Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 190500

Area Forecast Discussion
National Weather Service Huntsville AL
1100 PM CST Sun Nov 18 2018

For 06Z TAFS.


.NEAR TERM...(Tonight)
Issued at 804 PM CST Sun Nov 18 2018

After another very mild and pleasant day across the Tennessee
Valley, temperatures have fallen off into the mid to upper 40s as of
01z. With high pressure nudging off to the east, a surface cold front
currently draped across the lower-Mississippi Valley will continue
to approach the region overnight. Ahead of this boundary, decks of
mid to high clouds have already begun to filter into the area. This
has created mostly cloudy to overcast conditions late this evening.
These clouds will remain present throughout the night, with some
lower 4-6 kft ceilings potentially developing early Monday morning.
These clouds will put an end to any further radiational cooling and
help keep low temperatures about 10 degrees warmer than last night.
Lows tonight should drop no further than the low to mid 40s in most
spots. These clouds, along with a persistent light breeze, should
significantly limit fog development. However, enough boundary layer
moisture will warrant a mention of patchy fog along the usual fog-
prone river and lakes early Monday morning. Any precipitation along
the front will remain displaced to the northwest of the area.

.SHORT TERM...(Monday through Tuesday night)
Issued at 238 PM CST Sun Nov 18 2018

As the sheared vorticity axis approaches the ArkLaTex area tonight it
should be able to induce pressure falls at the surface and a weak
surface low is forecast to develop. This surface feature should be
moving across N MS/W TN early Monday morning and be shifting into
central TN shortly after sunrise. Models continue to waver on whether
or not the area will see any precip from this system. They all keep
a majority of the precip confined to near the center of the surface
low, which based on the current track would only clip far NW AL
Monday morning. However, the latest NAM and some additional hires
guidance try to bring a secondary impulse across the area later in
the day Monday. The feature would provide a bit more lift and allow
for a slight uptick in the coverage of showers across the southern
and eastern half of the area. So, have adjusted PoPs to reflect this
change. Could be a situation where the NW portion of the area gets
clipped, the front dissipates as it crosses north-central AL with
little in the way of rain. Then as the secondary impulse moves
across, rain begins to pick back up out east. In either case, not
expecting much in the way of rain totals, maybe at most a few
hundreths. With southerly winds expected for much of the day temps
will be able to approach the 60 degree mark Monday afternoon.

A cooler and drier airmass will then move in behind the front Monday
night into Tuesday. Think enough moisture will exist beneath an
inversion on Tuesday that we hold onto clouds a bit longer than
models currently forecast. CAA won`t truly kick in until later in the
day Tuesday, so even with the clouds we may be able to warm up into
the lower 50s. By Tuesday night though, winds increase out of the NW
and the cooler airmass moves in. Expect lows Tuesday night to be the
coldest of the week with values falling below freezing.

.LONG TERM...(Wednesday through Saturday)
Issued at 238 PM CST Sun Nov 18 2018

High pressure begins to settle over the area Wednesday and Thursday
but with light northerly winds temps should still remain on the
cooler side of normals. Highs in the low to mid 50s for Wednesday and
then into the upper 50s for Thanksgiving Day. A system moving along
the US/Mexico border will shift into the Gulf on Thursday and we
could see a slight increase in cloud cover but that should be it.

Focus then shifts to the potential for multiple rounds of systems to
move across the area from Friday into next weekend. There is still a
good deal of uncertainty here with models differing in the position
and progression of the systems as they cross the CONUS. The GFS has
remained the faster and furthest north with the initial system and
would bring us a quick round of showers on Friday. The ECMWF is
further south and strengthens the system right over the TN Valley,
resulting in a longer period of showers. Used a blend of guidance for
the forecast for Friday and Saturday due to the uncertainty. Even
larger differences exist in guidance towards the end of the weekend
and into the following week. But another round of rain is possible
either Sunday or Monday.

Temperatures for Friday and Saturday will be mild with highs in the
50s to lower 60s.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1030 PM CST Sun Nov 18 2018

Forecast hasn`t changed much from previous 00Z issuance. VFR
conditions with high clouds lowering to around 5000 feet remain in
the forecast through 16Z at MSL and 18Z at HSV. Then MVFR or lower
cigs and -SHRA are expected in the vicinity of both terminals. Some
guidance even drops cigs down below 1000 feet between 00Z and 04Z
this evening. For now, left that out for midnight shift to include if
that looks more certain after 00Z.




LONG TERM...Stumpf

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