-- Discussion containing changed information from previous version are highlighted. --
794
FXUS62 KRAH 061943
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
343 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/...
As of 1055 AM Monday...

The gridded morning forecast update was sent with just minor tweaks
to what should be another day of warm and unseasonably humid
conditions, with scattered to numerous convection that will come in
waves and may last through the night.

Both the GSO and MHX 12Z-observed soundings sampled minimal
convective inhibition and an already weakly unstable environment
over NC this morning. Showers and storms are consequently expected
to become numerous in coverage with additional diurnal heating and
destabilization through the afternoon, probably first associated
with ongoing clusters and weak MCVs moving newd from w-cntl SC/ern
GA and into the srn NC Piedmont.

.PREV DISCUSSION... /ISSUED 330 AM EDT Mon May 06 2024/

A shortwave trough over the middle MS Valley will deamplify as it
advances eastward, progged to reach the central and southern
Appalachians this evening and then across NC and the mid-Atlantic
States tonight. A weak area of low pressure is expected to develop
over Va during the afternoon and evening, with a surface trough
taking shape in the lee of the mountains. Renewed SWLY moisture
advection ahead of this trough will lead to a resurgence of
anomalous moisture into the region with PWATs 1.6-1.8, near record
daily maximum.

A parade of upper disturbances will move through the region during
the period. And based on upstream radar observations, there is a
high probability that a prominent MCV or two will emerge to support
a west to east moving band of deep moist convection(DMC),
potentially multiple bands, through the afternoon and evening.

Compared to previous days, more robust instability of 1000-1500 J/Kg
should develop across the area, likely maximized east of US 1 where
strongest insolation is expected. Shear will increase slightly, with
models indicating a pocket of enhanced shear of 25-30kts into
western NC late this afternoon and evening. Thus, cannot rule out an
isolated severe cluster or two Monday afternoon and evening. As
we`ve seen the past few days, the anomalous high moisture in place
will also support an isolated flooding threat, primarily in urban
and poor drainage areas.

Rain chances should decrease by the late evening, though some
lingering isolated convection overnight owing to the dampening upper
trough moving through the region.

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

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.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 /18Z MONDAY THROUGH SATURDAY/...
As of 235 PM Monday...

Patches of MVFR ceilings from earlier lower ones may linger for
another hour or two but otherwise lift to VFR this afternoon.
Scattered to locally numerous showers/storms --and associated brief
downpours, flight restrictions, and gusty surface winds-- will
then pose the primary aviation concern through early tonight.
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.

&&

.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...MWS/CBL
SHORT TERM...KC
LONG TERM...Luchetti
AVIATION...MWS
CLIMATE...RAH