Severe Thunderstorm Warning 122, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
1251 PM CDT Sat May 23 2020

.UPDATE...
For 18Z Aviation.

&&

.SHORT TERM...
/Updated at 0931 AM CDT Sat May 23 2020/
Through Tonight.

The good ole summer convective regime has "officially" begun
across Central Alabama. Yesterday presented the greatest forecast
challenge yet in terms of the overall coverage of showers and
storms due to mesoscale boundary interactions that triggered
storms well into the evening hours. Today will be a similar
forecast challenge, but with additional factors to take into
consideration.

From past experience, following a day like yesterday with so many
widespread storms it's hard for the atmosphere to fully recover
and get similar convective activity two days in a row. That being
said, we're taking a look at all the convective ingredients and
observation trends for this morning's update to determine if
strong or isolated severe storms will once again be possible
today. As we speak, storms have already developed across our
northwest counties that could contain some small hail.

Following a surface analysis, a 1020mb surface ridge currently
resides over eastern Alabama and western Georgia. Meanwhile, a
large outflow boundary leftover from an MCS that developed well
off to our west in Oklahoma and Arkansas has moved into NE
Mississippi and is slowly moving into NW Alabama. We're already
seeing a convergent axis forming between that remnant outflow and
the southeasterly surface flow on the west side of the surface
ridge. PoPs have already been adjusted higher in our northwest
counties to reflect current radar trends and projected additional
development.

Now, let's look at the 12z KBMX RAOB data. Based on modified
sounding parameters using forecast high temps today, we could be
looking at well over 3000 J/kg of SBCAPE this afternoon along
with fairly steep 0-3km lapse rates. Temps aloft are a bit higher
at 500mb than they were yesterday, but the most significant change
is the amount of dry air now present throughout the sounding. As
a result, the amount of DCAPE that could be realized with a strong
thunderstorm has greatly increased between 1000 and 1500 J/kg.
0-6km shear has greatly decreased compared to yesterday which will
lead to updrafts not being sustained as long, but have the threat
of wet microbursts due to the dry air aloft and lower wet-bulb
zero heights.

For this morning's update, we're going to go ahead and add text to
the HWO for the possibility of isolated severe storms capable of
producing hail and gusty winds up to 60mph. It's taking a while
for the clouds to mix out this morning across our west and
northwest counties, and that will dictate the amount of
instability that can be realized later this afternoon. Still, the
potential for an isolated damaging wind gust or some large hail
can't be ruled out.

The forecast through tonight will be highly dependent on outflow
boundary driven convection, but for now have the general trend of
low PoPs across the southern and southeast counties slightly
increasing through the late afternoon and into the early evening
hours. As has been done the previous couple of days, we've also
kept rain chances in the forecast through 9pm to account for any
leftover convective activity.

56/GDG

.LONG TERM...
/Updated at 400 AM CDT Sat May 23 2020/
Monday through Friday.

Upper level ridging continues to increase over the region on Monday
and Tuesday. The main axis of the ridge will be over the Mid-
Atlantic states, so a southerly flow will remain over the area for
much of the week. Meanwhile, troughing will continue over the
southern Plains. By Wednesday into Thursday an upper low gets cut-
off from the flow and will slowly retrograde to the south-southwest
through the end of the week. The main jet flow remains well to our
north, so most of the activity through the week will be more of the
typical summer time airmass thunderstorms. With plenty of moisture
in place, activity will likely be scattered each day, with the best
chances occurring on Tuesday/Tuesday night when the upper low is
closest to the area and the southerly flow looks to be strongest
with the building ridge. At this time the best chances would be in
the west. Look for highs in the upper 80s and lows in the upper 60s
to low 70s through the week.

&&

.AVIATION...
18Z TAF Discussion.

Following low clouds and fog this morning, all terminals are VFR
early this afternoon. VCTS can be expected at most terminals later
on this afternoon except for MGM and TOI where less coverage of
convection is expected. Fairly calm conditions are anticipated
overnight tonight with no strong indications of low stratus or fog
formation as of yet. As such, VFR conditions have been carried
through the remainder of the forecast period with light or
variable winds.

56/GDG

&&

.FIRE WEATHER...

Areas of low clouds and fog will be in place this morning across the
eastern two-thirds of Central Alabama. Otherwise, a more summer like
pattern with daily isolated to scattered showers and thunderstorms
is expected through the weekend and into the first of next week.
Minimum RH values are forecast to remain above 40 percent through
the upcoming weekend with generally light winds outside of any
thunderstorm activity.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     64  90  66  88  66 /  30  40  30  50  30
Anniston    66  90  66  88  67 /  30  50  30  50  30
Birmingham  69  91  69  89  69 /  30  50  30  50  30
Tuscaloosa  69  92  68  89  68 /  30  40  30  50  30
Calera      67  90  68  88  68 /  30  50  30  50  30
Auburn      67  89  68  85  67 /  30  40  30  50  30
Montgomery  67  92  68  89  68 /  30  40  30  50  30
Troy        67  90  68  88  68 /  40  40  30  50  30

&&

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

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
1031 AM CDT Sat May 23 2020

ALZ011>015-017>050-241845-
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-
1031 AM CDT Sat May 23 2020

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

.DAY ONE...Outlook through Tonight.

Isolated severe storms will be possible from noon to 8pm across all
of Central Alabama. Damaging winds up to 60mph and large hail will be
the primary threats.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management is not expected
at this time. Please follow all local, state, and CDC guidelines in
regards to travel.

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