331
FXUS62 KRAH 300623
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
223 AM EDT Sun Jun 30 2024

.SYNOPSIS...
Bermuda high pressure will remain locked in over central NC this
weekend. A cold front will push through the area Sunday night into
Monday.  Post-frontal high pressure will extend into the southeast
Monday and Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 940 PM Saturday...

A Heat Advisory remains in effect through Sunday for all but the nw
Piedmont and part of the srn Piedmont in cntl NC.

Afternoon-evening satellite data depict a couple of areas of
concentrated and persistent cumulus along 1) a quasi-stationary lee
trough/convergence axis from near CAE in SC nwd to near and just
west of AFP, VUJ, and EXX in cntl NC and 2) a nwwd-retreating sea
breeze evident in regional radar data from PTB in srn VA to RDU to
TTA in cntl NC. Each may continue to focus isolated to widely
scattered showers/storms until the sea breeze and following clearing
move nwwd and through the wrn/nwrn NC Piedmont through 05-06Z, based
on an extrapolation of its current speed of ~12-14 kts.

A prominent inversion evident around 15 thousand ft AGL on the GSO
and MHX RAOBs this evening seems to be limiting updraft depth and
intensity, given that 45-50 dbz or greater reflectivity has been
confined at and below that inversion level. So while no strong to
severe storms are expected, isolated locations may receive 0.5"-
1.00" of rain, as has been the case over cntl Moore Co. in the past
90 minutes, per MRMS data.

It will otherwise be quite warm and muggy overnight, with
temperatures slow to fall below 80 F and likely to only reach 75-80
by sunrise. In fact, temperatures even at 01Z were still at or above
90 F across the Triangle (90 at TQV and 91 at RDU) and in the upr
80s in the nw Piedmont/Triad (88 at INT and 87 at BUY).

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 142 PM Saturday...

The Heat Advisory has been extended for Sunday and to include the
southern/northeast Piedmont. Heat indices could be as high as 108 in
portions of the advisory area.

A shortwave trough over eastern Canada is forecast to reach the
northern Mid-Atlantic by early Mon. At the surface, a pre-frontal
lee trough will setup along the southern Appalachians during the
day. A cold front will then approach from the north and west
overnight Sun night into early Mon morning as high pressure builds
into the OH valley.

Prior to the onset of showers and storms, a very warm and humid
airmass will be entrenched over the area with broad southerly flow.
This should result in higher dewpoints with low to mid 70s. Combined
with highs in the low to mid 90s, and perhaps some upper 90s over
the Triangle, will result in heat indices between 103 and 109. As a
result, we expanded the advisory to cover much of the region
along/east of US-1.

As for the shower/storm potential, most of the models and high-res
guidance is indicating two potential waves of activity. The first
chance would come along the lee trough and become an effective
front, generating showers and storms during peak heating. These
storms would then track ESE from the NW Piedmont into the Coastal
Plain between about 2 PM and 8 PM. This first wave has the best
potential to be severe, with damaging winds the main threat,
resultant of high instability, 20-25 kts of shear, and the potential
for wet microbursts. The highest severe risk would appear along the
northern sections of central NC, where shear is highest along the
mid-level trough axis.

CAMs are showing a secondary wave of showers/storms late Sun night
along the actual cold front, that could produce additional activity
mainly from the Triangle/Sandills and points east. This wave should
not be severe given the time of day it will be moving through.

On top of the heat and severe risk, there is also a marginal risk
for excessive rainfall. While we have been very dry the past several
weeks, several factors are lining up where isolated flash flooding
is a concern. Precipitable water values range from 2.2 to 2.5
inches, well above the maximum for the end of June. Additionally,
slow storm motion and a deep warm cloud layer exists, favorable for
high rainfall rates in slow moving storms. The latest probability
matched mean from the HREF suggests the potential for 2+ inches for
some areas along/east of US-1. While this will not be widespread,
the potential is there given the above factors, especially over
urban areas. Overnight lows Sun night are expected to be in the mid
60s NE to low 70s SW.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 222 AM Sunday...

Aloft, the mid-level anticyclone will once again build into the
region from the west, sitting over the TN Valley/Deep South Tue and
Wed. A series of northern stream s/w disturbances will track
eastward from the northern Plains through the Great Lakes/OH Valley
from Tue through Sat, with each successive s/w slowly suppressing
the high southward. However, the high should generally remain over
the Deep South and Southeast US through Sat. At the surface, as the
high moves eastward through the Northeast/northern mid-Atlantic
Tue/Tue night, it will continue ridging southward into the area.
Once the high moves out over the Atlantic on Wed the ridge will also
shift east out of the area, with a lee trough developing Wed night
and remaining in place through Sat. Expect swly flow and the
advection of warm, moist air into the area to take over once again.
Temperatures may actually be near to slightly below normal Tue, but
once the warm advection commences on Wed, they will quickly rise
back above near/slightly above normal Wed and be well above normal
by the end of the week. As for rainfall, as the mid-level ridge
gradually gets suppressed south and the lee trough strengthens, some
diurnally driven convection will be possible Thu, but more likely
Fri and Sat aft/eve. Latest forecast heat index values do creep back
to around 105 again in a few spots on Thu. Heat index vaues of 105
to 109 becoming greater in coverage (much of central NC) for Fri and
Sat.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
As of 145 AM Sunday...

Generally VFR conditions will mostly prevail through the morning,
but some guidance shows potential for low stratus early this morning
around KFAY. Sunday afternoon about 17z to 00z, scattered to
possibly numerous thunderstorms are expected ahead of a cold front
and move E/SE from the NW Piedmont into the Coastal Plain. Brief
gusty winds, heavy rain and sub-VFR ceilings and visibilities are
possible with any storm. Outside of storms, winds will generally be
around 10-15 kts, veering slightly from southerly this morning
to more southwesterly today.

Beyond 00z-06z Monday: Showers and thunderstorms will continue to
push east through central NC into the evening hours. A few storms
could be strong to locally severe.

A secondary surge of weaker showers/storms with associated sub-VFR
ceilings and visibilities will be possible along the passing cold
front late tonight in the east.

VFR conditions should return Tuesday and Wednesday as dry high
pressure extends into central NC.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT Sunday for NCZ008>011-024>028-
040>043-075>078-083>086-088-089.

&&

$$
SYNOPSIS...Luchetti
NEAR TERM...MWS
SHORT TERM...Kren
LONG TERM...KC
AVIATION...Badgett/Danco