435
FXUS62 KRAH 190822
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
422 AM EDT Thu Sep 19 2024

.SYNOPSIS...
An upper level low over the Carolinas will drift east then
northeast, tracking along the Mid Atlantic and Northeast coast
through Friday. A trailing upper level trough will persist just off
the East Coast through the weekend, as an upper level high pressure
ridge builds over the Gulf States. This ridge will shift east into
the Southeast states early next week.

&&

.NEAR TERM /TODAY AND TONIGHT/...
As of 400 AM Thursday...

Water vapor imagery currently shows the mid/upper low centered over
southern NC. A moist airmass is still in place, with PW values in
the 1.5 to 1.8 inch range. A couple of weak surface boundaries have
provided a focus for scattered showers, with one nearly stationary
line stretching from Moore/Montgomery counties east to
Johnston/Wayne counties, and another cluster of showers more
recently developing from Granville County east to Halifax County.
The former line still has some lightning with it, but it continues
to gradually weaken. High-res guidance like the HRRR has picked up
on the latter cluster and depicts it strengthening further and
slowly moving south, stretching from the Triangle to around RWI by
mid morning. Increased POPs to chance in these areas to account for
these latest trends. Some thunder can`t be ruled out with this
either as RAP analysis indicates around 500 J/kg of MLCAPE through
this morning across the east. Heavy rainfall isn`t much of a
concern, but localized amounts up to a quarter to half inch can`t be
ruled out according to the 00z HREF PMM.

The mid/upper low will continue to open up into a trough as its axis
nears the NC coast this afternoon. Moisture and weak forcing from
this trough will combine with lingering surface boundaries and CAPE
of 500-1500 J/kg to result in additional scattered showers and
isolated storms this afternoon. According to the latest high-res
guidance, the best coverage will be from the Triangle south and
east, where the best moisture and instability will be and in closer
proximity to the trough. The flow will be very weak so not concerned
about anything severe. The temperature forecast is a bit tricky as
it will depend on how much breaks in the clouds we get. The surface
flow will be more northerly around a surface low lingering off the
northern Mid-Atlantic/southern New England coast, as well as weak
high pressure trying to ridge down from southern Canada. So it
should be a bit cooler than yesterday, with forecast highs in the
upper-70s to lower-80s.

A few showers may linger into the early overnight hours across the
far NW Piedmont, but otherwise Thursday night will be dry and cloud
cover should be less widespread than it has been tonight. This may
support some patchy fog development. Low temperatures will be
slightly cooler as well, in the lower-to-mid-60s.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 400 AM Thursday...

Friday will continue the drying trend as N/NW flow on the backside
of the mid/upper trough pushing into the western Atlantic brings PW
values closer to normal. At the surface, low pressure will continue
to deepen and drift around the western Atlantic to the east of NJ,
as weak high pressure ridges down from New England. The only real
chance of any precipitation looks to be in the western Piedmont,
associated with a vorticity maxima on the backside of the mid/upper
trough. The deterministic GFS, ECMWF and NAM all depict some light
precipitation there in the morning and afternoon, with the signal
showing up in the ensembles as well. So opted to add slight to low
chance POPs in the west. More sun on Friday will support highs in
the lower-to-mid-80s. Any showers or storms will diminish after
dark, with lows Friday night in the upper-50s to mid-60s.

&&

.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 /06Z THURSDAY THROUGH MONDAY/...
As of 210 AM Thursday...

A line of showers and isolated storms is currently draped along a
boundary across the southern Piedmont and northern Sandhills, but it
has remained stationary and is beginning to weaken. Guidance
continues to show additional showers developing later tonight into
mid morning around RDU and RWI. MVFR or IFR visibilities will be
possible in any showers. Fog potential continues to look limited at
best tonight given the widespread low stratus across most of central
NC, but it can`t be totally ruled out especially in the far south
(including FAY) where the low stratus will be slowest to reach.
Otherwise, the low stratus is resulting in widespread IFR ceilings
across the north (including INT/GSO/RDU/RWI), and they should lower
further to LIFR over the next 2-3 hours. The IFR/LIFR ceilings
should reach around FAY by 9-10z. Ceilings will gradually lift and
scatter 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
possible in the south and east (including RDU, RWI and FAY)
starting in the early afternoon, diminishing after 00z.

Outlook: Areas of overnight and early morning fog/low stratus will
remain possible Fri and Sat mornings, though coverage and chances
appear less compared to previous days. 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...Hartfield
NEAR TERM...Danco
SHORT TERM...Danco
LONG TERM...Hartfield
AVIATION...Danco/Kren