Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 271122
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
622 AM CDT Tue Oct 27 2020

.UPDATE...
For 12Z TAFS.

&&

.NEAR TERM...(Today)
Issued at 300 AM CDT Tue Oct 27 2020

Same song different verse with the current weather situation early
this morning across the Tennessee Valley. Low-level moisture remains
trapped below a rather stout inversion. A surface boundary is stalled
just to the south of the forecast area stretching to the southwest
to near a surface low across SE TX. Arctic air has poured into the
southern Plains with temperatures in the teens and 20s across
portions of TX and OK. To the south, Hurricane Zeta has made landfall
along the Yucatan Peninsula and will emerge into the Gulf of Mexico
later today. The upper pattern is characterized by a deep closed low
across the Desert Southwest with a ridge centered over the FL
peninsula. Current water vapor imagery indicates dry air in the mid
and upper level across the Southern U.S. into the northern Gulf of
Mexico.

Model soundings suggest that the low-level moisture will struggle to
mix out but the clouds could break up some later this afternoon
similar to yesterday. PW values will slowly increase today with
southwesterly flow aloft with the upper ridge centered to the south
and east. Upper level heights will also nudge higher as the ridge
amplifies ahead of the approaching closed low. Hurricane Zeta will
be trapped between these two upper level features and will accelerate
to the north later today. Highs today will be in the 70s.

.SHORT TERM...(Tonight through Thursday)
Issued at 300 AM CDT Tue Oct 27 2020

The main impacts in this forecast package will occur during the
short-term period. A shortwave trough is forecast to track northwards
across the area ahead of Hurricane Zeta tonight. At the same time,
southerly flow in the low-levels will advect moisture into the
region. Model soundings indicate deep moisture later tonight as the
atmosphere quickly saturates. Additionally, the lingering surface
boundary will aid in additional lifting. PW values will climb into
the 2+ inch range in the tropical airmass. These values are above the
maximum climatological values. Therefore, expect widespread heavy
rainfall overnight into Wednesday. With the saturated atmosphere,
model soundings indicate weak lapse rates around 5 c/km but there
could be a few rumbles of thunder with some very weak elevated
instability.

Still think there could be a break in the widespread rainfall late
Wednesday morning into the afternoon. The shortwave trough and
surface boundary shift to the north with the first round of strong
moisture advection. Still expect showers will continue but there
could be a brief reprieve in the intensity during the day on
Wednesday.

Hurricane Zeta will make landfall along the LA/MS/AL Gulf Coast late
Wednesday. Zeta will be racing to the northeast at this point as the
closed low moves across TX. There is still some model uncertainty on
the exact track and speed of the system but expect a second round of
heavy rainfall late Wednesday night into Thursday morning as Zeta
passes across or just to the south and east of the area. No severe
weather impacts are forecast but there could be a few downed trees
with the saturated soils and gradient winds from the weakening storm
system. Storm total rainfall will range from around 2-3 inches with
locally higher amounts possible. Fortunately, Zeta will be moving
quickly and recent dry weather has lead to higher flash flood
guidance values. Overall, do not expect any widespread flooding but
could see some localized issues, mainly in areas of poor drainage.

A cold front sweeps across the area on Thursday as Zeta races to the
northeast ahead of this boundary. PoPs will decrease from southwest
to northeast on Thursday as colder air moves into the region.

.LONG TERM...(Thursday night through Monday)
Issued at 300 AM CDT Tue Oct 27 2020

The trough axis will shift to the east Thursday night. Temperatures
will be noticeably cooler Friday with highs only in the mid 50s to
low 60s (these values have been our morning lows over the last
several days). Lows Friday night into Saturday morning will be in the
low to mid 40s. Highs will moderate over the weekend into the 60s on
both Saturday and Sunday. A cold front will bring in another round
of cooler air Sunday night. Conditions will be dry with the frontal
passage and temperatures will drop around 5-10 degrees on average to
start the upcoming work week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 622 AM CDT Tue Oct 27 2020

Low ceilings and visibilities at the terminals again this morning
with low-level moisture remaining trapped below an impressive
inversion. Expect similar conditions to the last few days with slow
improvements in flight conditions throughout the day with VFR
possible later this afternoon. Precipitation will move in late in the
TAF cycle as moisture surges into the area with ceilings lowering
again.

&&

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

$$

NEAR TERM...MA
SHORT TERM...MA
LONG TERM...MA
AVIATION...MA


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