Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 240652
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
1252 AM CST Sat Feb 24 2018

...SEVERE WEATHER EXPECTED SATURDAY NIGHT INTO SUNDAY MORNING...

.UPDATE...
Updated for 06Z aviation discussion

&&

.AVIATION...
06Z TAF discussion:
IFR category stratus will be the main concern overnight through
early Saturday morning, and it seems mixing will be enough to
limit significant fog formation. Increased mixing will raise
ceilings and southerly winds mid/late Saturday morning, then
expect VFR category ceilings to prevail for the most part Saturday
afternoon. Surface wind gusts at GLH/GWO will exceed 30kt at
times. A few SHRA will be possible, but the TSRA potential will
largely hold off until Saturday night period as a line of storms
pushes across the area with a cold front. /EC/

&&

.DISCUSSION...

Current radar and satellite trends show weakening showers over the
far northwest area near Columbus and West Point. Other showers
were noted further south along I55. With strong moist WAA
continuing through the night, expect an isolated shower chance to
continue for a little while longer. However, did bump pops down a
bit to account for lack of much in the way of forcing. Some patchy
advection fog is a good bet near HBG and along the Hwy 84
corridor as winds weaken to calm at times.

After sunrise, our unseasonably muggy and warm airmass will start
to give way to an increasingly windy and at times stormy day. As
the boundary layer starts to recouple, expect winds to gradually
gust to 15-20kts by late in morning.

Storm chances increase by noon, with modest lifted indices and
plentiful moisture available, an isolated shower or storm could
develop.

TWP/SKH

Prior discussion below:

Tonight through Saturday night...

A large area of showers with embedded thunderstorms will continue to
move north through much of the area this afternoon and into this
evening. This activity is located within a positive moisture and
ThetaE advection axis/broad warm air advection. A few more scattered
showers and storms were also noted further south over portions of
Louisiana and these will also move north through the area but will
be more isolated in nature versus the more widespread ongoing
showers. Any lingering showers will dissipate/move out of the area
tonight with only an isolated shower or two through the overnight
hours. Any heavy rainfall or repetitive storms over portions of the
Delta could quickly lead to some flash flooding concerns through the
early evening hours due to recent heavy rainfall so will continue to
advertise the ongoing flooding threat in the HWO/graphics.

On Saturday the weather turns much more active with multiple hazards
that will impact the ArkLaMiss. A stout shortwave trough will be
ejecting out of the Desert Southwest and into the Central Plains by
Saturday morning. This will help send a strong cold front through
the area as the shortwave becomes negatively tilted and the surface
low quickly deepens as it moves towards the Midwest. A few warm
advection showers and possibly a thunderstorm will be possible
Saturday afternoon across the area, but overall coverage is not
expected to be as great as today. The first hazard that will impact
the area will be gusty gradient winds during the afternoon into
early evening hours on Saturday. Strong surface pressure falls and
efficient boundary layer mixing as temps rise into the low to mid
80s will be favorable for mixing down of higher momentum air as the
wind fields strengthen. This will result in gusty winds, especially
across the Delta, so went ahead and issued a wind advisory for this
area where winds could gust as high as 40-45mph. Elsewhere, expect
gusty winds up to 35mph mainly along and north of the I-20 corridor.
This threat has also been highlighted in the HWO/graphics with an
elevated area for the Delta and limited elsewhere.

Attention then turns to the severe weather potential Saturday night
into Sunday morning. Latest hi-res CAM guidance is still in
agreement on a quickly moving and strongly forced line of
thunderstorms moving through the ArkLaMiss. While SBCAPE values will
generally be below 1000 J/kg, plenty of deep layer shear (50-60kts)
and strong wind fields will be more than enough to support severe
thunderstorms. The highest severe threat will be over the far
northwest portion of the CWA where the greatest juxtaposition of
instability and shear will occur. 0-1km shear and helicity of 30 kts
and 300 m2/s2 respectively will be supportive of embedded supercell
structures and increased tornado potential over this area so will
continue to advertise an "enhanced risk" in collaboration with SPC.
Storms will continue to quickly grow upscale into a fast moving line
and the severe threat will quickly shift to damaging winds with the
potential for a few embedded tornadoes. Any northeast moving line
segments that can become aligned with the 0-3km shear vectors would
be prime candidates for mesovortex generation and increased tornado
potential. This threat area will be highlighted with a "slight risk"
along and northwest of the Natchez Trace corridor. Further south and
east, the line of storms begins to become further removed form the
better upper level support and height falls and progression begins
to slow down. There will still be enough shear and instability to
support a few damaging wind gusts and perhaps an isolated tornado so
will also continue to highlight this area with a "marginal risk".
The progressive nature of the line will preclude a greater flash
flood risk, however isolated flooding issues will be possible across
the Delta due to already saturated soils and high rainfall rates
with the storms. While some timing differences remain (NAM is the
slowest, GFS fastest), there`s decent agreement that the line should
be over the far southeastern portion of the area by daybreak Sunday
morning. /TW/

Sunday through Thursday...

By early Sunday the front will be making its way through the
ArkLaMiss region. Most of the active stormy weather will be exiting
the region but the front is expected to lag behind and stall across
portions of the central to southern sections of the forecast area. A
surface low will develop along this front and move northeast into
the region on Sunday afternoon. This will once again bring more rain
and some storms to the region. Given recent rainfall, this could
exacerbate any flooding issues as soils remain saturated from rain
today and the QLCS expected to move through Saturday night. This
disturbance should finally push the front through the region by
early Monday, exiting the rain as well.

A brief lull in rain activity will occur for Monday across much of
the area behind this front, however, this won`t last long as
southerly flow will return to the region by Tuesday. By Tuesday
afternoon, showers will increase from the west as the warm front
moves north. Our next weather system looks to move through mid to
late week and looks to bring another round of severe weather to the
region.  A surface low will develop across the OK/TX Panhandles
through Wednesday. While much of the southern sections of the
forecast area may remain dry on Wednesday, as heights rise over the
area, this surface low will deepen as it tracks northeast into
northern Missouri. The upper trough associated with this powerful
storm system will also take on a negative tilt by Wednesday
afternoon across the south central Plains. All of this will make for
another round of potential severe weather late Wednesday into early
Thursday. Plenty of shear will be in place, lapse rates will be
ranging from 6 to near 7C/km and instability will be in place. This
will be something to monitor in later forecasts. SPC has already
highlighted some of our Delta region for this potential, but given
the incoming weather in the short term, will hold off on any mention
of this in graphics or HWO but definitely worth noting. /28/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       84  56  64  50 /  34  94  80  76
Meridian      82  61  65  53 /  34  94  83  78
Vicksburg     84  55  64  48 /  34  80  76  64
Hattiesburg   83  65  70  57 /  37  73  81  77
Natchez       83  58  64  50 /  34  95  85  77
Greenville    79  53  62  46 /  34  95  28  26
Greenwood     81  53  64  46 /  34  87  32  43

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Wind Advisory from noon today to midnight CST tonight for MSZ018-
     019-025-034-035-040-041.

LA...Wind Advisory from noon today to midnight CST tonight for
     LAZ007>009-015-016-023.

AR...Wind Advisory from noon today to midnight CST tonight for ARZ074-
     075.


&&


$$



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