Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 181143

Area Forecast Discussion
National Weather Service Huntsville AL
643 AM CDT Fri Aug 18 2017

For 12Z TAFS.


.NEAR TERM...(Today)
Issued at 218 AM CDT Fri Aug 18 2017

A weak cold front is approaching the TN Valley this morning as a
mesoscale shortwave trough moves east across the OH Valley/Great
Lakes Region. Showers and storms are expected to redevelop later this
morning as the cold front approaches. However, given that dry air
aloft is already impinging the area, only isolated to scattered
storms are anticipated especially ahead of the front over NE AL late
this morning into the early afternoon. Most Unstable CAPE is low
(~500-1000 J/kg), which should also keep impacts limited to lightning
for any deep convective updrafts. Analysis of microburst parameters
and substantial subsidence aloft indicate the potential for gusty
winds up to 30-45 MPH is possible but more limited.

Then, a dry airmass follows behind the front tonight with
temperatures dropping into the mid to upper 60s (a change from lows
in the low 70s) as clouds completely clear.

.SHORT TERM...(Saturday through Sunday night)
Issued at 218 AM CDT Fri Aug 18 2017

Dry, sunny, and warm conditions should prevail on Saturday as
a dampened ridge shifts westward across the Southeast with daytime
highs in the low 90s. The biggest change on Saturday will be less
humidity. However, this will be short-lived as ridge position aloft
and at the surface result in moisture advection beginning on Sunday
with greater cloud coverage (partly cloudy as opposed to mostly
sunny). A gradual increase in humidity will also follow with
dewpoints rising back into the low 70s. Cloud cover should increase
from the south over the north Gulf of Mexico coast on Sunday night
as moisture advection, saturation, and lift at around 850 mb cause
low cloud condensation.

.LONG TERM...(Monday through Thursday)
Issued at 218 AM CDT Fri Aug 18 2017

TUTT low will continue to track northwest through the western Gulf
of Mexico on Day 4.  A 5h ridge axis will remain anchored from SC
west through AR and north TX.  There remains a hint of weak
convergence which could spark off a shower or thunderstorms on
Monday afternoon, mainly over middle and southwest TN. Will keep the
slight chance PoP going for now. Any activity should die off by
sunset.  A bit more diurnal convection should develop on Tuesday as
southerly flow draws deeper moisture back northward.

The ridge will retrograde westward across the Gulf states through
the middle of next week as a rather strong trough position develops
over the eastern CONUS and the southeastern Canadian provinces.
The medium range models continue to indicate a resulting cold
frontal passage on Wednesday. Will keep mid range chance PoP going
Wednesday.  The models look to bring a much more comfortable airmass
in by Thursday (and beyond), with dew points lowering through the
60s and possibly the 50s Thursday Night.  Suggested blends look good
in this regard.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 642 AM CDT Fri Aug 18 2017

MVFR to IFR cigs (1500-900 ft) are occurring across north
Alabama/southern middle TN ahead of a front. These cigs should begin
to scatter over the next 2 hours. By 14Z, anticipating a return to
VFR conditions with a change in wind direction to the WNW and
increase to 10 kts. Cloud cover should continue to decrease behind
the front and wind should also decrease to variable after 19/00Z.
Isolated -TSRA may occur between 12Z-18Z and amendments to the TAFs
may be necessary, if any -TSRA approach KHSV/MSL.





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