Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 210556 AAB

Area Forecast Discussion...UPDATED
National Weather Service Birmingham AL
1156 PM CST Fri Jan 20 2017

For 06Z Aviation.



This discussion is focused on weather for tonight through Sunday.

--Severe weather mid-late overnight through Saturday morning, some
storms could yield significant occurrences of severe hazards.
Additional severe potential Saturday night into Sunday--

*Weather setup_round one: Thunderstorms are forecast to develop
tonight across the northwestern Gulf coast region in association
with a lead southwesterly upper jet impulse and 850mb jet
encroaching from the south/Gulf waters. The upper jet will then
overspread central Alabama, with the 850mb jet appearing to be
focused across roughly the southern-half of the forecast area.
Meanwhile, forecast soundings show a plume of increasing instability
arriving from the south, with the highest of values spanning
southern areas. Based on point soundings and ensemble output, we
should observe a fast-moving thunderstorm complex consisting of
segments/bows and supercells (of which could be near and/or ahead of
the larger bowing complex).

*Forecast changes: We have slightly trimmed the northern extent of
the elevated risk area, but are maintaining the remainder of the
elevated risk area. A limited risk remains for points north.
Refer to our webpage for the latest threat graphics.

*Impacts_Severe: There will be a risk of tornadoes, damaging
straight-line winds, and severe-caliber hail (1"+).

(We will keep an eye on trends Saturday afternoon. It still looks
like there will be a lull between the morning complex and what
arrives Saturday night into Sunday; however, given the energetic
southwesterly flow aloft and apparent instability recovery,
anything that does form would have severe potential. At this time,
the dry surge and capping should limit this threat).


*Weather setup_round two: Forecast models continue to point toward a
secondary low-level jet impulse Saturday night to early Sunday
morning, moving northeastward from the north-central Gulf coast to
southern Georgia. This feature could miss our southeastern counties
by a safe distance, or could be a glancing hit. Given the proximity
of the jet and another occurrence of increased instability/lapse
rates, severe storms could again manifest along and inland of the
Gulf coast, including our far southeastern counties.

*Impacts_Severe: If the low-level jet and associated storms find
their way into our southeastern counties, there will be another risk
of tornadic activity, hail, and damaging straight-line winds.

Additionally, colder air aloft associated with the parent upper low
is forecast to spread across Alabama through Sunday. Steep lapse
rates and elevated instability will support potential for a few
stronger convective updrafts with any cell.

*Impacts: Hail is possible with any stronger cell (mainly on the
small side, though some stones up to quarter size could occur).

*Impacts_Hydro: River flooding is not expected, though localized
flooding from downpours, especially in urbanized areas, could occur.



06Z TAF Discussion.

Main issues this TAF period continues to be timing out the storms
coming into the area later tonight into the morning hours. We are
expecting the possibility of strong to severe storms in the
morning. Shortwave will be coming in from the southwest and
spreading across Central Alabama late tonight into Saturday
morning with a low level jet to enhance it. We will be making
adjustments during the overnight as development begins to refine
TSRA start times. Before convection starts though, we have some
MVFR stratus/fog more IFR as you go south to start things off




A break in the rain today as the area is in between storm systems.
Afternoon relative humidity values will generally remain above 50
percent through Monday due to the moist and unseasonably warm
conditions. Some strong to severe storms can be expected Saturday
and Sunday, along with periods of heavy rainfall. Rainfall amounts
through Sunday will average 1 to 2 inches.


Gadsden     56  67  55  63  45 /  40 100  70  80  70
Anniston    57  69  57  65  46 /  50 100  70  80  70
Birmingham  59  69  57  64  46 /  60 100  70  80  60
Tuscaloosa  57  71  56  65  46 /  70 100  70  80  50
Calera      57  70  57  64  46 /  70 100  70  80  60
Auburn      62  70  60  67  48 /  70 100  70  80  50
Montgomery  64  74  59  68  47 /  80 100  70  80  50
Troy        65  73  58  69  47 /  80 100  70  70  40





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