Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 070808

Area Forecast Discussion
National Weather Service Birmingham AL
308 AM CDT Fri May 7 2021

/Updated at 122 AM CDT Fri May 07 2021/

The clipper system is now pushing through the southern portions
of Central Alabama. Skies have cleared and winds have dropped
behind this system in the north. With temperatures dropping off,
river fog has developed this morning. Watch for this trend to
continue southward this morning and will drop the fog chances
further south through sunrise. High pressure moves in later this
morning and will bring plenty of sunshine to the area over the
next 36 hours. With that said one outlier is bringing several
little shortwaves through on the north side of the high pressure.
Initial thought was to drop pops off through Saturday, ignoring
the outlier, but given the uncertainty will keep in some 10 PoP in
through the first of the weekend. Highs today will be in the 60s
and 70s, with warmer temperatures on Saturday in the 70s to near


/Updated at 0308 AM CDT Fri May 07 2021/
Sunday through Thursday.

Broad troughing will be located over the western CONUS on Sunday,
with stronger troughing over eastern Canada and adjacent portions
of the Great Lakes/Northeast regions, anchored by a persistent
upper low over Ontario. Central Alabama will reside under WSW flow
aloft between these features and subtropical ridging centered
near the Yucatan. A weak shortwave and associated surface low
will move through the Ozarks and Ohio Valley Sunday/Sunday night,
with an associated LLJ lifting off to the northeast during the
day. A trailing cold front will sag southeastward across Arkansas
during the day, eventually reaching northern Mississippi and far
northwest Alabama late Sunday night. A dry air mass will remain
in place over much of Central Alabama during the day, with
temperatures warming well into the 80s with southwest winds.
Moisture may increase enough for scattered showers/storms in the
far northwest by late afternoon. PWATs increase to 1.5 to 1.8
inches through the night Sunday night. While the main upper
forcing will be well north of the area, notable upper-level
diffluence does develop with some convectively generated vorticity
as well, resulting in PoPs increasing from the northwest with the
highest PoPs after midnight. If the convection becomes an MCS
then rain chances may increase quicker than currently forecast.
Best instability and shear will be in the far northwest during the
afternoon, but after sunset CAPE values drop off to less than 600
J/kg with 0-6 km bulk shear generally around 30 kts. Mid-level
lapse rates will be around 7 C/km, so some storms may be strong
with a low chance of an isolated severe storm. Confidence in any
organized threat is too low to mention in the HWO at this time
with the instability and shear dropping off by the time the
highest rain chances move in.

The cold front will continue to push through the area on Monday,
with high rain chances continuing. If surface-based instability
can develop ahead of the front, there could be some stronger
storms but this is questionable given the ongoing precipitation
and weak forcing. Overall rainfall amounts Sunday night into
Monday look to be in the 1 to 1.5 inch range, but will have to
monitor for any locally higher amounts given fairly high PWATs.
Seasonably cool high pressure across the CONUS should allow the
surface front to clear the area before stalling out along the
coast through Wednesday as it becomes parallel to the quasi-zonal
flow aloft, but the 850mb front will remain stalled across the
area. Isentropic lift over the stalled front will result in
another round of showers and possibly elevated thunderstorms
developing late Monday night into Tuesday but there is some model
uncertainty regarding the precipitation`s northward extent
depending on weak waves aloft. A stronger shortwave moves into the
central CONUS by Wednesday, which may cause a wave of low
pressure to move along the front, and will also serve to increase
rain chances. Some guidance indicates a CAD wedge moving into the
area which could limit instability. An additional 1 to 2 inches of
rainfall on top of what falls Sunday night into Monday will
result in total rainfall amounts of 2 to 3.5 inches through the
period, so there could be some flooding concerns by midweek. Dry
conditions finally return by Thursday night.



06Z TAF Discussion.

Some patchy river fog across the north will slowly build southward
this morning. Will include some tempo fog at EET, ASN, ANB and
TCL. Any fog burns off by 14z and sunshine will be the main play.
Winds will be strong today and included afternoon gusts. Winds
calm back down after 00z. A stray shower may be possible at MGM
through 12z, but chances are too low to include in the TAFs at
this time.

Note: AMD NOT SKED until further notice at KASN due to ongoing
equipment issues.




Dry conditions are expected through Sunday afternoon. Relative
humidity values will drop into 25 to 35 percent range this
afternoon and Saturday afternoon, and the 30 to 40 percent range
on Sunday afternoon. 20ft winds will be out of the northwest
today at 8 to 12 mph with higher gusts, with a turn to the
southwest and a decrease in speeds on Saturday. Rain chances
return by Sunday night as our next system approaches, with several
wet periods expected next week.


Gadsden     71  45  77  54  84 /   0   0  10   0  10
Anniston    71  46  77  55  85 /   0   0  10   0  10
Birmingham  72  50  78  58  86 /   0   0  10   0  10
Tuscaloosa  74  50  80  58  86 /   0  10   0   0  10
Calera      71  49  77  56  84 /   0   0   0   0  10
Auburn      71  49  77  55  83 /   0   0   0   0   0
Montgomery  76  50  82  56  86 /   0   0   0   0   0
Troy        75  50  81  56  86 /   0   0   0   0   0




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