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Area forecast discussion
National Weather Service Birmingham Alabama
639 am CST Thu Dec 12 2019

Update...
for 12z aviation.

&&

Short term...
/updated at 357 am CST Thu Dec 12 2019/
today and tonight.

Stable high pressure conditions with clear skies continue across a
portion of the eastern conus, including into the deep south this
morning. Northeasterly winds will veer throughout the afternoon as
anticyclonic flow wraps around into the southeast with high pressure
moving into the mid Atlantic. Flow above 700 mb, however, remains
more westerly to southwesterly with an upstream trough axis ejecting
into the High Plains. This energy aloft will continue east today and
position near the arklatex by 6 PM. This trend will help instigate a
period of moist isentropic ascent across the Gulf Coast region. 925-
850 mb Theta-E advection will move from south to north by mid-
morning, resulting in an increase in low/mid-level clouds and
drizzle/light rain showers. The initial onset may be delayed in some
places as dry air pockets below 850 mb saturate, thus only slight
chance pops before 9 am in the far southeast. Breezy easterly winds
are expected from mid-morning through the late afternoon area-wide.

Pops steadily increase into the evening as forecast soundings not
only become more saturated, but depict steepening mid-level lapse
rates ~7.0-7.5 c/km. Parcels ascending from a warm nose aloft
(~1,000 m) would contain MUCAPE ~500-750 j/kg. With an abundance of
wind shear and favorable lift, elevated thunderstorms are possible
south of I-20 from the late afternoon into the overnight period
despite cool temperatures at the surface. Cold temperatures aloft
and cape in the hail growth zone would infer that any more robust
cells would be capable of producing small hail. Otherwise, a good
coverage of moderate rain showers and embedded thunderstorms should
be expected across the east and southeast into Friday morning with
more isolated coverage farther northwest. High temperatures are
forecast into the 50s this afternoon, though rain may have an impact
on this notion for a few areas across the southeast. Temperatures
overnight would trend back toward their respective dewpoints, in the
low to upper 40s.

40/sizemore

Long term...
/updated at 357 am CST Thu Dec 12 2019/

Overall an active pattern will continue through the extended. A
system will impact the area every couple of days. Best chances for a
good amount of sunshine will be on Sunday and again on Wednesday.

Friday through Sunday.

Rainfall mentioned in the short term will continue to move northward
as the jet begins to work into the region. We will also see the
activity begin to fill in to the west. Thus rainfall becomes
widespread during the morning. Will continue with the elevated
thunder chances as the system moves in through the afternoon. We
will finally begin to see the rain chances end by Saturday morning
as the cold front works in. The upper low will swing through the
area on Saturday and will provide another increase in clouds,
especially in the north. At this time it looks like we will remain
dry but will need to keep an eye on the trends. Regardless, pressure
gradients will keep things quite windy Friday and Saturday. Dry on
Sunday with some potential sunshine during the day, before clouds
move back in during the evening hours. Highs pretty much will be in
the 50s with lows in the 30s and 40s.

Monday and Tuesday.

The next system will begin to work into the area overnight Sunday
and push through the area on Monday. Rain will linger through
Tuesday morning in the northwest to Tuesday afternoon in the
southeast. This system will be another potential beneficial rain for
the extended period. Highs will warm into the mid 60s to low 70s
degrees in the south in Monday ahead of the front that will move
through sometime overnight Monday night into Tuesday afternoon. With
the latest runs, model consensus is beginning to agree to a severe
chance during the day on Monday. There will be a pretty good window
for a moist and unstable environment across the southeast. Strong
vertical shear will be available across the area with the best
locations across the northwest. Here we could see 0 to 6 shear
around 60 kts, 0 to 1 km helicity around 300, bulk shear of 50 to 55
kts. Mid-level lapse rates will support the threat as well along
with a strong low level jet working into the area. Forecast soundings and
hodographs support supercell environments during the day as well.
With this update, there is enough confidence to add the threat
for severe weather on Monday, including the threat of tornadoes.
Much more on this over the next few runs. Dry weather returns on
Wednesday behind the cold front, with highs in the upper 40s and
low 50s.

16

&&

Aviation...
12z taf discussion.

An east to east-southeast low level jet continues this morning.
Will continue mentioning non-convective low level wind shear in terminals for a
few more hours until we get enough mixing, surface winds, etc. Low
level moisture will increase today ahead of an approaching
shortwave. Showers will move in from the south this afternoon into
tonight. A few thunderstorms will be possible tonight as well
with this system. Cigs will start out VFR today but will lower to
MVFR during the afternoon in the south near mgm/toi and spread
northward to the remainder of the sites toward 23-00z. Cigs should
continue to lower to IFR and below overnight as our column
continues to moisten and the activity becomes more widespread.

08

&&

Fire weather...

Light rain showers will begin to develop late this morning in the
southeast, lifting northward into the afternoon and evening. Rain
chances become more widespread by Friday morning as low pressure
develops and lifts off to the northeast. Embedded thunderstorms are
possible later this afternoon and into the overnight period, with
rain showers picking up in intensity as well. Winds will generally
be out of the east through this period, and gusty at times. With
expected rainfall and elevated relative humidity values, there
are no fire weather concerns at this time.

&&

Preliminary point temps/pops...
Gadsden 55 40 53 43 57 / 10 50 80 60 30
Anniston 55 41 54 45 60 / 30 60 80 60 30
Birmingham 55 44 54 46 58 / 20 50 80 50 20
Tuscaloosa 57 44 56 44 61 / 10 40 80 40 20
Calera 54 42 56 45 60 / 30 50 80 50 20
Auburn 51 41 54 48 60 / 60 80 80 60 20
Montgomery 55 44 59 48 64 / 50 70 80 50 20
Troy 53 45 59 48 64 / 60 80 80 50 20

&&

Bmx watches/warnings/advisories/...
none.

&&

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