Area Forecast Discussion
Issued by NWS Birmingham, AL

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464
FXUS64 KBMX 280454
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1054 PM CST Fri Nov 27 2020

.UPDATE...
For 06Z Aviation.

&&

.SHORT TERM...
/Updated at 0745 PM CST Fri Nov 27 2020/

A low-amplitude perturbation continues to advance eastward across
the Gulf Coast States with clusters of showers and embedded
thunderstorms stretched across most of Central AL at this time.
Thunderstorms have favored the south near the weak surface low
where MUCAPE <750 J/kg and ~40 kts 0-6 km shear are in place per
mesoanalysis. Winds remain light and variable, though should
become more northerly behind the system gradually exiting the
area to our east and south. This should begin to promote cool/dry
advection in the north and northwest into tomorrow. Until then
I`ve tweaked PoPs and temperatures in the near-term to account for
observational trends. Generally speaking, PoPs were increased as
a fairly large area of light rain remains in place across Alabama
and into the TN Valley. Rainfall amounts outside of convection
remains quite light. Trends indicate the departure of quality
moisture and overall forcing such that decreasing rainfall
intensity/coverage is forecast southeastward into tomorrow morning
where only mentionable PoPs are along and south of I-85 through
~18z.

40/Sizemore

.LONG TERM...
/Updated at 0210 PM CST Fri Nov 27 2020/

Saturday night through Thursday.

A fast moving short wave trof will move out of the four corners
region and track eastward towards Alabama Saturday night and
Sunday. Saturday evening will be rain free across Central
Alabama, with showers moving into the southwest counties between 3
and 6 AM Sunday. Strong forcing aloft will produce widespread
showers and isolated thunderstorms during the day Sunday. Strong
low level southerly flow on Sunday will advect 60+ surface
dewpoints northward into areas south of I-85. 0-6km bulk shear is
high enough for organized storms. There may be narrow window of
time where instability may be high enough for stronger storms,
but clouds and rain during the day Sunday will likely limit
instability. The coldest air mass of the season will overspread
Alabama Monday through Wednesday. Temperatures on Monday will stay
steady or fall through the 40s. Lows in the 20s areawide Tuesday
and Wednesday mornings. Another upper impulse will bring a chance
of showers during the day Thursday.

58/rose

Previous long-term discussion:
/Updated at 405 AM CST Fri Nov 27 2020/
Saturday night through Wednesday.

A split jet stream pattern will feature a closed upper low across
the Southern Plains and a shortwave diving southward toward the
Upper Mississippi Valley. The closed low to our west will become
an open wave, taking on a neutral to negative tilt as it interacts
with the northern wave on Sunday morning. This will promote a
deepening surface low over Alabama. An abundance of large-scale
ascent and isentropic lift will overspread our region, leading to
widespread rain and perhaps some thunder for the latter half of
Sunday morning through early Sunday night.

A dry slot is expected to rapidly put an end to the rain by
midnight Sunday night as a deepening area of low pressure moving
toward the Mid-Atlantic states. Significant height falls and
strong cold advection will take place Sunday night into Monday
night as the northern shortwave absorbs the southern shortwave.
Much of our forecast area is expected to remain in the 40s Monday
afternoon with brisk northwest winds of 10-15 mph. The first
widespread significant freeze will occur Tuesday morning with lows
ranging from the lower 20s in our northwest to the upper 20s in
our southeast. Temperatures will only rise into the 40s Tuesday
afternoon as cold northwest flow continues. Temperatures should
moderate for Wednesday as deep-layer westerly flow develops.


&&

.AVIATION...
06Z TAF Discussion.

Weather conditions have somewhat improved across Central AL as
convection has now exited to our east with drier air now moving in
from the northwest. For now we`ll continue to watch areas of
light rain move to the east with a broad diversity of cloud bases
showing on current surface observations. It`s been very
challenging to establish a trend with many sites bouncing around
various flight categories. For 06z TAFs I`ve placed northern
terminals in a VFR/MVFR theme overnight, with MGM/TOI more toward
MVFR/IFR, favoring guidance means. By tomorrow morning
improvement should continue to the south and east as rain chances
decrease, drier air moves in, and clouds lift & diminish in
coverage. Winds should become northerly at 4-7 kts throughout
that time.

40/Sizemore

&&

.FIRE WEATHER...

Showers and embedded thunderstorms will overspread the area
tonight, mainly for areas along and south of I-20. The rain will
be confined to areas along and south of I-85 on Saturday as a
weak cold moves through the area. Another rain event on Sunday.
Much colder and drier Monday through Wednesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     48  65  43  61  41 /  70   0  10 100  90
Anniston    52  66  48  64  43 /  70   0  10 100  90
Birmingham  52  65  50  63  42 /  70   0  20 100  70
Tuscaloosa  53  66  49  64  41 /  60   0  20 100  60
Calera      54  66  50  64  42 /  80  10  20 100  70
Auburn      58  68  54  62  46 /  90  20  10 100  80
Montgomery  59  70  56  68  46 /  90  20  20 100  70
Troy        61  69  57  67  47 /  90  40  20 100  70

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
None.

&&

$$



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