Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Birmingham Alabama
1113 PM CST Wed Nov 13 2019
for 06z aviation.
/updated at 0327 PM CST Wed Nov 13 2019/
Surface high pressure is centered over upstate New York this
afternoon, stretching down the East Coast and around the southern
extent of the Appalachians. This has kept light easterly to
southeasterly flow across the area, with mostly clear skies.
Seeing an increase in high clouds from the west in advance of a
storm system moving across northern Mexico. Low level flow will
swing around to the south overnight, providing a slight increase
in moisture. Coupled with increasing clouds, temperatures will be
8-15 degrees warmer tonight with lows in the low to mid 30s.
Overall evolution of the next system has not changed from previous
thinking, as northern and southern stream systems phase to our
west tomorrow. Made adjustments to rain chances, as models have
focused initial lift and best moisture return across the southeast
tomorrow morning, with rain slowly spreading northward. Best
chances remain along and south of I-85.
/updated at 0356 am CST Wed Nov 13 2019/
Thursday through Tuesday.
Models continue to converge toward the European model (ecmwf) solution for Thursday
through Saturday, indicating phasing of shortwaves in the northern
and southern streams to our west. As the two shortwaves merge,
lift may increase enough to produce a shield of light rain over
the southern two-thirds of the area on Thursday afternoon with
temperatures holding in the 40s under overcast skies. Strong
height falls over Mississippi will correspond with strengthening
isentropic lift and large-scale ascent across Alabama Thursday
night, resulting in a high chance of widespread light rain along
and south of I-20. Rain chances have been increased into the 60 to
90 percent range for this portion of our forecast area.
The forward speed of the developing upper low has decreased in
recent model runs, increasing the possibility of clouds and rain
lingering across our eastern half on Friday. A shear axis or
deformation zone may form just north of the closed upper low
Friday night and early Saturday morning, further delaying the
exit of the rain. Rain chances have been increased but will need
to be raised much higher if model trends continue.
The upper low should finally move out of our forecast area on
Saturday afternoon, leaving behind dry conditions and 50s to 60s
for afternoon highs on Saturday and Sunday. Another strong
shortwave is expected to dig across the deep south on Monday and
Tuesday with strong height falls extending well into the Gulf of
Mexico. Models currently show the strongest lift with this system
will be aimed too far south to include rain chances at this time.
06z taf discussion.
VFR conditions are expected for most tafs through 18z Thursday.
The exception to this will be toi. The easterly flow tonight will
have a spattering of low stratus in the southeast tonight.
Otherwise, shortwave activity will allow for MVFR cigs
accompanying some showers to move northward into central Alabama
toward mgm/toi. Further north, lower chances of showers are
present for tcl/eet/asn/anb for late afternoon, but the lower cigs
should stay south in the afternoon. Rain chances increase for the
evening spreading into the remainder of the taf sites. MVFR cigs
will spread to most except maybe tcl before the shortwave pushes
east. In the far south some IFR will be possible for mgm/toi where
the best moisture will be.
A slight increase in moisture is expected tonight, ahead of
widespread light rainfall generally along and south of Interstate
20 Thursday afternoon and Thursday night. Some of this rain could
linger into Friday across our eastern counties. Drier conditions
return for the weekend, with afternoon relative humidity values
remaining above critical levels.
Preliminary point temps/pops...
Gadsden 28 49 36 53 33 / 0 20 40 10 0
Anniston 31 50 37 53 34 / 0 30 50 20 10
Birmingham 34 50 38 52 33 / 0 20 40 10 0
Tuscaloosa 32 50 38 53 32 / 0 30 30 0 0
Calera 32 50 38 53 33 / 0 30 50 10 0
Auburn 34 49 39 50 38 / 0 50 80 30 20
Montgomery 33 50 41 54 37 / 0 50 80 20 10
Troy 33 50 41 53 37 / 0 60 80 20 10