Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 190552
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1252 AM CDT Sat Jun 19 2021

.UPDATE...
For 06Z Aviation.

&&

.SHORT TERM...
/Updated at 1059 PM CDT Fri Jun 18 2021/
Through tonight.

No major changes to the grids. Updated trends with hourly temp/dew
points. Overall lows are the same with milder readings than
yesterday as tropical system pushes closer and sky is overcast.
Conditions will deteriorate as overnight progresses and rain moves
in from the coast.

08

Previous short-term discussion:
/Updated at 1236 PM CDT Fri Jun 18 2021/
Through Saturday.

Our transition to the tropical air mass out ahead of the potential
tropical cyclone in the Gulf has officially begun. Dewpoints are
now in the 70s across our southern counties, with outer bands of
showers and a few storms moving northward into extreme southern
Alabama. Drier dewpoints and mostly sunny conditions still remain
across the majority of Central Alabama early this afternoon with
temps observed in the upper 80s. For rain chances through this
afternoon, we`ll maintain chance PoPs across our southern
counties, generally along and south of the U.S. 80/I-85 corridors
through the afternoon and early evening. PoPs will trim back
slightly as we approach midnight, ramping back up as tropical rain
bands surge northward as the low pressure center approaches the
Louisiana coastline.

Widespread rains with some embedded storms can be expected
areawide by Saturday morning, with the best chance of enough
instability for more widespread storms across the southern half of
the area. We could still see enough of a combination of shear and
instability for those rotating storms, and will keep the "Marginal
Risk" for a few tornadoes in the current forecast from 10am
through 10pm. In terms of rainfall amounts, 3 to 5 inches still
appear valid roughly along and south of the I-20 corridor, but
we`ll watch for any shifts in the forecast track of the potential
tropical cyclone. With all the clouds and rainfall expected highs
should remain mostly in the 70s and lower 80s. We may have to
consider a Wind Advisory for at least our far southern counties
based on how organized the system becomes before making landfall
overnight tonight.

56/GDG

.LONG TERM...
/Updated at 329 PM CDT Fri Jun 18 2021/
Sunday through Thursday.

The primary concern in the long-term forecast period will be the
potential impacts of Potential Tropical Cyclone Three currently
located over the North-Central Gulf of Mexico.

Features Aloft.

The northern stream flow will remain north of the area over the
Northern Tier into the Ohio River Valley Region through Saturday.

Surface Features.

The potential tropical cyclone will move inland across far
Southern Louisiana earl Saturday morning and will track north-
northeast with time. The surface low looks to roughly parallel the
Interstate 59 corridor from around midday Saturday through Sunday
morning.

Forecast.

There will be a few more formidable trough passages to our north
with the first one moving across the High Plains into the Ohio
Valley regions on Sunday followed by a more stout longwave trough
that will dip further south into the Central Plains and Tennessee
River Valley Region on Tuesday. Expect the troughing to move to
the east of the area on Wednesday as deep-layer ridging again
builds over the Southern Plains.

The more impactful conditions are expected to be along and to the
right of the surface low track. Though numerical modeling has come
into better agreement over the past 24 hours, there remains
uncertainty in the track forecast and some adjustments in the
forecast track and impacts are expected.

Tropical Concerns.

Heavy rainfall that may produce localized flash flooding and some
river flooding will be the primary concern with rainfall amounts
highest roughly along and south of the Interstate 20 corridor with
amounts ranging from 2 to 5 inches with a few spots potentially
seeing higher amounts.

The tropical surface low looks to move into Southern Louisiana
during the morning hours on Saturday and track generally to the
north and northeast with time. Deep-layer tropical moisture will
result in precipitable water amounts increasing quickly into the 2.0-
2.5 inch range late Saturday into early Sunday. The most likely
track right now look to be across the Northern and Central portions
of the state with the system moving into Northern Georgia by Sunday
evening. The rough time frame for this risk is from early Saturday
morning through late Sunday night.

Surface friction effects will help to weaken the wind field and
sustained winds look to remain up to 20 mph across the southern
third of the forecast area. Wind gusts may approach 30 mph generally
near and south of the U.S. Highway 80 and Interstate 85 corridors,
with lower wind speeds and gusts further to the north.

The risk for a few tornadoes will be possible generally to the south
of the Interstate 20 corridor, where wind shear values on the
favorable right-front quadrant of the system will increase over our
far southern counties by Saturday morning and expanding northward
with time south of the Interstate 20 corridor by midday Saturday. It
is expected that we will have decent low-level instability for some
tornado potential during this time frame.

Favorable wind shear profiles look to persist across portions of our
eastern and southeast counties as we move into Saturday night and
Sunday morning, though reduced low-level instability during this
time frame makes this risk time frame more questionable.

Latter Portion of the Long Term.

A cold front looks to approach the area from the northwest after the
tropical remnants move northeast of the area on Sunday. Residual
deep-layer moisture along with increased upper level support with
the longwave trough approaching will lead to isolated shower and
thunderstorm activity Monday and Tuesday. Locally heavy rains could
cause additional concerns for localized flooding and river flooding.
Some global model total rainfall estimates may range from 3-6 inches
with locally higher amounts possible through the entire long-term
forecast period generally in a swath from the southwest to the east-
central portion of the forecast area.

Most global modeling is in slightly better agreement of the front
pushing into our southeast counties on Wednesday, which would
provide a break for our northern and central counties from
additional rainfall. The front is expected to stall across our far
southeast counties and may eventually return northward into the day
Thursday, resulting in isolated shower and thunderstorm activity
across much of the area.

05


&&

.AVIATION...
06Z TAF Discussion.

A weak tropical low pressure system will move inland over southeast
LA early this morning. Rain has spread into southwest Alabama and
will continue to spread northward thru the morning hours, reaching
the I-20 corridor by 12Z. Showers will overspread all of central
Alabama by 18z with vsbys 3-5 miles. Isolated TSRA possible from
15z thru 02z. but too limited for inclusion in TAFS. MVFR cigs
will develop across southwest AL by 12z and spread to all TAF
sites by 15Z. By 18z IFR cigs will develop across much of western
AL and all sites by 21Z. Cigs will likely remain IFR for the
remainder of the forecast time. Sfc winds will be generally from
the southeast direction. The tropical low is forecast to track
across the I-20 corridor overnight. Because the low is not very
organized, highest sustained winds will only be in the 10-12 kt
range, with gusts to 22 kts.

Note: AMD NOT SKED until further notice at KASN due to ongoing
equipment issues.

58/rose

&&

.FIRE WEATHER...

Residual dry air will result in RH values in the 35 to 50 percent
range this afternoon. Light southerly winds are expected today. A
potential tropical system will bring much higher moisture content
and widespread rainfall to much of the area on Saturday and
Sunday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     80  67  84  69  89 /  80  70  80  30  70
Anniston    79  69  84  72  87 /  90  80  80  40  70
Birmingham  77  69  85  72  89 /  90  70  70  30  70
Tuscaloosa  77  70  85  72  88 /  90  60  60  20  70
Calera      76  69  84  72  86 / 100  80  80  30  70
Auburn      76  69  82  72  84 / 100  80 100  50  60
Montgomery  78  71  87  73  88 / 100  80  80  30  70
Troy        77  71  84  72  86 / 100  80  80  40  70

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
Flash Flood Watch from 7 AM CDT this morning through Sunday
evening for the following counties: Autauga...Barbour...Bibb...
Bullock...Calhoun...Chambers...Chilton...Clay...Cleburne...
Coosa...Dallas...Elmore...Greene...Hale...Jefferson...Lee...
Lowndes...Macon...Marengo...Montgomery...Perry...Pike...
Randolph...Russell...Shelby...St. Clair...Sumter...Talladega...
Tallapoosa...Tuscaloosa.

&&

$$


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