446
FXUS61 KLWX 130753
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
353 AM EDT Thu Jun 13 2024

.SYNOPSIS...
High pressure slowly pushes offshore today. 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 over the region.

&&

.NEAR TERM /THROUGH TONIGHT/...
A residual area of high pressure remains across the Mid-Atlantic
region this morning. However, with light winds out of the
south to southwest, early morning temperatures are certainly up
from previous nights. Per 07Z/3 AM observations, most locations
are in the low/mid 60s, locally down up in the upper 50s for
places that have fully decoupled. Skies remain mostly clear
although a few spots have seen some passing mid-level clouds.

Expect a much warmer day today with increasing heights aloft and
persistent low-level warm advection. 1000-500 mb thicknesses
increase by around 6 to 8 dm over the 24 hour period heading
into this afternoon. Net warming in the lower half of the
troposphere will support increasing temperatures this afternoon.
Current forecast highs are in the upper 80s, accompanied by a
few spotty 90 degree readings. To escape the heat, the mountains
are forecast to see temperatures in the mid/upper 70s. Subtle
lift in the quasi-zonal flow may spark some isolated afternoon
showers over the area. Some activity could become locally
enhanced around mesoscale features like bay and river breezes.
Do not expect updrafts to become strong/tall enough to produce
any lightning activity. Any showers wane after dark with a mild
night ahead.

The forecast calls for low temperatures in mid/upper 60s, with
near 60 degrees along the Alleghenies.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
A brief bout of summertime heat persists into Friday before a
cold front scours out all of the heat and humidity. The latest
forecast package brings this cold front across the I-95 corridor
between 5-8 PM Friday evening.

A period of south to southwesterly warm advection will
sufficiently moisten the low-levels of the atmosphere. Dew
points are forecast to rise into the low/mid 60s which helps
contribute to mixed-layer CAPE values to around 1,000 J/kg. For
early summertime standards, this is actually on the lower end.
However, forcing from the grazing trough coupled with low-level
convergence from the cold front should aid in scattered showers
and thunderstorms. Forecast soundings depict very steep low-
level lapse rates (near dry adiabatic) but with rather poor mid-
level lapse rates (5-5.5 C/km). Ultimately, updrafts may
struggle to get tall as they encounter this more lackluster
portion of the profile. Additionally, nearly unidirectional
westerlies may cause some drier air to mix in which would
possibly impede thunderstorm formation. With all that said, a
Slight risk is in place from central Maryland northeastward into
southeastern Pennsylvania. Damaging winds are the main hazard,
accompanied by the usual heavy downpours and frequent lightning
strikes. A Marginal risk is in place elsewhere across the
region. Any convection exits to the Eastern Shore by just after
midnight. Low temperatures stay mild although post-frontal
northwesterlies will ensue overnight.

High pressure settles over the Great Lakes and northeastern U.S.
on Saturday. This will favor a slight cooling trend, less
humidity, and a dry forecast. High temperatures are set to hit
the 80s with 70s in mountain locales. However, dew points return
to the 50s which removes the humidity factor from the equation.
Sunny skies are expected with the ridge in charge. This sets the
stages for a tranquil evening and night with low temperatures
falling into the 50s to low 60s.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
A dome of modified Canadian high pressure will settle across
interior New England down into the Carolinas on Sunday morning.
The 1024-1026 mb pressures are fairly impressive for mid-June
standards. Ample radiational cooling effects should make for a
cool start to the morning. Around sunrise, temperatures are
forecast to start off in the mid 50s to low 60s. The mentioned
ridge is expected to exit offshore by midday which allows for a
return southerly flow to kick in over the local area. Expect
fairly seasonable temperatures with readings in the mid/upper
80s, locally in the mid/upper 70s across the mountains. A few
additional clouds are possible as high cirrus spread in from
upstream convection. Nighttime conditions trend milder with the
south-southeasterly warm advection.

The work week ahead will be comprised of a lengthy period of
above average temperatures. The culprit is a large subtropical
ridge which settles over the Eastern Seaboard. Ensembles agree
on the presence of this ridge, but do differ with placement,
strength, and longevity. Additional, some instability-driven
convection is possible which would play a role in the daily
temperature forecasts. How all these factors play out will
ultimately dictate just how pronounced and lengthy this heat
wave will be.

Overall forecast numbers have dropped by a degree or two.
However, widespread mid 90s seem quite likely which is
accompanied by increasing humidity levels. Heat index values
should near the century mark each afternoon. Even mountain
locations will be quite toasty as daily high temperatures push
up into the mid 80s. Overnight low temperatures should also stay
quite warm with little relief expected. Most see overnight lows
in the low 70s, with mid 70s near the urban hubs. Even the
Allegheny Front should see lows in the mid 60s. Forecast lows
will generally be around 8 to 14 degrees above average next
week.

Heat products may be needed at times, particularly given the
duration of this potential heat wave. Ensembles favor this
lasting through the remainder of the work week, potentially even
into parts of next weekend.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
Some locally patchy fog is possible across the favored river and
mountain valleys. This would include KCHO and KMRB where MVFR
visibilities are possible between 5-9 AM this morning. Any fog
should quickly burn off by a few hours after sunrise. Otherwise,
VFR conditions are expected through tonight with southerly
afternoon gusts up to 15 knots. Isolated showers are possible
this afternoon, but these should not cause any restrictions.
Light southerlies continue into tonight around the western
periphery of high pressure off the coast. Another round of
patchy fog may impact the area late tonight into early Friday.

Although the first half of the day will likely bring VFR
conditions, an approaching cold front carries a risk for showers
and thunderstorms. Some of these could become locally severe,
especially for locations north of I-66/U.S. 50. A period of
restrictions are possible where thunderstorms reside. In the
wake of the cold front, winds eventually shift to northwesterly
on Friday evening. Mainly sunny skies are likely on Saturday as
high pressure returns. This comes with winds that meander
between northwesterly and northeasterly. Afternoon gusts could
approach 15 knots before subsiding after dusk.

VFR conditions are expected on Sunday underneath mostly sunny
skies. A retreating area of high pressure will yield a shift
over to mainly south to southeasterly flow on Sunday
afternoon/evening. By Monday, winds become mainly southerly with
increasing heat and humidity. This combination may spark a few
showers and thunderstorms. However, outside of any of these
showers, VFR conditions are expected at the area terminals.

&&

.MARINE...
High pressure persists across the area waters this morning with
light south-southwesterlies gusting to around 5 to 10 knots.
Expect southerly channeling this afternoon into tonight with
gusts up to 20 knots. As such, Small Craft Advisories are in
effect across the Chesapeake Bay and its adjoining tributaries,
as well as the lower tidal Potomac.

On Friday, additional southerly channeling could bring some
locations to near 18 knots at times. However, there is not
enough confidence to hoist additional advisories. An approaching
cold front increases the risk of strong to severe thunderstorms
between around 5-11 PM (later for the more southern/eastern
locations). Special Marine Warnings would be needed for the
stronger storms. Behind the cold front, winds shift to
northerly. A period of northerly channeling may require Small
Craft Advisories for the first half of Saturday. High pressure
eventually weakens winds through the remainder of the day.

Expect light winds to start off on Sunday morning thanks to the
ridge of surface high pressure. This gradually moves offshore
leading to a shift to south-southeasterlies during the second
half of Sunday. Mainly southerlies are likely on Monday with
some channeling effects possible over the Chesapeake Bay. Thus,
Small Craft Advisories may be needed at times Monday afternoon
into portions of the night. Any thunderstorm chances appear
confined to locations off to the west of the waters.

&&

.TIDES/COASTAL FLOODING...
Current tidal anomalies remain slightly elevated, generally
ranging between 0.5 to 0.7 feet. At this point, only the
sensitive locations like Annapolis and Straits Point are
expected to reach Action stage during the next several high
tides. Water levels do quickly drop off over the weekend behind
a cold front. North to northwesterly flow should push a lot of
the excess water back toward the south.

&&

.CLIMATE...
High temperatures early next week. Below is a list of record high
temperatures for June 17th, 18th, and 19th, 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)          93F
Washington-Dulles (IAD)       96F (2022)          94F
Baltimore (BWI)               96F (2022+)         92F
Martinsburg (MRB)             98F (1939+)         91F
Charlottesville (CHO)         97F (2022)          93F
Annapolis (NAK)               96F (1939)          87F
Hagerstown (HGR)              96F (1952)          92F

                                     Tuesday Jun 18th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     97F (1944)          95F
Washington-Dulles (IAD)       94F (2018+)         95F
Baltimore (BWI)               97F (1957+)         93F
Martinsburg (MRB)             99F (1943)          92F
Charlottesville (CHO)         96F (2014+)         93F
Annapolis (NAK)               96F (1957)          89F
Hagerstown (HGR)              95F (1957)          93F

                                    Wednesday Jun 19th
Climate Site                  Record High     Forecast High
Washington-National (DCA)     99F (1994)          95F
Washington-Dulles (IAD)       98F (1994)          95F
Baltimore (BWI)               99F (1994)          93F
Martinsburg (MRB)             96F (1994+)         92F
Charlottesville (CHO)         97F (2018)          94F
Annapolis (NAK)               96F (1993)          89F
Hagerstown (HGR)              97F (1994)          94F

+ 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 this afternoon to 5 AM EDT
     Friday for ANZ530>534-537>543.

&&

$$

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