Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 082027

Area Forecast Discussion
National Weather Service Birmingham AL
327 PM CDT Sat Aug 8 2020

/Updated at 1152 AM CDT Sat Aug 08 2020/
Today through Sunday.


In the upper levels, a broad ridge remains over the much of the
South while a shortwave trough was evident on multichannel vapor
channel imagery that extended from Western Illinois southwest
across much of Missouri and into Northern Arkansas.

In the mid levels, the forecast area remains between two areas of
high heights aloft, one over much of Western Texas with the other
more expansive area over much of the Southwest Atlantic, Northern
Caribbean Sea and over much of the Florida Peninsula.

In the lower levels, ridging was analyzed over the Northern
Caribbean Sea with high heights extending well to the northwest
into the Southern Plains.

The 08/12Z BMX sounding contained a fairly dry profile above 500
mb while some moistening has occurred over the past 48 hours i n
the lower levels. Despite relatively light winds, the forecast
area remains positioned on the west side of ridging in the lower
levels with the overall synoptic flow tendency favoring thermal
and moisture advection from the south.

Toward the surface, a weak surface boundary remains across the
southern portion of the state, extending from South of Demopolis
northeast to near Alexander City. Weak surface convergence is
occurring in the vicinity of this feature.


Expect cumulus clouds to continue to develop and build through
the afternoon hours and linger into the evening. Isolated to
scattered showers and thunderstorms are expected to continue to
develop with the best chances to the southeast closer to the
surface boundary position. Highs will reach the mid 90s areawide
today this afternoon.

Look for shower and storms to gradually decrease in coverage and
intensity through the evening and into the overnight hours. Skies
will become mostly clear overnight with lows ranging from near 70
north and east to the lower 70s south, west and near the larger
population centers.

A mid to upper level disturbance over the Mid Mississippi River
Valley today will move east tonight and tomorrow, increasing
chances for showers and storms into the Tennessee Valley and Ohio
River Valley regions tonight and into tomorrow. Most of this
activity is expected to remain to our north, however, outflow
boundaries resulting from the activity are expected to approach
the area from the north Sunday morning and into the afternoon
hours. Expect this feature to become a focus for potential
convective development. Meanwhile, the stationary boundary to our
south remains progged to return north as a warm front overnight
tonight and into the day Sunday.

The combination of these two features located across the forecast
area along with the expected upper-level trough positioned to our
north will favor slightly higher chances for showers and storms
Sunday with an isolated to scattered coverage expected. The better
chances remain across the south where deeper moisture content
looks to reside south of the northward advancing warm front. Highs
will again reach into the mid 90s with a few of the warmer
locations potentially reaching into the upper 90s south and west.
Heat index values may briefly exceed 105 degrees across portions
of our western and southern counties, however, the duration and
extent should remain too localized for an advisory at this time.


/Updated at 306 PM CDT Sat Aug 08 2020/
Monday through Friday.

There is little change to the overall thinking for the extended
forecast. I kept the trend going, increasing moisture with a
little high rain chances as we progress through the upcoming work
week. Extended guidance indicates occasional shortwaves with
decent overall moisture enhanced in the afternoon around SW US/N
Old Mexico/TX flat ridging. PWs across much of the Deep South will
be elevated through the extended with weak but open low level
onshore flow into Central Alabama. Humidity will increase as well
into the extended as a result.


Previous long-term discussion:
/Updated at 335 AM CDT Sat Aug 08 2020/
Monday through Friday.

An extended period of enhanced rain chances appears to be taking
shape for the upcoming week. Models are in agreement with the
formation of a 500 mb weakness/trough which becomes more prominent
thereafter. Development of daily showers and storms will be aided
by disturbances generated by convection from the previous day,
leading to a cumulative moistening effect across the region.
Monday will be the beginning of this pattern and probably the
least coverage of showers and storms at 40-50 percent. Coverage
each day should increase for Tuesday through Friday to around 60
percent or possibly higher. Temperatures are expected to trend
downward as a result of greater cloudiness and rainfall activity.



18Z TAF Discussion.

A weak surface boundary remains in the vicinity of our southern
terminal locations and this area is favored for the best potential
for isolated showers and storms this afternoon through early
evening. Chances for showers and storms remain too low to include
at any terminal location for this issuance. Low-level winds will
remain less than 10 kts at all sites outside of convective
activity with winds from the southwest to west.

Expect convection to decrease in coverage and extent through the
evening with mostly clear skies overnight. Some spots may
experience some reduction in visibility before sunrise Sunday
morning but duration and magnitude is not significant enough to
include in this issuance. Light winds are expected at all
locations overnight.

The boundary across the south will move north as a warm front
during the day Sunday while convection is forecast to our north to
move east across the Ohio and Tennessee River Valley regions.
Outflow from that activity may support convective development
across our northern counties from late morning into the afternoon
on Sunday. The result will be a slightly higher chance for showers
and storms but potential remained too low to include at any
terminal location through this forecast cycle.




Afternoon minimum relative humidity values should remain above 35
percent through Sunday along with isolated to scattered showers
and thunderstorms each day. Moisture and rain chances will
increase substantially into the upcoming week.


Gadsden     69  96  71  93  71 /  10  20  20  40  20
Anniston    71  96  72  94  72 /  10  20  20  50  20
Birmingham  74  96  74  95  74 /   0  20  20  40  20
Tuscaloosa  73  98  74  96  74 /   0  20  10  40  10
Calera      72  95  72  93  73 /   0  20  20  40  20
Auburn      72  95  72  93  72 /  10  30  20  50  20
Montgomery  73  97  75  96  74 /  10  30  20  50  20
Troy        73  95  74  95  73 /  10  40  20  60  20





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