Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Birmingham Alabama
559 PM CST sun Dec 21 2014
for 00z aviation.
Short term...tonight through Tuesday night.
Clouds continue to blanket Alabama due to a moist easterly flow. A
zone of deeper moisture across northwest Florida will shift slowly
northward overnight and there is a chance of light rain across
east Alabama. The deeper moisture will overspread central Alabama
on Monday..but lack of any significant forcing will be the
precipitation as scattered light showers. A deep closed upper low
over the plains states will push a fast moving short wave trough
across the lower Mississippi Valley Monday night...and bring a
round of heavier showers and thunderstorms into West Alabama Monday
night. The upper low will elongate into a highly amplified trough by
Tuesday and widespread showers and embedded thunderstorms are
expected Tuesday across all of central Alabama. This digging trough
will cause a southern surface low to develop across Louisiana
Tuesday afternoon and track northeast across north Alabama Tuesday
night. The models are in pretty good agreement in the track and
timing of the surface low. The surface low will drag a cold front
across central Alabama late Tuesday night.
A small threat for severe weather continues for all of central
Alabama ahead of the cold front. The two limiting factors for
severe storms will be the widespread convection expected across
the area during the day on Tuesday. This will limit instability
and make it difficult for the air mass to recover once the front
arrives. The other limiting factor is the possibility of
convection along the Gulf Coast...which will also limit the
amount of energy along the front. For these reasons we are keeping
the threat confidence low at this time. This is a very dynamic
system and there is ample shear and lift for the production of
thunderstorms. Prolonged southerly flow ahead of the front will
bring surface dewpoints in the the lower 60s into much of central
Alabama. This will provide just enough instability for limited
cape and any storms that can develop any upward height will have
the potential to rotate and become severe.
Long term...Wednesday through Sunday.
The surface cold front will be pushing across east Alabama early
Wednesday morning. The severe threat should be shifting into
Georgia by that time. Strong cold air advection will occur on
Wednesday and temperatures will either be falling or remain steady
for most of the day. There is enough wrap around moisture for the
possibility of some Post-frontal showers. Christmas day may be the
first day this week we experience abundant sunshine. Temperatures
on Thursday will be near average as the coldest portion of the air
mass will shift quickly eastward. A weak front will push through
the area Friday night and Saturday and bring a chance of showers.
Clearing out by Sunday.
00z taf discussion.
All signs continue to point to increasingly lower ceilings across
central Alabama terminals over the next 24 hours. Airports that
are MVFR early on should eventually get down to IFR. Those that
are IFR early (mainly toi) may go LIFR. Computer model guidance
suggests that conditions won't improve much if at all during the
day on Monday.