Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 141717

Area Forecast Discussion
National Weather Service Birmingham AL
1117 AM CST Tue Feb 14 2017

For 18Z Aviation.


Today and Tonight.

A weak surface and upper ridge over Alabama was producing calm
winds at the surface and a dry air mass aloft. Precipitable
water values were under one-half of an inch with surface dewpoints
in the 30s. High clouds will increase across the area today as a
storm system over Texas tracks eastward. This southern stream
short wave trof will produce a surface low along the Texas and
Louisiana state line this afternoon. The surface low will track
near the I-20 corridor across Mississippi and Alabama tonight.
Widespread showers and a few thunderstorms will accompany the
surface low. Shear profiles are fairly high with this system with
0-6km bulk shear values near 60 knots and a low level southwest
jet near 40 knots. Surface based instability will struggle to
penetrate inland across Alabama tonight due to a lack of a marine
rich air over the eastern Gulf of Mexico and the quick movement of
the system. 60+ plus surface dewpoints will likely stay along the
coastal counties, and a warm nose aloft will keep a lid on
stronger updrafts. The warm nose aloft is likely why the hi-res
models are not showing much organized convection south of the
surface low. Once cap is broken, forecast soundings at Troy show
minimal CAPE due to moist adiabatic lapse rates below 700mb. For
the above reasons, will not mention any severe weather threat
across central Alabama. Heavier rainfall with this system will
likely be just north of the surface low track, near low level
baroclinic zone. The surface low will shift into Georgia near
sunrise Wednesday and the rain will quickly end from west to east
Wednesday morning. Strong cold air advection on the back side of
the exiting surface low will keep temperatures from rising much
during the day on Wednesday. Northwest to north winds of 10 to 20
mph will make it feel even colder.


Wednesday night through Tuesday.

Dry cold advection will continue Wednesday evening as high
pressure moves in from the west. The pressure gradient should
gradually relax overnight and allow for good radiational cooling.
Temperatures may drop just below freezing for much of the northern
part of the forecast area.

There is better model agreement regarding another system affecting
the region Friday night into Saturday. Lift and moisture appear
stronger with the most recent model runs, and POPs have been added
accordingly. Rain chances will need to be increased significantly
in future updates if these same model trends continue.

A prominent deep-layer ridge will likely develop on Sunday into
Monday in response to a highly amplified trough over the western
and central CONUS. This should lead to dry and warm conditions
until the upper-level trough reaches our area on Day 8 (Tuesday)
with the next chance of rain.



18Z TAF Discussion.

A storm system located over eastern Texas this morning will move
east along the northern Gulf Coast tonight and Wednesday while a
surface warm front extending from west to east across southern
MS/AL/GA will lift northward tonight. Expect skies to become
SCT/BKN through the afternoon hours from west to east followed by
BKN/OVC skies overnight with rain showers possible generally after
03z with increasing coverage/intensity through mid morning
Wednesday. TS will be possible at MGM/TOI/TCL/EET early to mid
morning based upon expected northward progression of the warm
front. SHRA will taper from west to east by the end of the period.




Relative humidity values will drop into the 30s this afternoon
before moisture starts to increase. High rain chances return
tonight into early Wednesday. There are no fire weather concerns.


Gadsden     64  46  50  28  55 /   0  90  60   0   0
Anniston    67  49  52  30  57 /   0  90  70   0   0
Birmingham  65  47  52  32  57 /   0  90  60   0   0
Tuscaloosa  65  48  54  31  59 /   0  90  50   0   0
Calera      67  50  53  33  58 /   0  90  60   0   0
Auburn      70  56  57  34  57 /   0  90  80   0   0
Montgomery  73  59  59  36  60 /   0  90  70   0   0
Troy        74  59  61  33  59 /   0  90  80   0   0




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