Tornadoes and Hail in Alabama, April 5, 2017

Area Forecast Discussion
National Weather Service Birmingham AL
1203 AM CDT Wed Apr 5 2017

.UPDATE...
For 06Z Aviation.

&&

.SHORT TERM...

...Severe weather outbreak possible Late Tonight through Wednesday...

This evening, we will turn our attention to the south as we
monitor the northward progression of a warm front, and developing
showers and thunderstorms spreading into the area. Model guidance
continues to support the potential for significant severe weather
tomorrow, and the current forecast and threats are on track. The
previous discussion follows...

A stalled front to our south will begin to return northward
tonight as a classic 500 mb trough takes shape over the Plains. A
surface low should intensify and track from eastern Oklahoma
tonight toward the Ohio Valley on Wednesday, eventually putting
Alabama in the warm sector. Before that occurs, a warm front will
move inland and accelerate northward early Wednesday morning across
the forecast area. Scattered storms are expected to develop
around 4 AM as warm/moisture advection occurs near the warm
front. Additional storms could also form along a trailing
confluence band which may extend from central Alabama to the
southwest. With MLCAPE possibly as high as 2500 J/kg in the warm
sector and strong wind shear already in place through the entire
column, any surface-based storms could produce long-track
tornadoes. It is unclear how widespread this activity will be and
if storms will become more organized. This is an important
question we cannot answer at this time, but the morning activity
will greatly impact what happens later in the day.

One possible outcome is storms becoming organized and moving into
Georgia, focusing the low-level jet to the east with veering
surface winds to the west across Alabama. This could somewhat
reduce instability and shear and the overall threat for the
afternoon. A threat for tornadoes, very large hail and damaging
winds would still exist in this scenario. Several models are
buying into this idea, but with the presence of a elevated mixed
layer, it is possible they are too bullish with morning
thunderstorm development.

If the warm sector remains preserved, very strong instability and
shear would develop across much of the area, possibly leading to
an outbreak of long-track, destructive tornadoes trough 9 PM. The
westward extent of the afternoon threat is in question due to
timing of initiation, but the greatest chance for supercells would
probably occur east of a line from Birmingham to Selma. We should
have a better handle on this situation 24 hours from now.

87/Grantham/14

.LONG TERM...
Thursday through Monday.

Thursday through Sunday remains a fairly benign timeframe with
high  pressure taking control and bringing in some chilly air for
this time of the year. Low temperatures on Friday and Saturday
morning will be in the upper 30s to low 40s for most of the area,
with a few mid 30s in the northeast and normally cooler spots.
Have increased the chance of a possible frost in the northeast and
included in the forecast for Saturday morning. This will continue
to be monitored over the next several days and more details will
be forthcoming. Make plans for protecting outdoor vegetation and
plants for the weekend. There will be a warming trend beginning
Saturday afternoon that will continue into Sunday and Monday. The
next chance of rain will be Monday afternoon with the next storm
system, but there is still some timing issues with this system so
expect many changes over the next few days.

16

&&

.AVIATION...
06Z TAF Discussion.

Some big and rather fast changes take place in the first 6 hours.
The main change from the previous issuance was to slow the
increasing clouds by an hour or so. Warm air advection pattern
and low level jet kick between 06-09z with ceilings quickly
dropping to MVFR then IFR between 10-12z. The clouds will be
associated with a warm front and much increased moisture from the
south. Showers and thunderstorms will also develop with this
gradient of moisture around sunrise. Some improvement to all
ceilings expected by 16-18z as ceilings rise somewhat, but
additional showers and thunderstorms are possible through 00z area
wide. Low level winds will be in the neighborhood of 35-38kts
overnight, which is close but just shy of the LLWS criteria.

A volatile atmosphere will be in place across Central Alabama on
Wednesday and any of these storms may produce damaging winds,
tornadoes, and large hail.

75

&&

.FIRE WEATHER...

The next storm system arrives overnight, bringing rain and
thunderstorms to the area through tomorrow. Widespread rainfall is
not expected with activity remaining more scattered, but all
activity has the potential to be strong to severe. Rain-free
weather returns Thursday through the weekend. Critical fire
weather conditions are not expected through the next 7 days.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     59  78  47  61  40 /  50  70  30  20  10
Anniston    62  79  48  61  40 /  60  70  40  20  10
Birmingham  64  80  47  62  43 /  60  70  20  20  10
Tuscaloosa  64  81  47  65  43 /  50  60  10  10   0
Calera      63  80  48  63  43 /  60  70  20  10  10
Auburn      63  79  50  62  42 /  50  70  50  10  10
Montgomery  66  82  51  68  44 /  50  70  30  10   0
Troy        65  81  52  66  43 /  40  70  40  10   0

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
None.

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
120 PM CDT Tue Apr 4 2017

ALZ011>015-017>050-052130-
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-
120 PM CDT Tue Apr 4 2017

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

.DAY ONE...This Afternoon and Tonight.

Severe thunderstorms may develop as early as 4 AM Wednesday and
could affect all of Central Alabama. Large hail, damaging winds, and
tornadoes will be possible.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

The severe weather threat beginning in the pre-dawn hours of
Wednesday will continue through Wednesday evening with the
possibility of two or three rounds of scattered storms. Destructive
and long-track tornadoes will be possible, along with hail up to the
size of baseballs, and damaging straight-line winds. These threats
will encompass all of Central Alabama with the greatest threat area
along and east of a line from Blountsville to West Blocton to
Uniontown.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management is expected
from early Wednesday morning through Wednesday evening.