Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 300250 AAB

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
950 PM CDT Wed Mar 29 2017

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


.UPDATE...Have updated to add slight chance to chance pops mainly
to southeast Mississippi late tonight. A convective complex
currently advancing across southwest and central Louisiana is
expected to weaken overnight, but isolated to scattered showers
and storms will reach the far western portion of the area by late
tonight.  No other major changes at this time. /29


.PREV DISCUSSION... /issued 603 PM CDT Wed Mar 29 2017/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...VFR conditions prevail early this evening followed
by IFR/MVFR conditions (ceilings/fog) developing later this
evening into the overnight hours. The fog dissipates early
Thursday morning along with ceilings improving to MVFR/VFR. A line
of showers and storms will approach the area from the west
overnight, then moves into southeast Mississippi late Thursday
morning. The showers and storms continue eastward across much of
the remainder of the area through the late afternoon hours. Expect
IFR/MVFR conditions in the showers and storms along with the
potential for strong/severe storm development. /29

PREV DISCUSSION... /issued 240 PM CDT Wed Mar 29 2017/

NEAR TERM /Now Through Thursday/...Strong to severe thunderstorms
are still forecast for Thursday as a strong storm system approaches
the region from the west. A large upper level trough with embedded
closed low pressure area over north central Oklahoma will advance
eastward over the central and southern Great Plains tonight and
approach the Mississippi River on Thursday. A surface low pressure
area over the eastern portions of Kansas and Oklahoma this evening
will lift northeast, reaching Illinois by late Thursday afternoon,
with an associated frontal boundary advancing just east of the
Mississippi River.

A deep southerly wind flow ahead of the system will advect moisture
northward across the region, with precipitable water values climbing
to between 1.4 to 1.6 inches on Thursday. The severe weather
parameters in the GFS and NAM models continue to be higher when
compared to the ECMWF, with MLCAPE values between 900 to 1400 J/KG
Thursday afternoon compared to 300 to 600 J/KG from the ECMWF. SFC-
1km storm relative helicity values from all models range from 70 to
140 m2/s2. A 35 to 45 knot low level jet is also expected to
accompany this system, along with bulk shear values around 35 knots.
Upper level lapse rates are still expected to be in 7 to 7.5 C/KM
range. The pre-storm environment still favors the development of
strong to severe thunderstorms Thursday afternoon. Damaging winds,
large hail, and isolated tornadoes are all possible with this system.

Low temperatures tonight will range from 58 to 65 degrees. High
temperatures Thursday will range from 78 to 83 degrees inland areas,
and from 73 to 77 degrees along the coastal sections. /22

SHORT TERM /Thursday night Through Saturday night/...The cold
front and associated line of storms is expected to move east of
the area by early Friday morning. Strong to severe thunderstorms
will remain possible along the line and with any storms ahead of
the line. The severe threat will end Friday morning as the cold
front moves east of the area. A drier airmass moves into the area
on Friday as shortwave ridging builds over the area. Upper ridging
continues to build over the area on Saturday with temps warming
into the low and mid 80s. Moisture levels increase Saturday night
ahead of another developing system. However, no precip is expected
through Saturday night. /13

LONG TERM /Sunday Through Wednesday/...A very active pattern will
continue through the extended range. Moisture levels increase
rapidly on Sunday into Sunday night as a strong southern stream
shortwave digs across southern plains. This system is forecast to
take on a negative tilt across the lower Mississippi River Valley
Sunday night. Meanwhile, a surface low tracks from the Arklatex
to western Tennessee with a trailing cold front moving across the
area Sunday night into Monday. Parameters look favorable for all
modes of severe thunderstorms during this period along with very
heavy rainfall. All interests across the area should continue to
monitor future developments. A dry period follows through Tuesday,
before yet another system brings showers and thunderstorms back
into the area on Wednesday. /13

MARINE...A light to moderate southerly wind flow will continue to
increase through Thursday ahead of a deep area of low pressure and
surface cold front advancing east to the Mississippi River. South
winds at 15 to 20 knots can be expected by midday Thursday through
Thursday evening then shifting west to northwest late Thursday
evening through the overnight hours and diminish to 10 to 15 knots.
Expect scattered to numerous showers and thunderstorms to approach
from the west Thursday afternoon and move east of the marine area by
early Friday morning. A few strong to severe thunderstorms will be
possible with this pattern. Small craft should exercise caution
Thursday afternoon and evening. Southerly winds redevelop over the
weekend building by early next week as another upper system
approaches from the west. /22




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