Area Forecast Discussion
Issued by NWS Birmingham, AL

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052
FXUS64 KBMX 210835
AFDBMX

Area Forecast Discussion
National Weather Service Birmingham AL
335 AM CDT Sun Apr 21 2019

.SHORT TERM...
Today and Tonight.

High pressure is building into the region as the upper low moves
out. With calmer winds and clear skies, radiation cooling is in full
effect. The cooling in combination with waters beginning to warm up
across the area has resulted in patchy fog development. The
thickest fog is in the northeast where the cooler temperatures are.
Will monitor to see if this will become more of a widespread issue
issue versus patchy. After 9 am, any fog will be gone and sunny
skies will prevail. Highs will be in the 70s areawide with just
some light winds. As we move into the next period of darkness, winds
will die and skies will be clear. A little bit more moisture will be
in place so there is a potential for a little bit more in the way
of patchy fog but do not see it being a widespread issue at this
time.

16

.LONG TERM...
Monday through Wednesday.

Not looking at a lot of wholesale changes to the forecast for the
long-term tonight. Monday will start a transition period with regards
to upper-level considerations. Northwesterly flow aloft will have
already overtaken much of the Deep South with a ~1022 mb surface
high pressure across the Southeast. Stable weather conditions will
persist into mid-week with a general eastward progression of the
surface high. As such, southerly flow is expected to return by
Tuesday/Wednesday with high pressure positioned off the Carolina
Coast. Temperatures will respond with further warming into Tuesday
as a shortwave ridge develops along the Appalachians in response to
upstream & downstream trough axes. Meanwhile, a complex jet
stream/split-flow configuration sets up across the CONUS with a mid-
level disturbance, having previously separated from the Polar Jet,
digging southward into the Southern Rockies. By Wednesday evening
this is progged to eject into the Southern Plains & begin merging
with the sub-tropical jet. Nonetheless, there are no mentionable
rain chances through Wednesday night with forcing/moisture lacking
across the region. 70s & 80s will prevail for afternoon highs Mon-
Wed with Tuesday likely the warmest day of the upcoming week.

Thursday through Saturday.

The advertised disturbance is still on track to impact Central
Alabama Thursday/Friday. Downstream of the trough/upper-level low
(ULL), which should be near the ArkLaTex Thursday morning, broad
theta-e advection will signal increasing PoPs for areas across
the Gulf Coast & Lower Mississippi River Valley. Best chances for
the onset of rain across Alabama should take place Thursday
morning & was handled with ~50% in our western counties, generally
decreasing eastward. Better quality moisture return & insolation
during the afternoon will favor thunderstorm potential in an
environment with weak/marginal shear profiles (20-30 kts 0-6 km
bulk shear). However, thunderstorms should reside where best
synoptic forcing & instability line up which appears to be across
the west/south currently. Have left thunder out of forecast
elsewhere until it appears that better moisture & instability may
spread farther north/eastward in future updates.

As the vertically-stacked low progresses eastward overnight, better
area-wide coverage of showers & thunderstorms is expected & have
increased PoPs to 60-70% with `slight chance` of thunder mentioned
across the entire area. It continues to appear the system will
generally remain steady state or slightly weakening with eastward
progression into the Southeast CONUS. This notion, combined with
positioning favoring better convection along the Gulf Coast where a
better low-level jet, wind shear, and instability are likely,
suggests any thunderstorm activity across Central Alabama should
remain sub-severe. Friday afternoon a better thermodynamic
environment is possible given remnant boundary layer moisture & any
decent afternoon heating, though NVA & height rises (weakening ULL
moving to our east by now) suggest any short-lived, shallow
convection should behave. All things considered at this time, there
are no indications of severe weather or flooding with this system as
rain totals are currently forecast ~0.5-1.25", though locally higher
amounts are possible with thunderstorms in the forecast. Would
generally expect improving conditions to follow heading into the
weekend.

40/Sizemore

&&

.AVIATION...
06Z TAF Discussion.

Overall VFR conditions for the next 24 to 48 hours. With calm
winds there could be some patchy river fog in place through the
this morning. Light winds less than 7kts through the period as
high pressures builds in over the area.

16


&&

.FIRE WEATHER...

A much drier airmass works into the region today and will remain
across the area through mid-week. Clear skies and calm winds will
allow patchy river and valley fog to develop this morning and
again Monday morning. RH values will be in the 30 percent range
area-wide this afternoon, and for most of the area Monday
afternoon. The next chance of rain arrives early Thursday.

&&

.PRELIMINARY POINT TEMPS/POPS...
Gadsden     73  46  80  51  81 /   0   0   0   0   0
Anniston    73  48  81  51  83 /   0   0   0   0   0
Birmingham  75  53  82  55  83 /   0   0   0   0   0
Tuscaloosa  78  51  83  54  84 /   0   0   0   0   0
Calera      75  50  80  53  82 /   0   0   0   0   0
Auburn      72  52  80  54  82 /   0   0   0   0   0
Montgomery  76  49  82  53  84 /   0   0   0   0   0
Troy        75  50  82  53  84 /   0   0   0   0   0

&&

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

&&

$$



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