156
FXUS61 KLWX 291951
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
351 PM EDT Sat Jun 29 2024

.SYNOPSIS...
Low pressure will move across the Great Lakes region tonight. A
cold front will then push through on Sunday. A strong area of
high pressure settles over the area Monday and Tuesday before
drifting offshore the second half of the week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Convective initiation has occurred across the Potomac Highlands
as anticipated by most guidance, although initial storms have
struggled to survive. This area across western Maryland and
eastern West Virginia will be most prone to a strong to severe
storm for the remainder of the afternoon with up to 1500 J/kg of
MLCAPE and at least 30 knots of bulk shear. Additional storms
have developed across SW Pennsylvania and northern West
Virginia along the southern flank of previous clouds and weaker
convection. This placement is less well-handled by guidance,
putting some doubt on the remainder of the evening. The general
idea is that some storms will move in from the northwest and
progress eastward before gradually weakening. These storms could
be locally severe, although they will be encountering an
increasingly unfavorable thermodynamic environment with eastern
extent. The primary threat will be damaging wind gusts. A brief
tornado can`t be ruled out with increased low level shear in
northwestern parts of the area, but the amount of hodograph
curvature in the lowest kilometer may be limited. High
precipitable water values will result in heavy rain rates,
although progressive storm motion and very dry antecedent
conditions will limit the flood threat. With continued warm
advection and a very moist airmass in place, some showers and
isolated thunderstorms could linger well into the night. Patchy
fog may develop where it rains and there are breaks in the
clouds. Lows will be very mild, in the 70s outside of the higher
elevations, and potentially remaining near 80 in the urban
centers.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
Some residual showers are possible to start off the morning,
with some cloud cover possibly lingering into the core heating
period. However, do think there should be enough breaks to
allow ample heating of the boundary layer amidst a very moist
airmass with mid 70s dew points across the region. There has
been a trend in much of the 12Z guidance that keeps more clouds
around, as well as potential early convective initiation around
noon, that would limit temperature rises. The current forecast
still calls for low to mid 90s, but up to 5 degrees may need to
be subtracted in some areas if trends continue. Therefore, was
not confident enough to issue a Heat Advisory at this time.

Another round of strong to severe thunderstorms will likely
develop during the afternoon. The culprit is a seasonably
strong cold front which arrives during the peak in the diurnal
heating cycle. Forcing aloft is more pronounced than the
previous day, although the better height falls are confined to
northern portions of the Mid-Atlantic. Multiple rounds of
showers and thunderstorms are possible, especially east of the
Blue Ridge. The Storm Prediction Center has maintained a broad
Slight Risk for this area. Damaging wind gusts are the most
likely threat. Precipitable water values in excess of 2 inches
will result heavy rain rates, but progressive storm motions will
limit the flood threat. The eastward progressing cold front
reaches the Chesapeake Bay during the evening hours before
settling into the coastal Atlantic by late Sunday night. Shower
activity should come to an end as winds shift to northwesterly
in the wake. While most see lows in the 60s, many can expect
temperatures in the 50s to the west of the Blue Ridge.

A strong dome of surface high pressure advances from the Upper
Midwest toward the Great Lakes. A seasonably cool air mass
arrives on Monday with 850-mb temperatures falling to around
10-12C. The well-mixed boundary layer yields dry adiabatic
profiles down to the surface. This favors high temperatures in
the upper 70s to low 80s which is around 5 to 10 degrees below
average for early July. Expect plenty of sunshine with northerly
winds gusting up to 20 mph. Cooler nighttime conditions push
into locations to the east with lows in the upper 50s to mid 60s
east of the Blue Ridge. This is accompanied by clear skies as
the surface high is positioned over the northeastern U.S.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
High pressure on Tuesday will bring mostly dry conditions
across the area with highs in the low to mid 80s for the lower
elevations and mid to upper 70s for the mountains. A low
pressure centered across the central Canadian provinces will
begin moving further east on Wednesday, with an associated warm
front and cold front affected the local area Wednesday into
Thursday. The front may eventually stall across the northeast,
allowing increased chances for showers and thunderstorms for the
remainder of the work week and even into the early part of the
weekend.

Highlighting the Fourth of July, the aforementioned cold front will
likely be just off to the west of the area but a warm, moist airmass
ahead of it may increase chances for some strong to severe
thunderstorms during the afternoon and evening hours. Still some
uncertainty with this system but given there will be more outside
presence during that day, it warrants a bit more attention as we
head into the holiday period. Temperatures for the remaining long-
term stay hot into the low to mid 90s with heat indices approaching
triple digits Thursday through the start of the weekend.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Low/mid clouds are becoming a bit more scattered this afternoon
amongst southerly winds gusting to around 20 kt at times. MRB
does stand a chance of a thunderstorm in the vicinity through
the late afternoon. Timing of thunderstorms into the metro
terminals is more uncertain, especially given current upstream
storm placement, but still looks likely to be after 00Z. Have
placed a 4-hour VCTS group at all locations, although there is
some chance the storms do not hold together. Some showers
possibly linger through the night. MVFR conditions could develop
at MRB for several hours around dawn, whether through patchy fog
or lowered ceilings.

Sunday brings another potential active weather day, all ahead of
an approaching cold front. Right now the afternoon to early
evening would be the most likely timing of thunderstorms. These
storms appear more likely than Saturday and will pose a threat
of strong wind gusts and heavy rain. Any convective activity
should diminish by later in the evening with northwesterly flow
ensuing in the wake. For Monday, VFR conditions are expected
with northerly gusts up to 15 to 20 knots.

VFR conditions are expected Tuesday into early Wednesday before
isolated showers and thunderstorms return Wednesday afternoon and
could lead to instances of sub-VFR conditions. Southeasterly winds
on Tuesday will turn more southerly by Wednesday with afternoon
gusts 10 to 15 knots at times.

&&

.MARINE...
Small Craft Advisory is in effect for most waters this afternoon
and early evening with southerly gusts up to 20 knots. The
stronger winds will gradually contract to the main channel
tonight. Some convective potential later in the evening or
even early overnight may require Special Marine Warnings.
However, confidence is low at this time of strong storms
reaching the waters.

Small Craft Advisories may be need to be extended into early
Sunday for the mid bay, but will become more likely for all
waters behind a cold front late Sunday into Monday. In between,
strong to severe thunderstorms could impact the waters during
the afternoon to early/mid evening. Special Marine Warnings
become likely with this activity before the convection pushes
off to the east overnight.

No marine hazards are expected Tuesday with high pressure nearby.
SCA winds may return Wednesday afternoon ahead of incoming showers
and isolated thunderstorms.

&&

.TIDES/COASTAL FLOODING...
Tidal anomalies are rising today in southerly flow. Have issued
a Coastal Flood Advisory for Annapolis tonight. Havre de Grace
and DC SW Waterfront will also be close to minor flood stage. Winds
shift to more southwesterly Sunday afternoon, allowing for
tidal anomalies to fall slightly, and then more drastically with
northwest winds behind a cold front Sunday night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory from 11 PM this evening to 4 AM EDT
     Sunday for MDZ014.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 6 AM EDT Sunday for ANZ530>534-537-
     539>541-543.
     Small Craft Advisory until 9 PM EDT this evening for ANZ535.
     Small Craft Advisory until 1 AM EDT Sunday for ANZ538-542.

&&

$$

SYNOPSIS...ADS
NEAR TERM...ADS
SHORT TERM...ADS/BRO
LONG TERM...ADS/ADM
AVIATION...ADS/ADM
MARINE...ADS/BRO/ADM
TIDES/COASTAL FLOODING...ADS