Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus64 kbmx 210447 
afdbmx

Area forecast discussion
National Weather Service Birmingham Alabama
1047 PM CST Wed Nov 20 2019

Update...
for 06z aviation.

&&

Short term...
/updated at 0235 PM CST Wed Nov 20 2019/
through tonight.

A very nice November day across central Alabama with temperatures
in the middle to upper 60s. A low level ridge axis was near the
Alabama and Mississippi State line. North winds were noted over
areas east of I-65, but have switched to a southeast direction
over Mississippi. Surface winds will become calm soon after
sunset and temperatures will quickly fall into the 50s. Low level
warm air advection will kick in later tonight as the surface high
shifts east of Alabama, and that will result in warmer temperatures
than the previous few nights.

58/rose

Long term...
/updated at 0353 am CST Wed Nov 20 2019/
Thursday through Tuesday.

Subtropical ridging centered over the southern Gulf will continue to
exert its influence over central Alabama on Thursday. Meanwhile a
low pressure system and associated mid-level vort Max will lift
northeastward over the Great Lakes region, ahead of a northern
stream shortwave trough over the upper Midwest. In the southern
stream, an upper low centered near the Grand Canyon will continue to
drift eastward within a southwestern Continental U.S. Trough. Weak subtropical
disturbances in the flow aloft and enhanced mid/upper-level moisture
will result in some mid and high clouds at times. There could be
some virga/sprinkles associated with this activity across the far
north Thursday afternoon, but the low-level air mass is expected to
be too dry for measurable precipitation. Models have continued to
under-do high temperatures the past few days, and with southerly
flow at the surface, expect this trend to continue despite the high
clouds, so will forecast high temperatures warmer than guidance. The
cold front associated with the Great Lakes system will sink
southward over the mid-south region Thursday night. Our far northern
counties will be near the southern fringes off the pre-frontal
moisture axis and 30 kt llj, so a few showers are possible there
late Thursday night with some isentropic lift and weak disturbances
in the flow aloft. A west to east gradient in low temperatures is
expected, as increased dew points result in mild temperatures in the
west, while lingering high pressure over the east results in cooler
temperatures.

The southwest Continental U.S. Upper low will continue to move eastward to the
Central Plains Friday afternoon and the Ozarks Friday night as it
gets some pushes and pulls from northern stream shortwaves and a
push from an upper low over the eastern Pacific. A wave of low
pressure will develop over the arklatex region along the front,
causing the front to stall and sharpen as a warm front over northern
Mississippi and the Alabama/Tennessee border. Bulk of the precipitation will
remain just northwest of the forecast area near the front through at
least midday. But with increasing deep layer moisture and isentropic
lift east of the surface low and continued impulses in the flow
aloft, expect increasing coverage of showers across the northwest
half of the area through the afternoon. These clouds/precip may keep
high temperatures down across the far north, but further south
expect continued warming with highs continuing to be above guidance.

Models continue to wiggle regarding timing of the frontal passage
late Friday night and Saturday as the southern flank of the upper
low becomes a positively tilted shortwave trough. Isentropic lift
near the warm front will continue to support showers across the north
Friday evening, with widespread showers expected along and ahead of
the front late Friday night and Saturday. Instability still appears
very limited Friday night with saturated profiles and 60-62f dew
points, but did add in a slight chance of thunder given the forcing.
Depending on how quick the front moves, some 65f dewpoints may move
up into our southern counties on Saturday. This could allow for some
weak instability to develop though low-level flow veers by then as
the surface low lifts away from the area, and the 850mb low level jet never
gets particularly strong. Therefore, severe weather potential is
still far too low to mention in the hwo, but will continue to
monitor given the strong shear present. Rainfall amounts will mainly
be an inch or less, with some higher amounts possible in the far
northwest.

Mainly dry conditions move in Saturday night through Monday. A
strong low pressure system is expected to lift from the plains to
the Midwest Tuesday/Tuesday night, though there is the typical
spread in details. Strong wind fields will be present, but at this
time moisture return is expected to be somewhat limited within a
narrow warm sector, limiting potential instability. At minimum, high
rain chances and breezy conditions appear to be in store for Tuesday
night.

32/Davis



&&

Aviation...
06z taf discussion.

VFR conditions forecast with no restrictions anticipated. It
appears that any lower clouds/ceilings will hold off until beyond
06z. Winds will be light and variable at night and 5-7kts daytime.

Surface high pressure slides east and south through the period. A
cold front approaches from the west but does not bring any rain
or restrictions until early Friday.

75

&&

Fire weather...

Dry conditions are expected through Thursday night with high
pressure in place and mild temperatures. The chance for wetting
rains returns Thursday night and lasts through Saturday thanks to
a frontal system that will move across central Alabama. Minimum
relative humidity values into the mid 30s Thursday afternoon and
higher thereafter.

&&

Preliminary point temps/pops...
Gadsden 38 68 46 66 56 / 0 10 20 40 90
Anniston 39 70 47 69 57 / 0 0 10 30 80
Birmingham 44 71 51 69 58 / 0 10 10 40 90
Tuscaloosa 43 72 52 72 57 / 0 0 10 40 90
Calera 43 71 49 71 58 / 0 0 10 30 90
Auburn 44 68 48 70 58 / 0 0 0 10 60
Montgomery 42 73 50 76 60 / 0 0 0 10 60
Troy 40 72 48 75 60 / 0 0 0 10 40

&&

Bmx watches/warnings/advisories/...
none.

National Weather Service Glossary of Abbreviations