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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 202050

Area Forecast Discussion
National Weather Service Huntsville AL
350 PM CDT Tue Mar 20 2018

.NEAR TERM...(Tonight)
Issued at 350 PM CDT Tue Mar 20 2018

A storm system that in part brought a plethora of severe weather
across parts of this region yesterday has exited well to the east of
this region. A cold front extending south of a complex of low
pressure over the Mid Atlantic, continued to produce scattered 
severe weather from eastern North Carolina to Florida.

Warmer conditions that were across most of the Tennessee Valley on
Monday have shifted well to our east of the region, with mid
afternoon temperatures ranging from the mid 40s in southern middle 
Tennessee, to the lower 50s across northern Alabama. Post system 
moisture and upglide in the 290-300K region has resulted in more 
clouds than sun across the region, and periods of light rain. The 
colder air further to our north has resulted in a rain/snow 
changeover near Clarksville TN and across southern Kentucky. 

The colder air filtering southward this evening and in the 
overnight, will cause some of the light rains to become a mix of 
rain/snow, then possibly all snow for a brief period, before ending 
around daybreak Wednesday morning. Given the warm temperatures as of 
late, no accumulations are expected at this time. Moisture and 
associated clouds will also clear out from NW to SE as the drier and 
colder air build across the Valley. Night time lows should cool into 
the lower 30s (just above freezing), however a gusty at times 
northwest winds of 10-20 mph will produce wind chill values into the 
lower and mid 20s.

.SHORT TERM...(Wednesday through Thursday)
Issued at 350 PM CDT Tue Mar 20 2018

Generally sunny skies, but colder than normal conditions are forecast
for Wednesday, or the first full day of Spring, as cold high pressure 
builds in from the west. High temperatures will only warm into the 
upper 40s to lower 50s with NW winds of 5-15 mph. Somewhat colder 
conditions are expected Wed night as winds become light/variable
under the high as it moves across the region. Night time lows for
most if not all of the area should fall below freezing. We will
probably issue a Freeze Warning to cover this in a later shift, if
this trend continues, with forecast lows in the upper 20s to around
30. A slightly warming trend on Thursday is forecast with highs
recovering into the mid 50s to around 60. Normal highs this time of
year are around 67 degrees.

.LONG TERM...(Thursday night through Monday)
Issued at 350 PM CDT Tue Mar 20 2018

A return southerly flow will return more lower level moisture and
instability to the region. This will bring increased clouds, as well
as a slight chance of rain late Thursday night. An unsettled pattern
appears to be setting up again - for another weekend, as a series of
lows move along a frontal boundary that will set up in a west-east
manner across the eastern CONUS. Inter-model comparison between the
GFS/ECMWF/Canadian were in reasonably good agreement into early next
week. The models do indicate a frontal boundary draped mainly north 
of the area in the Saturday into Monday time frame. This placing the 
area in the warmer, more unstable sector warrants a mention of 
thunder within generally more widespread showers. The approach of a 
low and the front close enough made for scattered showers/storms on 
Sunday. Showers should continue into the first part of the next work 


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1230 PM CDT Tue Mar 20 2018

MVFR conditions will prevail through at least 02Z at the KMSL and
KHSV terminals. An upper low will swing through the region this
afternoon, bringing isolated to scattered light rain across the
region. Confidence is low on if this activity will reach the area,
however if it does, visibilities may be reduced as low as 4SM. Given
the lower confidence, have not included these lower visibilities in
the TAF. Otherwise, cigs around 1500 feet will persist through 02Z
and then lift to around 2500 feet between 02Z and 06Z. By 06Z, cigs
will lift and VFR conditions will return. Winds will generally remain
from the northwest and gust up to 18 to 20 kts this afternoon before
diminishing after 02Z.





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