Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Birmingham Alabama
545 PM CST Tuesday Mar 3 2015
for 00z aviation.
Another day...another tricky forecast as a we prepare for an
Arctic airmass to cause mischief across the region Wednesday
night into Thursday. In the meantime...a warm front is retreating
northward across the County Warning Area this afternoon...and temperatures have
surged to near 80 degrees across the southern counties. The main
focus for showers tonight should remain across the far northwest
or just north of the County Warning Area as an upper-level ridge holds firm over
the Gulf of Mexico.
The upper-level ridge is expected to flatten by Wednesday into
Thursday...but relatively high heights will remain across the
area. At the same time a shallow Arctic airmass will spread
southward setting the stage for a wintry mess across the southern
states...and potentially into the northwest part of our forecast
area. Models have trended toward a more consolidated trough axis
from the plains into the southwestern states...or in other
words...a slower and deeper solution. Such a scenario would
result in two key changes...slower timing with the passage of the
front...and precipitation lasting longer than previously expected.
At 12z Thursday...models agree that a trough axis will be
positioned well to our west...from Iowa to New Mexico...suggesting
the most intense precipitation across our area may not occur until
the 12-18z timeframe on Thursday as the trough approaches. Models
are having a tough time with the strength of the cold advection
and thermal gradient behind the Arctic front...making this a very
tricky forecast. For our five most northwestern counties...there
is enough of a potential for ice accumulations to approach or
possibly exceed 1/4 inch...that a Winter Storm Watch seems
prudent. Farther southeast...the freezing line is expected to
reach the Interstate 59 corridor between 15-18z on Thursday with
minor ice accumulations possible. Precipitation should be winding
down on Thursday afternoon as the trough axis shears out to our
north. Conditions will turn cold Thursday night...especially
across our north as high pressure settles southward...with lows in
the upper teens northwest to lower 30s southeast.
Dry conditions are expected for Friday and Saturday with persistent
northwesterly flow. Rain chances may increase by Sunday night into
Monday as a southern stream shortwave skirts along the northern Gulf
00z taf discussion.
Abundant moisture will lead to IFR ceilings again tonight.
Boundary layer winds will try to keep surface visibilities in
the MVFR range but ceilings of 100 to 500 feet will be possible
later in the morning. Dense advection fog/stratus possible in the
toi and mgm as southerly fetch off the Gulf continues. Light southerly
surface winds tonight.
Winter Storm Watch from late Wednesday night through Thursday
afternoon for the following counties: Fayette...Lamar...Marion...