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Area Forecast Discussion (AFD)

Issued by Huntsville, AL (HUN)

                            
000
FXUS64 KHUN 212358
AFDHUN

Area Forecast Discussion
National Weather Service Huntsville AL
658 PM CDT Fri Sep 21 2018

.UPDATE...
For 00Z TAFS.

&&

.NEAR TERM...(Tonight)
Issued at 233 PM CDT Fri Sep 21 2018

Scattered showers and a few thunderstorms continue to develop over
northern Alabama, especially east of a line from the Muscle Shoals
area to northwest of Columbus, Mississippi. Expect this activity to 
continue in the evening hours, before retreating north a bit. 
However, still cannot rule out a shower or thunderstorm after 
midnight (only 20-30 percent chance though). Expect cloud cover to 
become high and thin and winds fairly light after midnight. This 
should allow temperatures to drop into the upper 60s to lower 70s by 
Saturday morning. 

.SHORT TERM...(Saturday through Sunday)
Issued at 233 PM CDT Fri Sep 21 2018

As an approaching frontal boundary continues to edge southeast closer
to the region, models still stall the main front somewhere across
portions of Tennessee and northern Arkansas. Enough forcing and
instability should be in place in northwestern Alabama and southern
middle Tennessee to allow showers and thunderstorms to increase in
coverage. Shear doesn't look great, but fairly deep moisture is in
place ahead of the boundary. Kept higher pops (40-60 percent) in
northwestern Alabama and southern middle Tennessee. Elsewhere kept
mainly scattered chances of showers or thunderstorms. The boundary 
still doesn't move much Saturday night into Sunday night, keeping 
similar pops in the forecast. The biggest question much of this 
period, is will the higher changes of rain/frontal boundary remain 
further north than currently thinking. For now, sticking close to 
blended guidance. Shear doesn't look overly impressive through the 
period. Thus, normal general thunderstorm activity is expected. Lower
daytime highs in the lower to mid 80s are expected.

.LONG TERM...(Sunday night through Thursday)
Issued at 233 PM CDT Fri Sep 21 2018

A cold front will be in the vicinity of the region during the early
to middle part of the upcoming week. However, some uncertainty does
exist as to the behavior of this boundary and what it will mean for
PoPs and temperatures in the coming days. After a somewhat cloudy day
on Sunday (with scattered to numerous storms), a slightly drier
period may be in store for Monday and even Tuesday. Models are 
hinting that the aforementioned boundary may actually retreat back 
north and west on Monday as the Bermuda high temporarily tries to 
nose it's way back into the Piedmont region of the Southern
Appalachians. The result will likely be a few less clouds, slightly 
higher temperatures (mid 80s), and more widely scattered convection. 
Areas to the north and west (closer to the boundary itself) would 
likely see the greatest potential for this activity. Still, with 
southwest flow and abundant moisture in place, there will be plenty 
of ingredients for some scattered showers and storms areawide as 
referred to above.

A stronger shortwave trough over the Northern Plains will shift into
the Great Lakes/Ohio Valley Tuesday night into Wednesday and attempt
to force the front back south into Southern Middle Tennessee and
Northern Alabama. Regardless, it will be close enough to warrant an
increase in PoPs to likely across most of the region during this
period. These numerous showers and storms will hopefully bring the 
region some much needed precipitation as moderate drought conditions
have been starting to develop within the last couple of weeks. The 
best dynamics, however, will be well displaced of the region and thus
am not expecting any severe risk with this activity. 

The status of the main "cold air" push associated with a stronger 
cold front to the north the models have been advertising is still 
quite uncertain at this time -- at least this far south. The ECMWF is
now wanting to reestablish a ridge of high pressure late next week
over Central Georgia and Alabama -- and potentially into the 
following weekend. The GFS on the other hand does show a stronger 
upper-low pushing from the Northern Plains into the Ohio Valley by 
Friday, which could push this stronger "autumn" front at least close
to the area. Should this solution occur, it's possible we could see 
a taste of autumn to close out the last couple days of September. 
However, I'd still advice caution on totally buying into the GFS 
solution given the magnitude of this Bermuda High feature the models
are advertising. Temperatures will still be relatively cooler, but 
should the ECMWF solution verify, we'd be looking at mid to upper 80s
during the day and 60s at night -- with southerly flow maintaining 
the Gulf moisture over the region. Hardly a true taste of autumn. 
Stay tuned, a lot of details still to be worked out! 

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 658 PM CDT Fri Sep 21 2018

A few areas of mod/heavy shra continue to develop across parts of the
area heading into the evening hrs, especially near the KMSL airport
and on into srn mid TN. These shra are likely to continue across mid
TN and into portions of NW AL for much of the evening period, and a
prevailing VCSH will be in place at the KMSL airport thru 06Z. Given
the rainfall from today coupled with the light winds, some -br/MVFR
vis are then possible at both airports heading into the early morning
hrs. Any vis reductions should quickly improve with the onset of
daytime heating Sat. Additional shra are then xpcted later in the day
Sat, as a frontal boundary drops into the area.

&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
TN...NONE.
&&

$$

NEAR TERM...KTW
SHORT TERM...KTW
LONG TERM...AMP.24
AVIATION...09


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