914
FXUS61 KLWX 120734
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
334 AM EDT Fri Jul 12 2024

.SYNOPSIS...
A stalled frontal boundary will continue to drift in the vicinity of
the Interstate 95 corridor today through Saturday bringing
widespread showers and thunderstorms to areas east of the Blue
Ridge. Weak high pressure briefly builds back into the area Sunday
then gradually slides offshore Monday into Tuesday allowing the
excessive heat, humidity, and daily thunderstorm chances to return.
Another more substantial cold front approaches for the middle part
of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A cooler day in store today with thickening clouds from southeast to
northwest as a stationary front meanders back toward the west from
the Delmarva Peninsula. Accompanying this stationary front and
increasing moisture will be numerous showers and thunderstorms
through the day today and continuing through tonight. Showers and
storms are expected to develop as far west as the I-81 corridor by
later this afternoon. The heaviest rainfall should be across far
Northeast Maryland and much of southern Maryland. There is currently
a Flood Watch for the southern Maryland counties of Charles,
Calvert, and St. Mary`s from 2am this morning until midnight
tonight. There is also a Flood Watch for Cecil County from 6am this
morning until 2am early Saturday morning. High temperatures will be
mainly in the lower 80s for most with a few northwestern zones of
western Maryland and eastern West Virginia reaching the middle to
upper 80s as these locations will be the last to receive thickening
clouds and showers and thunderstorms.

While showers and scattered thunderstorms are expected to continue
tonight over Northeast Maryland, the I-95 corridor, the DC metro,
and southern Maryland, showers and thunderstorms will weaken,
diminish and end from west to east with the stationary front
wiggling its way to the east overnight and slowly during the day on
Saturday.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
During Saturday morning until around midday, showers and
thunderstorms will be predominantly located along and east of the I-
95 corridor. As for farther to the west of I-95 and the remainder of
the day Saturday, there will be a slight chance of a shower or popup
thunderstorm with daytime heating. High temperatures will have a
chance to rebound back up into the lower 90s on Saturday with clouds
breaking for sunshine and a light westerly wind. Total rainfall for
this event today through Saturday night will be 2 to 3 inches over a
30 hour period in Northeast Maryland and southern Maryland. Amounts
of 1 to 2 inches on both sides of I-95 from Harford County area in
Northeast Maryland to the Stafford County area of eastern Virginia.
Rain amounts of one-third up to 1 inch expected between the Blue
Ridge Mountains and the I-95 corridor.

Drier and hotter conditions expected Sunday and Sunday night with
highs Sunday in the middle to upper 90s possible. Increasing
humidity, combined with this heat, could result in heat headlines
Sunday and perhaps into early next week.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
A prolonged stretch of excessive heat and humidity are expected for
the beginning of the new workweek. Diurnally driven shower and
thunderstorms are expected each afternoon with more widespread
activity coming with a front mid to late week.

Synoptically, we`ll sit sandwiched between the broad upper level
ridge over the southeastern U.S and an incumbent neutral to
positively tilted upper level trough ejecting from the eastern Great
Lakes/upper Midwest region. Some uncertainty remains in regards to
the timing and strength of this trough along with it`s associated
cold front which is progged by the latest 00z guidance to cross the
area Wednesday into early Thursday. A notable change in airmass is
expected in the wake of this front with broad high pressure expected
to return for the upcoming weekend.

The biggest hazard during the majority of the extended period will
be the excessive heat and humidity. High temperatures Monday through
Wednesday will push into the mid to upper 90s (mountains mid to
upper 80s and low 90s). A few locations may even hit 100 degrees
with 850 mb temps running +21 to +24 degrees C which is right at the
97.5 to 99 percentile. Dewpoints remain in question through the
period as model guidance suggest values in the upper 60s and low to
mid 70s. Wind direction aloft appears to be more westerly/southwest
Monday into Tuesday before turning southerly mid next week. With
that said, we could mix down some lower dew points (mid 60s) during
the afternoons. This would be the one thing keeping us from another
lengthy period of heat headlines, but will continue to monitor model
trends as we get closer in time.

The excessive heat and humidity will bring the return of diurnally
driven showers and thunderstorms. Overall forcing and steering flow
will be lacking Monday and Tuesday leading to the bulk of any
convective activity tied to the mountains. Coverage should be fairly
isolated Monday into Tuesday due to the lack of any forcing
mechanisms to work with. Should a storm get locked over one
location for an hour or two, could see some isolated instances of
flooding in the higher terrain. However, the recent drought has
flash flood guidance very high area-wide.

The greatest coverage or uptick of thunderstorms looks to arrive
Wednesday and Thursday as the upper level trough and cold front
approach from the Ohio River Valley. Some these thunderstorms could
be strong to severe based upon increasing wind shear and the
antecedent airmass in place. Both SPC and the CSU Learning Machine
Probabilities also indicate this threat Tuesday and especially
Wednesday as the front pushes through. Long range model soundings
indicate plenty of SBCAPE and DCAPE to work with along with subtle
shear. One thing that could be lacking is our mid-level lapse rates
which seem to be an issue with convection last week. Something that
will have to continue to monitor over the next few days ahead.
Primary threats with storms during the extended period appears to be
damaging winds and isolated instances of flooding (mainly urban and
poor drainage areas). Once again this will not be a drought busting
front, but at this point anything helps. The front clears the area
Thursday into Friday with seasonable temps expected next
weekend.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
MVFR to IFR conditions are expected at terminals east of MRB
and SHD today as a stalled front wavers in the vicinity of the
I-95 corridor. Cigs will deteriorate from southeast to northeast
between 9- 12z/5am-8am this morning. The worst conditions and
highest probability for IFR will likely come later this
afternoon and into the overnight hours as heavier showers pivot
through. A few thunderstorms are also possible at KCHO, KIAD,
KDCA and KBWI although confidence is low given limited
instability with the increased cloud cover and persistent
precipitation chances throughout the day. Areas west of MRB will
likely remain VFR throughout the day although a few light to
moderate showers cannot be ruled out late morning and into the
afternoon hours. East winds will remain light around 5 to 10 kts
changing to the southeast later this afternoon and evening.

Terminals east of the Blue Ridge and especially along the I-95
corridor will see shower activity continuing through the overnight
hours. Cigs will remain low along with some vsby reductions due to
the showers and areas of fog/low stratus overhead. Conditions will
be slow to improve in these same locations Saturday as the front
washes out across the region. Additional periods of sub-VFR can be
expected for the corridor terminals Saturday morning and afternoon.
Areas further west will see the influence of drier air with weak
high pressure building into the region. VFR conditions return for
all terminals Saturday night into Sunday morning. Some fog is
possible leading to reductions in areas that see additional rainfall
heading into late Saturday night and early Sunday morning.

Prevailing VFR conditions are expected Sunday through Tuesday as
weak high pressure builds back into the region. Winds will turn
toward the west late Saturday before switching back to the southwest
Sunday into early next week. A few thunderstorms cannot be ruled out
at terminals along and west of the Blue Ridge (MRB, CHO, HGR, and
SHD) although coverage should be isolated. However, cannot
completely rule out an afternoon storm making it as far east as IAD
Monday , and even all the way to I-95 on Tuesday. If these were to
make it over the terminals, could see some gusty winds, VSBY
reductions, and of course lightning. High probabilities for
thunderstorm activity return to the forecast Wednesday and Thursday
next week as another front pushes into the area.

&&

.MARINE...
A stalled front over southeast VA and the Delmarva will
continue to waver over the local waters through Saturday. The
front will dissipate over the waters Saturday night with calmer
conditions under the weak influence of high pressure Sunday. SCA
conditions are likely over the open waters of the Chesapeake
Bay around sunrise this morning through this evening with
southerly wind gusts up to 20 kts. Elsewhere, across the waters
winds will remain variable out of the east and southeast at 5-10
kts with intermittent gusts up to 15 kts. Widespread showers
and scattered thunderstorms are expected all day Friday into
Friday night. A few Special Marine Warnings may be needed for
wind gusts of 35+ knots.

Additional showers and thunderstorms are expected over the
waters Saturday although coverage will gradually decrease
throughout the day as the front sweeps back to the east. Weak
high pressure brings sub-SCA level winds to the waters Saturday
night into Sunday. This trend continues into much of the day
Monday although winds will switch back to the south west and
eventually south Monday night. Some southerly channeling could
occur Monday night into Tuesday morning over the open waters
although confidence is low. A shower or thunderstorm also cannot
be ruled out, but the coverage will remain isolated. A greater
potential of showers and thunderstorms is possible Wednesday
and THursday as a strong cold front crosses the waters.

&&

.TIDES/COASTAL FLOODING...
Tides will remain below action stage through the next 24 hours.
Winds will be light out of the north and perhaps northeast through
tonight before becoming more southeasterly Saturday into early
Sunday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Flood Watch through late tonight for MDZ008.
     Flood Watch through this evening for MDZ016>018.
VA...Flood Watch through this evening for VAZ057.
WV...None.
MARINE...Flood Watch through late tonight for ANZ530.
     Small Craft Advisory until 6 AM EDT Saturday for ANZ534-543.

&&

$$

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