Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 250902
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
402 AM CDT Tue Jul 25 2017

.SHORT TERM...
Today and Tonight.

A mid level trof axis extends from Louisiana northeast across south
central Alabama and into the mid Atlantic states.  This feature will
be the trigger for scattered to numerous showers and thunderstorms
today, mainly south of I-20 and in the afternoon. Drier air was
located north of the trof axis, and the trof axis is forecast to
shift slowly southward this afternoon.  Rain chances will be highest
across south Alabama where deeper moisture and better forcing will
co-exist. Also, satellite imagery early this morning shows an MCV
over south Alabama which was producing showers on the north side of
the MCV. Steering level winds will be less than 10 knots near the
upper trof axis. With PWAT`s around 2 inches, slow moving
thunderstorms could produce localized flooding. Scattered showers
and thunderstorms will continue through the evening hours, but most
of the rain will likely dissipate by 9 pm. The warmest temperatures
today will be north of I-20 where lower 90s are forecast, with highs
in the upper 80s across the southern counties due to rain and lower
1000-850mb thickness values.

58/rose

.LONG TERM...
Wednesday through Tuesday.

Upper level ridging builds in behind the departing trough axis early
Wednesday. Latest model runs have this building in quicker,
increasing 1000-850mb thickness to 1430-1435m, which could support
temperatures in the mid 90s. Have therefore increased afternoon
temperatures area-wide. Winds are generally out of the west instead
of being southerly, which might limit dewpoints to the low 70s. Some
areas west of the I-65 corridor could exceed 100 degree heat
indices. Currently, the forecast has some localized areas hitting
105 heat index briefly Wednesday afternoon. Therefore, I have added
a low confidence mention of heat impacts in the HWO. While we might
not reach heat advisory criteria, we`re still likely to see triple
digit heat indices across the western counties.

The 1000-850mb thickness values increase to 1440m across the western
half of Central AL on Thursday, which would support temps in the mid
to upper 90s. Models are hinting at weak low level convergence in
the eastern half of Central AL Thursday afternoon, so have kept
chance PoPs in the forecast for those areas.  This could also help
moderate heat indices east of the I-65 corridor. Will leave mention
of heat impacts in the HWO Thursday afternoon and monitor model
trends. At this time, expect many areas to approach or exceed 100
degree heat indices with areas in the western counties hitting 105.
Meanwhile on Thursday, and upper trough begins to dig through the
Great Lakes region and a surface low moves through the Ohio River
Valley. A cold front will stretch through the TN Valley overnight
Thursday into Friday morning. This cold front will slowly push
southward through Central AL Friday and into early Saturday morning.
PWATs associated with this system are above the maximum
climatologically at around 2.3 - 2.5". This could lead to heavy
rainfall-producing storms along the frontal boundary as it pushes
south.

Behind the front, expect cooler and drier conditions for the
weekend. Have left mention for scattered showers since we`ll still
be near the trough axis and could see some extra lift for afternoon
convection. This trough axis essentially stays in place across the
Southeastern states through Tuesday, so expect northerly flow,
cooler than normal temperatures, and scattered afternoon storms into
early next week.

25/Owen

&&

.AVIATION...
06Z TAF Discussion.

A few showers remain but should not be an issue at the terminals
tonight. We are continuing to look at another night of low
stratus and some patchy fog across many sites, especially in areas
that had rain during the day. TSRA are possible once again during
the afternoon on Tuesday as we will still have a weak upper
trough stretching back from GA across the southern half of the
state.

08


&&

.FIRE WEATHER...

Rain chances remain above normal for a summer day and night
through Today, as a mid to upper level trough enters the region.
Plenty of moisture, instability and convergence/focus will aide in
this development. Temperatures not quite as hot as the previous
several days as heat indices only reach around 100. Dispersion
values will be low due to relatively light surface winds and light
transport winds.

75

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     91  73  92  73  92 /  30  20  20  10  30
Anniston    90  73  92  73  92 /  30  20  20  10  30
Birmingham  91  75  94  76  94 /  30  20  20  10  20
Tuscaloosa  90  74  95  75  95 /  40  20  20  10  20
Calera      89  74  93  74  93 /  40  20  20  10  20
Auburn      86  73  90  73  90 /  50  20  30  20  30
Montgomery  89  75  93  75  94 /  60  30  30  10  30
Troy        86  72  91  73  93 /  80  30  30  20  30

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
None.

&&

$$



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