Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 230845

Area Forecast Discussion
National Weather Service Birmingham AL
345 AM CDT Wed May 23 2018

Today and Tonight.

A concentrated area of heavy rainfall fell over Lee County overnight
with radar rainfall estimates of 4-6 inches over the far southeast
portion of Lee County. This activity was along a low level trof axis
and decent convergence enhancing rainfall rates. The low level trof
axis is forecast to push slightly southward today, with convergence
weakening due to a decrease in low level inflow south of the
boundary. Do not expect a repeat of excessive rainfall rates today
or tonight, but the areas along and south of I-85 will have the best
chance of rain today and tonight. There also appears to be a zone of
mid level convergence setting up across west Alabama by early
afternoon, so there is a chance of showers and a few thunderstorms
for a majority of central Alabama. Better chances for thunderstorm
activity today will be west of I-65 where surface temperatures will
be warmer. Shower and thunderstorm activity will diminish in areal
coverage this evening, but some activity will likely linger
overnight south of I-20.


Thursday through Tuesday.

High rain chances continue on Thursday as the moist air mass
remains in place. The low to mid-level circulation/remnant MCV
that has been hanging around the past couple days will initially
be over Georgia, but some high-res models retrograde its remnants
westward during the day. Drier air will briefly filter in across
the far northern/northwest counties.

A very stagnant upper-level pattern will be in place across the
Southeast and the Gulf throughout the forecast period, as a
southern-stream anomalous trough becomes trapped underneath mean
ridging in the northern stream. At the surface, low pressure is
expected to develop near the Yucatan by the end of the week and
lift northward towards the northern Gulf Coast this weekend. NHC`s
latest outlook indicates a 50% chance that this will become a
subtropical or tropical system. The GFS remains an eastern outlier
with this system tracking this system along the Florida
Peninsula. The ECMWF and its ensembles as well as the Canadian are
in better agreement that this system will lift towards the
northern Gulf Coast, putting much if not all of Central Alabama in
the moist eastern side of the system. Once it moves inland, it is
expected to stall out as a cutoff low next week. While wind shear
associated with the upper-level trough will probably prevent a
strong system from forming, slow-moving tropical depressions and
weak tropical storms have historically been heavy rainfall
producers. A tropical-like air mass is already in place and deeper
tropical moisture will move in by this weekend. Isolated flash
flooding will be possible almost any day. Daily high rain chances
will have a cumulative effect, and the best chance for more
organized flooding will come when 850mb moisture transport
associated with the low pressure system arrives by Sunday. There`s
still plenty of uncertainty regarding rainfall amounts and
timing, keeping confidence on the lower end at this time, but it
seems prudent to add a mention of flooding to the HWO for the
Sunday-Tuesday timeframe. Latest 7-day QPF from WPC indicates 3-6
inch area-average amounts across the area. Low-level wind fields
appear too weak to support any tropical tornado threat at this



06Z TAF Discussion.

Isolated showers and storms continue tonight, mainly south of the I-
85 corridor. Cannot rule out isolated showers anywhere overnight,
but chances are low near forecast terminals. Low level moisture
remains high and with calm winds at most locations, expect low cigs
and fog to build from east to west across the area, as low as IFR at
times. Scattered showers redevelop before mid day tomorrow. With a
similar setup as today, activity will be slower to affect TCL. Have
included VCSH at all terminals except TCL for now.




A moist pattern is expected over the next seven days and should
result in daily rain chances. Patchy fog/low clouds will be
possible each morning particularly where rainfall occurs during
the prior afternoon and evening.


Gadsden     85  67  86  67  82 /  40  20  40  30  60
Anniston    84  67  85  68  82 /  50  30  60  40  60
Birmingham  85  69  87  69  85 /  40  20  40  30  60
Tuscaloosa  87  69  89  69  86 /  40  30  40  40  60
Calera      83  68  86  68  84 /  50  30  60  40  60
Auburn      80  68  82  68  81 /  70  40  70  40  70
Montgomery  85  69  86  69  85 /  70  40  70  40  70
Troy        83  68  85  68  84 /  70  40  80  40  70




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