Scientific Forecaster Discussion
fxus61 klwx 181821
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
221 PM EDT Fri Oct 18 2019
High pressure will settle over our region through Saturday. A
subtropical low will pass through our region from the south Saturday
evening through Sunday afternoon bringing up to half inch of rain.
Another cold front will move through our region Tuesday into early
Wednesday next week bringing another chance for rain.
Near term /through tonight/...
The tight pressure gradient that has been causing the breezy
conditions will continue to weakened as the strong low to our north
moves over eastern Canada. Winds should taper off after sunset as
the daytime mixing shuts off. Model trends have been suggesting that
winds will drop below five knots overnight. High pressure will move
overhead our region during the overnight periods. The combination of
light winds and clear skies along with the high over head will lead
to ideal conditions for radiation cooling. This will lead to
overnight lows dropping down into the low to mid 30s this evening
for most areas west of the I-95 corridor. The combination of
freezing to near freezing temps in the shenadoah valley, the Potomac
Highlands, and the Blue Ridge mountains has led US to issue a freeze
warning for these areas through Saturday morning. A frost advisory
has been issued for most areas west of the I-95 corridor through
Short term /Saturday through Sunday night/...
High pressure over our region will slowly shift of the Atlantic
coast on by Saturday afternoon. Winds will remain light but will
become more southerly in nature. This will lead to weak advection of
warm and moist air into our region. The southerly flow is not
expected to transport a lot of moisture into our region which means
skies should remain mostly clear on Saturday. As skies will be
mostly clear, day time temperatures are expected to be slightly
warmer on Saturday in the mid to upper 60s. Dry conditions are
expected through Saturday afternoon and the early evening periods.
A subtropical low over the Gulf of Mexico is forecast to move
northeastward through the Carolinas and southern portions of
Virginia. Global models have trended further northward with the
precipitation shield associated with this low. This has lead to
increase precipitation chances for our region especially for areas
in the District of Columbia Metro and southward. The Euro ensembles and
deterministic models suggest precipitation will start overnight
Saturday and linger through Sunday afternoon. Areas in central
Virginia and southern Maryland could see as much as a half inch of
rain from this system. This tropical low is expected be a quick
hitting system that is out of our region by Sunday evening. Rain
combined with overcast skies will likely tamp down the daytime
temperatures on Sunday. I may drop temperatures down by a few
degrees for Sunday since the most recent guidance has been coming
in as much cooler than previous days.
Long term /Monday through Thursday/...
Sfc ridge will be in place Mon with next frontal zone associated
with deep western great lks low pressure system expected to cross
the area on Tue. Pre-frontal showers are anticipated late Mon night
and continuing through Tuesday. Beneficial rain amounts of half inch
or more can be expected with this next system. High pressure builds
for the second half of next week with fair weather conditions
Aviation /18z Friday through Wednesday/...
High pressure will slowly move over our region today through
Saturday. Winds will become light this evening out of the northwest
with mostly clear skies. Winds will become southerly on Saturday and
remain light in the 5 to 10 knot range. VFR conditions expected
through Saturday afternoon. A tropical surface low pressure system
will move into our region late Saturday into Sunday afternoon. Rain
will overspread the region from the southwest to northeast with the
most impacted terminals being cho, iad and dca terminals. Aviation
restrictions will be likely during the rain with terminals
experiencing periods of MVFR conditions. The rain should be out of
the region by Sunday afternoon and VFR conditions expected Sunday
evening and into Monday.
MVFR cigs in rain possible Sat night into sun.
High pressure will be overhead the waters today through Saturday.
Small craft advisories remain in effect for all the waters until
6pm. Winds will weakened this evening and small craft advisories
aren't expected for the overnight and Saturday periods. A coastal
low will pass through the waters late Saturday and into Sunday.
Small craft advisories will likely be needed once again Saturday
overnight and into Sunday.
Small Craft Advisory conditions possible Tuesday into Wednesday.
Tides are running below normal and no flooding issues are
expected in the next 24 hours.
Onshore (easterly) flow is expected to increase ahead low
pressure approaching from the south Saturday night into
Sunday, resulting in increasing water levels. There remains a
moderate level of uncertainty as to the extent and duration of
onshore flow, as that will be reliant upon the exact strength
and track of approaching low pressure. Therefore, the confidence
in exact water levels is low, though the confidence in seeing
at least minor flooding at the more vulnerable tidal sites seems
Light northerly flow should cause water levels to decrease a bit
heading into Monday, before onshore flow (southeasterly) flow
resumes Monday night into Tuesday, leading to a subsequent rise
in water levels once again.
District of Columbia...none.
Maryland...frost advisory from 2 am to 9 am EDT Saturday for mdz004>006-
Freeze warning from 2 am to 9 am EDT Saturday for mdz003-501-
Virginia...frost advisory from 2 am to 9 am EDT Saturday for vaz025>027-
Freeze warning from 2 am to 9 am EDT Saturday for vaz028-031.
WV...frost advisory from 2 am to 9 am EDT Saturday for wvz505-506.
Freeze warning from 2 am to 9 am EDT Saturday for wvz050>053-
Marine...Small Craft Advisory until 6 PM EDT this evening for