Scientific Forecaster Discussion
fxus64 kbmx 230009
Area forecast discussion
National Weather Service Birmingham Alabama
609 PM CST Fri Feb 22 2019
for 00z aviation.
The surface warm front gradually lifted northward today and was
currently located near a Demopolis to Jemison to Wedowee line.
The warm front has not moved much the past few hours, and forecast
boundary layer winds do not show much northward push until later
tonight. Temperatures south of the warm front have risen into the
lower and middle 80s, with 50s north of the front. Most of the
shower activity has lifted north of central Alabama, but some
showers have developed just south of the warm front. Do not expect
much shower activity this evening, but increasing isentropic lift
after midnight will likely produce more shower activity, especially
north of I-20. Temperatures trends will be difficult overnight as
clouds decrease north, then increase later tonight. Lows north of
the cool front will stay steady this evening, then rise after
midnight as low level winds veer. Temperatures in the warm sector
will fall with the usual diurnal trend, but may bottom out by
midnight. Fog may become an issue overnight, especially if clouds
clear near or just north of warm front.
Saturday afternoon and Saturday night.
An upgrade to the severe weather risk appears warranted across our
far northwestern counties for Saturday night. Some important changes
have occurred in the latest model runs, including the appearance of
a more prominent elevated mixed layer and steeper mid-level lapse
rates. Dewpoints are also trending higher as models catch on to the
highly anomalous airmass lurking across the Gulf of Mexico. Several
days of moisture advection has resulted in 72-73f dewpoints in the
northern Gulf, and widespread 67-70f dewpoints should move inland
across Mississippi and West Alabama on Saturday afternoon. 2-3
decameter 500 mb height falls are indicated by the European model (ecmwf) from noon
to 6 PM across our northwestern counties as a sharpening surface
trough approaches from the west. This feature is likely to result in
development of deep convection to our west in the presence of strong
low-level and deep-layer shear. Shear vectors over the warm sector
are oriented at a approximately a 45 degree angle to the surface
trough, which will be favorable for a broken line of supercells or
perhaps discrete supercells through about 9 PM as storms enter our
northwestern counties. Thereafter, shear vectors become more
parallel to the convective band, and storms should become more
linear as they approach I-59. Height and pressure falls may extend
far enough south for our northwestern counties to be impacted by one
or two robust supercells with risk for strong tornadoes. Confidence
decreases with southward extent toward the I-59 corridor, but a
tornado and damaging winds cannot be ruled out if the surface
pressure trough ends up as strong as indicated by some model
Sunday through Thursday.
Improved weather & a much needed dry/drier period looks to move into
the region as a stable Continental airmass & zonal split-flow aloft
encompasses much of the Continental U.S. & The southern Gulf Coast after Sunday
morning. Expect this to stick around through at least mid-week
before some rain showers possibly impact the area on Wednesday as a
shortwave trough moves along the Gulf Coast. Otherwise the overall
weather theme for next week should remain mostly tame with no
significant storm systems currently expected. Would hopefully start
to see some improvement with any lingering river flooding concerns
during this time.
00z taf discussion.
A big mixed bag of flight categories this evening...VFR to IFR.
Expect these varying conditions to continue this evening with some
improvement noted. Ceiling/vis restrictions quickly materialize
after 06z. Winds will start increasing and veering around sunrise.
This will also trigger the ceiling/vis improvement with MVFR by
18z. A cold front will move into western areas around the 00z time
frame with thunderstorms/ceiling restrictions developing again.
A warm front still located between bhm/mgm has the northern sites
in lower ceilings, while southern sites have some clearing. There
will be a period this evening where things improve, outside the
shower areas. Then, clouds redevelop area wide with patchy low
vis. The shower activity will generally be scattered at the
terminal locations and most likely will amend for specific timing
of any rain at any particular site.
Ahead of an approaching front on Saturday, winds will increase
into the 10-20kt range and possibly higher. These winds will
linger into the evening hours ahead of the front. This will occur
outside the rain areas.
A prolonged period of rainfall will continue through the end of the
week, with a strong storm system expected to move through central
Alabama Saturday night. Very wet conditions are expected, especially
across the northern half of the area. Drier conditions return to the
area for at least a couple days to start next week. There are no
fire weather concerns at this time.
Preliminary point temps/pops...
Gadsden 55 73 50 60 34 / 60 40 80 0 0
Anniston 58 75 53 63 36 / 40 30 80 0 0
Birmingham 60 77 52 62 37 / 40 40 80 0 0
Tuscaloosa 62 79 50 63 37 / 40 50 80 0 0
Calera 62 78 52 63 37 / 30 40 70 0 0
Auburn 61 78 57 66 39 / 20 20 70 10 0
Montgomery 66 82 58 68 40 / 20 20 70 10 0
Troy 65 83 59 68 41 / 20 20 60 10 0
Flood Watch through late Saturday night for the following