March 13, 1999
Forecast for Sunday-Monday getting clearer, but not crystal clear yet. Without making
references continuously about which model says what, I will give you my outlook for
tomorrow and Monday as best I can at this time. At the time I am typing this, no winter
storm watches or warnings have been issued for Delaware County, but I'd expect at least
a watch issued by the time the afternoon package comes in. All of the models are in
agreement that a storm will be in the southeast and then redevelop off of the coast
somewhere. Differences occur in the upper and mid -level of the atmosphere in regards to
phasing of north and southern jets and also in regards to temperature profiles. My
thinking as to where the secondary low will redevelop annd head: Secondary development
shoud occur off of the southeast coast near coastal North Carolina. Meanwhile, the main
low is in the process of moving NNE/NE. Moisture in association with the primary low
should make it into our area roughly by early afternoon (check back *late* tonight for
more on timing). Precip will be light to moderate and will fall in the form of snow.
Meanwhile, energy aloft is being transferred to the coast and the secondary is now
beginning to draw in more moisture as it begins to head NNE towards the DelMarVa
(actually off the southeast DMV peninsula). This type of transfer will likely leave some
areas in the dry slot, but I feel that the dry slot will not reach the PHL area. We should
continue to see moderate snow as it gets dark. Obviously, timing of precip moving in is
subject to change, so be sure to check back. Now, after dark and on into Monday is when
things get sort of iffy, but I will make my call as I see things right now. As the secondary
low continues to intensify and take over, it should be about 50 miles off of the DelMarVa
by late Sunday night/ Monday morning. Snow could be falling heavily here at that time
also. With a track so close to the coast, and with it being the middle of March, warmer air
will undoubtedly try to work it's way into the system from the east (remember the
counter-clockwise spin to areas of low pressure in the N. Hemisphere). What do I think? I
think as always, we wil be right on the rain-snow line as it begins pushing NW from the
coast (the rain-snow line that is, not the low). Yes, I think that PHL will likely turn to rain
for a period during this, but then back to snow before the whole system pulls out by late
Monday. This will affect snow totals (see below for my thinking on totals). So, in case you
got lost, we have light snow beginning by early afternoon tomorrow, continuing into
tomorrow night as it becomes moderate and even heavy. By morning on Monday, the low
should be about 50-60 miles to the east of Atlantic City (~993mb). Enough warm air will
have been drawn in to change us to rain for a while during the day on Monday as I see
things now. Finally, before all is said and done, precip should go back to snow as the
rain-snow line begins pushing eastward in response to the passing storm. Now on to
*preliminary* totals for this one. Between the time the snow starts tomorrow and finally
ends Tuesday, I would think that we would see at least 4-5 inches of snow (at least). Keep
in mind that this is taking into account any changeover to rain. Also keep in mind that
right now, I am being very conservative with totals. There are some signs that this storm
may keep us all snow as the heaviest moves thru during the day on Monday (dynamic
cooling). If this storm should remain all frozen, I do not think that one foot of snow would
be out of the question at all. There is alot of moisture associated with this system, and still
several questions that need to be answered. So, for now, this is as specific as I would like
to get. I actually think I got a bit too specific, but these are my feelings for now. Things
could change very rapidly with this as is often the case when we find ourselves on the
infamous rain-snow divider. I will be updating this page *late* tonight, and remember,
things could change rapidly for either the better or worse. Stay tuned!
