Area Forecast Discussion
Issued by NWS Birmingham, AL

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000
FXUS64 KBMX 231751
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1251 PM CDT Fri Jun 23 2017

.UPDATE...
For 18Z Aviation.

&&

.DISCUSSION...

12Z KBMX sounding shows an unstable environment already developing
across central Alabama with surface based CAPE around 1600 J/kg
with a lifted index of -4. Expect surface based instability values
to increase as surface temperatures slowly rise through late
morning and into the afternoon hours. Convective temperature
values generally are around 82 degrees so expect some showers to
begin to develop from mid to late morning across the area.

The morning sounding additionally reveals low level directional
wind shear with surface winds slightly east of due south while
southwest winds generally develop above 950 mb. Speed shear also
is evident as speeds range from around 10 knots off the surface to
50 knots roughly between 850 and 900 mb. This speed and
directional shear produces 0-1 kilometer storm relative helicity
values over 250 m2/s2 with 0-3 km values over 280 m2/s2 while bulk
shear values around 40 knots within the 1 to 3 kilometer depths.

A review of regional Velocity Azimuth Display time height displays
this morning shows generally unidirectional south-southwesterly
flow with some tendency for more southerly flow at times. Again,
speed shear is more evident with values generally from 10-20
knots above the surface to values around 50 knots from 5,000 and
above.

Surface analysis depicts the remnants of Cindy located just
northwest of Memphis, Tennessee with estimated minimum central
pressure around 1000 mb per WPC analysis. The surface low will
continue to move northeast today, entering the Ohio River Valley
region tonight. A weak surface trough appeared to extend from the
surface low center southeast through north-central Mississippi
this morning.

Radar and satellite boundary analysis revealed a few low-level
boundaries moving northwest across our eastern counties. The
analysis was hampered further west due to cloud cover and
generally light precipitation.

Based upon these observations and analyses, best potential for
strong to severe thunderstorms remains across our western and
northwest counties with the greatest risk roughly along and
northwest of the Interstate 59 corridor from Gadsden to Birmingham
to Demopolis. The greatest low-level shear will be found across
west Tennessee, northern Mississippi and north-central Alabama
today while the higher amounts of available instability appear to
be found from northern and eastern Mississippi into west-central
and northern Alabama.

The best window of opportunity for strong to severe storms appear
to exist from late this morning through late this afternoon.
Surface heating will provide the necessary instability for the
development of convection while wind profiles will support
organized convection. Wind profiles are expected to become less
favorable for strong to severe storms this evening and overnight
as the surface low pulls further northeast away from the region.

05


&&

.AVIATION...
18Z TAF Discussion.

Primary Impacts: A line of shwrs/tstms will spread eastward across
north central Alabama thru 00z. Gradient winds ahead of the convective
line will be from the SSW at 12-18 knots with gusts to 25 knots,
but could gust to 40-50 knots along the leading edge of the line.

Cigs outside the convective line should stay above 3000 feet agl.
Vsbys will likely lower to less than 1 mile in any showers or
thunderstorms due to the tropical nature of the air mass. Little
if any aviation concerns at KMGM and KTOI thru 23z, but southern
end of the convective line should be reach these airports after
23z. The air mass will stabilize after 01z and tstm activity will
diminish greatly as the convective line pushes into Georgia. VCSH
expected overnight as a surface front approaches from the
northwest. IFR cigs will also likely form after 09z area wide due
to weak convergence ahead of the sfc front and very moist
conditons.

58/rose

&&

.FIRE WEATHER...

High rain chances will continue through Saturday with rain chances
decreasing for Sunday and Monday behind a cold front. There are
no fire weather concerns.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     72  83  65  83  60 /  90  50  20  10  10
Anniston    72  82  67  82  61 /  80  60  20  10  10
Birmingham  73  82  66  83  63 /  80  60  20  10  10
Tuscaloosa  73  83  67  85  64 /  80  60  20  10  10
Calera      73  83  68  83  63 /  80  70  30  10  10
Auburn      73  83  69  82  65 /  50  80  30  20  10
Montgomery  75  86  72  85  65 /  50  80  40  20  10
Troy        75  86  71  85  65 /  40  80  40  30  10

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Flash Flood Watch until 7 PM CDT this evening for the following
counties: Bibb...Blount...Chilton...Coosa...Etowah...Fayette...
Greene...Hale...Jefferson...Lamar...Marengo...Marion...Perry...
Pickens...Shelby...St. Clair...Sumter...Talladega...Tuscaloosa...
Walker...Winston.

&&

$$


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