-- Discussion containing changed information from previous version are highlighted. --
378
FXUS62 KRAH 191705
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
105 PM EDT Thu Sep 19 2024

.SYNOPSIS...
An upper level low over the eastern Carolinas this afternoon will
lift northeast along the Mid Atlantic coast through Friday and then
persist as an upper level trough just off the East Coast through the
weekend. An upper level ridge of high pressure will move into the
northern Gulf States late in the weekend and then extend into the
Southeast states through early next week.
&&

.NEAR TERM /TODAY AND TONIGHT/...
As of 1055 AM Thursday...

* An unsettled pattern will continue through tonight as a persistent
  upper level trough slowly exits the area.

The latest surface analysis shows surface high pressure centered
over Quebec that extends southwest across the eastern Great Lakes
and into the southern Appalachians. A frontal zone with weak areas
of low pressure extends northeast to southwest just off the East
Coast. A light north to northeasterly low level flow persists across
the region in rather moist air mass with PW values of 1.6 to 1.8
inches or about 125% of normal. Further aloft, a persistent upper-
level low was centered across southeastern VA and northeast NC with
500 mb temps of -10C and a cyclonic flow from the northwest across
central NC.

The forecast through tonight is complicated as a moist and weakly
unstable airmass across central NC is activated by mid and upper
level disturbances in the cyclone flow aloft. An initial area of
rain with some heavier embedded showers will slowly shift south
across the northern and central Coastal Plain and the eastern
Triangle through the early afternoon before weakening and settling
into the southern Coastal Plain. Additional widely scattered
convection is apt to develop later this afternoon favored across the
southern Piedmont and Sandhills areas. With a moist airmass, the
rain may be heavy at times and along with a slow storm motion and
saturated soils, some localized flooding is possible. The airmass
will destabilize a bit this afternoon with MLCAPE values of 500-1500
J/kg which will support some thunderstorms. The flow is rather weak
and the CAPE is skinny so not too concerned about any severe storms.
Another disturbance in the flow aloft is forecast to dive south
across the western Piedmont of VA and NC late this afternoon and
evening resulting in a threat of showers across the western Piedmont
of NC this evening. Another round of stratus and fog is expected
late tonight with perhaps a bit more fog than last night.

Temperatures today will be difficult and depended on how much sun
breaks into the overcast. Highs should range in the in the upper 70s
to lower 80s. Lows tonight should range in the lower to mid 60s.
-Blaes

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
-- Changed Discussion --
As of 105 PM Thursday...

Aloft, the trough off the mid-Atlantic coast will continue to shift
ewd over the Atlantic, allowing high pressure to ridge enewd into
the area. A lobe of vorticity in the upper levels will swing sewd
through central NC Fri morn/aft, while a trailing mid-level
disturbance follows Fri aft/eve. At the surface, a low will continue
to meander off the northern mid-Atlantic/New England Coast Fri/Fri
night, while high pressure ridges swd through central NC. Some lower
dewpoint air should push into the far northeast portions of central
NC as the high ridges in. While widespread convection is not
anticipated, if showers do develop, the best chance would be over
the western Piedmont during the morn/aft with the passage of the
vort max aloft, and over the northeast Piedmont/northern Coastal
Plain during the aft/eve, generally along the dewpoint gradient as
the high ridges swd. The NAM does have some MUCAPE in the 500-1000
J/Kg range Fri morn through the eve, thus an isolated storm or two
is still possible if/where convection occurs. Highs should generally
range from around 80 degrees NE to mid 80s south, with lows in the
upper 50s to mid 60s expected.
-- End Changed Discussion --

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 325 AM Thursday...

The weekend into early next week still looks mostly dry, although
rain chances are poised to return by late Tue. Above-normal temps
Sat-Sun will trend to near or a bit below normal Mon-Wed.

Sat-Sun: The mid-upper level trough will hold just to our E off the
East Coast this weekend, while ridging builds from the TX/Mexico
border northeast into the Gulf States and Mid South. A narrow weak
surface high will continue to extend from New England and the
Canadian Maritimes SSW through central NC, held in place by the
persistence of a deep surface low well off the Mid Atlantic coast.
By early Sun, models roughly agree on a weak shortwave trough
originating near Lk Huron tracking SE through the Mid Atlantic
region, dragging a reinforcing backdoor cold front SSW through
central NC. Some deterministic models such as the GFS favor some
shallow showers with this front passage late Sat night/early Sun,
but given that deep moisture will be lacking with a NW low-mid level
flow and below normal PWs, will keep pops under 20% for now.
Whatever showers do manage to form are apt to be very light and
sparse. The backdoor front will usher in some cooler air by late
Sun, but before that, thicknesses suggest highs both days in the
upper 70s to mid 80s, coolest NE.

Mon-Wed: The surface ridge will continue to nose through our area
Mon into Tue, as the surface low drifts steadily S from off the Mid
Atlantic to off the Carolina coast. The mid level ridge from TX into
the Gulf States/Mid South will shift E into the Southeast during the
early work week, nudged by deep mid-upper troughing over central
Canada through the US Plains states. This onset of WSW flow aloft
into the W Carolinas could support rising chances for convection
over the NC mountains and foothills, and perhaps into the W
Piedmont, esp near the old backdoor frontal zone with lift enhanced
by upslope low level flow. Expect mostly dry weather to hold Mon and
through much of Tue, but with improving moisture return in our W,
will bring in 20-30% pops (higher NW and just isolated elsewhere)
late Tue through Wed, still mostly under climatology. Thicknesses
will stay a bit below normal Mon before trending back toward normal
Wed as the resident air mass modifies, but overall expected temps to
be just a shade below normal with increasing clouds. -GIH

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
As of 705 AM Thursday...

A cluster of showers with even some thunder has developed across
parts of the NE Piedmont and northern Coastal Plain early this
morning. They will continue to drop south and potentially affect RDU
and RWI over the next few hours. MVFR or IFR visibilities will be
possible in any showers. Otherwise, low stratus is resulting in
widespread LIFR ceilings across the north (including INT/GSO/RDU).
It remains unclear whether the low stratus will make it as far south
as FAY, which is still VFR, but there is still a chance for some
MVFR ceilings there this morning. Ceilings will gradually lift and
scatter everywhere through the day, with MVFR by late morning and
early afternoon, and VFR by late afternoon into the evening. After a
brief lull in precipitation, scattered showers and isolated storms
are again possible in the south and east (including RDU, RWI and
FAY) starting in the early afternoon, diminishing after 00z. There
is also a chance for a shower or storm at GSO and especially INT
later in the evening, but didn`t have enough confidence to put it in
the TAFs at this time.

Outlook: Areas of overnight and early morning fog/low stratus will
remain possible Fri and Sat mornings. With drying aloft, it may be
more of a fog concern vs low stratus. Aviation conditions should
largely trend VFR Sun and Mon. Precipitation chances will be minimal
if any through the period.

&&

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

&&

$$

SYNOPSIS...Blaes
NEAR TERM...Blaes
SHORT TERM...KC
LONG TERM...Hartfield
AVIATION...Danco/Kren