Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 181812

National Weather Service Raleigh NC
212 PM EDT Wed May 18 2022

Weak high pressure over the area will move east and offshore by this
evening, as a weak front lifts north through North Carolina as a
warm front. A warm southwest flow will bring hot temperatures
Thursday through Saturday, as a series of upper level disturbances
tracks eastward through the Mid Atlantic region. A cold front will
approach on Sunday and cross the area Sunday night, with cooler air
arriving Monday.


As of 920 AM Wednesday...

Just minor tweaks to the forecast needed. The MSLP pattern in our
region remains ill-defined but features a weak front across our S
sections with weak high pressure nosing in from the N as it shifts
quickly eastward through the Mid Atlantic region. The resident air
mass is fairly dry through the column with sub-1" PW at GSO and dry
air noted on GOES low-mid level WV bands, which, along with mild mid
levels, should curb convection despite good surface heating, as
surface dewpoints drop with mixing resulting in minimal CAPE. We
will see an increase in mid clouds this afternoon mainly across the
NW and far N as the remnants of mid-Miss Valley convection cross the
central Appalachians, but these should be dissipating as they head
east into a more hostile environment. Attention next turns to the
MCV over S IL which is on track to cross the mountains and into
VA/NC after sunset. This too should be weakening as it gets into our
area, but will still likely bring some increase in clouds and a few
showers. Models vary with the track of this remnant MCV, with some
bringing showers more into VA and others more into NC, so will
monitor its movement and check later guidance before making
significant changes to pops this evening/tonight. For now will
retain a trend toward slight chance starting late evening. Still on
track to reach highs in the low 80s to around 90. -GIH

Earlier discussion from 345 AM: A cold front currently analyzed over
southern VA will continue to push southward into northern portions
of central NC this morning, before surface high pressure pushes off
the Mid-Atlantic coast this afternoon, helping to lift the front
back north. Thus N/NE winds this morning will shift back to
southerly this afternoon. With mostly sunny skies and low-level
thicknesses about 10 m higher than yesterday, high temperatures
should be 2-4 degrees warmer in most places outside of the far NE,
generally mid-80s to near 90. Meanwhile, an MCS will be moving east
across the Ohio Valley this afternoon, the remnants of which will
bring increased clouds to central NC this evening into the early
overnight hours. This could potentially bring a few isolated showers
to the far northern Piedmont, but considering the MCS will be
passing to well north of us, CAMS agree any rainfall amounts would
be light and only have slight chance POPs there. A separate MCV
coming from the TN Valley will then pass directly over central NC
early Thursday morning, which may result in a better chance of
showers during this time. However, with a lack of instability, the
convection will be dying out as it moves east and no storms are
expected. Thus the best chance of precipitation is over the NW
Piedmont, and POPs are still only low chance there. Temperatures
Wednesday night will be mild (lows in the mid-to-upper-60s) with
continued southerly flow.


As of 400 AM Wednesday...

As the MCV moves offshore, a lull in precipitation chances is
expected on Thursday morning into early afternoon. But by mid-to-
late afternoon, a Piedmont trough will set up, and another
disturbance may move across the region in the NW flow aloft. Strong
surface heating, increasing dew points into the 60s, and steep mid-
level lapse rates (7-8 C/km) will support CAPE of 1500-2500 J/kg. 0-
6 km shear of 25-35 kts will be possible, which isn`t overly
impressive, but could still support multicell clusters and perhaps a
supercell. Thus the SPC has introduced a marginal risk for severe
storms in the afternoon and evening. Hail and damaging winds would
be the main hazards, as the flow looks unidirectional enough to
limit the tornado threat. Still only keep POPs in the 25-40% range
since CAMS disagree on the extent and location of convection, and
there will be a lack of large-scale upper forcing. High temperatures
will be very warm, generally upper-80s to mid-90s (potentially
approaching the record high of 96F at FAY), thanks to SW flow and
even higher thicknesses. Convection should die out Thursday night
with a loss of daytime heating, but low temperatures will again be
quite mild, mid-60s to lower-70s.


As of 210 PM Wednesday...

Aloft, the upper level flow will transition from zonal to meridional
on Friday as the trough amplifies out west and the sub-tropical
ridge amplifies to the east. Several waves will swing through the
trough, while deep southwesterly flow will increase advection of
warm, moist air from the Gulf through the lower MS Valley into the
Appalachians. As the trough shifts eastward (and with the help of a
shortwave passing to the north), the moisture axis will move over
the mid-Atlantic Sun and Mon. Another shortwave will move through
the Rockies, Plains and MS Valley Sun night through Tue, before
moving slowly eastward mid-week. Timing of this wave into the area
is uncertain and continues to change with each successive model run,
thus will hold off on specific details at this time. At the surface,
central NC will be under the influence of southwesterly flow,
situated on the western edge of Bermuda High pressure. Meanwhile to
the west, a cold front will begin moving east over the weekend as a
low lifts northeastward through the OH Valley and into the Northeast
Sat night/Sun. The trough will extend through the mid-Atlantic Sun
as high pressure builds east through the Great Lakes. The front may
stall invof NC/SC on Mon and Tue, with the high ridging southward
into the Carolina Foothills and Piedmont. Forecast confidence for
Tue and Wed remains low at this time.

Precipitation: The best chance for showers and storms will be Sunday
through Monday with the front moving into and through the area. For
now, central NC is not outlooked for either severe weather or
excessive rainfall. However, given the heating and good moisture
advection into the area, both strong storms and heavy rain will be
possible, though it is a bit early to say with any real confidence.
A slight chance of showers will linger through mid-week given the
forecast uncertainty.

Temperatures: Record highs and high-minimum temperatures are in
jeopardy through Sunday. Friday and Saturday will still be the
warmest of the year, with highs in the mid to upper 90s and lows
generally in the upper 60s to low 70s. Highs on Friday continue to
be forecast at or above current records. Sunday should still be
warm, but perhaps a few/several degrees lower with highs in the
upper 80s to mid 90s and lows in the mid to upper 60s. Temperatures
should drop back to within a category or two of average early-mid


As of 130 PM Wednesday...

VFR conditions are likely through the next 24 hours, although clouds
will be increasing, and there is a chance for low level wind shear
tonight. The weak surface high pressure over the region will
continue shifting E and offshore as the weak frontal zone across our
south sections shifts northward as a warm front, initiating a mean
surface flow from the SW through Thu. Meanwhile, upper level
disturbances to our WNW over the Mid Miss Valley into the Ohio
Valley will track toward the ESE and through the Mid Atlantic
region. This will lead to a steady increase in mid and high clouds
that will peak tonight, esp across the N, before decreasing toward
the end of the TAF valid period. Mostly dry weather is expected,
although a few showers are possible this evening through tonight,
mainly at INT/GSO/RDU, as a disturbance aloft crosses the region.
Finally, due to a 35-40 kt jet from the SW at around 2000 ft AGL
that crosses the region after midnight tonight, a period of low
level wind shear is possible, mainly 04z to 10z.

Looking beyond 18z Thu, scattered to numerous showers and storms are
expected to develop starting late Thu afternoon and lasting well
into the nighttime hours. Some of these storms could be strong with
gusty winds. Mostly dry weather is expected Fri into Sat, although
southeast sections (FAY) could see early-morning sub-VFR fog/stratus
Sat morning. A few storms are possible late Sat afternoon into
evening, mainly west, with a better chance of storms late Sun
through Mon ahead of a slowly approaching cold front. -GIH


Here are the record high temperatures for May 19-22 and the year
they were last set:

        May 19         May 20          May 21          May 22
GSO     96 (1911)      95 (1917)       96 (1941)       97 (1941)
RDU     95 (1962)      94 (1938)       96 (1941)       97 (1941)
FAY     96 (1996)      99 (1938)       99 (1941)       100 (1941)





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