January 29, 2000
Another week, another wintry threat on the way. This time, however, the forecast is more
tricky as there are some important factors involved which the models are not handling
very well attm. One important factor is the heavy snowpack we currently have on the
ground. Models are very diverse in regards to the amount of low-level(LL)cold that will
remain entrenched. For example, on the one side, the ETA seems to totally disregard the
LL cold air. On the other hand, the NGM/AVN and the NPG all seem to show some sort
of LL cold hanging tough in the Delaware Valley. Another factor the models are still
disagreeing on, is the exact location where the redeveloping low pressure system will
begin to form, as well as exactly where it will track when it does so. In short, this will be a
tough call, especially for the I-95 corridor near PHL (as often seems to be the case as we
head later into the winter). So, what will cause this wintry weather? Let's look at the
forecast: A large upper-level low currently situated in the upper midwest should continue
to push eastward. A disturbance is currently wrapping around the backside of the upper
low, thus a) carving out a trough over the east and b) spinning up a surface low over the
southeast. This surface low pressure will redevelop somewhere just west of the North
Carolina coastline around midday on Sunday. Precipitation should overspread our area
sometime between 12 and 5in the afternoon tomorrow. Timing is still somewhat uncertain
as the slowest of the models would hold off precip until around 7PM Sunday night. Check
back later for an update on start time. Precip will begin as snow, and may be heavy for a
while early tomorrow night. Therafter, the picture gets a bit clouded. A likely changeover
to sleet should happen tomorrow night, followed by a possible changeover to freezing rain
(especially west of the city) and plain rain farther south and east. It looks like the mix
should turn back to plain snow for a period before it ends sometime Monday. Check back
tonight for an accumulation outlook. The easiest way to summarize this forecast would be
a wintry mix for our area. Again, there are still a few factors which need to be nailed down
such as track and any cold air damming which could occur (although this is not looking like
an ideal CAD event). Things will certainly get quite messy in our neck of the woods
tomorrow night, so stay tuned. A modest icing event is not out of the cards either, as I feel
someone nearby will see a prolonged period of freezing rain. Right now, it does not looks
like Delaware County will fall into that prolonged freezing rain zone, but forecasts can
change quickly. Our main problem, the way I see it, will be snow and sleet back to snow.
Be sure to check back later today, if not late tonight. I will certainly be updating before I
hit the hay. Take care, and get that rock salt while you can!
