Scientific Forecaster Discussion
fxus64 kbmx 191727
Area forecast discussion
National Weather Service Birmingham Alabama
1127 am CST Tue Nov 19 2019
for 18z aviation.
/updated at 0314 am CST Tue Nov 19 2019/
today and tonight.
A few very light rain showers and/or some patchy drizzle will be
possible through this morning across the far northern counties of
central Alabama. Also, a few spots may see some patchy valley fog
early this am. The precipitation activity will be thanks to an
upper shortwave moving through the base of a longwave trough that
is traversing eastward across eastern conus at this time. Most
areas will not measure or will only record very small amounts if
they do. In the wake of the trough, skies should clear for most
this afternoon and tonight. A few clouds may be noted in the far
northeast counties though. With cloudiness expected to decrease by
midday, we should warm nicely this afternoon topping out a few
degrees warmer than Monday. Overnight low ranges tonight will be
similar with lows from the mid 30s to the lower 40s.
/updated at 0314 am CST Tue Nov 19 2019/
Wednesday through Monday.
A mid-level ridge axis will move overhead on Wednesday, downstream
of several disturbances over the western Continental U.S.. in the southern
stream, a closed low will form over Southern California near the
base of a digging West Coast trough, causing the cutoff low
currently off the coast of Baja California to eject northeastward
over the Central High plains while inducing Lee cyclogenesis.
Meanwhile, a northern stream shortwave trough will be digging over
the northern rockies. At the surface, a ridge axis will be
located over central Alabama. Guidance has trended a little
stronger with cold air advection downstream of this ridge axis
across the eastern counties Wednesday morning, so high
temperatures were nudged downward. But still favored the warmest
guidance as temperatures have over-performed the past few days.
Wednesday night, the southern stream shortwave trough and
associated low pressure system will lift northeastward to Iowa,
and allow for some mid and high-level clouds to move over central
Alabama. These clouds and light southeast winds will keep low
temperatures a bit milder, but still on the cooler side of
Guidance seems to be trending towards better agreement regarding the
timing of the next system. Ridging and dry air look to remain in
place during the day on Thursday, as the shortwave trough that was
once in the southern stream continues to lift northeastward into
Canada ahead of the northern stream shortwave trough now over
Minnesota. Meanwhile the southwest Continental U.S. Upper low will drift
eastward towards Las Vegas. Pops have been removed from Thursday
afternoon given the dry air mass, with the cold front remaining
well northwest of the area. Southwesterly low-level flow and the
dry air mass should allow most areas to reach the low 70s for
highs. The cold front will stall over northern Arkansas Thursday
night as it becomes parallel to the upper flow and as a wave of
low pressure forms in response to troughing ejecting over the
southern High Plains. Pops for Thursday night continue to trend
downward with the only forcing being warm air advection and weak waves in the
flow aloft, with widely scattered light showers possible at most
across the northwest counties. Low temperatures will be milder and
temperatures may even rise a couple degrees after midnight as dew
points begin to increase.
Ensembles have trended quicker with the frontal passage Friday night
into Saturday morning, as the northern stream shortwave moving from
the Great Lakes to New England gives a push to the front and the
trough moving out of the Southern Plains. Pwats briefly increase to
1.6 inches, but the system should remain progressive, keeping
rainfall totals around 1.25 inches or less. Temperatures will warm
up into the 70s across the southern half of the area ahead of the
front on Friday. As the front moves through Friday night, there
will be plenty of shear, but instability still appears to
negligible given 60-62f dew points and nocturnal timing, along
with weak mid-level lapse rates and a fairly weak surface low.
Therefore, will continue to not forecast thunder or severe storms
at this time. If the quicker trend in the guidance continues, then
most areas would end up being rain-free but cool for any outdoor
activities Saturday afternoon. Dry and cool conditions are
expected Sunday and Monday ahead of another system expected to
move in beyond the current forecast period.
18z taf discussion.
VFR conds expected thru the period with clear skies and unlimited
vsbys. A weak sfc front will thru the area this afternoon and sfc
winds will veer from southwest to west. No clouds expected with
Localized valley fog will lift quickly this morning after
sunrise. Some light rain or drizzle will be possible as well
across the north half of the state this morning as a disturbance
moves across from west to east. Dry conditions continue through
much of this week otherwise with relative humidity values near or
above 40 percent each afternoon. The exception will be late
Thursday through Saturday as another frontal system moves through
with wetting rains expected.
Preliminary point temps/pops...
Gadsden 62 37 65 38 67 / 10 0 0 0 10
Anniston 63 38 66 41 69 / 10 0 0 0 10
Birmingham 65 40 68 43 70 / 10 0 0 0 10
Tuscaloosa 68 40 70 43 72 / 0 0 0 0 10
Calera 65 39 68 43 70 / 0 0 0 0 10
Auburn 61 41 67 43 68 / 0 0 0 0 0
Montgomery 69 41 72 43 73 / 0 0 0 0 0
Troy 68 41 70 42 72 / 0 0 0 0 0