385
FXUS62 KRAH 111449
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1045 AM EDT Sat May 11 2024

.SYNOPSIS...
A surface trough and upper level disturbance will move across the
Mid Atlantic region this evening. High pressure will build across
the Southeast and Mid Atlantic region on Sunday, then shift off the
Southeast coast Monday. A storm system will move in from the west
Monday night through Wednesday, bringing periods of rainy weather.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1045 AM Saturday...

Minimal changes this morning, mainly spatial and timing tweaks to
evening shower chances over N into central sections. A strong
shortwave trough over lower MI this morning and a potent upper jet
streak diving into the trough base from the Midwest is generating
strong forcing for ascent from SE Ontario through the E Ohio Valley,
contributing to a band of showers with embedded fairly robust
convection from Lk Erie through E OH. As this shortwave trough and
its preceding moisture plume dive SE through the Mid Atlantic
through this evening, we`ll see our current fair skies (save for
some lingering stratocu in the Coastal Plain) yield to increasing
clouds in the NW late, with isolated to scattered showers swinging
through areas along and N of Hwy 64, leading to little more than a
few hundredths falling over an hour or less in any given location.
Until then, we`re already seeing cu popping up to our NW and stable
cloud streets in the Coastal Plain, so have nudged afternoon sky
cover up a bit. Expect highs in the low-mid 70s. -GIH

Earlier discussion from 345 AM: Surface observations depict a region
of higher low-level moisture associated with a weak inverted trough
over the Coastal Plain and far NE Piedmont, as the parent low is
centered east of the NC coast. Current dew points there are in the
mid-to-upper-50s. A deck of stratocumulus has moved south of our
southern Coastal Plain, with more areas of stratocumulus over
eastern VA that will move into the Coastal Plain through the
morning. However, any associated showers have dissipated. Northerly
winds were gusting as high as 25-35 mph at times earlier this
evening, especially over the Coastal Plain, but they have subsided
with many areas now reporting calm or very light winds.

Looking aloft, water vapor imagery shows a pair of shortwaves, one
just off the mid-Atlantic coast, while the other is over WI and the
upper peninsula of MI. During the day today, we will be under the
influence of dry WNW flow and height rises as the former shortwave
exits NE into the Atlantic, with just some scattered cumulus below
the subsident inversion at 700 mb. It will be a very pleasant
afternoon with highs only reaching the lower-to-mid-70s (around 5
degrees below normal) and dew points only in the 40s.

However, as the latter shortwave moves SE and reaches the northern
Mid-Atlantic by Saturday night/Sunday morning, we could experience
some weak mid-level height falls on Saturday evening. A surface
trough will also be passing through and there will be a period of
WAA around 850 mb. So a deck of clouds around 5-10 kft is likely to
move through from NW to SE in the evening, and CAMS suggest it could
be accompanied by a band of showers/sprinkles. However, the best
upper forcing will be well to our north and there will be very
little to no instability to speak of with CAPE values around 100
J/kg or less. So any showers should be light and brief, with total
amounts less than a tenth of an inch. The entire area will be mostly
clear after about 06z, which should be favorable for any additional
aurora viewing, and lows will again drop into the upper-40s to mid-
50s.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 400 AM Saturday...

Dry NW flow will prevail on Sunday between the departing mid/upper
trough over the Northeast US and ridging over the lower MS Valley.
At the surface, high pressure will move east from the TN Valley to
become centered over the mid-Atlantic on Monday morning. This
pattern will support sunny skies and another very pleasant day, as
dew points are again only in the 40s (some statistical guidance even
shows some upper-30s in the far NW Piedmont). NW winds could gust up
to 15-25 mph during the day with good mixing. High temperatures will
range from mid-70s to 80. Decent radiational cooling conditions will
help lows Sunday night drop to the mid-40s to lower-50s.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 315 AM Saturday...

Monday morning will find surface high pressure moving off the mid-
Atlantic states along with an upper level ridge moving over the
eastern United States. However, another upper level trough over the
central Plains will move east, helping to form a surface low over
southern Illinois by Tuesday morning. The bulk of the rain will fall
ahead of this low, and although Monday will remain dry, western
locations should have rain move in Monday night and the showers will
expand everywhere Tuesday. It`s too early to look at particular
rainfall amounts, but the heaviest rain is currently forecast for
Tuesday afternoon. Showers and thunderstorms will continue Tuesday
night into Wednesday as the surface low moves over Washington DC and
moves offshore New Jersey by Wednesday evening. This should bring a
lull in precipitation Wednesday night through Thursday night before
another system moves east from the Plains. Some model guidance wants
to go with likely to categorical pops on Friday, but am not willing
to go with pops that high on day 7 and will cap pops at high chance.
Average temperatures this time of year are generally around 80 and
60, and forecast temperatures are generally around these numbers,
although highs will be a little cooler on Tuesday with the
widespread rain.

&&

.AVIATION /11Z SATURDAY THROUGH WEDNESDAY/...
As of 650 AM Saturday...

Dry weather and VFR conditions will prevail across central NC
through this afternoon, with the one exception of some lingering
stratocumulus over the far NE Piedmont and Coastal Plain (including
RWI) which has resulted in periods of MVFR and even isolated IFR
ceilings. This will dissipate by mid morning. Then a deck of clouds
from about 6-10 kft will move across central NC from NW to SE this
evening, and it may be accompanied by a band of showers with the
best chance at the northern TAF sites. Confidence in any brief sub-
VFR visibilities with the showers is low, but it cannot be entirely
ruled out. Any precipitation will exit by 06z Sunday with clear
skies the rest of the night. Northerly winds this morning will
become more westerly/southwesterly by this afternoon and evening,
remaining less than 10 kts sustained and possibly gusting up to 15
kts at times during the day.

Outlook: Rain and IFR-MVFR restrictions, lowest over the Piedmont at
INT/GSO, will overspread cntl NC Tue morning, with a following
chances of showers/storms Tue afternoon through Wed.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...Hartfield/Danco
SHORT TERM...Danco
LONG TERM...Green
AVIATION...Danco/MWS