389
FXUS62 KRAH 120129
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
929 PM EDT Sat May 11 2024

.SYNOPSIS...
A surface trough and upper level disturbance will move across the
Mid Atlantic region tonight. High pressure will build across the
Southeast and Mid Atlantic region on Sunday, then shift off the
Southeast coast Monday.

&&

.NEAR TERM /TONIGHT/...
As of 925 PM Saturday...

The gridded evening forecast updates were sent primarily with
adjustments to hourly temperatures, which will be slower to decrease
than previously forecast owing to the 60-100 mile band of altocumulus
and embedded, scattered showers now moving across the nrn Piedmont
and nrn Coastal Plain.


.PREV DISCUSSION... /ISSUED 330 PM EDT Sat May 11 2024/

Through tonight: Still expect a brief window of isolated to
scattered showers this evening, mainly across the Piedmont and N
Coastal Plain. The potent mid-upper low now over S Lk Huron has a
trailing shortwave trough don through E OH into KY. The upper jet
streak diving into the trough base from IN continues to generate
strong forcing for ascent to the east of the low, contributing to a
band of showers with embedded isolated stronger convection from SE
Ontario through PA/WV. Sufficient recovery has occurred west of this
band within 1000 J/kg SBCAPE amidst 7+ C/km mid level lapse rates
and 8-9 C/km low level lapse rates to contribute to a secondary band
of strong to severe convection in E OH. We shouldn`t see these kinds
of steep lapse rates by the time the shortwave trough shifts E into
and through the Mid Atlantic region, as nocturnal stabilization will
be starting by then with CINH developing, but we are likely to see
the tail end of the shower band, now over WV into E KY swinging
through our area this evening, just ahead of the mid level trough
axis. The scattered to occasionally broken high-base convective cu
now over central NC (esp E half) will dissipate a bit toward sunset,
then clouds will quickly increase anew from the NW as the pre-trough
moisture plume spreads in. The best chance of showers should be 22z-
03z in the NW trending to 01z-06z further SE, although our far SE
sections are likely to stay dry as the trough dampens upon approach
with our SE farthest removed from the forcing for ascent and
potential weak elevated CAPE. Any one location should see little
more than a few hundredths falling over an hour or less, and we
could see a few gusts ahead of and with these showers. Skies will
then clear out NW-SE behind the showers. Expect lows in the upper
40s to mid 50s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 120 PM Saturday...

Sunday/Sunday night: With overall very low PW moving in as surface
high pressure builds overhead, quiet and dry conditions are likely,
with little more than a period of scattered to broken high-base flat
cu in the afternoon and increasing high clouds from the NW late Sun
night within predominant NW steering flow. Low level thicknesses
will have recovered a bit from this morning but will still be 15 to
perhaps 20 m below normal, and this balanced with decent insolation
favors highs in the mid 70s to around 80, near to slightly below
normal. Lows in the mid 40s to mid 50s Sun night with good
radiational cooling conditions expected.

Monday/Monday night: 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/...
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.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
As of 800 PM Saturday...

A line of light showers stretching from Danville (KDAN) to Boone
(KTNB) has shown brief periods of increases WNW gusts of 10-20 kts
and sporadic reduced visibility to MVFR as it has traversed upstream
observations. This line currently moving through the Triad terminals
and will continue towards RDU by 02z. A weakening trend is expected
as it continues towards RWI (03z) and FAY (03/04z) with light
amounts keeping visibility VFR. Clearing from NW to SE is expected
through tonight. NWP guidance has shown hints of very shallow fog
possible where 0.05 or greater rain is measured and calm surface
conditions develop, but should stay outside of any TAF sites if it
were to develop. Westerly winds will increase after 14z to 15-20 kts
gusts with FEW/SCT VFR afternoon cu development.

Looking beyond 00z Mon, 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.

&&

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

&&

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