Scientific Forecaster Discussion
fxus61 klwx 210801
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
401 am EDT Mon Oct 21 2019
high pressure will briefly build over the region today as the
remnants of Nestor head out to sea. A cold front will approach
from the west tonight before crossing the region later Tuesday
into Tuesday night. High pressure will build back across the
region Wednesday. Another storm system may approach the region
during the weekend.
Near term /through tonight/...
as of early this morning, nestor's remnant low pressure, still a
potent extratropical system, is east of Ocean City Maryland and
continuing to head out to sea. Low level moisture remains high,
however, and low clouds are persistent. Those few areas which
have seen the low clouds break have seen patchy fog develop, and
this risk will continue until after the sun rises. Those areas
which remain cloudy through sunrise should see the clouds
gradually break as the morning progresses thanks to a weak ridge
of high pressure building southward from southern Canada, so
most locations should see more sun than clouds by mid afternoon.
The sun will aid temp rises, and we should rebound well into the
60s across most of the region, with some places flirting with
70. Winds will be northerly this morning, becoming light and
variable by afternoon as nestor's influence wanes.
Tonight, most areas start out mostly clear, but the approaching
system from the Midwest will begin to spread high clouds across
the region. The southeasterly flow which will develop ahead of
the system will also aid low-level moisture advection, and low
clouds are likely to develop too. There may even be some patchy
fog in spots, though it is more likely to be mist or even a
little drizzle later at night. A few showers might reach western
zones by night's end, but most areas likely stay relatively dry
through tonight. With the southeasterly flow and increasing
clouds, lows likely stay mild, with 50s common.
Short term /Tuesday through Wednesday night/...
cold front approaching from the west is the main player in the
short term. Guidance depicts a neutral or even weakly positively
tilted trough aloft with the best forcing staying north. At the
surface, most models depict a wave forming along the front to
the south, which may pass over southern Maryland as the system crosses
the region, though it also might stay just south. The
implication here is that while rain showers are very likely, and
there is some shear present, the surface instability is not
significant and upper-level forcing also is not particularly
helpful. Thus, have pops going categorical in the afternoon and
evening from west to east across the County Warning Area on Tuesday as the front
crosses the region and the wave of low pressure moves on by, but
have held back on any thunder mention thus far. Can't rule it
out completely, but odds look to low to include in main forecast
at this point. Otherwise, the relatively late arrival of the
front and mild start should allow most of the region to rebound
into the 60s by afternoon, though likely it will stay a little
cooler than today thanks to the clouds.
Front sweeps through during the evening and cooler air moves on
in, with the rain showers quickly ending. It will be breezy as
well, but not particularly windy behind this one. High pressure
will then dominate through the following 24 hours, but with the
center staying well south, downslope flow and relatively mild
air flowing over the top of the high should keep temps fairly
benign, with 60s expected once again Wednesday. Some lows may
reach the 30s Wednesday night in the colder locales, but think
it won't be quite as cold as Friday night was. With many of our
colder zones now cleared from further frost/freeze headlines
thanks to the widespread freeze on Friday night, do not
currently anticipate widespread frost/freeze headlines for
Long term /Thursday through Sunday/...
sprawling high pressure will build from the Tennessee Valley
across the mid-Atlantic Thursday into Friday with mainly dry
weather anticipated, though a weak shortwave likely swings by to
our north on Friday with a bit of an increase in clouds,
especially near the Mason-Dixon line. High temperatures
generally 65-70 expected late this week, which is right around
normal for late October.
Model timing discrepancies continue for the potential storm
system next weekend, though have mostly backed off precip
chances for Friday (except for GFS/gefs). Have focused pops
Saturday night into Sunday. Timing uncertainties Stem from when
an upper trough approaches from the west, which will depend on
whether or not it remains attached to larger scale westerly flow
(quicker progression, trending less likely) or cuts off (slower
eastward progression, trending more likely).
Aviation /08z Monday through Friday/...
low cigs in the MVFR range likely linger into the morning hours,
and locations which see breaks (i.E., Cho) will then run the
risk of IFR vsby with fog developing. Improvement looks likely
by late morning with VFR by early afternoon at latest. However,
southeasterly flow may bring low cigs back to the region later
tonight which could persist most of Tuesday into Tuesday
evening, accompanied by showers by Tuesday afternoon. VFR likely
returns behind a cold front Tuesday night, which should persist
under high pressure through Wednesday night.
VFR expected in SW flow Thu-Fri.
Small Craft Advisory gradually winding down early this morning as nestor's
remnants slowly head out to sea. Expect all headlines gone by
noon if not sooner. Light winds likely tonight under high
pressure, but Small Craft Advisory may develop just ahead of a cold front Tuesday
afternoon. Small Craft Advisory then more likely behind the front Tuesday night
into Wednesday before dropping off by Wednesday night.
Gradient should remain light enough to preclude any Small Craft Advisory level
winds Thursday into Friday as high pressure builds overhead.
water levels have decreased on northeast to north flow, but
water remains piled (anomalies of +1.5) at the mouth of the
Chesapeake Bay. This water will return northward through Tuesday
as winds become southeasterly, which will likely result in
widespread minor to perhaps near moderate flooding (most likely
moderate flooding would be at Straits Point and Annapolis,
slightly less likely but not out of the realm of possibility
District of Columbia...none.
Marine...Small Craft Advisory until 9 am EDT this morning for anz532-
Small Craft Advisory until noon EDT today for anz534-537-543.
Small Craft Advisory until 6 am EDT early this morning for