fxus64 kmob 171208 aaa 

Area forecast discussion...updated 
National Weather Service Mobile Alabama 
608 am CST Thu Jan 17 2019 

Discussion...updated for latest aviation discussion below. 


12z issuance...generally VFR conditions with occasional MVFR 
through the afternoon in scattered showers. Ceilings lower to LIFR 
late tonight with patchy fog developing. /13 


Previous discussion... /issued 450 am CST Thu Jan 17 2019/ 

Near term /now through Thursday night/...a weak cold front will 
move slowly into the region today and stall just to our northwest 
tonight as a weakening shortwave moves across the Ohio Valley. 
Ahead of the front, clouds will increase through the day as 
moisture levels increase due to a light southerly flow. Scattered 
showers will increase from the northwest and slowly move southeast 
through tonight. Weak forcing and the lack of significant deep 
layer moisture will keep rainfall amounts light, generally less 
than a quarter of an inch in most areas. Increasing moisture will 
lead to the development of patchy fog late tonight. Highs today 
will range from the upper 50s to the north to low 60s across 
southern portions of the area. Lows tonight will generally be in 
the low to mid 50s. /13 

Short term /Friday through Saturday night/...a drier zonal mid 
level flow pattern will return to the forecast area on Friday, 
though some residual weak isentropic ascent may result in isolated 
light rain showers flowing from the northern Gulf toward the 
western Florida Panhandle and adjacent portions of south central 
and far southwest Alabama. We will maintain a slight chance of 
rain generally along and to the southeast of a Luverne to Dauphin 
Island line through Friday afternoon. Low level southerly flow 
will otherwise persist across the region as the surface ridge of 
high pressure shifts off the southeast U.S. Coast and the next 
area of low pressure deepens over the Southern Plains. Low level 
moisture will continue to increase across the area into Friday 
night, with surface dewpoints rising into the mid 50s to around 60 
degrees. The mid level flow pattern begins to turn more southwesterly 
on Friday night ahead of the trough axis that will be translating 
across the central and Southern Plains and toward the Mississippi 
Valley region. Deep layer moisture should be on the gradual 
increase underneath the southwest flow pattern aloft Friday night, 
and additional ascent ahead of this feature will support a low 
chance of rain showers across much of the forecast area, with the 
slightly better pops around 30% favored over southeast Mississippi 
and interior southwest Alabama. We may also have to monitor for 
patchy fog development across the region again late Friday night 
into early Saturday morning. Warmer temperatures are anticipated 
Friday, with highs in the mid 60s to around 70 degrees. Increased 
low level moisture will also bring above normal temperatures to 
the region for Friday night, with lows in the mid 50s to around 60 

The upper level trough is forecast to progress eastward from the 
vicinity of the Mississippi Valley Saturday morning to across the 
Tennessee Valley and north central Gulf Coast region Saturday 
night into early Sunday morning. A deep area of surface low 
pressure centered over Arkansas around 12z Saturday morning 
should lift eastward across the Tennessee Valley by early 
Saturday evening, before rapidly pushing toward the eastern 
Seaboard by early Sunday morning. An attendant cold front 
trailing south from this area of low pressure will sweep across 
our forecast area Saturday afternoon into early Saturday evening. 
Large scale ascent ahead of the approaching trough and cold front 
will support an organized quasi-linear convective complex that 
should enter our western zones sometime late Saturday morning or 
early Saturday afternoon, and translate across our region through 
early Saturday evening. We have pops increasing to 50-60% over 
western portions of our County Warning Area prior to noon Saturday, with 
categorical coverage around 80% over the entire region through 
Saturday afternoon. Pops should quickly decrease from west to east 
into early Saturday evening following the passage of the cold 
front. A high shear/Low Cape environment will be in place across 
our region Saturday, as is typical with a number of our qlcs type 
events. Surface dewpoints in the upper 50s to lower 60s may 
support MLCAPE values up to 500-700 j/kg across our region 
Saturday, and this available instability when combined with strong 
low level flow (850 mb winds 45-55 knots) may be supportive of a 
few embedded bowing segments within the convective line, capable 
of producing localized wind damage. A brief, weak tornado also 
cannot be entirely ruled out. The day 3 severe weather outlook now 
has our entire County Warning Area outlined in a marginal risk for Saturday, 
which looks reasonable. Increased winds and colder temperatures 
will return Saturday night following the frontal passage. /21 

Long term /Sunday through Wednesday/...a much drier northwest 
flow pattern aloft will return to the region on Sunday in the wake 
of the frontal passage. Continued breezy conditions are expected 
given the mslp gradient. Temperatures will be chilly on Sunday 
with highs only reaching the mid 40s to around 50 degrees. Winds 
should begin to diminish Sunday night, setting up favorable 
conditions for a light freeze with lows in the mid 20s to around 
30 degrees over much of the area away from the immediate coast. 
The surface ridge moves east Monday, allowing for a return 
southerly flow Monday night into Tuesday. The next area of deep 
moisture and large scale ascent ahead of another approaching 
trough will bring the next good chance of rain to our region 
Tuesday into Wednesday, though timing of this next system is still 
uncertain. /21 

Marine...a light to moderate southerly flow will increase Friday 
night into Saturday as a strong cold front approaches the area. The 
front will move through the marine area Saturday night with a strong 
northwest flow developing and continuing through Sunday. Gusts to 
gale force are possible Saturday night. Southerly flow returns early 
next week in advance of another approaching cold front. /13 


Mob watches/warnings/advisories... 

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