Scientific Forecaster Discussion
fxus61 klwx 221830
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
230 PM EDT sun Sep 22 2019
high pressure will shift south and east tonight, allowing a cold
front to approach from the Ohio Valley on Monday, and move through
by Monday evening. High pressure then builds in again through
midweek before another cold front approaches late in the week.
Near term /through Monday/...
the autumnal equinox may be tonight, but the weather is still
fully in Summer Mode. Temperatures today are even warmer than
yesterday, and today's highs won't be all that far from the
records. Can't rule out a pop-up shower on/near the terrain
through early evening, but coverage should be less than
yesterday. Tonight should be dry, mostly clear, and warm. Urban
areas probably won't drop below 70 again with most everyone else
in the 60s.
The upper ridge weakens enough to allow an upper trough to dig into
the Great Lakes region and an associated cold front to get here.
Model trends the last few runs have been a bit slower and fairly
significantly drier. Rain chances were removed completely from
Charlottesville southward, and lowered almost everywhere else
(especially east of I-81). Can't rule out a rumble of thunder but
chances are awfully slim, with the surface front outrunning the
upper support. The 12z GFS is just as warm -- if not a bit warmer --
tomorrow in the eastern 1/2 of the County Warning Area as it is today, so Max temps
for tomorrow were raised to be similar to today. Western half should
be cooler than today with more cloud cover.
Short term /Monday night through Tuesday night/...
cold front passes the entire area by midnight Monday night. Perhaps
a lingering shower east of I-95 in the evening. Tuesday will be much
more seasonable as far as temps and humidity are concerned -- highs
in the 70s to around 80s with dewpoints in the 50s or maybe even
40s. Lows Tuesday night also near seasonal normals under a nearly
Long term /Wednesday through Saturday/...
surface high pressure and upper level ridging will dominate over the
region Wednesday, leading to dry conditions and above normal
temperatures in the lower 80s. The ridge begins to break down
Wednesday evening as the surface high shifts off the southeast coast
and a cold front nears the Great Lakes region. This will allow for
increasing southerly flow ahead of the front on Thursday, which will
bring our next chance of rain to the area. Unfortunately, this will
be much like the front we are expecting Monday, moisture starved and
weakening as it crosses the mountains with the best upper level
support residing to our north. We will see a brief drop in
temperatures on Friday in the wake of the front, with dry conditions
forecast. Surface high pressure will quickly transit the mid
Atlantic region, shifting east of the Delmarva Friday night,
allowing for a return flow to setup once again. After which, a
strong upper ridge builds over the eastern U.S., Delivering
temperatures well above normal. Latest guidance indicates 850 temps
nearing 20c, which would result in temperatures nearing 90 degrees
as we head into the last weekend of September.
Aviation /18z Sunday through Friday/...
VFR generally expected throughout the valid taf period. Guidance has
been trending away from the idea of fog overnight, but still has
some MVFR potential mainly at mrb (but close to cho and mountain too).
Can't rule out a shower at mrb today, or a shower or even
thunderstorm at any terminal tomorrow, but chances are so small that
they won't be included in the taf and any restrictions they would
cause would be extremely short-lived.
Cold front Monday evening will shift winds out of the northwest on
Tuesday with some gusts to 20 mph possible during the day.
VFR conditions Wednesday under high pressure and light southerly
flow. A moisture starved cold front will cross the terminals
Thursday, with a non-zero chance of a brief episode of sub VFR
conditions in a passing shower/storm. Southerly winds will veer
northerly in the wake of front Thursday night, but remain light as
high pressure quickly settles over the terminals.
winds picking up over the waters out of the south with channeling
likely this evening and overnight. Small Craft Advisory is already
in effect from the Bay Bridge south. The advisory was expanded in
time to cover the entire overnight, but not expanded any in area.
An isolated shower is possible over the waters late Monday afternoon
or Monday night. At this time, the only potential for thunder and
lightning is indicated over the northernmost Bay waters.
The channeling ends as the front approaches and then moves through.
Behind the front late Monday night into Tuesday, gusty northwest
winds will approach 15-20 knots. It currently appears that the
potential 20 knot gusts don't start until near daybreak Tuesday, so
have elected to hold off on issuing an advisory yet.
High pressure on Wednesday will deliver light winds over our marine
district. A cold front will approach from the Great Lakes on
Thursday, increasing southerly winds Wednesday night and Thursday,
bringing the potential for Small Craft Advisory conditions to return to the
tidal anomaly has been decreasing slightly all day and currently is
1/3 to 1/2 foot. Winds are turning southerly but are forecast to be
just slightly west of due south, which may limit the piling up of
water due to wind. Went pretty close to the ensemble mean of the
forecast guidance, which keeps all sites below minor flood tonight.
However, Annapolis in particular should be fairly close and
will have to be monitored.
District of Columbia...none.
Marine...Small Craft Advisory from 9 PM this evening to 8 am EDT Monday