Special Weather Statement, NWS Raleigh, NC

Area Forecast Discussion
National Weather Service Raleigh NC
1040 PM EDT THU JUN 23 2016

.SYNOPSIS...
An active northwest flow aloft will prevail over the Carolinas and
Mid-Atlantic through Friday night. Dry conditions will return later
this weekend as an upper level ridge builds northeast along the
Appalachians, however, a more active pattern will return early next
week as the ridge weakens and NW flow aloft becomes established over
the region again.

&&

.NEAR TERM /through Tonight/...
As of 1040 PM...

A Severe Thunderstorm Watch remains in effect for portions of
Central NC through 11 PM. Showers and thunderstorms will continue to
move through Central NC over the next several hours. The HRRR has
been doing well with the development and progression of this event,
thus will lean toward that analysis. The line of storms currently
moving into the triad will likely progress ESE through the area
through 06Z, with some light rain possibly lingering a bit later.
Though heavy rain and winds are still a threat, the storms have
weakened a bit as they've approached and should continue that trend
as they move through the area. There is still lingering instability
and strong DCAPE and the PWAT values are between 1.5 and 2 inches.
As a result, expect heavy rain and isolated strong wind gusts to be
the main threat for the next few hours. Lows tonight will depend on
how and where the rain occurs, but generally expect lows in the mid
60s to mid 70s.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 330 PM Thursday...

Forecast confidence for Fri/Fri night has actually decreased over
the past 24 hours. A train of MCSs propagating SE/ESE through the
Virginias early this morning through the middle of this afternoon
(i.e. currently) has significantly altered the mesoscale pattern
(low-level height/wind fields) over the Mid-Atlantic, including
washing out or completely masking the backdoor cold front previously
expected to track southward through VA into northern portions of
central NC late tonight. As a result, model guidance no longer
indicates a cooler airmass advecting into the region from the north
on Friday. Instead, guidance suggests that the 1010 mb sfc low
currently in OH will transition SE into central VA/northern NC
Friday afternoon as DPVA attendant shortwave energy progressing
eastward through the Mid-Atlantic tracks in close vicinity to an
'effective' frontal zone, one which separates a cloudy/rain cooled
airmass (assoc/w persistent convection/MCS remnants in VA) from a
hot/unstable airmass assoc/w strong insolation to the south in NC.
This low is expected to gradually transition to the NC coast Fri
night as northerly flow develops across VA/DELMARVA (in response to
surface pressure rises /subsidence/ over New England and the
northern Mid-Atlantic), pushing the frontal zone S/SE through
central NC Fri night.

Guidance suggests thermodynamic conditions Fri afternoon will be
similar to today, i.e. strong insolation, rich low-level moisture
and a modified elevated mixed layer contributing to strong diurnal
destabilization. Expect convection to develop during the mid/late
afternoon as low-level convergences increases in vicinity of the sfc
low and (later) along the S/SE advancing frontal zone Fri eve/night.
Given effective bulk shear values supportive of supercells, expect a
potential for isolated severe storms capable of producing large hail
and damaging winds. -Vincent

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
As of 400 PM Thursday...

Little change in overall forecast rationale through the medium
range. Ridging at the surface and aloft will build across the
Middle Atlantic states this weekend, with associated cooler and
mainly dry conditions. The exception will be on Sat, as the cold
front forecast to cross central NC Fri night settles through the
Coastal Plain, with an associated lingering chance of showers.
Broken to overcast low clouds in NE low level flow are also likely
to expand SWD throughout the CWFA during the morning-midday hours
Sat, and probably linger into at least the first half of the
afternoon east of I-95. Temperatures should accordingly remain at
or below guidance values over the far NE Piedmont and Coastal
Plain, with highs ranging from near 90 SW to around 80 or so NE.
Low clouds will be shunted progressively further SWWD through
early Sunday, with subsequent mostly sunny and warmer conditions,
and highs in the middle 80s to lower 90s, on Sunday.

A mid to upper-level trough is forecast to become re-established over
the ERN U.S early to mid next week, with an associated wavy
frontal zone at the surface --and associated above average
chances of showers and storms-- expected to waver across the
Middle Atlantic states. Any relatively lower probability of
convection will likely be late Tue night-Wed, when the models
indicate the frontal zone is most likely to drift south of central
NC, albeit only briefly.

&&

.AVIATION /00Z Friday through Wednesday/...
As of 727 PM Thursday...

24-Hour TAF period: Additional showers and thunderstorms are still
expected this evening into tonight at all terminals. The best
overall potential for convection (and perhaps an isolated severe
storm) will occur at RDU/RWI terminals between 00Z and 03Z tonight
and at KINT/KGSO/KFAY between 03Z and 06Z. Otherwise, expect VFR
conditions to prevail through the remainder of the TAF period. -KC

Looking ahead: Sub-VFR conditions associated with showers/storms
will remain possible Fri/Fri night. Drier /VFR/ conditions will
prevail over the weekend as an upper level ridge builds over the
Appalachians. A more active pattern of NW flow aloft will return
early next week. -Vincent

&&

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

&&

SYNOPSIS...VINCENT
NEAR TERM...KC
SHORT TERM...VINCENT
LONG TERM...26
AVIATION...KC/VINCENT

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