-- Discussion containing changed information from previous version are highlighted. --
475
FXUS62 KRAH 221847
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
248 PM EDT Sun Sep 22 2024

.SYNOPSIS...
A back-door cool front will drop south into the area this afternoon
and evening and tonight. The front is expected to become quasi-
stationary INVOF of upstate SC and southern NC, eventually washing
out early week as weak high pressure extends south down the mid-
Atlantic coast.

&&

.NEAR TERM /TODAY AND TONIGHT/...
As of 1100 AM Sunday...

Only made a few minor tweaks to the temperatures this morning based
on recent obs. Otherwise the forecast remains on track. The 12Z
upper air analyses show a H25 jet streak extending from western NY
to northeast NC, on the back side of the upper trough/northeast
periphery of the sub-tropical ridge. At H5 there was a 40m 12-hr
height fall at Wallops Island, with weaker 20m falls over VA and NC.
While coastal NC was relatively saturated at both H7 and H85, there
was some drier air evident at H7 from the GSO sounding, indicating a
decent moisture gradient from W to E across the area at H7. The 12Z
surface analysis showed a couple of weak surface lows, one near the
Triad and the other over northeast NC. The backdoor front was likely
still back over sern VA at 12Z. At 15Z, satellite imagery shows the
area of low-stratus over northeast NC, slowly moving swwd toward the
Triangle. -KC

From the previous discussion (as of 330 AM): The low clouds could
linger/hold on over NE portions of central NC for a fairly
substantial portion of the diurnal heating cycle, which will likely
set-up an impressive NE to SW temperature gradient across the area,
while also making for a challenging max Temp forecast today,
especially along it`s eventual western fringes. HREF probabilistic
guidance indicates as much as 8 degree spread in afternoon temps,
with the greatest uncertainty centered over the central Piedmont,
including the Triangle. Highs ranging from mid/upper 70s northern
coastal plain, lower/mid 80s interior sections, and upper 80s/near
90 across the southern Piedmont.

Isolated showers/storms will be possible as the front slips south,
mainly across eastern Piedmont/coastal plain sections where the best
instability is forecast. Widespread low clouds/stratus will spread
NE to SW during the the evening and overnight hours. Additionally,
some showers could spread into the western/NW Piedmont tonight as
shortwave impulses spread in from the west within a mid-level plume
of enhanced moisture and WAA. Lows ranging from lower 60s NE to
upper 60s southwest.  -CBL

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
As of 330 AM Sunday...

Weak H5 rises are expected over the region on Monday as the upper
ridge over the GOM builds towards the Florida Peninsula. The
aforementioned back-door cool front near the SC/NC border early
Monday could retreat back north during they day. Meanwhile,
downstream of the an upper shortwave trough over the Mid/Lower MO
Valley, weak disturbances will continue to eject east atop the mid-
level ridge axis and through the region, keeping a plume of enhanced
mid-level moist and WAA focused over NC and VA, with PWATS forecast
to increase to ~2.0" by Monday evening.

We`ll see considerable multi-layer cloudiness across central NC,
especially the western Piedmont. Weak to moderate destablization
across the southern and western Piedmont will support a chance of
showers and storms, especially during the afternoon and evening,
with general model consensus the potential for scattered
shower/convection to spread east into central and eastern NC Monday
night.

Highs Monday ranging from mid/upper 70s north to mid 80s south. Lows
again in the lower 60s NE to upper 60s south.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
As of 248 PM Sunday...

The frontal boundary from Mon is likely to linger across the western
and southern Piedmont early Tue, before slowly shifting northward on
Wed. Aloft, models are showing an impulse of energy tied to a
shortwave in the OH valley tracking across the region in the SW flow
aloft. Morning stratus across the region is likely to also set up a
differential heating boundary as it slowly erodes over the southern
Piedmont and Sandhills, with highs mid 70s NE to mid 80s SW. While
SPC does not have us outlooked, models are showing MLCAPE between
1000-1500 J/kg with deep-layer shear of 30-35 kts, focused over the
southern Piedmont. This could pose a non-zero severe threat. As a
result, guidance is fairly high on shower/storm chances. Morning
showers are possible in the NE, but aftn/eve convection is favored
to develop first in the west/southern Piedmont and track ENE in the
evening to overnight.

By Wed, the surface boundary is largely favored to lift into VA as a
warm front. A cold front will be weakening to our west in the OH
Valley. Highest storm chances Wed will be over the NW in closer
proximity to the northward moving front and mid-level energy,
focused in the afternoon and evening with diurnal heating. Highs
should trend warmer than average in the upper 70s N to mid 80s S.

Thu to Sun: The overall synoptic pattern and potential impacts from
what develops in the Gulf remains uncertain. While the latest
deterministic GFS, ECMWF, and CMC show decent agreement that the
potential tropical system forecast to develop in the Gulf (80-
percent now from NHC) will get pull northward by troughing over the
mid to lower MS valley sometime late Thu or Fri over the SE US,
their respective ensembles still show a large spread in possible
scenarios. As a result, confidence on expected impacts from heavy
rainfall or gusty winds late this week to weekend, remain low. Where
the tropical system tracks ultimately will depend on the location of
the trough in the midsection of the country, as well as the ridge
off the SE coast, and whether any blocking sets up over the Great
Lakes or northern Great Plains. The inland landfall could be as far
west as the coast of AL or as far east as NE florida, per the ECENS
00z low tracks. For now, we have highest PoPs late Thu into Sat of
30-40 percent, decreasing to 20 percent by late in the weekend Sun.
This is likely to change, however, as models come into better
agreement in the coming days. Consequently, temperatures are also
uncertain, but for now are favored to be near or slightly below
average in the mid/upper 70s to around 80 Fri-Sun.
-- End Changed Discussion --


&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
As of 200 PM Sunday...

24 hour TAF period: An area of MVFR cigs lingers roughly from KRDU
to KRWI and north, with few/scattered cu at 15-25 kft developing
across the rest of central NC. Skies may bounce between sct and bkn
MVFR for the next several hours, most likely at KRDU and KRWI, but
possible also at KFAY and maybe even the Triad briefly. Otherwise,
VFR conditions should prevail through sunset, with winds generally
nely to ely. Some hi-res guidance still suggests some isolated
showers could develop this aft, but should largely miss the
terminals, coming closest to KRWI and KFAY.

Widespread IFR/LIFR stratus will spread across central NC, mainly
around and after midnight, with a period of MVFR/IFR vsbys expected
Mon morning. Skies will be slow to scatter/lift on Mon, with only
KRWI and possibly KFAY improving to VFR before the end of the TAF
period and MVFR/IFR everywhere else through 18Z.

Outlook: Mainly VFR conditions expected each day, with the exception
of sub-VFR fog/stratus each morning. There is a chance for mainly
afternoon/evening showers/tstms each day, which could result in
periods of sub-VFR conditions where/when they occur.

&&

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

&&

$$

SYNOPSIS...CBL
NEAR TERM...KC/CBL
SHORT TERM...CBL
LONG TERM...Kren
AVIATION...KC