Scientific Forecaster Discussion
fxus61 klwx 201427 aaa
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
1027 am EDT sun Oct 20 2019
the remnants of Nestor will move across the Carolinas today,
pushing offshore of the Outer Banks by this evening. High
pressure will briefly return for Monday. A cold front will cross
the region Tuesday. High pressure will follow for Wednesday and
Thursday. Another storm system may approach the mid-Atlantic by
the end of the week.
Near term /through Monday/...
Mid-level dry slot is already working into the Shenandoah
Valley and central Blue Ridge mountains this morning. Hi-res
models show rain exiting the area early this afternoon faster
than global models. Giving radar trends, believe the hi-res
models appear more likely to verify. So, have cut pops
significantly after 19z. Otherwise, remaining cloudy and cool
after the rain ends.
The system heads off the coast tonight and a weak wedge of high
pressure builds overhead. However, low level moisture may not
clear out quickly, so low clouds appear likely to linger. This
may keep dense fog from developing after today's rain, but those
areas which do see breaks overnight are likely to get foggy, and
this is most likely near and west of the Blue Ridge. Low tonight
mostly in the 40s.
High pressure should linger Monday, with sun finally returning
after low clouds and fog break in the morning. The return of sun
should allow temps to rebound, with readings approaching 70 by
afternoon. Winds should be light with the high overhead.
Short term /Monday night through Tuesday night/...
still some timing differences with the showers associated with
the cold front crossing the region on Tuesday, but they have
narrowed. Thus, focused highest pops in the mid afternoon across
the Metro, earlier to the west. Southerly flow will develop
sooner, however, as the high will move out Monday night, so some
upslope low clouds or drizzle could develop at night across
higher elevations. Temps will stay milder with the southerly
flow and clouds, with 50s more likely Monday night and 60s
during the day Tuesday. However, cape looks limited to non-
existant on Tuesday, so do not expect significant thunder or
severe potential. Showers quickly pass eastward at night, so
most of Tuesday Hight should be dry behind the front. Lows
mostly in the 40s.
Long term /Wednesday through Saturday/...
surface high pressure will build from the Tennessee Valley
toward the mid-Atlantic and then offshore Wednesday through
Friday. Guidance is in relatively good agreement on this and has
been consistent. Thereafter, guidance diverges substantially
with the evolution of a large trough digging across the central
Continental U.S. As it moves east. Some guidance keeps the trough intact
with the larger scale westerlies, and other models cut the
trough off resulting in a slower eastward progression. Chose to
not go above chance pops in any one 12-hour period Friday into
the weekend, instead using a tempered blend of available
guidance (though hedging a bit slower since that's the most
recent trend and given the amplified flow pattern over North
America during this time).
Aviation /14z Sunday through Thursday/...
expect IFR cigs with occasional IFR vsbys at all terminals by
midday and lingering into this evening. Some improvement may
occur tonight as high pressure tries to build in, but weak winds
likely cause restrictions to linger into early Monday before
VFR returns. Showers with restrictions likely to return Tuesday
but VFR should return Tuesday night behind a cold front.
VFR expected in west or northwest flow Wed-Thu.
Small Craft Advisory conditions expected today and tonight as remnants of Nestor
pass to the southeast. Could be near gale but not confident
enough to issue. Winds gradually diminish tonight as high builds
back in. Small Craft Advisory may be necessary with and behind a cold front as
winds strengthen again.
Small Craft Advisory gusts possible in west or northwest flow Wednesday behind a departing
cold front. Winds subside Wednesday night into Thursday.
Strengthening northerly flow should cause water levels to
decrease in our neck of the Woods, but higher anomalies will
likely bottle up near the mouth of the Chesapeake Bay. As winds
go light and then southerly by late Monday, these anomalies will
come back up the Bay and tidal Potomac River, probably
resulting in flooding through Tuesday. Offshore flow should then
cause water levels to decrease by Wednesday.
District of Columbia...none.
Marine...Small Craft Advisory until 6 am EDT Monday for anz539.
Small Craft Advisory until midnight EDT tonight for anz530-531-
Small Craft Advisory until 6 am EDT Monday for anz532-533-
Small Craft Advisory until noon EDT Monday for anz534-537-543.