Special Weather Statement, NWS Jackson, MS

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1220 PM CDT Fri Aug 17 2018

.UPDATE...
Updated for 18Z aviation discussion

&&

.AVIATION...
18Z TAF discussion:
An active convective period will be in store for most TAF sites
through this evening. Abundant cloud cover this afternoon will
lead to periods of MVFR ceilings, especially where storms occur as
visibilities will be reduced and winds will be gusty. The
convection will wind down somewhat by late evening, but
possibilities will continue overnight and through the end of the
period./26/

&&

.DISCUSSION...
Latest CAM guidance showing convective area, over northwest AR at
the moment, will drop into northwest portions of the forecast
area during peak heating. Increased severe storms risk level to
slight as near 40 knots of 0-3km bulk shear will be driving this
convection southeast. This along with high microburst composite
parameter should make for increased damaging wind potential over
mostly northwest sections this afternoon into the evening.

Lowered dewpoints somewhat this afternoon which should result in
lower heat indices. The highest heat indices, around 105, will
occur mainly west of the MS river, but thunderstorms developing
during the afternoon will limit the duration of this heat./26/

Prior discussion below:

Today and tonight:

The southern fringe of a relatively strong upper level shortwave
will be moving into the region today and this feature is already
helping to generate numerous showers and thunderstorms just to our
northwest early this morning. Latest radar imagery reveals outflow
now progressing south toward the Arklamiss Delta and this
boundary should help trigger scattered shower and thunderstorm
activity this morning, at least along and north of the Highway 82
corridor. High resolution model guidance consensus is good that
showers and thunderstorms will gradually build south and southwest
during the midday through afternoon hours as outflow cascading
south juxtaposes with increasing synoptic lift (from the mentioned
incoming short wave) and moisture convergence and advection in
the lower portion of the troposphere. Convection should be most
numerous along and north of the I-20 corridor through early this
evening and in these areas briefly training storms are possible.
Considering the atmosphere fueling thunderstorms should have
surface-based CAPE values of 2000+ j/kg and precipitable water
values of 2+ inches, any training of storms could yield a quick
deluge of a few inches of rainfall. The ground is not really
saturated in too many locations, but lingering torrential
downpours can still cause some flooding issues with these in situ
conditions. For this reason we have introduced a LIMITED flood
risk in the graphics and HWO.

This flood risk (for mainly northern zones) will also continue
tonight as model consensus suggests moisture convergence and
advection into the backside of the upper trough over our region
should spur some additional convection in the wake of the
afternoon's activity. Instability should be tame enough late
tonight to preclude organized severe weather concerns, which of
course is good.

Unfortunately, better instability today, with CAPE likely peaking
from 3000 to 4000 j/kg in spots, should work in concert with
modest wind shear in the low to mid levels to temporarily organize
convective clusters (at least loosely). The main threat with any
organized clusters will be damaging wind gusts and we agree with
SPC that a MARGINAL risk of severe storms exists over central and
northern zones. The main risk will be damaging wind gusts.

Otherwise, high temperatures were boosted upward just a touch in
many lcoations today given the prospect of some morning sun in
central and southern zones. Still anticipating highs will remain
less than 95 in nearly all areas, but humidity will be through the
roof and thus yield pockets where heat index values could peak
close to 105 degrees. The HWO and graphics has been updated to
reflect this threat as well.

Saturday through next week...

The ArkLaMiss will experience a few active and wet mid August
days this weekend and into early next week before a rare August
cold front sweeps through the region by midweek next week.

By Saturday morning, a stalled surface front that will stretch
from New England down into the lower MS River Valley. This front
will continue to serve as a focus for convective initiation for
storms in our region through on Saturday and Sunday. The better
coverage of storms will remain north of the I-20 corridor, closer
to the boundary. Pwats will range from 2"-2.5" through the period
providing the storms ample moisture to tap into. Storms during
this period will be efficient rain producers and some training is
possible. A limited flood threat was added to the HWO along and
north of the I-20 corridor to account for the threat of flash
flooding through the day on Saturday. Although the pattern will
hold steady through the region on Sunday, there was not enough
confidence in the flash flooding threat to extend the limited
threat at this time. Although flash flooding will be the main
threat through the weekend, there will be enough instability and
shear around on Saturday and Sunday to support some severe storms
with the primary threat of gusty winds.

A deeper disturbance will begin to cross the Plains as we get into
early next week, eventually crossing the MS River Valley and into
the Great Lakes region. WPC has noted that surface low pressure
records for the upper Ohio Valley region in August could be in
jeopardy as the strong surface low associated with this
disturbance pushes east dragging a strong cold front with it. A
very moist airmass will still be in place over the ArkLaMiss as
the front approaches the region from the west late Monday into
Tuesday. Storms along and ahead of the front will also be
efficient rain producers with flash flooding becoming a threat
once again. A cooler, drier airmass will begin to filter into the
region behind the front, resulting in a dry end to the week.

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       91  71  88  73 /  41  78  72  52
Meridian      90  72  89  73 /  43  46  71  52
Vicksburg     95  73  90  74 /  35  72  72  52
Hattiesburg   90  72  91  73 /  41  17  70  28
Natchez       93  72  90  74 /  27  33  70  32
Greenville    91  72  88  73 /  81  43  74  64
Greenwood     88  72  87  73 /  81  55  74  65

&&

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

&&

Hazardous Weather Outlook
National Weather Service Jackson MS
307 PM CDT Fri Aug 17 2018

ARZ074-075-LAZ007>009-015-016-MSZ018-019-025-034>037-040>044-
047>050-182015-
Ashley-Chicot-Morehouse-West Carroll-East Carroll-Richland-
Madison LA-Bolivar-Sunflower-Leflore-Washington-Humphreys-Holmes-
Attala-Issaquena-Sharkey-Yazoo-Madison MS-Leake-Warren-Hinds-
Rankin-Scott-
307 PM CDT Fri Aug 17 2018

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

.DAY ONE...Tonight and Saturday

FLOODING
THREAT...Limited
TIMING...Tonight through Saturday

SEVERE THUNDERSTORMS
THREAT...Slight
TIMING...Tonight

Severe thunderstorms are possible for locations mainly north of
the Interstate Twenty corridor through this evening. The main
risk will be damaging wind gusts.

(https://www.weather.gov/images/jan/graphicast/1.png)

Flash flooding will be possible, again mainly for locations along
and north of the Interstate Twenty corridor. In these areas
isolated locations could receive 2 to 3 inches of rainfall in a
short amount of time, which could lead to flash flooding.

(https://www.weather.gov/images/jan/graphicast/2.png)

.DAYS TWO THROUGH SEVEN...Saturday night through Thursday

The probability for widespread hazardous weather is low.

.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 tonight.

MSZ026>033-038-039-045-046-051-052-182015-
Grenada-Carroll-Montgomery-Webster-Clay-Lowndes-Choctaw-Oktibbeha-
Winston-Noxubee-Neshoba-Kemper-Newton-Lauderdale-
307 PM CDT Fri Aug 17 2018

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

.DAY ONE...Tonight and Saturday

FLOODING
THREAT...Limited
TIMING...Tonight through Saturday

SEVERE THUNDERSTORMS
THREAT...Marginal
TIMING...Tonight

Isolated severe thunderstorms are possible for locations mainly
north of the Interstate Twenty corridor through this evening. The
main risk will be damaging wind gusts.

(https://www.weather.gov/images/jan/graphicast/1.png)

Flash flooding will be possible, again mainly for locations along
and north of the Interstate Twenty corridor. In these areas
isolated locations could receive 2 to 3 inches of rainfall in a
short amount of time, which could lead to flash flooding.

(https://www.weather.gov/images/jan/graphicast/2.png)

.DAYS TWO THROUGH SEVEN...Saturday night through Thursday

The probability for widespread hazardous weather is low.

.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 tonight.

LAZ023>025-MSZ053>059-182015-
Franklin LA-Catahoula-Tensas-Claiborne-Copiah-Simpson-Smith-
Jasper-Clarke-Jefferson-
307 PM CDT Fri Aug 17 2018

This hazardous weather outlook is for portions of northeast
Louisiana, central Mississippi, east central Mississippi, and
southwest Mississippi.

.DAY ONE...Tonight and Saturday

SEVERE THUNDERSTORMS
THREAT...Marginal
TIMING...Tonight

Isolated severe thunderstorms are possible for locations mainly
north of the Interstate Twenty corridor through this evening. The
main risk will be damaging wind gusts.

(https://www.weather.gov/images/jan/graphicast/1.png)

.DAYS TWO THROUGH SEVEN...Saturday night through Thursday

The probability for widespread hazardous weather is low.

.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 tonight.

LAZ026-MSZ060>066-072>074-182015-
Concordia-Adams-Franklin MS-Lincoln-Lawrence-Jefferson Davis-
Covington-Jones-Marion-Lamar-Forrest-
307 PM CDT Fri Aug 17 2018

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

.DAY ONE...Tonight and Saturday

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Saturday night through Thursday

The probability for widespread hazardous weather is low.

.SPOTTER CALL TO ACTION STATEMENT...
The activation of storm spotters, HAM radio operators, and
emergency management personnel in support of severe weather
operations is not expected through next Thursday.

26

&&

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

Tropical page...
   https://www.weather.gov/jan/srh/tropical?office=jan
National Hurricane Center Home Page...
   https://www.nhc.noaa.gov/
Find NWS JAN on Facebook...
   https://www.facebook.com/NWSJacksonMS
Follow NWS JAN on Twitter...
   @NWSJacksonMS
Follow NWS JAN on Youtube...
   https://www.youtube.com/user/NWSJacksonMiss

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

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

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

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

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

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Special Weather Statement
National Weather Service Jackson MS
309 PM CDT FRI AUG 17 2018

MSZ040>042-172100-
Sharkey MS-Yazoo MS-Issaquena MS-
309 PM CDT FRI AUG 17 2018

...A STRONG THUNDERSTORM WILL AFFECT YAZOO...CENTRAL ISSAQUENA AND
SHARKEY COUNTIES UNTIL 400 PM CDT...

At 309 PM CDT, Meteorologists were tracking strong thunderstorms
along a line extending from 8 miles southeast of Midnight to near
Lake Providence. Movement was southeast at 10 mph.

Winds in excess of 40 mph will be possible with these storms.

Strong thunderstorms will be near...
  Yazoo City around 350 PM CDT.
  Benton and Onward around 400 PM CDT.

Other locations impacted by these storms include Eden and Cary.

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.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3281 9116 3284 9114 3297 9066 3292 9066
      3292 9045 3301 9045 3302 9035 3285 9000
      3254 9097 3258 9096 3258 9104 3262 9100
      3264 9102 3263 9104 3261 9105 3259 9112
      3262 9115 3264 9115 3272 9105 3275 9116
TIME...MOT...LOC 2009Z 309DEG 10KT 3298 9045 3280 9111

NF

Special Weather Statement
National Weather Service Jackson MS
317 PM CDT FRI AUG 17 2018

MSZ025-027-036-172100-
Carroll MS-Leflore MS-Holmes MS-
317 PM CDT FRI AUG 17 2018

...A STRONG THUNDERSTORM WILL AFFECT NORTHERN HOLMES...WESTERN
CARROLL AND CENTRAL LEFLORE COUNTIES UNTIL 400 PM CDT...

At 317 PM CDT, Meteorologists were tracking strong thunderstorms
along a line extending from near Moorhead to near Tchula. Movement
was east at 25 mph.

Winds in excess of 40 mph will be possible with these storms.

Strong thunderstorms will be near...
  Tchula around 320 PM CDT.
  Howard around 325 PM CDT.
  Itta Bena around 335 PM CDT.
  Quito around 340 PM CDT.
  Sidon around 350 PM CDT.
  Greenwood, Black Hawk and Emory around 400 PM CDT.

Other locations impacted by these storms include West, Morgan City
and Cruger.

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.

These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

&&

LAT...LON 3324 8973 3320 8975 3309 9027 3330 9033
      3340 9045 3353 9045 3368 9011 3368 9008
TIME...MOT...LOC 2017Z 253DEG 20KT 3343 9045 3319 9026

NF