406
FXUS61 KLWX 191406
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1006 AM EDT Sun May 19 2024

.SYNOPSIS...
Low pressure will drift off the Carolina Coast through today. High
pressure will build overhead Monday into Tuesday. A cold front will
approach from the Midwest Wednesday, then cross by Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
MID-MORNING UPDATE...
Visible satellite shows some clearing of the thin low clouds
this morning, primarily along the mountains and portions of the
Chesapeake Bay. Earlier this morning a boundary cut west from
the Potomac and cleared skies around IAD briefly, which has now
filled back in. Overall the cloud is thin however, with some
visible thinning and breaks. Reduced visibility from patchy fog
is currently restricted to near Baltimore with the marine layer.

Gradual improvement in conditions is expected through the day.
Hires guidance suggests high end MVFR only by this afternoon,
but could reach high end MVFR/low end VFR by late morning for
some TAF sites, especially west of DCA without the influence of
the marine layer.

Guidance currently suggests isolated to widely scattered showers
at most this afternoon, focused along the mountains and east of
the Blue Ridge.

Temperatures today remain dependent on cloud clearing, but still
anticipate 70s for most of the area. May have to adjust MaxT
within the next few hours based on obs.

PREVIOUS DISCUSSION FOLLOWS...
Early morning satellite imagery reveals abundant stratus. The
cloud layer is somewhat thin per regional soundings, so some
breaks in the clouds are possible through the morning hours.
Where these breaks develop prior to sunrise, fog may develop
given the saturated near surface layer and recent rain. A spotty
sprinkle, shower, or drizzle is possible in continued E/NE flow
through early this morning.

Clouds should gradually lift and erode today as dry air attempts to
filter in ever so slowly. A lingering axis of low-level moisture
combined with daytime heating could result in a couple of showers by
later this afternoon, focused (1) east of the Blue Ridge where low-
level moisture may be a bit higher, and (2) near the Appalachians
with slightly more lift aided by terrain circulations. A couple
members of the 00z HREF have a few inches of rain near the ridges
just west of Highland County, which bears monitoring.

High temperatures today are expected to be warmer than recent days,
into the 70s for most, but exact values will be contingent on cloud
cover. Low temperatures tonight should fall into the 50s to near 60
with patches of fog and low clouds possible.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
An elongated upper trough will continue to pull away from the
Carolina coast. At the same time, a broad ridge begins to settle
over the Eastern Seaboard. Subsidence within the column will
begin to squash any rain shower chances during the first couple
of days of the work week. However, the surface pattern does
maintain easterly onshore gradients on Monday. Consequently, an
area of low stratus is likely to linger during the morning
hours. Model guidance gradually shows this low cloud deck should
erode by midday which leads to a mixed bag of sun and clouds.
Ample warming given mid-May solar insolation angles will help
raise high temperatures into the upper 70s. Some low 80s are
possible across the Shenandoah Valley and Allegheny mountain
valleys where morning cloud cover burns off earlier. For the
overnight hours, light southerly winds underneath clear skies
will yield some patchy fog over the area. Low temperatures are
forecast to be in the 50s.

Ridging aloft persists coupled with a shift to a low-level warm
advection pattern. This combination will yield further warming
along with a gradual uptick in humidity levels. However, for mid
to late May standards, dew point temperatures do remain fairly
in check. Additionally, expect a mainly sunny skies across the
region with skies remaining mostly clear into the night.
Forecast high temperatures rise into the low to perhaps mid 80s,
with 70s over the mountains. The shift to southerly flow will
make for a slightly milder night with lows in the upper 50s to
low 60s.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Upper ridging eventually begins to break down in response to
upstream height falls across the Midwest to Great Lakes region.
Relative to previous days, the slowing trend has generally held
which brings the associated cold front through the I-95 corridor
midday Thursday. In advance of this frontal system, instability
increases owing to warmer temperatures and additional moisture
content. Multi-ensemble CAPE values range from 500-1000 J/kg on
Wednesday before rising into the 1000-1500 J/kg range by
Thursday afternoon. With the approach of the front, it remains
to be seen if the increasing vertical shear can coincide with
the higher CAPE values. While uncertain, there is a strong to
severe thunderstorm risk, especially by Thursday. Mid-week
temperatures will rise into the mid/upper 80s, accompanied by
dew points into the mid 60s. Depending on the exact timing of
this front, some stormy conditions could persist into the
evening as well.

To finish out the work week, the Mid-Atlantic region will be in a
post-frontal environment with prevailing northwesterly flow.
Temperatures fall off by around 5 degrees, but the bigger change
is the decrease in humidity owing to the wind shift. This
frontal zone drops down near the Virginia/North Carolina border
before lifting back to the north by late Friday into Saturday.
Given the frontal boundary nearby, shower chances return to
start off next weekend. There is a lot of uncertainty in the
pattern, so it will be difficult to say with confidence if it
will be another wet weekend.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
Early morning observations (as of 06z) at the TAF sites show
generally MVFR CIGs with patchy mist and light to calm winds.
LAMP/NAM guidance continues to show lowering CIGs through daybreak
to IFR, though most guidance has been shrinking the window of IFR
potential. Any breaks in the clouds, however, could yield to quick
development of fog given nearly saturated low levels and recent rain.

VFR should return 16-18z today. A spotty shower can`t be ruled out,
but any associated restrictions should be brief and thunder
potential looks too low to include in the TAF at this juncture.
Additional low clouds and fog may develop given lingering low-level
moisture and light winds tonight into Monday, and again Monday night
into Tuesday, but otherwise mainly VFR and dry weather is expected.

A cold front will slowly approach the area by mid-week before
crossing through the I-95 corridor by midday Thursday. The
increasing shower and thunderstorm chances may afford some
restrictions, particularly late Wednesday into Thursday. Behind
the cold front, winds shift to westerly for the second half of
Thursday.

&&

.MARINE...
Light NE to SE winds are expected over the next few days as
high pressure scoots overhead and then offshore. Other than a
pop up shower this afternoon, dry weather is expected early this
week.

Increasing southerly winds ahead of a cold front may lead to
some channeling effects Wednesday evening into the night. This
could approach Small Craft Advisory thresholds across portions
of the waters. A cold front tracks through midday Thursday which
brings an accompanying risk of showers and thunderstorms.
Special Marine Warnings may be required for the stronger storms.
Winds shift to west-northwesterly behind the front.

&&

.TIDES/COASTAL FLOODING...
While tidal levels are currently elevated, a shift to
northeasterly winds should help gradually reduce the risk for
coastal flooding. However, the more sensitive locations like the
Southwest D.C. Waterfront and Annapolis could see minor flooding
during the next high tide or two. Anomalies do creep back up
again late Sunday into Monday. This is in response to a light
wind which may allow some of the elevated water levels to slosh
back. Winds turn more easterly again on Monday yielding the
further rises. Additional tidal flooding is possible as this
occurs.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 7 PM EDT this evening for DCZ001.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$

SYNOPSIS...DHOF
NEAR TERM...DHOF/CAS
SHORT TERM...BRO
LONG TERM...BRO
AVIATION...BRO/DHOF
MARINE...BRO/DHOF
TIDES/COASTAL FLOODING...BRO