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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 132335

Area Forecast Discussion
National Weather Service Huntsville AL
635 PM CDT Sat Oct 13 2018

For 00Z TAFS.


.NEAR TERM...(Tonight)
Issued at 314 PM CDT Sat Oct 13 2018

In wake of a cold front that moved through the region last night, a
cool northeast flow has reinforced an autumn air mass. Still, the 
morning status deck has mostly dissipated, allowing temperatures to 
climb from the mid 60s to around 70 degrees. A mostly clear evening 
will allow for some decent radiational cooling initially as 
temperatures fall into back into the 50s. However, clouds will be on 
the increase by 03-06z as an upper-level disturbance will move out of
the South Plains into the mid to lower Mississippi Valley overnight.
Ahead of this feature, a shortwave trough and its associated LLJ 
will lift from the ArkLaMiss and into Northwest Alabama and Middle 
Tennessee late tonight into Sunday morning. This feature will serve 
as lifting mechanism for isolated to scattered rain showers 
overnight, especially areas north of the Tennessee River and the 
Mississippi border (closer to a weak boundary). This activity should 
be light, however, as the heaviest activity will remain to the 
northwest of the region. With winds veering to the southeast/south 
later tonight, some warm air advection may actually occur late, 
especially across the southwest zones. Regardless, lows will run in 
mid 50s to around 60 degrees in most spots. 

.SHORT TERM...(Sunday through Monday)
Issued at 314 PM CDT Sat Oct 13 2018

With a weak front just to the north and west of the region early this
week, opportunities for scattered showers (and perhaps a few 
isolated storms, especially Monday) will be possible. Essentially, 
the region will be caught in the middle between a building 
subtropical ridge over Florida and an amplifying upper-trough over 
the Great Lakes. A series of weak disturbances will rotate along the 
southeast edge of the trough, helping to initiate this activity. 
There is a bit of model uncertainty as to how far to the southeast
the front will sag. However, the latest model trends suggest that it 
will remain across Western and Middle Tennessee, allowing for more 
southerly flow across North Alabama, and thus warmer temperatures 
(mid 70s to around 80 degrees) and more scattered precipitation 
chances. As one would expected, the highest chances will exist across
far northwest Alabama (closest to the boundary), with more widely 
scattered to isolated chances further to the south and east over 
Marshall and DeKalb Counties. 

.LONG TERM...(Monday night through Friday)
Issued at 314 PM CDT Sat Oct 13 2018

A piece of energy over Canada will help shove the longwave trough
east into the Northeastern US and thus the cold front into the region
late Monday night into Tuesday. Another round of scattered showers
and perhaps a few isolated storms will accompany this frontal
passage during this period. However, the biggest headline will again
be a push of cooler and drier air in its wake as high temperatures 
will fall into upper 50s to 60s, with lows back into the mid to 
upper 40s by Tuesday night. The rest of the extended period will be 
characterized by generally clear conditions and a cool, dry air mass
with highs in the 60s to low 70s -- thank to a subtropical ridge 
building in from the Gulf of Mexico. There is a significant 
difference in the models by Friday, with the GFS showing a strong 
upper-trough moving into the Ohio Valley and the ECMWF maintaining 
the upper- ridge. For now, have not altered much from the previous 
forecast of slight chance PoPs and 60s temperatures. 


.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 635 PM CDT Sat Oct 13 2018

VFR conds prevail for now at both main terminals this early Sat
evening. Mid/high clouds though will begin to spread into the area
from the west later this evening in advance of a storm system forming
over the wrn Gulf states. Some light/occasionally mod shra may also
begin to develop/move into the area from the SW later tonight, and a
prevailing VCSH has been added to the forecast starting near 06-07Z.
With the shra/associated cloud cover, mid level cigs may lower to
around 5-7K ft Sun morning, but should remain well above VFR criteria
thru the remainder of the TAF period.





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