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

FXUS61 KLWX 070749

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
349 AM EDT Sun Jun 7 2020

Canadian high pressure will build over the Mid-Atlantic through
Monday, then move offshore Monday night into Tuesday. The
remnants of Cristobal will merge with another area of low
pressure over the Upper Mississippi River Valley during the
middle of the week, and the merged low will move northeastward
into Ontario. This will drag a cold front toward the region
later in the week, though its progress will be slowed by the
aforementioned offshore area of high pressure. A second front
may follow for next weekend.


Today will not be as hot as recent days with lower humidity.
Precipitation chances will be next to none after early this
morning, with minimal cloud cover expected.

An upper-level trough was diving southward from New England just
before daybreak. Lift ahead of this trough combined with a
southward-sagging cold front poised over central Virginia to
result in a few isolated showers overnight. These showers were
diminishing as of early this morning as the front drops farther
southward and drier air continues to advect into the region.

Other than a few fair weather cumulus or perhaps some wispy
high cirrus clouds today, it should be mainly sunny. I went just
a bit above the NBM for high temperatures (more towards a
MAV/MET blend which was warmer) due to downsloping northwesterly
flow which tends to lead to warmer temperatures for our area.
This results in high temperatures eclipsing 80 for most, perhaps
touching the middle 80s across central Virginia.

I then undercut NBM a pinch for overnight low temperatures,
hedging them towards the dew points. A mainly clear sky with
very little wind should allow for ideal radiational cooling
conditions tonight as high pressure builds overhead. This yields
low temperatures in the 50s (except lower 60s in the major
downtown urban centers of DC/Baltimore).


High pressure will drift overhead during the day Monday before
moving offshore Monday night into Tuesday. Thicknesses and
lower-level temperatures appear to be relatively steady-state or
only slowly increasing Monday which should yield temperatures
similar to Sunday with little in the way of precipitation or
cloud cover as the high passes.

Thicknesses/temperatures increase more notably into Tuesday, and
the trend has been for them to increase a little more/a bit
quicker in recent model runs. Therefore, high temperatures will
likely make a run at 90 F on Tuesday. Overnight low temperatures
Monday night are likely to be only slightly warmer than Sunday
night (a few degrees on either side of 60 F) as the high shifts
offshore, but Tuesday night should be 5 to 10 degrees warmer
and increasingly humid as southwesterly flow persists and clouds
build in, trapping heat.

A few ensemble members try to bring some light precipitation
a little east of the Allegheny Highlands late Tuesday night,
but believe it will turn out mainly dry east of the mountains
due to the strength of the high pressure area offshore.


By Wednesday morning, Cristobal (or its remnants) will be phasing
with an upper trough axis across the Northern Plains. The resultant
system will be sending a cold front toward the Mid Atlantic coast
Wednesday night-Thursday morning. First it will need to break down
East Coast ridging, but believe there will be enough energy/moisture
to do so. Its forward motion thereafter is a little uncertain
as additional shortwave energy digging will enhance the longwave
trough in the center of the CONUS leaving the front somewhat
coincident with upper flow. Will maintain chance PoPs Wed-Thu
due to fropa. Will be backing down a little bit Fri as a
majority of guidance suggesting QPF will be minimal at best.

With 850 mb temperatures up close to 20C and at least some sun,
highs Wednesday should be able to make a run at 90F. As
heights/temps aloft ease through the week, expect a gradual
reduction in heat.

Another front may approach from the Great Lakes/Ohio River
Valley next weekend with a renewed chance of precipitation.


VFR through the TAF period. N/NW flow thru Mon. G15-20 kts
possible this aft mainly near KBWI/KMTN. Patchy fog possible
Mon night. VFR persists as winds turn S Tue.

VFR conditions should prevail during the day Wednesday. A cold front
is expected to arrive Wednesday night or early Thursday; associated
showers and maybe a thunderstorm could provide flight restrictions.


Vertical motions behind an upper-level trough/surface cold
front have been just enough to induce transient mixing and a few
N/NW gusts to around 20 knots early this morning. This may
continue to be the case for a few hours, but believe the
gradient and mixing are just too weak to warrant a Small Craft
Advisory (SCA) for frequent gusts during the morning hours.
Mixing increases this afternoon over the near shore waters with
the best (albeit marginal) gradient relegated to the upper
Chesapeake Bay waters. Have issued a SCA there. Elsewhere, the
gradient is weaker, and/or waters are wider and cooler which
should prevent mixing of an already marginal wind field on more
than a highly localized/brief scale.

Winds then go light tonight into Monday, then flip to the south
Tuesday as high pressure moves overhead then offshore.

Increasing southerly flow ahead of a cold front could gust up
to SCA thresholds late Wednesday. That mixing should be
interrupted by fropa Wednesday night into Thursday.


MARINE...Small Craft Advisory from noon today to 6 PM EDT this evening
     for ANZ530-531-538-539.



NWS LWX Office Area Forecast Discussion