Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 201118

Area Forecast Discussion
National Weather Service Birmingham AL
618 AM CDT Sun Aug 20 2017

For 12Z Aviation.


Today and Tonight.

Weather conditions today will be similar to those on Saturday,
although there will be some changes in the upper air pattern.
Northwest flow prevailed on Saturday from the surface through 500mb
with a relatively dry air mass in place. The flow pattern will
become easterly today due to the influence of an upper low over the
eastern Gulf of Mexico. With drier air to the east of Alabama, low
rain chances will continue, with only isolated storms expected
across west Alabama. An upper ridge will build over Alabama on the
poleward side of the Gulf Low, and rising heights over central
Alabama will result in slightly warmer afternoon temperatures than
those on Saturday. Highs today will be in the mid 90s for most areas
along and west of I-65, with lower 90s across east Alabama. Despite
warm temperatures, heat indices are forecast to stay below 105
degrees, so no heat advisory at this time. Mostly clear tonight and


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



12Z TAF Discussion.

VFR conds thru the period. Few-sct cumulus with bases around 4000
ft agl will develop between 15z and 00z. A few storms mat develop
west of I-65, but coverage too small to include at any TAF site.
Sfc winds will become east northeast at 4-6 mph during the
daylight hours.




Very isolated afternoon showers are possible for the far western
portions of Central Alabama this afternoon. Moisture and chances
of isolated to scattered thunderstorms begin to increase from the
south Monday into Tuesday. There are no fire weather concerns at
this time.


Gadsden     92  71  93  72  91 /  10  10  10  10  20
Anniston    92  72  93  73  91 /  10   0  10  10  30
Birmingham  94  75  94  76  93 /  10   0  10  10  30
Tuscaloosa  94  74  95  75  93 /  10  10  10  10  30
Calera      93  74  94  75  92 /  10   0  10  10  30
Auburn      93  74  91  74  90 /  10  10  20  20  40
Montgomery  96  75  95  76  94 /  10  10  20  20  40
Troy        94  73  93  73  92 /  10  10  30  20  40




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