Special Weather Statement, NWS Raleigh, NC

AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
326 PM EDT Tue May 4 2021

.SYNOPSIS...
High pressure off the Southeast coast will help transport warm and
humid air into the Carolinas through Wednesday. A cold front will
move across the area late Wednesday and Wednesday night. A cooler
and less humid air mass will build into the area Wednesday night and
Thursday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
As of 240 PM Tuesday...

Latest surface analysis continues to show surface high pressure
centered off the Southeast coast with a warm and moist southwesterly
flow into the Carolinas. At the mid levels, transient short wave
ridging extending across the Carolinas is moving offshore. A mid
level short wave trough near the MS Valley, will move east and reach
the central/southern Appalachians late tonight/early Wednesday
morning. Ahead of this primary feature, several weak vortices and
MCVs will move across the Carolinas this afternoon.

Widespread convection associated with an MCS across the western
Carolinas will shift east this afternoon and redevelop/organize into
a line of convection that spreads across central NC through mid
evening. A few rogue storms may develop out ahead of the main line.
The time with the best chance of storms will be from 3 to 6 pm in
the Triad, 4 to 8 pm in the Triangle and 6 to 9 pm across the
Coastal Plain and Sandhills.

The wind field and resulting shear is noticeably less today with 0-
6km bulk shear values of 20kts or less with a southwest to west-
southwesterly flow, generally 30 kts or less through the column.
Instability is a bit stronger than on Monday with fairly steep mid
level lapse rates that range from about 6.5 to 7.5 Deg C/km
resulting from an EML. DCAPE values exceed 1100 j/kg. Given the
unidirectional flow, DCAPE, linear structure, expect wind damage to
be the main threat. With moderate instability, good mid level lapse
rates, and normalized CAPE values greater than 0.15, storms today
will likely be healthy lightning producers and perhaps the most
electrically active day thus far this season. While the widespread
convection should push east of central NC by around 03Z, there will
be enough upper level support for a small chance of showers
overnight and possibly a thunderstorm. It will be mild overnight
with lows in the mid 60s to around 70. -Blaes

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
As of 300 PM Tuesday...

A fairly broad positively tilted upper level trough extending from the
eastern Great Lakes south into the northern Gulf Coast on Wednesday
morning will lift and shift east on Wednesday night. An associated
cold front approaching the southern Appalachians at daybreak on
Wednesday will move east across the Carolinas during the afternoon
and evening Wednesday before moving offshore Wednesday night.
Despite a fairly robust cold front and its associated forcing moving
across the area during a favorable time of day, convective coverage
will likely be a bit more limited than today. A more westerly flow, more
limited instabiilty with afternoon MLCAPE values generally 1000 J/Kg
or less, and a generally drier atmosphere will limit storm coverage.
With the trough approaching, a stronger flow is noted with 0-6km
shear values at or exceeding 40kts, but much of the strong flow is
confined above 3km. For now, will continue with chance PoPs for
scattered afternoon and evening storms with a potential for a few
strong storms. Highs will range in the lower 80s in the Triad and
mid to perhaps upper 80s elsewhere. Behind the front, temperatures
will cool into the 50s for Wednesday night. -Blaes

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 145 PM Monday...

In the upper-levels, a broad trough will slowly move from the TN
Valley Thursday, across the Mid-Atlantic Friday, then across the
Northeast Saturday. Weak ridging across the Mid-Mississippi Valley
Saturday will flatten as it moves east across the Carolinas on
Sunday, setting up zonal flow across the region. A weak shortwave
will move across the Mid-Atlantic late Sunday, then ensembles keep
NC under zonal flow through early next week.

At the surface, high pressure across the mid-Mississippi Valley and
central Plains will continue northerly flow and cold air advection
across central NC on Thursday. A weak low will develop off the SC
coast Thursday night, and move NE along the NC coast Friday morning
and afternoon. High pressure then builds across the Southeast
Saturday, shifting flow to westerly across NC. The high will push
off the coast and head toward Bermuda Sunday as low pressure and a
cold front move into the mid-Mississippi/Ohio Valley before
eventually pushing across central NC sometime Tuesday.

A more comfortable Thursday is on track with lower temperatures and
lower dewpoints behind the cold front on Wednesday. Dry weather is
expected Thursday, then isolated showers are possible across the
eastern half of the region on Friday as the surface low track along
the NC coast and the shortwave aloft moves by. Conditions look too
stable for now for thunderstorm development, and any showers that do
develop should exit east by Friday evening. Thursday and Friday
highs will be fairly similar, ranging from the upper 60s N to mid-
70s S. Fair weather is expected Saturday with highs still below
normal, then the surface high moving off the coast will help advect
a warmer and eventually a more moist airmass into the region early
next week. Most areas should remain dry Sunday, although the
approaching weak shortwave will create a small chance for showers
across northern areas later in the day on Sunday. Highs in the upper
70s to mid-80s are expected Sunday and Monday. Precipitation chances
increase Monday and Tuesday as the surface front approaches the area
and a few weak pulses move across the region aloft, however
confidence still remains low until the details come more together.
Tuesday looks more comfortable in the 70s behind the front with a
possible CAD setting up.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
As of 225 PM Tuesday...

After lingering morning stratus burned off in the Triad, mainly
clear skies and VFR conditions have dominated the weather across
central NC this afternoon. A band of showers and thunderstorms
across the Foothills early this afternoon will push east across
central NC this afternoon and evening. Expect good storm coverage
and high confidence of adverse aviation conditions with some
thunderstorms will be strong with possibly damaging winds. Storms
should impact the KINT/KGSO terminals from 19 to 22Z, the KRDU
terminal between 20 and 23Z, and the KFAY/KRWI terminals between 21
and 01Z. Expect improvement in aviation conditions this evening
before another small chance of a shower or storm overnight and a
limited risk of some SCT-BKN stratus with CIGS around 1500 feet
toward daybreak in the Triad. Aviation conditions will improve again
on Wednesday morning with widespread VFR conditions expected by mid
morning. Expect southwesterly winds at 10 to 15 kts with some gusts
of 20 to 25 kts this afternoon and localized gusts in excess of 35
kts in the strong storms. Gusts will abate overnight but a southwest
breeze at 8 to 10kts is expected for much of the night.

Outlook:  Another round of scattered showers/storms and associated
adverse aviation conditions is expected on Wednesday afternoon and
evening. Generally fair weather is expected for overnight Wednesday
through Thursday. There is a risk of some sub-VFR conditions late
Thursday into Friday as a storm system may develop and move up
along coast. Fair weather is expected on Saturday before another
front approaches late Sunday. -Blaes

&&

.CLIMATE...
Record HI-Min temperatures for 5/4 and 5/5:

GSO: 65 (2019) on 5/4 and 65 (2019) on 5/5
RDU: 68 (1938) on 5/4 and 67 (1950) on 5/5
FAY: 68 (1942) on 5/4 and 68 (2012) on 5/5

&&

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

&&

SYNOPSIS...Blaes
NEAR TERM...Blaes
SHORT TERM...Blaes
LONG TERM...JT
AVIATION...Blaes

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