803
FXUS61 KLWX 050752
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
352 AM EDT Fri Jul 5 2024

.SYNOPSIS...
A cold front will slowly approach from the Ohio River Valley through
tonight, then cross the region Saturday. High pressure will briefly
follow for Sunday as the front stalls just to the south and east.
The high will move offshore early next week as additional weak
fronts impinge upon the area.

&&

.NEAR TERM /THROUGH TONIGHT/...
A very saturated airmass is in place across the region early this
morning. The 00Z IAD sounding from last evening had a PWAT of 2.27"
and dew points currently sit in the low to mid 70s. A broad frontal
boundary is situated to our north, stretching across the OH Valley
into PA/NY.

Scattered showers and thunderstorms are developing in the open warm
sector early this morning across central/eastern WV. These storms
will move into the Alleghenies over the next few hours, then mostly
dissipate as they move eastward into the Shenandoah Valley. Dry
conditions elsewhere, though given the saturated airmass, cannot
rule out a stray shower developing at any point. Additionally,
patchy fog has developed in parts of the Piedmont toward the I-95
corridor in VA and MD. This fog should burn off quickly after
sunrise. Needless to say, very muggy and warm conditions prevail.

The latest guidance has really backed off on convection during the
first half of the day, with little to no precip expected. Rain
chances have been cut back through early afternoon, then ramp up
during the late afternoon to evening. The frontal boundary to our
north slowly starts to sag southward, with some clusters of showers
and thunderstorms forecast to develop in the highlands of WV. These
showers/storms push east into our area, though the highest coverage
is expected to be along and south of I-66 this evening. SPC
continues to highlight a Marginal Risk for severe storms (level 1 of
5) along/west of I-81. As storms move across that area this evening,
a severe storm or two will be capable of producing damaging wind
gusts.

The biggest story today is going to be the exceedingly hot and humid
conditions. The latest guidance continues to trend upwards in
regards to temperatures this afternoon. The forecast calls for mid
to upper 90s across most of the area, with low to mid 80s in the
mountains. A few spots are likely to could hit 100, including DC,
Fredericksburg, and others in Central VA east of the Blue Ridge. On
top of the heat, dew points during peak heating are likely to be in
the low 70s, and upper 60s for those west of US-15. Around the
Fredericksburg area and in far southern MD, dew points are forecast
to be in the low to mid 70s for most of the day.

The combination of hot temps and high humidity is expected to
produce oppressive conditions. An Excessive Heat Warning has been
issued for the Fredericksburg area and southern MD, due to peak heat
indices of 110-112F. Heat Advisories are in effect for the rest of
the area of the Alleghenies. Heat indices reach 100-105 west of the
Blue Ridge, and 105-110 to the east. If you plan to be outdoors
today, it is recommended you stay hydrated, wear light colored
clothing, and take plenty of breaks in an air conditioned building.

Shower/storm activity pushes east across the area through late
evening, then conditions dry out overnight. Still, given the very
moist environment, cannot rule out a stray shower tonight. Overnight
lows settle in the mid to upper 70s. Some urban centers won`t drop
below 80F until after midnight.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
A stout mid/upper-level wave will most likely be located over lower
Michigan by daybreak Saturday. Flow aloft will increase ahead of
this trough, but the trough itself is expected to buckle and lift up
the Saint Lawrence River Valley and away from the region as it
encounters persistent ridging over the northwest Atlantic Ocean.
This actually results in weak height rises as the trough`s
associated surface cold front slowly crosses the Mid-Atlantic.

Low-level flow looks to be west to northwesterly for much of the
area west of I-95. This flow pattern would reduce surface moisture
(due to downsloping effects) and convergence. Therefore, convective
coverage west of I-95 may be very sparse. Further east, higher low-
level moisture and surface flow backed a bit more to the south
results in a bit more favorable environment. The best large scale
forcing for ascent will be lifting away from the region, so any
activity will have to result from a combination of the slowing
surface front, heating, and bay/river breeze boundaries. Given the
hot and humid airmass in place, any thunderstorms that do form could
produce heavy downpours, gusty to damaging winds, and frequent
lightning during the afternoon to evening hours.

The front looks to move just south and east of the local area
heading into Sunday as high pressure briefly builds in. This greatly
reduces the prospects for precipitation. Temperatures will still be
hot, but it will be much less humid.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
Ridging is forecast to persist over the northwest Atlantic Ocean
while broad troughing slowly drifts east over the central CONUS much
of next week. This pattern results in several weak surface fronts
drifting into the area and washing out, with daily low-end chances
for showers and thunderstorms each afternoon/evening. Without a more
obvious large scale feature, the prospects for any widespread
drought busting rainfall look rather slim.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
The saturated atmosphere has allowed low stratus and patchy mist to
develop across parts of the area this morning, producing IFR CIGs at
affected terminals. It has been difficult to time the development
and spread of this stratus, so expect additional amendments and
TEMPO groups to be needed through early morning. Stratus should
dissipate a few hours after sunrise.

Otherwise, VFR conditions are expected for most of today as mostly
dry conditions prevail through early afternoon. Scattered showers
and thunderstorms are expected once again this evening, though the
highest chances will be at CHO, IAD, and DCA. TEMPO groups may be
needed for gusty winds and brief periods of sub-VFR conditions if
any stronger storm moves over a terminal. Convection ends late this
evening, with mostly dry conditions overnight. Given the saturated
environment, additional low stratus is possible late tonight.

Prevailing VFR conditions are forecast Saturday through early next
week. Shower and thunderstorm coverage looks rather sparse, except
east of I-95 on Saturday. W/SW flow is generally expected at 5-10
kts with occasional gusts to around 15 kts possible in the
afternoon.

&&

.MARINE...
Southerly winds prevail through tonight, with varying from southwest
to southeast over parts of the water throughout the day. Southerly
channeling is expected to produce SCA winds in the middle portion of
the Chesapeake Bay between Smith Point and Drum Point this evening.
A Small Craft Advisory has been issued for those waters through
tonight, and it may need to be expanded a bit further up the bay if
winds are stronger than forecast. Otherwise, sub-SCA winds gusting
to around 10-15 knots. Mostly dry conditions today, then scattered
showers and thunderstorms are possible this evening.

Westerly to southwesterly flow is expected to continue right through
early next week. The wind should stay generally light, though some
strong thunderstorms may be possible particularly Saturday afternoon
into Saturday evening.

&&

.TIDES/COASTAL FLOODING...
Generally light southerly to southwesterly flow will result in
elevated tide levels through the weekend. Vulnerable shoreline may
come close to minor flooding during the early morning high tides.

&&

.CLIMATE...
Hot temperatures are today across the entire area, though this heat
is likely to fall just short of record for the day. Below is a list
of record high temperatures for July 5, and the current forecast
high temperatures for those days. RERs are only issued for DCA, IAD,
BWI, and MRB, but other sites are shown for reference.

                                     Friday Jun 21st
Climate Site                  Record High     Forecast High
Washington-National (DCA)    102F (1999)         100F
Washington-Dulles (IAD)       99F (1999)          99F
Baltimore (BWI)              102F (1999+)         99F
Martinsburg (MRB)            103F (1999)          97F
Charlottesville (CHO)        104F (2012)          99F
Annapolis (NAK)              100F (1999)          95F
Hagerstown (HGR)             102F (1919)          96F

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Heat Advisory from noon today to 8 PM EDT this evening for
     DCZ001.
MD...Heat Advisory from noon today to 8 PM EDT this evening for
     MDZ003>006-008-011-013-014-503>508.
     Excessive Heat Warning from noon today to 8 PM EDT this
     evening for MDZ016>018.
VA...Heat Advisory from noon today to 8 PM EDT this evening for
     VAZ025>031-036>040-050-051-053-054-501-502-505>508-526-
     527.
     Excessive Heat Warning from noon today to 8 PM EDT this
     evening for VAZ055>057.
WV...Heat Advisory from noon today to 8 PM EDT this evening for
     WVZ051>053.
MARINE...Heat Advisory from noon today to 8 PM EDT this evening for
     ANZ530.
     Small Craft Advisory from 4 PM this afternoon to 6 AM EDT
     Saturday for ANZ534-543.

&&

$$

SYNOPSIS...DHOF
NEAR TERM...KRR
SHORT TERM...DHOF
LONG TERM...DHOF
AVIATION...KRR/DHOF
MARINE...KRR/DHOF
TIDES/COASTAL FLOODING...DHOF
CLIMATE...KRR