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

FXUS61 KLWX 191843

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
243 PM EDT Tue Mar 19 2019


High pressure will remain in place over the region through
Wednesday. A coastal low will develop off the coast of the
Carolinas and move northward into our region Thursday. A
cold front will approach our region from the west on
Thursday and linger through early Friday. High pressure will
build into our region from the Great Lakes through the weekend.
Another system will affect our region Monday into Tuesday next



We have scattered cumulus clouds lingering over northwest
Maryland, western Virginia and eastern West Virginia currently.
This has dropped cloud levels down to six thousand feet in some
areas but there are signs of these clouds thinning moving into
this afternoon. Winds are expected to remain light and variable
through this evening. High pressure will remain over the region
through this evening.

Some high clouds will be possible this evening but clouds are
expected to remain thin. Temperatures are expected to be chilly
in the 30s and the 20s in some areas as light winds will allow
good radiational cooling overnight



High pressure will shift northeastward out of our region through
Wednesday evening. As the high shifts out of our region, winds
will become southerly leading to good warm air advection into
our area. Temperatures during the day on Wednesday are expected
to trend upwards into the mid 50s. High clouds will start to
build into our region from the west as a cold front approaches
from the midwest.

Multiple areas of upper level energy will shift eastward toward
our region late Wednesday into Thursday. The northern stream of
energy will dig southward from the upper Midwest into the Great
Lakes region and our area late Wednesday into Thursday. The
southern stream is forecast to be kicked southward into the
Southeastern US and form a coastal low along the Carolina
coast. The models have the two energy streams merging over the
Carolinas by late Thursday into Friday. Temperatures on Thursday
are expected to warm ahead of the cold frontal passage.

The coastal low forming in the Carolinas is expected to move
northward into our region Thursday morning into afternoon
periods. A cold front will approach at the same time from the
west. There is general model agreement that precipitation will
start to affect our region some time after 00z on Thursday with
best chance being after 6Z. Rain will likely overspread most of
the region by the 12 to 18Z period. I have upped the pops
slightly in the 00Z to 6Z period to account for some models
having the coastal low moving quicker into our region. As the
cold front approaches from the west the higher elevations out
west could experience a few scattered snow showers. Rain is
expected to finally move out of our region by late Thursday into
Friday with some showers lingering into Friday near the Mason
Dixon Line. Some upslope snow showers can`t be ruled out behind
the cold frontal passage Friday morning.



An upper-level low will swing down from the north on Friday, as the
coastal low that will bring rain on Thursday departs off to the
northeast. As the upper low tracks southward, it will drive a
surface cold front through the area Friday afternoon. A few showers
will be possible along the surface cold front, and also within the
steep low-level lapse rate environment beneath the upper low. Some
of these showers could potentially fall in the form of snow or
graupel over the higher elevations. Gusty winds will also be
possible Friday afternoon and evening in post frontal northwesterly

High pressure will gradually build over the region through the day
Saturday as shortwave ridging aloft moves into the Ohio Valley. The
high will slide offshore on Sunday, which will allow southerly
return flow to develop. Both days this weekend look dry, but Sunday
will be substantially warmer than Saturday as southerly winds start
to transport a warmer airmass into the area.

On Monday, disturbances in both the northern and southern streams
will start to approach the area. The northern stream trough will be
quite dynamic, forcing the development of a large area of high
pressure in it`s wake. This high will shift southward in conjunction
with the upper trough, driving a powerful cold front southeastward
toward our area. The combination of the southern stream disturbance
approaching from the Tennessee Valley, coupled with the southward
surging cold front could produce precipitation across the area by
Monday afternoon. However, the positioning of the front and the
resultant chances for precipitation are still rather uncertain six
days out. The airmass behind the cold front looks very cold for late
March, and wintry precipitation may be possible behind the front,
even at lower elevations.



We have lower clouds currently affecting areas near Martinsburg
airport but I expect these clouds to break later this afternoon.
VFR conditions expected through Wednesday but high clouds will
start to build into our region Wednesday afternoon. As a coastal
low approaches from the south and a cold front approaches from
the west, cloud bases will lower to MVFR late Wednesday evening
and IFR conditions possible starting Thursday morning. As rain
moves into our region on Thursday, IFR conditions are likely
with lowering cloud levels.

VFR conditions are expected on Friday through the weekend. However,
a brief shower can`t be ruled out during the day on Friday.



High pressure expected to remain in place through Wednesday
leading to light and variable winds. A coastal low will approach
and move through the waters on Thursday leading to the
possibility that Small Craft Advisories maybe needed Thursday
evening into Friday.

A cold front will pass over the waters during the day Friday. SCA
level winds appear likely behind this front, and there`s a chance
that winds may even reach gale force late Friday afternoon. SCA
level winds appear possible Friday Night through much of the day
Saturday, before winds gradually drop to sub-SCA levels Saturday





NWS LWX Office Area Forecast Discussion