Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 200026

Area Forecast Discussion
National Weather Service Birmingham AL
726 PM CDT Sat Aug 19 2017

For 00Z Aviation.


Through Tonight.

A few isolated showers/storms have developed across west Central
Alabama this afternoon, moving southward, in association with a
weak shortwave. This activity will diminish this evening, as the
shortwave moves south of the area and instability weakens with the
loss of daytime heating. Dewpoints will be slightly warmer tonight
than last night, and could see light fog in the typical locations,
mainly confined to valleys or near bodies of water. Otherwise,
skies will be mostly clear. Lows will be in the upper 60s in the
northeast and low to mid 70s elsewhere.


Sunday through Friday.

A 500 mb ridge axis will continue to build into the Deep South on
Sunday, extending westward from a strong subtropical ridge over
the Atlantic. Meanwhile a TUTT low/upper low will slowly
retrograde westward over the Gulf. Light easterly flow between
these two features will continue to maintain a seasonably dry air
mass over the area. Dry air aloft will continue to mainly suppress
diurnal convection due to entrainment processes. Chances of an
isolated shower/storm will be limited to far West Alabama where
slightly higher PWATs/1000-500mb mean RH values will reside. The
relatively dry air mass will warm efficiently, aided by the
presence of the ridge, resulting in highs ranging from the low to
mid 90s north to the mid and even upper 90s south. Heat index
values are forecast to stay just below heat advisory criteria as
deep mixing will allow dewpoints to lower during the afternoon.

The pattern only changes slowly on Monday as a 595-596 decameter
ridge axis will extend westward from the Carolinas into Tennessee
and north Alabama, and the upper low continues to drift westward
over the Gulf. The upper low will move far enough westward for a
southeasterly flow to develop over the southern half of Alabama,
allowing moisture to begin to increase there. Models have trended
slower with moisture return due to the effects of the ridge.
Therefore, removed rain chances for areas along and north of I-20.
The relatively best chances of scattered diurnal convection will
be south of I-85. Looking at the cloudcover forecast, expect that
there will be some diurnally driven scattered cumulus. Some thin
cirrus may also move in due to the upper low over the Gulf, with
some mid-level moisture also noted over far southeast Alabama.
Overall, the greatest coverage of cloudcover will be for areas
south of I-85, decreasing to scattered to few as you go north
closer to the ridge axis. So most areas especially
(coincidentally) closer to the path of totality should see decent
viewing conditions.

Expect greater coverage of scattered convection beginning Tuesday.
This will occur as moisture continues to return to the area and
the ridge weakens some as a trough digs into the Great Lakes. A
cold front will begin to sag southward towards the area late
Tuesday night into Wednesday as a trough amplifies over the
eastern CONUS and a surface low deepens near Maine. Best rain
chances look to be Wednesday afternoon across our far northern
counties close to the front. A decrease in coverage along the
front is expected as we go into Wednesday night due to the loss of
daytime heating, lack of upper-level forcing, and drier air moving
in at mid-levels. Rain chances will diminish from north to south
Thursday and Friday as drier air moves in behind the front.
Nothing particularly strong to severe is expected with the front
due to weak lapse rates/shear.



00Z TAF Discussion.

The small area of convection in W AL has died off and no more
activity is expected overnight. Also, no convection is expected at
the terminal on Sunday. Except for some blow off cirrus near
MGM/TOI no other cloud cover should be noted tonight with clearing
skies and light/near calm winds. Some minor patchy fog with
slightly elevated dew points will be possible tonight in our low
lying areas near bodies of water. So some TAFs could see 4-5SM as
they are close to creeks during the late night hours to shortly
after dawn.




Drier weather is expected through the weekend with relative
humidity values remaining above 40 percent. Isolated afternoon
showers are possible for portions of far western Central Alabama
Sunday afternoons. Moisture and chances of scattered thunderstorms
begin to increase from the south on Monday. There are no fire
weather concerns at this time.


Gadsden     69  92  71  92  72 /  10   0  10  10   0
Anniston    70  93  73  93  73 /   0   0   0  10   0
Birmingham  74  93  75  94  75 /  10  10   0  10   0
Tuscaloosa  74  95  73  95  74 /  10  10  10  20  10
Calera      73  93  74  93  74 /  10  10   0  20  10
Auburn      73  94  73  91  74 /  10   0  10  30  20
Montgomery  74  97  75  95  75 /  10  10  10  30  20
Troy        73  95  73  93  73 /  10  10  10  40  20





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