505
FXUS64 KHUN 210122
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
822 PM CDT Sat Jul 20 2024

...New NEAR TERM...

.NEAR TERM...
(Tonight)
Issued at 822 PM CDT Sat Jul 20 2024

This evening, a weak stationary boundary (represented more by
surface wind convergence than a true air mass change) was
positioned just north and west of the TN Valley. Residual outflows
from diurnally-driven convection earlier this afternoon are
leading to sparse shower development that may increase in coverage
and track eastward late this evening. This forecast maintains a
20-40% chance for rain primarily along and east of I-65 after 9 PM
before dropping to 10-20% for only far northeast AL.

The only other modification to the previous forecast was to align
the sky forecast with observational trends, lowering cloud cover
overnight. With lower coverage of convection, less cloud cover
overnight would mean slightly cooler low temperatures in the mid
to upper 60s with a few areas staying in the low 70s. Another
change would be greater coverage of fog, locally dense in
sheltered valleys or near areas that saw rainfall earlier today.
Confidence is too low that coverage of any dense fog would warrant
a dense fog advisory, but this will be a focus overnight.

&&

.SHORT TERM...
(Sunday through Monday night)
Issued at 127 PM CDT Sat Jul 20 2024

The overall pattern will remain fairly stagnant thru the remainder
of the weekend and into the new work week, as a broad upper trough
pattern drops more into the SE region. High pressure entrenched
across the southern Atlantic will also maintain an influx of Gulf
moisture out of the S/SW. This along with SBCAPE values climbing
into the 1000-1500 J/kg range Sun/Mon and weak synoptic lift in
place will maintain a medium-high chc of showers/tstms (50-70%),
primarily during the afternoon. Similar to the previous forecast
package, POPs from the Blended Guidance were lowered a tad Sun/Mon
given a thick cloud cover expected to linger into the new week.
Brief heavy rainfall/gusty winds also remain the primary threats
with any stronger storms. Patchy fog remains a possibility as well
Sun/Mon nights, although the presence of iso/sct showers/tstms may
offset the prob for more widespread fog coverage. With the cloud
cover, afternoon highs both Sun/Mon will struggle to surpass the
mid/upper 80s, while overnight lows into early Tue trend in the
upper 60s/near 70F for most spots.

&&

.LONG TERM...
(Tuesday through Friday)
Issued at 136 AM CDT Sat Jul 20 2024

A deep upper low currently over the eastern Hudson Bay, by next Tue
should be weaker and moving off of the Canadian coast. Rather strong
troughing this low produced (extending to the Gulf Coast) did help
put an end to the relentless heat of late, and brought much needed
rainfall to the region. This upper troughing pattern should persist
into the middle of next week, with strong upper ridging over much of
the north Atlantic basin. A southerly flow rounding this high (aloft
and at the surface) will return lots of lower level moisture from a
very warm Gulf of Mexico (sea temperatures in the mid/upper 80s) well
inland. Some of the guidance, especially the GFS has around 2" or
higher of precipitable water moisture content in this period.

Overall QPF mainly from WPC are showing .10" to .25", but with
amounts upwards to .50" in the afternoon. But with such high precip
water values, it would very easy for stronger showers or storms
produce much higher amounts. Although the area is still in a long
term drought, rainfall amounts exceeding say 1-2" an hour, or heavy
showers repeatedly impact an area could produce water ponding as well
as instances of flash flooding. Larger scale stream/river flooding
look more unlikely at this time, unless more widespread heavy
rainfall occurs.

Daytime heating of this moisture and resultant instability, will
yield daily chances of showers and thunderstorms, especially in the
afternoon and evening. Have stayed on that track this issuance. The
blends show this well, but think the PoPs are too high (going into
the categorical 75-100%) range for much of the period without a real
focusing mechanism or organized system. Thus have trimmed back into
the likely 55-74% range for maximum values in the afternoon hours.
With a mix of clouds and sun, plus good rain chances, forecasting
high temperatures is a little more challenging. More sun breaking
through would result in even more unstable environment and
potentially stronger and wetter showers. Will raise the lower end of
the high temperatures up a degree or two. Low temperatures look to be
okay.

&&

.AVIATION...
(00Z TAFS)
Issued at 631 PM CDT Sat Jul 20 2024

Shower and storm activity has dropped off this evening, but there
is a low chance of additional development this evening. Confidence
remains too low to mention in the TAF. There is higher confidence
in clearer skies overnight, which would introduce a fog threat.
IFR to MVFR visibilities are likely overnight across the area,
including both terminals. Any fog or low stratus would mix out and
lift early tomorrow morning. Showers and storms return again
tomorrow evening, but with greater likelihood at HSV than MSL.

&&

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

$$

NEAR TERM...30
SHORT TERM....09
LONG TERM....RSB
AVIATION...30