Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 klwx 120241 

Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
941 PM EST Wed Dec 11 2019

a strong area of high pressure, originating from
Canada, will build overhead tonight before shifting to our
northeast tomorrow. Meanwhile, an area of low pressure will
develop over the Gulf of Mexico Friday and track north across
the eastern United States as high pressure departs offshore.
Low pressure will then move across the area Saturday, with
another area of low pressure approaching Monday into Tuesday.


Near term /through Thursday/...
strong high pressure will build overhead tonight. With the high
originating from Canada, the air mass is quite chilly, with
temperatures generally 10 degrees below normal or so. Low
temperatures overnight will dip down into the 20s, with the
normal colder spots getting into the teens.

With high pressure shifting to our northeast tomorrow,
temperatures will remain cool, with highs in the mid 30s to low
40s. No precipitation to speak of though, and winds will be
light, so wind chills won't be an issue. Overall, a dry and chilly
day across the area.


Short term /Thursday night through Friday night/...
high pressure will slide offshore Thursday night, as low pressure
develops along the Gulf Coast and heads north toward the region. A
wedge of cold air will remain through much of Friday morning,
especially in the valleys west of the Blue Ridge. This could create
some problems with freezing rain at the onset of the event Friday
morning, when warm advection precipitation is likely to begin across
the area. The most significant risk of freezing rain appears to be
along the I-81 and I-64 corridors, where the precipitation arrives
earlier and the cold air lingers the longest. Farther north and east
of these areas, thinking that surface temperatures should warm just
quick enough to avoid any major issues, but certainly can't rule out
some light accumulations north and east of I-64. Right now,
generally thinking this will be a light event, with less than a
tenth of an inch along the I-81 and I-64 corridors, and perhaps a
couple hundredths farther north and east, if conditions line up just

Outside of the freezing rain threat comes a soaking rain event
areawide starting Friday night, as low pressure moves over the
area. Temperatures may actually rise overnight in some spots,
but most locations should stay in the 30s and 40s.


Long term /Saturday through Wednesday/...
low pressure overhead Saturday will move off to the north later
Saturday morning and afternoon. A soaking rain will be around to
start, but a dry slot will work its way into the area during this
time, and this may cause a lull in the precipitation. Confidence in
timing the lull of precipitation remains low at this time. A second
round of precipitation will be possible Saturday evening into early
Sunday morning due to forcing by the upper level low passing over
our area and the surface low's associated cold front. Some upslope
wintry precipitation can be ruled out over and along the higher

High pressure will build back into our region Sunday through early
Monday morning. Clear skies along with cooler temperatures in the
mid 40s during the day and the 20s and 30s overnight. A warm front
is forecast to lift through our region Monday morning. Overruning
precipitation will be possible as this frontal boundary moves
through our region. As high pressure is in place over the northeast
US, models have been hinting at a cold air damming situation. As the
warm front lifts through our area, this precipitation could
potentially fall as wintry precipitation. We will need to continue
to track the model trend. Models have the damming setup breaking
early Tuesday as the main cold front moves through our area. A brief
warm up into the 40s will lead to rain Tuesday afternoon. It looks
like the cold front is forecast to fully move through our area by
Tuesday evening with cooler temps building back into our area
Tuesday overnight into Wednesday.


Aviation /02z Thursday through Monday/...
VFR conditions will continue overnight tonight, with a light
wind out of the west-northwest. VFR conditions will persist tomorrow, with
mostly sunny skies and light winds.

A low pressure system will track near our area Friday through
Saturday. Showers are expected on Friday, and could lead to
sub-VFR conditions. Rain should become steadier Friday night
through early Saturday morning and will likely cause sub-VFR
conditions. Rain should dissipate late Saturday into early
Sunday. Some showers can't be ruled out with brief restrictions
on Sunday, but prevailing VFR conditions expected on Sunday at
this time.


Small Craft Advisory remains in effect for much of the Bay and
the lower tidal Potomac. Winds will gradually subside overnight,
so will keep with the previous Small Craft Advisory for the
central Bay and lower tidal Potomac into Thursday morning.

As coastal low passes near our area, winds will likely reach Small
Craft Advisory levels Saturday and Sunday. Small craft advisories
will likely be needed this weekend.


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory until midnight EST tonight for anz531>533-
Small Craft Advisory until noon EST Thursday for anz534-537-


near term...cjl/kjp

National Weather Service Glossary of Abbreviations