FXUS64 KBMX 230556

Area Forecast Discussion
National Weather Service Birmingham AL
1156 PM CST Tue Jan 22 2019

For 06Z Aviation.


Through Wednesday.

Low level southerly flow, between a surface ridge to our east and
approaching surface low/front to our west, has increased today,
advecting moisture northward. Expect a continued increase in cloud
cover and gusty winds through the evening hours. Expect showers to
develop around midnight, as the low level jet increases. Coverage
will gradually increase overnight, with best chances in the west.

By sunrise, a deep longwave trough will stretch through the
central CONUS, with a surface low moving into the Midwest and a cold
front crossing the Lower Mississippi River Valley. As moisture and
lift increase ahead of the front, showers will increase across
Central Alabama through the morning hours. With the passage of the
front, widespread rainfall is expected. Cannot rule out a few
thunderstorms, but instability is weak and increasing showers
ahead of the front should further limit daytime instability. The
front moves through tomorrow afternoon and evening, with cold air
filtering in behind the front. Guidance continues to show moisture
exiting to the east a little quicker, with colder air lingering to
the northwest. Best chance of a wintry mix (with no accumulation)
could be portions of the east, where the cold air catches up to
deeper moisture. Otherwise, only flurries are expected.

After an initial cooling trend with sunset, will likely see a
slight warming trend overnight. Generally, overnight temperatures
will be in the mid 40s to mid 50s. Highs will warm into the mid
50s to upper 60s ahead of the cold front tomorrow, with locations
in the northwest seeing a quick cooling trend by mid afternoon as
the front passes. As moisture pulls off to the east and cold air
spreads into the area tomorrow night, lows will fall into the
upper 20s northwest to around 40F in the far southeast.


Thursday morning through Tuesday.

Some minor adjustments were made to the long-term forecast suite to
account for current spatial & temporal trends within latest
guidance. Negative height & temperature anomalies will be more
noticable in the Friday evening/Saturday morning timeframe as
another Canadian airmass moves in behind an exiting system Thursday
morning. The initial airmass change comes from a surface cold front
ushering in cooler & drier air via northwesterly flow overnight
Wednesday and into Thursday morning. Have kept a slight chance of
very light rain/snow showers through 6-9 AM across the eastern
portion of the forecast area as residual low-level moisture
interacts with cold-air advection. A mid/upper-level shortwave
should bring a reinforcing shot of cold air and is expected to move
in overnight Thursday/Friday morning as the primary longwave trough
feature settles across the eastern CONUS.

Thereafter, a few mid-level perturbations may rotate around the base
of the dominant longwave trough (as many as three or four through
the end of the weekend), each carrying their own small opportunities
for brief light precipitation as positive vorticity advection helps
enhance localized lift. For now the strongest shortwave looks to
pass through our area early Sunday and have kept a slight chance for
light rain & snow showers in the forecast to account for associated
ageostrophic lift & marginal low-level moisture availability.
However, given the overall nature of the dry & cool continental
airmass it will be difficult to get any measurable or impactful
areas of light rain or snow, especially this far south.

With the complex and unpredictable upper-level configuration in
place, future cycles will warrant adjustments as necessary including
any changes in forecast expectations to the aforementioned shortwave
features. For now, the best agreement in forecast progs are for a
cold front (and parent mid/upper-level trough) to pass through the
area early next week and carry another round of rain/snow showers to
the area. Despite better deterministic agreement currently, forecast
confidence is low as ensemble spread indicates many varying outcomes
this far out (as expected). Thus, this could be best handled as a
signal that global models are trying to indicate the next anomalous
trough to affect the eastern CONUS early next week with an
associated cold Canadian airmass. Something to watch as the trends
in the busy pattern continues.



06Z TAF Discussion.

Weather conds will deteriorate thru the period as a strong cold
front approaches west Alabama this afternoon. A southeast low
level flow is providing an influx of relatively drier air early in
the period, and pushed back the arrival time of MVFR cigs.
Showers will increase in coverage across west Alabama between 06z
and 12z due to strong warm air advection aloft. The showers
initially will be mostly light with vsbys aoa 3 miles. Widespread
MVFR cigs expected between 15z and 21z, with southeast winds
sustained 10-15 kts with gusts up to 25 kts. Heavier showers will
accompany the cold front. The cold front is expected to be near
KTCL arnd 21z and at KBHM/KEET/KASN between 23z and 00z. IFR cigs
looking more likely after fropa along with a quick switch to
west-northwest winds. Instability ahead of the front will be
confined to extreme south Alabama and only included VCTS at KTOI.




Moisture continues to increase across the area tonight ahead of
an approaching cold front. Winds will remain gusty from the
southeast to south. Showers will increase in coverage late
tonight, with widespread rainfall and a few thunderstorms possible
Wednesday, as the cold front moves through the area. Cold and
drier air will spread into the area behind the front, but RH
values remain above critical values. Overall, there are no fire
weather concerns.


Gadsden 45 58 31 45 26 / 40 100 100 10 10
Anniston 48 61 33 46 27 / 30 100 100 10 10
Birmingham 51 60 31 47 28 / 50 100 90 10 10
Tuscaloosa 54 61 32 48 28 / 60 100 80 10 10
Calera 50 60 31 47 28 / 50 100 100 10 10
Auburn 49 61 36 48 30 / 20 90 100 20 10
Montgomery 52 65 36 49 30 / 20 100 100 10 10
Troy 52 66 37 50 31 / 20 90 100 20 10




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