Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 171127

Area Forecast Discussion
National Weather Service Birmingham AL
627 AM CDT Thu Aug 17 2017

For 12Z Aviation.


Today and Tonight.

A deep layered ridge was located over the Southeast States with a
short wave trof over the Upper Mississippi Valley. A band of
convection was located from north Texas to Illinois along an upper
trof axis extending southwest from the short wave trof. For today
across central Alabama, rain chances will be on the low side
due to the presence of the ridge. For most areas, isolated
thunderstorms are possible in the heating of the afternoon, but
better chances will be across the northwest counties as lift
increases ahead of the approaching upper trof axis.  The energy on
the southern end of the trof axis wanes as it approaches the upper
ridge, but this trof axis will provide enough lift for scattered
thunderstorms across the northwest counties during the afternoon.
The trof axis will push slowly southward into north Alabama this
evening, and keep the thunderstorms going well into the evening

Afternoon temperatures will be close to those on Wednesday, may a
degree higher. Heat indices will approach 105 degrees across some of
the the southern counties. Will continue to highlight in the HWO,
but given limited areal and spatial coverage, will not issue any


Friday through Thursday.

By Friday morning a weak cold front is making its way into Central
AL, stretching southward from a surface low located in the Great
Lakes region. The cold front doesn`t have too much forcing behind it
during the day Friday, so it progresses very slowly and likely won`t
provide substantial lift during the early part of Friday;
therefore, I have decreased PoPs Friday morning to roughly 30%
across much of Central AL. By Friday night, the overall synoptic
trough digs southward, and pushes the cold front southward. The
troughing will provide some extra lift combined with the diurnal
heating, which will lead to increased rain chances along the front
later Friday in the southeastern counties.

The cold front is south of our area by Saturday morning as an Upper
Low retrogrades through the Gulf of Mexico. Will keep rain chances
for the northern half of Central AL low on Saturday, with 30-40%
still possible in the southernmost counties due to proximity of the
now stationary cold front in Southern AL. On Sunday, the frontal
boundary is lifted slightly northwards, but remains fairly weak.
Have therefore kept chance PoPs generally south of the I-20 corridor
with slight chance in the north. Could argue for even lower PoPs in
the northernmost counties, but will keep them around 15% for now.

Upper-level ridging builds in Monday and Tuesday. The GFS wants to
keep the area drier, while the ECMWF develops the typical summertime
airmass thunderstorms in the afternoons. Have leaned towards the EC
and climatology here and gone with 30-40% PoPs area-wide simply
based on the synoptic pattern and the moist boundary layer. The
pattern changes as we reach the middle part of next week as
troughing builds into the Eastern US. Models hint at another cold
front pushing southward, which would increase rain chances across
Central AL on Wednesday and Thursday.



12Z TAF Discussion.

Outside of low clouds this morning, VFR conds expected through the
period. An area of cigs blo 1000 ft agl have developed along the
I-20 corridor, impacting KTCL, KEET, KASN, KANB. The cigs should
lift quickly and become scattered by 14z. A sfc ridge along the
Alabama and Georgia state line will result in southwest winds 5-10
knots. Scattered clouds with bases 3-4 thousand feet will develop
by 16z. An upper ridge will suppress convection, but an upper
level trof axis will move into northwest Alabama late in the
afternoon, and could trigger sct tstms across north Alabama
starting around 21z and lasting thru 06z.




Scattered rain chances possible today, increasing slightly for
Friday. There are no fire weather concerns at this time due to
the abundant moisture.


Gadsden     90  73  89  70  91 /  20  30  30  10  10
Anniston    91  74  90  72  91 /  20  30  30  10  10
Birmingham  92  76  91  73  92 /  20  30  30  10  10
Tuscaloosa  92  75  93  74  94 /  20  30  30  10  20
Calera      91  75  91  73  92 /  20  30  30  10  20
Auburn      90  75  90  74  90 /  20  10  40  20  20
Montgomery  94  76  93  76  93 /  20  10  40  20  30
Troy        92  74  93  74  92 /  20  10  40  30  40




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