Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 202039

Area Forecast Discussion
National Weather Service Birmingham AL
339 PM CDT Sun Aug 20 2017

Through Tonight.

Isolated showers and storms have developed this afternoon, mainly
across the northern half of the area. This activity will drift
southward, and diminish with sunset. Mostly clear skies are
expected overnight, with light fog as low level moisture remains
high. Overnight lows will be in the low to mid 70s.


Monday through Saturday.

An elongated deep layer ridge will remain in place on Monday
across the Deep South eastward to the Atlantic. Models continue to
trend slower in bringing mid-level moisture back into Central
Alabama in the east-southeast flow south of the ridge axis, due to
a stronger ridge and further southwest track of the TUTT low
moving into the northwestern Gulf. Have slight chance PoPs for diurnal
convection along the I-85 corridor, with scattered coverage
limited to our far southeastern counties. Across the northern half
of Central Alabama, a very isolated shower/storm can`t be ruled
out given the lack of a strong cap, but coverage should be 10% or
less as updrafts will entrain very dry air aloft. Few to scattered
cumulus are expected across the area, with more cumulus in
southeast Alabama though even there some breaks are likely.
Cirrus is expected to be very limited due to the further southwest
track of the TUTT low, and will be dependent on any convective
debris. So conditions still look favorable for eclipse viewing.
Another warm day with highs in the low to mid 90s expected, with
perhaps some slight relief from decreased insolation during the
eclipse. Convection should dissipate after sunset.

The ridge begins to weaken during the day on Tuesday as a trough
digs into the Great Lakes. Deep layer moisture will increase with
PWATs increasing to around 2 inches in our southern and western
counties. Expect scattered diurnal convection across much of the
area, a bit more isolated in the far northeast. Some models try to
indicate a weak MCV drifting westward over Georgia which will have
to be monitored for any enhancement in coverage over our southeast
counties. Meanwhile a cold front will be pushing southward through
the Ohio Valley/Ozarks. Will keep some small rain chances going
overnight across the far north in case any remnants of pre-frontal
activity makes it there.

The cold front will move into Central Alabama Wednesday/Wednesday
night, enhancing rain chances over the area. A developing lee
trough along the East Coast may also enhance pre-frontal
development but also limit convergence along the front. There are
some lingering questions about whether any weak upper-level
forcing will be present and how quickly mid-levels dry out. So did
bump up rain chances a bit but some additional adjustments will
probably be needed. Lapse rates/shear look weak so severe storms
are not expected.

Thursday and Friday will see a northwest-southeast gradient in
rain chances, with lower to nil chances further north due to dry
post-frontal air and higher chances southeast closer to the front.
The pattern will de-amplify into a west-northwest flow pattern by
Saturday, while weak wedging develops along the East Coast.
Placement of increased moisture along the leading edge of
developing easterly low-level flow will determine rain chances on



18Z TAF Discussion.

Surface high pressure analyzed over central Alabama will continue
to support general VFR conditions through this forecast cycle. A
few SHRA and perhaps one or two TSRA may develop this afternoon
but probabilities remain too low to mention at this time.
Generally light easterly winds will prevail this afternoon
followed by near calm conditions overnight. High humidity will
overnight will encourage some reduction in VIS toward sunrise on
Monday but any reductions should be minor and will cease toward
14Z. A few more clouds will develop toward the end of the forecast
period, especially south, with rain chances at MGM/TOI becoming
enough to mention starting around 17Z. Low level winds will become
southeast during the day on Monday but are expected to remain
generally light.




Moisture and chances rain increase gradually through the week,
ahead of a cold front that will move through the area Wednesday.
There are no fire weather concerns at this time.


Gadsden     71  93  72  91  72 /  10  10  10  20  20
Anniston    72  93  73  91  74 /   0  10  10  30  20
Birmingham  75  94  76  93  76 /   0  10  10  30  20
Tuscaloosa  74  95  75  93  75 /  10  10  10  30  20
Calera      74  94  75  92  75 /   0  10  10  30  20
Auburn      74  91  74  90  74 /  10  20  20  40  20
Montgomery  75  95  76  94  76 /  10  20  20  40  20
Troy        73  93  73  92  73 /  10  30  20  40  20




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