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Area Forecast Discussion (AFD)

Issued by Mobile/Pensacola (MOB)

FXUS64 KMOB 211147

Area Forecast Discussion
National Weather Service Mobile AL
547 AM CST Sun Jan 21 2018

.DISCUSSION...Updated for latest aviation discussion below.


21/12Z issuance...General VFR conditions through this evening (around
22/03z), when IFR to LIFR cigs (low status) and visibilities (fog) 
develop. Surface winds becoming southeast around 10 knots today
and continuing through tonight. 12/DS


.PREV DISCUSSION... /issued 426 AM CST Sun Jan 21 2018/ 

NEAR TERM /Now Through Sunday night/...The upper shortwave noted 
yesterday has now moved east of the forecast area, now over northern 
Florida, and will move off the Atlantic coast today. As the upper 
low moves off to the east, upper ridging will drift east across the 
forecast area today. Tonight, the upper ridging is expected to move 
quickly off to the east of the forecast area as deep low pressure 
and troughing develops over the plains states. Surface high pressure 
located along the southeast Atlantic coast early this morning will 
move out over the Atlantic through tonight, while a cold front 
associated with the developing plains system approaches from the 
west. This cold front will be approaching the Mississippi River by 
daybreak Monday, with perhaps a few showers moving into our far 
western counties very late tonight as the front approaches and upper 
ridging weakens. Persistent low level southeasterly flow today and 
tonight will bring increasing moisture into the region, and this 
onshore flow combined with the cool near shore marine waters will 
likely result in some fog across the area tonight, especially over 
the southern locations near the coast. High temperatures today 
finally return to the lower 70s for most locations, except along the 
immediate coastal areas where the onshore flow will keep highs in 
the mid to upper 60s. Warmer tonight too, with lows ranging from the 
upper 40s over northeastern counties to the low to mid 50s 
elsewhere. A few upper 50s possible along the immediate coast. 

SHORT TERM /Monday Through Tuesday night/...Monday through Monday
night, a closed upper system moves from over the Central plains
east-northeast over the Mid/Upper Mississippi River Valley before
getting a more northeast push due to a building upper ridge over
the western Atlantic. This system pushes a surface front across
southeast Mississippi late Monday afternoon, then east of central
Alabama and the western Florida Panhandle shortly after midnight 
Monday night. Shra/Tsra pretty much a given ahead of the front 
Monday afternoon into the evening hours. Biggest question is the 
chance of any severe. Guidance remains on the marginal side for 
any strong to severe (topping out around 500 j/kg). 0-3km shear is
enough (200-300 m^2/s^2 in the afternoon) for some rotators. 
Mid/upper level support has shifted north a bit, north of the 
forecast area in our case. SPC continues to advertise a marginal 
risk of severe weather with damaging winds the primary threat and 
see no reason to alter this at this point, with less overlap of 
surface and upper ingredients than yesterday. Temps above seasonal
expected Monday. With cooler air moving over the area behind the 
front, Monday night's lows will see a gradient of around seasonal 
lows west to above east.

Tuesday through Tuesday night will see a return of near seasonal
temps as cooler/drier air overspreads the entire forecast area. 


LONG TERM /Wednesday Through Saturday/...Shortwave energy moves
over the Plains mid week into the weekend, pushing surface high
pressure from the Plains to off the Mid Atlantic coast. This
prings back southerly flow off the Gulf by friday. Moisture levels
increase into the weekend until another front moves across the 
area Saturday night. Rain returns Friday night, with a better
chance of rain Saturday. Temps moderate slowly upwards from around
seasonal mid week to above seasonal with the return of southerly
flow end of the week.


MARINE...For the most part, no hazards in the near term except for 
winds nearing Exercise Caution levels for the offshore Gulf Zones 
this afternoon. A cold front approaches the marine area from the 
west tonight and early Monday bringing an increased chance of 
showers and embedded storms, as well as an continued increase in 
seas associated with the increased onshore flow. The front is 
expected to move east across the marine area Monday night. Showers 
and storms ending with the frontal passage and a moderate to strong 
offshore flow is expected in the wake of the front Tuesday through 
late week. Winds and seas primarily in the Exercise Caution category 
( 15 to 20 knots and up to 6 feet)through most of the week for the 
offshore Gulf waters, but possibly reaching Small Craft Advisory 
levels (20 knots plus) by weeks end as a reinforcing surge of 
offshore flow develops. 12/DS 




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