Scientific Forecaster Discussion
fxus61 klwx 132009
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
309 PM EST Wed Nov 13 2019
Arctic high pressure will migrate overhead tonight, then
shift offshore on Thursday. A weak cold front will cross the
area Thursday night with high pressure returning through Friday
night. Coastal low pressure will intensify off the southeast
coast Saturday before moving northeast off the mid- Atlantic
coast Sunday. High pressure will build over New England during
this time. Another low may impact the area early next week.
Near term /through tonight/...
Arctic high pressure will track overhead tonight, leading to dry
conditions and light winds. There will be some high clouds
overhead, but do think they will be thin enough and scattered in
coverage to allow for radiational cooling to commence. This
should allow temperatures to drop back down into the teens and
20s once again. Likely only to see BWI challenged for a record
low (18f), as iad/dca records are a bit chillier (13f/19f).
Should we see a bit more cloud cover than currently forecast,
that will help hold temperatures up a bit, but still well below
normal for the middle of November.
Short term /Thursday through Friday night/...
we start to slowly moderate on Thursday and Thursday night as
the high shifts offshore and winds turn southerly. Partly to
mostly sunny skies are expected on Thursday, with temperatures
topping out in the 40s areawide.
A weak cold front will cross the area Thursday night as low
pressure emerges off the southeast coastline. These features
will bring a chance for light rain to portions of southern
Maryland and the Virginia Piedmont late Thursday night into
Friday morning. Guidance is in decent agreement with the precip
remaining south and east of the Washington Metro as the
northern/southern stream interact and an upper low migrates off
the southeast coast. If this plays out as model consensus
currently indicates, ptype will remain plain rain over the above
mentioned areas. If the precip makes a more northward extent
into the colder air at the surface, there would be the potential
for freezing rain, but confidence in this occurrence at this
time is low.
High pressure over the Great Lakes builds eastward into New
England on Friday as precip is shunted to our south and east and
dry conditions prevail for the entire area. Temperatures
moderate further Friday and Friday night, but remain slightly
Long term /Saturday through Wednesday/...
a somewhat active pattern over the long term with multiple
shortwaves passing overhead inducing two main surfaces lows off the
East Coast through early next week.
Saturday, throughout the day, looks to remain dry as a large area of
high pressure centered over New England suppresses a developing
coastal low off the Carolina coast. A relatively tight pressure
gradient between the two systems will induce gusty winds (perhaps
gusts as high as 30-40 mph near/east of the Blue Ridge where the
pressure gradient will be the strongest). The combination of
temperatures (struggling to get out of the 40's) and gusty winds
will create wind chill values in the upper 20's. The low begins
departing off the Carolina coast late Saturday/early Sunday morning.
While the heaviest precipitation will remain east of the Delmarva, a
few spotty showers are possible early Sunday morning for westernmost
Metro areas. However, conditions look to remain dry through the
weekend at this time.
By early next week, an amplified trough digs southeastward, catching
whatever vorticity/shortwave energy is left near the southeastern
U.S. On Tuesday, a second, more potent, coastal low once again
develops off the Carolina coast. However, timing and placement of
the trough moving through the southeast will dictate the exact
placement of any associated precipitation. The trend of the U.S
models has kept most of the precipitation offshore while the Euro
has the low developing closer to the coast which would bring the
precipitation shield more west. In any case, any storm system
that develops should be lifting northeastward, away from the
region on Wednesday. Overall, temperatures should be on a slight
warming trend through early next week. However the question
becomes how quickly, especially for mountainous areas and
perhaps near the PA border.
Aviation /19z Wednesday through Monday/...
VFR conditions at the terminals through tonight as Arctic high
pressure builds over the region. Northwesterly breezes have
backed off at less than 10 knots this afternoon and will trend
light & variable overnight. The high shifts offshore Thursday
and Thursday night as the flow turns light and southerly. A weak
cold front will cross the terminals Thursday night, with a
northerly flow prevailing through Friday night. With dry
conditions forecast at the terminals, VFR conditions will win
VFR conditions are expected on Saturday and the early part of
Sunday. A strengthening area of low pressure off the Carolina coast
will bring some low to mid level clouds into the area throughout the
day on Sunday, primarily affecting BWI, mountain and dca. Could see some
sub-VFR conditions at these taf sites on Sunday. Precipitation
chances begin to increase late Sunday as low pressure rides up the
East Coast, but remains pretty far offshore. Could see some gusty
winds both days, depending on how close the low gets to the coast,
so something to watch. Winds will generally be out of the north-northeast.
winds have diminished this afternoon as high pressure nears the
waters. Light winds overnight and Thursday as high pressure
traverses the area, shifting off the coast, turning winds
Low pressure will intensify near the southeast coast Friday
through Friday night. An Small Craft Advisory will likely be needed for portions
of the waters during this time. A Gale Warning may also be
needed for portions of the waters late Friday night.
Small craft advisories will be needed Saturday and Sunday, as an
area of low pressure strengthens off the Carolina coast and drifts
northeast. Gale conditions also appear possible, especially late
strong offshore flow has resulted in below normal tides, with
near blowout from near Baltimore Inner Harbor northward on the
Chesapeake Bay. We have seen improvement this afternoon as winds
trended lighter and tide levels begun to rise.
with the Arctic airmass over the region, record low temperatures
were set this morning at iad (19f), and tied at BWI (22f). Here
are additional record lows and record cold highs.
Site low 11/13 high 11/13 low 11/14
dca 22/1911 31/1911 19/1920
BWI 22/2019 32/1911 18/1986
iad 19/2019 38/1996 13/1986
District of Columbia...none.