Area Forecast Discussion
Issued by NWS Birmingham, AL

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FXUS64 KBMX 161729

Area Forecast Discussion
National Weather Service Birmingham AL
1129 AM CST Mon Jan 16 2017

For 18Z Aviation.


Today and Tonight.

High pressure remains in control of Central Alabama through tonight.
Southerly flow remains the dominate pattern so temperatures will
once again climb in the mid to upper 70s area wide. Little bit more
in cloud cover today may keep areas from reaching 80. A few models
are once again indicating an isolated shower developing during the
peak heating of the day. Should this occur it will likely only be
possible in the higher terrain as the extra lift from the natural
orographic lift may be enough to generate a shower. Chances are
still to low to mention at this time, but if it were to occur it
would be between 2 and 5 pm in the northeast. After sunset will go
with status quo as temperatures drop into the 50s with patchy fog
possible. A few of the high res models are indicating an increase
in winds overnight and this could limit the fog potential.


Tuesday through Sunday.

Models are coming into much better agreement on the various synoptic
features in the extended period of the forecast. Showers and
possibly a couple embedded thunderstorms will be ongoing over
Mississippi Tuesday morning and will move into the northwest
counties by Tuesday afternoon. Best rain chances will be north of I-59
during the day on Tuesday with isolated showers possible across the rest
of the area with continued warm temperatures. Severe storms are not
expected due to the combination of weak instability, weak forcing,
weak 0-3km shear, and weak SRH. The front will stall out somewhere
near the I-20 corridor Tuesday night. Rain chances will continue for
areas mainly along and north of I-20 Tuesday night in the moisture axis
along the front, but will diminish through the night as southern
stream shortwave ridging develops overhead. Rain chances will
continue to diminish during the day on Wednesday with an upper-
level ridge axis overhead.

A southern stream trough over the Southwest will eject into the
Plains Wednesday night ahead of a strong kicker wave moving onshore
from the Pacific. Southwest flow and isentropic lift will develop
across the area as the front lifts back north as a warm front. Light
rain will be possible as early as late Wednesday night mainly in the
west. Isentropic lift and moisture continue to increase on Thursday
ahead of the system. Rain chances were increased for areas west of I-
65 for this period. Thursday night the trough will swing around to a
negative tilt as it lifts northeastward, while also beginning to
shear apart into two pieces as it encounters an amplifying ridge
over Ontario. A surface low will develop over the Ozarks and move
northeastward while a trailing wind shift moves across the forecast
area. Will continue to monitor for a possible marginal weak tornado
threat given a 45-50 kt LLJ. However, instability looks very weak
due to isentropic lift precipitation ahead of the system, a limited
period of time for higher dew points to advect in, and poor mid-
level lapse rates. Therefore will continue to not mention anything
in the HWO. With plenty of upper-level forcing and high PWATs a
soaking rain is expected and increased rain chances to categorical
across the entire forecast area Thursday night. Will keep an eye
on rainfall totals but expect the system to be too progressive to
cause any flooding issues.

We will see a break in between systems on Friday. Attention will
then turn to the weekend system. A strong Pacific jet and multiple
Pacific systems will carve out a deep broad trough over the western
half of the country. One shortwave will lift northeast through the
Plains on Friday night and not be much of a factor for our areas. A
second shortwave will become a closed low on Saturday and move
towards our area on Sunday. Very steep mid-level lapse rates will
advect over our area for the weekend with strong mid and upper-level
winds. We will continue to closely monitor the severe weather
potential with this system with the CIPS analog guidance and CFS
plots indicating a pattern conducive for severe weather somewhere
across the Deep South. However, there are some important mesoscale
factors that remain unclear at this time. On Saturday models
indicate a coastal warm front becoming established along the Gulf
Coast and becoming a focus for convection. This convection may
prevent surface-based instability from lifting northward into the
forecast area which is often not handled well by the models. Also,
at this time the LLJ looks to be displaced to the east of the
upper-level forcing and the front. Will hold off on mentioning
anything in the HWO for now given these uncertainties regarding
surface-based convection overlapping with low-level shear/helicity
parameters favorable for tornadoes, and models may also break down
the high-amplitude downstream blocking ridge extending from the
Atlantic to Quebec too quickly. At minimum elevated storms will be
capable of producing severe hail.



18Z TAF Discussion.

A warm front lifted north of the area overnight and now extends
from central AR across N TN. A wedge front extended from E TN
south into N GA southeast off the GA coast and is drifting
westward. Cloud cover is expected to increase this afternoon from
the southwest as a cold front across east OK and east TX moves
toward the Mississippi River. Expect a south to east low level
flow to persist across the area through this cycle. Low level
moisture will be sufficient for IFR conditions early Tuesday
morning with lower CIG`s. Some patchy fog will be possible early
on Tuesday generally south and east but confidence is
questionable. A few SHRA will be possible this afternoon and
evening but potential is too low to mention at any specific
terminal at this time.




Unseasonably mild temperatures through the weekend and into the
middle of next week. Rain chances return Tuesday with a wet pattern
setting up Wednesday through Friday. Despite warm temperatures,
afternoon relative humidity values will likely stay above 40 percent
due to the southerly winds bringing gulf moisture northward.


Record High Temperatures (Record year)

Monday, January 16:

Anniston   75 (1949)
Birmingham 77 (1943)
Tuscaloosa 77 (1949)
Montgomery 79 (1952)

Tuesday, January 17:

Anniston   74 (1953)
Birmingham 79 (1943)
Tuscaloosa 75 (1990)
Montgomery 78 (1990)


Gadsden     71  56  70  56  65 /  10  20  40  60  40
Anniston    71  55  73  59  69 /  10  20  20  50  40
Birmingham  72  59  73  59  68 /  10  20  40  60  40
Tuscaloosa  74  59  76  59  71 /  20  20  40  50  40
Calera      74  58  74  60  70 /  10  20  20  50  40
Auburn      74  56  74  61  72 /  10  10  20  30  30
Montgomery  75  56  78  61  75 /  20  10  20  20  30
Troy        74  55  77  61  76 /  10  10  20  20  30




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