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

899
FXUS61 KLWX 260122
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
922 PM EDT Thu Apr 25 2019

.SYNOPSIS...
A warm front stalled in central Virginia tonight will lift north
across the region Friday morning. Low pressure will track
from the Ohio Valley to the eastern Great Lakes Friday, pulling
a cold front across the area Friday afternoon. High pressure
will build in behind this front for the early part of the
weekend. Another storm system could approach the region Sunday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Frontal boundary is residing in central Virginia this evening
will more or less remain in place overnight. Warm advection and
approaching upper trough will enhance shower activity overnight.
Some mainly elevated instability may develop and an isolated
thunderstorm or two is also possible, mainly across eastern WV
and VA. Lows tonight will range from the mid 50s to low 60s.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Surface warm front will remain in central VA early Friday
morning, but should rapidly progress northeastward through the
area during the mid and late morning hours. Meanwhile, surface
low pressure will move northeastward through the eastern Great
Lakes during the day, with its attendant surface cold front
crossing the region during the afternoon and early evening
hours. Some showers and/or elevated isolated thunderstorms may
be ongoing early Friday morning, with activity waning during the
late morning hours after the surface warm front lifts north.
This will allow for temperatures to rise and cause surface-based
instability to develop. A few models suggest significant
instability of greater thatn 1500 J/kg, but most are not as
unstable, likely due to lingering clouds limiting insolation.
However, this should be adequate, when combined with strong low
to mid level wind field and 40 knots or so of bulk shear, to
set the stage for strong to locally severe thunderstorms, mainly
from the Blue Ridge Mountains eastward, with the highest
probability of severe across portions of central VA, eastward to
DC, and into southern Maryland where a Slight Risk of severe
thunderstorms was introduced.

Showers/thunderstorms will likely develop around noon or so
across eastern WV and central VA, and move eastward across the
region, exiting east of the Chesapeake Bay by 7 PM. The highest
threat window for severe thunderstorms will likely exist between
2 PM and 6 PM. Several discrete cells are possible ahead of what
may become a more organized developing squall line. The primary
threat will be isolated damaging wind gusts, but given
low level directional shear and relatively high helicity values,
an isolated tornado is also possible, with the highest
probabilities in southern MD.

Heavy rainfall will also occur with these showers/thunderstorms,
and while a widespread flood event is not likely, an isolated
incident of flooding is possible if any training thunderstorms
occur. The flood threat is somewhat lower than a week ago since
the weather has been dry for nearly a week now.

Highs on Friday will range from the 60s to low 70s, with coolest
readings in the mountains where the surface cold front will
arrive first, fairly early in the day.

The front will then push eastward Friday night with strong
west-northwest flow following behind. Gusty winds are expected
with 30-40 mph likely, although mixing may be limited at night.
It`s possible a Wind Advisory may be needed, especially across
the higher elevations, but uncertainty exists at this time. The
wind field begins to weaken Saturday but mixing will increase
during the daylight hours, so gusty winds may actually max out
Saturday morning. Highs Saturday in the 60s to around 70F.

A weak ridge of high pressure moves overhead Saturday evening
before shifting eastward and offshore by Sunday morning as a
weak area of low pressure approaches. Some showers become
possible Saturday night.Lows in the 40s to low 50s.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
A cold front will cross the area Sunday afternoon. Moisture and
instability will be limited with the best moisture and
instability focused to our region`s north. Rainfall amounts will
be light. Dry weather is expected Sunday night as strong high
pressure builds in from the northwest.

Moisture returns Monday night as high pressure shifts east. A
developing front over the Ohio Valley will be the focus for
showers and thunderstorms. Although disturbances will move along
the front, the front will remain nearly stationary with very
little shower or thunderstorm activity initially. Expect
unsettled weather to redevelop toward the middle and latter part
of the week with a chance for thunderstorms.

&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
Showers and even a few isolated thunderstorms will develop this
evening and continue into Friday morning. Reductions to MVFR
are expected, with the highest probabilities of more consistent
MVFR ceilings at MTN/MRB.

A strong cold front will then cross the terminals Friday.
Predominant VFR/MVFR anticipated, but local IFR likely within
showers/storms. In addition, local gusty winds (40-50 kt)
possible in stronger storms. Placement of these cells
problematic this far out, but the general time frame for strong
winds/wind shift will be mid afternoon MRB/CHO and late
afternoon at the hubs (IAD/DCA/BWI).

Gusty northwest winds will continue behind the front Friday
night into Saturday before diminishing Saturday night. Gusty
NW winds anticipated once again Sunday afternoon through Sunday
evening behind another frontal passage.

A few showers are also possible Monday night. Conditions could
briefly become MVFR in these showers.

&&

.MARINE...
Generally light winds expected on the waters through tonight.
Flow which is predominantly northerly this afternoon will
become south this evening and tonight as a warm front slowly
crosses the waters.

By Friday, a sharp cold front will be approaching the waters.
While mixing won`t be ideal, there will be a healthy gradient
wind in advance of this front. A Small Craft Advisory is in
effect beginning at 12 Noon. The environment will also become
favorable for development of clustered showers/thunderstorms
Friday afternoon capable of producing gusty winds in excess of
34 knots and possibly up to 50 knots, and Special Marine
Warnings may become necessary.

In the wake of the cold front Friday night into Saturday the
gradient remains tight, with 30-35 kt (and depending upon model
solution, perhaps up to 40 kt) still available. Momentum
transfer will be more optimal. A SCA is in effect, but an
upgrade to Gale may be needed. The strong winds will continue
into Saturday morning before gradually relaxing during the
afternoon hours.

Small craft advisory conditions expected Sunday and Sunday
night with frequent gusts to around 25 knots. Winds diminish
below criteria later Sunday night through Monday night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 9 AM Friday to 6 AM EDT Saturday for
     ANZ530>543.

&&

$$
SYNOPSIS...MM/RCM
NEAR TERM...MM/RCM
SHORT TERM...MM/RCM
LONG TERM...KLW
AVIATION...MM/KLW/RCM
MARINE...MM/KLW

NWS LWX Office Area Forecast Discussion