Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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404
FXUS62 KRAH 281846
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
245 PM EDT Sun May 28 2017

.SYNOPSIS...
A series of upper level disturbances will track east across the
Carolinas this afternoon through Monday evening.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 200 PM EDT Sunday...

The EML in place over the Carolinas the past few days has been
modified and suppressed southward by numerous rounds of convection
over the past 24 hours, with H7-H5 lapse rates ranging from ~5.5c/km
near the VA border to 6.0-6.5C/km near the SC border. Diurnal
destabilization this afternoon is expected to range from marginal
(~500 J/kg MLCAPE) near the VA border to moderate (1500-2500 J/kg
MLCAPE) near the SC border where the strongest insolation and
richest low-level moisture will be juxtaposed with mid-level lapse
rates on the order of 6.0-6.5c/km.

With numerous MCVs upstream of the Carolinas, significant
uncertainty persists with regard to the timing/coverage of
convection this aft/eve. Convection allowing models such as the 12Z
HRRR and NAM NEST suggest scattered convection will develop over
western NC around ~21Z and propagate east across central NC through
~03Z this evening, presumably in association with one of several
MCVs expected to track across portions of the Carolinas. Moderate
destabilization, effective shear on the order of 40-50 knots,
straight hodographs, and relatively steep mid-level lapse rates
across the SW Piedmont/Sandhills suggest the primary mode of
convection (should it develop) will be splitting supercells with an
attendant threat for large hail (1.00-1.75"). Damaging winds cannot
be ruled out, however, the environment in place across central NC
today is significantly less supportive than in previous days (DCAPE
500-750 J/kg (primarily near the SC border) this afternoon. Diurnal
destabilization will be weakest north of Hwy 64, particularly in the
NE Coastal Plain where weak mid-level lapse rates will be juxtaposed
with a cooler airmass in vicinity of a stalled front near the VA
border. With the above in mind, a conditional potential for
splitting supercells will exist later this aft/eve, with a primary
threat of severe hail (1.00-1.75").

Expect highs this afternoon to range from the lower 90s near the SC
border to the lower 80s near the VA border in the Northern Piedmont
and NE Coastal Plain. Lows tonight should range from the mid/upper
60s near the VA border to lower 70s near the SC border. -Vincent

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
As of 300 PM Sunday...

Monday and Monday night:

The closed low over the Upper Great Lakes will wobble slowly east on
Monday. The primary northern stream shortwave trough is expected to
weaken as it lifts northeast away from the area, shearing out across
the northern Mid-Atlantic and NE U.S., with attendant trailing sfc
cold front expected to stall out across the area late Monday into
Monday night. The arrival of this front into the area Monday
afternoon/night coupled with individual perturbations ejecting NEWD
in the broad cyclonic flow, along the southern fringes of the strong
belt of westerlies, will bring another round of showers and
thunderstorms to the area that could linger well into the overnight
hours as the front begins to stall out.

Strong daytime heating within the moist and moderately unstable
airmass combined with continued strong mid-level flow that will
support favorable/strong deep layer shear of 40-45 kts, will result
in another slight risk for severe storms across the area with
damaging winds and large hail the primary threats. Storm intensity
should weaken significantly with loss of daytime heating, so the
severe threat should fall between 2 to 10 pm.

Highs in the mid 80s north to lower 90s south. Lows Monday night
will depend on the location of the front, ranging from lower/mid 60s
NW to lower 70s SE.

Tuesday and Tuesday night: As the upper low continues to wobble
slowly eastward over southern Ontario/Upper Great Lakes, the quasi-
stationary frontal zone and attendant axis of deeper moisture
bisecting central NC Tuesday morning will inch ever so slightly
east/southeastward through Tuesday night/early Wednesday. Any
shortwave energy moving through the upper jet streak extending from
the Tn Valley into the Mid-Atlantic region could result in a
convective flare-up and locally heavy rain near the front. As such,
expect areas south of east of the Triangle to see the highest rain
chances Tuesday afternoon and evening. While, deep layer shear won`t
be as good as in previous days, 30-35 kts will still be sufficient
to support a few strong to severe multicell clusters during peak
afternoon heating.

Highs ranging from lower to mid 80s north to upper 80/near 90 south.
Lows in the lower 60s NW to upper 60s/near 70 south.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 245 PM EDT Sunday...

General model consensus for the mid to late week period is that the
closed low over Ontario and associated northern stream trough will
get kicked east-northeastward late Wednesday, only to get replaced
by a reinforcing closed cyclone diving SE out of central Canada. The
eastward progression of the lead trough passage through the NE U.S.
and Mid-Atlantic States late Wednesday will push another cold front
from the northwest late Wednesday afternoon and evening, which will
allow for a continued threat of showers and storms area-wide
Wednesday.

West-northwesterly flow in the wake of the trough passage on
Thursday, may be just enough to push the front south of the region
with drier more stable air advecting in from the west, potentially
keeping central NC convection free on Thursday. However, these dry
conditions look to be short-lived with low-level SWLY flow in
advanced of a phased shortwave trough approaching from the west,
marking the return of higher humidity and instability, along with
the daily chance of mostly diurnal convection Friday and into the
weekend.

Seasonable temperatures Wednesday and Thursday will return into the
above normal ranges by the weekend.

&&

.AVIATION /18Z SUNDAY THROUGH THURSDAY/...
As of 200 PM EDT Sunday...

24-HR TAF Period: VFR conditions are generally expected to prevail
through the TAF period. Isolated/scattered convection will be
possible late this afternoon and evening at all terminals, however,
confidence in coverage/timing will preclude mention thereof with the
18Z TAF issuance. Expect W/SW winds at ~10 knots with occasional
gusts to 15-20 knots.

Looking ahead: Aside from a potential for isolated/scattered diurnal
convection during the afternoon/evening hours each day, VFR
conditions are expected to prevail through mid-week. -Vincent

&&

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

&&

$$

SYNOPSIS...Vincent
NEAR TERM...Vincent
SHORT TERM...CBL
LONG TERM...CBL
AVIATION...Vincent



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