Special Weather Statement, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
701 PM CDT Wed Aug 19 2020

.UPDATE...
For 00Z Aviation.

&&

.SHORT TERM...
/Updated at 1054 AM CDT Wed Aug 19 2020/

Only minor changes needed for the next 36 hour forecast. The
outside threat for isolated severe weather continues this
afternoon. Temperatures aloft are cooler today aiding the
instability as the upper trough digs further south. There is also
a fairly decent lower level moisture pool developing across
southeast Alabama ahead of the surface boundary. Storm coverage
will increase over the next several hours, mainly east of I65 or
closer to the surface front, and will rapidly subside just after
sunset. Most of the morning parameters indicate a high risk for
wet microbursts from I59, south and east.

17/KLAWS

Previous short-term discussion:
/Updated at 345 AM CDT Wed Aug 19 2020/
Today and Tonight.

A relatively amplified mid to upper-level pattern remains
stretched across the CONUS with ridging in place across the West
and a longwave trough east of the Mississippi River. Water vapor
imagery depicts an embedded shortwave now moving southeast from
the mid MRV headed toward Central AL along with associated mid-
level height falls. At the surface, a boundary is now positioned
from near Marengo County northeastward to near Cleburne County per
recent surface obs and RADAR imagery. This feature and combined
aloft will allow for an increase in convective activity this
afternoon as temperatures rise into the upper 80s to lower 90s.

Guidance suggests the shortwave will position to near the AL/MS
line and generally approach Central AL this afternoon. Though with
time the vort max may weaken, a more broad area of height
falls/vorticity aloft will continue to dig into the Deep South.
Meanwhile, low-level moistening is expected to the east and
southeast of a ~1008-1009 mb low pressure set to develop near
south Central AL this afternoon along the surface boundary. As
such, I placed 'likely' PoPs east of I-65 with a decreasing trend
northwestward with expected decline in forcing and moisture
quality.

The presence of mid-level dry air & low-level moisture advection
will combine with other factors to promote the development of
isolated strong to severe thunderstorms by this afternoon. These
factors include SBCAPE of 2,000-3,000 J/kg and rather steep low-
level lapse rates in places (8-9 C/km). Though I'd like to see PWs
a little bit higher (HREF mean suggests 1.4-1.6" in likely PoP
area), I can't rule out instances of damaging wind gusts due to
microbursts. Additional forcing considerations help overcome this
factor as updrafts would otherwise struggle to maintain their
rigor due to dry air entrainment aloft. (It is this dry air
entrainment that strengthens the downdraft core for microburst
potential, however.)

At face value, the above reasons warrant a low-confidence mention
of strong to severe thunderstorms in the HWO, albeit of an
unorganized nature. This will include brief damaging wind gusts up
to 60 mph and small to quarter size hail for the more robust
updrafts/cores able to take advantage of the ~20 kts eff. bulk
shear.

Thursday morning and afternoon.

As mentioned before, a more broad area of synoptic height falls
and associated vorticity is expected to settle across the Deep
South and generally retrograde west & center near the lower MRV by
Thursday morning. A more robust reservoir of low-level
moisture/theta-e are expected to overspread much of the downstream
areas across the Southeast with PWs ~1.7-1.9". Cooling
temperatures aloft (around -9 to -10 C at 500 mb) and a moisture-
rich boundary layer are pointing toward 3,000-4,000+ SBCAPE
profiles amidst 15-25 kts eff. bulk shear (increasing
southwesterly flow in the southeast areas). I've increased PoPs as
this and the left exit region of an upper-level jet streak should
foster numerous thunderstorms, including the potential for
multicell clusters and bowing segments capable of damaging winds.
More isolated cells earlier in the convective life cycle will
carry the potential for severe criteria hail given the relatively
cool temps aloft and favorable buoyancy in the hail growth zone.
For these reasons I'll mention strong to severe thunderstorms in
the HWO with the afternoon and early evening the time of greatest
potential. Kinematics and other parameters suggest areas along and
south of I-20 having the best chance at this time, though the
entire Southeast CONUS has a chance given the overall PoPs despite
'weaker' shear values elsewhere.

40/Sizemore

.LONG TERM...
/Updated at 208 PM CDT Wed Aug 19 2020/
Friday through Tuesday.

Features.

An anomalous pattern will persist through the first portion of
the long term forecast period with the forecast area positioned on
the east side of a deep layer trough centered over the Lower
Mississippi River Valley region. Upper-level winds will increase
form the south in the upper levels as the trough becomes centered
closer to the area on Saturday.

Expect the trough to lift to the northeast of the area during the
day on Sunday. As we progress from Monday into Tuesday, expect
ridging to increase in the upper levels from the southeast.

Precipitable water values will remain high on Friday followed by
a brief decrease on Saturday as some drier air moves over the area
from the southwest behind the departing trough. There is some
disagreement among global modeling regarding precipitable water
values from late Sunday through Tuesday but the overall trend is
for increasing values.

Attention will begin to turn to the tropics toward the end of the
forecast with some global models developing a system and bringing
it northwest from the Northern Caribbean Sea into the Southeast
Gulf of Mexico by Tuesday. Please monitor updates to the forecast
from our office along with products issued by the National
Hurricane Center as we move from this weekend into next week.

Forecast.

Friday through Sunday.

Scattered to numerous showers and storms are expected on Friday.
Expect some decrease to the isolated to scattered categories
southwest on Saturday as some drier air aloft does work its way
into the area. Isolated to scattered activity is forecast
generally along and south of Interstate 59 corridor. Highs will
range from the mid 80s east to the mid 80s south and west on
Friday and Saturday and from the upper 80s east to the low 90s
west on Sunday.

Monday and Tuesday.

Isolated showers and storms are forecast across the entire area
with scattered activity south and east from Monday through
Tuesday. Highs will range from the upper 80s east and south to the
low 90s west and north.

05

&&

.AVIATION...
00Z TAF Discussion.

At this hour, we have convection along and ahead of a surface
boundary and associated low pressure feature slowly nudging
eastward. Some gusty winds are possibly with storms. Rain chances
should decrease for the 6-15z timeframe with an overall lull in
the activity. More widespread convection will be possible on
Thursday (best chances afternoon) as the boundary lingers across
the area. Some MVFR to IFR conditions may occur briefly in
stronger convection.

08

&&

.FIRE WEATHER...

Scattered to numerous showers and storms are expected this
afternoon and again tomorrow afternoon. Isolated showers and
storms are expected on Saturday followed by a developing pattern
with scattered showers and storms across the south and east into
early next week.

Minimum relative humidity values are expected to dip into the mid
40 percent range this afternoon followed by values only dipping
into the upper 40 to low 50 percent range tomorrow through
Tuesday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     66  88  67  85  67 /  50  80  70  70  50
Anniston    68  89  68  86  68 /  50  80  70  70  50
Birmingham  69  89  69  86  69 /  50  80  70  70  40
Tuscaloosa  69  90  69  86  69 /  40  80  60  70  30
Calera      68  89  68  84  67 /  40  80  70  70  40
Auburn      68  87  68  83  68 /  50  80  80  70  50
Montgomery  70  90  69  86  70 /  40  80  70  70  40
Troy        69  88  68  85  69 /  50  80  70  70  40

&&

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

&&

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

Special Weather Statement
National Weather Service Birmingham AL
834 PM CDT Wed Aug 19 2020

ALZ037-200200-
Tallapoosa AL-
834 PM CDT Wed Aug 19 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHWESTERN TALLAPOOSA COUNTY
UNTIL 900 PM CDT...

At 833 PM CDT, Doppler radar was tracking a strong thunderstorm over
Hillabee Creek, or near Alexander City. This storm was nearly
stationary.

Winds in excess of 40 mph will be possible with this storm.

Locations impacted include...
Alexander City, Jacksons' Gap, New Site, Hillabee Creek, Northern
Lake Martin, Eagle Creek, Horseshoe Bend and Horseshoe Bend National
Military Park.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3289 8576 3294 8593 3309 8586 3304 8566
TIME...MOT...LOC 0133Z 197DEG 2KT 3296 8583

89^GSatterwhite

Special Weather Statement
National Weather Service Birmingham AL
852 PM CDT Wed Aug 19 2020

ALZ036-037-043-045-200230-
Tallapoosa AL-Macon AL-Coosa AL-Elmore AL-
852 PM CDT Wed Aug 19 2020

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN ELMORE...NORTH
CENTRAL MACON...CENTRAL TALLAPOOSA AND SOUTHEASTERN COOSA COUNTIES
UNTIL 930 PM CDT...

At 852 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Wind Creek State Park to near Eclectic.
Movement was southeast at 15 mph.

Winds in excess of 40 mph will be possible with these storms.

Locations impacted include...
Alexander City, Tuskegee, Tallassee, Dadeville, Notasulga, Eclectic,
Jacksons' Gap, Martin Dam, Southern Lake Martin, Eastern Lake Martin,
Liberty City, Western Lake Martin, Tallapoosa City, Northern Lake
Martin, Kowaliga Bridge, Wind Creek State Park, Still Waters Resort,
Fishpond, Dare Park and Yates Reservoir.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with these storms, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

&&

LAT...LON 3250 8570 3256 8612 3291 8603 3283 8569
TIME...MOT...LOC 0152Z 300DEG 13KT 3281 8598 3260 8603

89^GSatterwhite

Special Weather Statement
National Weather Service Birmingham AL
920 PM CDT Wed Aug 19 2020

ALZ041-043-044-200300-
Autauga AL-Montgomery AL-Elmore AL-
920 PM CDT Wed Aug 19 2020

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN AUTAUGA...
SOUTHWESTERN ELMORE AND NORTHWESTERN MONTGOMERY COUNTIES UNTIL 1000
PM CDT...

At 920 PM CDT, Doppler radar was tracking a strong thunderstorm near
Autauga County Airport, or near Prattville, moving east at 15 mph.

Pea size hail and winds in excess of 40 mph will be possible with
this storm.

Locations impacted include...
Montgomery, Prattville, Millbrook, Pike Road, Coosada, Hunter,
Montgomery Zoo, Boylston, Alabama State University, Auburn University
In Montgomery, Bob Woodruff Lake, Woodcrest, Eastdale Mall, Maxwell
Air Force Base, Montgomery Riverwalk Stadium, Blue Ridge, Pinedale,
Lagoon Park, Gunter Air Force Base and Alabama State Capitol.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.

To report severe weather, contact your nearest law enforcement
agency. They will relay your report to the National Weather Service
office in Birmingham.

&&

LAT...LON 3232 8644 3232 8648 3233 8647 3233 8648
      3234 8648 3234 8650 3247 8650 3250 8613
      3228 8613
TIME...MOT...LOC 0220Z 276DEG 11KT 3239 8647

40/Sizemore