073
FXUS61 KLWX 171808
AFDLWX
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
208 PM EDT Fri Jul 17 2026
.WHAT HAS CHANGED...
Other than refining the times of highest storm chances through
Saturday, no changes have been made to the forecast.
&&
.KEY MESSAGES...
- 1) Poor air quality due to smoke can be expected through
tonight along with a few showers and thunderstorms.
- 2) A strong cold front brings the threat of severe weather
Saturday, possibly lingering into Sunday to the south.
- 3) A strong cold front and trough of low pressure may bring
severe weather Tuesday and/or Wednesday.
&&
.DISCUSSION...
KEY MESSAGE 1...Poor air quality due to smoke can be expected
through tonight along with a few showers and thunderstorms.
A few showers and thunderstorms may try to develop by early this
evening near the central Shenandoah Valley before drifting east
and northeast as a stalled front begins to lift north. This
frontal zone may be enhanced a bit on the gradient of thicker
smoke to its northeast.
The front will continue to push back northward tonight in
response to low pressure moving through the Great Lakes. While
the low levels will likely be stable for most, instability will
advect northward with the front, especially closer to the
Chesapeake Bay where even surface-based parcels may become
conditionally unstable by daybreak Saturday. The main question
is whether there is a strong enough trigger to produce any
convection. Most guidance has storms on the nose of moisture
advection focused to our north, with limited coverage locally.
Should a storm tap into the instability, there is enough shear
to result in an organized stronger storm, although most of that
potential holds off until after sunrise Saturday.
KEY MESSAGE 2...A strong cold front brings the threat of severe
weather Saturday, possibly lingering into Sunday to the south.
An unseasonably strong upper trough and embedded shortwave/jet
streak will pivot near and north of the area Saturday. Strong
height falls associated with this trough, coupled with high
low-level moisture content and modest mid-level lapse rates will
likely result in strong instability, perhaps even if cloud
breaks are muted by early day clouds. The other question mark
is whether smoke could have any lingering effects, though the
shift in wind direction should lead to noticeable improvements
in that regard by afternoon. The strong deep layer flow will
lead to effective shear magnitudes of 30-40 kts, helping to
organize storms that develop in the vicinity of a pre-frontal
surface trough. Low-level flow will be a bit weaker during the
day, so although transient supercell structures are possible,
the main risk should be damaging wind gusts and perhaps large
hail as opposed to tornadoes. This could change if the effective
warm front lingers overhead or mesoscale boundaries back the
low-level flow.
Depending on storm coverage, temps could reach well into the 90s
Saturday, especially along the I-95 corridor. With high
humidity, heat indices may reach 100-105 east of the Blue Ridge.
Heading into Saturday evening, low-level flow increases again
ahead of the approaching synoptic cold front associated with
the aforementioned upper trough. This sends PWATs hurdling to
over 2.2" and keeps CAPE elevated well into the evening. The
expectation is for a strongly forced line of storms to develop
in the unstable airmass from the eastern Great Lakes into the
upper Ohio Valley (i.e. western NY/PA into OH/WV). This line of
storms may be slow to weaken as it treks into the area from the
northwest through the evening, especially if there is moderate
to strong instability left (depends on earlier activity). The
main threat at this point would appear to be gusty to damaging
winds and heavy rain due to multiple rounds of storms. High
instantaneous/sub-hourly rain rates would be plausible in this
setup. If any discrete activity develops in the evening ahead of
the line as the LLJ increases, there may be a risk for large
hail as well as a couple tornadoes, particularly in areas for
surface flow is backed. With that said, much of the guidance
shows this upstream convection weakening as it reaches the CWA
during the evening. Some training is possible on the western
slopes which may raise the flood concerns there.
Activity should wane during the overnight hours Saturday as the
front and associated convection drop south and the atmosphere
gradually stabilizes. The front will probably end up near or
south of I-64 Sunday, with any remaining severe threat being
near and south of the effective frontal boundary. Expect cooler
temperatures in the wake of the front.
KEY MESSAGE 3...A strong cold front and trough of low pressure
may bring severe weather Tuesday and/or Wednesday.
After a quiet start to the workweek, the threat of hazardous
weather returns as a strong upper-level trough and cold front
crosses the region.
Some uncertainty remains in regards to the timing/placement of
this system, but broadly it looks to cross during the Tuesday
and Wednesday timeframe. Currently, most of the guidance has a
warm front lifting through the area late Monday into Tuesday,
with a pre-frontal shortwave trough ejecting eastward ahead of
the boundary Tuesday afternoon and evening. The synoptic cold
front looks to cross the region Tuesday night into Wednesday
with the mean upper-level trough axis and possibly a secondary
cold front to follow Wednesday afternoon and evening.
As a result, there is a threat of severe thunderstorms Tuesday
and Wednesday, especially during the typical diurnal period.
Some linear organization to the storms is likely given the high
shear environment, although confidence this far out is limited.
SPC outlooks denote roughly at 15% risk Tuesday into Wednesday
from west to east, with various ML/AI guidance a tick or two
higher than that. Damaging winds will likely be the primary
threat with storms, although other hazards cannot be ruled out
pending the placement of the trough and ingredients at play.
Behind this system will be lower humidity and cooler than
normal temperatures for the second half of next week with high
pressure returning to the region.
&&
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
IFR conditions in smoke will likely linger through at least
early Saturday morning. Given that modeling of visibility in
smoke is far from perfect, the TAFs represent a combination of
what has been happening upstream with anticipated changes due to
daytime mixing and wind shifts as the front lifts back north
tonight. While a shower or storm could approach CHO this
afternoon or evening, and across the rest of the area late
tonight, the probability is currently too low to include in the
TAF outside of a brief PROB30 at CHO. Light north winds will
shift southerly tonight as the front lifts north.
Smoke should disperse by Saturday afternoon, with perhaps a
period of MVFR CIGs Saturday morning. Multiple rounds of
showers and thunderstorms are possible between Saturday morning
and Saturday evening. Some of these could be strong to severe.
The highest chances appear to be with a surface trough Saturday
afternoon, then with a possibly weakening line of strong storms
mid to late Saturday evening as it drops in from the northwest.
Winds will shift back to the N and NW behind a cold front
heading into Sunday. Some low CIGs could persist into Sunday,
with a low TS risk near CHO.
Prevailing VFR conditions are expected Monday with additional sub-
VFR reductions possible Tuesday and Wednesday pending any shower
or thunderstorm development.
&&
.MARINE...
Lowered visibility in smoke can be anticipated through Friday.
Winds flip to southerly tonight as a front lifts back north.
Advisories may be needed for portions of the waters starting
tonight, but are more likely Saturday into Saturday evening.
Strong storms are possible Saturday into Saturday evening as
well, which may prompt Special Marine Warnings.
Leftover storms on Sunday would probably be limited to areas around
southern MD, but there is uncertainty in just how far south the
front gets. Otherwise winds become northerly in the front`s wake.
Expect sub-SCA level conditions Sunday into Monday in lighter NW
flow behind the front. SCA level channeling may return Tuesday
and Wednesday as the gradient tightens ahead of an associated
upper-level trough/cold front. Strong storms are possible
Tuesday into Wednesday afternoon.
&&
.TIDES/COASTAL FLOODING...
Increasing southerly flow on Saturday and again on Tuesday could
lead to water levels approaching minor flood stage, especially
at Annapolis.
&&
.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...Air Quality Alert until midnight EDT tonight for VAZ025>027-
029-030-036>040-050-051-055>057-501>504-507-508.
WV...Air Quality Alert until midnight EDT tonight for WVZ050-055-
501>506.
MARINE...None.
&&
$$
DISCUSSION...ADS/DHOF/EST
AVIATION...ADS/DHOF/EST
MARINE...ADS/DHOF/EST
TIDES/COASTAL FLOODING...LWX
NWS LWX Office Area Forecast Discussion