119
FXUS64 KHUN 170829
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
Issued by National Weather Service Jackson MS
329 AM CDT Wed Jul 17 2024

...New NEAR TERM, SHORT TERM, LONG TERM...

.NEAR TERM...
(Today)
Issued at 329 AM CDT Wed Jul 17 2024

A warm and moist air mass resides across the TN Valley early this
morning, featuring temps ranging from the u60s-l70s (E) to
u70s-l80s (W). With dew points in the lower 70s and only a few
high-level clouds overhead, locally dense fog has developed in the
valleys of northeast AL, and an SPS for visibility reductions may
be needed prior to the end of the shift.

On the synoptic scale, a pattern change is currently underway as
WSW winds aloft are beginning to strengthen in response to a
strong northern stream trough digging southeastward into the
northern Great Lakes. This trend will persist today as the trough
advances eastward across southern Ontario, resulting in
consolidation of a downstream surface cyclone across northern New
England/southern Quebec. Clusters of showers and thunderstorms
continue early this morning both in the vicinity of the cyclones
trailing cold front (to our NW) and convective outflow boundaries,
and we will need to monitor for development of thunderstorms to
our north prior to sunrise as one such boundary drifts
southeastward into Middle TN. Additional showers and thunderstorms
may develop within a conditionally unstable air mass (featuring
MUCAPE up to 1000-1500 J/kg) and region of enhanced low-level warm
advection and moisture transport across central AL, and this
activity may clip our southeastern zones prior to sunrise as well.

Over the course of the late morning, the combination of lower-
tropospheric warm advection and a rapidly destabilizing boundary
layer will result in a development of scattered thunderstorms
across northern AL. However, through mid-day, the greatest
concentration of convection will likely remain to our north. By
this afternoon, the outflow boundary will slip southward into AL,
enhancing the coverage of storms region-wide between 18-00Z. With
temps in the lower 90s supporting CAPE in the 1500-2500 J/kg range
and a gradual increase in flow aloft/deep-layer shear, a few
strong multicell clusters will be possible, capable of producing
locally damaging wind gusts (up to 50-60 MPH), small hail and
frequent lightning.

&&

.SHORT TERM...
(Tonight through Saturday)
Issued at 329 AM CDT Wed Jul 17 2024

Storm coverage will remain high across the CWFA this evening and
throughout the morning hours on Thursday as the actual cold front
makes its way southward into the region. However, we expect
instability to diminish with the loss of insolation this evening
and CAPE values will not recover much during the day tomorrow due
to widespread convective overturning and debris cloudiness. Thus,
our primary focus will shift from strong storms to locally heavy
rainfall, as many locations will receive multiple rounds of heavy
precipitation. Present indications are that the front will stall
near or immediately southeast of the forecast area from Thursday
night-Friday night, and our highest POPs have been reserved for
the southeastern zones with this in mind. Fortunately, highs will
only reach the m-u 80s, with no heat-related concerns on either
Thursday or Friday.

&&

.LONG TERM...
(Saturday night through Tuesday)
Issued at 329 AM CDT Wed Jul 17 2024

The local forecast area will remain to the east of a mid-level
longwave trough (extending from the Great Lakes into the
northwestern Gulf of Mexico) for much of the extended period, with
initially light SSW flow aloft expected to strengthen by
Monday/Tuesday as the height gradient contracts between a
subtropical ridge retrograding across FL and a developing upper
low over the MO Valley. As this occurs, a weak area of surface low
pressure is expected to evolve across west-central TX Friday
night, which will force the stalled frontal boundary to lift
northwestward through the region once again on Saturday. Precisely
how far north and west the front makes it is highly uncertain at
this time, but regardless of position, we will be either
sufficiently close to the boundary or within the moist warm
sector, and this will promote several rounds of rain and
thunderstorms from Sunday-Tuesday (both during the day and at
night). Although shear may strengthen a bit by Monday/Tuesday,
deep moisture and weak lapse rates will limit storm intensity,
with lightning and locally heavy rainfall the main threats. Heat
Risk will not be a concern through the end of the extended period.

&&

.AVIATION...
(06Z TAFS)
Issued at 1213 AM CDT Wed Jul 17 2024

VFR conditions will be the predominant flight category overnight,
with only high-clouds expected to go along with some patchy/light
BR in a few locations. Late in the period, medium to high chances
for SHRA/TSRA are forecast at both sites during the afternoon
hours. Should a storm impact either terminal, localized MVFR
conditions may develop due to reduced visibility and ceilings.
Have included a PROB30 btwn18-00Z to account for this, and
AWWs/amendments may also be needed during this time frame.
Additional storms may develop invof the terminals during the
evening hours as a frontal boundary slips southward into the
region, but due to uncertainty in timing/coverage, we have only
included VCTS at this time.

&&

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

$$

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