Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 221758 AAC
AFDMOB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1258 PM CDT Mon May 22 2017

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

&&

.AVIATION...
18Z issuance...Generally VFR conditions this afternoon with VCSH.
Ceilings and visibilities will lowers through tonight as showers
and thunderstorms increase from the west and move across the area.
/13

&&

.PREV DISCUSSION... /issued 1142 AM CDT Mon May 22 2017/

DISCUSSION...See updated information for land areas below.

UPDATE...Mesoscale models continue to keep much of the area dry
through mid-afternoon. The best chances of rain remain to west of
the area awaiting low pressure to develop and slide east this
evening and overnight. As a result, rain chances were lowered
slightly across the area for the remainder of the day. However,
maintained likely pops across the western parts of the area as the
combination of daytime heating and plenty of deep layer moisture
along with the stalled front will lead to the development of
showers and thunderstorms.

PREV DISCUSSION... /issued 623 AM CDT Mon May 22 2017/

DISCUSSION...See updated information for land areas and aviation
discussion below.

UPDATE...High risk of rip currents has been extended through
Wednesday. Will see a drop to a moderate today, but with strong
onshore flow returning tonight, a return to a high risk is
expected. Also, the end of the FFA was adjusted to better fit the
day/night cutoff

16/22

AVIATION...
12Z issuance...AS an upper system moves over the area today, it
interacts with a stalled surface boundary to being a drop in CIGS
to low end MVFR/IFR levels. Local drops to LIFR are possible,
especially along and north of the I65 corridor.

/16

PREV DISCUSSION... /issued 507 AM CDT Mon May 22 2017/

NEAR TERM /Now Through Monday night/...For the first two periods of
the current package, biggest item to deal with is how much rain.
Looking at the current surface analysis, a weak surface front has
moved just southeast of I65. Today, shortwave energy currently over
the Sabine River swings east over the Lower the Mississippi River
and the Southeast today into tonight. As it does, guidance is
consistent in isentropic upglide setting up along and north of the
surface boundary, binging widespread rain to the area, along with
training cells. Timing on when this begins to set-up over the
forecast area is pretty consistent in the guidance, with Mississippi
and western Alabama portions of the forecast area seeing the upglide
by noontime, then spreads east covering the entire forecast area by
00z this evening. Looking at the model soundings, enough instability
for strong storms with heavy rains is present. With some areas
seeing training cells later today through tonight, flash flooding is
a very good possibility, so have left the flash flood watch
currently in effect as is. Along and south of the surface boundary,
enough instability is present for strong to severe tsra to develop.
Where depends upon where the heavy rain sets up a pool of rain
cooled air. at this point, am leaning towards a south of I65
placement for any strong to severe storms. Looking a mode, with 0-
3km helicities rising to around 200 m^2/s^2 along and south of the
bounday, spinners are possible. WetBulb 0 heights are around 13k` or
higher, so large hail is unlikely anywhere. Summarizing north to
south over the forecast area, heavy rain is likely over the entire
land portion of the forecast area, with strong to damaging winds,
with a non-zero possibility of a tor south of I65 this afternoon
into tonight.

Last item to deal with is temps. With areas seeing more daytime
heating today the farther east one moves from the Al/Ms state line,
a gradient sets up for highs today. Highs are expected to range from
the mid 80s over southeast of I65 to upper 70s along the Al/MS state
line. /16

SHORT TERM /Tuesday Through Wednesday night/...A closed upper low
pressure area over Minnesota Tuesday morning will migrate south
along the Mississippi River, reaching northern Mississippi by
midnight Wednesday night. As a result, the broad upper trough
over the eastern two-thirds of the nation will become more
amplified and dig further south to the southern Gulf of Mexico
through the short term. A weak surface trough or low pressure
area just north of the coast across the forecast area Tuesday
morning will dissipate while a stronger separate low pressure area
forms across the Ohio River valley region. An associated cold
front with this low will approach from the west Tuesday evening,
and move across the forecast late Tuesday night into Wednesday
morning. Ongoing numerous to widespread showers and thunderstorms
on Tuesday, with locally heavy rain possible, will gradually
taper off from west to east through midweek. Flash and areal
flooding from heavy rainfall will be the main threat through the
short term, with additional widespread rainfall amounts ranging
from 0.6 to 1.6 inches west of I-65, and from 1.6 to 2.5 inches
east of I-65, with locally higher amounts. A Flash Flood Watch
remains in effect through Tuesday night. In addition, some storms
will produce gusty surface winds along with frequent lightning,
however widespread severe weather is not anticipated.

High temperatures Tuesday will range from 78 to 82 degrees. Low
temperatures Tuesday night will range from 63 to 67 degrees along
and northwest of I-65, and from 67 to 72 degrees to the
southeast. High temperatures Wednesday will range from 75 to 80
degrees. Low temperatures Wednesday night will range from 54 to
59 degrees inland areas, with lower 60s along the coast. /22

LONG TERM /Thursday Through Sunday/...The upper trough over the
eastern conus and northeastern Gulf of Mexico will move east of
the region through the remainder of the week, followed by a west-
northwest wind flow aloft. A broad upper level trough over the
central and northern plains will swing east to the Mississippi
River over the weekend. Meanwhile, a developing surface low across
the southern plains Saturday morning will lift northeast to the
Great Lakes region over the weekend. An associated cold front will
approach the region from the northwest on Sunday, and is forecast
to stall as it moves into the forecast area Sunday night. A dry
period will persist across the region Thursday and Friday,
followed by isolated to scattered showers and thunderstorms over
the weekend, mainly on Sunday, as the front approaches. High
temperatures Thursday in the upper 70s and lower 80s will warm
back into the mid and upper 80s over the weekend. /22

MARINE...A light onshore flow will become more organized today into
tonight as a series of impulses pass today into tonight. Am
expecting winds south of the coast to rise into SCY levels, with
this portion being south of a stationary boundary along I65. The
winds should remain a moderate to strong onshore over unprotected
waters into Tuesday night, then become offshore by the end of the
day Wednesday as a front crosses area waters. The offshore flow will
then weaken through the rest of the work week as surface high
pressure moves towards, then starts over the forecast area. /16

&&

.MOB WATCHES/WARNINGS/ADVISORIES...
AL...Flash Flood Watch through late Tuesday night for ALZ051>060-
     261>266.

     High Rip Current Risk through Wednesday evening for ALZ265-266.

FL...Flash Flood Watch through late Tuesday night for FLZ201>206.

     High Rip Current Risk through Wednesday evening for FLZ202-204-
     206.

MS...Flash Flood Watch through late Tuesday night for MSZ067-075-076-
     078-079.

GM...Small Craft Advisory from 1 AM Tuesday to 7 PM CDT Wednesday for
     GMZ650-655-670-675.

&&

$$

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