Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 120315

Area Forecast Discussion
National Weather Service Huntsville AL
915 PM CST Wed Dec 11 2019

.NEAR TERM...(Tonight)
Issued at 915 PM CST Wed Dec 11 2019

Clear skies prevailed across the region this evening, thanks to
surface high pressure moving eastward across the eastern Ohio Valley
and Appalachians. An anticyclonic flow around this ridge provided
light NE-E winds over the Tennessee Valley. 9 PM temperatures have
cooled into the upper 20s to mid 30s, with Winchester the coldest
spot at 28F, and Albertville the warmest at 36F.

Snowfall that occurred yesterday afternoon/evening for the most part
has entirely melted, except where some survived mainly on north
facing aspects that blocked direct sun. A wide temperature/dewpoint
separation from the surface to boundary layer continued to be
forecast by the models, and will make any fog formation unlikely.
Even with no snow on the ground, light winds and clear skies do
support night time lows falling into the mid/upper 20s. May lower
some spots a degree or so in the forthcoming update. An area of
cirrus over the south central Great Plains was nearing the
Mississippi River. They should have minimal effect on dampening
radiative cooling effects before daybreak Thursday.

.SHORT TERM...(Thursday through Friday night)
Issued at 134 PM CST Wed Dec 11 2019

A brisk zonal pattern will bring a rapid progression of shortwaves
off the Pacific and east through the southern CONUS late this week
into the early weekend. The first of these waves arrives on Thursday
night. In advance of this wave, flow will turn southerly and
increase quickly on Thursday afternoon into the evening. This yields
a good low level moisture fetch from the Atlantic and Gulf beneath a
strong temp inversion. The shallow nature of the isentropic lift
should sustain stratiform -RA beginning Thursday evening, mainly in
our eastern counties. The chance will shift a bit further west later
Thursday night into Friday morning as the wave moves through aloft.
However, the most sustained and stronger isentropic lift will occur
in eastern AL into GA and east TN as the next next stronger wave and
resulting UVVs arrives. Rain amounts from Thu night into Friday night
will range from 1/4-1/3 inch west to 3/4 inch east. Friday will be a
cool and damp day, with temperatures only reaching the mid-upper

.LONG TERM...(Saturday through Tuesday)
Issued at 134 PM CST Wed Dec 11 2019

On Saturday, a stronger wave drops southeast from the central Plains
into the lower OH and TN valleys, along with a potent speed max in
mid to upper levels. Our forecast area will likely experience
subsidence by Saturday afternoon as this wave pivots east and
northeast through eastern TN and KY. Lingering light rain or shower
chances will lower through the day as a result. Temp advection will
quickly revert to neutral, then warm by Sunday as flow becomes zonal
yet again over the south central and southeast U.S. This is in
advance of yet another wave digging into the southern Rockies. Sunday
should be a dry day as a result, with southerly flow increasing.
Highs should reach the 50s Sunday afternoon as the warm sector
expands northward. Temperatures will likely remain mild Sunday night
into Monday morning, with steady or rising temperatures. On Monday,
suggested guidance suggests lower to middle 60s at least for highs in
advance of a possible QLCS. The northern extent of instability is
uncertain at this time. Thermodynamic and shear parameters suggest a
high-shear/low-CAPE environment in the lower MS valley as is typical
for mid December convective systems. The question is will it reach
the TN valley. At this point, will leave thunderstorms and potential
impacts out until this becomes more certain. Surface dew points
climb into the upper 50s to lower 60s in advance of the cold front
and precipitation, which should arrive Monday afternoon into Monday
evening. There may be a few spots that could mix with snow behind the
front before ending late Monday night in the highest Plateau areas.
Temperatures will turn sharply colder behind this cold front, but
with a sunny sky, so forecasting highs in the lower to middle 40s.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 538 PM CST Wed Dec 11 2019

VFR flying weather should continue across the Tennessee Valley into
late Thursday afternoon. Surface high pressure over the Appalachians
will move off of the Mid Atlantic coast on Thu, resulting in light
east winds becoming SE, increasing into the 5-15 kt range by the late
morning. Winds should be slightly stronger at the KHSV terminal. The
SE flow will also return lower level moisture from the Gulf,
bringing an increase in VFR clouds late in the TAF.





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