Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 020815
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
415 AM EDT Tue Jun 2 2020

.SYNOPSIS...
High pressure will shift offshore today. A warm front will
slowly advance northeast across the region through tonight,
allowing a hot and humid air mass to overspread the region for
the rest of the week. A cold front will then cross the region
this weekend, with cooler Canadian air returning by early next
week.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Latest analysis depicts high pressure near Cape Hatteras. A warm
front extends northwestward from the southern Appalachians to a
surface low north of the Great Lakes. A cold front extends
southwestward from there across the northern Plains. Aloft, A
ridge is centered over the southern Plains, with a closed low
near Nova Scotia, with fast northwesterly flow over our region.
A weak shortwave is crossing the eastern Great Lakes with
another over the western Great Lakes, and a third over Montana.

Today, warm advection will get underway as the high shifts east
into the Atlantic and the warm front to the southwest advances
north. Weak forcing will result in plentiful clouds, with a few
showers possible, but nothing more significant than that is
anticipated. The clouds will keep temps lower than possible,
but still warmer and more humid than yesterday, with mid 70s to
mid 80s expected. Coolest readings will be in northeastern
Maryland with much warmer temps in the lower Shenandoah Valley
and points near Charlottesville.

The actual warm front will struggle to push north of our region
today, with it continuing to slowly push northeastward tonight.
However, with forcing waning, little if any precip is expected.
Lows will be mostly in the 60s.

The warm front will finally clear the region early Wednesday,
allowing the first truly hot air mass to overspread the region.
Latest short-range guidance is starting to hint that some
convective remnants from earlier may overspread the region on
Wednesday morning, which could put a damper on temps. However,
at this point we will continue with a mostly dry morning
forecast until better concensus is reached, allowing temps to
soar into the 90s. This will add plenty of instability and with
a shortwave passing north and another cold front starting to
approach, some strong storms may develop late in the day. Any
storms could be severe given some shear and plenty of CAPE, but
a trigger is still questionable.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
Wednesday evening appears to be the best time for severe
weather, as storms which develop further north closer to the
cold front advance into the hot, unstable air mass over our
region and tap into the high CAPE and moderate shear. That said,
it remains possible that storms start diminishing before
reaching our region, with best odds of severe weather remaining
near the PA state line. That having been said, SPC has
continued and expanded the slight risk southward somewhat.

Storms should mostly end overnight with warm muggy conditions
early Thursday morning. This will set the stage for what likely
is a stormier Thursday in general, as the front stalls just
north of us and additional shortwave energy moves overhead. The
shear is not nearly as strong, but CAPE should be adequate for
plenty of storms, a few of which could be borderline severe as
well as potentially dropping locally heavy rain. A marginal
outlook for heavy rain and severe weather has been placed over
our region from WPC and SPC, respectively. Storms likely wane
again overnight as we lose heating, but it will again remain
muggy.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
A stalled/weakening frontal boundary will remain overhead
Friday. Given multiple waves aloft and a warm/humid and unstable
airmass, at least scattered showers and a few thunderstorms
seem plausible. The prospect for severe weather is uncertain and
will be predicated upon cloud cover or residual boundaries
leftover from prior convection as well as the extent of
instability and shear present in relation to any small-scale
disturbances with inherently low predictability at the Day 4
time range.

There may be a little more convective organization late Friday
into Saturday as a stronger synoptic cold front and upper wave
approach the region, but certainty is lower for the reasons
outlined above, in addition to timing discrepancies among the
latest guidance. If organized convective complexes develop
upstream, and/or if frontal timing aligns closer to peak diurnal
heating, then the severe weather threat would increase.

Canadian high pressure should build in by the second half of
the weekend into early next week as per a consensus of the
latest model guidance. This would lead to a period of dry
weather and temperatures near to slightly below normal.

&&

.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
VFR through Thursday night overall. Main concern will be for
scattered thunderstorms Wednesday afternoon/evening and again
Thursday afternoon/evening. Better risk of storms is Thursday,
but a better severe risk exists Wednesday.

Sub-VFR possible in shower/t-storm activity Fri-Sat. NW G20kts
possible Sat aft.

&&

.MARINE...
Marginal SCA currently over middle bay/lower Potomac should end
by dawn or shortly thereafter. Warm front moving through should
keep winds just below SCA, but may need short-fused SCA later
today/tonight/Wednesday as winds will not be far from criteria
with warm air advancing northward. However, main boating hazard
is likely to be Wednesday afternoon/evening and again Thursday
afternoon/evening, as scattered thunderstorms could produce
gusty winds on the waters. Special Marine Warnings may be
necessary.

Scattered showers and thunderstorms (a few of which may be on
the stronger side) are possible mainly late Friday into Saturday
ahead of a cold front. Winds will be S/SW Friday, switching to
NW and gusting to perhaps around 20 kts Saturday behind the cold
front.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies have increased markedly overnight due at least
in part to increasing SW flow. This resulted in threshold/minor
flooding for Annapolis and is likely to do the same at DC SW
Waterfront early this morning. Subsequent tide cycles are lower
astronomically and should fall short of flooding thresholds, but
continued close monitoring will be required in a similar large-
scale pattern through mid week.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 7 AM EDT this morning for DCZ001.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 7 AM EDT this morning for ANZ533-
     534-537-543.

&&

$$
SYNOPSIS...RCM
NEAR TERM...RCM
SHORT TERM...RCM
LONG TERM...DHOF
AVIATION...RCM/DHOF
MARINE...RCM/DHOF
TIDES/COASTAL FLOODING...



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