Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 250459

Area Forecast Discussion
National Weather Service Birmingham AL
1159 PM CDT Mon Apr 24 2017

For 06Z Aviation.


Through Tonight.

Upper level low will continue to push eastward into the Atlantic
tonight, with northwesterly flow continuing across the area. An
overall drying trend is expected tonight, with cloud cover
dissipating across most of the area. With moist ground conditions,
patchy fog is possible areawide. Models show low level lift across
the east that should result in stratus being the predominant sky
condition rather than fog overnight. Lows will be in the low to
mid 50s.


Tuesday through Monday.

Upper-level ridging builds into the area today ahead of a deepening
trough over the Great Plains. Winds will shift from the north to
more westerly, then from the south late in the afternoon. A surface
low develops as part of the larger trough over the Southern Plains
early Wednesday. Models disagree with the track of the surface low
and evolution of the trough as we go into Thursday. The GFS has the
trough digging further south into the Ozarks with a stronger vort
max at the base of the trough. The ECMWF has a less-amplified trough
moving more quickly into the Great Lakes region. Both models stretch
a cold front down through the Mississippi River Valley and moving
eastwards through Central AL on Thursday. Instability is forecast to
be in excess of 2000 J/kg and sufficient 0-6km Bulk Shear is
expected for organized storms. However, the upper-level jet is well
to the north and west of the area, which limits the upper level
support. The biggest question will be the timing of the front as it
moves through and whether or not the trough digs south, leading to
height falls. For now, will leave mention of severe threat out of
the HWO and continue to monitor trends in the models. Would not be
surprised to see at least see a few strong storms across the area

Along with any potential severe threat, models have 1.7-
1.8" PWATS, which is well above the climatological maximum for this
time of year. NAEFS and GEFS show PWAT above the 99th percentile as
well, which adds confidence in the potential for heavy rain in any
storms that do develop on Thursday, regardless of the severe

Southerly flow returns quickly after the frontal passage as low-
level ridging builds in under generally zonal flow aloft on Friday,
leading to above normal temperatures. The ECMWF hints at a warm
front surging northward late Friday ahead of a developing trough in
the Plains. This could lead to some shower activity along our
northern counties Friday afternoon, so have mentioned slight chance
or chance of rain/thunderstorms north of I-80.

The next system takes shape on Saturday as a surface low develops
over the Southern Plains as a trough digs into the Central US.
Models are in decent agreement with the surface low moving
northeastward into the Great Lakes region Sunday and into Monday,
stretching a cold front down through the Mississippi River Valley.
Here in Central AL, expect an increase in southerly flow ahead of
the deepening trough and temperatures remaining well above normal
for this time of year. For now, models disagree on exactly when the
cold front pushes through Central AL just beyond the extended
forecast period (late Monday into Tuesday). Will continue to monitor
this system for timing and any severe potential in the coming days.



06Z TAF Discussion.

Skies have cleared for many, except for near MGM/TOI where some
CIGS near 5 KFT remain but are dwindling. The upper low continues
to be centered over the South Carolina coast. Some MVFR cigs are
present across Georgia but this extent of the MVFR cigs should
remain east of the Central Alabama terminals. With clearing and
lighter winds, we will likely have some patchy fog during the late
night and early morning hours. At this time, MVFR visibilities
are in all TAFs for the pre-dawn hours. Do have tempos going down
to IFR visibility at EET/ASN/ANB for a few hours around sunrise
where the best lingering low level moisture remains. Expecting VFR
TAFs by 15/16z on Tuesday with mixing.




Low stratus across the far east and patchy fog are possible
overnight tonight as an upper low pulls further away from the
area. Drier conditions are then expected through mid week before
moisture returns ahead of the next system Wednesday night into
Thursday. Critical fire weather conditions are not expected at
this time.


Gadsden     51  81  54  84  61 /   0   0   0   0  20
Anniston    53  80  57  84  62 /   0   0   0   0  20
Birmingham  54  82  60  85  66 /   0   0   0   0  30
Tuscaloosa  52  83  57  85  64 /   0   0   0   0  60
Calera      54  82  59  84  64 /   0   0   0   0  30
Auburn      55  80  59  83  63 /   0   0   0   0  10
Montgomery  55  84  59  87  64 /   0   0   0   0  20
Troy        53  83  57  84  62 /   0   0   0   0  10





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