Area Forecast Discussion
Issued by NWS Birmingham, AL
FXUS64 KBMX 241718
Area Forecast Discussion
National Weather Service Birmingham AL
1218 PM CDT Fri Mar 24 2017
For 18Z Aviation.
Today and Tonight.
This AM, a large surface high pressure ridge was centered just off
the Atlantic Seaboard with southeast to south low level flow into
Alabama. The satellite picture over Central Alabama, unlike
yesterday at this time, is almost completely overcast across
Central Alabama as a result of this change. High pressure across
across the state will continue to weaken with southerly flow
increasing as the ridge moves further into the Atlantic. This is
due to our continued advancement of a developing low pressure
system across Eastern Colorado into Western Kansas with an
associated front extending southward into West Texas. This low
should push toward Missouri through tonight and drag the front
toward the Mississippi River Valley extending into Southeast Texas
in the process.
The main change expected for today will be a smaller diurnal
temperature range with the extra cloud cover and thus not quite as
warm high temperatures. Also, dew points will continue to slowly
creep up with the continued warm sector onshore flow. Mild
conditions continue into tonight ahead of our approaching weather
system. All guidance including hires, except GFS, hold off precip
until the daytime on Saturday. I only left in very low pops in the
far west from 9-12z.
Saturday through Thursday.
Storms should be ongoing across MS at daybreak Saturday with a
respectable 40-60 kt low-level jet to our west. An organized band
of storms moving eastward from MS should encounter a less
favorable environment with the low-level jet weakening as the
system becomes vertically stacked. SBCAPE values should range from
300-700 J/kg and combine with 0-6 km shear of 40-45 kt yielding a
low-end threat for damaging winds mainly west of I-65 late
Saturday morning and into the early afternoon. The severe weather
threat should gradually decrease with eastward extent as
instability decreases. Additional showers and an occasional
thunderstorm may develop Saturday night with the surface front and
500 mb trough axis hanging back to the west.
Moist southwesterly low-level flow is expected to continue into
Sunday, and isolated showers/storms cannot be ruled out. Another
upper trough will move toward the area on Monday and has trended
more impressive in terms of the severe weather threat. SBCAPE is
now expected to reach 1000-2000 J/kg with steep lapse rates
spreading eastward across MS into West AL. Lift/forcing with the
upper trough appears to be subtle which would allow higher CAPE to
build before convective initiation occurs. Moderate 500mb
westerlies of 30-40 kt could yield clusters and supercells
capable of producing hail possibly larger than quarter size and
damaging winds. The tornado threat appears very low at this time
due to marginal surface to 700mb shear. The upper trough will be
slow to move through, and convection could linger into Tuesday
morning across the north with a moist southwesterly fetch
remaining in place.
Yet another system will move into the Plains on Wednesday with
drier and warmer conditions across Alabama as a 500 mb ridge
amplifies over the region. It is too early for specifics, but
another severe weather threat could be on the table for Thursday
especially if the trough trends toward more of an open wave than
18Z TAF Discussion.
The surface pressure gradient between high pressure off the eastern
seaboard and low pressure across western Oklahoma will continue to
tighten today, resulting in gusty winds at times from the southeast.
Expect clouds to increase from the west this afternoon and evening
with gradually lowering CIG`s but VFR criteria should be maintained
at most terminals through daybreak Saturday. Winds will discourage
visibility reductions overnight and will again become gusty on
Saturday. RA with possible TS will approach from the west toward
the end of this cycle as TCL may experience SHRA toward 12Z then
possible TSRA toward 15Z Saturday. SHRA will be possible at
BHM/EET/ASN/MGM around 15Z and at ANB/TOI toward 17Z on Saturday.
Low level moisture will gradually increases today ahead of
increased rain chances for this weekend. Thunderstorms are
expected, with locally heavy rainfall. Another system will bring
more rain chances for Monday and Tuesday. Critical fire weather
conditions are not expected through the next 7 days.
.PRELIMINARY POINT TEMPS/POPS...
Gadsden 57 77 58 76 57 / 10 80 80 50 20
Anniston 57 76 58 77 58 / 0 70 80 50 20
Birmingham 60 76 60 78 59 / 10 80 80 40 20
Tuscaloosa 60 73 61 81 61 / 10 90 60 30 10
Calera 59 77 60 79 60 / 10 80 70 40 10
Auburn 57 76 58 78 59 / 0 50 60 40 10
Montgomery 60 79 60 84 61 / 10 70 60 30 10
Troy 58 78 60 82 61 / 0 50 50 30 10