Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 031110

Area Forecast Discussion
National Weather Service Birmingham AL
510 AM CST Sat Dec 3 2016

For 12Z Aviation.


Today and tonight.

A classic isentropic lift rain event is in the process of developing
for today into tonight as southwesterly warm advection occurs above
cool easterly low-level flow. Have trended faster with the onset of
precipitation through the daylight hours based on current radar
trends. The highest rain chances and heaviest rain through 12z
Sunday should occur generally along and north of Interstate 20.
Temperatures have been lowered closer to raw model numbers for highs
today in anticipation of the faster onset of precip and widespread
cloud cover.


Sunday through Friday.

Central Alabama will experience of prolonged period of showers and
thunderstorms Sunday through Tuesday, which will go a long way to
alleviate the severe drought conditions. Forecast rainfall amounts
are in the 2.5 to 3.5 inch range through Tuesday. The models are
in fairly good agreement showing the heavier rainfall occurring
during the day Sunday and again Monday night. The uptick in
rainfall intensity on Sunday is associated with a northern stream
short wave trof, while a strong short wave trof moving out of
Texas will bring a threat of severe weather and heavier rainfall
Monday night. Easterly low level flow Sunday through through the
day Monday will restrict northward advancement of more unstable
Gulf moisture, but model cross sections indicate some elevated
instability, and there will likely be some elevated storms. By
Monday afternoon a surface low will develop near the upper Texas
coast and track rapidly northeast in response to short wave trof
becoming negatively tilted. The warm sector along the Alabama
coast will push northward Monday evening. 0-6km Bulk Shear and
favorable low level hodographs will support the formation of
supercells with tornadoes in the warm sector. Main limiting
factor across central Alabama will be the amount of destabilization
within the boundary layer due to widespread rainfall north of
warm front. A low confidence tornado threat will be added to the
Hazardous Weather Outlook for Monday night for areas areas south
of Highway 80 and I-85.

The rain will push east of the area during the day Tuesday as the
main short wave trof lifts into the Ohio Valley region. The
exiting system may leave enough residual moisture Tuesday night
and Wednesday for skies to remain mostly cloudy, but dry aloft
will keep rain out of the area. A rapidly advancing northern
stream trof will push a strong cold front through Alabama on
Thursday. Moisture looks somewhat limited ahead of the front, and
kept rain chances below 40 percent. The coldest air mass of the
winter season will move into Alabama Thursday and Friday, with
highs on Friday in the upper 30s north to middle 40s south.



12Z TAF Discussion.

High to mid-level clouds are overspreading and persist as VFR
through the remainder of the daylight hours. Dry air will
initially prevent rain from reaching the ground, but light rain
seems likely to affect the northern sites beginning later this
morning into the early afternoon. Off and on light rain is
expected to continue through the end of the period.

At KMGM and KTOI, rain will probably stay north of those sites
until very late in the TAF period.

VIS and CIGs should eventually fall into the MVFR range at all
sites near the end of the TAF period as isentropic lift and rain
intensity increases.




Light rain will spread from west to east today. Heavier rainfall
and a few thunderstorms will occur tonight through early Tuesday.
Forecast rainfall amounts will average 2.5 to 3.5 inches through




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