Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 191746

Area Forecast Discussion
National Weather Service Birmingham AL
1246 PM CDT Thu Apr 19 2018

For 18Z Aviation.


Today and Tonight.

A moisture-starved cold front is pushing southeastward through
Central Alabama early this morning. 08Z surface obs show
northwesterly winds now at Tuscaloosa and Haleyville, with dewpoints
dropping from the low 60s along the I-59 corridor to the low 40s
across the far northwest. An earlier band of light rain showers
associated with the front has dissipated, and only seeing a few
bands of broken clouds on satellite.

The front will clear the area by mid morning, with cool advection
occurring through the day. Despite mostly sunny skies, highs will
only warm into the upper 50s far northwest to mid 70s far southeast.
Winds will be breezy at times today. For tonight, drier air should
prevent fog development and lows will drop into the mid 30s to lower
40s. Expect winds to remain strong enough overnight to prevent frost.


Friday through Wednesday.

Upper-level ridging between an approaching upper low and persistent
troughing over New England and the Canadian Maritimes will result in
rain-free conditions Friday and through the daylight hours on
Saturday. Expansive low-level ridging centered near the Great Lakes
will be dominant over the eastern CONUS, resulting in easterly low-
level flow over the Southeast. Temperatures will moderate from where
they will be today, but the east winds will prevent a dramatic warm-
up. This will result in pleasant spring high temperatures in the
upper 60s to low 70s on Friday and the low 70s on Saturday.

The trough currently moving through the West Coast will break off
from the northern stream and attach itself to the slower southern
stream as an upper low. The upper low will have a southeastward
motion due to steering provided by the persistent northeastern
trough. Surface high pressure along the East Coast will result in a
CAD wedge, helping maintain an easterly component to the winds
across Central Alabama. A wave of low pressure will approach from
the west along a developing frontal zone near the Gulf Coast. A
strong northwesterly upper-level jet streak will set up on the
southwestern flank of the upper low, oriented from the Southern
Plains to the Gulf Coast, placing Central Alabama in the region of
strong upper-level diffluence in the left exit region of the jet
streak. Isentropic lift/warm advection aloft over the easterly
flow at the surface will promote shower development beginning late
Saturday night, with widespread rainfall expected across the area
Sunday into Sunday night.

The track of the weak surface low has trended a bit further north in
the latest model runs, as the trough associated with the upper low
takes on a bit of a negative tilt. Added in a slight chance mention
of thunder across the southern counties due to the presence of some
weak elevated instability. However, prospects for any surface-based
instability and threat of severe storms remains very low at this
time, as strong easterly flow and precipitation falling north of the
warm front will likely strongly impede the northward progress of the
warm front. Also, the upper jet orientation also indicates the
potential for disruptive Gulf Coast convection as well. The main LLJ
axis also looks to be located on the cool side of the warm front,
and the best instability is located in the mid-level dry slot.

The upper low looks to stall out/meander across the area Sunday
night through the first half of next week. A mid-level dry slot will
begin to wrap into the area Sunday night into Monday morning, with
the best deep layer moisture looking to move primarily east/north of
the area during this time. However, a strong ESE LLJ will provide
favorable low-level moisture transport from the Atlantic, and the
cold core aloft (-15 to -18C at 500 mb) will be over the area.
Therefore, rain chances and cloudiness will continue with overall
dreary conditions and limited diurnal temperatures ranges. It`s a
little too early to get a good handle on storm total rainfall
amounts given convective feedbacks in the models but these will be
monitored for any potential flooding threat. Area rivers and
streams will have had a little over a week to recover from last
weekend`s heavy rainfall, and the highest rainfall amounts may end
up being across the eastern counties which generally saw the
lowest rainfall amounts last weekend. A strong shortwave moving
into the Upper Midwest on Tuesday will serve as a kicker to
finally move this system out of here by the end of the forecast



18Z TAF Discussion.

VFR conditions to persist through the next 24 to 36 hours. Really
only a wind forecast now that the front has passed through all
sites. Generally 12 to 15 kts this afternoon. These winds will
drop to 5 to 8 kts tonight, then pick pack up tomorrow to around
10 to 14 kts.




With drier air in place tonight, fog is not expected. Afternoon
RH values will fall to or below 30 percent Friday and Saturday
afternoons. A few locations in extreme east Central Alabama will
drop to 25 percent for a couple hours Friday. 20ft winds remain
below 10mph. Critical fire weather conditions are not expected to
be met. The next chance of widespread rainfall comes Sunday.


Gadsden     38  69  42  72  50 /   0   0   0   0  20
Anniston    39  69  43  73  52 /   0   0   0   0  30
Birmingham  40  71  47  74  54 /   0   0   0   0  30
Tuscaloosa  40  71  46  75  55 /   0   0   0   0  40
Calera      40  70  46  74  54 /   0   0   0   0  40
Auburn      42  69  46  72  54 /   0   0   0   0  30
Montgomery  41  72  47  75  56 /   0   0   0   0  40
Troy        42  71  46  75  56 /   0   0   0   0  40




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