-- Discussion containing changed information from previous version are highlighted. --
351
FXUS61 KLWX 221352
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
952 AM EDT Wed May 22 2024

.SYNOPSIS...
A cold front will approach from the Midwest through tonight,
then cross the northern Mid-Atlantic Thursday. The front will
stall to the north across Pennsylvania keeping the local area in
a warm and humid air mass through early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
930AM satellite loop shows valley fog dissipating as cumulus
clouds move eastward with mostly sunny skies across the region.
CAMs are continuing to disagree on initial time of convective
initiation with the HRRR showing convection starting around 22Z
and the NAM showing convection beginning as early as 17Z.
Latest surface analysis shows a pressure trough dipping over the
Blue Ridge. The exact position of this trough will drive
convection initiation with greatest chances for storms
initiation along and west of I-81 before tracking eastward.

Previous Discussion Follows:
High pressure sliding offshore and gradually lowering heights
aloft will act to sharpen a lee surface pressure trough this
afternoon. This trough will act as a trigger to scattered
showers and thunderstorms amid CAPE of 1000-2000 J/kg this
afternoon into this evening. Subtle differences in the sharpness
of the trough and extent of surface heating will dictate exactly
when convection ignites, with guidance varying by a few hours.
If convection develops early enough, the initial storms may not
be too overly strong, but would leave enough energy behind with
continued gradually falling heights/additional vorts allowing a
second round of strong storms heading into this evening. If
storms develop a bit later, any second round may be less
intense. Overall, synoptic forcing isn`t very strong and shear
will be modest at best, though subtle enhancement of 20-30 kts
in the 850-700 hPa layer could aid in multicellular organization
and subsequent gusty/damaging winds.

PWs will be increasing, and although individual storm motions
should be sufficiently quick to preclude flooding, multiple
rounds over areas of lowered FFG could result in a low and
conditional excessive rainfall risk.

Showers and thunderstorms seem most likely along and ahead of
the pressure trough from just west of I-81, east toward I-95
where subsidence from the departing ridge will be a bit
stronger. Storms may also approach the Appalachians from the
Ohio Valley this evening.

With regards to temperatures, today will feature very warm to
hot and humid conditions with highs well into the 80s to around
90. Tonight looks muggy with lows in the 60s to around 70.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
Stronger forcing for ascent will move into the area Thursday
attendant to an upper trough and strong surface cold front
approaching from the Midwest. Cloud debris and the front
approaching during the early part of the peak heating window
casts some uncertainty to the extent of instability. But, with
stronger forcing and shear, there is at least a conditional risk
for more organized strong to severe thunderstorms. It remains to
be seen just how widespread the threat is, but storms may tend
to focus further south and east toward the I-95 corridor where
the potential for heating will last longest.

Trends will need to be closely monitored over the next 24 hours,
as upstream convection over the Midwest will dictate subtle
shifts in (1) vort maxes embedded in the large scale flow, and
(2) the extent of cloud debris that could inhibit heating.

The front itself likely stalls to the north, but a wind shift or
pre-frontal trough type feature should shift south Thursday
night. Given the front(s) nearby, and lingering troughing and
moisture, shower activity could last well into the night.

Additional waves along the stalled front may lead to an
unsettled Friday, as well. Although forcing and instability look
to be a bit less, shower and thunderstorm potential will still
be there especially further south near the I-64 corridor closer
to the wind shift. It does not look like it will rain the entire
day, but rather the potential for showers and thunderstorms will
linger, with chances cresting during peak diurnal heating.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
The weather pattern over the Memorial Day holiday weekend will
be characterized by gradually lowering heights and surface
pressures leading to a stormy pattern. Saturday should turn out
rather active due to a low amplitude shortwave trough moving
across the area that should act to enhance t-storm activity.
Sunday appears to be the least active day due to shortwave
ridging and some drying. Severe weather risk appears to increase
markedly on Memorial Day due to strengthening wind fields aloft
and strong shortwave energy moving across the area around the
base of a deep upper level trough over the eastern Great Lks. A
strong cold front will follow Monday night bringing cooler and
drier conditions for the middle of next week.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
Prevailing VFR conditions are expected through the end of the
workweek. Showers and thunderstorms may cause temporary
restrictions mainly near KCHO/KMRB/KIAD this afternoon and
evening, with multiple rounds possible. The 06Z TAF package
tried to hone in on the most likely 4-hour window for VCTS (with
KMRB appearing the most likely airfield to see multiple rounds).
Left VCTS out of KDCA/KBWI/KMTN for now given a bit lower
confidence further east, but this will all need refinement in
later packages. Otherwise, southerly flow near 10 kts is
expected through tonight.

Additional shower and thunderstorm activity is expected Thursday
from around midday through early evening east of the Blue Ridge
(most likely). Winds will shift to NW at 5-10 kts Thursday into
Friday. Yet another round of showers and thunderstorms is
possible Friday, this time focusing near the southern terminals.
Some patchy overnight/early morning fog can`t be ruled out.

Sct-nmrs t-storms Saturday afternoon. Less t-storm coverage
expected Sunday.

&&

.MARINE...
Southerly flow will increase heading into this afternoon, with a
period of 15-25 kt wind gusts expected over the main channel of
the Chesapeake Bay and most adjoining tributaries this afternoon
and evening. A few thunderstorms may approach the waters this
evening. Winds will become lighter and eventually shift to
northwest Thursday into Friday. Additional periods of showers
and thunderstorms are possible, especially Thursday afternoon
and evening, and some may be strong requiring SMWs.

SCA conditions likely Sunday night into Memorial Day. Sct-nmrs
Saturday afternoon. Lightning appears to be the main threat at
this time. Severe thunderstorm risk increases markedly for
Memorial Day.

&&

.TIDES/COASTAL FLOODING...
Minor coastal flooding will remain possible at Annapolis and at
DC Waterfront over the next several days.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 2 PM this afternoon to 2 AM EDT
     Thursday for ANZ530>534-537>541-543.
-- End Changed Discussion --

&&

$$

SYNOPSIS...DHOF
NEAR TERM...AVS/DHOF
SHORT TERM...DHOF
LONG TERM...LFR
AVIATION...LFR/DHOF
MARINE...LFR/DHOF
TIDES/COASTAL FLOODING...LFR