-- Discussion containing changed information from previous version are highlighted. --
879
FXUS61 KLWX 130047
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
847 PM EDT Wed Jun 12 2024

.SYNOPSIS...
High pressure returns through Thursday leading to mainly dry
conditions. A cold front tracks through the area on Friday
leading to renewed shower and thunderstorm chances. High
pressure settles over the area this weekend with lower humidity.
Next week looks to become hot as a very strong upper ridge
builds towards the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Evening update: Skies are clearing out this evening across much
of the area as daytime mixing wanes. Some cumulus remains
across the Central Shenandoah Valley and Potomac Highlands.
Recent runs of the HRRR hint that a few showers may try to form
there this evening, so 20 PoPs have been maintained in those
locations through the evening hours. Elsewhere, dry conditions
are expected overnight. Previous discussion follows...

High pressure will remain overhead tonight, resulting in light
winds once again. This will make for yet another cool night for
mid-June standards. Upper 50s to low 60s are expected across
most areas, accompanied by some mid 60s in the usual warmer
pockets. Some patchy fog may materialize overnight for locations
west of I-95. However, its development could be hindered by any
cloud cover that lingers into the night. Best chance for fog
would likely be in the valleys and along the eastern slopes of
the Blue Ridge.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Thursday and Friday will bring about a big shift into a much
warmer weather pattern that likely continues into next week (see
long term below). Thursday should generally remain dry across
the area as high pressure finishes its traverse of the region
and moves offshore. This will begin to usher in warmer and more
moist air into the region. High temperatures Thursday are
expected to reach the mid to upper 80s (upper 70s to low 80s in
the mountains). Could see an isolated thunderstorm or two
along/west of the Blue Ridge over the higher terrain during the
afternoon. These will largely be driven by terrain circulations
and would likely be very short-lived given an overall lack of
CAPE and steep lapse rates.

Thursday night will be warmer and more humid than previous
nights. Low temperatures will be in the 60s for most, with some
patchy fog possible once again.

By Friday morning, a cold front tracking across the Lower Great
Lakes and Ohio Valley will set the stages for a possible round
of showers and thunderstorms. Before this occurs, Friday will
mark the hottest day of the week and perhaps the first crack at
a 95 degree day in 2024. Heat indices should be in the mid/upper
90s based on the latest dew point forecast. While falling short
of typical heat headlines, it is the first real bout of summertime
heat this season.

This heat will not come without its consequences however. Dew
points are forecast to be in the mid to upper 60s, which paired
with highs in the 90s will set the stage for thunderstorms in
the afternoon as the front approaches. Forecast vertical shear
values between 35-45 knots would be more than enough to support
organized convection. Some of these storms could become severe,
with damaging winds and large hail being the main threats. This
will all be very dependent on just how much instability is in
place. Some ensembles have us at around 1000-1500 J/kg, while
others struggle to get us above 500 J/kg of CAPE Friday
afternoon. The 12z run of the NAMNest was our first look at a
convective- allowing model (CAM) regarding this system. For what
it is worth, it depicts the highest threat in our northeast,
where the highest shear values are. However, it does struggle to
get us over 1000 J/kg of CAPE. Even with that being said, low-
level lapse rates are very impressive given the temperatures in
the 90s, so at least some marginal threat for damaging winds
exists. Of note though is the gap in convection over central VA.
One of the things I am a bit concerned about is westerly flow
in the mid-levels, which can introduce extra dry air and really
keep things from developing depending on the scenario. This is
of course just one model run, but it does at least address the
few concerns I have with this setup.

This activity should all exit into the Eastern Shore by late
Friday night. In the wake, prevailing northwesterly flow will
gradually usher in some drier air from central Canada. However,
temperatures do stay slightly above average with widespread 60s
expected (50s over the mountains).

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Dry conditions expected this weekend as surface ridge over the Mid-
Atlantic region pushes offshore by the end of this weekend. Upper
troughing early Saturday also quickly departs to the northeast.
Afternoon highs in the 80s each day, with Saturday night lows in the
upper 50s to low 60s.

An extended period of hot temperatures is expected next week as a
mid-level ridge sets up atop the Mid-Atlantic. At the surface, the
western extent of the Bermuda High builds in across the Carolinas
through at least the middle of next week, producing light southerly
flow over our area. Afternoon highs are forecast to reach the low to
mid 90s Monday, then mid to upper 90s Tuesday. Even though it is
beyond the current forecast, highs look to be in the mid to upper
90s each day through next week Friday. Increasing humidity likely
results in peak heat indices to around 100-105 each afternoon.
Overnight lows become milder as the week progresses, likely only
dropping to the low 70s Tuesday night.

A plume of deep tropical moisture advects north along the western
periphery of the surface and mid-level ridges. This yields high rain
chances across parts of the Deep South, and TN/OH River Valleys.
While most of the resulting convection remains west of our area,
some showers and thunderstorms are possible each afternoon along and
west of I-81.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
VFR conditions continue as high pressure builds into the region.
Some model guidance hints at some trapped moisture in the valleys
and along the eastern slopes of the Blue Ridge tonight. This
could perhaps bring the chance for some fog to CHO and MRB, so
have included that in the latest TAF. Winds will be very light
during this time and generally out of the south.

Southerly winds will begin to pick up in intensity on Thursday
by mid-late morning, with gusts in the 10-15 knot range by the
afternoon at all terminals. MTN could see some locally higher
gusts coming off the waters closer to 20 knots. There is a very
slight chance of a pop-up shower or storm near CHO Thursday
afternoon, but chances are around 20 percent at this time, so
left out of the TAF at this time.

The period heading into Friday afternoon into the evening will
likely lead to some restrictions given the threat for showers
and thunderstorms along an approaching cold front. Some of
these could become severe given the degree of warmth and
instability in the atmosphere. Winds quickly shift over to west-
northwesterly in the wake Friday night.

Dry and VFR conditions expected this weekend as light northerly
winds Saturday veer east Saturday night, then become southerly
Sunday afternoon.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
Southerly winds remain sub-SCA in nature through tonight. This
will continue through Thursday morning as high pressure
gradually pushes offshore.

By Thursday afternoon, expect southerly channeling to really
pick up in intensity as high pressure moves offshore. Wind gusts
of up to 25 knots can be expected over the wide waters of the
Chesapeake Bay. An SCA was issued for this threat for all Bay
zones as well as the lower Potomac. Could see an expansion up
the Potomac potentially, but wasn`t confident enough at this
time to do so.

A cold front tracking across the area Friday afternoon/evening
will lead to the threat of strong to severe convection. This
could require some Special Marine Warnings for the area waterways.

Dry conditions expected this weekend as high pressure moves across
the region. Northerly channeling during the first half of Saturday
could produce SCA conditions in the open waters of the Chesapeake
Bay. Winds diminish Saturday night and become east. As surface high
pressure moves offshore Sunday, winds quickly turn southerly and
could gust to near-SCA levels Sunday evening.
-- End Changed Discussion --

&&

.CLIMATE...
High temperatures early next week. Below is a list of record high
temperatures for June 17th and 18th, the year the record
was set, and the current forecast high temperatures for those
days. Daily temperature records are currently only maintained at
DCA, IAD, BWI, and MRB. Others are shown for reference.

                                     Monday Jun 17th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     99F (2022)          95F
Washington-Dulles (IAD)       96F (2022)          95F
Baltimore (BWI)               96F (2022+)         93F
Martinsburg (MRB)             98F (1939+)         93F
Charlottesville (CHO)         97F (2022)          94F
Annapolis (NAK)               96F (1939)          88F
Hagerstown (HGR)              96F (1952)          94F

                                     Tuesday Jun 18th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     97F (1944)          96F
Washington-Dulles (IAD)       94F (2018+)         96F
Baltimore (BWI)               97F (1957+)         95F
Martinsburg (MRB)             99F (1943)          94F
Charlottesville (CHO)         96F (2014+)         95F
Annapolis (NAK)               96F (1957)          91F
Hagerstown (HGR)              95F (1957)          96F


+ indicates that value has been reached on multiple years, with
the year displayed being the most recent.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 2 PM Thursday to 5 AM EDT Friday for
     ANZ530>534-537>543.

&&

$$

SYNOPSIS...CJL
NEAR TERM...CJL/KJP
SHORT TERM...CJL
LONG TERM...KRR
AVIATION...CJL/KRR
MARINE...CJL/KRR
CLIMATE...BRO/CJL