455
FXUS61 KLWX 300123
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
923 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/...
Multiple waves of convection are noted on radar as of 9pm. One
wave is sliding across southeast Pennsylvania. On the southwest
flank or side of this wave, there are a few strong thunderstorms
that need to be monitored as they could move close to Cecil
County. The second wave of heavier showers and intense
thunderstorms are noted from northwest Carroll County to
northern Frederick County in Virginia. This appears to be the
most intense wave. Main threats are downpours, lightning and
possible damaging wind gusts. An isolated tornado or two can`t
ruled out given the amount of wind shear in the lower levels.
The third wave is moving across western Maryland and parts of
northeast West Virginia. This wave has mainly moderate to heavy
rain with a few thunderstorms on the south end near Grant County
in West Virginia.

We will closely monitor all of this convection as there still
appears to be considerable instability and wind shear across our
northern half of our region. Additional activity could develop
farther south and west than these waves, but without daytime
heating, they could lose their punch. Patchy fog may develop in
areas where it rained during this evening. 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/...
Previous discussion...
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. Guidance tends to
reveal some showers and thunderstorms developing with daytime
heating in the Noon to 2pm timeframe and along and east of the
Blue Ridge. Highs could reach the lower to middle 90s, but up
to 5 degrees may need to be subtracted in some areas if trends
continue for increasing or thickening clouds. Still not
confident that a Heat Advisory will be needed on Sunday.

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 /01Z SUNDAY THROUGH THURSDAY/...
Heavy showers and thunderstorms are and will continue to move
over MRB terminal for another hour or so. Additional showers and
thunderstorms could reach our northeastern terminals shortly
before midnight but uncertain as to how much punch they will
have when it comes to damaging winds and lowering ceilings. MVFR
would be more probable at MRB overnight depending on rainfall
intensity or perhaps some patchy fog.

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 this evening 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 remains in effect for most waters early
this 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...
A Coastal Flood Advisory for Annapolis remains in effect. 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 until 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 1 AM EDT Sunday for ANZ538-542.

&&

$$

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