270
FXUS61 KLWX 041330
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
930 AM EDT Tue Jun 4 2024

.SYNOPSIS...
Spotty shower and thunderstorm chances continue today as low
pressure pushes offshore and weak high pressure builds into the
region. More widespread shower and thunderstorm activity arrives
Wednesday and Thursday as a series of fronts cross the region.
Precipitation chances decrease on Friday in the wake of the cold
front. A slow moving upper trough approaches the area from the Great
Lakes this weekend leading to more unsettled conditions.

&&

.NEAR TERM /THROUGH TONIGHT/...
MORNING UPDATE: Showers from earlier across the Shenandoah
Valley and portions of the Virginia Piedmont have generally
disappeared over the past couple of hours. However, some
lingering mid- level clouds remain in those areas, although
they look to be slowly dissipating. Otherwise, no changes to the
previous forecast at this time.

PREVIOUS DISCUSSION: The forecast for today still calls for
isolated to scattered showers and thunderstorms for near and
west of the Blue Ridge this afternoon and evening. As high
pressure off to the northeast brings SE onshore flow and
moisture into the region, a boundary remains stalled to our
south and shortwave energy approaches from the west. Latest
hires guidance has the focus for showers and t-storms being
along the Alleghenies and Shenandoah Valley early in the
afternoon before shifting to the Blue Ridge and east in the
evening hours, though the best chance looks to remain south of
the DC metro. Highs climb into the mid to upper 80s for much of
the area under SE flow.

Similar to previous nights, patchy fog development is possible,
particularly where showers occur in the afternoon and evening. Lows
fall into the 60s to low 70s.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
A potent upper low moves into the Great Lakes on Wednesday, lifting
a warm front into our area by Wednesday afternoon. The latest HREF
has most convection initiating along a line extending from Garrett
southeast to and along the I-66 corridor in the early afternoon and
expanding northeast from there through the afternoon, followed by a
second round in the late afternoon moving generally west to east
from the Alleghenies towards the Potomac with focus along the terrain.
The potential for isolated flooding remains as rainfall could be
locally heavy at times. Areas that received showers in the last few
days (such as the central Shenandoah Valley, Blue Ridge and the
foothills) could be more vulnerable to this.

While models have 1000-1500 J/kg CAPE Wednesday, shear looks to top
out around 20-25 kt, so not currently expecting a significant severe
threat. Some storms could be strong, but primary threat remains isolated
flooding. Shower activity likely continues into the overnight, primarily
along the Alleghenies and over MD. Wednesday night will be a few degrees
warmer with much of the area east of the Blue Ridge only getting down
to the upper 60s, and metros hovering in the low- mid 70s.

The cold front arrives Thursday morning and showers and possible
thunderstorms could linger in these same areas into the evening,
with chances decreasing over time as we dry behind the cold front.
Low temperatures drop into the 50s to upper 60s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
An extended period of upper level troughing is likely to take hold
across the Mid-Atlantic late this week through the first half of
next week. A large cutoff upper low over the central Great Lakes
will meander there for several days, then slowly push south/east
toward the eastern Great Lakes region Monday, then to the Northeast
states by mid next week. As a result, a steady west to northwest
wind around 10-15 mph develops each afternoon during this time, with
lighter winds at night. In terms of rain chances, the highest Friday
and Saturday look to be in the Alleghenies and Potomac Highlands (20-
40pct), with only a slight chance of showers along/east of I-81.

The wettest time period could be Sunday afternoon into Sunday night
if a wave of low pressure traverses the area, bringing widespread
showers and possibly thunderstorms. However, this is highly
uncertain at this time due to large model spread late this weekend.

Temperatures are forecast to be near to possibly slightly below
normal due to greater cloud cover. Highs in the upper 70s to lower
80s, with overnight lows in the mid 50s to low 60s.

&&

.AVIATION /14Z TUESDAY THROUGH SATURDAY/...
VFR conditions are expected to prevail today. Isolated to scattered
showers and thunderstorms are possible in the afternoon and evening,
but coverage is being tamped down by weak upper ridging. Storms
that move over the terminals could bring brief restrictions.
Otherwise, patchy fog early this morning and again tonight could
bring MVFR or lower vsbys to CHO and MRB. IAD could also see
some reductions in vsby but with less confidence, and only down
to MVFR if so. Fog coverage will be less tonight.

Numerous showers and thunderstorms will bring restrictions to
the terminals on Wednesday, with the best chance in the afternoon
and evening. Some showers and possible t-storms could linger
into the overnight for MRB, BWI and MTN. Conditions improve on
Thursday.

VFR conditions look likely Friday and Saturday as westerly winds
around 5-10 knots prevail. Isolated showers possible each afternoon,
though rain chances overall are low at all terminals.

&&

.MARINE...
Sub-SCA winds are expected today. Winds increase out of the
southeast but are expected to remain sub-SCA. A frontal system
arrives on Wednesday with gusty southerly winds over the waters
approaching SCA criteria by Wednesday afternoon. SCAs will
likely be needed Wednesday night into Thursday morning. Winds
diminish behind the cold front on Thursday.

Generally west winds prevail Friday into the weekend across the
waters, with winds remaining mostly below SCA criteria during this
time. There could be a brief period of gusts around 15-20 knots late
Friday night in the open waters of the central Chesapeake Bay.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies gradually rise throughout the week due to a
developing onshore flow by Tuesday, followed by a persistent
southerly flow through around Thursday. Sensitive locations at
Annapolis, Straits Point, DC SW Waterfront will continue to reach
Action Stage during high tide. Minor coastal flooding is becoming
more likely during the early Wednesday morning and early Thursday
morning high tide cycles. Coastal Flood Advisories may need to be
issued soon for those sensitive locations mentioned above.

A weak cold front crosses the area early Thursday, with the
resulting west winds causing tidal anomalies to drop.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

SYNOPSIS...BRO/EST
NEAR TERM...CJL/CAS
SHORT TERM...CAS
LONG TERM...KRR
AVIATION...CAS/KRR
MARINE...CAS/KRR
TIDES/COASTAL FLOODING...KRR