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

FXUS61 KLWX 220141

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
941 PM EDT Thu Jun 21 2018

A front will remain stalled over the Mid-Atlantic overnight
before slowly returning north as a warm front Friday into
Saturday. Low pressure will move from the Ohio Valley to the
eastern Great Lakes during this time, then eastward across New
England Sunday bring a cold front across the region. High
pressure will then build in from the eastern Great Lakes and
remain in control through the middle of next week.


A front will remain stalled across the central Shenandoah
Valley into the central Virginia Piedmont overnight into early
Friday. This front will gradually move north as a warm front
during the day Friday, but not before spreading several rounds
of showers with embedded thunderstorms across our western and
central zones.

The main threat with the showers and thunderstorms will be
heavy rainfall and lightning. PWATS near or slightly above 2
inches are a good signal for heavy rainfall with this activity.
A Flash Flood Watch remains in effect for parts of the central
Shenandoah Valley and Virginia Piedmont through the overnight.
We already have issued a couple of flood warnings in Augusta,
Greene, Albemarle, Madison, and Orange Counties in Virginia.
Reports came in to us of multiple roads and intersections closed
due to high water.

The air remains relatively drier farther north and northeast;
therefore, it is making it difficult for the showers and
thunderstorms to move to northeast Virginia and northeast and
southern Maryland. Some light to moderate rain will eventually
spread into these regions overnight and early Friday with the
stalled front in close proximity, but intensity and coverage
remains somewhat uncertain.


Showers and thunderstorms are likely to linger near the boundary,
and heavier rain is possible near the Potomac Highlands into
central Virginia into Friday night. Isolated flooding cannot be
ruled out across these areas due to the already saturated
grounds from previous rainfall.

The boundary will begin to lift north as a warm front overnight
Friday through Saturday. Additional showers are likely Friday
night into Saturday morning. There may be a break in
precipitation later Saturday morning behind the warm front.
However, a warm and humid airmass will lead to more scattered
showers and thunderstorms Saturday afternoon into Saturday
evening. Deep layer shear profiles will be stronger due to
upper-level low and surface low nearby over the Great Lakes. The
deep layer shear and unstable atmosphere may lead to stronger
thunderstorms Saturday afternoon and evening. Convection should
dissipate overnight Saturday due to the loss of daytime heating.


A cold front will approach the area Sunday before passing
through Sunday night into Monday. Warm and humid air is expected
Sunday. A few showers and thunderstorms are possible, but
coverage may be scattered due to a westerly component to the
low-level flow. Canadian high pressure will build overhead for
Monday and Tuesday, causing drier and cooler conditions. The
high will move offshore during the middle portion of the week,
causing hot and humid conditions to return.


Scattered to numerous showers and thunderstorms are expected
near KCHO during the rest of this evening into the overnight.
SubVFR cigs/vsbys are expected in any thunderstorms.

Some shower activity and perhaps a rumble of thunder may also
move across MRB, IAD, DCA terminals later this evening and
overnight. Soon to follow later overnight into early Friday will
be BWI and MTN. Once again SubVFR cigs/vcbys are expected in
heavier showers and any thunderstorms.

An easterly flow will cause low clouds to return later overnight
across the eastern and northeastern terminals with MVFR conditions
expected and IFR cigs possible.

This rain activity, preceded by low clouds, are expected Friday.
IFR conditions are likely Friday night into Saturday ahead of a
returning warm front. Scattered thunderstorms are expected
behind the warm front Saturday afternoon and evening, and some
of the storms may be strong.

A cold front will approach the terminals Sunday before passing
through Sunday night into Monday. VFR conditions are expected
for most of this time. A thunderstorm is possible Sunday
afternoon/evening on the warm side of the boundary.


A boundary will stall south of the waters through Friday before
lifting north as a warm front Friday night into Saturday. A
pressure surge will cause easterly winds to strengthen Friday
and a Small Craft Advisory is in effect through Friday evening.
Winds should subside a bit as the gradient weakens overnight
Friday and Saturday. Scattered thunderstorms Saturday into
Saturday night may produce gusty winds.

A cold front will approach the waters Sunday before passing
through Sunday night into Monday. A Small Craft Advisory may be
needed for portions of the waters both ahead of and behind the
cold front through Monday night. High pressure will build
overhead Tuesday.


PWATs exceeding 2 inches late this evening over central Virginia
and southern Maryland will lead us to heavy downpours in showers
and embedded thunderstorms that linger into the nigh. Rainfall
amounts by Friday morning will average 1 to 2 inches, with
locally much higher amounts possible. A Flash Flood Watch
remains in effect for central Virginia into the Potomac
Highlands overnight.

Rain will spread northeastward Friday and Friday night. However,
it will be a bit more stable so the rainfall rates should not be
as heavy. However, isolated instances of flooding cannot be
ruled out...especially across the Potomac Highlands into central
Virginia (closer to the boundary).


Tidal anomalies should remain steady overnight with light
northerly becoming easterly winds. Slight increases in tidal
anomalies will ensue later overnight and early Friday. Some
sensitive locations may approach minor flood thresholds Friday
night, although most guidance has peak anomalies and the highest
chance of minor flooding Saturday night after winds turn
southerly. A cold frontal passage will end the threat on Sunday.


VA...Flash Flood Watch until 6 AM EDT Friday for VAZ025>027-029-
WV...Flash Flood Watch until 6 AM EDT Friday for WVZ055-505-506.
MARINE...Small Craft Advisory from 6 AM Friday to midnight EDT Friday
     night for ANZ530>543.



NWS LWX Office Area Forecast Discussion