-- Discussion containing changed information from previous version are highlighted. --
828
FXUS62 KRAH 111850
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
247 PM 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 /MONDAY THROUGH MONDAY NIGHT/...
As of 120 PM Saturday...

A shortwave trough presently located near the Four Corners region is
forecast in most of the guidance to reach central/eastern MO by Tue
morning. Before that happens, we will see shortwave ridging most of
Mon. Some subtle waves of energy will stream in during the day but
would only lead to some increased mid/high clouds. Warm advection in
return southerly flow from a high shifting offshore should allow
highs rise near or a few degrees above normal in the upper 70s to
low 80s. As the aforementioned trough shifts into the MS Valley
overnight into Tue, low-level WAA and moisture transport will
increase from the southwest as a warm front lifts north into the SE
US. Precipitable water will increase some 150-percent of normal to
1.4-1.5 inches as isentropic ascent increases. Most guidance holds
off on showers toward the late-evening and overnight period,
spreading across the west/southern Piedmont earliest. Have kept high
chance to likely showers overnight into Tue morning as a result.
Showers may not reach the Coastal Plain until sunrise Tue. Lows are
forecast in the upper 50s to low 60s.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
As of 247 PM Saturday...

Tuesday/Wednesday: There is good consensus amongst models supporting
an upper trough lifting through the TN Valley and into the southeast
Tuesday into Wednesday.  This feature will support increasing swly
flow aloft and deep moisture advection into the southeast with PWAT
rising 150 to 175 % of normal.

At the sfc, a series of lows are forecast to develop: one over the
IN/IL/TN/AK vicinity, and then perhaps another one somewhere over
the Carolinas. There is some uncertainty wrt to the latter low and
where it develops/evolves with varying solutions. However, in
general, these features, along with upper support associated with
the trough should combine to produce a series of wet day for central
NC Tuesday and Wednesday.

Guidance suggests some instability will likely develop Tuesday
afternoon, but the better combination of shear/instability appears
to mostly be to our south at this point. However, if the low
traverses a bit more west through our Piedmont, would not be
surprised if locations south and east of Raleigh tap into a bit
better instability/shear which could promote the potential for some
stronger storms. However, there`s a bit too much uncertainty this
far out and thus we`ll continue to monitor.

Additional showers and a few storms will remain possible on
Wednesday as a cold front moves into the area with highest chances
in the afternoon/early evening. Ensemble guidance currently
maintains a bit better shear along the coast on Wednesday, but again
would not be surprised if some of this better shear trickles into
our far southeast zones Wednesday afternoon.

Temperatures on Tuesday will largely depend on where the southeast
low tracks, but for now leaned on a bit warmer guidance with low to
mid 70s for highs. Temps should rise a bit more on Wednesday,
reaching the upper 70s/lower 80s.

Thursday through Saturday: Ensemble guidance is pretty consistent in
moving the upper trough and associated anomalous moisture offshore
by 12Z Thursday (although the deterministic EURO lags behind an
upper low over the Chesapeake through late Thursday). Brief upper
ridging follows, which should promote dry conditions Thursday. Temps
on Thursday will remain warm in the upper 70s/lower 80s.

The ridge quickly breaks down as another upper trough lifts into the
TN valley Friday into Saturday. Increasing moisture transport and
upper forcing will promote additional showers/thunderstorm chances
Friday into the weekend. Temperatures in this time range will remain
in the upper 70s/lower 80s.
-- End Changed Discussion --

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 1245 PM Saturday...

Dry weather and VFR conditions will dominate across central NC
through Sun, although passage of a strong upper level disturbance
through the Mid Atlantic region this evening into the early
overnight hours will bring a band of showers across the area from NW
to SE, mainly affecting the northern terminals. But cloud bases are
expected to remain largely VFR even within showers, with a low
chance of brief MVFR cigs/vsbys. Surface winds may briefly be gusty
and erratic in and near these showers. Any clouds will clear out
late tonight, leaving fair skies through Sun.

Looking beyond 18z Sun, VFR conditions and dry weather are expected
through at least Mon. Rain and isolated storms, with a high chance
of sub-VFR conditions and increasing winds aloft, are expected to
overspread the area starting Mon night, with sub-VFR conditions
lasting through Wed morning, although shower chances will persist
through Wed. Dry VFR conditions should return for Thu. -GIH

&&

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

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...Hartfield/Danco
SHORT TERM...Kren
LONG TERM...Luchetti
AVIATION...Hartfield