082
FXUS62 KRAH 151452
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1051 AM 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 300 AM Monday...

Remaining under the influence of the subtropical ridging aloft and
Bermuda high pressure in the lower levels, PWATs increase 2.2-2.3"
across the area Tuesday. Rain chances should be up from previous
days, more in the climatological ranges(~40%), as models suggested a
noted increase in the potential for weak perturbations to move
through the region. While the increase in cloud cover and rain
chances should temper high temps 2-3 degrees, the higher
humidity/dewpoints should offset the slightly cooler temps to yield
similar heat indices in the 105-109 range. Thus, additional Heat
Advisories will be needed be much of the same areas.

Given the moist airmass, convection could linger well into the
overnight hours. Balmy overnight lows in the mid to upper 70s.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 345 AM Monday...

A classic very wet pattern and heavy rain threat will set up across
central NC for the extended period. PW values increase further on
Wednesday to 2-2.5 inches as mid-level troughing digs into the Great
Lakes and southern Canada, turning the flow aloft over central NC
more southwesterly. This will also shunt the western Atlantic
ridging farther east and begin to gradually lower heights. At the
surface, a strong cold front will stretch from the northern Mid-
Atlantic to the southern Appalachians by Wednesday night, as low
pressure over southern Canada enhances the lee trough over the Mid-
Atlantic. While the best forcing for precipitation will still be to
our north and west, shower and storm coverage should still be fairly
widespread, highest NW in closest proximity to the front.
Temperatures will be kept down a bit from the clouds and
precipitation, but it will still be quite warm and humid with little
drop in thicknesses. Forecast highs are mostly mid-90s and heat
indices around 105 from around the Triangle south and east. Low
temperatures Wednesday night won`t provide a lot of relief, only
dropping to the mid-to-upper-70s.

Thursday and Friday look to have the best chance for heavy rain in
the period as the cold front reaches central NC and slows down. Deep
southwesterly flow aloft ahead of broad mid-level troughing that
digs from the Northeast US into the lower MS Valley will continue to
bring in above-normal PW values. So there will be plenty of moisture
for this front to tap, along with moderate instability of around 500-
1500 J/kg. The vast majority of GEFS/EPS/CMC ensemble members depict
precipitation. Thus likely to categorical POPs are justified,
maximized with daytime heating in the afternoon/evening, though
chance POPs still linger overnight. WPC now has a slight (level 2 of
4) risk for excessive rain on Thursday from roughly US-1 eastward in
NC where the frontal progression looks slowest, with a marginal
(level 1 of 4) risk elsewhere. The greatest POPs shift to the south
and east on Friday as the front settles near the NC/SC border.

The front may retrograde back NW a bit on Saturday and Sunday, and
likely POPs continue each day. However, overall rainfall amounts may
decrease slightly as the front starts to wash out and upper support
wanes, with Atlantic ridging building back westward. Ensemble mean
QPF from Thursday through Sunday is generally 2 to 3 inches,
greatest south and east, and of course locally higher amounts will
always be possible where storms occur. While so much rain for
multiple days in a row will cause some flooding concerns, it will
provide more welcome drought relief. It will also help bring down
high temperatures to upper-80s to lower-90s on Thursday (near
normal) and only upper-70s to mid-80s on Friday and Saturday. A
slight warming trend may commence on Sunday. Lows will be in the
upper-60s to lower-70s. Fortunately widespread severe weather is not
a major concern during the period given the weak shear.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...
As of 630 AM Monday...

Patchy ground fog at KRWI will quickly dissipate.

Isolated to widely scattered showers/storms will develop again this
afternoon, with best chances near KFAY as convection along the sea
breeze penetrates inland.

Outlook: Isolated storms remain in the forecast early this week, but
generally VFR is expected. A better chance of widespread showers and
storms, and thus flight restrictions, occurs in the Wed-Fri period
as a front settles into the region.

&&

.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 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...CBL
LONG TERM...Danco
AVIATION...CBL/Kren
CLIMATE...RAH