-- Discussion containing changed information from previous version are highlighted. --
601
FXUS62 KRAH 181905
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
305 PM EDT Wed Sep 18 2024

.SYNOPSIS...
A weak area of low pressure off the Mid-Atlantic coast will lift
northeast through Thursday and be replaced by high pressure that
will gradually build into central North Carolina through the weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 240 PM Wednesday...

A weakening mid/level low churning over upstate SC this afternoon
will slowly sag southeast through SC and southern NC before
transitioning into a broad open wave over the Mid-Atlantic by Thurs
morning. At the surface, an area of low pressure off the NC/VA coast
this afternoon is expected to gradually deepen through the overnight
hours. In the process, an area of richer theta-e air over southeast
VA and northeast NC, characterized by dew points in the 70s and
temps in the 80s, will sag south this afternoon within a weak
pressure trough and northerly wind shift.

Diurnal heating of the richer theta-e airmass oozing into the
northern Coastal Plain and northeast Piedmont will result in weak to
moderate instability to develop (1000-1500 J/kg MLCAPE) by the early
afternoon. Weak convergence along the front and little inhibition
through the troposphere should result in scattered showers and
isolated thunderstorms. Hi-Res guidance shows this area will
continue to spread southward through the early overnight period.
Organized storm mode is not expected as central NC is nestled in a
weakness in the 500mb flow and results in light, erratic winds
through the lowest 500mb. Additional showers and isolated storms
will be possible over the southern Piedmont, Sandhills, into the
southern Coastal Plain associated with the weakening mid-level vort
max as it drifts just south of this area.

Hi-Res guidance suggests that a weakly stable airmass will remain in
place over central NC for most of the night and will likely continue
some isolated showers through midnight with gradual
weakening/dispersing thereafter. Thick and low overcast will
overspread the area from north to south through the overnight hours.
Some patchy fog may be possible early Thurs morning as cloud bases
briefly lower, but guidance has lowered probabilities of fog in
favor of mostly stratus. Overnight lows will settle in the mid/upper
60s for most areas.

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
-- Changed Discussion --
As of 305 PM Wednesday...

Aloft, the trough situated over the East Coast should slowly slide
eastward through Thu night, but remain along/just off the East Coast
by Fri morn as high pressure builds over the Plains and MS Valley.
At the surface, a low will meander off the northern mid-Atlantic/New
England Coast Thu/Thu night, while high pressure over the ern Great
Lakes ridges swd along the Appalachians. Meanwhile, the low that has
lingered over the northeast NC coast should shift esewd but linger
just off the central NC coast Thu before moving further southeast
over the Atlantic. Expect generally nly/nely flow across central NC
through Thu night. Some showers may linger into Thu morning over the
Piedmont. There could be a brief lull in activity before additional
scattered showers and isolated storms develop Thu aft, mainly along
lingering surface boundaries. Skies may remain mostly cloudy through
Thu morn and into the aft, which could further limit daytime
heating. Highs should top out in the mid 70s to low 80s, but could
be a couple/few degrees higher if cloud cover decreases earlier that
forecast. While the weather should dry out, there should be
lingering partly to mostly cloudy skies Thu night, with lows
expected to range from upper 50s north to mid 60s south.
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
As of 245 PM Wednesday...

Overall, the surface pattern for the extended forecast period should
be relatively quiet. At the beginning of the period, high pressure
will be over eastern Canada with a ridge extending to the southeast
across the Carolinas. This will change little through the period
until a cold front approaches the Appalachian Mountains on
Wednesday. However, at mid/upper levels, there will be occasional
ripples of energy moving across the western half of North Carolina.
Friday through Tuesday all show minimal precipitation clipping the
Triad in the ECMWF and GFS ensembles, yet with the exception of
Monday, the deterministic models don`t show any precipitation during
that time period. Having inherited a dry forecast and seeing little
conclusive evidence in the models, am inclined to keep the forecast
dry. However, Will go ahead and put in slight chance pops to the
forecast for Wednesday afternoon across northwestern counties for
the new day 7 forecast with the approaching front. Normal
temperatures for late September are around 80 and 60 - forecast
values are slightly above average for Friday through Sunday, then
near average for Monday through Wednesday.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 140 PM Wednesday...

Isolated to scattered airmass showers and widely scattered storms
are possible in the vicinity of all TAF sites through the afternoon
hours, lowest confidence at FAY. A northerly wind shift over
southeast VA will slowly sag south this afternoon before collapsing
through central NC this evening into the overnight hours. Along and
behind the wind shift, cigs will quickly fall to IFR and remain
there through the early morning hours Thurs. Landing minimums will
be most probable at INT/GSO early Thurs morning, but confidence
remains low at this time. A slightly higher chance for a shower will
also accompany this wind shift as weak instability and minimal
inhibition will continue through midnight. Cigs are expected to
gradually rise to MVFR by early afternoon.

Outlook: An unsettled period will continue through Thursday with
areas of overnight and early morning stratus and a risk of some
afternoon showers and possibly a storm. Aviation conditions will
generally improve for the weekend.

&&

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

&&

$$

SYNOPSIS...Swiggett
NEAR TERM...Swiggett
SHORT TERM...KC
LONG TERM...Green
AVIATION...Swiggett/Luchetti