River Flood Warning 74, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
516 AM CST Thu Mar 5 2020

.UPDATE...
For 12Z Aviation.

&&

.SHORT TERM...
/Updated at 0242 AM CST Thu Mar 05 2020/

Through Friday.

The large plume of rain and storms will continue across the area
through the morning. Flooding will continue to be a concern
through the early afternoon. Based on the latest model data and
observations, there will be continued showers and embedded
thunderstorms moving over the Flash Flood Watch area. The best
convergence of the moisture appears to be between Alabaster and
Montgomery. The original estimate of 1 to 3 inches or rain looks
good through the morning hours, with higher local amounts
possible.

Another concern would be some stronger elevated storms in the far
southeast. Warm/moist advection continues north of the surface front
which is currently stationary along the coastline of the northern
Gulf of Mexico. This may very slowly shift north later this
morning as southerly winds just off the surface continue. Thinking
is that the front stays well to our south but could be close
enough for a few stronger elevated storms to make it into our
southeast. Small hail and gusty winds would be the main concern
through the morning.

Finally the rain shield will begin to shift south and east as the
surface low pressure along the coast begins to accelerate eastward
this afternoon. This will be in advance of a strong cold front that
will slide through this evening. Looks like the front will be near
the I-20 corridor by Midnight and then south of the area by sunrise
Friday. Temperatures will be cooler on Friday behind the cold
front, but may feel warmer than today as the "sun" actually
returns from its inactive status.

16

.LONG TERM...
/Updated at 0242 AM CST Thu Mar 05 2020/
Friday night through Wednesday.

Broad mid/upper-level ridging will encompass much of the CONUS
over the weekend between a trough and associated nor'easter departing
eastward over the western Atlantic and another trough near the
West Coast. The pressure gradient between the nor'easter and a
1035mb high centered over the Lower Ohio Valley will maintain
northerly winds and cold air advection. A light freeze is expected
over generally the northern half of the area, and while the
growing season has not officially started, steps may need to be
taken to protect sensitive plants. Light northerly winds will keep
temperatures a few degrees below normal on Saturday but there
will be plenty of sunshine. The pressure gradient relaxes Saturday
night as high pressure reaches the Carolinas. This results in
ideal radiational cooling conditions during the evening hours, but
east winds will pick up a bit later in the night, while some high
clouds move through due to a weak wave aloft. This will probably
keep any freezing temperatures confined to typically cooler
locations. Low-level southerly flow results in very pleasant early
spring conditions for Sunday with just a few passing mid-level
clouds.

By early next week a closed low will have formed well off the
California coast with broad ridging over the Gulf. A few weak
waves will eject out the upper low through the southern stream,
while a more active northern stream will be located near the
Canadian border. This results in warm temperatures for Central
Alabama with seemingly ever-present rain chances, but widespread
heavy rainfall is not expected at this time. A shortwave moves
through Monday afternoon/Monday night. Upper level lift with the
wave is not particularly strong, but isentropic lift associated
with a 40kt LLJ and near-saturated 850-700mb mean RH values will
promote widespread light showers with no instability present.

The wave departs by midday on Tuesday, while the cold front
associated with the system stalls out just north of the area as it
becomes parallel to the westerly flow aloft. A warm, somewhat
moist air mass lingers south of the front, and showers and
possibly an isolated thunderstorms may linger Tuesday
afternoon/Tuesday night. A clipper-like system moves into the
Great Lakes region Wednesday, sending the front first northward as
a warm front ahead of it and then back southwards as a cold front
Wednesday night. Will have to keep an eye on potential
showers/storms developing along the cold front as they move in
from the northwest Wednesday night.

32/Davis

&&

.AVIATION...
12Z TAF Discussion.

We are looking at 10 to 18 more hours of MVFR/IFR conditions and
then finally some improvement. A cold front will finally clear the
area by sunrise Friday. Winds will be out of the N for the most
part but then will shift to the WNW as the front pushes through.

16

&&

.FIRE WEATHER...

Widespread rain continues this morning before ending from west to
east during the afternoon. A dry air mass then moves in for Friday
and the weekend. Afternoon relative humidity values will fall to
35-40 percent Friday afternoon with northwesterly 20ft winds
around 10-15 mph with higher gusts. Afternoon relative humidity
values fall to around 30-35 percent over the weekend with lighter
winds.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     56  38  54  30  57 / 100   0   0   0   0
Anniston    56  39  55  31  58 / 100  10   0   0   0
Birmingham  58  41  56  32  59 / 100   0   0   0   0
Tuscaloosa  62  42  59  32  60 / 100   0   0   0   0
Calera      58  41  56  33  59 / 100   0   0   0   0
Auburn      56  42  56  32  58 / 100  10   0   0   0
Montgomery  60  43  60  35  62 / 100   0   0   0   0
Troy        61  44  61  35  61 / 100   0   0   0   0

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Flash Flood Watch until noon CST today for the following
counties: Autauga...Barbour...Bibb...Bullock...Calhoun...
Chambers...Chilton...Clay...Cleburne...Coosa...Dallas...Elmore...
Greene...Hale...Jefferson...Lee...Lowndes...Macon...Marengo...
Montgomery...Perry...Pickens...Pike...Randolph...Russell...
Shelby...St. Clair...Sumter...Talladega...Tallapoosa...
Tuscaloosa.

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
254 AM CST Thu Mar 5 2020

ALZ011>015-017>050-061200-
Marion-Lamar-Fayette-Winston-Walker-Blount-Etowah-Calhoun-Cherokee-
Cleburne-Pickens-Tuscaloosa-Jefferson-Shelby-St. Clair-Talladega-
Clay-Randolph-Sumter-Greene-Hale-Perry-Bibb-Chilton-Coosa-Tallapoosa-
Chambers-Marengo-Dallas-Autauga-Lowndes-Elmore-Montgomery-Macon-
Bullock-Lee-Russell-Pike-Barbour-
254 AM CST Thu Mar 5 2020

This Hazardous Weather Outlook is for the counties served by the
National Weather Service office in Birmingham.

.DAY ONE...Today and Tonight.

Periods of moderate to heavy rainfall will continue to result in the
potential for isolated flash flooding through noon.

Flooding will continue on many area rivers. Please refer to the
latest river statements for details.

.DAYS TWO THROUGH SEVEN...Thursday through Wednesday.

Flooding will continue on many area rivers. Please refer to the
latest river statements for details.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management may be needed
through this morning.