Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 190558 AAA
AFDBMX

Area Forecast Discussion...UPDATED
National Weather Service Birmingham AL
1158 PM CST Wed Jan 18 2017

.UPDATE...
For Evening Forecast and 06Z Aviation.

&&

.DISCUSSION...

Area of showers across Mississippi is moving toward West Alabama
at this time. There have been a few lightning strikes across the
southern portion of the activity, but mostly just showers. I have
made a few hourly pop tweaks for tonight based on latest HRRR which
seems to be handling timing on radar decently. There are no major
temperature changes as we are fairly mild tonight. I have in the
grids some fog across portions of the area with the lowest
visibilities tonight to be expected across the southeast.

08

&&

.AVIATION...
06Z TAF Discussion.

Area of light showers is moving into West Alabama. We could see
some light showers at TCL/BHM and maybe EET before sunrise. TS is
not expected at terminals tonight. Areas of fog may develop
during the late night, especially across the south TAFs (MGM/TOI)
as the warm front is expected to continue to push northward
overnight across north half of Alabama. MVFR cigs should develop
across Central Alabama over the next few hours with some lower
IFR/LIFR cigs possible toward sunrise and in early morning.
Showers will become more widespread during the morning with TSRA
becoming possible by the afternoon and into the evening on
Thursday. A few strong storms cannot be ruled out.

08

&&

.FIRE WEATHER...

Unseasonably mild temperatures will continue through the entire
week. Best rain chances remain north of the today as a cold front
remains stalled over northern Alabama. Best chances today will be
the far northern counties. Better rain chances return overnight
tonight into Thursday. A wet and chaotic pattern sets up Thursday
through Sunday. Afternoon relative humidity values will generally
remain above 40 percent due to the southerly winds bringing gulf
moisture northward. Some strong to severe storms can be expected
Thursday, Saturday and Sunday. Rain amounts through Sunday will be 3
to 4 inches.

&&

.PREV DISCUSSION...
/Issued 354 PM CST Wed Jan 18 2017/
SHORT TERM...

This afternoon through Thursday Night. A quasi-stationary front was
located near Clanton and Alexander City this afternoon.  Clouds have
decreased since this morning in most places on both sides of the
front. The airmass south of the front has been similar to previous
days with near record heat. Temperatures were 75 to 80 degrees.
North of the front, cooler conditions exist with temperatures in the
low to mid 60s. Light echoes on radar have also decreased since this
morning but kept a mention of some drizzle this afternoon. No one
should receive any more measurable rain this afternoon.

Overnight, the quasi-stationary front should become oriented more
northwest to southeast as the next upper system approaches. Expect
clouds to redevelop and some fog south. This will be very similar to
last night. The big difference is that mean layer moisture and lift
will begin getting close enough keep rain chances overnight,
increasing from west to east after midnight. The best chances will
be far northwest.

Models have been in pretty good agreement that a negative tilt
trough will rotate across Central Alabama Thursday afternoon into
Thursday night. Model soundings continue to indicate a rapid
saturation of the atmospheric layer and therefore a limited severe
thunderstorm risk. Bulk shear is just high enough for some organized
line segments to form with the buoyancy in place. Additionally,
there is just enough shear to indicate a tornado threat. Clouds and
ongoing precipitation will hamper the mesoscale environment. At this
time, believe there is just enough to keep the limited mention of a
severe storm or two going. Will lean toward the light side with a
brief/weak tornado possible and maybe a damaging wind gust or two.
Rain amounts with this system generally appear to be in the 1 to 2
inch range. The negative tilt trough should move by fairly quickly
with the risk timing will be 3 pm to 3 am, west to east.

75

Long Term...

--Potentially significant severe weather this weekend--

*Headline: Multiple rounds of thunderstorms are expected to move
through the region this weekend. Saturday morning to Sunday morning
appears to hold the greatest risk for severe weather, compared to
the remainder of Sunday. This discussion will focus on the mentioned
time frame.

*Weather setup: In wake of the late-week shortwave trough,
 attention will be on a strong jet streak currently (as of
 Wednesday afternoon) southwest of Alaksa`s Aleutian Island chain.
 This feature will dive into northern Mexico and initiate an upper
 low, spreading a large upper diffluence zone across the north-
 central Gulf coast region. At the surface, southerly flow between
 the upstream front/surface low and downstream Atlantic ridge will
 maintain a supportive moisture influx and low LCL heights. While
 model-to-model and inter-model variations exist, forecast
 soundings and parameter fields are still signaling potential for
 strong instability and dynamic variables with this system. This
 includes, to some deviation: moderate (potentially strong) SB-
 and MU/ML-CAPE values (including some CAPE spanning the hail
 growth zone); 850mb jet; favorable 0-1/0-3 km SHR and bulk shear,
 and 0-6/0-8 km bulk shear). Together, the environment will be
 supportive of supercells and segmented thunderstorms with all
 severe weather hazards achievable.

We continue to assess model spreads, as a couple models continue to
show a potent setup on Saturday, while the Euro remains on the lower
end of the spectrum.

*Impacts_Severe: There will be a risk for tornadoes, severe-caliber
hail (1"+), and severe straight-line winds. Some of this activity
could be significant in nature if the variables come together.

We want to emphasize that there will be multiple rounds of
thunderstorms: 1) a batch Saturday morning; 2) a questionable period
Saturday afternoon when storm development is uncertain, but could be
significant if the environment recovers to the extent of some models
(especially considering the modeled mid-level dry slot surge/EML,
some capping, and recovering instability within the dynamic wind
field); and 3) Saturday evening to early Sunday morning, which
could also have higher impacts.

*Impacts_Hydro: Analysis from our senior hydrologist indicates
 that stream flow remains low across area rivers. It is
 anticipated that basins will be able to handle forecast storm
 total rainfall amounts of 2-4 inches. However, localized flooding
 could occur in poor- drainage areas or small streams, associated
 with any heavy downpours.

89^GSatterwhite

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     50  68  55  69  53 /  20  80  90  40  40
Anniston    54  69  57  70  55 /  20  70  90  40  40
Birmingham  57  69  59  71  56 /  30  90  90  30  40
Tuscaloosa  57  70  58  72  57 /  40  90  90  20  50
Calera      56  70  58  71  57 /  20  90  90  30  50
Auburn      57  71  59  71  58 /  10  60  90  40  50
Montgomery  58  75  60  73  58 /  10  80  90  40  50
Troy        58  74  60  74  59 /  10  70  90  40  50

&&

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

&&

$$

08/75/89



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