FXUS64 KBMX 142117

Area Forecast Discussion
National Weather Service Birmingham AL
313 PM CST Fri Dec 14 2018

Evening Update.



A highly amplified pattern is present across the much of the
country this afternoon with a closed upper level low evident on
moisture channel imagery over east-central Louisiana while a
longwave ridge is present to the east off the Atlantic Coast and
to the west over the four corners states.

Toward the surface, an occluding surface low was positioned near
Shreveport Louisiana while another surface low was developing near
Greenwood Mississippi. A warm front extended east of the new
surface low and stretched roughly along the U.S. Highway 80
corridor across our southern counties while a cold front extended
southeast of the new low pressure center and extended southeast to
near Meridian Mississippi and further southeast toward Pensacola



Tonight through Saturday.

The closed low aloft will slide northeast this afternoon and
tonight and will move over our far northwest counties early
Saturday morning. The low will track near Chattanooga by tomorrow
afternoon and will move into Virginia Saturday night.

The surface low will track northeast across north Mississippi
tonight and will move into south-central Tennessee by early
Saturday morning and will move into the eastern Ohio River Valley
by Saturday afternoon.

For the short-term period some drier air has advected in from the
southwest aloft and that has resulted in reduced rain shower
activity this afternoon. Weak warm advection at the surface has
allowed temperatures to climb into the 60`s south near and south
of the warm front while falling heights aloft with the approaching
upper low are both contributing to steepening lapse rates aloft.
Some thunderstorms will be possible with the shower activity for
the remainder of this afternoon and into the evening hours,
especially across our western and southern counties.

There is a conditional risk for hail form elevated convection
over our northwest counties through the mid evening hours tonight.

More subtle height falls aloft along with relatively low surface-
based instability has developed near and south of the warm front
and a conditional risk for strong winds and some hail will be
possible across our southern counties (roughly along/south of the
U.S. Highway 80 corridor) through the mid evening hours tonight.

The limited time and areal extent of these conditional risks will
keep it from being mentioned in the HWO product.

Convective activity should wane overnight with rain showers
remaining likely across our northern and eastern counties into
early Saturday morning. Through the day expect the best rain
chances to shift north and east with time with the departing
surface and upper level low. A few lingering rain showers are
expected Saturday night generally along and north of the
Interstate 22 corridor west of Birmingham and along and north of
the Interstate 20 corridor east of Birmingham.

Cooler temperatures will be experienced across our western
counties tonight due to height falls aloft. Expect lows to range
from the low 40`s northwest to near 50 southeast. Highs Saturday
will range from around 50 far northwest to the upper 50`s southeast.
Expect lows Saturday night to range from around 40 far north to the
mid 40`s southeast.


Sunday through Saturday morning.

Conditions will continue to dry out on Sunday as the upper level
low continues to progress to the north and east. High temperatures
will be in the 50s and lowering to the mid to upper 30s Sunday
evening. Upper level flow begins to take on a northwesterly
component as upper level ridging and high pressure begin building
in from the west on Monday. High pressure becomes centralized over
Alabama by Tuesday. Overall conditions will be relatively dry,
with slightly warmer daytime highs and cooler overnight lows.

An upper level low begins to develop just north of the Mexican
plateau causing the upper level ridge/high pressure pattern to
flatten and slide eastward Wednesday morning. There are some
inconsistencies regarding how quickly this upper level low will
progress eastward and if there is any means of Gulf moisture
return. Therefore, leading to uncertainty regarding when the next
chances for rain will be. I have started to trend towards
increasing rain chances beginning Wednesday night through Thursday
by adding in 15% PoP. For now will continue to monitor the
progression and development of this next upper level pattern.



18Z TAF Discussion.

A large scale closed upper low near the Texas/Louisiana state
line will track northeast across north Alabama tonight. Widespread
low cigs will prevail across Central Alabama thru the period. A
band of showers over east Alabama early in the period will shift
eastward towards Georgia. A mid level dry slot will bring rain
free conds into west Alabama this afternoon, with the drier air
spreading into east Alabama by mid afternoon. As the upper low
approaches west Alabama this evening, surface winds will become
south- southwest. Cigs will likely rise above 1000 feet agl for
several hours as drier low level air advects into the region. Cigs
should lower again after 06z as a cooler and moist air mass moves
back into the region on the back side of the upper low. Scattered
showers will accompany the upper low, but timing will be
difficult for any TAF site and just handled with VCSH.




Rain chances will gradually decrease from southwest to northeast
through tonight with a few isolated thunderstorms possible through
early evening tonight. Some patchy fog will be possible Saturday
morning. Rain chances taper even further from south to north by
late Saturday with drier conditions through the day on Sunday. Dry
conditions are forecast through midweek next week although RH
values remain above critical values. There are no fire weather
concerns at this time.


Gadsden     46  52  42  53  36 /  50  40  20   0   0
Anniston    46  53  43  55  37 /  50  40  20   0   0
Birmingham  46  52  44  55  38 /  50  40  20   0   0
Tuscaloosa  46  54  43  57  37 /  30  20  10   0   0
Calera      45  52  43  55  38 /  40  30  10   0   0
Auburn      47  54  44  54  40 /  50  20  10   0   0
Montgomery  47  57  45  57  40 /  30  20  10   0   0
Troy        47  56  45  56  41 /  30  10  10   0   0





NWS BMX Office Area Forecast Discussion