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433
FXUS61 KLWX 301834
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
234 PM EDT Tue Apr 30 2024

.SYNOPSIS...
A cold front will slowly push through the region this afternoon and
evening bringing scattered showers and thunderstorms. A few showers
linger Wednesday morning with dry high pressure settling back in for
the afternoon. Warm and dry conditions continue Thursday before
shower and thunderstorm chances return with another front Friday
into the start of the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
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Subtle relief from the heat in the form of a cold front/lee trough
is expected to pass through the region later this afternoon and
evening. The front is evident on radar with a band of precipitation
extending from Lake Erie south along the Ohio River into eastern
Kentucky. This area of precipitation will continue to slowly move
east this afternoon allowing for an uptick in cloud cover across our
region heading into mid-afternoon. As for precipitation chances, 12z
hi-res CAM guidance continues to show varying differences in regards
to timing and coverage.

Most of the guidance shows the leading edge of the
precipitation entering our western most counties (i.e Garrett
Co. MD and Pendleton/Hardy Co. WV ) around 2-5pm with isolated
showers along the higher ridgetops of the Blue Ridge/Alleghenies
during this same timing window. The main band of shower and
thunderstorm activity will work into the I-81/Blue Ridge
corridor between 5-8pm before shifting toward the metros and
dissipating after sunset. As for the threat of severe weather,
it remains low, but not zero. Instability will remain fairly low
on the order of 500- 1000 j/kg with 0-6km bulk effective shear
values running 20-30 kts and mid-level lapse rates around 6-7
degree C km. Both SPC, CSU Machine Learning, and CIPS analogue
products continue to point to a very low probability of severe
weather. Even with that said, one or two storms could become
strong given the antecedent conditions especially west of the
Blue Ridge. Biggest threats with any storms this afternoon and
evening looks to be wind gusts 40-50 mph, frequent lightning,
and locally heavy rainfall (PWATS running 0.75- 1.25 inches).

High temperatures today will push back into the mid to upper 80s
with 70s over the mountains/near the bay. Metro areas could flirt
with 90 degrees. Heat index values will remain below 90 degrees
given the fact that dewpoints will remain in the mid to upper
50s and low 60s.

Storms move out of the area before midnight, with a slight chance of
showers lingering through early Wednesday morning as the front moves
to our south and east. Lows tonight will fall back into the upper
50s and low 60s with areas of patchy fog that due see the rain.
-- End Changed Discussion --


&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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The cold front that passed through the region Tuesday night will
lift back to the north Wednesday morning into Wednesday afternoon as
the upper level trough pivots overhead. This will allow for the
continuation of a few scattered showers and perhaps an isolated
thunderstorm for areas mainly east of I-81 Wednesday morning into
Wednesday midday. Beyond midday Wednesday, 12z guidance continues to
trend drier with quick clearing from west to east as shortwave
ridging/high pressure over the Lower Tennessee/Ohio River Valleys
builds back into the region. At the same time an additional isolated
shower or thunderstorm cannot be ruled out over eastern VA and
southern MD as shortwave low pressure drifts across the Carolinas.
High pressure slides over the southern Appalachians and Blue Ridge
Wednesday evening into Thursday leading to a continuation of quiet
weather conditions. Highs Wednesday will push into the mid to upper
70s and low 80s with overnight lows in the mid to upper 50s.

Upper level ridging firmly builds over the area Thursday leading to
a continuation of warm and dry conditions. 850 mb temperatures will
be back up around +13 to +17 degrees C with PWAT values around 1".
Meanwhile, a moisture starved cold front will sit across western
portions of the forecast area acting as a catalyst for perhaps an
isolated mountain shower or thunderstorm. Elsewhere across the
region expect dry conditions with passing fairly weather strato-
cumulus during the peak heating of the day. High temperatures will
remain above average in the low to mid 80s with 70s over the
mountains. Metro areas will be a tad warmer with highs closer to 90
degrees. Lows Thursday night will fall back into the mid to upper
50s.
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
A mostly dry period on Friday will soon be met with increasing
moisture ahead of the next front system early Saturday and through
much of the weekend. The front will slowly move through the Mid-
Atlantic region during the weekend, with QPF totals reaching nearly
an inch in localized areas. Some isolated instances of flooding will
be possible with increase precipitation and the drier antecedent
conditions across the area. Convection should be fairly weak if it
were to occur this weekend given the lack of instability parameters.
More afternoon, summertime precipitation will likely spawn Monday
and Tuesday with a lingering boundary nearby off to the south of the
area.

Temperatures will fluctuate late this week into early next weekend
with the cold front passage. Highs in the upper 70s to low 80s on
Friday will be followed by low to mid 60s by Saturday. A progressive
warmup will follow Sunday into early next week with highs in the low
to mid 80s by Tuesday.
-- End Changed Discussion --

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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VFR conditions are expected this afternoon ahead of precipitation
associated with a cold front later this evening and into the first
part of the overnight period. The front will push into areas west of
KCBE/KEKN between 18-21z/2-5pm before advancing east toward KMRB,
KHGR, and KSHD around 21-00z/5-8pm. Beyond this point, shower and
thunderstorm activity will advance eastward into the corridor
(between 00-03z/8-11pm) while gradually weakening. Overall
coverage will be scattered across the terminals this evening and
into the overnight hours. Some thunderstorms may be locally
strong especially west of a line from KHGR down to KSHD where
better instability can be found. Gusts of 35 knots or greater
are possible with some of these stronger storms, along with
frequent lightning strikes and locally heavy rainfall. With that
said, some MVFR cig and vsby reductions are possible in and
around any shower or thunderstorm activity that forms. Any
showers or thunderstorms should move out of the terminals before
04z/12am with just a few spotty showers lingering at terminals
east of the Blue Ridge during the pre-dawn hours Wednesday
morning.

VFR conditions are expected to continue Wednesday despite a few
lingering morning showers and perhaps an isolated thunderstorm
for terminals south and east of KDCA and KCHO. 12z model
guidance has trended drier as strong upper level ridging/high
pressure build back into the region. Southwesterly winds today
will shift to northwesterly winds on Wednesday. Winds gust
between 10-15 knots this afternoon with winds gusting up to 20
knots at DCA. Winds diminish overnight before remaining light on
Wednesday, blowing between 5-10 knots.

VFR conditions are expected through Friday, with sub-VFR ceilings
possible Saturday as increasing showers approach the terminals.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
SCAs continue through midnight for southwest winds 10 to 15 knots
with gusts up to 20 kts at times. These winds are due in part to a
tightened gradient ahead of a cold front and lee trough set to swing
across the waters later this evening. The front will bring the risk
for scattered showers and thunderstorms especially after 7pm/23z. An
SMW (Special Marine Warnings) or two may be needed for any strong
thunderstorms that do look to form. Most of the activity will be
below severe limits and fairly isolated to scattered in nature.
Within stronger storms expect gusts of 35 knots or greater, frequent
lightning, and locally heavy rainfall.

A few showers will linger near the waters Wednesday morning as an
additional piece of upper level energy swings through. Winds will
shift to the northwest in the wake of the front and will likely
stay below SCA criteria.

Marginal SCA conditions could occur in channeling on the bay
Thursday and Friday afternoon/evening. Otherwise no marine hazards
are expected with south winds Thursday switching to the southeast
Friday.

Marginal SCA winds will be possible through the weekend. SCAs may be
needed during this period as another front passes through.
-- End Changed Discussion --


&&

.CLIMATE...
Below is a list of record high temperatures for today, April
30th.

                                       Apr 30th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     92F (1942+)     87F
Washington-Dulles (IAD)       86F (2017+)     85F
Baltimore (BWI)               92F (1910)      87F
Martinsburg (MRB)             91F (1974+)     84F

+ denotes that multiple years reached this value, but the depicted
  year is the most recent

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543.

&&

$$

SYNOPSIS...EST
NEAR TERM...EST
SHORT TERM...EST
LONG TERM...ADM
AVIATION...ADM/EST
MARINE...ADM/EST
CLIMATE...LWX