Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 252354

Area Forecast Discussion
National Weather Service Birmingham AL
654 PM CDT Wed Apr 25 2018

Aviation Discussion.


Through Thursday.

Those pesky low clouds have finally cleared for areas along and
west of I-65. The remaining clouds over east Alabama will clear
out by sunset. On its heels are high clouds associated with a
quickly evolving storm system over the Southern Plains States.
Rain will likely reach northwest Alabama late this evening and
spread into west Alabama by 3 am. Expect the rain to reach the
I-65 corridor just before sunrise. Despite stable near surface
conditions, moderate mid level lapse rates and strong forcing
could produce some embedded thunderstorms in the rain shield,
mainly for areas west of I-65. This is a quick moving system, and
the leading edge of the heavier rain band will be near the Alabama
and Georgia state line by late morning. A dry slot on the back
edge of the rain shield will likely bring some clearing of the
cloud cover across the southern counties Thursday afternoon, but
deeper moisture associated with the upper low will keep skies
mostly cloudy across north Alabama. The center of the 500mb low
will track across north Alabama Thursday afternoon. Models show
temperatures near -20C near the center of the upper low. This will
produce a band of moderate instability across east Alabama in the
afternoon. However, bulk shear values will be deceasing in the
afternoon and forcing will be limited. 1000-850mb flow will also
be unidirectional, so air mass will not be very supportive for
parcel ascent to produce updrafts for robust storms. For now will
not mention any severe text in the HWO.


Thursday Night through Wednesday.

The surface low and associated cold front will slide off to our east
fairly quickly, and by Friday morning, rain chances across Central
AL look limited as dry air moves in behind the departing low.
Surface high pressure builds in over the weekend as an upper level
ridge slides over the eastern half of the CONUS. This will in a
warming trend for our afternoon highs over the weekend with mostly
clear skies.

The first half of the next week looks to follow a similar trend as
the weekend. Synoptic scale ridging persists over the Eastern CONUS
as a trough digs into the Pacific NW and into the Great Basin by
Monday evening. The high pressure over the Southeast US blocks the
trough to our west through at least mid-week, resulting in warm and
dry weather.



00Z TAF Discussion.

Rain and possibly thunderstorms will spread into Central Alabama
late tonight/early Thursday morning. Expect reductions in vis and
cigs to MVFR, and possible brief periods of IFR, with this activity.
Will need to watch for light fog ahead of the rain at MGM and TOI,
but for now have not included reduce vis for that area. Behind an
area of more persistent and heavier rain, showers are likely to
continue through the day tomorrow, with cigs slowly rising. However,
do not anticipate any cig heights above 3kft through this forecast

Winds will be the most problematic part of the forecast, as the
surface low with this system will move across the area. Generally,
winds will be from the north to northeast this evening, and
gradually shift to the southeast ahead of the approaching low. Winds
at times will be variable at times, but speeds should remain below
6kts until rain/TS arrives. Winds will increase and gradually turn
to the south and then west as the rainfall ends. Due to a tightened
pressure gradient, wind gusts up to 20kts are possible Thursday

No amendments are scheduled for KASN due to unreliable wind data
being reported at that site over the past few days.




A break in rain chances will occur during the day today. A cold
front moving through late tonight and Thursday will then bring
wetting rains. Afternoon minimum relative humidity values will
remain above 50 percent through Thursday. There are no fire
weather concerns at this time.


Gadsden     52  64  48  70  46 /  50  90  20  10   0
Anniston    54  66  49  72  47 /  30  90  20  10   0
Birmingham  55  67  50  72  49 /  50  90  10  10   0
Tuscaloosa  56  68  50  72  49 /  80  90  10  10   0
Calera      56  67  49  71  48 /  50  90  10  10   0
Auburn      54  69  51  71  50 /  10  80  20  10  10
Montgomery  56  72  51  73  50 /  20  80  10  10   0
Troy        55  73  52  73  51 /  10  70  10  10  10




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