672
FXUS61 KLWX 120800
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
400 AM EDT Mon May 12 2025

.SYNOPSIS...
High pressure will slide by to the northeast today. Meanwhile,
an upper level low will slowly approach from the southwest
through Wednesday, before shearing out into an open wave and
departing off toward our northeast on Thursday. Another system
will quickly approach the region Friday into Saturday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
High pressure is positioned over New England this morning. A
closed low remains near Louisiana, blocked by ridging to the
north and east. Still mainly high clouds across the area for
now, with the nearest showers in North Carolina. That will
change through the day, as the high slides off the coast and
allows moisture to be advected northward. However, it will be
battling residual dry air, so it will take time for anything
more than light showers/sprinkles to advance
northward...generally late morning/afternoon for locations south
of I-66 and evening farther north. However, Baltimore/northeast
MD may not see much rain until Tuesday morning being closer to
the ridge. The showers and isolated thunderstorms that move into
central Virginia today should be intermittent and not produce
enough rain to cause any flooding issues. High temperatures
today will be dependent on the advance of thicker clouds, but
more of the area may reach the upper 70s to near 80 now with the
slower onset. The southwestern corner of the CWA will stay in
the mid 60s to lower 70s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
The upper low will begin to pivot to the northeast tonight into
Tuesday as ridging moves off the coast and a trough moves into
the Intermountain West. This will focus moisture transport into
the CWA with precipitable water values in excess of 1.5 inches.
A southeasterly low level flow will enhance lift as it
encounters the mountains, especially the Blue Ridge. While some
embedded thunderstorms are possible during this period,
relatively weak instability may limit instantaneous rainfall
rates. However, the long duration of rain will result in average
totals of 1 to 4 inches, with the highest amounts likely in the
vicinity of the Blue Ridge. While the drought will provide some
buffer to flooding, the prolonged period of favorable
conditions for heavy rain may ultimately lead to some flooding.
Have issued a Flood Watch for areas bordering the Blue Ridge
where the highest totals are expected from this evening through
Tuesday evening. While relatively lower totals (and shorter
duration of heavier rain) are expected north of the watch, flash
flood guidance suggests there may be more susceptibility in
this area due to recent rainfall. Future shifts will evaluate
whether this balance is enough to warrant an expansion of the
watch. Temperatures Tuesday will be muted in the upper 60s/lower
70s. A relative dry slot may reduce shower coverage and
intensity by Tuesday evening, although some showers likely
continue through the night.

The upper low will be near the central Appalachians Wednesday
but slowly opening. A few breaks in the clouds are possible, or
at least enough low level drying to support temperatures rising
into the 70s. Combined with the approaching trough, some limited
instability will be able to develop, leading to widespread
showers and some thunderstorms by the afternoon hours.
Precipitable water values will be lower, and QPF forecasts are
not too excessive. However, slow moving thunderstorms that move
over any sensitive areas that already received heavy rainfall
could result in a few additional instances of flooding. Rain
chances will likely decrease Wednesday night as instability
wanes and the opening trough axis moves overhead.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As the ULL becomes sheared out over the Northeast United States Thu,
clouds should break over the local area. This will result in milder
temperatures Thu (generally upper 70s to low 80s), but will increase
instability over the area. Model soundings show more flow than Wed,
so storms should move more. Main uncertainty with Thu is coverage,
but some showers/thunderstorms appear possible at this time.

By Fri, another ULL will track eastward toward the Great Lakes. At
the surface, a notable moisture return will occur from the Gulf of
America into the Ohio Valley and Mid-Atlantic Fri into Sat. This
will be coupled with some of the warmest temperatures of the spring
thus far (mid to upper 80s both days), resulting in modest
instability. The combination of low-level moisture, steep low-level
lapse rates, steep for the Mid-Atlantic mid-level lapse rates, and
strong flow will yield the potential for strong to severe
thunderstorms. Depending on timing of cold front, Saturday may be
the more active day, or it may be to the south of the area. Will
continue to monitor. Regardless, the end of the week could yield a
couple days of severe weather. High pressure may briefly move in
Sun, but uncertainties with frontal positioning and the next
shortwave over the Ohio Valley exist.

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
Moisture will gradually advect northward today between high
pressure moving off the coast and low pressure in the deep
south. CHO will be the first to see lower ceilings and rain
showers, perhaps by mid to late morning. The remainder of the
terminals will see deteriorating conditions late this afternoon
or evening. Have been conservative with decreasing ceilings
compared to guidance given a trend to slower timing as well as
residual dry air. A stray thunderstorm could also affect CHO
late this afternoon or evening.

Moderate to locally heavy rain will spread across the area
tonight into Tuesday, with CHO expected to have the heaviest
rain. IFR conditions likely set in tonight, perhaps lifting to
MVFR for a time Tuesday. A few thunderstorms could be embedded
by Tuesday afternoon. Shower coverage and intensity should
decrease Tuesday night, but IFR to LIFR ceilings will become
likely.

Some improvement to MVFR, or even VFR, is possible Wednesday.
However, showers and embedded thunderstorms remain likely,
especially during the afternoon and evening. IFR to perhaps LIFR
conditions will return Wednesday night as rain tapers off.

Main aviation hazard Thu and Fri will be potential for afternoon
showers and thunderstorms. Winds southerly Thu, more southwesterly
Fri. Generally light outside of any thunderstorms.

&&

.MARINE...
High pressure will depart offshore today, resulting in winds
becoming southeasterly. Tricky forecast from later this
afternoon into tonight as winds increase aloft but mixing may be
poor. Some sporadic gusts to 20 kt could occur, especially
tonight on the middle bay and lower Potomac. However, confidence
is not currently high enough to hoist an advisory.

Winds increase a bit further on Tuesday, with advisories going
into effect for all waters. A soaking rain will develop late
tonight into Tuesday, which may come with a few thunderstorms,
particularly during the second half of Tuesday. Advisories will
likely continue into Tuesday night, with some indication of a
stronger surge of wind (at least 25 kt) on the southern Maryland
waters during the evening. Lighter SE to S winds are forecast
Wednesday and Wednesday night, although thunderstorms will be
possible again Wednesday afternoon.

Winds likely remain below SCA criteria Thu and Fri. Southerly winds
Thu become more southwesterly Fri. Afternoon thunderstorms are
possible Thu and Fri afternoon, which could result in gusty
winds.

&&

.TIDES/COASTAL FLOODING...
As a low pressure system slowly approaches through mid week,
continued onshore flow will gradually build anomalies. Sensitive
shoreline could approach minor tidal flood levels between
Tuesday and early Thursday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory from 10 AM to 6 PM EDT Tuesday for MDZ008.
VA...Flood Watch from this evening through Tuesday evening for
     VAZ025>027-029-030-036>040-507-508.
WV...None.
MARINE...Small Craft Advisory from 10 AM to 6 PM EDT Tuesday for
     ANZ530>532-535-536-538>542.
     Small Craft Advisory from 6 AM to 6 PM EDT Tuesday for ANZ533-
     534-537-543.

&&

$$

SYNOPSIS...ADS
NEAR TERM...ADS
SHORT TERM...ADS
LONG TERM...CPB
AVIATION...ADS/CPB
MARINE...ADS/CPB
TIDES/COASTAL FLOODING...ADS