346
FXUS61 KLWX 161901
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
301 PM EDT Mon Sep 16 2024

.SYNOPSIS...
Blocking high pressure will remain south off the New England coast
while Potential Tropical Cyclone Eight pushes into the Carolinas.
Rain chances will increase from southeast to northwest late tonight
into Tuesday as the low pressure system drifts across North and
South Carolina. Another low pressure system may develop off the
coast of North Carolina and Virginia Wednesday into Thursday
providing additional rain chances. A backdoor cold front will push
through Friday into Saturday with wedging high pressure returning
Sunday into early next week.


&&

.NEAR TERM /THROUGH TUESDAY/...
Dry conditions continue today although low and mid level clouds will
increase this afternoon as Potential Tropical Cyclone Eight moves
into the NC/SC coast. The Potential Tropical Cyclone (low
pressure system) is currently located along the coastal NC/SC
border (in the vicinity of Wilmington, NC and North Myrtle
Beach, SC) and is expected to move further inland later this
afternoon. Up to 15+ inches of rain has already been observed in
these locations (as of 2pm) with the northern extent of the
rain shield pushing out Raleigh/Greensboro, NC toward
Danville/Wakefield, VA. This activity is scattered/light in
nature and will gradually fill in through late afternoon with
the far northern reach of the rain shield reaching into far
south-central portions of VA Piedmont this evening into the
overnight hours. PWATS per the 12z IAD sounding remain around
0.53 inches which is almost a 0.25 inch from where were on the
00z IAD sounding yesterday at 0.78 inches. Similar values can be
found on the 12z RNK sounding from earlier this morning
although a bit more moisture is noted in the mid to upper levels
of the atmosphere since the influence of the blocking high to
the north is farther away.

With all that said, moisture will continue to build across the
region this afternoon and evening especially in areas along and
south of I-66/US-50. These locations could see a few spotty showers
or areas of patchy drizzle/mist later this evening into the front
half of the overnight period. It`s really not until Tuesday morning
into Tuesday afternoon when more widespread rain chances move into
the region. Most of us will see a continuation of BKN-OVC skies this
afternoon and evening with perhaps a little drizzle/spotty shower
activity making it as far north as central Virginia. Areas of
drizzle are likely north of I-66/US-50 late tonight into Tuesday
morning with light to moderate showers pushing into central VA and
the Shenandaoh Valley. PWATS will likely increase into the 1.0-1.5"
range this evening before hopping up into 1.25-1.75" late tonight
into Tuesday. No flooding is expected given antecedent drought
concerns. Rain amounts through Tuesday will range between a tenth to
a half an inch areawide. Heaviest totals of a half to one inch can
be found across the central Blue Ridge and Shenandoah Valley
due in part to upslope enhancement.

Outside of the rain will be the wind. Gusts up to 30 mph are
possible along the higher ridges of the WV/VA Highlands and
central Blue Ridge. Elsewhere gusts of 15 to 20 mph are possible
especially in areas along the waters.

Little to no heating is expected today with minimal breaks of
sunshine. Highs today will reach into the mid to upper 70s east of
the Blue Ridge with upper 60s and low 70s further west. Lows tonight
in the low to mid 60s with a few low 50s in the western mountains.
Slightly cooler conditions are expected Tuesday with highs in the
mid to upper 60s and low 70s west of the Blue Ridge and mid 70s
further east.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
On and off rain chances look to continue through midweek as the
remnants of Potential Tropical Cyclone Eight slowly move north
through the Carolinas into the central Appalachians region. 12z
model guidance continues to shift the system further south and west
of the region Tuesday into Wednesday with uncertainty remaining in
regards to the placement of the low along the coast Thursday into
late week. This is due largely in part to a lack of a steering
mechanism aloft, blocking high pressure to the north, and lack of a
front at the surface. Most of the 12z modeling has the remnants of
PTC Eight basically spinning over the Carolinas into the central
Appalachians before meandering back toward the coast Thursday.
The bulk of any substantial rainfall looks to fall Tuesday into
Wednesday. Flooding does not appear to be a concern given the
antecedent drought concerns. With the track of the system
further south rainfall amounts have come down substantially
over the 24-36 hours. Most locations will see a 0.25" to 0.75"
of rain with 1" to 2" rain totals across the central VA Piedmont
and Shenandoah Valley. Some upslope enhancement is possible on
the eastern facing slopes of the central Blue Ridge where
localized 2" rain totals are possible. Some instability and bulk
shear around 25 knots associated with the system as it pivots
into and through the Carolinas could lead to a few spotty
thunderstorms Wednesday afternoon, though confidence is very
low.

With added cloud cover and increased rain chances expect
temperatures to struggle. Lows Tuesday night will fall into the
upper 50s and low to mid 60s with highs Wednesday in the upper 60s
and low to mid 70s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
A broad upper trough remains in the vicinity of the Mid-Atlantic and
Carolinas through the end of the work week. Eventually heights start
to build over the Great Lakes which pushes this negative height
anomaly farther south into the weekend. At the same time, a large
positively-tilted trough works its way across far eastern Canada
before departing into the Atlantic. While the core of height falls
remains well to the north, there is enough southward push to help
draw a backdoor cold front through the local area. Based on the
latest guidance, this frontal system slips through the region late
Friday. In the wake, high pressure returns and settles over the
entire Eastern Seaboard over the weekend. By early next week, one
notable feature to pay attention to is an inverted trough arcing
along the Carolina to Delmarva coast. This could re-introduce some
shower chances by Monday.

In terms of sensible weather, the presence of the upper low will
maintain scattered showers over the area on Thursday and Friday.
Unlike earlier in the week, there should be some breaks in the
clouds at times. Daily high temperatures stay fairly close to mid-
September normals, generally in the upper 70s to perhaps low 80s.
With winds eventually shifting to northerly, overnight lows are able
to cool back down into the mid 50s to low 60s. The pattern turns
drier over the weekend given the mentioned shift to high pressure.
Toward the conclusion of the weekend, highs drop back into the low
70s with 60s across the mountains. Winds will mainly be out of the
northeast with afternoon gusts to around 15 to 20 mph. These winds
could be slightly stronger depending on how tight the gradient is
with high pressure over New England and low pressure off the
Carolina coast.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
VFR to high end MVFR conditions are expected to continue through
this evening despite the remnants of Potential Tropical Cyclone
Eight pushing inland across the coastal Carolinas. A spotty shower
cannot be ruled out south of KCHO/KRIC although confidence is
low. MVFR to IFR cugs will likely return tonight as PTC Eight
pushes further into the Carolinas Drizzle and rain shower
activity will move into terminals south of the corridor late
tonight before spreading north Tuesday morning into Tuesday
afternoon. IFR ceilings are likely during this time with the
bulk of the rain falling late Tuesday morning into Tuesday
night. Rain showers will likely continue on and off through
Wednesday as low pressure meanders nearby. Winds will remain
E/NE 5-15 kts through Wednesday. Gusts of 15-25 kts are possible
each afternoon and evening especially at terminals close to the
waters and along the ridges. With the residual low pressure
nearby, expect periods of sub-VFR conditions, particularly on
Wednesday.

Underneath a persistent upper low, scattered showers may fire up
across the area on Thursday into Friday. However, there should be
plenty of dry time during the period. Clouds should be abundant
which may afford periods of sub-VFR conditions. Winds will generally
be north to northwesterly through Friday before shifting to
northeasterly on Saturday as a backdoor front exits to the
south.

&&

.MARINE...
SCA conditions will continue to increase this evening into the
overnight hours especially over the open waters of the bay/tidal
Potomac/ This is in association with a tightened pressure gradient
from blocking high pressure to the north and Potential Tropical
Cyclone Eight moving inland across the coastal Carolinas. At
this time, the risk of gale force winds appears low. As a
weakening area of low pressure tracks through the area, winds
will be out of the east on Wednesday while remaining at SCA
levels.

Expect mainly northerly winds through Friday with wind gusts staying
below Small Craft Advisory levels. A backdoor cold front pushes
through late Friday into Saturday morning. in the wake, an increase
in northeasterly winds may lead to 20 to 25 knot gusts on Saturday.


&&

.TIDES/COASTAL FLOODING...
Onshore flow strengthens through Tuesday morning with minor
coastal flooding becoming increasingly likely. However, surge
guidance has been trending downward, perhaps due to the low
remaining farther south and winds a touch weaker and more from a
northeasterly direction. Advisories remain in effect but may
need adjustments. Moderate flooding is much less likely now.
However, between the full moon and continued onshore flow, tide
levels will likely remain elevated and near minor flood
thresholds much of the week.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Advisory until 10 PM EDT Tuesday for DCZ001.
MD...Small Craft Advisory until 6 PM EDT Tuesday for MDZ008.
     Coastal Flood Advisory from 2 AM to 10 PM EDT Tuesday for
     MDZ014.
     Coastal Flood Advisory from midnight tonight to 6 PM EDT
     Tuesday for MDZ016-018.
VA...Coastal Flood Advisory from midnight tonight to 6 PM EDT
     Tuesday for VAZ057.
WV...None.
MARINE...Small Craft Advisory until 6 PM EDT Tuesday for ANZ530>543.

&&

$$

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