Area Forecast Discussion
Issued by NWS Huntsville, AL

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FXUS64 KHUN 060818

Area Forecast Discussion
National Weather Service Huntsville AL
218 AM CST Tue Dec 6 2016

.NEAR TERM...(Today)
Issued at 215 AM CST Tue Dec 6 2016

The mid-level shortwave trough that is currently moving across the
TX/LA/AR area will continue to impact the weather today as it shifts
northeast. The surface low that is currently over eastern LA will
rapidly move northeast over N MS/NW AL/central TN this morning. WV
sat imagery is depicting a dry slot from eastern TX, central LA, to
central MS that will likely impinge over northern AL over the next
several hours. This may act to limit rainfall amounts over northeast
AL/split the rainfall. As the trough and surface low move further
northeast over MS and TN, respectively, looking at the possibility of
showers and isolated to scattered thunderstorms this morning. With
moderate wind shear in place, could see some bowing segments within
any convective clusters this morning mainly between 12Z-14Z (6AM-
8AM). A cold front will then pass over the region later this
afternoon with northwest winds increasing to 10-15 MPH while low
clouds remain entrenched across the TN/MS Valleys.

.SHORT TERM...(Tonight through Thursday)
Issued at 215 AM CST Tue Dec 6 2016

The main impact for tonight will be the low clouds that may drop
further (towards 1000 feet) which could create a visibility issue
with fog over the higher elevations of northeast AL/southern middle
TN. Protected valleys in northeast AL may also experience the patchy
fog, but this has a lower probability of occurring with the light
winds. Low dewpoint depressions in the low-levels may also be an
ingredient for the fog.

Then, on Wednesday, as has been mentioned in previous forecasts, the
broad trough originating from the Pacific Northwest will move towards
the central Plains. This trough is sending an Arctic cold front over
much of the country including the Midwest today and approaching the
TN Valley on Wednesday afternoon. Ahead of this front, enough
saturation in the low-mid levels will be present to support the
development of light rain over the TN Valley. Little in the way of
rain accumulations are anticipated prior to the frontal passage on
Wednesday evening into the overnight.

Strong cold air advection will follow behind the front with
temperatures falling through the early morning hours on Thursday
morning as clouds finally clear. This is primarily due to the strong
pressure gradient between the 1046mb anti-cyclone that will be over
the plains on Thursday night, source region of the airmass, and
little in the way of airmass modification. Dewpoint temperatures are
also expected to quickly drop into the 20s and 10s during the day.
Little in the way of airmass modification will occur even with sunny
sky conditions on Thursday. Daytime highs should only be in the low
40s with brisk 10-15 MPH northwest winds gusting to 20 MPH over the
higher elevations. Temperatures should then rapidly drop below
freezing Thursday evening with overnight lows expected to be in the
teens to near 20 degrees on Friday morning. Winds will likely stay
between 5-10 MPH during the early morning hours on Friday which will
create a with wind chills--in the single digits across southern
middle TN and low teens elsewhere.

.LONG TERM...(Thursday night through Monday)
Issued at 215 AM CST Tue Dec 6 2016

Forecast will not vary much from suggested blended guidance during
this period except for going with likely POP (above guidance) on
Monday Quasi-zonal pattern which develops during this period. This
will allow for a rapid modification of the arctic airmass this
weekend. By Sunday, cyclogenesis in the Plains and lower MO Valley
will enable a south-southwesterly warm advection pattern to develop.
So, after highs only in the 30s Friday and 40s Saturday, they will
rebound well into the 50s Sunday and Monday. The frontal system
associated with the low will bring an airmass of more Pacific origin.
Although QG dynamics will not be too dramatic with the frontal
passage Sunday Night into Monday, it will be sufficient along with
the moisture return and convergence to generate a rather solid band
of rain showers within the warm conveyor belt.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1055 PM CST Mon Dec 5 2016

Reduced flying conds continue at both main terminals this late Mon
evening, as additional ra/shra begin to move newd into the wrn half
of the area. Very low clouds are well in place across most of the
area, with IFR cigs aoa 500 ft. Precip is xpcted to linger into the
morning hrs Tue, as upper disturbances continue to traverse newd
across the region. Cloud cover may lift closer to 1K ft late in the
morning period, as -shra taper off from the w. However, with abundant
moisture thickness well in place, low cigs will prevail into the
early evening hrs. Sfc winds also look to remain out of the SE near
10-12KT heading into the morning period.





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