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Area forecast discussion...corrected text... 
National Weather Service Mobile Alabama 
510 am CST Wednesday Mar 10 2010 


Short term...(today and tonight) a very impressive 170+ knots 250 mb 
jet continues to to maintain its position across northern Mexico 
eastward to the northern Gulf Coast. The best divergence has been 
located to the north of the forecast area across central Alabama 
where the heaviest convection has been overnight. However...numerous 
showers and thunderstorms have occurred across our area this 
morning...mainly in far eastern and northwestern portions of the 
County Warning Area. A warm front has also developed across the Gulf Coast and is 
currently located from just north of Meridian to just south of 
Evergreen and Andalusia. To the south of the boundary temperatures have 
climbed into the low to middle 60s and dewpoints are in the lower 60s. 


Chances for showers and thunderstorms through the daylight hours 
will be driven primarily by continued warm air advection and upper 
level divergence...which may become even stronger over our area 
today the axis of the jet shifts slightly back to the south. The 
airmass is also expected to become increasingly unstable as the warm 
sector becomes more firmly entrenched and high temperatures climb to around 
70 degrees. Therefore... expected showers and thunderstorms to 
continue developing through the course of the day. 


The strong shortwave over New Mexico will pivot northeast into 
Kansas overnight. While the best deep layer forcing will be located 
to the northwest of our forecast area...a trailing vorticity maximum 
will be all that it takes to spark a further increase in convection 
when combined with the continued impressive upper jet dynamics. Much 
of the night will be stormy...but conditions will begin to improve 
slowly from west to east toward daybreak. 


Heavy rain threat: we have already seen about 1-1.5 inches across 
portions of the Florida Panhandle as well as north of Highway 84. It 
is hard to pinpoint the heaviest precipitation for today with the lack of a 
low level focus...but with precipitable waters climbing to 1.5 
inches...any stronger convection will be capable of producing a 
quick 1-2 inches in an hours time. As the best overall forcing moves 
in tonight...a more widespread 2-3 inches of precipitation is expected. 
Overall...we are anticipating storm totals of 2-5 inches but 
acknowledge there could be locally higher totals depending on where 
the training of stronger cells occur. A Flash Flood Watch continues 
for the area tonight. 


Severe weather threat: deep layer shear increases to 40-50 knots this 
afternoon...coinciding with an expected increase in MLCAPE 
(generally between 500-1000 j/kg). Therefore...isolated strong to 
severe storms will become possible by this afternoon. Large hail may 
be one of the bigger threats through the afternoon with 700-500 mb 
lapse rates over 7 c/km. As the shortwave energy and height falls 
approach tonight...the low level jet is prognosticated to increase to 
around 45 knots while surface winds stay backed out of the southeast. This 
translates to a marked increase in 0-1 km srh (200-300 m2/s2) and 
that will set the stage for a damaging wind/tornado threat. Biggest 
concern overnight is surface based instability and the effects of the 
rain from earlier in the day. Instability may become limited 
overnight...reducing the threat of surface based severe/tornado potential. 
However...large hail will still be a concern given cold middle level 
temperatures. 34/jfb 


&& 


Long term...by 12z Thursday vigorous middle level short wave begins to move 
off to the northeast with morning showers lingering mostly over 
eastern sections of the County warning forecast area. To the northwest main upper low centered over 
the north Central Plains states will begin to shift southeastward 
then track east across the middle MS and Tennessee River valleys Friday 
night through early Sun morning. As this system shifts southeastward 
on Friday better lift or forcing in the middle levels is noted over the southeast 
Continental U.S. And adjacent Gulf waters leading to another round of scattered 
showers and thunderstorms mostly over eastern sections of the County warning forecast area 
stretching southward over the adjacent Gulf waters generally east of 
pns or Navarre Beach. With 500 mb temperatures around -20 c and wetbulb values 
around 7500 feet believe we could see a few strong cells to the east 
possibly producing medium to large hail mostly during the daylight 
hours. Showers and thunderstorms will eventually move off to the 
east late Friday night into Sat with still an ample amount of residual 
moisture rounding the southern tip of main upper low. This pattern 
will likely give way to more clouds than sun over the first half of 
the weekend...eroding from west to east late Sat night through sun. 
As for temperatures will stay close to the current mex guidance making minor 
tweaks to high temperatures mainly near the immediate coast. 


For Monday through midweek...weak ridging in the middle to upper levels 
is noted over the lower MS River Valley shifting eastward and 
weakening over the central Gulf states Monday night into Tuesday in 
response to another cutoff low tracking east northeast over Lower Texas 
Monday night and early Tuesday. Both the GFS and European model (ecmwf) depict this upper 
vortex shifting eastward through midweek with the GFS depicting a 
more southern track then the Euro. Believe the GFS solution will 
likely come in line with the Euro by early next week resulting in 
another round of showers and thunderstorms Tuesday into Wednesday. As for 
temperatures will continue to stay close to the current 00z mex guidance 
only making minor tweaks to the highs along immediate coast. 32/ee 


&& 


Aviation...12z taf cycle. 
Advection of warm moist air into the region has resulted in 
widespread IFR ceilings early this morning. These ceilings expected to 
persist through the first half of the morning...but will likely rise 
to MVFR levels (1-2 kft) as daytime mixing and heating commence. 
Periods of showers and thunderstorms expected today as instability 
increases with thunderstorms persisting through the night. Some of 
the storms may become strong to severe and heavy rain will likely 
reduce visibilities to a mile or less at times. Winds become breezy out of 
the southeast today...becoming southerly overnight with gusts of 20 
knots expected. 34/jfb 


&& 


Marine...south to southeast winds will gradually increase across 
the marine area today is response to a tightening pressure gradient 
as a low pressure system deepens over the Southern Plains. A Small 
Craft Advisory will go into effect for the offshore waters late this 
afternoon and expire middle Thursday morning. Mobile Bay has also been 
included in the Small Craft Advisory tonight. Seas are likely to 
build to 5 to 8 feet offshore in response to southerly winds of 20-25 
knots. Showers and thunderstorms will increase in coverage later today 
and especially tonight. Winds and seas will be locally higher near 
thunderstorms...and we will have to monitor for the potential of 
special marine warnings. Fog is another concern as warm moist air is 
being ushered into the area via the southerly winds. Visibility 
sensors in northern Mobile Bay already showing 1-3 sm visibility. 
Visible could go lower than 1 mile at times through Thursday morning... 
especially near shore and in area bays where water temperatures are the 
coldest. Winds and seas subside by midday Thursday but will increase 
again on Friday in the wake of a frontal passage. Strong west-northwest wind 
expected through the first half of the weekend before diminishing on 
Sunday. 34/jfb 


&& 


Fire weather...periods of rain with embedded thunderstorms and 
high humidities will keep conditions well above critical thresholds 
through Thursday...with drier conditions Friday through early next week. At 
this time I don't see afternoon humidities below critical thresholds 
through early next. As main upper low to the north begins to move 
off to the NE by early Sat a moderate to strong westerly flow aloft 
will develop in its wake most likely mixing down to the surface during 
daylight hours both Sat and sun...resulting in higher than normal 
transport winds over the weekend. 32/ee 


&& 


Preliminary point temps/pops... 
Mobile 71 62 77 52 / 80 100 30 20 
Pensacola 71 63 74 56 / 70 100 50 30 
Destin 68 64 71 58 / 60 100 60 30 
Evergreen 72 61 77 49 / 80 100 40 20 
Waynesboro 71 60 76 45 / 90 100 20 20 
Camden 71 60 78 47 / 90 100 40 20 
Crestview 72 62 77 48 / 70 100 50 30 


&& 


Mob watches/warnings/advisories... 
Alabama...Flash Flood Watch from 6 PM Wednesday to noon Thursday for the 
following zones: Butler...Choctaw...Clarke...Conecuh... 
Covington...Crenshaw...Escambia...lower Baldwin...lower 
Mobile...Monroe...upper Baldwin...upper Mobile... 
Washington...and Wilcox. 


Florida...Flash Flood Watch from 6 PM Wednesday to noon Thursday for the 
following zones: coastal Escambia...coastal Okaloosa... 
coastal Santa Rosa...inland Escambia...inland Okaloosa... 
and inland Santa Rosa. 


MS...Flash Flood Watch from 6 PM Wednesday to noon Thursday for the 
following zones: George...Greene...Perry...stone...and 
Wayne. 


GM...Small Craft Advisory from 6 PM Wednesday to 6 am Thursday for 
the following zones: and Mobile Bay. 


Small Craft Advisory from 3 PM Wednesday to 9 am Thursday for 
the following zones: coastal waters from Destin to 
Pensacola Florida out 20 nm...coastal waters from Pensacola Florida 
to Pascagoula MS out 20 nm...waters from Destin to 
Pensacola Florida from 20 to 60 nm...and waters from Pensacola 
Florida to Pascagoula MS from 20 to 60 nm. 


&& 


$$ 

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