575
FXUS61 KLWX 021837
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
237 PM EDT Tue Jul 2 2024

.SYNOPSIS...
Dry conditions, seasonable temperatures, and low humidity look to
continue through Wednesday as surface high pressure slowly pushes
offshore. A frontal boundary will approach the area and stall to the
northwest Thursday before crossing the region this weekend. Heat and
humidity will return as a result for the Independence Day holiday
along with increased chances for thunderstorms.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Broad 1027-1028 mb high pressure over Finger Lakes of New York will
continue to wedge it`s way south along the eastern face of the
Appalachians today before shifting toward the New England coast
late tonight and into Wednesday. Dry conditions are expected as
a result along with low humidity and seasonable temperatures.
Highs today will be a touch warmer than Monday with
ridging/rising heights aloft. Highs will range from the mid to
upper 70s over the mountains with mid to upper 80s east of the
Alleghenies. Passing stratocumulus is likely throughout the
afternoon with subtle moisture noted in the low levels between
850-1000 mb per the 12z KIAD sounding (Low Level RH 71% and Mid
Level RH 3%). PWATS are also down around 0.52" signaling the dry
air which is evident across much of the Eastern Seaboard on the
current water vapor imagery.

Winds will turn to the southeast later this afternoon and into
tonight as high pressure slowly shifts offshore. This will allow for
a subtle uptick in moisture heading into Wednesday. Even with that
said, enough dry air should remain to keep low temperatures in the
upper 50s and low to mid 60s across the region.

Broad high pressure will continue off the New England/Mid-
Atlantic coast Wednesday morning into Wednesday afternoon.
Moist southeast flow off the Atlantic will return as a result
allowing for a subtle boost in humidity. Dry conditions are
expected with mostly sunny to partly cloudy skies expected. High
temperatures Wednesday will run a few degrees above normal with
highs near 90 degrees east of the Alleghenies (low to mid 80s
mountains). A mountain shower or thunderstorm cannot be ruled
out ahead of the front Wednesday afternoon and evening.


&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...

High pressure continues offshore Wednesday night with a cold front
entering in from the Ohio River Valley for the Independence Day
holiday. Clouds will increase as result along with the influx of
moisture across the region on southeasterly flow. Showers and
thunderstorms remain possible Wednesday night especially west of the
Allegheny Front. Most locations will remain dry with increasing
humidity and cloud cover. Lows Wednesday night will hold steady in
the mid to upper 60s and low 70s.

The real change comes Thursday as the subtropical ridge moves into
the southeastern U.S. This will allow for the return of excessive
heat and humidity along with increased chances for strong
thunderstorms. A pre-frontal shortwave trough combined with an
approaching cold front from the Ohio River Valley will lead to
scattered to numerous showers and thunderstorms across the area
Thursday afternoon into Thursday evening. Current hi-res CAM
guidance and synoptic models also illustrate this notion with a
front slowly pushing eastward into the mountains before stalling
over the area and even retreating back to the north heading into
Friday. With that said, uncertainty remains in regards to the
coverage of thunderstorm activity for Independence Day
festivities including fireworks Thursday evening into Thursday
night.

High temperatures Thursday will range from the upper 70s and low 80s
over the higher elevations west of the Blue Ridge with low to mid
90s further east. Heat index values east of the Alleghenies will run
anywhere between 98-104 degrees. Higher elevations will see
heat index values in the upper 80s and mid 90s Thursday
afternoon. These temperatures combined with increased humidity
will harbor ample instability for storms to feed off of Thursday
afternoon and evening. CAPE values will be on the order of
1500-2500 j/kg with 0- 6km shear values less than 35 kts. Lapse
rates will also remain poor less than 6.5 C/km. Precipitable
water values seem to be the bigger concern here as the
atmosphere becomes juiced with values in excess of 2-2.5 inches
across majority of the forecast region. As a result expect a
mix of pulse to multi-cell clusters of storms propagating east
Thursday afternoon and evening. Primary threats with storms are
locally damaging winds and isolated instances of urban
flooding. Once again confidence is lower pending increasing
cloud cover and the overall placement/timing of the cold
front/prefrontal shortwave trough. Overnight low temperatures
Thursday will be in the low to mid 70s for most locations.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
A rather persistent longwave pattern will remain in place through
the long term period of the forecast. During that time, broad
longwave troughing will reside over the center of the country, with
ridging in place along the West Coast, as well as in the North
Atlantic. Through the period, multiple shortwave disturbances will
round the base of the trough and pass off to our northwest in
southwesterly flow aloft. At the surface, high pressure will remain
in place offshore, leading to southerly flow. Southerly flow will
maintain a warm and very humid airmass over the area, leading to
daily chances for thunderstorms.

On Friday we`ll be somewhat displaced from stronger forcing for
ascent off to our west, with heights holding near neutral within
southwesterly flow aloft. As a result, coverage of storms may be
lower compared to surrounding days. Nonetheless, thunderstorms
should form during the afternoon in response to daytime heating.
Storms should continue through the evening before dissipating during
the first half of the overnight with loss of daytime heating.

A potent shortwave and associated surface low/trailing cold front
will track through the Ohio Valley and Eastern Great Lakes on
Saturday. This system will provide stronger large scale forcing for
ascent, leading to a higher coverage of storms on Saturday.
Increasing flow aloft (30-40 knots of mid-level flow) will overlap
with deep moisture (PWATs well over 2 inches) and ample instability
(MLCAPE values well in excess of 1000 J/kg) to create an environment
that is favorable for both severe thunderstorms and flash flooding.
However, antecedent dry conditions should limit the flood threat
outside of urban areas.

The system`s cold front will move through Saturday night,
potentially allowing a slightly cooler and less humid airmass to
move in for Sunday. An overall lower coverage of storms is expected
Sunday, with the activity primarily focused across southeastern
portions of the forecast area.

Most guidance shows deeper moisture (PWATs in excess of 2 inches)
being drawn northward into the area again on Monday. Afternoon
thunderstorms will be possible once again, along with the potential
for localized downbursts and isolated instances of flooding.

It will be hot and humid through much of the long term period,
especially on Friday and Saturday. Heat indices may potentially
exceed 100 degrees on both Friday and Saturday.

&&

.AVIATION /19Z TUESDAY THROUGH SUNDAY/...
Prevailing VFR conditions are expected through Wednesday night as
high pressure slowly pushes offshore. Stratocumulus is expected to
continue this afternoon and evening with clearing overnight. An
additional period of stratocumulus is likely at all terminals from
early Wednesday morning through Wednesday afternoon. SCT-BKN cloud
bases will run 060-080 kft. Winds will remain light out of the south
and southeast through Wednesday morning. Intermittent gusts up
to 15 kts are possible at terminals mainly north of I-66/US-50
Wednesday afternoon.

Sub-VFR conditions return Thursday afternoon and evening as a
prefrontal trough and front enter the region. Scattered to numerous
strong to severe thunderstorms look to pose an impact to the
terminals during this time. The primary threats include gusty winds,
small hail, heavy rainfall, and frequent lightning. Thunderstorm
activity will diminish late Thursday night into Friday morning.
Winds will start out of the southwest Thursday morning before
switching to the west Thursday afternoon and evening.

Prevailing VFR conditions are expected on both Friday and Saturday,
but temporary drops to sub-VFR conditions may be possible in
thunderstorms either afternoon or evening. Winds will generally be
light out of the south.


&&

.MARINE...
Quiet conditions are expected across the waters this afternoon as
high pressure pivots overhead. Winds will turn to the south and
southeast while remaining below SCA levels. Some channeling may
occur over the northern and middle part of the bay later this
evening and into tonight. Additional channeling is possible
Wednesday afternoon and evening as the wind changes to the south.

On Thursday, winds remain out of the south/southeast with SCA
criteria gusts possible in the southern portions of the waters.
SMWs may be needed during showers and thunderstorms that afternoon.

Sub-SCA level southerly winds are expected over the waters on both
Friday and Saturday. Thunderstorms may also be possible either
afternoon or evening.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies are forecast to steadily rise through the week as
southeast to south winds prevail. Some sensitive locations will
reach Action Stage, and Annapolis is the most likely to go into
minor flooding Wednesday morning. Additional periods of coastal
flooding are possible during the morning high tide Thursday and
Friday.


&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

SYNOPSIS...EST
NEAR TERM...EST
SHORT TERM...EST
LONG TERM...KJP
AVIATION...KJP/EST
MARINE...KJP/EST
TIDES/COASTAL FLOODING...LWX