Aspen Hill, Maryland 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

011
FXUS61 KLWX 130127
AFDLWX

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

.SYNOPSIS...
An upper low will slowly drift northeastward toward the area
through Wednesday, before shearing out and lifting to our
northeast on Thursday. An area of low pressure will track into
the Northern Plains/Western Great Lakes by Friday, before
tracking eastward across Ontario, Quebec, and the Northeast
this weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 9pm, water vapor imagery shows a well defined upper low
centered over northern Alabama, with its attendant circulation
encompassing much of the eastern US. At the surface, an
accompanying surface low is located over east-central Alabama
as well, with high pressure in place offshore. The latest upper
air sounding shows some dry air in the lower 2000 feet of the
atmosphere, then in portions of the mid-levels. Above the mid-
levels, saturation is much more defined. It is a matter of time
late this evening until more light intermittent or steady rain
reaches the ground. For now, much of any rainfall of this
magnitude or persistent will hit the ground mainly along and
west of the Blue Ridge Mountains. To the east, sprinkles to
perhaps an occasional shower will be felt. These could be some
exception in Northeast Maryland as it is much drier in many
levels so it may take an additional few hours into the past
midnight timeframe until the rain reaches the ground.

Most of the rain overnight should stay light, but a few embedded
thunderstorms can`t be ruled out. Any of these thunderstorms
could be capable of producing a quick half inch to an inch of
rain in an hour, but coverage of storms is expected to be low. A
Flood Watch goes into effect for locations in the vicinity of
the Blue Ridge at 2 AM, but most flooding impacts are expected
to hold off until Tuesday into Tuesday night. Temperatures will
remain mild overnight, with lows generally in the 60s (upper 50s
mountains).

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
Previous discussion...
The aforementioned upper low will continue to drift
northeastward toward the area tomorrow, and will eventually
become centered overhead during the day on Wednesday. A steady
rain will continue through much of the morning tomorrow within
the zone of large scale ascent downstream of the approaching
upper low. As we work into the afternoon hours, a mid-level dry
slot may start to work in from the southwest, which may allow
for a few breaks of sun and some limited surface
heating/development of surface based instability. If this
occurs, thunderstorms may start to develop within the dry slot
and lift northward into the area during the late
afternoon/evening hours. These thunderstorms may be capable of
producing heavier rainfall rates, and may potentially lead to
some instances of flooding. The earlier issued Flood Watch was
expanded to include all of the WV Panhandle, most of Northern
Virginia, and Allegany County in Maryland. A general 2-4 inches
of rain is expected by late Tuesday night across the watch area,
with localized higher totals along the eastern facing slopes of
the Blue Ridge and Alleghenies, where upslope southeasterly flow
should enhance totals. Further north and east, rainfall totals
are expected to be slightly lower, but an instance or two of
flooding can`t be completely ruled out. The steadier rain should
come to an end from southwest to northeast during the second
half of the night, with the Flood Watch ending as well late
Tuesday night.

The upper low will drift overhead on Wednesday. Some more breaks
in the cloud cover are expected to form compared to Tuesday,
which should lead to a bit stronger surface heating and a bit
more instability. Showers and thunderstorms will form in
response to that surface heating, and most locations will
experience on and off showers and storms through the afternoon
and evening hours. Although there doesn`t appear to be a
boundary to focus any thunderstorm activity, storm motions will
be relatively slow beneath the upper low, and storms will be
capable of producing heavy rainfall. Following heavy rains on
Monday and Tuesday, some more localized instances of flooding
may be possible. High temperatures on Wednesday should generally
be in the 70s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
A continued high amplitude pattern remains in place across the
nation. The early week trough is likely to be exiting off the
Atlantic coast on Thursday morning. As this occurs, a strong
subtropical ridge over the Gulf of America will begin to nudge
northward. The period of height rises should be rather short lived
as the upstream upper low crosses the Upper Midwest late Thursday
into Friday morning. Although the core of lower heights with this
system remain confined to latitudes north of the Mason-Dixon Line, a
grazing blow from this trough is expected.

The potent nature of this trough is reflected in the 40 to 50 knot
westerly winds streaming overhead at 500-mb. By Friday, continued
warm/moist advection ushers temperatures well into the 80s,
accompanied by dew points reaching the upper 60s to low 70s. This
will contribute to decent instability profiles with surface-based
CAPEs around 1,500 to 2,000 J/kg. However, some guidance indicate
some inhibition the atmosphere may be contending with. The
combination of deep-layer shear and ample instability will support a
severe thunderstorm risk over the area on Friday into Friday night.
If capping inversions and earlier anvil cirrus do not get in the
way, a decent severe episode may unfold.

The broad upper low to the north is forecast to track across the
lower Great Lakes by Saturday. This is accompanied by a series of
additional shortwaves which race across the Ohio Valley into the Mid-
Atlantic region. Thermodynamically speaking, temperatures and dew
points drop off by around 3 to 5 degrees on Saturday. Overall
instability profiles may not be quite as potent as the previous day.
However, forcing from the trough amidst strong atmospheric flow may
afford an additional threat for strong to severe thunderstorms.
Winds begin to turn westerly behind a cold front by Saturday
evening. A post-frontal air mass fills out the region into the
second half of the weekend. This favors a drier finish on Sunday
with highs in the upper 70s to low 80s. The westerly downslope flow
also begins to decrease humidity levels heading into the new work
week.

By Monday, high pressure builds to the north of the region before
another frontal system approaches from the middle of the country.
Based on the global ensembles, the local area will be in between
systems as a trough sits offshore of the Eastern Seaboard and
another amplifies across the Rockies. Some shower chances should
eventually emerge toward the middle of next week.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
Conditions are VFR at all terminals except CHO, where MVFR
conditions are noted, but ceilings are expected to rapidly drop
this evening as showers move in, with conditions becoming IFR
overnight. Prevailing IFR and rainy conditions will continue
through the day Tuesday into Tuesday night, with a thunderstorm
also possible, especially during the afternoon and evening. We
may see some improvement back to MVFR or even VFR for a time
Wednesday, but drops back to IFR ceilings are expected again
Wednesday night. An afternoon thunderstorm may be possible once
again on Wednesday.

Winds will be light out of the south to southeast, before
picking up a bit out of the southeast tomorrow (gusts to around
20 knots during the afternoon). Lighter easterly winds are
expected on Wednesday.

On Thursday, mainly VFR conditions are expected although an
afternoon/evening risk of thunderstorms could lead to a few
restrictions. The better chance for convection lies on Friday and
Saturday ahead of a potent frontal system. Strong to severe
thunderstorms are possible each day which will support some
convection-related restrictions at times. Winds during the period
will initially be southerly before shifting to southwesterly by
Friday. A cold front brings westerlies back to the area on Saturday
with gusts up to 15 to 20 knots.

&&

.MARINE...
Sub- SCA level southeasterly winds are expected. The
southeasterly winds will start to pick up late tonight into
tomorrow, when SCAs are in effect for all waters. A few models
indicate that winds may even near low-end Gale levels tomorrow
evening. Sub- SCA level easterly winds are expected on
Wednesday. A stray thunderstorm can`t be ruled out over the
waters this evening through tomorrow evening.

Expect sub-advisory caliber winds on Thursday and Friday with winds
shifting from southerly to southwesterly during this period. There
will be a risk of thunderstorms each day, particularly on Friday as
stronger storms may impact the waters. Special Marine Warnings may
be necessary for the more robust convection.

&&

.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.
     Flood Watch from 6 AM EDT Tuesday through late Tuesday night
     for MDZ501-502-510.
VA...Flood Watch from 6 AM EDT Tuesday through late Tuesday night
     for VAZ028-031-050-051-053>056-501-502-505-506-526-527.
     Flood Watch through late Tuesday night for VAZ025>027-029-030-
     036>040-503-504-507-508.
WV...Flood Watch from 6 AM EDT Tuesday through late Tuesday night
     for WVZ050>053-503-504.
     Flood Watch through late Tuesday night for WVZ055-501-502-505-
     506.
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...KLW
NEAR TERM...KLW/KJP
SHORT TERM...KJP
LONG TERM...BRO
AVIATION...BRO/KLW
MARINE...BRO/KLW
TIDES/COASTAL FLOODING...KLW