424
FXUS61 KAKQ 170532
AFDAKQ

AREA FORECAST DISCUSSION
National Weather Service Wakefield VA
132 AM EDT Sat Aug 17 2024

.SYNOPSIS...
Scattered showers and storms are possible through Monday as an upper
level trough moves into the area. Cooler and drier conditions are
expected from Tuesday through the rest of next week as high pressure
remains to the north of the local area under a trough aloft.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
As of 945 pm EDT Friday...

No major changes to the going forecast. Showers over the
Piedmont and Blue Ridge have all but dissipated as they moved
east and into the drier airmass. However, dew points are
starting to creep up across the area this evening with most
areas in the mid-upper 60s. Latest HRRR is not terribly excited
about prospects of precip overnight as the short wave currently
over the Ohio Valley moves east. Still, given the increased dew
points and the isolated showers already developing over the
mountains, I do not want to decrease PoPs considerably.
However, I have delayed the highest PoPs into the I-95 corridor
until late tonight.

As of 355 PM EDT Friday...

Key Messages:

- Scattered showers and perhaps an isolated storm or two are possible
  late tonight into early Saturday morning.

Afternoon sfc analysis depicts high pressure off the East Coast.
Aloft, a weak ridge moves E across the Great Lakes with a trough off
the East Coast moving E. Temps as of 320 PM range from the mid-upper
80s with highs in the upper 80s for most (potentially around 90F at
Richmond). Lows tonight in the upper 60s to around 70F expected for
most with mid-upper 60s possible across SE VA/NE NC and the Eastern
Shore (where less cloud cover is expected). Dry this afternoon.
However, a shortwave moves E tonight into Sat morning with scattered
showers (and perhaps an isolated storm or two) possible overnight.
Greatest confidence is along the I-95 corridor (40% PoPs). Given the
increase in cloud cover, lows tonight will likely be coolest across
the SE (where less cloud cover is expected) and warmest in the
Piedmont with lows in the upper 60s (mid 60s across the SE) to lower
70s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH MONDAY NIGHT/...
As of 355 PM EDT Friday...

Key Messages:

-Seasonally warm and humid with daily chances for scattered
 showers and storms.

-Storms may be strong to severe Saturday and Sunday with a
 better chance for more widespread convection on Sunday.

Aloft, an upper level low slowly moves from the Great Lakes to the
East Coast Sat-Mon, gradually losing it`s circulation and becoming a
trough. Meanwhile, a series of shortwaves rounds the base of
trough/upper level low creating daily chances for showers/storms. At
the surface, a cold front slowly approaches from the Ohio Valley Sat-
Sun before crossing the local area Sun night into Mon.

Ahead of the trough/cold front, humidity increases with dew points
in the low-mid 70s Sat and Sun. Dew points still remain elevated Mon
(upper 60s to around 70F), particularly across E portions of the FA.
Temps are expected to rise into the mid-upper 80s each day with heat
indices in the low-mid 90s (highest Sun with 90-97F heat indices).
CAMs show uncertainty with respect to timing of convection Sat with
the HRRR showing multiple rounds of convection through the day and
the NAM 3km showing the late afternoon lee trough convection
dissipating before making it to the I-95 corridor. Have therefore
gone with a blended approach, anticipating the potential for at
least two main rounds of convection (the morning round and the late
afternoon/evening lee trough round). As such, have chance PoPs
through the day (30-50%) with the highest confidence late Sat
afternoon into Sat evening with the lee trough convection moving E
in the form of a line. Synoptically, it makes sense that any
convection forming off the lee trough should become organized into
linear segments and move E, likely sustaining to at least the
I-95 corridor given HREF mean CAPE around 1000 J/kg (max values
are around 2000 J/kg). Expect storms to weaken as they approach
the coast given lessening CAPE values. A few additional isolated
showers/storms are possible overnight Sat night, but confidence
is low in coverage. Additionally, given sufficient CAPE and
0-6km shear of 25-30 kt, some storms may be strong to severe
with strong to damaging winds the primary threat. SPC has areas
along and W of I-95 in a marginal risk (level 1/5) for severe
weather.

The upper level trough moves over the area Sun providing synoptic
forcing sufficient for more widespread scattered showers and storms
during the afternoon and evening. In addition to the forcing aloft,
a cold front moves E towards the local area late Sun afternoon into
Sun night. As such, have increased PoPs to likely (60%) Sun
afternoon with PoPs quickly tapering off Sun night as the cold
front slowly moves through. Similar to Sat, 0-6km shear of 25-30
kt (locally 35 kt) is expected with higher CAPE (MLCAPE of
1500-2000 J/kg+). Given higher instability, greater forcing, and
decent shear (for mid August), expect the potential for
scattered strong to severe storms with damaging winds the
primary threat. SPC has a marginal risk (level 1/5) for the
entire FA and clips portions of NE NC in a slight (level 2/5)
risk. Would not be surprised if the slight gets expanded NE in
the future updates. While storms should be moving given 25-30
kt+ of deep layer shear, cannot rule out localized flooding,
particularly if storms train over the same areas. As such, WPC
has areas N of I-64 in a marginal risk for excessive rainfall
Sat and the entire area under a marginal risk on Sun.

The upper level trough remains over the area on Mon with a final
shortwave pushing through Mon afternoon into Mon evening.
Instability (MLCAPE of 500-1000 J/kg) will be lower but still
sufficient for widespread scattered showers and perhaps isolated
storms. However, given WSW sfc winds behind the cold front, severe
weather is not anticipated at this time. That being said, cannot
rule out some gusty winds (30-45 mph) with any showers given
steepening mid level lapse rates (~6.5C). Any showers taper off
quickly by Mon evening. Lows are expected to range from around 70F
Sat night, mid-upper 60s W to lower 70s E Sun night, and lower 60s W
to upper 60s E Mon night.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 405 PM EDT Friday...

Key Messages:

-Cooler, drier weather is expected next week.

A seasonally strong upper level trough remains over the East Coast
through next week with high pressure centered to the N of the local
area. This will allow for a prolonged period of cool and dry weather
with below normal temps expected from Tue-Fri. Highs range from
around 80F Tue-Thu and low-mid 80s Fri with lows in the mid-upper
50s W to the mid-upper 60s along the coast Tue and Wed nights, upper
50s to around 60F W to the mid-upper 60s E Thu night, and lower 60s
W to upper 60s to around 70F E Fri night. Wed and Thu mornings look
to be very pleasant with widespread temps in the upper 50s possible
inland (away from urban areas). Additionally, dew points drop behind
the cold front on Tue into the upper 50s to lower 60s and remain in
the mid 50s to lower 60s through late week. Mainly dry weather is
expected through the week apart from a low chance for an isolated
shower or storm across the N Tue afternoon.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
As of 130 AM Saturday...

A weak disturbance moves through the area tonight into Saturday
morning. Showers may reach RIC overnight, but there is simply
not enough confidence to include in the terminal forecast beyond
VCSH. More likely, MFVR cigs will develop early Saturday
morning at RIC as low level moisture increases. However,
guidance suggests the reduced CIGS will be short lived as they
raise to VFR by 18z. Showers/storms are possible tomorrow
afternoon especially at RIC from the lee side trough. Southeast
winds of 5 to 10 kt tonight becoming southerly on Saturday.

Outlook: A slow moving cold front will approach from the west
Sunday into Monday with chances for scattered aftn/evening
showers/storms each day, especially Sunday. Storms may be strong
to severe on Sunday with gusty winds the primary threat.

&&

.MARINE...
As of 355 PM EDT Friday...

Key Messages:

- Small Craft Advisories are in effect for all coastal waters starting
  tonight north of Cape Charles, with the remaining coastal
  waters and the Mouth of the Bay starting on Saturday as swells
  from Hurricane Ernesto reach the coast.

- SCAs remain a possibility in the Bay Sat aftn/Sat night for southerly
  wind gusts of 20 - 25 kt with the best chance N of New Pt
  Comfort.

The area of high pressure that has been in place for the last several
days is gradually weakening and sliding off the New England Coast
this afternoon.  Meanwhile, a storm system over the Great Lakes is
making slow progress toward the Mid-Atlantic States today and will
take several days to move through the area, before departing early
next week.  Right now Winds are generally from S at 5-10 kt but are
stating to increasing from the S - SE. As the area of high pressure
slides offshore and the low pressure system approaches from the
midwest, expect to see enough tightening of the pressure gradient
for S winds 10-15kt with gusts to 20 kt tonight, and winds a little
higher Sat aftn/Sat night. SCA conditions from wind are possible in
the Ches Bay north of New Pt Comfort. Meanwhile, Hurricane Ernesto,
currently about 180 miles SW of Bermuda, is forecast to lift NNE,
over Bermuda by early Sat before heading into the North Central
Atlantic. Impacts locally will be restricted to increasing swell and
the threat for deadly rip currents. SCA flags start for the Atlantic
waters north of Cape Charles Light at 02z/10pm tonight, with the
remaining Atlantic waters and the mouth of the Bay starting SCAs by
Sat aftn. Seas Saturday will average 5-7 ft N of Cape Charles, and 4-
5 ft to the south, while then averaging 5-6 ft by late Sat night
through Sunday. Waves near the mouth of the bay will increase as
well, generally 2-3 ft on Saturday with 3-5 ft possible late Sat
night into Sunday before things start to calm down Monday (though
will likely have seas offshore linger at 4-5 ft possibly into early
Tuesday). The models are in decent agreement that another eastern
CONUS upper trough develops next week, allowing a cold front to move
through the local waters Mon night/Tuesday with winds shifting to
the N/NW. Current models do not show more than 10-15kt of wind Mon
night/Tue, but as the details become more precise, would expect
winds to be stronger given good mixing as rather cool air (by August
standards) moves over the warm waters.

&&

.TIDES/COASTAL FLOODING...
As of 420 AM EDT Friday...

Key Message:

-  A Moderate Risk of Rip Currents today, with a High Rip Risk
   likely for both Saturday and Sunday as long period swell from
   distant Hurricane Ernesto affects the region.

The latest 16/00Z run of the NWPS supports high rip risk for
all Atlantic coastal zones for the weekend given seas of 4-6 ft
with a dominant period of 13-15 seconds. Today begins low with
seas only 1-2 ft, but with the building seas to ~3 ft or 3-4 ft
this aftn, and an increase in the wave period, will have a
Moderate rip risk in effect today. Some minor tidal flooding
will be possible along the Bayside of the MD eastern shore by
Sun/Mon as the persistent long period swell may help trap water
in the Bay for several tide cycles (the southerly wind direction
favors transporting any trapped water northward).

&&

.AKQ WATCHES/WARNINGS/ADVISORIES...
MD...None.
NC...None.
VA...None.
MARINE...Small Craft Advisory from 2 PM this afternoon to 6 AM EDT
     Monday for ANZ634.
     Small Craft Advisory until 6 AM EDT Monday for ANZ650-652-654.
     Small Craft Advisory from noon today to 6 AM EDT Monday for
     ANZ656-658.

&&

$$

SYNOPSIS...RMM
NEAR TERM...RMM/MRD
SHORT TERM...RMM
LONG TERM...RMM
AVIATION...AM/MRD
MARINE...ESS/LKB
TIDES/COASTAL FLOODING...