-- Discussion containing changed information from previous version are highlighted. --
217
FXUS62 KRAH 040650
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
250 AM EDT Sat May 4 2024

.SYNOPSIS...
A backdoor cold front will settle into north-central North Carolina
tonight, where it will stall through Saturday night, then weaken and
move northward into Virginia on Sunday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 835 PM Friday...

A backdoor cold front has moved into the extreme northeastern
portion of the forecast area - KIXA had a wind shift from southerly
at 6pm to easterly at 7pm. In addition, several sites across
southeastern Virginia and northeastern North Carolina have had a
shift to easterly wind with much cooler temperatures. Meanwhile, an
area of showers and thunderstorms is moving to the north out of
Person County, with an area of showers extending farther to the
south where a differential heating boundary developed earlier.

The chance for showers and thunderstorms should diminish through the
evening, then rise again overnight as the back door front moves
farther into the area. The location of the front and just how far
southwest it moves could have a significant impact on overnight
temperatures. The current forecast calls for temperatures in the
low 60s across the northeast to the mid 60s in the southwest. In
addition, an area of low stratus appears likely to move in behind
the front.
&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 230 PM Friday...

Aloft, the sub-tropical ridge will stall along the eastern seaboard
through Sat night. A southern stream disturbance will move into the
Southeast US on Sat, then lift newd through the area as a sheared
out northern stream s/w moves through the OH Valley/Great Lakes Sat
night. The sub-tropical ridge will shift offshore and breakdown
Sun/Sun night as the disturbances move through the mid-Atlantic and
Northeast US. Another southern stream s/w will develop over the
southern Plains on Sun, then move eastward into the lower/mid-MS
Valley Sun night. At the surface, as high pressure sits over the New
England coast, the backdoor cold front is expected to stall over
nrn/nern NC through Sat and into Sat night then lift northward late
Sat night/Sun. The high should move eastward over the Atlantic as a
low moves through the Great Lakes and into the Northeast Sun/Sun
night.

Precipitation/Convection: Still fairly high confidence/chances for
showers and possible storms Sat and Sun. Best threat for storms will
be across the Piedmont, mainly along and south of the surface
boundary, where surface-based CAPE will be maximized. Bulk shear
still appears weak, and PWATs are expected to range from 1.4 to 1.8
inches. Do not expect the entire day to be a wash-out by any means,
and Sat could start dry for most, but there will be a chance for
showers across all of central NC, with greatest coverage from Sat
eve through Sun aft. Highest chances NW, lowest SE. Given the high
PWATs and scattered, somewhat disorganized mode of convection,
isolated locations could receive locally heavy rainfall, with any
potential for minor flooding issues largely limited to urban areas.

Temperatures: A bit tricky on Sat, as there is some bust potential
north of the front. Widespread overcast skies should somewhat limit
heating as well. For now expect highs to range from the mid 70s
along the NC/VA border to mid 80s SE. Sat night temps should be
continued mild, mainly in the low to mid 60s. On Sun, with the
retreat of the front northward, areas across the north may be a few
degrees higher than Sat, but given the expected showers/storms
through the day, temps may otherwise be limited. Highs in the upper
70s north to low 80s south.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
As of 250 AM Saturday...

The extended forecast will feature a continued chance of unsettled
weather to start the week Mon, followed by somewhat drier and hot
temperatures by the middle of the week. A potent late-week
system/trough looks to increase storm chances again by week`s end.

On Monday, models continue to show a shortwave over the TN valley
tracking east across the region in the afternoon/evening, before
exiting along the coast by Tue morning. A surface Piedmont trough
will be in place and combined with 200-percent of normal PW`s should
favor another day of scattered to perhaps numerous showers and
storms, maximizing during peak heating. Instability is between 500-
1000 J/kg but shear is weak, so severe chances are not expected,
though slow-moving storms could bring heavy rain. Activity should
wane overnight with loss of heating and as the trough slides toward
the coast. Highs should hover in the low/mid 80s with higher rain
chances and cloud cover.

As the trough moves to our east Tue, weak ridging starts to build
in, although the CMC/GFS show a weak perturbation riding along the
ridge. With a lack of large-scale forcing, confidence on coverage of
storms, if any, is low, such that storm activity should be
isolated/scattered in nature and focused along differential heating
boundaries and/or the sea-breeze. Highs should warm to the low to
upper 80s.

A drier pattern still appears to be favored midweek Wed and part of
Thu as ridging and southwest flow builds back into the region. This
will also be when the airmass will warm quite a bit with a lee
trough setting up east of the Appalachians and low-level thicknesses
well above average and highs some 12-15 degrees above normal in the
upper 80s to low 90s. The NBM still indicates a 60-80 percent chance
of 90 or greater maxT values across portions of the Sandhills,
Triangle region, and Coastal Plain during this period. Heat index
value could reach the mid 90s over these areas, making for an early
taste of summer. While this period looks drier, most guidance shows
a developing trough over the upper MS valley Thu, with solutions
indicating a decent plume of moisture tied to a perturbation
advecting ahead of a cold front draped over the OH valley. This
would favor better chances of isolated/scattered storms Thu aftn/eve
with higher instability coupled to higher shear.

Although model solutions diverge by late in the week with a frontal
system location, there is broad consensus that chances of storms
appear to remain elevated to close out the week as the trough slides
closer to the TN/OH valley and Great Lakes region with
instability/shear still favorable over the Carolinas.
-- End Changed Discussion --

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
As of 220 AM Saturday...

A back-door cold front, noted by a E-NELY wind shift, will settle
south across the northern TAF sites over the next few hours before
stalling. Moisture pooling along the front should lead to the
development of IFR to MVFR ceilings at all TAF sites 08 to 12z.

Ceilings at KFAY, KRDU, and KRWI should gradually lift to VFR from
south to north through 17-18z, with scattered showers and storms
possible during the afternoon and evening, especially at KRDU.

At KGSO and KINT, ceilings could remain IFR to MVFR through the
afternoon and evening as intermittent showers and storms develop and
move through the area through much of the forecast period.

Showers will linger across the area tonight, with the re-development
of LIFR to MVFR conditions across the area, lowest at KINt and KGSO
where the deepest moisture resides. -CBL

Outlook: IFR-MVFR ceilings are likely to redevelop each night-
morning through Monday, as are scattered to locally numerous
showers/storms each afternoon-evening. -MWS

&&

.CLIMATE...

Record High Minimum Temperatures:

May 4:
KGSO: 65/2022
KRDU: 68/1938
KFAY: 68/1942

&&

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

&&

$$
SYNOPSIS...Green
NEAR TERM...Green
SHORT TERM...KC
LONG TERM...Kren
AVIATION...CBL/MWS