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FXUS64 KBMX 211705 AAC

Area Forecast Discussion...UPDATED
National Weather Service Birmingham AL
1205 PM CDT Sun Jul 21 2019

For 18Z Aviation.


A rather cloudy start to this Sunday across much of Central
Alabama with stratus covering a large swath of the state. Recent
satellite and observational trends indicate some overall
improvement in ceilings and general dissipation, and expect to see
more sunshine as we progress through the mid to late morning

The morning (12z) sounding from KBMX was fairly similar to the
previous two days though just a touch (relatively speaking) drier
with a PWAT values of 1.86 inches. The overall profile was rather
moist up to 500 millibars with only modest DCAPE somewhat 
limiting microburst potential. Although gusty winds with stronger 
cells, outflows, and mergers cannot be ruled out certainly the 
biggest threat(s) today will be locally heavy rainfall and 
frequent lightning. 

In terms of a focusing mechanism for convection today, you always
have to look at differential heating boundaries. More noticeable
on water vapor is an elongated trough axis from middle TN back
into central MS. This would place our western/northwestern
counties in a favorable location for this afternoon. The high res
guidance has mixed signals overall (perhaps due to the morning
cloud cover) with NSSL WRF rather aggressive with convection 
across our western half this afternoon while some other guidance 
has much less.

Current thinking is to continue trends of previous forecast and
taper pops from west to east today. Will issue quick update to
tweak grids based on current trends/conditions but overall no
major changes planned. 


Previous short-term discussion:
/Issued at 0340 AM CDT Sun Jul 21 2019/

Today and Tonight.

The upper low that developed over the Florida Panhandle on
Saturday has now become an inverted trof over eastern Mississippi
and northwest Alabama. The axis of deeper moisture now resides 
along the AL/MS state line where PW's are near 2 inches. Upper 
ridging to the east of the inverted trof will nudge into southeast
Alabama today and reduce rain chances in this area. Best rain 
chances today will be west of I-65. Weak steering winds aloft will
result in slow storm movement and locally heavy rainfall. Most of
the activity will be diurnally driven, with highest coverage of 
storms during the afternoon, with decreasing coverage quickly 
after sunset. Highs today will be in mainly in the middle to upper 
80s, with lower 90s across the southeast.


/Issued at 0340 AM CDT Sun Jul 21 2019/

Monday through Saturday. 

Moisture content has increased in recent model guidance for
Monday, particularly northwest of I-85, where PWAT values should 
exceed 2 inches. Weak low-level convergence along with daytime 
heating will contribute to scattered/numerous showers and storms. 
On Monday night, a cold front will be approaching from the 
northwest, providing a focus for additional convective 
development. Rain chances should increase during the evening and 
overnight hours with rain chances of 60 to 70 percent near and 
north of I-20 through daybreak on Tuesday. While the southern half
of the forecast area appears to be in line for widespread showers
and storms on Tuesday afternoon, rainfall amounts along and north
of I-20 during the late morning and early afternoon will depend 
on the timing of the cold front. Models have trended a touch 
faster with the front which suggests the bulk of the rain will be 
focused south of I-20.

Much drier air will be advected in behind the front for Wednesday 
and Thursday with 20-30 percent rain chances confined to our 
southeastern counties, just northwest of the stalling front. 
Models are in worse agreement regarding the speed of the moisture 
recovery for Friday and Saturday. Rain chances have been nudged 
downward as a hedge between the dry ECMWF and rather wet GFS. 



18Z TAF Discussion.

Isolated to widely scattered convection was ongoing again early
this afternoon across central Alabama. The fairly widespread early
morning fog and stratus has since lifted and dissipated leaving
behind generally VFR conditions outside of the aforementioned

For this TAF issuance, will maintain VCTS at all TAF sites through
late afternoon/early evening. Given the proximity to the upper
trough have included a window of predominant MVFR cigs/visibility
in precipitation for northern and western sites for this 
afternoon. Expect somewhat of a repeat performance tonight with 
stratus redeveloping at most locations toward morning slowly 
lifting late.




Scattered to numerous showers and storms are expected today and on
Monday particularly across northern and western portions of the
area. A cold front should bring more widespread rain for Monday 
night into Tuesday. With a moist airmass in place, there are no 
fire weather concerns at this time.


Gadsden     88  72  86  69  82 /  50  20  60  60  50 
Anniston    88  73  87  71  82 /  50  20  50  60  70 
Birmingham  89  74  88  72  84 /  60  20  60  60  50 
Tuscaloosa  90  74  89  72  85 /  60  30  50  60  50 
Calera      88  72  87  71  83 /  50  20  50  60  70 
Auburn      89  73  87  71  83 /  20  10  30  40  80 
Montgomery  90  74  91  73  85 /  40  20  40  40  80 
Troy        90  73  90  71  86 /  40  20  40  30  80 



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