Aspen Hill, Maryland 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

337
FXUS61 KLWX 151924
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
324 PM EDT Thu May 15 2025

.SYNOPSIS...
Low pressure will drift toward the northeast today while a warm
front approaches from the west by tonight. Low pressure will
move into the Great Lakes Region Friday, with a trailing cold
front pushing through the area Saturday. High pressure will
build in from the north Sunday and Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Substantial clearing has occurred today area-wide, with
instability growing as a result. There is generally a gradient
of CAPE over the region from NE to SW of around 1000-1500
J/kg in northeast MD to around 2000-2500 J/kg across
central to southwestern VA. Also evident in latest analyses is a
strong convergence zone over the Potomac Highlands. Along this
zone of convergence is a fairly agitated cumulus field,
indicative that convective initiation is likely not far off.
This environment is also characterized by around 30 to 40 knots
of bulk shear. Forecast soundings show some pretty fat CAPE,
especially within the hail growth layer, in the region generally
from the Potomac Highlands down through central/southeast VA and
areas south and west from there. As thunderstorms develop this
afternoon within this environment, though coverage may be
isolated to widely scattered, expect some very tall supercells
to be the primary storm mode. Large hail and damaging winds will
be the primary threats today, and in fact SPC has highlighted
the area for significant (2"+) hail. Storms today should have
decent motion...however with this area being hydrologically
sensitive with many streams running high, can`t rule out an
isolated flood issue. WPC maintains a marginal risk for
excessive rainfall across the region for this reason. Most of
the guidance continues to keep these stronger storms south of
I-66 (if not much farther south).

Locations that see appreciable sun today should approach/exceed
80, while locations to the northeast stay in the mid 70s.

After storms move to the southeast during the evening there
should be a quiet period as temperatures fall back to the 60s.
Some patchy fog or low clouds could develop overnight, especially
in area where it rains this afternoon/evening.

By late tonight, a decaying line of thunderstorms may push
through the northern half of our region. This should be
relatively quick-moving, and decaying in strength as it moves
east. Can`t rule out a few rumbles of thunder, but not seeing a
risk of severe weather with it into Friday morning.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
For the rest of Friday through Saturday, much more uncertainty
exists around thunderstorm chances...with a high dependence on
what happens upstream, both in terms of advection, and how the
local environment may be modified. Current guidance favors
several periods, but this could obviously change: First is
something originating from the southwest and moving into the
area on Friday afternoon, though this carries the most
uncertainty. If no forcing can move into the area Friday, it
could turn out pretty dry, as forecast soundings exhibit a
fairly strong cap. Second, and potentially the most
significant, will be upstream convection that may arrive late
Friday night into Saturday morning. The question is whether this
survives in tact or regenerates during the day Saturday along
its outflow. Throughout the period, CAPE and shear would be
supportive of severe thunderstorms, especially any that are
previously organized and/or develop locally during peak heating.
Storms should generally be progressive, but will have to
monitor the flooding threat as well. Hopefully details can be
refined moving forward. The Storm prediction center has actually
introduced a widespread Slight Risk for severe thunderstorms on
Friday, primarily focused on this potential MCS threat into the
evening hours. So, confidence seems to be on the increase, but
these setups are always rather tricky to handle. At any rate,
will be monitoring trends closely with each model run ahead of
the event.

Assuming early clouds/rain are not too widespread, Friday will
turn out rather hot and humid with highs well into the 80s. Some
locations could have heat indices in the lower 90s. The same can
be said for Saturday after a very mild start. It`s possible the
cold front clears the area Saturday morning, with
clearing/drying and breezy conditions in the afternoon however.
The secondary cold front may bring some upslope showers Saturday
night. Otherwise temperatures will start cooling off.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
Surface high pressure traversing the region Sunday into the start of
next week will bring dry conditions to the area. Even with some
passing shortwaves aloft, not really expecting convection given dry
airmass at the surface. Seasonal temperatures in the 70s to near 80F
Sunday and Monday, with overnight lows in the 50s. A dry reinforcing
cold front Monday night bring some cooler temps, with lows in the
40s west of the Blue Ridge.

The weather pattern looks to become very active again for the middle
of next week. Split flow aloft confluences over the TN and OH
Valleys Tuesday into Wednesday, with two strong upper troughs
merging in some capacity as they move across the Mid-South, Midwest
and Mid-Atlantic. A frontal zone looks to set up over our area
sometime Tuesday night into Wednesday as a warm front lifts in from
the south. Several waves of low pressure traversing the frontal zone
bring us rounds of showers and thunderstorms. Too early to tell if
any will be severe, though heavy rainfall is possible depending on
where the boundary sets up.

Another noteworthy trend for mid to late next week is the return of
cooler than normal temperatures. Highs are currently forecast to be
in the 60s to around 70F Wednesday and Thursday, with that possibly
continuing into the following weekend. Overnight lows though still
around seasonal values in the 50s.

&&

.AVIATION /19Z THURSDAY THROUGH TUESDAY/...
Starting to see some more agitated cumulus out over eastern WV
into the Shenandoah Valley along an area of strong convergence.
This will be the spark for thunderstorms to develop this
afternoon over the higher elevations and move towards the
southeast. Still questioning how far north the development will
be, hence there are still only PROB30s at IAD and DCA. However,
CHO is more likely to get in on the action, so have added a
prevailing TSRA group in later this afternoon/evening. This will
be a very short duration event, with large hail and damaging
winds both threats to watch out for. If under a storm that
develops today, the hail could even approach 2" in diameter, so
that threat is a bit more elevated today than the average
thunderstorm day in the region.

Sub-VFR conditions (ceilings or fog) may return to mainly
MRB/BWI/MTN tonight into early Friday. There is also potential
for one or more rounds of showers and thunderstorms late
tonight through Friday afternoon. The first of which will move
through the northern half of the area early on Friday morning.
This should mainly be in the form of showers, so no mention of
thunder in the TAF. However, can`t completely rule out a few
lightning strikes in this, especially at MRB. Otherwise VFR
conditions should prevail.

Then on Friday afternoon, this is when things get very
uncertain. Heat and humidity will build, so some isolated to
scattered storms may develop Friday afternoon as well.
Confidence was too low to put into the TAFs at the moment, but
it is a possibility that may need to be explored on future TAFs.

Another round of thunderstorms could arrive late Friday night
into Saturday morning. This round has the most uncertainty at
this point. An MCS moving in from the Ohio Valley may make it
into our region late Friday evening into Friday night. This
could be yet another risk for damaging wind gusts, but the
timing and certainty of occurrence is still just not quite there
yet. So, will hopefully have more details as this moves into the
TAF period.

There may be a few storms ahead of a frontal passage on Saturday as
well, which could also contain damaging wind gusts. This should
push through rather early on in the day, giving way to drier
and windy conditions in its wake.

VFR conditions are expected Sunday into the start of next week as
high pressure maintains control across the region.

&&

.MARINE...
Sub-SCA conditions should prevail through Friday night with
winds becoming southerly today and southwesterly Friday. Strong
to severe thunderstorms are possible across mainly the southern
Maryland waters late this evening. However, highest confidence
area for storms is south of the waters at this time, so keeping
that threat around 20 to 30 percent at most.

A decaying line of showers, and perhaps a few thunderstorms,
will push through the area Friday morning. This could bring some
gusty winds, but SMWs don`t seem likely at this time thanks to
the nocturnal inversion being in place. The rest of Friday
generally looks quiet, though hot and humid conditions during
the afternoon could spark a few thunderstorms near the waters,
and of which could bring down some gusty winds.

The best chance for severe weather looks to push through late
Friday night through early Saturday. Timing and location of an
MCS approaching from the west is still very uncertain, but
conditions will be favorable for damaging wind gusts if this
does traverse the mountains and make it to the waters. SMWs
would likely be needed if this feature tracks directly over our
area.

Additionally, a cold front will push through Saturday, with SCA
conditions likely in its wake. A few storms may develop ahead of
this front early in the day as well, which could bring their own
gusty wind threat.

SCA conditions likely on Sunday as winds gust around 20-25 knots
across all the waters. High pressure settles overhead Sunday night
into Monday, bringing sub-SCA winds.

&&

.TIDES/COASTAL FLOODING...
Freshwater flooding will continue at Georgetown through the
Friday afternoon high tide cycle, with the site currently in
moderate flood stage. A Coastal Flood Warning is in effect for
this threat. Water should recede Friday evening and drop back
below flood stage after the Friday overnight high tide cycle.

Elsewhere, sensitive tidal sites remain somewhat elevated this
afternoon, with several sites in action stage at times of high
tide. DC waterfront and Alexandria may even approach minor over
the next few high tide cycles. This pattern may continue through
this weekend.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Warning until 4 PM EDT Friday for DCZ001.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

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