Special Weather Statement, NWS Jackson, MS

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1016 AM CDT Sat May 20 2017

.UPDATE...
Updated for morning discussion.

&&

.DISCUSSION...
The morning JAN sounding showed a moist layer below 700mb making
up most of the 1.45in PWAT across the CWA. Despite low stratus
this morning, our moist airmass was destabilizing with daytime
heating and a rash of showers were already noted on local radars
breaking out across our southeast zones into central Mississippi.
Several other showers were noted over our southwest and edging
into our northwest zones along a weak outflow boundary. This
activity is expected to increase through the afternoon with
numerous storms expected today across our whole CWA. A few of
these storms may become severe producing damaging wind gusts and
hail. The slower movement of the storms and PWATs increasing to
near an inch and three quarters this afternoon will support
locally heavy rainfall as well. /22/

Prior discussion below:

Today and Tonight: An active weather pattern will take shape this
weekend over the ArkLaMiss as a powerful trough over the
Plains/Midwest shifts eastward and helps to break down the ridge
currently centered over the Southeast. As heights fall, the
airmass will destabilize over the forecast area today and combined
with heating and fairly rich boundary layer moisture will result
in mixed layer CAPE values in excess of 2500 J/kg by this
afternoon.

As is often the case with weaker synoptic forcing events in late
Spring, convective evolution will be the biggest challenge with this
forecast. Initial thunderstorm development should begin by late
morning, especially east of the MS River, and be scattered and
disorganized due to relatively weak deep layer shear and low level
flow ~ 20 kts, but this initial activity could be enhanced by the
outflow emanating from the overnight convection in the ArkLaTex
region per recent HRRR and other CAM guidance.

Then things become more uncertain with the trough axis and cold
front approaching tonight. Will stick with the idea that the most
the larger scale lift may help to organize storms resulting in
greater storm coverage during the evening similar to most members of
the NCAR ensemble, but a good bit of guidance suggests a lull in the
convective activity overnight until the cold front can interact with
better instability/moisture early Sunday.  It still looks like a few
intense storms could reach severe limits later this afternoon into
the evening given the degree of instability. In addition, with
precipitable water values getting above 1.7 inches in the humid
airmass combined with with dewpoints in the lower 70s, locally heavy
rainfall continues to be a concern. Will continue to highlight the
severe weather/heavy rain potential in the HWO/graphics. /EC/

Sunday through Friday: The upper-level system which is bringing
today and tonight's weather will continue to spin over the Great
Lakes on Sunday, while at the surface a weak cold front extending
southward through the Mississippi River Valley will push through
the ArkLaMiss region. Depending on how fast today/tonight's round
of weather clears the area, there may another window of time for
strong to marginally severe thunderstorms to develop across
southeastern portions of our area during the day Sunday. MLCAPE
values upwards of 1500 to 2000 J/kg could be available to storms
ahead of the cold front if sufficient heating can occur, but deep
layer shear will on the weaker side (around 20 to 30 kts). Thus
more of a multicell convection situation again with greatest
potential hazards being damaging wind gusts, marginally severe
hail, and locally heavy rainfall. PWAT values nearing 1.75 to 2.0
inches and relatively slow storm motions parallel to the cold
front will warrant a continued Limited threat for flooding south
and east of the front on Sunday.

Confidence in the next potential round of showers and
thunderstorms has increased some. Short and medium range guidance
has come into better agreement for the frontal boundary to stall
out as it nears the Gulf Coast and the next upper-level shortwave
digs into the Southern Plains. This pattern should see a surface
wave develop along the front Monday, probably somewhere between
the eastern TX and central LA coastline. As the surface low
deepens and slides eastward along the old front, a saturated
airmass will be lifted back northward over the boundary, providing
a focus for heavy rainfall sometime between Monday night and
Tuesday night. The most favored area for heavy rain during this
time is currently expected to be south of Interstate 20 (possibly
south of US Highway 84 even). We will keep a Limited Threat for
flooding south of I-20 in the Hazardous Weather Outlook for
Tuesday until details come into better focus. A stronger cold
front should push through the region Tuesday night into Wednesday,
possibly another focus for showers or storms depending on how the
coastal system plays out. Rebounding temperatures expected for
the end of the week as shortwave ridging builds over the eastern
CONUS behind the departing upper low. /NF/

&&

.AVIATION...

12Z TAF discussion:
IFR/MVFR ceilings will be common over the ArkLaMiss through mid
morning before mixing helps to lift them to VFR category. The
primary hazard as we go into the afternoon will be numerous
SHRA/TSRA that could impact most sites and persist through much of
the evening as well.  Additional convective activity should develop
later tonight or Sunday ahead of an approaching cold front. /EC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       84  70  81  64 /  60  59  68  30
Meridian      83  70  80  64 /  68  67  76  44
Vicksburg     85  70  81  64 /  63  63  53  23
Hattiesburg   84  71  82  66 /  68  56  78  44
Natchez       85  70  81  65 /  65  59  65  27
Greenville    85  69  79  62 /  59  65  33  10
Greenwood     83  69  79  61 /  67  63  48  16

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.

&&

NF/22/EC

Hazardous Weather Outlook
National Weather Service Jackson MS
243 AM CDT Sat May 20 2017

ARZ074-075-LAZ007>009-015-016-023>026-MSZ018-019-025>057-059>065-
072-210745-
Ashley-Chicot-Morehouse-West Carroll-East Carroll-Richland-
Madison LA-Franklin LA-Catahoula-Tensas-Concordia-Bolivar-
Sunflower-Leflore-Grenada-Carroll-Montgomery-Webster-Clay-Lowndes-
Choctaw-Oktibbeha-Washington-Humphreys-Holmes-Attala-Winston-
Noxubee-Issaquena-Sharkey-Yazoo-Madison MS-Leake-Neshoba-Kemper-
Warren-Hinds-Rankin-Scott-Newton-Lauderdale-Claiborne-Copiah-
Simpson-Smith-Jasper-Jefferson-Adams-Franklin MS-Lincoln-Lawrence-
Jefferson Davis-Covington-Marion-
243 AM CDT Sat May 20 2017

This hazardous weather outlook is for portions of southeast
Arkansas, northeast Louisiana, central Mississippi, north central
Mississippi, and south central Mississippi.

.DAY ONE...Today and Tonight

SEVERE THUNDERSTORMS
THREAT...Slight
TIMING...Today through Tonight

FLOODING
THREAT...Limited
TIMING...Today through Tonight

Numerous thunderstorms are expected to develop over the ArkLaMiss
this afternoon and continue into the evening. It is possible that
storms may become more organized at some point in the afternoon
and evening resulting in a greater chance for severe storms and
heavy rain. The most intense storms could be severe and capable
of producing damaging wind gusts of 60 mph and quarter size hail.
In addition, locally heavy rainfall of one to two inches in a
short duration could cause some flooding of low-lying areas and
streets.

(www.weather.gov/images/jan/graphicast/image1.png)
(www.weather.gov/images/jan/graphicast/image2.png)

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Thunderstorms with heavy rain are expected to redevelop Sunday and
this will prolong the threat for localized flooding of low-lying
areas and roads.

(www.weather.gov/images/jan/graphicast/image2.png)

.SPOTTER CALL TO ACTION STATEMENT...
The activation of storm spotters, HAM radio operators, and
emergency management personnel in support of severe weather
operations may be needed for portions of the region today
through tonight.

MSZ058-066-073-074-210745-
Clarke-Jones-Lamar-Forrest-
243 AM CDT Sat May 20 2017

This hazardous weather outlook is for portions of east central
Mississippi, and southeast Mississippi.

.DAY ONE...Today and Tonight

SEVERE THUNDERSTORMS
THREAT...Marginal
TIMING...Today through Tonight

FLOODING
THREAT...Limited
TIMING...Today through Tonight

Scattered thunderstorms are expected to develop this afternoon
and continue into the evening. Isolated severe storms could be
capable of producing damaging wind gusts up to 60 mph and hail up
to quarter size. In addition, locally heavy rainfall of one to two
inches in a short duration could cause some flooding of low-
lying areas and streets.

(www.weather.gov/images/jan/graphicast/image1.png)
(www.weather.gov/images/jan/graphicast/image2.png)

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

Thunderstorms with heavy rain are expected to redevelop Sunday and
this will prolong the threat for localized flooding of low-lying
areas and roads.

(www.weather.gov/images/jan/graphicast/image2.png)

.SPOTTER CALL TO ACTION STATEMENT...
The activation of storm spotters, HAM radio operators, and
emergency management personnel in support of severe weather
operations may be needed for portions of the region today
through tonight.

21

&&

...HAZARD LEGEND...

*SEVERE THUNDERSTORMS*
High...Significant severe thunderstorms are expected.
Moderate...Severe storms expected with significant
 severe weather possible.
Enhanced...Severe storms expected.
Slight...Severe storms possible.
Marginal...Isolated severe storms possible.

*FLOODING*
Extreme...Confident in significant flooding.
Significant...Significant flooding possible.
Elevated...Confident in flooding.
Limited...Flooding possible.

...USEFUL WEATHER WEB PAGES (URLS)...

NWS JAN Home page...
   www.weather.gov/jan
Stay Aware, Stay Safe NWS JAN Briefing Page...
   www.weather.gov/jan/safe
Latest Weather Briefing...
   www.weather.gov/jan/weather_briefing

Find NWS JAN on Facebook...
   www.facebook.com/NWSJacksonMS
Follow NWS JAN on Twitter...
   @NWSJacksonMS
Follow NWS JAN on Youtube...
   www.youtube.com/user/NWSJacksonMiss

...ADDITIONAL URLS FOR SEVERE WEATHER ISSUES...

Storm Prediction Center (SPC)...
   www.spc.noaa.gov/
Meso Analysis...
   www.spc.noaa.gov/exper/mesoanalysis/Day 1 through 3 Outlooks...
   www.spc.noaa.gov/products/outlook/
Storm Reports...
   www.spc.noaa.gov/climo/online/
...ADDITIONAL URLS FOR FLOODING ISSUES...

Current Watches and Warnings...
   www.weather.gov/jan/safe_HeavyRain

Observed Precipitation Images...
   www.weather.gov/jan/precipmaps

River Forecast Center...
   www.weather.gov/lmrfc/
Significant River Flood Outlook...
   www.wpc.ncep.noaa.gov/nationalfloodoutlook/index.html
Day 1 through 3 Excessive Rainfall...
   www.wpc.ncep.noaa.gov/qpf/excess_rain.shtml
Excessive Rainfall Discussion...
   www.wpc.ncep.noaa.gov/discussions/qpferd.html
Day 1 through 7 QPF...
   www.wpc.ncep.noaa.gov/qpf/qpf2.shtml
QPF Discussion...
   www.wpc.ncep.noaa.gov/discussions/qpfpfd.html

Special Weather Statement
National Weather Service Jackson MS
1216 PM CDT SAT MAY 20 2017

MSZ029-030-201745-
Clay MS-Webster MS-
1216 PM CDT SAT MAY 20 2017

...A STRONG THUNDERSTORM WILL AFFECT NORTHEASTERN WEBSTER AND
NORTHWESTERN CLAY COUNTIES UNTIL 1245 PM CDT...

At 1215 PM CDT, Meteorologists were tracking a strong thunderstorm
over Cumberland, or 7 miles southwest of Montpelier, moving north at
20 mph.

Dime size hail and winds in excess of 40 mph will be possible with
this storm.

This strong thunderstorm will be near...
  Montpelier around 1235 PM CDT.

Other locations impacted by this storm include Mantee.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

High winds can bring down trees and large limbs resulting in serious
injury or property damage. Exercise extreme caution when outdoors
during such strong winds...and be especially aware of older trees.

&&

LAT...LON 3356 8897 3356 8905 3360 8918 3374 8915
      3374 8904 3375 8903 3376 8893 3381 8893
      3381 8881
TIME...MOT...LOC 1715Z 199DEG 19KT 3365 8906

JC

Special Weather Statement
National Weather Service Jackson MS
1249 PM CDT SAT MAY 20 2017

MSZ064-201815-
Jefferson Davis MS-
1249 PM CDT SAT MAY 20 2017

...A STRONG THUNDERSTORM WILL AFFECT NORTHWESTERN JEFFERSON DAVIS
COUNTY UNTIL 115 PM CDT...

At 1249 PM CDT, Meteorologists were tracking a strong thunderstorm
near Prentiss, or 15 miles south of Pinola, moving north at 20 mph.

Dime size hail and wind gusts up to 50 mph will be possible with this
storm.

This strong thunderstorm will be near...
  Clem around 105 PM CDT.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

High winds can bring down trees and large limbs resulting in serious
injury or property damage. Exercise extreme caution when outdoors
during such strong winds...and be especially aware of older trees.

&&

LAT...LON 3160 8997 3165 8998 3176 8996 3177 8976
      3176 8976 3158 8981
TIME...MOT...LOC 1749Z 199DEG 18KT 3166 8992

JC