Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 270902

Area Forecast Discussion
National Weather Service Birmingham AL
402 AM CDT Thu Jul 27 2017

Today and Tonight.

A similar set-up today as yesterday with central Alabama on the
eastern periphery of a large upper ridge over the central United
States. Drier and more stable air aloft will advect eastward into
west Alabama this morning with a narrow axis of mid level moisture
across east Alabama.  Any convective activity today should be east
of I-65. The NAM/RUC models indicate high microburst potential
across east Alabama this afternoon, and will mention isolated severe
storms possible east of I-65. Warmer low level air will continue to
feed into Alabama today in westerly low level flow. 1000-850mb
thickness values support mid 90s across west Alabama with lower 90s
east of I-65.  With surface dewpoints in the lower 70s this
afternoon across west Alabama, heat indices will approach 105
degrees.  Based on values from yesterday, will go ahead and issue a
heat advisory for the afternoon hours for areas generally west of a
line from Bear Creek, to Brookwood, to Six Mile, to Selma. Isolated
storms will linger into the evening hours across east Alabama. A
surface low moving across the mid Mississippi Valley region late
tonight will trigger a band of convection which could enter
northwest Alabama between 3 am and 6 am Friday, and small rain
chances continued across the far northwest counties.


Friday through Thursday.

We begin Friday with a cold front stretched through the Ohio River
Valley pushing southward into Northern AL. This cold front is
associated with a broad surface low near the base of a developing
longwave trough. The upper level low pressure system is offset well
to the north, over the Great Lakes. We could see some early
shower/thunderstorm activity across the far northern counties Friday
morning. The cold front slowly moves southward during the early part
of the day Friday. By Friday evening, the surface low strengthens
and troughing pattern amplifies over the Eastern US. This
strengthens the northerly flow and pushes the cold front through the
area quickly Friday evening into early Saturday morning. There are
still timing differences in the models, so specific arrival times
will need to be re-evaluated with future model runs. Expect some
decrease in storm coverage after sunset Friday night, increasing
again Saturday morning across the southern most counties as the cold
front finally pushes south of the area. Ahead of the cold front,
PWATs are still showing up in the 2.3-2.4" range, so expect very
heavy rainfall with any storms that do develop. Due to the increased
forcing from the cold front and increased precip loading, I can`t
rule out the potential for some storms to produce strong to severe
downburst winds. 850mb temps are around 20C, making lapse rates very
low; therefore, not expected a large hail threat. We could see some
small hail in the strongest storms, but otherwise the main threat
will be isolated damaging winds and localized flooding. Have
continued mention for low confidence severe for these threats.

The low pressure system slides southeastward Saturday and
essentially stalls out over the Tidewater Region of Coastal Virginia
through early next week. This keeps us under northerly flow on the
back side of the deep trough, leading to drier and cooler weather
through at least mid-week. Models hint at another impulse digging
through the main trough towards the end of next week that could
bring another round or showers/storms. Otherwise, expect below
average temps and precip coverage for most of the upcoming week.



06Z TAF Discussion.

Most of convection was done for the night. However, within the
last couple of hours we have had some small widely scattered
SHRA/TSRA drift SW into C AL from GA. There is a small chance
activity could hold together or develop over MGM/TOI. Will be
keeping an eye for possible necessary amendments. Some MVFR,
possibly lower fog will be possible tonight as we are SKC across
much of the area (except for some 5-7 KFT clouds SE of I85
corridor) as our dew point depressions lower. Confidence is too
low to add cigs. Although we had plenty of rain across C AL
today, not as much fell at the terminals. This may bode well
against dense fog/low cigs late tonight.




Isolated to scattered rain chances today, with best chances in the
east. Hot and humid weather expected today. Cold front approaches
on Friday, increasing rain chances. Cooler and drier weather
behind the front through the weekend. No fire weather concerns at
this time.


Gadsden     93  73  88  71  87 /  20  10  60  50  10
Anniston    92  73  89  72  87 /  30  10  50  50  20
Birmingham  94  76  90  73  87 /  20  10  50  50  20
Tuscaloosa  96  75  92  74  89 /  10  10  50  50  20
Calera      93  75  90  74  88 /  20  10  40  50  30
Auburn      91  74  91  73  86 /  30  10  30  40  40
Montgomery  94  76  94  75  89 /  30  10  30  40  50
Troy        93  73  94  74  87 /  30  10  20  40  60


Heat Advisory from noon today to 7 PM CDT this evening for the
following counties: Bibb...Dallas...Fayette...Greene...Hale...


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