737
FXUS64 KHUN 021654
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1154 AM CDT Tue Jul 2 2024

...New AVIATION...

.NEAR TERM...
(Rest of Today)
Issued at 1059 AM CDT Tue Jul 2 2024

A strong subtropical high (centered across the Arklamiss region
earlier this morning) is predicted to expand east-northeastward
into the TN Valley over the course of the day, resulting in drying
profiles aloft and the development of a pronounced mid-level
subsidence inversion that will inhibit the development of
convective updrafts today. In the low-levels, moderately strong
SSE flow of 10-15 MPH (with occasional gusts up to 20 MPH) will
exist as a ridge noses southwestward around the base of the
southern Appalachians from a parent surface high over the northern
Mid-Atlantic states. A shallow layer of enhanced low-level
moisture advection in this regime has contributed to widespread
low stratus clouds across the eastern half of the forecast area.
The clouds should be slow to erode over the course of the
afternoon and we have increased sky cover in this region and
reduced the max temperature forecast to reflect highs in the
u80s-l90s. Based on current satellite data, broken-overcast
conditions appear unlikely to reach northwest AL, where highs will
reach the mid 90s (with HI values in the 100-105F range).

&&

.SHORT TERM...
(Tonight through Thursday Night)
Issued at 250 AM CDT Tue Jul 2 2024

The aforementioned upper ridge will persist through midweek, but
begin to flatten Wednesday night into Thursday as a shortwave
trough makes its way over the north-central CONUS and into the
Midwest. Surface high pressure will be shunted off the eastern
seaboard but be stretched a bit, maintaining its hold over the
Appalachians. This is due to the approach of a cold front (over
the Midwest on Wednesday) that looks to stall over the mid-
Mississippi Valley and Ohio Valley Wednesday night and Thursday.

Chances of showers and storms steadily increase from midweek on,
with very low chances (10-20%) on Wednesday to low to medium
chances (30-50%) on Thursday (highest chances during peak heating
in the afternoon each day). As has been the trend with model
guidance the past couple of days, instability looks plentiful but
shear will be meager. Therefore, while severe weather is not
anticipated, storms will have the potential of producing brief,
heavy downpours, lightning, and some gusty winds (usual of the
summertime).

The other, and honestly biggest, concern will be the heat for
both Wednesday and Thursday (Independence Day). Highs are forecast
to reach the lower to mid 90s, with some spots in the upper 90s,
both days. This, combined with elevated moisture and warm
overnight temperatures (in the 70s Tuesday through Thursday
nights) will lead to areas along/west of I-65 on Wednesday and
most of the area on Thursday being in a major risk of heat-related
impacts according to the NWS HeatRisk tool. Looking specifically
at heat indices, we`re likely facing between 105-109 degrees
especially along and west of I-65 on Wednesday and between 103-110
degrees area-wide on Thursday. This may necessitate a Heat
Advisory for portions of the area on Wednesday and perhaps an
Excessive Heat Warning on Thursday should these trends continue.
Stay tuned, but in the meantime, please take the heat risk
seriously this 4th of July holiday! Plan ahead for dangerous heat
conditions! Take frequent breaks in the shade, wear loose-fitting
and light-colored clothing, and stay hydrated!

&&

.LONG TERM...
(Friday through Monday)
Issued at 250 AM CDT Tue Jul 2 2024

The center of the high pressure ridge that will bring us the
dangerous heat earlier in the week will become squeezed to the SE
of the area over the GA/SC/NC coast. To our north, a fairly robust
mid/upper trough will swing from the northern Plains into the
Great Lakes, with its associated cold front pushing from the mid-
Mississippi and lower Ohio Valleys into the Tennessee Valley and
Deep South region on Friday. Ahead of the front, southerly flow
will once again push temperatures into the low to mid 90s -- with
dewpoints in the mid/upper 70s pushing heat index values above 105
degrees once again. By the afternoon however, the front will be
approaching the area with SBCAPE values around 2500-3000 J/kg.
Subsequently, the forcing mechanism will be in place to trigger
high chances (70-80%) for showers and thunderstorms -- some of
which could be strong.

The boundary will slowly sag south through the area into central
Alabama by Saturday. However, since it will remain in the vicinity
of the area medium chances for showers/storms (40-60%) will
remain in the forecast for Saturday. Cloud cover will help to keep
temperatures just a few degrees lower, likely keeping heat
indices below Advisory criteria. With the boundary to our south
Sunday and Monday, much lower chances for showers/storms are
forecast (10-20%) with highs remaining near normal in the lower
90s. The combination of these lower temperatures and dewpoints
should keep peak heat index values below 100 degrees through
Monday.

&&

.AVIATION...
(18Z TAFS)
Issued at 1154 AM CDT Tue Jul 2 2024

Low stratus clouds (within a moderately strong SSE flow regime)
persist across the eastern half of northern AL late this morning,
with latest satellite data indicating that the clouds are slowly
spreading west-northwestward toward MSL. Although cigs may remain
in the MVFR category for another 1-2 hours at HSV, deeper mixing
this aftn should promote scattering and gradual lifting of the
cloud layer, and we will advertise VFR conditions at the beginning
of the TAF. Forecast soundings suggest that skies will partially
clear around sunset, but that lower stratus will return between
Midnight and sunrise on Wednesday. Periods of MVFR cigs will be
possible at both terminals btwn 11-15Z, but this has not been
indicated in the official forecast attm. Sfc winds will remain
from SSE at 8G16 kts this aftn, but should weaken to 5-10 kts
around sunset and veer to SW after 12Z Wednesday.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...None.
TN...None.

&&

$$

NEAR TERM...70/DD
SHORT TERM...26
LONG TERM...AMP
AVIATION...70/DD