333
FXUS61 KLWX 271901
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
301 PM EDT Fri Sep 27 2024

.SYNOPSIS...
Tropical Storm Helene will continue to weaken and become
absorbed by an upper level low pressure system over the
Tennessee Valley through tonight and remain in that general
region through much of the weekend. Widespread rain will
continue across our region, especially across central Virginia.
Rain showers could linger through most of the weekend into early
next week with the upper level low propagating eastward.

&&

.NEAR TERM /THROUGH TONIGHT/...
The remnants of Helene are currently over southeast Kentucky. It
is in this general area and south into Tennessee where the
remnants will become absorbed by an upper level low tonight into
the weekend.

While light rain pushes north across Maryland and along the
Mason-Dixon region, a heavier rain along with a few
thunderstorms are noted over the central Shenandoah Valley and
the Virginia Piedmont. A separate shield of moderate rain is
moving northeast into Southeast Virginia from eastern North
Carolina.

It is the activity that is spiraling across the Virginia
Piedmont and Shenandoah Valley that is of a more pressing
concern with the possibility of tornadoes and flooding rainfall
through the remainder of the afternoon into this evening.

Temperatures have topped out in the lower to middle 70s with
dewpoint temperatures very much in the 70s as well given the
amount of moisture in a tropical airmass.

The following hazard still remain a threat to our area:

- Heavy rain threat...PWatt values of 1.5 to 2.2 inches across
  the area have aided in the heavier rain bands that are
  spiraling northward this afternoon. Going into this evening,
  clusters and/or bands of rain will become more scattered in
  nature. The higher elevations have the greater possibility of
  encountering Flash Flooding (especially where recent rains
  have exceeded 2-4"). Another 2-4" look possible across the
  higher terrain of the watch area this evening. Flood Watch
  remains in effect.

- Strong Winds...As the remnants of Helene move north, the winds
  will increase out of the easterly direction especially across
  the Blue Ridge and Alleghenies. A Wind Advisory remains in
  effect through early this evening. The saturated ground will
  likely allow for trees to fall as well with gusty winds.
  Across the lower elevations and metros, gusts to 20-30 kts are
  possible.

- Severe Potential (including tornadoes)...Heavy showers and a
  few thunderstorms are showing signs of having rotation in a
  tornadic sense. No tornado warnings as of now; however, we are
  getting a few reports of trees down near the heavier rotating
  showers/storms. The best overlap in instability/shear/SRH is
  across central VA. SPC has a Marginal Risk (Level 1 out of 5)
  that is tornado driven (2%). The further north into the
  forecast area, there is less instability.

The region will stay in a tropical airmass tonight with lows
only falling into the upper 60s in the metros with upper 50s
west of the Blue Ridge. Dew points will be near the air temp, so
fog formation appears rather likely. Rain chances look to be
low overnight with PWs actually decreasing heading into
Saturday.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
A break from the tropical rainfall seems more probable during
the day Saturday as drier air works its way across the region.
Furthur north toward the Mason-Dixon region, showers will be
popping up during the midday and afternoon hours. Highs in the
70s.

The remnants of Helene, having been absorbed by an upper level
low, will move across the region from the west during the day
Sunday into Sunday evening. This extra lift could spawn more
shower activity along with a few thunderstorms. Highs in the
70s.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
Large upper level low over the lower OH River Valley will gradually
weaken through time opening into a trof by Tue. Expect showers and
possible thunderstorms Mon-Tue. A second northern stream trough will
be crossing the area Wed pushing a strong cold front through the
area Wed morning or Wed afternoon depending on model of choice.
Autumn weather will follow in the wake of this front with high
temperatures failing reaching 70F and lows in the 40s. Dry weather
is expected during the second half of next week.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Rain showers will be spreading across the terminals from south
to north later this afternoon and this evening as the remnants
of Helene rotate from southeast to northwest across the southern
Appalachians and Tennessee Valley. While VIS are in the IFR to
MVFR threshhold, CIGs remain IFR and could lower to LIFR this
evening into tonight. Fog could play an aspect for the LIFR
conditions moreso overnight.

Conditions likely remain sub-VFR into Saturday due to a stalled
frontal boundary over the region.

Shower and possible thunderstorm chances continue Sunday as the
remnants of Helene and an upper level low make their way east.
Additionally, persistent E/NE flow is expected with surface high
pressure to the north, so sub-VFR conditions remain possible at
times, especially during any shower activity near the
terminals.

Possible flight restrictions Mon-Tue in showers.

&&

.MARINE...
SCAs remain in effect for all waters through this evening with
easterly winds up to 25 kts expected. Winds decrease Saturday
to 5-10 kts, then turn southerly in the afternoon.

By Sunday, the remnants of Helene and an upper level low will
swing through the are into Monday. This will result in elevated
winds over the waters out of the east with SCAs possible.

SCA conditions possible Monday night into Tue, then likely late Tue
night through the end of next week.

&&

.TIDES/COASTAL FLOODING...
As the remnants of Helene get absorbed into an upper level low
late this afternoon into tonight, high pressure will remain to
the north and east. The interaction between the two will allow
for surface winds to remain easterly and push water into the
western sides of the Potomac and Chesapeake. Currently, there
are Coastal Flood Advisories for D.C., Straits Point, and
Annapolis. As we drop down to low tide in the tide cycle at
Annapolis, the rebound could be a Coastal Flooding Advisory on
the next go around of the high tide cycle. Currently there is a
Coastal Flood Watch for Annapolis. Multiple locations could
encounter Coastal Flooding throughout the weekend as we are
dealing with a persistent favorable flow.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...Coastal Flood Watch from 2 AM EDT Saturday through Saturday
     morning for DCZ001.
MD...Small Craft Advisory until 3 AM EDT Saturday for MDZ008.
     Wind Advisory until 11 PM EDT this evening for MDZ001-501.
     Coastal Flood Advisory until 8 PM EDT this evening for MDZ014.
     Coastal Flood Watch from 8 PM EDT this evening through
     Saturday morning for MDZ014.
     Coastal Flood Advisory until 3 AM EDT Saturday for MDZ017.
VA...Wind Advisory until 11 PM EDT this evening for VAZ025-503-504-
     507-508.
     Flood Watch until 8 PM EDT this evening for VAZ025-026-036>040-
     503-504-507-508.
     Coastal Flood Advisory until 7 PM EDT this evening for VAZ054.
WV...Wind Advisory until 11 PM EDT this evening for WVZ501-503-505-
     506.
     Flood Watch until 8 PM EDT this evening for WVZ505-506.
MARINE...Small Craft Advisory until 3 AM EDT Saturday for ANZ530>532-
     538>540.
     Small Craft Advisory until 3 AM EDT Saturday for ANZ533>537-
     541>543.

&&

$$

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