441
FXUS62 KRAH 151930
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
330 PM EDT Mon Jul 15 2024

.SYNOPSIS...
A strong subtropical ridge will gradually weaken over the Southeast
though mid-week. A cold front will settle into the Carolinas on
Thursday, then become quasi-stationary while weakening into the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1050 AM Monday...

The Heat Advisory has been upgraded to Excessive Heat Warning for
the southern and central Coastal Plain, ern Sandhills, and Wake Co.,
where observed heat index values on Sunday were 108-112 F. Given
that forecast temperatures today will be hotter than those of Sunday
(by ~3 F on average) and with similar mixed afternoon dewpoints,
heat index values today should tick similarly higher. The forecast
remains otherwise unchanged from the previous one.

.PREV DISCUSSION... /ISSUED 300 AM EDT Mon Jul 15 2024/

...Heat Advisory Has Been Expanded to include the Southern
Piedmont...

...Record Breaking Temperatures...

Subtropical ridging atop offshore Bermuda high pressure with a lee
troughing along the eastern slopes of the Appalachians will persist
through mid week.

Models continue to indicate that the heat will build ever so
slightly today as h8 temps warm from 22C to 23C and low-level
thicknesses increase 1442m to 1447m. This should translate into 1-2
degrees of warming with record breaking high temps expected at 2 of
our 3 climate sites(GSO and RDU) as most locations warm into the
upper 90s, with some triple digits/lower 100s possible in the
typically warmer locations. Meanwhile, the soupy dewpoints will
continue to pool across the eastern half of the forecast area, which
will exacerbate the effects heat and lead to heat indices of 105 to
109 degrees. Have expanded the Heat Advisory into the southern
Piedmont counties, which now encompasses all but 4 of our
northern/northwest Piedmont counties.

We will see another day of isolated to widely scattered diurnal
showers and storms, with the lee trough, seabreeze, and weak
perturbations moving off the higher terrain providing the foci.

Convection will fizzle out after loss of heating with dry conditions
overnight. Muggy lows in the mid to upper 70s, with little to no
overnight relief from the heat.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 320 PM Monday...

...A heat advisory has been issued for Tuesday from 12 PM to 8
PM...

...Little overnight recovery from dangerous afternoon heat increases
the risk for heat related illnesses...

Dangerous heat will certainly be possible Tues as the persistently
hot and humid airmass remains in place over central NC. High
temperatures again will quickly rise into the upper 90s to around
100 degrees, with heat index values of 100 to 109 expected. Low-
level thicknesses and 850mb temperatures will be relatively
comparable to Mon, but the biggest question mark is the degree of
cloud cover through the early afternoon. A mid/upper level
anticyclone just off the Southeast coast will sag south and east by
Mon morning and help draw in increased PWAT values of 2 to 2.25
inches by Tues afternoon. This increased moisture may facilitate
greater cloud cover as well as earlier storm initiation and greater
storm coverage by early afternoon. These factors may result in some
areas not reaching heat advisory criteria, but the locations that
miss out on storms and cooling convective outflow will likely
experience dangerous heat on Tues within the advisory area.

Additionally, multiple days of dangerous heat and little to no
overnight recovery only exacerbate the potential for heat related
illnesses if proper precautions are not taken. Anyone without
effective cooling or adequate hydration will be at greatest risk.

Storm coverage could be greater on Tues given the potential for more
efficient updrafts, but severe threat continues to be limited given
weak deep layer shear (around 15 kts 0-6km shear). Strong wind gusts
from wet downburst will be possible as well as isolated instances of
minor flooding given slow storm motions and deep warm cloud layer.
Training storms over the same area will likely be required to cause
any flash flooding.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
As of 315 PM Monday...

The long term period is shaping up to be unsettled each day, and
potentially wet on Thursday and Friday.  The period will start off
Wednesday with a trough digging and moving east over the Great Lakes
region.  A sfc front during this time will be moving across the Ohio
Valley.  Meanwhile, over our region, moist sw flow, pwat well over 2
inches, along with an ongoing Piedmont trough will set the stage for
scattered showers and tstms during the afternoon and evening.  Until
these storms move through, look for highs to quickly climb into the
mid 90s with heat index values in excess of 100 across much of the
state and possible heat advisory criteria across the eastern half of
our CWA.

Thursday and Friday still look to be the wettest days in the long
term period with the aforementioned front moving into our area and
tapping the moist air mass thats in place.   Given the slow-moving
nature of the front, there could be slow-moving and repetitive
showers/tstms both days.   The latest WPC ERO for these two days
basically show marginal across the western half of the state and
slight across the eastern half of the state, while marginal exists
across the entire state on Friday.  Given the anticipated cloud and
shower/tstm coverage, temps will be cooler both days with highs in
near 90 on Thursday and perhaps mid 80s on Friday.

The upper trough will gradually lift out over the weekend and by
Monday the ridge will become re-established over the Southeast.   As
such, the late-week front will lift back to the north and become
stationary invof the VA/NC border by late in the weekend and for
Monday. That boundary, along with the typical Piedmont trough over
the area, will result in daily mostly-diurnal aoa climo PoPs each
day Sat through Mon.  Temps during this time may continue to be held
back by cloud cover, so will lean toward lower end of the temp
guidance envelope, with highs in the upper 80s to around 90.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
As of 210 PM Monday...

Widely scattered convection will continue to develop with afternoon
heating/destabilization and focus along a pronounced lee surface
trough and associated sharp moisture gradient - evident in
observational data for the past few hours from near IXA to RDU to
CLT. While VFR primarily VFR conditions and light swly surface winds
are otherwise forecast through the 18Z TAF period, patchy fog/mist
will once again be possible at RWI Tue morning.

Outlook: Mainly VFR conditions are expected to continue away from
diurnally-driven convection, which will gradually increase in
coverage through Wed. A cold front will move into NC late Wed-Wed
night, then become quasi-stationary over the region Thu-Sat. Higher
chances of flight restrictions, both in and away from diurnally-
maximized convection, will consequently result Thu-Sat.

&&

.CLIMATE...
Record High Temperatures:

July 15:
KGSO: 97/1974
KRDU: 99/1997
KFAY: 106/1932

July 16:
KGSO: 99/1915
KRDU: 101/1887
KFAY: 103/1937

July 17:
KRDU: 100/1887
KFAY: 102/1932


Record High Minimum Temperatures:

July 15:
KGSO: 74/2019
KRDU: 76/1992
KFAY: 78/2015

July 16:
KGSO: 75/2010
KRDU: 77/2010
KFAY: 78/1992

July 17:
KGSO: 75/2013
KRDU: 80/1887
KFAY: 77/2019

July 18:
KGSO: 76/1986
KRDU: 79/1887
KFAY: 77/2019

July 19:
KGSO: 75/2016
KFAY: 77/2023

July 20:
KGSO: 75/2019
KRDU: 76/2020

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon to 8 PM EDT Tuesday for NCZ007>011-
023>028-039>043-074>078-083>086-088-089.
Heat Advisory until 8 PM EDT this evening for NCZ008>011-
023>028-039-040-043-073>076-083>086.
Excessive Heat Warning until 8 PM EDT this evening for NCZ041-
042-077-078-088-089.

&&

$$

SYNOPSIS...MWS
NEAR TERM...MWS/CBL
SHORT TERM...Swiggett
LONG TERM...np
AVIATION...MWS
CLIMATE...RAH