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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

FXUS64 KHUN 221954

Area Forecast Discussion
National Weather Service Huntsville AL
254 PM CDT Mon Apr 22 2019

.NEAR TERM...(Tonight)
Issued at 254 PM CDT Mon Apr 22 2019

Upper level ridging continues to amplify this afternoon as we warm 
into the upper 70s to low 80s. Satellite imagery shows mostly clear 
skies, thanks to surface high pressure over the Northern Gulf 
blocking us off from moisture and keeping dew points in the 40s. Calm
winds and mostly clear skies continue tonight, but increasing 
ridging aloft will also increase warm air advection. As the surface 
high begins to slide eastward, weak south to southwesterly flow will 
resume and dew points will increase to the low 50s. Some convective 
blowoff cirrus from strong storms over the Southern Plains will 
increase coverage of high clouds tonight, further limiting the 
potential for radiational cooling. Therefore, lows tonight will only 
get down to the mid 50s. 

.SHORT TERM...(Tuesday through Wednesday)
Issued at 254 PM CDT Mon Apr 22 2019

Above average temperatures persist through midweek with highs each 
day in the upper 70s to low 80s and lows in the upper 50s. A cutoff 
low at 500mb will remain over the Southern Plains through Wednesday, 
as it will be blocked by the ridging aloft over the Southeast. 
Southwesterly flow at the surface will allow moisture to gradually 
return, as seen by dew points reaching the upper 50s, causing cloud 
cover to steadily increase Wednesday. Winds remain fairly light both
Tuesday and Wednesday.

.LONG TERM...(Wednesday night through Sunday)
Issued at 254 PM CDT Mon Apr 22 2019

Late Wednesday into Thursday, the cutoff low over the Southern 
Plains will phase with a shortwave crossing the Great Lakes region 
late next week. This trough will then progress through the Tennessee
Valley on Thursday. A surface low will develop over the Western Gulf
and deepen ahead of the trough, as the trough begins to lift and 
weaken into an open wave. Ahead of the surface low, a boundary will 
stall over the Ohio Valley late Wednesday into early Thursday. 
Moderate southwesterly flow at 850 mb will raise PWATs above 1" as 
moisture pools south of the stalled boundary. Combined with weak
isentropic lift and vorticity advection, rain chances increase on 
Thursday ahead of an approaching cold front. Fitting with the summer-
like pattern this week, instability will increase Thursday, implying
at least a slight chance for thunderstorms to develop Thursday 
afternoon. These are expected to increase in coverage through 
Thursday night as the low and cold front approach the TN Valley. 
While there are still discrepancies with timing of the front and 
where the low will track, forecast precipitation remains between 0.5"
and 1" total with this event. Some lingering showers, perhaps an 
isolated thunderstorm, are possible Friday morning and early 
afternoon as the weak cold front passes through the area.

Overall air mass changes will not be significant behind the front, 
as lows Friday night will be in the mid 50s, approximately five 
degrees cooler than Thursday night. Saturday should be a warm, 
pleasant day with highs again reaching the low 80s, mostly clear 
skies, and low chances for rain. Another shortwave will enter the NW 
Pac on Sunday morning and rapidly traverse into the Midwest by Sunday
afternoon. The marginal PVA and lee surface cyclone tracking toward 
the Great Lakes may be enough to bring a second chance of rain Sunday
morning, with an isolated threat for thunderstorms. Confidence in 
this is low and will need to be monitored over the next several days.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1212 PM CDT Mon Apr 22 2019

VFR conditions will prevail through the TAF period across the region.
Light winds will become calm this evening as they back to
southeasterly, then increase between 5 and 10 knots tomorrow from the





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