Severe Thunderstorm Warning 331, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
348 PM CDT Sat Jul 28 2018

.DISCUSSION...
Tonight and Sunday: Convection continues to refire on outflow from
earlier convection over south AR. This should continue to be the
trend through the rest of the afternoon into early evening as 0-3km
bulk shear vectors steer the majority over the southwestern third
where the deepest moisture and instability currently exists.
Thereafter, convection will wind down with the loss of heating.

GFS continues to show very perturbed northwest mid level flow over
the forecast area in the short term, which will continue to aid
in mostly diurnal convective activity again Sunday. This looks to
continue to be most concentrated over the southwestern half as the
wedge of low level dry air continues to hold on over the
northeast.

Though heating got off to a slow start due to morning cloud cover,
heat indices have still managed to rise into the lower 100s over
east central Louisiana and southwest Mississippi. This area and
areas further to the north and east will see similar conditions
Sunday as lack of cloud cover Sunday morning will allow heating to
get an earlier start. Maximums near 95 will combine with low to mid
70s dewpoints to push heat indices to near 105./26/

Monday through Wednesday: A sharper upper trough/mid level
shortwave will carve out of the longer wave trough over the
eastern CONUS on Monday and track from the Upper Plains into the
Mississippi River Valley through midweek. Ahead of this feature,
lingering relative dryness over mainly northeastern portions of
the area will be replaced by an influx of richer deep layer
moisture. This surge in moisture will occur in earnest from Monday
afternoon into Tuesday ahead of an approaching cold front
associated with the aforementioned mid/upper level features. This
will bring increasing chances for showers and storms, mainly
beginning later on Monday and especially on Tuesday. There is some
uncertainty with how potent this system will be, with the ECMWF
and GEM depicting a more organized surface cyclone, but there is
decent model agreement with respect to the timing and placement of
the front. There is also good agreement in a deep upper trough
with anomalous mid level height falls and deep layer shear for
this time of year. Though there is inherent uncertainty about the
evolution of convection during this time frame (whether earlier
convection might disrupt heating/instability, etc), with the other
factors in play favoring better storm organization, conditions
will be more favorable for severe thunderstorms than on a typical
summer day. SPC has outlooked a marginal risk for severe storms
for Day 3 (Monday). We might have slightly greater potential in
our area on Tuesday, so we'll update the HWO include mention of a
threat for isolated severe storms Monday into Tuesday. We'll be
able to refine timing/location details of this threat in the
coming days.

The upper trough will hang up over our region and become more
shallow as we head into the second half of the week. As this
happens, the surface front will stall across our area Tuesday
into Wednesday. This should still allow a drier airmass to work
into a good chunk of the area, with reduced rain chances and
slightly cooler/less hot conditions especially over the northwest
half by Wednesday. Decent rain chances may very well stick around
the I-59 corridor, however, due to the front stalling.

Thursday through next Saturday: The front will begin to dissipate
as it remains stalled across our region, but a regime of generally
greater deep layer moisture in the SE versus less in the NW will
persist through the end of the week. POPs will also follow that
theme of greater in our southeast, but temps will steadily
increase areawide as the airmass gradually becomes modified
through the end of the week. /DL/

&&

.AVIATION...
18Z TAF discussion:
Scattered showers and thunderstorms will continue to develop this
afternoon mainly in the vicinities of GLH, GWO, JAN, HKS, PIB and
HBG. Where storms occur, brief reductions in ceiling and visibility
can be expected. Otherwise, VFR conditions will prevail through
the period./26/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       72  94  73  92 /  37  32  13  63
Meridian      72  95  72  94 /  12  19  14  48
Vicksburg     72  93  74  91 /  32  29  14  66
Hattiesburg   73  95  73  94 /  23  39  16  54
Natchez       73  93  74  92 /  31  36  18  64
Greenville    70  90  73  88 /  17  27  24  70
Greenwood     70  92  72  90 /  15  16  18  65

&&

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

&&

26/DL

Hazardous Weather Outlook...UPDATED
National Weather Service Jackson MS
406 PM CDT Sat Jul 28 2018

ARZ074-075-LAZ007>009-MSZ018-019-025>046-049>052-056>058-065-066-
292115-
Ashley-Chicot-Morehouse-West Carroll-East Carroll-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-
Rankin-Scott-Newton-Lauderdale-Smith-Jasper-Clarke-Covington-
Jones-
406 PM CDT Sat Jul 28 2018

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

.DAY ONE...Tonight and Sunday

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Sunday night through Friday

Isolated severe thunderstorms, capable of producing damaging wind
gusts and hail to the size of quarters, are possible Monday and
Tuesday.

(https://www.weather.gov/images/jan/graphicast/2.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 Monday
through Tuesday.

LAZ015-016-023>026-MSZ047-048-053>055-059>064-072>074-292115-
Richland-Madison LA-Franklin LA-Catahoula-Tensas-Concordia-Warren-
Hinds-Claiborne-Copiah-Simpson-Jefferson-Adams-Franklin MS-
Lincoln-Lawrence-Jefferson Davis-Marion-Lamar-Forrest-
406 PM CDT Sat Jul 28 2018

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

.DAY ONE...Tonight and Sunday

EXCESSIVE HEAT
THREAT...Limited
TIMING...mainly Sunday afternoon

Temperatures in the low to mid 90s will combine with high
humidity to produce heat indices near 105 degrees. Precautions
should be taken to avoid heat stress. Stay hydrated and wear
light, loose fitted clothing.

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

.DAYS TWO THROUGH SEVEN...Sunday night through Friday

Temperatures in the low to mid 90s will combine with high
humidity to produce heat indices near 105 degrees again Monday
afternoon. Precautions should be taken to avoid heat stress. Stay
hydrated and wear light, loose fitted clothing.

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

Isolated severe thunderstorms, capable of producing damaging wind
gusts and hail to the size of quarters, are possible Monday and
Tuesday.

(https://www.weather.gov/images/jan/graphicast/2.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 Monday
through Tuesday.

26/DL

&&

...HAZARD LEGEND...

*EXCESSIVE HEAT*
Extreme...Maximum heat index greater than 110 degrees for 3 or
 more days in a row and/or air temperatures greater than 107
 degrees.
Significant...Maximum heat index greater than 110 degrees
 and/or air temperatures greater than 105 degrees.
Elevated...Maximum heat index 105 to 110 degrees and/or air
 temperatures greater than 103 degrees.
Limited...Maximum heat index near 105 degrees and/or air
 temperatures 100 to 103 degrees.

...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