Area Forecast Discussion
Issued by NWS Mobile, AL

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FXUS64 KMOB 190306 AAA

Area Forecast Discussion...UPDATED
National Weather Service Mobile AL
1006 PM CDT Sun Mar 18 2018

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


.UPDATE...The showers and thunderstorms that impacted a good
portion of our region earlier this afternoon and evening have
moved east and diminished, but radar imagery has recently shown
additional development of isolated to locally scattered light rain
showers over parts of southeast MS and southwest AL within the
past hour. We will keep a low chance (around 30 percent) of rain
showers and maybe a rumble of thunder in the forecast through 06Z
or 1 AM CDT.

The forecast for the overnight and early Monday morning hours
remains a challenge given the variability in high resolution and
deterministic model guidance, not to mention inconsistency with
the past few runs of the HRRR. However, we are still monitoring
for potential development of severe weather across portions of our
area overnight into early Monday morning. Clusters of severe
storms that impacted east and southeast TX earlier this evening
are now developing eastward into LA as of 945 PM CDT. SPC
mesoscale analysis continues to show an axis of instability, with
MLCAPE values of 500 to a little over 1000 J/KG stretching across
southeast MS into portions of southwest AL as of 9 PM. There is
potential for upstream convection to continue developing east-
southeast along the instability axis into southeast MS and
portions of southwest AL and possibly as far east as the
northwest FL panhandle overnight into the early morning hours
Monday. Another possible scenario is for convection to develop
southeastward through LA before pushing southeastward into our
Gulf of Mexico zones early Monday morning, leaving the better
severe potential farther west and south. Given the favorable
environment, we think the SPC Day 1 outlook keeping the Slight
Risk oriented generally along and southwest of a Waynesboro, MS to
Milton FL line remains reasonable as this general portion of the
area will be aligned along the axis of better instability through
early Monday morning. We will continue to monitor trends closely
overnight. We have opted to increase POPs overnight given current
radar trends and potential convective development late.

Patchy to areas of fog are still likely to develop overnight,
locally becoming dense. /21


.PREV DISCUSSION... /issued 649 PM CDT Sun Mar 18 2018/

DISCUSSION...Updated for latest aviation discussion below.

00Z issuance...Ceilings and visbys will lower overnight with
patchy dense fog expected to develop. IFR to LIFR conditions
expected overnight with brief periods of VLIFR possible.
Conditions improve by late Monday morning. /13

PREV DISCUSSION... /issued 357 PM CDT Sun Mar 18 2018/

NEAR TERM /Now Through Monday/...Two primary thunderstorm
complexes are ongoing across the region this afternoon. The
first is currently pushing out of our forecast area to the
northeast. Only observing a limited amount of lightning activity
in this complex, so heavy downpours are the primary threat. The
few embedded thunderstorms that have developed could produce small
hail and gusty winds as well, though that threat is low at this
time. The second complex is currently moving across coastal
southeast Mississippi and is expected to surge southeast towards
coastal Mobile and Baldwin counties before ultimately pushing
offshore. Have observed periods of broad rotation with some of the
storms in this complex, indicating a bit more organization.
Latest SPC mesoanalysis indicates roughly 500-1000 J/kg MLCAPE has
developed near the coast ahead of this complex, and 40-50 knots
of effective bulk shear overspreading the area. Thus, these storms
could remain organized enough to produce gusty winds and small
hail along the southwest Alabama and extreme western Florida
panhandle coasts later this afternoon and evening.

Expecting a brief lull in activity tonight before the next wave
moves in from the west early Monday morning in the form of
scattered showers and thunderstorms. With impressive 700-500 mb
lapse rates near 8.0 C/km overspreading the region, will see a
marginal severe threat for hail and straight-line winds linger as
storms could tap into the available elevated instability (MUCAPE
around 1000-1500 J/kg). Still quite a bit of uncertainty between
CAMs regarding convective initiation and coverage across our area
Monday afternoon and evening. Being so far separated from the
upper shortwave (and best forcing) to our north, it will be
difficult for storms to overcome the capping inversion. However,
if storms are able to initiate, instability and shear will be
sufficient enough to support organized convection capable of
producing hail and strong winds. Please refer to the Storm
Prediction Center ( or our homepage
( for the latest information regarding severe
weather potential. /49

SHORT TERM /Monday night Through Wednesday night/...An area of
low pressure will move eastward just south of the Ohio River
Valley Monday night into Tuesday. A cold front associated with
the low will approach the region from the west Monday evening,
and pass through the forecast area late Monday night through mid
afternoon Tuesday. Meanwhile, an upper level shortwave approaching
the region from the northwest Monday night will pass over the
region on Tuesday. Isolated to scattered showers and thunderstorms
will taper off from west to east Monday night as drier air pushes
in from the west. Patchy fog should linger along the coastal
sections through late Monday night. A few wrap-around showers may
also linger through Tuesday across our northern zones, followed
by the beginning of a dry period through the remainder of the
short term as high pressure build over the region. Temperatures
behind the cold front will lower into the 40s Tuesday night, and
the upper 30s to mid 40s Wednesday night. /22

LONG TERM /Thursday Through Sunday/...A large upper level trough
over the eastern conus will move east over the western Atlantic,
followed by weak upper ridging building in from the west late in
the week. Surface high pressure will also dominate the eastern
conus through Friday morning, followed by a southerly return flow
setting up on the backside late in the week. The dry period will
continue through Friday night, with isolated showers returning
over the weekend across our inland areas. Temperatures will
moderate through the period. /22

MARINE...Light to moderate onshore flow continues through Monday
afternoon before winds shift to westerly ahead of an approaching
cold front. Showers and thunderstorms remain possible during this
time and areas of dense fog will continue over near shore waters and
area bays and sounds. The front passes through Tuesday morning, with
strong northwest flow and building seas expected in its wake. A
Small Craft Advisory will likely be required Tuesday and Wednesday
as a result. Weakening offshore flow and subsiding seas then
continue through the remainder of the week. /49


AL...High Rip Current Risk from 7 AM CDT Monday through Wednesday
     morning for ALZ265-266.

FL...High Rip Current Risk from 7 AM CDT Monday through Wednesday
     morning for FLZ202-204-206.

GM...Dense Fog Advisory until 1 PM CDT Monday for GMZ630>632-650.



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