monday (on top of what may have already fallen from Friday night-Saturday). Yes, the GGEM Canadian models implies what amounts to be a heck of a snowfall in parts of VA and MD though I am not entirely sold on this solution at this time.
On the other hand, if this second shortwave on Saturday heads East before it really starts to dig Southward and then combines with the Tenn. Valley shortwave, it could force the Sunday-Monday storm Eastward sparing many from what could be a very heavy snow event. If one decides to take the middle road, PHL and NYC would be in line for a decent snow event fromt he Sunday-Monday system, though I caution that I am again not sold on the fact the a heavy snowstorm develop or where it may or may not set up the heaviest band(s) of snow.
Before getting into crazy snowfall amounts and precise specifics, I would prefer to see another run or two of guidance to see what impact the first storm on Friday night-Saturday will have on the potential Sunday-Monday storm and vice versa. For now, snow Friday night looks light to moderate with any snow likely changing to a mix of freezing rain, sleet, and snow on Saturday. Temps will hover around freezing on Saturday with off and on mixed precipitation during the day. Precip could be moderate at times. Saturday evening or early night, mixed precip turns back to plain snow. Total accumulations to this point look to be minor at this time, but mixed precip on Saturday could be quite a mess.
I will be honest, this is perhaps the most complex storm potential that I have seen since early March of 2001, the storm that spoiled many a forecaster's predictions. While I have (and I hope others) have learned many lessons from, and since, that particular storm, I cannot ignore the signals that this late-weekend has the potential to be an historic episode for some parts of the East, and/or a complete miss on the other hand. Though confidence in this forecast period is low in terms of who, where, and how much, confidence in some sort of wintry precip for the area is very high. Rather than waste more energy than needed on this discussion, I will update again Thursday night at a similar time for all the snow birds. There are still many, many details that need to be hammered out in what is appearing to be becoming a weekend of headaches for forecasters. For now, bundle up and stay warm....we have some Canadian Prarie-like weather upon us for the next day or two. Take care!
S.B.
