Severe Thunderstorm Warning 178, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
720 PM CDT Thu Jul 21 2022

.UPDATE...
Evening Update and 00Z Aviation.

&&

.SHORT TERM...
/Updated at 0701 PM CDT Thu Jul 21 2022/

Excessive heat has ended abruptly in most locations. Have allowed
the advisories and warnings to expire.

A quasi-stationary front was just north of the area early this
evening. The front will hang around the next few days and meander
around in north Alabama. Several strong outflows were in Central
Alabama at this writing. These boundaries have been further
strengthened by the convection. Rapid and severe convection
developed over the area and will continue the next several hours
as it slowly pushed south southeast. SBCAPE values still 3500-5000
with MLCAPE in the same general range. DCAPE values are not as
robust as earlier, but some patches of less worked over air are
still over 1000. The airmass is tropical with precipitable water
values well over 2 inches. Instead of punching holes in the
current watch for cancellations, will reevaluate in another hour
as the remaining energy gets used up.

Convective cloud cover slowly erodes overnight. Some low clouds
may develop especially east and where the heaviest rain fell.
There may also be some patchy fog in the same areas. Lows tonight
in the lower to middle 70s as the front remains north.

75

Previous short-term discussion:
/Updated at 0130 PM CDT Thu Jul 21 2022/

Through This Afternoon.

Still dealing with a tough forecast today which will be
characterized by dangerous heat conditions across the area followed
by scattered to numerous thunderstorm development late this
afternoon and evening. An east to west oriented surface front is
becoming generally parallel to the AL/TN stateline. Moisture is
pooling south of the front and resulting in widespread dewpoints in
the mid to upper 70s across Central AL with PWATs ranging from 2-2.2
inches. With temperatures in the lower to mid 90s, dangerously hot
conditions will continue through the afternoon. Unfortunately, the
only relief from the heat will come in the form of thunderstorms,
some of which could become severe. Large amounts of instability were
already in place this morning, and now upwards of 4000-4500 J/kg
of MLCAPE is collocated with 1200-1400 J/kg of DCAPE across much
of the northern half of Alabama where lapse rates have steepened
and where eff. bulk shear is ~15-20kt. There is some uncertainty
on exact location where storms will initiate, but generally
expecting development across northern portions of the forecast
area late this afternoon as the boundary slowly sinks towards the
south. Expect robust updrafts with strong storms propagating
southward capable of producing damaging straight-line winds from
downdrafts and perhaps a few cases of large hail. Heavy tropical
downpours could also result in localized flooding.

Tonight Through Friday.

Convection is expected to linger into the evening hours and
become focused near and south of the US HWY 80 corridor by
midnight with some continuing risk of strong storms until then.
Drier air will move in across our northern half on Friday with
PoPs becoming focused across our south. We could see a strong
storm or two, but appears less likely as the airmass should be
fairly worked over after the overnight convection. Temperatures
will be on the warm side again tomorrow with highs ranging from
the upper 80s east to mid 90s west. This could push heat indices
towards 105F for a couple hours west of I-65. Will continue to
evaluate the potential need for a Heat Advisory for tomorrow.

86

.LONG TERM...
/Updated at 0415 AM CDT Thu Jul 21 2022/

Saturday through Wednesday.

A low amplitude mid- to upper-level ridge is progged to encompass
much of the southern and southeastern CONUS through the long-term
forecast period. Most operational models suggest it will remain most
prominent/centered just to our west which will flow aloft out of the
north across Alabama. Ridging will coincide with a large low-level
anticyclone extending from the western Atlantic well into the lower
Mississippi Valley which will foster light southerly to
southwesterly surface/low-level flow each day. This will allow for
PWs favorable for diurnal convection to become more evenly
distributed across the forecast area by early next week, rather than
the better moisture confined to areas farther south this weekend.
This overall pattern will lead to little weather diversity over the
next several days outside of any mesoscale features. Diurnal
temperatures will run at or above average and the combination of
heat and humidity could lead to areas meeting Heat Advisory criteria
for most of the period as well. This will remain in the HWO and will
be the biggest weather headline over the next several days.

40/Sizemore

&&

.AVIATION...
00Z TAF Discussion.

Thunder and vis restrictions mentioned to start off all the
terminal forecast. These storms will migrate south southeast.
There are numerous boundaries over the area ahead of a quasi-
stationary front over north Alabama. The storms should develop and
use up all the remaining untapped energy the next few hours.
Thereafter, the convective clouds slowly erode. Before 12z, it
appears that some lower ceilings will develop and mentioned a few
hours of MVFR/IFR at all terminals. There may also be some patchy
fog. Clouds/ceilings decrease by around 15z with VFR and light
southwest winds anticipated.

75

&&

.FIRE WEATHER...

Soaking rainfall is expected across a good portion if not all of
the forecast area through tonight. Southwesterly surface and
transport wind at 5-10 mph will continue. Minimum RH values remain
above 45%. Excessive heat conditions are also expected for much
of the area with heat index values 105 to 110 degrees at times.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     71  93  71  93  72 /  50  10  10  20  10
Anniston    72  91  71  93  73 /  80  30  10  30  10
Birmingham  73  92  73  94  75 /  90  20  10  30  10
Tuscaloosa  74  93  74  95  75 /  90  30  10  20  10
Calera      74  91  74  93  74 /  90  40  20  30  10
Auburn      73  88  72  90  73 /  90  60  20  30  10
Montgomery  75  92  74  95  75 /  90  60  20  30  10
Troy        73  89  72  92  73 /  60  70  20  30  10

&&

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

&&

Hazardous Weather Outlook...UPDATED
National Weather Service Birmingham AL
412 PM CDT Thu Jul 21 2022

ALZ011>015-017>050-230015-
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-
412 PM CDT Thu Jul 21 2022

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

.DAY ONE...Outlook through Tonight.

Heat indices will range from 105 to 112 degrees across much of
Central Alabama this afternoon.

Severe thunderstorms are likely across Central Alabama through
midnight tonight. Threats include damaging wind gusts up to 65 mph
and hail up to quarter size. Localized flooding is also possible in
low lying or flood prone areas.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday.

Heat indices could reach or exceed 105 degrees across portions of
Central Alabama Friday through Tuesday.

.SPOTTER INFORMATION STATEMENT...

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

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