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FXUS64 KMOB 150032

Area Forecast Discussion
National Weather Service Mobile AL
632 PM CST Sat Dec 14 2019

.DISCUSSION...Updated for latest marine discussion below.


.MARINE...Went ahead and issued a Marine Dense Fog Advisory for
Mobile Bay, MS Sound and the adjacent near shore Gulf waters. 
So far the dense fog has be rather patchy and visibilities
somewhat variable, but will likely become more widespread and
persistent overnight. Currently the fog seems to be focused 
around the Dauphin Island area. MWW already sent, new CWF product
coming soon. /12


.PREV DISCUSSION... /issued 555 PM CST Sat Dec 14 2019/ 

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...MVFR conditions this evening will become IFR
overnight as patchy dense fog develops. VFR conditions return by
late Sunday morning. /13

PREV DISCUSSION... /issued 359 PM CST Sat Dec 14 2019/ 

NEAR TERM /Now Through Sunday/...Surface high pressure moves
north over the Florida Peninsula tonight into Sunday, bringing a
more southerly flow to the forecast area. A warm front is 
expected to move north across the region Sunday. For tonight, the 
return of a more southerly flow north of the approaching warm 
front will increase the expanse of stratus that has stubbornly 
remained over areas along and west of the Tombigbee River to the 
rest of the forecast area. As temperatures cool tonight, fog 
development is likely, though guidance is inconsistent on where 
and how dense the fog will be north of the approaching warm front.
Have went with general fog development tonight, but have leaned 
towards the SREF position of lower visibilities north of the coast
and west of I-65, with the SREF having a better placement of 
lower visibilities the last few days. Have worded patchy dense at 
this point, to highlight the possibility, but allow for some 
flexibility in handling the development tonight. As the stratus 
and fog increase in coverage, radiational cooling will become 
increasing cut off, with northeastern portions of the forecast 
area seeing the most cooling. Have leaned on the warm side of 
guidance, especially western portions of the forecast area with 
the forecast starting off with a persistent stratus deck these 
areas. Low temperatures in the low to mid 50s southwestern 
portions of the forecast area and along the coast to mid 40s 
northeastern-most portions.

Sunday, the stratus desk will be slow to mix out north of the 
approaching warm front. The warm front is expected to move north 
across the forecast area late morning into the afternoon. With the 
limited daytime heating, have leaned on the cooler side of guidance, 
especially northern portions of the forecast area. Another wild card 
is the possibility of sea fog development along the coast over and 
west of Mobile bay due to the warmer flow following the front's 
passage over cooler near coastal waters. Guidance is not indicating 
at this point, but will continue to monitor. High temperatures 
Sunday are expected to range from around 70 closer to the coast to 
low 60s north of Highway 84. /16

SHORT TERM /Sunday night Through Tuesday night/...The risk of
strong to severe thunderstorms late Monday afternoon and Monday 
night continues to increase with each model run. The zonal flow 
aloft on Sunday transitions to deep southwest flow as a strong 
upper level trough exiting the Rocky Mountains moves over the 
Great Plains, with precipitable water values increasing to 
between 1.5 to 1.7 inches by late Monday evening. This upper 
trough will initiate a surface low pressure area across the 
ARKLATEX region by Monday morning that will lift northeast, 
reaching West Virginia by midnight. In addition, an associated 
strong cold front approaching the region from the northwest will 
pass through the forecast area late Monday night into Tuesday. The
region will reside well within the warm sector on Monday, with 
high temperatures ranging from 75 to 80 degrees, along with 
surface dewpoints ranging from 63 to 68 degrees.

Precipitation will increase Monday afternoon to 60 to 80 percent 
over southeast Mississippi and inland southwest Alabama, with a 20 
to 50 percent chance further east. An 80 to 90 percent chance is 
forecast over the entire area Monday night. The atmosphere will 
become increasingly unstable with MLCAPES ranging from 1500 to 2500 
J/KG. SBCAPES will be even higher, possibly reaching as high as 3500 
J/KG Monday evening according to the NAM12. Deep layer effective 
shear on the order of 55 to 65 knots is currently forecast ahead of 
and along the squall line moving in from the west. Strong low and 
mid level shear will increase on Monday as well, with 0-3km SR 
Helicity values ranging from 200-350 m2/s2. Strong mid/upper ascent 
will also be present as we reside under the right entrance region
of a 130 knot 300mb jet max. This type of environment should 
support all severe weather hazards, including damaging wind gusts,
isolated tornadoes, and localized small hail.

The cold front moves through late Monday night into Tuesday
morning, with the precipitation tapering off through the day
Tuesday. Dry conditions area-wide will follow Tuesday night.
Dramatic change in temperatures occurs on Tuesday in the wake of
the cold front, with highs in the 50s northwest of I-65, and low
to mid 60s to the southeast. Lows Tuesday night will fall into the
upper 20s to mid 30s. /22

LONG TERM /Wednesday Through Saturday/...The Cold and dry weather
will persist Wednesday and Thursday as high pressure builds east 
across the Deep South and into the Southeast. Highs each afternoon
stay in the 50s and lows each night range from upper 20s inland 
to low 30s closer to the coast. Freezing temperatures will be 
possible all the way down to the coast Wednesday night. A gradual 
warming trend begins Thursday as the surface high builds into the 
Southeast and western Atlantic and local flow shifts to easterly 
and then southeasterly. Moisture begins to return heading into 
Friday as another system approaches from the west, with rain 
chances increasing as a result. Highs Thursday and Friday reach 
the upper 50s to low 60s and lows range from upper 30s to low 40s.

MARINE...Surface high pressure will move north over the Florida 
tonight into Sunday, bringing a light, more steady southerly flow to 
area waters. A strong cold front will move east towards the regions 
Sunday night through Monday, bringing an increase in the onshore 
flow to more moderate Monday, then moderate to strong Monday night. 
A Small Craft Advisory will likely be needed. The cold front will 
cross area coastal waters late Monday night through Tuesday morning, 
bringing a strong to very strong offshore flow. Wind gusts to gale 
force is likely Tuesday through Tuesday night over unprotected 
coastal waters and southern Mobile Bay. Wednesday night through 
Thursday, winds will transition to easterly and ease over protected 
waters as surface high pressure moves towards and begins to move 
east over the Southeast. Winds over unprotected waters will 
transition to a more moderate easterly through the same period. /16


AL...High Rip Current Risk from 6 AM CST Sunday through Tuesday 
     afternoon for ALZ265-266.

FL...High Rip Current Risk from 6 AM CST Sunday through Tuesday 
     afternoon for FLZ202-204-206.

GM...Dense Fog Advisory until 10 AM CST Sunday for GMZ630>632-650.


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