Forecast Discussion for Willowsford Farm and vicinity from the NWS in Sterling, Virginia

FXUS61 KLWX 220800

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EDT Wed May 22 2019

Canadian high pressure will continue to dominate over the region
today, shifting offshore by this evening. A warm front will
pass through the area late tonight into Thursday. A cold front
will approach Thursday night before stalling out nearby for
Friday and Saturday. The boundary will likely linger through the
remainder of the weekend and into Memorial day, resulting in the
potential for unsettled conditions.


Canadian high pressure will start to shift eastward out of our
region as a warm front approaches and moves into our region from
the west. As the front moves through our area during the late
afternoon period into evening, chances for showers should remain
nonexistent due to the upper level ridge axis remaining
situated over most of the Mid-Atlantic and SE US. Winds will
begin out of the north this morning but as the warm front moves
through our region, winds will become southerly leading to
advection of warm and moist air into our area. This will lead to
afternoon temperatures trending upwards into the mid to upper
70s today with overnight temperature remaining mild in the 60s.
Clouds will build into our region from the west this evening and


The warm front will pass through the region early Thursday morning
and lift off to our northeast. As the front moves through our
area there may be enough instability to kick off a few showers
during the morning period on Thursday. Once the front moves to
our northeast, our region will be in the warm sector ahead of an
approaching cold front. A southerly flow will lead to continued
warm air advection which will transport moisture and warmer
temperatures into our region. Increasing humid conditions along
with temperatures rising up into the mid to upper 80s will allow
CAPE values to increase into the 1500 to 2500 range. This will
be an environment conducive for the formation of thunderstorms
if there is a good lifting mechanism or if there is enough
daytime heating to break the capping inversion.

A cold front is expected to cross into our region Thursday
afternoon into evening. There still remains a lot of uncertainty
on when this front will pass through our area. The models have
been trending quicker with this frontal passage with the GFS
being the fastest solution along with having the stronger upper
level forcing. The Storm Prediction Center has elevated the
areas across extreme north central Maryland to an Enhanced Risk
for severe weather with a Slight Risk reaching as far south as
DC and mainly north of I-66, while a Marginal Risk is
highlighted for the remainder of the CWA. There will be plenty
of energy for storms to feed on in this environment and the
potential formation of severe storms will rely on the timing of
the frontal passage and how much heating can occur before the
front moves through our area. The main threat window for
thunderstorms and severe weather will be the afternoon period
and early evening on Thursday during peak heating. There
remains a lot of uncertainty on how widespread thunderstorms and
showers will be but POPs have been increased along the Mason
Dixon Line to account for the increased SPC risk and new
guidance keeping the highest chances for precip over our northern
zones. Overnight temperatures will remain mild in the mid to
upper 60s.

The cold front is expected to move through our region by early
Friday. A few showers could linger into the Friday morning mainly
along the Mason-Dixon Line in western Maryland. High pressure will
build back into our region behind the frontal passage for Friday.
Skies will become mostly clear on Friday with a mainly westerly
flow. Temperatures during the day will be cooler in the low to mid
80s as compared to Thursday. Overnight temperatures into Saturday
will continue to be mild in the low to mid 60s.


Saturday morning, mid to upper level ridging will crest over the
Eastern Seaboard with surface high pressure stretched across the
region. The high will migrate offshore on Saturday as the flow
aloft transitions to more zonal in nature. At the surface, low
pressure tracking across the Great Lakes will place the area in
the warm sector as winds turn south southwesterly and
temperatures run well above normal for the latter half of May.
As a result, chance POPs will be highlighted in the forecast,
mainly over the higher elevations and near the Mason Dixon Line
Saturday afternoon and evening.

A cold front will approach from the north on Sunday, lingering
nearby through Monday. Daily chances for showers/storms will
continue, focused around peak heating hours as shortwave energy
tracks overhead, and above normal temperatures and humidity
persists. Looks to be a brief reprieve from the heat and
humidity on Tuesday as high pressure transits the region.
However, another shot of shortwave energy quickly approaching
from the northwest may spark late day showers and thunderstorms
again over the higher elevations.


High pressure will begin to shift northeastward out of the our
region today. Winds will begin out of the north but will become
southerly by this afternoon. Skies will remain mostly clear
with a few mid to high level clouds. VFR conditions are expected
at this time.

Mid level clouds will build into our region late today and
overnight as a warm front moves through our area. Some showers
will be possible early Thursday but the best chance for showers
and thunderstorms will be during the afternoon and evening
periods on Thursday. Mainly VFR conditions expected but some
MVFR conditions will be possible with showers and thunderstorms
on Thursday. Winds will continue out of the south and then
become westerly behind a cold frontal passage late Thursday into
Friday. Clear skies are expected for Friday as high pressure
settles over our region. VFR conditions expected on Friday for

Afternoon showers and thunderstorms will favor our mountain
zones Saturday and Sunday, with MRB serving to have the best
shot of brief sub VFR conditions. Otherwise, predominate VFR
conditions are expected with winds favoring a light southerly
trajectory Saturday, veering westerly on Sunday as a frontal
boundary settles across the region.


High pressure will move northeastward out of our region leading to
winds becoming southerly as a front boundary moves through this
afternoon into this evening. Stronger winds over the waters will be
possible on Thursday as a cold front approaches and moves through the
waters. Strong thunderstorms will be possible on Thursday which may
require special marine warnings due to strong gusty winds and an
isolated waterspout. Small Craft Advisories may be needed
Thursday afternoon and into early Friday.

Light southerly flow on Saturday will increase Saturday night as
a cold front approaches from the north. Marginal SCA conditions
will be possible during this time. The frontal boundary will
settle near the waters on Sunday, with the gradient remaining
weak, however isolated showers and storms will be possible each





NWS LWX Office Area Forecast Discussion