Special Weather Statement, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
258 PM CDT Mon Jun 29 2020

.SHORT TERM...
/Updated at 0227 PM CDT Mon Jun 29 2020/

Through Tuesday.

The mid-level ridge axis will move across the area today,
positioning to our east tonight. In the lower levels, a more
southwesterly fetch continues to advect moisture northeastward over
southern Mississippi and into western Alabama. Further aloft, winds
become west-northwesterly and the resultant airmass lacks notable
moisture content. Similar to yesterday, this leads to an enhancement
in mid-level evaporative cooling processes and microburst potential
associated with our typical afternoon summertime convection. As
surface air temperatures rise into the 90s, dewpoints are progged to
remain in the mid 70s, producing a very volatile troposphere in
terms of instability. This morning's 12Z BMX RAOB indicated the
airmass is slightly drier than yesterday. Therefore, the spatial
coverage of storms should be limited by the dry air and ridging, but
any that do develop will have the potential to become strong with
gusty winds, frequent lightning, and small hail, potentially
becoming severe in an isolated instance. Kept our highest PoPs ~40%
north of I-20. Some moistening may occur in the northwest late this
afternoon associated with a mid-level shortwave trough tracking
northeastward over the Ozarks, but the longevity of the storms will
follow the diurnal curve and diminish this evening. Look for another
warm, muggy night with lows in the lower to mid 70s.

Should see a similar situation on Tuesday, but the main change will
be the increased moisture in place which will advect around the base
of the aforementioned shortwave trough. Less dry air in the mid-
levels should lessen the microburst risk, but we will likely see
scattered to numerous showers and storms tomorrow afternoon, some
potentially strong. Breaks in the clouds will allow temperatures to
warm into the lower 90s.

86

.LONG TERM...
/Updated at 0227 PM CDT Mon Jun 29 2020/

Wednesday through Sunday.

Models have been in good agreement the past several days showing
the Atlantic Coast upper trof pushing southwest into the Southeast
States. This pattern shift will be favorable for more coverage of
showers and thunderstorms on Wednesday and Thursday. Steeper mid
level lapse rates and increasing 0-6km bulk shear on Wednesday
could lead to the development of stronger storms, mainly west of
I-65 where warmer surface temperatures will be coincident with
better mid level lapse rates. By Thursday the upper trof axis will
shift into south Alabama, and changed pops to show a gradient,
with lowest rain chances northeast. The upper trof axis should
hang out near the Florida Panhandle for the period Friday thru
Sunday, although there appears to be enough moisture and lift
north of the trof axis for mostly diurnal daily rain chances
through the weekend.

58/rose

Previous long-term discussion:
/Updated at 0319 AM CDT Mon Jun 29 2020/

Wednesday through Sunday.

Features:

Wednesday through Friday.

Deep-layer ridging will be centered over the Western Gulf of
Mexico. A sprawling trough will extend from Southwest Canada
southeast over Montana and into Wyoming while another closed low
will be positioned over Boston.

An Omega-Block pattern will persist into Thursday as the ridge
remains off the South Texas coast while broad troughing prevails
over much of the Intermountain West. The closed low to our northwest
will remain near the Boston area.

By Friday, the ridge looks to be centered over Central Texas while
the broad low moves northeast into Western and Central Canada. The
closed low to our northeast opens into a trough and lifts out.
Closer to home, the ridge positioned further to our west, permits
the developing of broad troughing along the Eastern Seaboard to
extend further southwest into the Deep South region.

Some global models are maintaining the idea of a convective complex
moving south across the area late Wednesday into Thursday. This
solution is similar to what was depicted last night, however, there
remains considerable disagreement among model members. Also, some
global models continue to entertain the idea of a closed low
developing and moving across the area late Friday into the next
weekend. However, there is considerable uncertainty regarding timing
and location as model field spreads become quite divergent with
time. The result will be notable uncertainty with regard to PoPs and
high temperatures especially as we progress from the midweek through
next weekend time frame.

Saturday and Sunday.

Ridging aloft becomes centered over New Mexico and expands to
encompass much of the Desert Southwest, Southern and Central Plains,
and reaches further north into the High Plains and South Central
Canada. Broad troughing will persist across the Western third of the
country along with across the Northeast while remnant troughing
looks to persist down the spine of the Appalachians from the
Carolinas toward the Central Gulf Coast region.

Forecast:

Wednesday and Thursday.

Expect scattered to numerous showers and thunderstorms during this
time frame with coverage increasing during the day Wednesday and
potentially persisting overnight and into the day Thursday. For the
second night in a row, some modeling depicts a convective complex
moving south across much of the area. There remains considerable
disagreement and uncertainty but it is a potential to consider given
expected north to northwesterly flow over the area. High PoPs will
be maintained into the Day Thursday followed by isolated activity
into the overnight hours. Highs will range from the mid to upper 80s
north and east to readings in the low 90s south and west. Lows will
range from the upper 60s north and east to the low 70s south and
west.

Friday through Sunday.

A return to more typical isolated to scattered shower and
thunderstorm activity is forecast late week into the next weekend as
the weak troughing remains in place aloft. Expect showers and
thunderstorms to be greatest in coverage from the afternoon through
early evening hours. Expect highs to range from the mid to upper 80s
north and east to readings around 90 south and west. Lows will range
from the upper 60s north and east to the low 70s south and west.

Given the present uncertainty in model solutions, PoPs and
especially high temperatures during this time frame are considered
low confidence. Higher PoPs may be warranted and would result in
lower temperatures in the afternoon hours.

05

&&

.AVIATION...
18Z TAF Discussion.

Isolated to scattered showers and thunderstorms will continue
developing this afternoon. Added a mention of VCTS in at all
terminals this afternoon and will make amendments for TSRA as
needed. Ceilings will briefly rise overnight as any lingering
thunderstorms diminish by 03Z. Low-level moisture will remain
elevated tomorrow morning due to light southwesterly winds.
Ceilings will likely lower just before sunrise, but should remain
just above MVFR criteria. Should see a higher coverage of showers
and thunderstorms tomorrow afternoon beginning towards the end of
this TAF cycle as higher moisture content advects in from the
northwest. Included a PROB30 at most of our northern terminals to
trend towards this potential.

86

&&

.FIRE WEATHER...

Shower and thunderstorm chances will increase as we progress through
midweek. The highest chances will be on Wednesday and Thursday,
where we may see widespread activity. Expect some decrease in the
activity moving into the weekend. Ample moisture in the low
levels will keep afternoon relative humidity values generally
above 45 percent through the forecast period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     72  90  69  89  70 /  20  70  40  80  70
Anniston    72  89  70  90  70 /  30  70  30  80  60
Birmingham  75  92  73  91  72 /  30  60  30  70  60
Tuscaloosa  74  93  74  93  72 /  20  50  20  50  50
Calera      74  91  72  91  72 /  30  60  20  60  50
Auburn      73  89  72  89  70 /  30  60  20  70  50
Montgomery  75  93  74  93  73 /  20  50  10  50  40
Troy        74  92  74  93  73 /  20  40  10  60  40

&&

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

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
1022 AM CDT Mon Jun 29 2020

ALZ011>015-017>050-301830-
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-
1022 AM CDT Mon Jun 29 2020

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

.DAY ONE...Outlook through Tonight.

A few strong to severe storms are possible this afternoon capable of
producing damaging winds up to 60 mph.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

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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