-- Discussion containing changed information from previous version are highlighted. --
566
FXUS62 KRAH 070137
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
935 PM EDT Mon May 6 2024

.SYNOPSIS...
A series of mid to upper-level disturbances will interact with an
unseasonably moist airmass as they move across NC through Thursday,
while sub-tropical high pressure will otherwise extend across the
South Atlantic states. A cold front will move across the region on
Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 935 PM Monday...

An area of showers and isolated thunderstorms that tracked across
much of the northern half of the forecast area is currently falling
apart around Rocky Mount, while another broken line of showers and
thunderstorms extending from Myrtle Beach to Charlotte and eastern
Tennessee is now approaching from the west. An increasing low-level
temperature inversion should reduce the amount of instability for
thunderstorms, but still think that thunderstorms will be a
possibility through the night, although severe potential is minimal.
The observed precipitable water value from the 00Z GSO sounding was
1.18 inches, just over the 75th percentile for the date, meaning
that the showers/thunderstorms could be efficient rain makers as
well. Expect another muggy night with overnight temperatures in the
low to mid 60s.
-- End Changed Discussion --

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 340 PM Monday...

Tuesday and Tuesday night: Aloft, as the s/w moves east and off the
mid-Atlantic coast, a brief period of omega blocking will set up as
the sub-tropical ridge builds northward through the Southeast US,
central Appalachians, OH Valley and western Great Lakes. To the east
of the block, a low will progress eastward through Quebec and
Newfoundland Tue, then out over the northern Atlantic Tue night. To
the west, a large low will sit over the northern Plains as several
s/w disturbances rotate around it. The eastern low progressing
eastward Tue night will weaken the block, allowing a leading s/w
moving through the OH Valley around the western low to push the
ridge slightly eastward and suppress it southward. At the surface, a
warm front will lift newd through the area early Tue, with a
Piedmont trough setting up east of the mtns and strengthening
through Tue night as a low develops over the southern Great Lakes.
Expect continued advection of warm, moist air into the area, with
PWATS starting the day around 1.7 inches, decreasing slightly with
daytime mixing, but remaining largely in the 1.4-1.6 inch range. The
12Z NAM and 12Z GFS both have MLCAPE values of about 1000-2000 J/Kg
(GFS lower than the NAM) across all of central NC Tue aft/eve, with
effective shear around 30 kts. The SPC has included just about all
of central NC in a marginal risk for Tue. The big question will be
the presence of a forcing mechanism to get storms firing. Look for
showers/storms to largely form along the developing lee trough
and/or differential heating boundaries if they are present. An
isolated strong to severe storm is possible, with the primary threat
of damaging wind gusts and possibly hail. As for temperatures, highs
should top out in the mid to upper 80s, while lows in the mid 60s to
around 70 degrees are expected.

Wednesday and Wednesday night: Aloft, the leading s/w will continue
eastward through the Northeast US toward the eastern low, while the
western low finally begins to migrate slowly eastward. A second s/w
will swing through the Plains and the MS Valley Wed/Wed night. At
the surface, the surface low will move slowly eastward through the
Northeast US Wed and offshore Wed night. Another low will develop
along the front over the southern Plains early Wed, lifting newd
into the upper MS Valley through Wed eve before drifting eastward
into the OH Valley Wed night. The trough over central NC will weaken
and lift northward out of the area as the low move east and offshore
Wed night. The frontal zone between the two lows should generally
remain north of the area through Wed night, with continued swly flow
over the area. Expect continued advection of warm, moist air into
the area, with PWATS largely in the 1.4-1.7 inch range. The 12Z NAM
and 12Z GFS both have MLCAPE values of about 1500-2500 J/Kg across
all of central NC Tue aft/eve, maximized over the eastern Piedmont
and Coastal Plain, with effective shear again around 30 kts. The SPC
has included all of central NC in a marginal risk for Wed. The
forcing mechanism will likely be the lee trough as it moves eastward
through the area. An isolated strong to severe storm will once again
be possible. As for temperatures, highs should be about a category
higher than Tue, topping out in the upper 80s to low 90s. Lows
should be in the upper 60s to low 70s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 202 PM Monday...

Thursday/Friday: There is good consensus amongst models supporting
an upper trough moving east from the Great Lakes/Midwest across the
eastern seaboard Thursday into Friday. This feature will promote
increasingly swly flow and deep moisture advection into the
southeast with PWAT rising to 150 to 200 % of normal.

At the sfc, a weak low initially over IN/OH Thursday morning, will
deepen some as it progresses east into the Mid-Atlantic through
Thursday night. An associated cold front will approach the Southern
Appalachians Thursday night, before passing through central NC on
Friday. Given high humidity and temperatures reaching the upper
80s/lower 90s on Thursday, moderate instability is expected to
develop across our area ahead of the approaching front.

Aloft, increasing mid-level height falls and associated
perturbations will help to generate widespread pre-frontal showers
and storms which should grow in coverage/intensity Thursday
afternoon. Additionally, severe parameters including bulk-layer
shear (30 to 40 kts), 0-1 km shear (15 to 25 kts), mid-level lapse
rates (>7 C/km), and even helicity (200 to 300 units) will all be
elevated.  As such, there still appears to be a good chance for
severe weather (potentially widespread) Thursday and Thursday night.
Damaging wind gusts, large hail, and isolated tornadoes would all be
possible. The SPC has outlined our entire area with a 15% chance for
severe storms four days in advance, increasing confidence that
Thursday could be a complex severe weather day.

Depending on the eventual evolution of the cold front, some guidance
does show instability forming ahead of the front as it moves through
our area on Friday. As such, maintained thunder in the forecast for
those south of Raleigh on Friday. Additionally, the upper trough
will swing through on Friday which could generate additional
showers/storms into the evening period.  Highs on Friday may be a
bit tricky given uncertainty wrt to the advancing cold front. For
now, highlighting mid to upper 70s north to lower to mid 80s south.

Saturday through Monday: The cold front will have pushed east of the
area by Saturday morning, behind which considerably drier and cooler
air will filter across central NC.  An additional weak perturbation
aloft will pass over later Saturday which may generate a few showers
across our northern areas, but overall the area should stay mostly
dry. Similar conditions are expected Sunday through Monday, with dry
and cooler temps in the upper 70s.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
As of 840 PM Monday...

There is a chance of showers/storms overnight, with mostly
associated MVFR to IFR CIGS/VSBYS with a disturbance arriving from
the west. Otherwise, continued unseasonably humid air will also
favor the redevelopment of areas of IFR-MVFR stratus late tonight-
Tue morning. Associated ceilings should then lift and scatter and
yield to a gusty swly surface wind by ~14-16Z Tue.

Outlook: There will be a chance of mainly afternoon-evening showers
and storms throughout cntl NC through Thu, then ahead of a passing
cold front, mainly at FAY, on Fri.
-- End Changed Discussion --

&&

.CLIMATE...

Record High Minimum Temperatures:

May 8: KGSO: 66/1938 KRDU: 68/1930 KFAY: 70/2003

May 9: KGSO: 68/2002 KRDU: 70/1936 KFAY: 71/2009

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...Green
SHORT TERM...KC
LONG TERM...Luchetti
AVIATION...pwb/MWS
CLIMATE...RAH