Area Forecast Discussion
Issued by NWS Huntsville, AL

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193
FXUS64 KHUN 221815
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1215 PM CST Mon Jan 22 2018

.UPDATE...
For Near Term and 18Z TAFS.

&&

.NEAR TERM...(Rest of Today)
Issued at 1215 PM CST Mon Jan 22 2018

A mid-level low currently across northeastern KS will continue to
slowly deepen and become more negatively-tilted as it lifts east-
northeastward over northern MO this afternoon, with the system`s
related surface cyclone over southern IA forecast to redevelop
northeastward into the southwestern Great Lakes.

Strengthening southwesterly flow aloft has resulted in the return of
sufficient deep-layer moisture to support a band of moderate- heavy
showers and a few embedded thunderstorms along a subtle prefrontal
surface trough axis currently pushing eastward through the TN Valley.
However, this feature is progressing eastward a bit faster than
previously advertised, and hourly POP/weather grids have been
adjusted to reflect a faster end to precipitation across northwest
AL. In terms of threats from the convection, it still appears as if
the forecast area will only be grazed by the strongest synoptic scale
forcing for ascent associated with the primary synoptic trough to
our northwest. This will mitigate the threat for even strong storms,
as will the limited northward return of low- level moisture/surface-
based instability. Nonetheless, based on intensity of prefrontal
environmental flow, the strongest storms will be capable of producing
brief wind gusts up to 50 mph. Due to an early onset of thicker low
cloud cover and precipitation, max temps have also been reduced by a
few degrees for the entire region.

.SHORT TERM...(Tonight through Tuesday)
Issued at 315 AM CST Mon Jan 22 2018

A few lingering showers are possible across NE AL but expect these to
be quickly moving out of the area. All precip should be to the east
by midnight. The true cold front won`t arrive until closer to 8-10pm
for much of the area. But expect temps to plummet into the 30s behind
the front with lows Tuesday morning in the mid to upper 30s. Winds
remain elevated overnight and as a result wind chills in the upper
20s are possible Tuesday morning.

As the main trough axis swings through expect cloud cover to increase
with the greatest coverage across the northern half of the area.
The clouds will keep temps even cooler on Tuesday with locations
north of the TN River staying below the 50 degree mark. It`s possible
that there is enough lift associated with the trough axis to squeeze
out a few sprinkles across our TN counties but have kept the forecast
dry.

.LONG TERM...(Tuesday night through Sunday)
Issued at 315 AM CST Mon Jan 22 2018

Zonal flow aloft and high pressure at the surface will promote
tranquil weather Tuesday Night, with lingering clouds behind an
earlier FROPA exiting to the northeast. A clear sky and some
northwest flow at the surface and aloft will bring in a cooler, dry
air mass. Good radiational cooling will allow for temperatures to
drop below the freezing mark for the first time in a few days, with
lows bottoming out in the mid to upper 20s. After some ample
sunshine for a decent warmup Wednesday morning, another shortwave
trough will swing another dry cold front into the Ohio and Tennessee
Valleys during the afternoon. This will bring another shot of
"cooler" air and cap off highs in the upper 40s to lower 50s for the
day, as well as result in chilly conditions in the 20s later that
night.

Quiet weather will continue through the remainder of the work week
on Thursday and Friday as a gradual warming trend takes place. High
pressure will begin to build in from the west on Thursday and become
centered over the region Thursday Night into Friday. This will
result in a wind shift to the south to go along with a mostly clear
sky. Highs will warm into the mid 50s to near 60 degrees each day.
Accompanying these southerly winds will be a gradual moisture return
back into the area. The aforementioned upper-high will slide off to
the SE and become centered over Florida Friday night. Winds will
shift to the SW/WSW Friday night into Saturday as a weak warm front
advancing northeastward accompanying a weak upper-trough moving into
the region. This feature (along with some isentropic lift) will
provide enough lift to generate some scattered showers Friday night.

PoPs will increase Saturday into Saturday night as a deepening upper-
trough swings from the Central Plains into the Ohio Valley. A cold
front will generate a broad line of convective showers during this
window, giving us the best chance for widespread wetting rains in
some time. Given the lack of instability and dewpoints struggling to
reach 50 degrees, have opted to leave a mention of thunder out of
the forecast. Breezy southwest winds will accompany this frontal
system, however, as the pressure gradient tightens ahead of the
FROPA. It should be noted that exact timing of this feature is
uncertain given some subtle differences with the models. As a result,
have been slower to taper PoPs off from west to east Saturday night.
However, think by Sunday morning the front should be moving through
the region, with slightly cooler and much drier air to follow. This
air mass change will bring a swift end to precipitation on Sunday,
along with some highs in the mid 40s to low 50s to kickoff the new
week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1215 PM CST Mon Jan 22 2018

A prefrontal trough axis and its associated band of moderate/heavy
shra and embedded tsra will continue to shift steadily ewd early this
afternoon. Although this activity may impact HSV through 20Z, it
appears that the threat for precip has now ended at MSL. MVFR stratus
deck based arnd 2500 ft will be slower to clear the terminals in the
wake of the sfc trough, with the most pronounced clearing of low
clouds expected to occur late this afternoon as a Pacific cold front
pushes ewd and low-level flow veers to WSW. A few high-based cu will
remain possible overnight, beneath sct ci. However, guidance suggests
that another deck of lower stratocu will spread sewd tomorrow
morning after 12Z, with high-end MVFR cigs anticipated by end of the
TAF period. Southerly sfc flow in the 15G25 knot range will gradually
diminish as winds shift to the SSW this aftn, with a moderate SW
flow continuing overnight. Winds will veer to WNW tomorrow morning,
with gusts increasing up to 16 knots once again.

&&

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

$$

NEAR TERM...70/DD
SHORT TERM...Stumpf
LONG TERM...AMP.24
AVIATION...70/DD


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