Area Forecast Discussion
Issued by NWS Huntsville, AL

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000
FXUS64 KHUN 180534
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
1134 PM CST Fri Nov 17 2017

.UPDATE...
For 06Z TAFS.

&&

.NEAR TERM...(Tonight)
Issued at 645 PM CST Fri Nov 17 2017

High cloudiness has pushed into northern Alabama south of a weak
convergence/frontal boundary extending from eastern TN northwest into
SE Missouri. However, it is very thin at this time. Somewhat thicker
mid/high cloud cover is in place over MS and Arkansas. This is all
moving to the southeast fairly quickly. However, cloud cover thick
enough to limit radiational cooling more significantly likely won`t
push into the area until around midnight. This leaves at least a few
hours, before southwest winds really pick up (likely between 10 PM
and midnight) east of I-65. With temperatures already in the mid to
upper 40s and dewpoints in the upper 30s east of I-65, these
temperatures will likely fall into the lower to mid 40s before winds
pick up around 10 PM. Further west, temperatures look pretty good,
and winds are already picking up there closer to the increasing
pressure gradient. Then temperatures should remain fairly steady and
rise into the 50 to lower 60s (west of I-65) after midnight through
daybreak. Current cloud forecast looks good with thicker cloud
cover/opaque mostly cloudy conditions pushing into the area around
midnight. Southeast winds 10 to around 15 mph spreading east after
midnight look reasonable. Updated grids and forecast to reflect lower
temperatures.

.SHORT TERM...(Saturday through Sunday)
Issued at 200 PM CST Fri Nov 17 2017

The surface low will deepen and lift northeast over the next 24 to 36
hours. This will help drag a cold front toward the Tennessee Valley
Saturday afternoon and evening. Ahead of the front, we will see a
narrow plume of higher dewpoints surge northward within a modified
warm sector. The NAM looks overdone in this regard and have trended
more toward the GFS. The parameter space ahead of the front would
favor very low topped convection with fairly strong low level shear
but CAPE values below 500 J/kg.

It`s also uncertain based on the proximity soundings whether the
boundary layer would ever completely destabilize. Given the rather
robust low level jet cannot rule out an isolated strong/severe storm
along the line with gusty downdraft winds. The most notable concern
might be the gradient winds however and will likely hoist a wind
advisory areawide for Saturday/Saturday night.

A fairly strong dry slot will work in along the nose of a 80-90 knot
mid level jet on Saturday night so expect an abrupt end to the
precip from west to end. The newer guidance is now a bit more
pessimistic on cloud cover through at least Sunday with some low
clouds trapped under a notable inversion. Will likely trend that way
as well. Given the morning clouds and cold air advection, expect
Sunday to be a rather chilly day to say the least.

The surface high will build directly overhead Sunday night. Light
winds, clearing skies and a notably cold airmass will bring a
widespread killing freeze to the entire area by Monday morning.

.LONG TERM...(Sunday night through Thursday)
Issued at 200 PM CST Fri Nov 17 2017

The extended portion of the forecast begins Sunday night into Monday
under the influence of a surface high that`s transitioning W to E
across the area. As such, under ideal radiational cooling conditions,
morning lows will begin in the middle to upper 20s across much of
the area, with the colder readings expected in Southern Middle
Tennessee and sheltered valley locations in Northeastern Alabama.
Given the sfc high shifting to the E, though, winds will become more
S/SE through the day, making for afternoon highs in the middle 50s
under sunny skies.

Dry weather continues through midweek despite a shortwave traversing
the region again on Tuesday into Wednesday. With the CAA originally
in place and the recent shift of winds to more of a S/SE direction,
there won`t be enough time to introduce much in the way of moisture
ahead of this feature, so a dry passage is expected. Some of the
model blends are trying to spit out a little QPF during this time,
but believe that soundings are just too dry aloft to support
anything, so will maintain a dry forecast for this time period.

Temperatures through the week will remain mild as a result of zonal
flow aloft, but yet another disturbance in H5 flow develops a cutoff
low over the Srn Gulf Coast states by Thanksgiving. Though much of
the support with this feature will remain well S/E of the local area,
northerly winds in place here will maintain a dry forecast for the TN
Valley, keeping any moisture relegated to our S. Temps during this
time look to be below normal (with CAA remaining in place), with
daytime highs in the middle 50s and morning lows in the lower/middle
30s.

Models diverge on the next weathermaker for the CWFA, the majority of
long-range models remaining dry, but a few runs here/there show the
area being clipped by a shortwave diving down the backside of an
upper trof in place across much of the Ern CONUS by Day 8-10. This
may spread some light rain/drizzle for our NErn counties during this
time, but will not bite on this solution just yet.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1100 PM CST Fri Nov 17 2017

High and mid level cloudiness (VFR in nature) will continue to
move across the area through 09Z at KMSL and 12Z at KHSV. As a cold
front moves quickly into MS and approaches the area from the west on
Saturday, better lift/low level moisture will cause ceilings to drop
into the MVFR range through the afternoon and evening hours. Winds
should become SW ahead of the front at KMSL ~15Z and KHSV ~18Z and
be around 25KTS with gusts to 35 KTS. Between 21Z/01Z, KMSL could see
some -TSRA affect the terminal. A bit later timing is expected for
-TSRA activity between 01Z and 03Z at KHSV. Some IFR or LIFR vsbys
or cigs could occur as the the front and -TSRA activity moves across
the terminals.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...Wind Advisory from 6 AM to 9 PM CST Saturday for ALZ001>010-016.

TN...Wind Advisory from 6 AM to 9 PM CST Saturday for TNZ076-096-097.

&&

$$

NEAR TERM...KTW
SHORT TERM...15
LONG TERM...12
AVIATION...KTW


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