Area Forecast Discussion
Issued by NWS Birmingham, AL
FXUS64 KBMX 270003
Area Forecast Discussion
National Weather Service Birmingham AL
603 PM CST Sun Feb 26 2017
For 00Z Aviation.
Tonight and Monday.
Clear skies and low humidity prevailed across central Alabama
Sunday afternoon. It is hard to believe that 24 hours from now
there will be widespread showers and a few thunderstorms across
central Alabama. High clouds were advancing rapidly eastward
towards Alabama as a weak short wave trof moves into Texas.
Southerly low winds will increase overnight, especially west of
Alabama. This will set-up a convergence zone across east Texas and
Arkansas, where showers and a few thunderstorms will develop by
midnight. The activity will likely organize into an MCS and track
eastward overnight reaching west Alabama near sunrise Monday. The
best forcing will occur across west Alabama, between 6 am and 12
noon. This is when rainfall intensities will be highest and the
best chance for thunderstorms. The air mass will be very stable
at the surface due to low dewpoint temperatures, but strong
forcing aloft could produce some elevated storms. The activity
will shift eastward and southward in the afternoon and decrease in
intensity as the low level forcing weakens. There will likely be
a big difference in temperatures Monday afternoon between the rain
cooled far northern counties where readings may not get out of
the 50s, and the southeast counties where temperatures could rise
into lower 70s before the rain arrives.
Tuesday through Saturday.
The main area of precipitation should be out of the area by
Monday evening. The warm front, which may be impeded by rain
during the day, should then lift northward through the area.
Height rises will occur due to the influence of upper-ridging
located near the Florida Straits, indicating some subsidence.
Moist southerly flow and isentropic lift will continue, however,
so a few showers and perhaps an isolated thunderstorm will
continue to be possible, with the focus shifting to the far
northern counties near a low- level moisture axis. This will
continue to be the case on Tuesday, with some rain chances along
the northern periphery of the upper ridge while some drier air
aloft begins to work in from the south. CAPE values will reach
1000 J/kg on Tuesday with dew points around 65 and around 45 kts
of deep layer shear. Given steep mid- level lapse rates in place,
if a storm developed it could be strong or even severe. However,
due to the lack of a trigger mechanism and subsidence aloft this
still seems like a low chance.
Confidence is increasing in the severe weather potential for
Wednesday. While the primary upper-level forcing will remain north
of the area with the shortwave trough, 500 mb height falls will
occur across the area as a 80+ kt mid-level jet streak and 120 kt
upper-level streak move in. A quality warm sector will be in place
ahead of the front with highs in the mid to upper 70s (around 80
in some locations), dewpoints in the mid 60s, and mid-level lapse
rates of 7+ C/km allowing for CAPE values in excess of 1000 J/kg.
Models have varied a bit on LLJ strength, now indicated to be
around 45 kts, and winds will be veered, however sufficient
helicity and low-level shear will be present with curved
hodographs indicating the potential for a couple tornadoes.
Additionally, the deep layer shear will have enough of a
perpendicular component for supercells to be present ahead of a
squall line along the front. Damaging winds will be a threat with
a squall line, and steep mid-level lapse rates will result in a
threat for hail with supercells. The timeframe looks to be
Wednesday afternoon and evening with the relatively greatest
threat being across the northwest half. Behind the front, dry
conditions will move in Thursday through the rest of the forecast
00Z TAF Discussion.
The 00z forecast will advertise VFR conditions for the first 12
hours and then some MVFR vis possible. Surface high pressure will
continue moving eastward this period as a developing storm system
moves into the southern plains. Winds over Central Alabama will
maintain and easterly component much of the period picking up to
6-9kts on Monday. All terminals will remain just to the north of a
warm front moving northward into southern Alabama. An upper level
disturbance moves west to east across the area and increases
moisture just to the north of that warm front. Therefore, clouds
should gradually lower but maintain VFR and rain showers are
possible by 15z. Rain looks likely into the afternoon at most
sites. Took vis to MVFR and ceilings may eventually get there too.
There will be limited instability aloft and did not mention
thunder at this time, but an outside shot at some isolated thunder
is in the cards too.
Moisture will increase rapidly after midnight as a warm front
lifts northward from the Gulf Coast. Rain with embedded
thunderstorms will move into west Alabama near sunrise Monday and
spread across central Alabama during the day. A warm and wet
pattern will continue through Wednesday. A cold front will bring
an end to the rain Wednesday night.
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 40 59 53 73 63 / 10 80 50 60 30
Anniston 41 62 55 75 63 / 10 80 40 40 20
Birmingham 44 63 58 76 65 / 10 80 40 40 30
Tuscaloosa 44 66 59 78 66 / 20 80 40 40 20
Calera 44 64 58 76 65 / 10 80 40 40 20
Auburn 44 67 58 76 62 / 0 40 20 30 10
Montgomery 44 71 60 81 65 / 0 60 20 20 10
Troy 45 72 59 80 64 / 0 40 20 20 10