798
FXUS62 KRAH 061839
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
239 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 AND TUESDAY NIGHT/...
As of 330 AM Monday...

The aforementioned dampening trough will move off the mid-Atlantic
coast during mid to late morning. Synoptic scale subsidence will
overspread the area in it`s wake, with a westerly downslope
component noted over the area. However, moisture/PWATS will remain
exceptionally high as strong insolation fuels moderate instability
during the afternoon. Discernible forcing is weak, limited to
daytime heating, weak sfc convergence along a lee side trough across
the area, and quite possibly a subtle upper perturbation with the
back/anticyclonic side of the exiting trough. If storms do develop,
sufficient deep layer shear of 30-35 kts could support an isolated
severe storm, with damaging winds the primary threat. Warmer with
highs ranging from mid 80s north to upper 80s/near 90 south.

Convection will dissipate after sunset. Lows 65-70.

&&

.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...CBL
LONG TERM...Luchetti
AVIATION...MWS
CLIMATE...RAH