Special Weather Statement, NWS Birmingham, AL

Area Forecast Discussion
National Weather Service Birmingham AL
1245 PM CDT Tue Jun 26 2018

.UPDATE...
For Near Term and Aviation.

&&

.Near Term...
Through this Evening.

Convection have been slower to develop today due to slightly warmer
temperatures aloft. As of 1230PM, seeing a expansive cu field across
much of the area, with a shower or two across the southeast. Expect
showers and storms to increase in coverage as day time heating
continues. Microburst potential is high again today, and any
stronger storm could produce strong wind gusts.

The Heat Advisory remains in place for portions of the west and
south. Expect Heat Indices to reach 105F this afternoon.

14

&&

.SHORT TERM...
Today and Tonight.

We continue with much of a status quo in our weather pattern, at
least through tonight. Convection from yesterday did lower readings
in the east, with lower dew points into the upper 60s. However, dew
points are expected to recover quickly this morning as more moist
low level flow off of the Gulf of Mexico returns into Central
Alabama around the still present Atlantic ridge. In the upper
levels, we continue to have a somewhat flat ridge across Southern
Conus. We are again expecting very warm temperatures today. The
highest readings should be in the west today. Readings may be a tad
lower in the east as the airmass recovers from yesterday. The
current heat advisory for the southwest half of Central Alabama
looks to be good, and we are not planning on adding any more
counties at this time.

Convection should again be heat induced this afternoon with
scattered thunderstorms possible once again as precipitable H2O
values remain up. Not expecting any organized severe today, but we
will get too hot not to expect some development maybe even a few
strong storms.

08

.LONG TERM...
Wednesday through Tuesday.

The ridge that has been in place over Central AL the past few days
finally breaks down slightly as a trough and low pressure system
move through the Upper Midwest and into the Great Lakes Region. The
GFS tries to stretch a weak cold front down through the TN Valley
and through Central AL Wednesday afternoon, but don't get too
excited because temps only drop 3-4 degrees. The NAM and ECMWF don't
have this discernible cold front and instead keep the system as
more of an upper level trough axis passage rather than anything
meaningful at the surface. Either way, expect some extra synoptic
forcing with the trough axis moving through, so we could see extra
cloud cover and higher coverage of afternoon
showers/thunderstorms on Wednesday. The NAM keeps the area dry,
but the GFS, ECMWF, and higher resolution CAMs develop the
afternoon precip, especially in the North and East. Therefore,
will increase PoPs for those areas. 1000-850mb thickness values
decrease slightly with the trough passage as well, so afternoon
highs could be slightly lower than the previous couple of days,
but overall, still expect borderline heat advisory criteria in the
heat indices. Will continue mention in the HWO for heat impacts
on Wednesday, but will hold off on any expansion of the heat
advisory because of the uncertainty with the "cold" front.

I wish I could say that the forecast gets easier for the second half
of the week, but it doesn't. The GFS tries to cut off a weak upper
level low from the base of the passing trough axis and retrograde is
back over Central AL on Thursday as the ridging at 850mb
strengthens. This would lead to an increase in 1000-850mb thickness
values, supporting afternoon high temps in the mid 90s or above and
continued heat advisory conditions. However, with the weak upper
level low, we could see increase synoptic lift allowing higher
coverage of afternoon convective storms, which depending on time and
location of initiation could limit the afternoon temps. Meanwhile,
the ECMWF and Canadian are more progressive and don't have the cut-
off upper level low development until the system is off the Atlantic
Coast. This would bring in the amplified ridge across Central AL
again, leading to more typical afternoon convection with heat
indices in the 100-105 range through the end of the week. Will
continue edging the forecast more towards the ECMWF and Canadian,
which meshes well with the National Blend Model for high temps
through the end of the week. Will also go closer to climo on diurnal
precipitation patterns and maintain low confidence mentions for heat
impacts in the HWO through Saturday. The determining factor for the
heat advisories for this week will likely be coverage and timing of
afternoon convection, which unfortunately will require more of a day-
to-day reassessment.

For later part of the weekend and into early next week, the GFS and
ECMWF are in decent agreement with the ridging pattern remaining in
place across the Eastern CONUS with typical summertime diurnal
thunderstorm activity. However, the center of the 850mb ridge should
shift more over the East Coast and into the Atlantic, allowing our
1000-850mb thickness values to decrease, returning Central AL to
afternoon highs in the upper 80s to near 90 degree mark. This
pattern change towards the extended is supported by NAEFS, GEFS, and
ENS, which are all showing near or above max values for mean temps
and mean geopotential heights over the Northeastern CONUS.
Therefore, will not go past Saturday for heat impacts in the HWO and
will adjust temps back towards the typical model blends.

25/Owen

&&

.AVIATION...
18Z TAF Discussion.

Cu field and a few showers now developing across Central Alabama.
Expect showers and storms to increase in coverage as day time
heating continues. Have included VCTS at all terminals this
afternoon. With activity already on radar near TOI, have included a
tempo from 19-22Z due to higher confidence. Microburst potential is
high today, and any stronger storms could produce strong winds,
frequent lightning, and torrential rainfall. Activity will diminish
this evening with loss of daytime heating.

Outside of convection, winds should be fairly light with weak
surface pressure gradients. Will need to monitor rainfall this
afternoon and evening for the potential for localized fog and
reduced vis Wednesday morning.

14

&&

.FIRE WEATHER...

Isolated to scattered afternoon storms are possible with daytime
heating for the next few days. Very warm temperatures with triple
digit heat indices will be the biggest issue for crews. Humidity
values remain high, and there are no fire weather concerns at this
time.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     91  71  91  74  93 /  40  30  50  20  40
Anniston    91  72  91  74  92 /  40  30  50  20  40
Birmingham  93  74  93  76  93 /  30  30  40  20  40
Tuscaloosa  95  75  95  76  96 /  30  20  20  20  40
Calera      92  73  92  75  92 /  40  30  30  20  40
Auburn      91  74  91  74  91 /  50  30  30  20  40
Montgomery  95  75  94  75  93 /  50  20  30  10  40
Troy        92  74  93  74  92 /  50  20  30  10  40

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Heat Advisory until 8 PM CDT this evening for the following
counties: Autauga...Barbour...Bibb...Bullock...Chilton...
Dallas...Elmore...Fayette...Greene...Hale...Lamar...Lowndes...
Macon...Marengo...Montgomery...Perry...Pickens...Pike...
Russell...Sumter...Tuscaloosa.

&&

Hazardous Weather Outlook
National Weather Service Birmingham AL
939 AM CDT Tue Jun 26 2018

ALZ011>015-017>050-271745-
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-
939 AM CDT Tue Jun 26 2018

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

.DAY ONE...Today and Tonight.

Isolated damaging wind gusts will be possible across Central Alabama
through 8 PM this evening.

Heat indices will reach or exceed 105 degrees for many locations in
Central Alabama this afternoon; therefore, a heat advisory is in
place from 10AM to 8PM this afternoon. Plan to limit outdoor
activities and drink plenty of water during the afternoon hours.

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

Heat indices will approach or reach 105 degrees for many locations
in Central Alabama each afternoon Tuesday through Saturday. Plan to
limit outdoor activities and drink plenty of water.

.SPOTTER INFORMATION STATEMENT...

Activation of storm spotters and emergency management is not
anticipated at this time.

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