700
FXUS62 KRAH 161816
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
216 PM EDT Tue Jul 16 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 1145 AM Tuesday...

...Dangerous and Near Record Heat To Continue...

...Heat Advisory Remains in Effect from Noon to 8 PM...

An upgrade to Excessive Heat Warning was strongly considered for the
Coastal Plain, given a continuation of record-breaking surface
through 850 mb temperatures observed across the srn Middle Atlantic
the past couple of days. Additionally, mean mixing ratio values have
increased 2 g/kg at RNK and GSO since 12Z Mon, indicative of less
mixing out of afternoon dewpoints today over the Piedmont, while
near steady, 17 g/kg will favor persistence dewpoints over ern NC.
Yet, multi-layered mid/high-level clouds have kept temperatures 2-7
F cooler on average than this time Mon; and these are likely to
persist into the afternoon and may consequently yield slightly lower
hourly and high temperatures, and heat index values, over all but
the srn Sandhills and srn Coastal Plain. Regardless of whether the
heat index values reach 108 or 110 F, it will remain dangerously
hot; and appropriate precautions should be taken.


.PREV DISCUSSION... /ISSUED 330 AM EDT Tue Jul 16 2024/

 There is very little to no change in the synoptic pattern and
antecedent airmass in place as subtropical ridging and Bermuda high
pressure unite to sustain dangerous and near record heat across the
region. Highs will be very similar to yesterday, in 95-100 range,
with heat indices ranging from lower 100s in the NW Piedmont to as
high as 109-110 across interior and eastern/southern portions. As
such, Heat Advisory has been issued for generally the same
climatological divisions across central NC.

PWATs are progged to inch up slightly to around 2.2-2.3" and there
remains a signal in the hi-res models that convective coverage
should be higher than recent days as weak upper impulses emanating
through the ridge and atop lee troughing could potentially help to
drive a west to east moving cluster of showers and storms across
central NC between 18 to 03z. Given the moist environment, some
locally heavy rain rainfall and minor flooding is possible. Also,
given the high CAPE/steep lapse rate environment, cannot rule out an
isolated strong/severe downburst.

Bulk of convection should dissipate by midnight. Balmy overnight
lows in the mid to upper 70s, except for some lower 70s across the
far northern Piedmont counties.


&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 330 AM Tuesday...

...One Last Day of Dangerous Heat....

Moisture will continue to increase in advance of an upper trough and
attendant cold front that will progress SEwd into the Ohio and Tn
Valley late Wednesday-Wednesday night. The influx of ~2.5" PWATs
into the area will result in an uptick in showers and storms
Wednesday afternoon and Wednesday night as another parade of vort
impulses spread through the region during max heating/
destablization. While the increase in cloud cover and PoPs will
temper the dry-bulb temps more into the lower/mid 90 ranges, there
will be less mixing out of afternoon dewpoints. Thus, we`ll see one
last day of heat advisory criteria of heat indices in the 103-107
range across much of the same area.

Deep layer shear is forecast to increase to ~25kts, which is higher
than recent days. As such, SPC has introduced a level 1/marginal
severe threat across the northern half of the forecast area, with
wind the primary threat.

Given the moist airmass and weak height falls starting to spread
into the region , convection could linger well into the overnight
hours. Lows in the 70s.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
As of 216 PM Tuesday...

* Widespread rainfall expected Thursday into Friday
* Unsettled weather continues this weekend into early next week
* Cooler temperatures from Friday through early next week

The forecast remains on track for widespread showers on Thursday as
a slow moving cold front arrives in central NC, stalls, and remains
in the vicinity through the weekend. The surface boundary will be
slow to move through the area given front-parallel flow aloft from
the southwest and as such, showers and thunderstorms will be slow
moving/prone to training over the same areas. PW`s will range from
1.75 to 2 inches immediately ahead of the front and showers will
certainly be efficient rain producers. Marginal amounts of
instability ranging from 500 J/KG in the NW Piedmont to upwards of
1500 J/KG will be present ahead of the front although deep layer
shear will only peak around 15-20kts and the severe weather threat
appears to be limited. Taking a look at the grand ensemble of
Canadian, GFS, and EC members, anywhere from 80-90 percent of
members advertise measurable precip across the area late Thursday
morning into the afternoon/evening hours, with a handful of members
suggesting more than 2 inches of rain Thursday afternoon through
Friday morning. 90th percentile NBM QPF is also in this range as
well, and PoPs will be increased a bit during this period. Exact QPF
amounts are still a challenge to pin down but the highest amounts
should fall across the central/eastern portions of NC.

The front will stall across eastern NC on Friday, then slowly
retreat northwestward through the afternoon/evening. While the day
may start off mostly dry, showers will quickly redevelop across the
Coastal Plain and Sandhills by mid morning, then expand
northwestward as the front shifts back over the NW Piedmont. Once
again, nearly 80-90 percent of ensemble members indicate precip
during this period and PoPs will be bumped upward through early
Saturday morning. It`s conceivable an additional 1-2 inches of rain
could occur during this period although it`s hard to say with
certainty where this secondary QPF axis will set up as the front
retreats through the area. Regardless, Thursday and Friday should be
the wettest days of the forecast with periods of heavy rain and
flooding possible. Temps during the day Thursday will remain near or
above normal ahead of the front, turning noticeably cooler on Friday
given cloud cover and rain with highs generally 5-8 degrees below
normal.

Looking at Saturday through Tuesday, ridging over Bermuda will
gradually strengthen and shift westward, resulting in a return to a
fairly typical July distribution of precip chances with the highest
chances across the western Piedmont and a secondary focus area from
sea breeze convection migrating inland. Temperatures will remain
below normal this weekend, gradually moderating closer to normal by
early next week.

&&

.AVIATION /11Z MONDAY THROUGH SATURDAY/...
As of 630 AM Tuesday...

Shower and storm coverage this afternoon and evening is expected to
be higher than the past couple of days, with a general consensus
that a cluster of storms will move west to east across the area
between 18 to 00z. Have added a prob30 for all TAF sites. Convection
should dissipate between 03 to 06z.

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

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


Record High Minimum Temperatures:

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 today to 8 PM EDT this evening for
NCZ007>011-023>028-039>043-073>078-083>086-088-089.

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS/CBL
SHORT TERM...CBL
LONG TERM...Leins
AVIATION...CBL/Luchetti
CLIMATE...RAH