Scientific Forecaster Discussion
fxus61 klwx 211850
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
250 PM EDT Sat Sep 21 2019
high pressure will remain over the mid Atlantic region the
remainder of the weekend with mostly dry conditions and above
normal temperatures expected. The high will drift further off
the southeast coast by Monday as a cold front approaches from
the Ohio Valley. In the wake of the frontal passage, high
pressure will situate itself over the region once again through
the middle of next week.
Near term /through tonight/...
high pressure sits atop the mid Atlantic region this afternoon
as a weak shortwave tracks into western PA and WV. This is
evident in satellite imagery with a cumulus field west of the
Blue Ridge and radar returns to our west showing isolated
coverage of showers and thunderstorms. As this shortwave
continues moving across PA this afternoon, and temperatures
around the County Warning Area rise into the low to middle 80s, some
instability will build west of the Blue Ridge. This will be
enough to trigger widely scattered shower activity with support
of terrain circulations, while an isolated thunderstorm can't be
Activity wanes quickly this evening as the sun sets and
stability returns. Dry conditions overnight as mostly clear to
partly cloudy skies prevail. Temperatures will trend a touch
warmer than previous nights, likely holding in the 60s areawide.
Patchy fog will be possible given increasing low level moisture
and calm winds, especially for areas that see rainfall and
remain cloud free.
Short term /Sunday through Monday night/...
high pressure will center itself along the Outer Banks and into
the western Atlantic on Sunday, providing warm air advection
over the region under persistent southerly flow. As a result,
Summer like conditions return as temperatures climb into the mid
to upper 80s, with dewpoints elevated into the mid to upper
60s. Some hi res guidance is trying to initiate isolated shower
activity over the mountains once again Sunday afternoon. Have
introduced slight chance pops into the forecast to account for
this, but with the mid to upper ridging cresting over the region
and we'll be lacking a trigger, terrain circulations will have
to be the main initiator. So do think a majority of the region
Another chance of rain exists Monday as a cold front approaches
to our west Monday afternoon and evening. However guidance is in
fairly good agreement with shower/storm coverage decaying as
the front limps across the mountains. This makes sense as the
primary upper trough and shortwave energy lifts well to our
north. Will continue to advertise low end chance pops in the
forecast as a result. Temperatures will run well above normal
for the latter half of September, topping out in the middle 80s
to near 90 degrees. Dry conditions Monday night in the wake of
the front as high pressure quickly builds in from the west.
Lows Monday night back off into the upper 50s to middle 60s.
Long term /Tuesday through Saturday/...
a cold front should be pushing offshore Tuesday morning as high
pressure builds over the Tennessee Valley. The high is forecast to
move overhead Wednesday, then offshore Thursday with dry weather.
Another cold front may approach by week's end, but in this pattern
will likely be moisture-starved. Therefore, any rainfall chances in
the long term period should be relatively minimal.
Aviation /18z Saturday through Thursday/...
VFR conditions at the terminals through the remainder of the
weekend as high pressure sits off the Carolina coast and light
southerly flow prevails. Can't rule out a passing shower/storm
at mrb/cho, but likelihood of occurrence remains too low to
include in the taf at this time. Patchy fog possible at night as
low level moisture ticks upwards and winds trend calm.
A cold front will approach the terminals on Monday, crossing
Monday night. A passing shower/storm is possible, but coverage
not looking overly impressive as the any precip with the front
weakens as it crosses the mountains. Southerly winds will
increase and become gusty 15-20 knots ahead of the front Monday
afternoon and evening.
Mainly VFR Tue-Wed with light northwest flow expected.
sub Small Craft Advisory conditions over the waters tonight through the day on
Sunday as light southerly winds prevail with high pressure off
the Carolina coast. Southerly winds will increase Sunday night
and into Monday ahead of an approaching cold front. Not entirely
sold on Small Craft Advisory gusts occurring over the lower and Middle Bay
waters Sunday evening giving mixing concerns, but southerly
channeling may end up requiring an Small Craft Advisory for said waters Sunday
night. Small Craft Advisory conditions borderline again Monday as winds veer west
southwest ahead of the approaching front, turning west
northwest in its wake Monday night.
Generally sub-Small Craft Advisory northwest flow expected Tuesday-Wednesday.
water levels will remain elevated on southerly flow through
Monday, with near minor flooding possible mainly during the tide
cycle Sunday night. Water levels will recede on northwest flow
here are the rankings for driest septembers on record.
Washington, District of Columbia area (ronald Reagan Washington National Airport, dca)
1. 0.11 inches (2019, so far)
0.11 inches (2005)
3. 0.14 inches (1884)
4. 0.20 inches (1967)
5. 0.32 inches (1977)
1981-2010 normal monthly rainfall for september: 3.72 inches
Note: weather records for the Washington, District of Columbia area have been kept at
what is now Ronald Reagan Washington National Airport (dca) since
1941. The official weather record consists of that data back to
1945, and additional precipitation records observed in downtown
Washington, District of Columbia extend the period of record back to 1871.
Baltimore Maryland area (baltimore-Washington international thurgood
Marshall Airport, bwi)
1. 0.09 inches (1884)
2. 0.15 inches (2019, so far)
3. 0.21 inches (1967)
4. 0.32 inches (1906)
5. 0.35 inches (2007)
1981-2010 normal monthly rainfall for september: 4.03 inches
Note: weather records for the Baltimore, Maryland area have been kept at
what is now Baltimore-Washington international thurgood Marshall
Airport (bwi) since 1950. Additional precipitation records observed
in downtown Baltimore extend the period of record back to 1871.
Sterling/Dulles Virginia area (washington Dulles international Airport, iad)
1. 0.15 inches (2005)
2. 0.33 inches (2019, so far)
3. 0.62 inches (1967)
4. 0.78 inches (1978)
5. 0.93 inches (2014)
1981-2010 normal monthly rainfall for september: 3.92 inches
Note: weather records for the Sterling/Dulles Virginia area have been kept
at what is now Washington Dulles International Airport (iad) since
District of Columbia...none.