470
FXUS61 KLWX 061911
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
311 PM EDT Sat Jul 6 2024

.SYNOPSIS...
A cold front drifts across through tonight. The front brings
shower and thunderstorm chances east of the I-95 today.
Humidity decreases Sunday in the wake of the front with high
pressure briefly building overhead. Heat, humidity, and daily
thunderstorm chances return for much of next week as the frontal
zone stalls nearby.

&&

.NEAR TERM /THROUGH TONIGHT/...
As anticipated, the period of excessive heat and humidity
continues with early afternoon temperatures rising into the
low/mid 90s. This is coupled with dew points in the upper 60s to
mid 70s which brings heat indices into the 100 to 105 degree
range, locally a bit higher in locations near the waters. For
areas west of the Blue Ridge, dew points have begun to fall in
response to a weak cold front crossing the Alleghenies. These
locations are where the greatest relief from the humidity is
occurring. Otherwise, heat products continue with Excessive Heat
Warnings along the bayshore up to southern Baltimore County, and
Heat Advisories westward to around U.S. 15. Given the excessive
heat, continue to seek shelter, wear light clothing, and stay
hydrated.

The weaker mid-level lapse rates appear to be winning out so far
as the current Cu field is pretty suppressed looking on GOES-16
visible satellite imagery. As the weak trough/frontal zone
appoaches from the west, some of the high-resolution models fire
up some convection east of I-95. Such solutions favor convective
initiation around 5 to 7 PM, and particularly over the southern
Maryland and up the bayshore owing to mesoscale circulations.
With current precipitable water values around 1.75 inches, the
atmosphere remains very moist. With that said, any isolated
showers that do fire up could produce a quick half inch to inch
in a short period of time. A Marginal Risk for flash flooding
remains east of I-95 through tonight.

Compared to previous nights, conditions will be a bit less humid
as the mentioned cold front drifts eastward across the area.
Underneath some additional cold cover, low temperatures are
forecast to be in the low/mid 70s east of the Blue Ridge (60s to
the west). Some patchy fog is also possible across the
Alleghenies and adjacent mountain valleys.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
The south and east push of this frontal zone gradually halts
with the system stalling in the vicinity into next week. Given
the nature of the boundary and time of year, this frontal zone
will largely be a dew point gradient. Although a brief reprieve
from the humidity is expected on Sunday, expect the dew points
to ramp back up leading to humid conditions heading into Monday.
The area is largely dry on Sunday before turning wetter on
Monday as weak perturbations aloft interact with this stalled
system. The forecast calls for a chance of showers and
thunderstorms on Monday afternoon and evening, possibly
continuing after dark. Forecast highs generally sit in the low
90s each day, locally pushing to around 95 degrees. While heat
index values stay below the century mark on Sunday, they should
return to around 100 degrees by Monday. How warm the area gets
early next week will depend on how much cloud cover interferes
with the main period of diurnal heating.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
On Tuesday, a large trough is expected over the central CONUS, with
ridging along both coasts. As the upper trough advances east, it`s
also expected to absorb remnants of Beryl. Meanwhile, a surface low
located over the Great Lakes will be draping a cold front south
through the Ohio and Mississippi river valleys. The warm front with
this system is currently forecast to lift through the area
accompanied by a surface trough. These features will act as a focus
for shower and thunderstorm activity on Tuesday.

More widespread rain is expected with the cold front`s arrival on
Wednesday. Depending on how Beryl evolves, this could also coincide
with Beryl`s remnant energy passing overhead. The front could linger
into Thursday, making the most of Beryl`s energy before it departs
and continuing the higher PoPs over the area. PoPs on both Wednesday
and Thursday are 50-60%. For Friday, a second cold front could swing
in from the northwest, but also stall in the area as the trough over
the central CONUS weakens and the Bermuda high strengthens.

Overall, the extended looks to continue a pattern of soggy weather
with fairly persistent southerly flow. There is some "relief" from
highs in the 90s on Thursday, with highs in the 80s, but it likely
won`t feel very relieving with dewpoints and low temperatures
remaining in the low to mid 70s through the duration of the
extended. Even if daytime highs/heat indices don`t reach headline
criteria each day (though they still could) the prolonged period of
muggy conditions with poor overnight recovery poses a heat risk.


&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
VFR conditions are likely across the terminals this weekend. An
isolated shower or thunderstorm could impact the Baltimore
terminals by early this evening, but confidence is too low to
introduce into the TAF. Winds shift to north/northwesterly this
evening and night as a weak cold front pushes through.

Expect a return southerly flow by Monday as the boundary returns
back as a warm front before stalling. Increasing opportunities
for showers and thunderstorms could lead to some
afternoon/evening restrictions on Monday.

VFR conditions are expected most of the time Tuesday and
Wednesday, but afternoon and evening showers and thunderstorms
could bring sub-VFR restrictions to the terminals. Wednesday is
currently expected to have the higher coverage of showers. This
pattern persists into Thursday as well given the frontal zone
nearby.

&&

.MARINE...
A cold front will slowly approach from the west with a brief
surge of northerly wind possible late tonight. Some of the
guidance has near Small Craft Advisory winds for around 3 to 6
hours. However, there is too much uncertainty at this point to
hoist any marine headlines at this time. Before this occurs,
isolated showers and thunderstorms could impact the waters
through this evening. The strongest thunderstorms may require a
Special Marine Warning or two. However, the area appears pretty
capped for now so any convection would be at least a couple
hours away.

Northerly winds persist into Monday before shifting to southerly
the second half of the day. This is in response to the stalled
front returning northward as a warm front. In addition, a
convective threat accompanies this frontal surge which could
lead to hazardous marine conditions at times, especially on
Monday afternoon/evening.

Southerly flow is expected both Tuesday and Wednesday and could
increase to SCA criteria in the afternoon and early evening with
southerly channeling.

&&

.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...
While temperatures will be hot this afternoon, they will fall
short of daily records as the local climate sites currently
consist of records ranging from 102 to 105 degrees. However, a
very warm night could lead to a couple record overnight low
temperatures. Daily climate data runs from 1 AM EDT Saturday until
1 AM EDT Sunday. Some of the forecast numbers below have already
occurred earlier this morning.

Records (RERs) are only issued for DCA, IAD, BWI, and MRB, but
other sites are shown for reference.

           ***Saturday night (July 6th)***
                            Current record (Year)  Forecast low
Washington-National (DCA)         83F (1999)           81F
Washington-Dulles (IAD)           76F (2012)           76F
Baltimore (BWI)                   80F (1881)           81F
Martinsburg (MRB)                 75F (1900)           73F
Charlottesville (CHO)             76F (2012)           74F
Annapolis (NAK)                   81F (2018)           82F
Hagerstown (HGR)                  78F (1999)           74F

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Heat Advisory until 8 PM EDT this evening for DCZ001.
MD...Heat Advisory until 8 PM EDT this evening for MDZ005-006-008-
     013-016-503>508.
     Excessive Heat Warning until 8 PM EDT this evening for MDZ011-
     014-017-018.
VA...Heat Advisory until 8 PM EDT this evening for VAZ050-051-
     053>057-502-506-526-527.
WV...None.
MARINE...Heat Advisory until 8 PM EDT this evening for ANZ530.

&&

$$

SYNOPSIS...BRO
NEAR TERM...BRO
SHORT TERM...BRO
LONG TERM...CAS
AVIATION...BRO/CAS
MARINE...BRO/CAS
TIDES/COASTAL FLOODING...LWX
CLIMATE...BRO