320
FXUS61 KLWX 171908
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
308 PM EDT Sat Aug 17 2024

.SYNOPSIS...
Widely scattered to numerous showers and thunderstorms are expected
through Sunday as a slow moving cold front passes through the
region. The highest thunderstorm chances look to occur Sunday
afternoon and evening as the front sits overhead. Additional showers
and thunderstorms are possible Monday as the front pushes toward the
coast. Cool Canadian high pressure builds over the region Tuesday
and last through the remainder of the upcoming workweek.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Not a washout start to the weekend although the threat of showers
and thunderstorms will remain increased across the region with
multiple shortwave troughs of low pressure passing through. One
round of showers will continue to PUSH east of I-81 this afternoon
with another round of showers traversing the Alleghenies later this
evening. The overall convective coverage appears to be lower today
than Sunday given the extra cloud debris from the activity earlier
in the day. Even with that said, confidence is average on coverage
due to the diffluent upper level flow and embedded vorts/shortwaves
track across the region. Current 12z hi-res CAMS shows spotty
development later this afternoon and into the evening hours with
potential development overnight west of Blue ridge. For now,
will keep the bulk of any chance PoPs or higher east of the
Alleghenies and into the I-95 metros late this afternoon after
3-5pm and into the late evening hours. The HRRR/NAMnest continue
to peg widely scattered convection working from west to east
off the Alleghenies and southwest to northeast from central VA
into southern and eastern MD. This area has the greatest
potential to see the most filtered sunshine today leading to
higher confidence for instability to be maximized.

Today`s convective environment appears more favorable with around
1000-2000 J/kg of CAPE during peak heating and 30 to 35 kts, all
with the cold front parking between the Alleghenies and I-81
corridor. DCAPE values will run 800-1100 j/kg. SPC maintains a
Marginal risk (1/5) for along and west of the I-95 corridor today
with wind as the primary threat. Flooding does not appear a
widespread concern although localized issues could crop up given the
extra runoff with the recent drought and rains from the remnants of
Debby. PWATS will increase between 1.50 to 2 inches as a result of
increased low level southerly flow. The most vulnerable areas will
be those in NE Maryland and in metro areas that are sensitive to
urban flooding.

High temperatures this afternoon will be dictated by the cloud cover
and how much sun can break through. Most locations will top out in
the 80s with some valley locations east of the Alleghenies and west
of Blue Ridge hitting 90 degrees. Higher elevations will remain in
the 70s throughout the day as low and mid level clouds persists into
the early afternoon.

Shower and thunderstorm activity will continue into tonight with
decreasing coverage mainly east of the mountains. This is due part
to better upper level support and additional piece of shortwave
energy passing through ahead of the incumbent cold frontal boundary.
Overnight low temperatures will dip into the mid 60s to low 70s
areawide with patchy fog heading into early Sunday morning.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
The end of the weekend into the start of the new workweek will
feature more showers and thunderstorms. A deepening trough and it`s
associated cold front over the Great Lakes and Ohio River Valley
will be the main weather features to watch during the period. Since
the trough is slow to move across the region, chances for showers
and thunderstorms will become more widespread especially during the
Sunday afternoon and Sunday night timeframe. Precipitation chances
will linger into Monday although coverage will decrease as the front
pushes east with the upper level trough axis slowly lagging behind.

Sunday`s environment looks similar to Saturday with CAPE values
of a 1000-2000 j/kg and 0-6 km bulk effective shear values of
25-35 kts. SPC has outlooked areas mainly along/east of the Blue
Ridge both Sunday and Monday for a marginal risk of severe
thunderstorms. Main concern Sunday would be wind as some linear
organization will be possible with better dynamics in place in
advance of the main trough. Besides the severe threat, locally
heavy rainfall continues to be a concern with PWATS hovering
between 1.50 to 1.75 inches mainly east of the Blue Ridge.
Isolated instances of urban flooding could occur especially
across central and northeast MD (including Baltimore metro)
given the recent rounds of rainfall as the front is slow to pass
through.

High temperatures Sunday will once again be reliant upon how much
sun breaks through. Most locations east of the Alleghenies will push
into the mid to upper 80s. Mountain locations will be cooler in the
mid to upper 70s. Overnight lows Sunday night will fall into the mid
to upper 60s and low 70s.

Additional showers and spotty thunderstorms are likely to
linger into Monday as the upper level low digs further south
behind the departing frontal boundary. With that said, any
thunderstorm activity that may form mainly east of the Blue
Ridge will have the potential for a little hail given the colder
air aloft and steepening lapse rates. Overall convective
parameters will be far less compared to Sunday given the switch
toward more of a west to northwest flow. Outside of the storm
chances Monday winds will pick out out of the west and northwest
ushering in cooler and drier air. Gusts of 20-25 mph are
possible during the afternoon and evening hours yielding highs
in the mid 60s over the mountains to mid 80s within the I-95
corridor. Overnight low temperatures Monday night will be in the
mid to upper 50s and low 60s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
Quiet conditions locally will persist through much of next week as
Canadian high pressure dominates the region through at least Friday.
Only noticeable precip chances will be Tuesday afternoon across
northeast MD where the departing upper trough will continue to shift
further east. Afternoon highs will start out below normal on
Tuesday, with mid to upper 70s for most areas east of the
Alleghenies. Temps will continue to warm up as the week progresses
before highs on Friday reach the low to mid 80s for the lower
elevations.

Similar trends in the overnight lows with some areas along the
Allegheny Front reaching the low 40s with low to mid 50s expected
further east. Would not be surprised to see some of the valleys make
a run at below 40 degrees Tuesday night. A slow warming trend in the
overnight lows will end the workweek with lows in the mid to upper
50s for most areas on Friday. Winds will remain elevated Tuesday
with the departing upper trough, gusts out of the northwest could
reach 20 mph at times in the afternoon and evening before
dissipating for the remainder of the work week.


&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
Prevailing VFR to high end MVFR conditions are expected to continue
through this evening for all terminals as several pieces of
shortwave energy pivot through the region. Scattered showers and
thunderstorms will impact terminals east of line extending from KMRB
to KSHD. VCTS enters the corridor between 19-23z/3-7pm. Coverage
will be widely scattered through early evening with a lull heading
into the first half of the overnight hours. Additional showers and
thunderstorms will push toward terminals west of KMRB and KSHD
heading into the overnight hours as an additional shortwave trough
pushes through. By Sunday, expect increased shower and thunderstorm
chances for all terminals during the afternoon and evening hours.
Some storms could be strong to severe with wind as the primary
concern as the cold front and upper level trough swing into the
region.

Outside of the shower and thunderstorm chances expect sustained
southerly winds between 5 to 10 kts gusting upwards of 15 to 20 kts
at times this afternoon and evening. Similar winds are expected
Sunday.

Sub-VFR ceilings will be possible at times Monday afternoon and
evening with additional shower and thunderstorm chances as one last
piece of shortwave energy pivots through. Winds will switch to
the west and northwest with gusts up to 20 kts.

VFR conditions are expected Tuesday and Wednesday with gusty
northwesterly winds 15-20 knots in place Tuesday afternoon and
evening before high pressure builds in by Wednesday with prevailing
VFR conditions expected.

&&

.MARINE...
SCAs have been extended into Sunday afternoon with southerly
winds gusting 20 to 25 kts. Additionally, showers and
thunderstorms are possible each afternoon and evening bringing
stronger gusts to the waters. Stronger storms could require
Special Marine Warnings on this afternoon and again on Sunday as
a cold front pushes through.

SCA winds are possible Monday afternoon and night for the
waters as the pressure gradient remain amplified over the
region. Cannot rule out an isolated SMW Monday afternoon/evening
if any thunderstorms cross the waters. SCA winds are becoming
increasingly likely Tuesday as an upper trough departs to the
east and high pressure builds in from the northwest. These winds
should diminish Wednesday and into the remainder of the work
week.



&&

.TIDES/COASTAL FLOODING...
Water levels will remain elevated under increased southerly flow
through the remainder of the weekend. Expect additional minor
flooding concerns over the next 3 high tide cycles at Havre de
Grace, Annapolis, and DC Waterfront. Annapolis may come close to
moderate flooding threshold for the Sunday morning high tide cycle.
This is backed up by both the ETSS and CBOFS model guidance. Water
levels will drop with offshore flow developing early next week.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Small Craft Advisory until 8 AM EDT Sunday for MDZ008.
     Coastal Flood Advisory until 6 PM EDT this evening for MDZ014.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 8 AM EDT Sunday for ANZ530>534-
     537>543.

&&

$$

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