Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 202345

Area Forecast Discussion
National Weather Service Birmingham AL
645 PM CDT Sat Jul 20 2019

For 00Z Aviation.


Through Sunday.

Widespread showers and storms have developed this afternoon in
response to the lift associated with the upper level low pressure
centered just off the Gulf Coast. With PWATs well over 2 inches
for most of Central Alabama, these storms have been efficient
rainfall producers. One storm that popped up over the Bessemer
Airport dropped 1.74 inches in just over an hour. A wind gust to
31 knots was also reported in Bessemer, but gusty winds haven`t
been very prevalent with these storms today due to the saturated
air mass that`s in place. Fortunately, we haven`t had any storms
last long enough to cause any flood concerns like we had during
the day on Friday. Even with the widespread showers and storms
there have still been a few spots that remain bone dry. One of
those spots is our office here at the Shelby County Airport.
That`s certainly the nature of summer convection here across
Central Alabama. We can expect at least numerous showers and
storms to continue through the early evening hours, and we`re
watching some fairly strong outflow boundaries pushing northward
out of southern Alabama. Those boundaries have triggered showers
and a few storms in Troy and will be capable of keeping convection
going through at least the next 3 to 4 hours farther north.

Convective activity and coverage will diminish with the loss of
daytime heating this evening. However, with the upper low still in
the vicinity as a lifting mechanism on the synoptic scale there
have been some indications in guidance of showers and storms
continuing to persist during the overnight hours. That would
especially be the case across the western and northern counties,
and have left mention of chance and slight chance PoPs in the
forecast through the overnight hours.

Sunday should feature less coverage of showers and storms, as was
covered in the previous discussion. Drier air, as can be clearly
seen in WV Satellite this afternoon over much of Georgia and South
Carolina, will start pushing into eastern Alabama by Sunday
afternoon. Only isolated to scattered PoPs can be expected, with
highest coverage expected across the western and northwest


/Updated at 0337 AM CDT Sat Jul 20 2019/

Sunday through Friday.

Moisture quality should decrease on Sunday as a weak 500 mb low
continues to move westward away from the forecast area. A ridge
to our east is expected to provide weak subsidence across our
central and eastern counties, where PWAT values may fall to around
1.7 inches. This will support POPs ranging from 30 percent in the
southeastern counties to 50 percent in the northwestern counties,
and a further reduction in rain chances may be needed. A similar
setup is likely for Monday as 2 inch PWAT values remain confined
to the northwest of I-59.

On Monday night, the first cold front in quite some time will be
approaching from the northwest, providing a focus for showers and
storms. Rain chances should increase during the evening and
overnight hours from the northwest, with rain chances of 60 to 70
percent along and north of I-20 through daybreak on Tuesday.
While the southern half of the forecast area appears to be in line
for widespread showers and storms on Tuesday afternoon, rainfall
amounts near I-20 will depend on the timing of the cold front. If
the front passes through during the early morning hours, a lack
of daytime heating could lead to a relative lull in convection and
rainfall intensity.

Much drier air will be advected in behind the front for Wednesday
and Thursday, leading to rain chances being confined to our
southeastern counties near the stalled front. Moisture recovery
and higher rain chances are expected on Friday with the onset of
moist southerly flow.



00Z TAF Discussion.

At 23:40Z/6:40PM, there were plenty of (VFR) convective debris
clouds across the region, with a few clusters of showers & storms.
For now, I`ve carried VCSH at ASN-ANB-MGM early this evening to
account for ongoing nearby showers. Otherwise, the main thing to
watch is whether or not a northward-moving outflow boundary &
associated convection holds on long enough to affect northern-tier
terminals (specifically ASN-ANB) later this evening. For now,
such activity is not included.

Then, forecast guidance continues to suggest a low-level setup
conducive for the development of low clouds overnight/early Sunday.
I haven`t made any significant changes from the prior forecast,
and a mix of MVFR-IFR clouds/visibility is included across the
board. We`ll monitor trends in case adjustments are needed to
better pinpoint the extent of sub-VFR conditions. Surface winds
tonight will be calm to very light.

We`ll return to VFR conditions after morning low clouds, with
VCSH/PROB30 TSRA during the afternoon to evening time frame.
Surface winds will average between 5-10 knots from the southwest.




Following numerous showers and storms today, some reduction in
rain chances appear likely for Sunday and Monday across the
central and eastern counties of Central Alabama. A cold front
should bring more widespread rain for Monday night into Tuesday.
With a moist airmass in place, there are no fire weather concerns
at this time.


Gadsden     72  88  71  88  70 /  50  30  20  60  70
Anniston    71  88  72  89  71 /  40  30  20  60  70
Birmingham  73  89  73  89  72 /  30  30  20  60  70
Tuscaloosa  73  90  73  90  72 /  30  50  30  60  70
Calera      71  88  71  89  71 /  30  30  20  50  60
Auburn      72  89  72  89  72 /  50  20  20  30  50
Montgomery  73  91  73  92  73 /  30  30  20  30  50
Troy        72  90  71  91  71 /  30  30  20  30  30




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