Flash Flood Warning 70, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
442 AM CDT Wed Jun 21 2017

.DISCUSSION...

Through Thursday night:

Tropical Storm Cindy continues to spin south of the LA coast this
morning with the forecast track changing little from the previous
update. Even though the overall system continues to have quite a
subtropical look to it (with a good bit of the rain and
associated thunderstorms displaced well to the north and east of
the center) the low level circulation has gotten better defined
overnight.

Through the night a large rain shield with perhaps a stray rumble
of thunder or two has migrated north from the Pine Belt toward
central MS. Rain has been locally heavy and totals near the
Highway 98 corridor already range from 2 to 3 inches. Rainfall
rates have been too low thus far to prompt flash flood warnings,
but it may not take long before those are necessary. Latest model
consensus suggests the solid rain shield with heavy rain potential
will build north through mainly the eastern half of the region
through today in tandem with strongest moisture advection and
additional lifting aid from the right entrance region of an upper
level jet streak. Interesting that some model solutions have a
tough time through today generating much precip getting to the
ground over many western zones of the forecast area. This is
certainly plausible due to at least weak low level divergence in
wind fields as flow nearer the coast peels back toward the low
center in the Gulf. All the above taken into account went into the
decision to expand the going flash flood watch for far southern
zones through tomorrow up through portions of south central and
eastern Mississippi (excluding the Jackson Metro area). Some
adjustment of this watch could certainly be needed but the current
layout right now is the best thinking for area flooding rain
potential through tomorrow.

Another aspect of the forecast to watch for today into tonight
will be the slow creep of surface based instability north into the
region on the tail of the widespread rain shield shifting to the
north. Low to mid layer wind shear supportive of tornado
generation will be building into the region at this time as well
although instability in our area this afternoon through tonight
will likely be too low to expect more than a marginal risk of this
activity. Of course the flooding and tornado risks will be
highlighted in the HWO/graphics. We will also be monitoring the
strength of east to southeast surface winds as the day progresses.
Current thinking is that these winds in our region will largely
remain below advisory strength (and certainly below tropical storm
strength).

On Thursday our region will likely be in between widespread heavy
rain areas to our west and southwest (associated with the
landfalling center of Cindy) and to our east over AL. In between
we should see some breaks in cloud cover with heating well up into
the 80s in many locations contributing to troubling instability
(surface based CAPE near or better than 2000 j/kg) considering at
least modest low to mid layer shear that is anticipated. The
Storm Prediction Center has highlighted our western and central
zones with a slight risk of severe storms due to the expectation
of at least isolated storms achieving temporary supercell
characteristics and having the ability to perhaps produce a
tornado or two. This risk will be somewhat lesser over eastern
portions of the area, but will still exist there. In addition,
bands of showers and thunderstorms could still be capable of
tremendous rainfall rates in some locations so a background
flooding threat will persist.

Thursday night a good deal of the afternoon showers and storms
will probably diminish over central and eastern zones. However,
the expected movement of Cindy north (just to or west) will
eventually bring a more consolidated band of locally heavy rains
and embedded thunderstorms to portions of the MS Delta before the
night is over. This may enhance flooding potential there and could
definitely require the flash flood watch to get shifted up in the
that neck of the woods as well before the day is out. /BB/

Friday through Tuesday:

Models and their ensembles were showing an active period with
Cindy and its residing moisture in its wake. As progged by NHC,
Tropical Depression Cindy will be tracking across our northwest
delta region on Friday. Models shows that we will have some good
low level shear of around 35 knots, surface base cape around
2500-3000 j/kg. This combined with daytime heating will bring a
risk of some severe weather esp in our northeast counties during
Friday into Friday night period per SPC day 3 outlook. There will
also be the risk of some heavy rainfall from Tropical Depression
Cindy with pwats over 2.5 inches. The primary risks will be
damaging winds and some tornadoes. The tropical system will exit
the region by early Saturday as it gets caught up in mid latitude
westerly flow. Meanwhile a broad latitude upper trough will bring
a front into the region over the weekend. Pwats ahead of the front
will continue to be 2 plus inches which spells the continued risk
of some locally heavy rainfall. As we go into early next week the
cold front will slide across the region by early Monday. It will
leave some dryer air in its wake which sometimes happens in the
wake of a tropical system. Dryer air will push across the region
on Monday night into Tuesday with lower 60s dewpoints. This will
cause nightly lows to dip into the lower to middle 60s for early
next week. Daily highs will be in the 80s./17/

&&

.AVIATION...
06Z TAF discussion:

Tropical Storm Cindy south of the LA coast and drifting
northwestward will bring sites increasing rain chances through the
TAF period (especially over PIB/HBG/MEI/NMM where rain is already
occurring or will begin shortly). Rain showers will get hard
enough to occasionally reduce vis, especially this afternoon into
this evening, over most sites other than GLH/GWO, and with the
exception of the latter sites ceilings will oscillate between IFR
and MVFR most of the period starting later this morning. Otherwise
anticipate occasionally gusty generally east winds through the
period with gusts up to 30 mph at times getting more likely by
later this afternoon into this evening. /BB/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       79  73  86  75 /  87  76  71  51
Meridian      78  73  83  75 / 100  95  78  56
Vicksburg     80  73  86  76 /  52  58  71  60
Hattiesburg   79  74  85  75 / 100  99  78  61
Natchez       81  74  85  76 /  69  76  72  59
Greenville    82  73  85  75 /  59  40  73  73
Greenwood     80  73  85  76 /  92  61  68  59

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Flash Flood Watch through Thursday evening for MSZ031-038-039-
     045-046-050>052-055>058-060>066-072>074.

LA...Flash Flood Watch through Thursday evening for LAZ024-026.

AR...None.

&&

BB/17

Hazardous Weather Outlook
National Weather Service Jackson MS
417 PM CDT Tue Jun 20 2017

ARZ074-075-LAZ007>009-015-016-023-025-MSZ018-019-025>042-047-
212130-
Ashley-Chicot-Morehouse-West Carroll-East Carroll-Richland-
Madison LA-Franklin LA-Tensas-Bolivar-Sunflower-Leflore-Grenada-
Carroll-Montgomery-Webster-Clay-Lowndes-Choctaw-Oktibbeha-
Washington-Humphreys-Holmes-Attala-Winston-Noxubee-Issaquena-
Sharkey-Yazoo-Warren-
417 PM CDT Tue Jun 20 2017

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

.DAY ONE...Tonight through Wednesday night

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Thursday through Monday

As the remnants of the Tropical Storm Cindy move to the west and
eventually to the Northeast of the area, a few strong to severe
thunderstorms are possible for the entire outlook area on
Thursday. There will also be the potential for flash flooding on
Thursday, and this risk will continue into the weekend.

(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 Thursday.

LAZ024-026-MSZ043>046-048>060-212130-
Catahoula-Concordia-Madison MS-Leake-Neshoba-Kemper-Hinds-Rankin-
Scott-Newton-Lauderdale-Claiborne-Copiah-Simpson-Smith-Jasper-
Clarke-Jefferson-Adams-
417 PM CDT Tue Jun 20 2017

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

.DAY ONE...Tonight through Wednesday night

FLOODING
THREAT...Limited
TIMING...Wednesday and Wednesday Night

Flash flooding is possible across the area with storm total
accumulations of 1 to 2 inches with locally higher amounts.

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

.DAYS TWO THROUGH SEVEN...Thursday through Monday

As the remnants of the Tropical Storm Cindy move to the west and
eventually to the Northeast of the area, a few strong to severe
thunderstorms are possible for the entire outlook area on
Thursday. There will also be the potential for flash flooding on
Thursday, and this risk will continue into the weekend.

(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 Thursday.

MSZ061>066-072-212130-
Franklin MS-Lincoln-Lawrence-Jefferson Davis-Covington-Jones-
Marion-
417 PM CDT Tue Jun 20 2017

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

.DAY ONE...Tonight through Wednesday night

FLOODING
THREAT...Elevated
TIMING...Wednesday and Wednesday Night

Flash flooding is expected with storm total accumulations of 2 to
4 inches with locally higher amounts.

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

.DAYS TWO THROUGH SEVEN...Thursday through Monday

As the remnants of the Tropical Storm Cindy move to the west and
eventually to the Northeast of the area, a few strong to severe
thunderstorms are possible for the entire outlook area on
Thursday. There will also be the potential for flash flooding on
Thursday, and this risk will continue into the weekend.

(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 Thursday.

MSZ073-074-212130-
Lamar-Forrest-
417 PM CDT Tue Jun 20 2017

This hazardous weather outlook is for portions of southeast
Mississippi.

.DAY ONE...Tonight through Wednesday night

FLOODING
THREAT...Significant
TIMING...Wednesday and Wednesday Night

Significant flash flooding is possible with storm total
accumulations of 4 to 6 inches with locally higher amounts.

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

.DAYS TWO THROUGH SEVEN...Thursday through Monday

As the remnants of the Tropical Storm Cindy move to the west and
eventually to the Northeast of the area, a few strong to severe
thunderstorms are possible for the entire outlook area on
Thursday. There will also be the potential for flash flooding on
Thursday, and this risk will continue into the weekend.

(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 Thursday.

15

&&

...HAZARD LEGEND...

*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...
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...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