Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 171501
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1100 AM EDT Fri Aug 17 2018

.SYNOPSIS...
A mid level trough and surface cold front will slowly approach the
area from the west on Saturday. The front is expected to stall
out in the vicinity of the Carolinas on Sunday and will linger
over the area through early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1100 AM Friday...

Morning analysis indicates greater low-level moisture with dew
points in the mid 70s across the Coastal Plain and, thus, greater
instability than was previously forecast. Higher confidence for
showers and thunderstorms exists in western NC with the approaching
trough and in eastern NC with the sea breeze circulation driving
convection. Some questions still exist regarding a potential lifting
mechanism in central NC. However, some widely scattered, largely
diurnally-driven showers and thunderstorms are possible with MLCAPE
exceeding 1500 J/kg across the western Piedmont and approaching 2500
J/kg across the Coastal Plain.

Have adjusted max temperatures upward a degree or two as morning
ROABS note low-level thickness values have increase 5 to 9m from
yesterday and with lots of sunshine this morning, temperatures have
already reached the mid and upper 80s.

Previous discussion from 340 AM... A positively tilted shortwave
trough over the middle MS valley this morning and attendant cold
front will advance east into the Ohio and Tn Valley by 12z Saturday.
Deepening SWLY flow aloft in advance of the system will advect
higher 1.8-2.0" PWATS into the area today. Th4 increase in deep
layer moisture, in conjunction with a sharpening pre-frontal lee
side trough across western NC and and the sea breeze circulation
over eastern NC, will fuel scattered convection within the
moderately unstable airmass in place. Week deep layer shear of 15
kts or less will limit severe threat. Convection looks largely
diurnally driven, with diminishing coverage during the evening and
overnight.

Highs today very similar to what we saw on Thursday, perhaps a
degree or two cooler. Highs ranging from near 90 NW to lower 90s SE.
Lows Friday night 70 to 75.


&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 340 AM Friday...

Mid/upper level trough over the Ohio and Tn Valleys Saturday morning
will continue to move east, progged to cross the central and
southern Appalachians late Saturday afternoon/early evening and then
across the Mid-Atlantic region Saturday night and into the day on
Sunday. Modest synoptic scale height falls( -20 to 30 meter height
falls) attendant to the upper trough traversing the area, in concert
with several embedded shortwave impulses will result in high chance
to likely pops across the area Saturday afternoon and evening.
Improved deep layer shear of 20 to 25 kts near the Va border, closer
to the better trough dynamics, could support a few strong/severe
multi-cell clusters across the area. Additionally given PWATS of 2-
2.25", locally heavy rainfall and flash flooding will be possible,
mainly in urban or poor drainage areas.

While storm intensity/severe threat should decrease with loss of
heating Saturday evening, given the timing of the upper trough into
the area and with the front likely to be in the invof the Carolinas,
convection could linger well into the overnight hours.

Cooler on Saturday given the robust rain chances. Highs 85 to 90.
Lows 70 to 75.

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 340 AM Friday...

Mid level trough axis will shift to the east of central NC on
Sunday. However, with a lingering surface front/trough expected to
be located across the area, expect we should see scattered
afternoon/evening showers and storms develop. Deep layer is expected
to be weak, however, with a least moderate MLCAPE values (1500-2500
J/kg) expected and continued high PW values (1.7" to 2.0") expect we
could have several storms/clusters produce some isolated damaging
wind gusts and/or localized flash flooding. High temps Sunday are
expected to generally be in the mid to upper 80s, with a few lower
90s across the south. Low temps Sunday night/Monday morning are
expected to be in the lower to mid 70s, with generally dry
conditions overnight.

Brief s/w ridging is expected on Monday. However, with the lingering
surface trough across the area, expect we still should see another
day of isolated to scattered showers and storms. A more amplified
disturbance and associated cold is expected to approach the area
from the west on Tuesday, then moving into the area on
Wednesday/Thursday. This will result in a continued threat for
showers and storms, though differences remain on how this system
will evolve (which will affect the pops and temps).

High temps Monday and Tuesday are expected to range from the mid to
upper 80s north to the lower 90s south. Highs temps are expected to
be a category or two lower on Wednesday into Thursday as the surface
front moves into the area, yielding increasing chances for showers
and storms. Low temps will generally be in the 70s, with perhaps a
few mid to upper 60s across the northwest Piedmont on Thursday
morning as the surface cold front moves into the area.


&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
As of 130 AM Friday...

Model guidance suggest less in the way of fog development overnight,
owing to more areas seeing a light southerly breeze. However, still
can`t rule out a brief period of light fog/MVFR restrictions during
the few hours around daybreak, mainly at KFAY and KRWI. Any sub-VFR
conditions will improve to VFR by 13z Fri, followed by a trend to
broken VFR clouds in the afternoon. There will be a slight to small
chance of showers and storms this afternoon and evening, with the
best chance at eastern terminals.

Outlook: Numerous/likely storms are expected across the area
Saturday and into Saturday night as an upper level trough and
attendant cold front move into the region. The front is expected
to stall across the area Sunday through early next week, resulting
in higher than average convective coverage each afternoon. Expect
periods of sub-restrictions in heavy showers/storms along with the
threat of morning low clouds and fog.


&&

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

&&

$$

SYNOPSIS...CBL
NEAR TERM...LTL/Blaes/CBL
SHORT TERM...CBL
LONG TERM...BSD
AVIATION...CBL


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