Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 202158

Area Forecast Discussion
National Weather Service Birmingham AL
358 PM CST Fri Jan 20 2017


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.



18Z TAF Discussion.

Cigs will improve this afternoon, with broken decks rising to VFR
category heights. Southwesterly winds will increase to 10-12kts this
afternoon with an expected decrease this evening. There could be an
occasional stronger gust this afternoon. As southerly flow
increases ahead of an approaching squall line tonight, cigs will
lower to MVFR. Current timing of TSRA into west Central Alabama and
TCL is approx 21/11Z. This line will likely produce severe storms
with strong wind gusts, and timing will likely need to be refined as
storms develop to our west.




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     58  69  55  63  46 /  40 100  70  80  70
Anniston    60  72  56  67  47 /  50 100  70  80  70
Birmingham  61  71  58  65  47 /  60 100  70  80  60
Tuscaloosa  61  72  55  64  46 /  70 100  70  80  50
Calera      61  72  56  64  46 /  70 100  70  80  50
Auburn      63  72  59  68  48 /  70 100  70  80  50
Montgomery  64  76  58  67  47 /  80 100  70  70  50
Troy        65  75  57  69  46 /  80 100  70  70  40




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