Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 231149

Area Forecast Discussion
National Weather Service Birmingham AL
549 AM CST Thu Feb 23 2017

Aviation Discussion.


Today and Tonight.

A low stratus deck is building westward across the area this
morning, with fog development ahead of the clouds. Expect clouds to
continue spreading across locations west of I-65, with fog possible
outside of cloud areas. Fog will dissipate with sunrise Thursday
morning, with clouds diminishing through the morning hours.

Upper level ridge axis builds across the area today from the west,
while a surface ridge axis slides southward, gradually turning low
level winds from the east southeast to the south late tonight.
Thickness values increase today under the ridge as drier air spreads
eastward. Afternoon highs will be rather warm with temperatures in
the 70s. Another mild night can be expected tonight, with lows in
the low to mid 50s.


Friday through Wednesday.

Deep layer south-southwest to southwesterly flow will be in place
during the day on Friday as a shortwave trough and embedded closed
low moves from the Central Plains eastward to the Midwest.
Meanwhile a surface low will move northeastward from Missouri to
Lake Michigan with a trailing cold front that will remain well
west of the forecast area during the day, not reaching the
Mississippi River at this latitude until around 0Z. A strong
elevated mixed layer and associated warm, dry air aloft will
serve as a strong cap to prevent any convection from forming
during the daytime hours. Very warm conditions are expected with
1000-850 mb thickness values supporting highs being near or above
80 degrees in many locations. Please see the climate section for
record highs that will be in jeopardy. It will also be breezy as

Shower and thunderstorm development along the front and possibly
along a pre-frontal trough will hold off until Friday evening as
the southern end of the upper-level forcing reaches the front. A
broken line at most in a very narrow moisture axis is expected
with the best rain chances in the far north. Some thunder will be
possible north if any stronger updrafts can form given the steep
mid-level lapse rates. However, any severe storms should remain
north of the area. This is due to the main upper- level forcing
remaining north of the area as well as warm, dry air aloft which
will result in some capping and dry air entrainment. The 850 mb
LLJ will only be around 30 kts with veering low-level flow as the
surface low occludes and continues to lift into Ontario. Longer
range CAM guidance keeps any stronger updrafts well north of the
area. The front should quickly exit the area by Saturday morning.

A brief period of more seasonable temperatures and dry conditions
will occur over the weekend behind the front. Lows will be around
freezing Saturday night as a surface high moves through the area.

An unsettled pattern will take hold for the first half of next
week with moist southwest flow in place between an elongated
upper-level ridge from the southern Gulf to the Bahamas and broad
troughing over the western US. In this southwest flow some
shortwaves will move through, predominately just north of the
area, with low predictability. Meanwhile PWATs will be increasing
to near 1.5 inches, with the potential for beneficial rainfall in
some areas. An unstable, sheared air mass will develop with steep
mid-level lapse rates, so some stronger storms may be possible in
this period, but with weak upper-level forcing there is nothing
synoptically that warrants inclusion of anything severe in the HWO
at this time.

The GFS is stronger than the ECMWF with an initial shortwave and
associated surface low ejecting from the Southern Plains to the
Ohio Valley Sunday night into Monday. This solution lifts a warm
front quickly northward through the area Monday with a moist and
unstable air mass developing south of the front. The strongest
LLJ and low-level shear parameters remain north of the warm front,
however. The ECMWF is weaker with these features and slower to
move the warm front northward, but looks wet on Monday as well.
The GFS sends a trailing cold front into the area that stalls
across the area on Tuesday and serves as a focus for continued
showers and thunderstorms while the ECMWF keeps the forecast area
solidly in the warm sector. Despite these differences, models are
generally in agreement on a warm and wet period.

Models are in good agreement on a stronger shortwave moving across
the northern US on Wednesday and an associated frontal passage for
Central Alabama. Both the GFS and ECMWF indicate plenty of
instability with the frontal passage and strong deep layer shear,
but the LLJ is weak and very veered as the surface low will be
over the northern Great Lakes. This will be monitored as the time
gets closer.



12Z TAF Discussion.

Low stratus deck spreading westward across the area from GA. Ahead
of the cloud deck, fog has reduced vis to IFR or lower at times.
Currently all terminals are at MVFR conditions or better. Have
included prevailing MVFR cigs at BHM and TCl due to the proximity
and westward progression of the stratus deck.

Cigs will improve and scatter out through the morning, with winds
from the east becoming southeast, at 5-7kts by early afternoon.  VFR
conditions will prevail through the evening hours. Could see early
morning stratus/fog again Friday morning. Uplift doesnt appear to be
as organized, but there will be enough low level moisture around to
include at least a scattered deck at 2kft for now.




Dry and warm conditions are expected today and Friday. The next
chance of light rain should come Friday night with a front, followed
by low relative humidity values over the weekend. There are no fire
weather concerns.



Record high temperatures for Friday, February 24:

Birmingham: 78 (1930)
Montgomery: 80 (1890)
Tuscaloosa: 78 (2011)
Anniston: 78 (1982)


Gadsden     74  53  77  51  58 /   0   0  10  60  10
Anniston    74  55  78  53  59 /   0   0  10  40  10
Birmingham  75  59  79  50  58 /   0   0  10  40   0
Tuscaloosa  77  57  81  49  60 /   0   0  10  40   0
Calera      76  57  79  52  60 /   0   0  10  40   0
Auburn      75  56  78  57  63 /   0   0  10  20  10
Montgomery  78  57  82  57  65 /   0   0  10  20  10
Troy        77  56  81  58  65 /   0   0  10  20  10




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