186
FXUS62 KRAH 120709
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
305 AM EDT Sun May 12 2024

.SYNOPSIS...
High pressure will build across the southeastern United States today
before moving offshore Monday. Expect an unsettled weather pattern
starting Tuesday and continuing through the rest of the week.

&&

.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 305 AM Sunday...

Surface low pressure should be over southern Illinois at the
beginning of the extended forecast and precipitation will extend
well to the east, with rain increasing in coverage through the day.
Models begin to diverge with the surface feature Tuesday night, with
the 00Z GFS showing two low centers by Wednesday morning (over KY/TN
and DE) while the 00Z ECMWF has one broad center over OH. Regardless
of which scenario plays out, think that a bit of a dry slot will
develop over the Carolinas Tuesday night and there should be a bit
of a lull in shower coverage. The last two runs of the ECMWF are
suggesting that the upper trough helping to support the surface low
could close off into an upper low over the mid-Atlantic on
Wednesday, helping to intensify the surface low as it passes to the
north. While some rain could linger Wednesday evening, conditions
should then dry out as high pressure settles over Quebec and a ridge
extends along the eastern seaboard on Thursday. Meanwhile, the next
system will be developing in the Plains, and with models indicating
it may move east a little more slowly, have removed all pops from
the forecast Thursday night. Had enough confidence to add likely
pops across western counties Friday, but the models diverge too much
after this to go with anything higher than chance pops through
Saturday. Tuesday remains the coolest day in the forecast with
widespread highs in the 70s and possibly even upper 60s near the
Virginia border, otherwise temperatures should be near climatology,
around 80 and 60 degrees.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
As of 150 AM Sunday...

VFR conditions will prevail through the next 24 hours. A band of
cloud ceilings around 7-10 kft and weakening sprinkles/showers is
currently moving south across the southern Piedmont and Sandhills
(including FAY). The precipitation will be south of FAY in the next
half hour or so and completely out of central NC or dissipated
within the next hour or two at most. They are so light that
visibilities will remain VFR wherever it does rain. The band of
clouds will push SE of the entire area by 09z, with clear skies
behind it. More scattered cumulus are possible during the day today,
but they will stay above the VFR threshold. NW winds will pick up by
mid morning, gusting up to 15-20 kts, which will last into the
afternoon before diminishing in the evening.

Looking beyond 06z 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...Green
NEAR TERM...MWS/Hartfield
SHORT TERM...Hartfield/Kren
LONG TERM...Green
AVIATION...Danco/Hartfield