Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 281744
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
1244 PM CDT Sat Mar 28 2020

.UPDATE...
Short-term Update & 18Z Aviation.

&&

.SHORT TERM...
/Updated at 1230 PM CDT Sat Mar 28 2020/

No major changes were made to the short-term forecast other than
to bump up this afternoon`s expected highs a degree or two in some
spots. This will put areas along and south of I-85 in the upper
80s to just at 90 degrees - including Montgomery. Otherwise, rain
chances with tonight`s storm system are still on track. Details
with regards to severe weather will be looked at again shortly
though don`t expect any needed changes on that end. Thereafter,
warm temperatures are expected again tomorrow despite frontal
passage. Low 70s to mid 80s are forecast from northwest to
southeast.

40/Sizemore

Previous short-term discussion:
/Updated at 0350 AM CDT Sat Mar 28 2020/

Through Sunday.

Looks like we will start out cloudy this morning. There will be some
breaks in the clouds early morning and then decreasing clouds by the
afternoon. Still going to be a warm day along with some near record
heat once again. Trends have been slower with the onset of the front
as the upper level ridging remains over the region, albeit a touch
to the south and east. With that said, have removed rain chances for
the afternoon. At the same time an upper level trough over the
Intermountain West will eject northeast over the Central Plains and
quickly moves northeast toward the Great Lakes region by
tonight.

This upper level trough will bring a cold front into the Southeast
tonight and into the state by 10 PM at the earliest. Surface-based
instability will be more than sufficient for shower and thunderstorm
activity along and ahead of the front tonight. However, we will see
though instability values will be decreasing with time after sunset.
The best forcing and dynamics will be displaced to the north of the
area in the Tennessee and Ohio River Valley regions, though enough
shear and forcing may be present to support a few strong to severe
storms. The best potential would be across our far northwest
counties generally from 11 PM til 4 AM Sunday morning.

The front continues to slide south and east Sunday morning. With the
support dissipating look for the activity to decrease in overall
coverage. Most of the rainfall will be done by 1 PM and clearing
skies behind the front.

16

.LONG TERM...
/Updated at 0350 AM CDT Sat Mar 28 2020/

Sunday night through Friday.

The cold front will slow across the far southeast corner of Alabama
where it briefly stalls along the Gulf Coast at the start of the
work week. On Monday, surface to 850mb flow becomes
northerly/northeasterly as a weak low-level ridge and surface high
pressure center works across the Tennessee Valley. These conditions,
in combination with mid/high level clouds, will allow for cooler
temps than previous days with highs ranging from the upper 60s north
to lower 80s south. Meanwhile, a quick moving upper trough will
deepen across the Rockies with a surface low developing over the
Southern Plains. In response, the stalled boundary across the Gulf
will be lifted northward early Tuesday morning shortly before the
low tracks west to east across Central AL. Large-scale cyclonic flow
atop the region will result in widespread rain for much of the day.

The threat for severe weather with the system depends largely on the
eventual track and placement of the surface low. Strong deep-layer
wind shear (Eff. bulk shear ~60-70kt) will provide more than enough
support for organized updrafts, but the northward extent of the warm
sector remains in question. Latest data indicates a slight southward
shift in the low center. This would confine mid/upper 60s dewpoints
and progged SBCAPE values ~500-1000 J/kg to generally the southern
third of the forecast area, primarily along & south of the I-85
corridor. Any storms that develop in this region late Tuesday
morning would be capable of producing damaging winds up to 60 mph
and quarter-size hail. Additionally, low-level curvature on forecast
hodographs with eff. SRH values ~300-400 m2/s2 would indicate a
potential tornado threat, but due to the quick eastward movement of
this system, there is a notable displacement between the center of
favorable helicity and instability axis. Nonetheless, a brief
tornado may be possible in our far southeast late Tuesday morning to
early afternoon where both ingredients may briefly align before
the favorable dynamics quickly shifts toward the Mid-Atlantic.
The overall uncertainty precludes adding anything higher than one
confidence TOR in the HWO for now, but the forecast will be
updated accordingly as guidance comes into better agreement.

Conditions behind the system will be cooler for the remainder of the
extended forecast as low-level ridging builds across the Lower
Mississippi Valley and dry, west/northwesterly flow become prevalent
over Central AL. Lows in the 40s/50s are expected area-wide
Wednesday through Friday. Another weak front may approach the area
towards the end of the week, but did not raise PoPs in this
update since there is much disagreement between guidance.

86

&&

.AVIATION...
18Z TAF Discussion.

Generally experiencing VFR scattered ceilings ~4-5k ft across
Central Alabama with a band of upper-level cirrus north of I-20
per satellite imagery. A broad fetch of southwesterly winds
continue ~7-12 kts with higher gusts. TAFs reflect early wind
forecast with gusts weakening later this afternoon. Thereafter, a
transition to MVFR with increasing rain chances is forecast along
an advancing front later tonight. Expect possible reduction in
ceilings to IFR with a broken line of showers and embedded
thunderstorms. CB mentioning was only included at BHM/EET/TCL as
probability decreases through time at remaining airfields. Shower
activity will continue along the front and after FROPA overall.
Unless the front stalls earlier than expected, a return to VFR is
expected later tomorrow morning, generally ~15-17Z from northwest
to southeast.

40/Sizemore


&&

.FIRE WEATHER...

Above normal temperatures and humidity values through tonight
with no rain across central Alabama through early this evening
due to strong ridge aloft. Relative humidity values will fall into
the 50-55 percent range this afternoon. Showers and a few storms
will spread across the area late tonight ahead of a weak cold
front. Expect some lingering showers across the southeast counties
Sunday morning. Drier and cooler low level air will move in
behind the cold front on Sunday, and RH`s will drop into the 35-45
percent range north, and 45-50 percent south.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     63  76  53  70  54 /  70  40  10  10  60
Anniston    66  77  55  72  54 /  30  50  10  10  50
Birmingham  65  77  56  72  56 /  80  30  10  10  70
Tuscaloosa  65  78  57  73  56 /  90  20  10  20  80
Calera      65  77  57  73  56 /  60  40  10  10  60
Auburn      67  78  58  77  59 /  10  40  10  10  30
Montgomery  70  80  58  78  61 /  20  40  10  10  30
Troy        69  82  61  80  62 /  10  40  10  10  20

&&

.BMX WATCHES/WARNINGS/ADVISORIES/...
None.

&&

$$



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