Special Weather Statement, NWS Jackson, MS

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1236 PM CDT Thu Jul 19 2018

.UPDATE...
Updated for 18Z aviation discussion

&&

.AVIATION...
18Z TAF discussion:
Mostly isolated convection this afternoon will affect GWO, GTR,
MEI, HBG and PIB with brief lowerings of ceiling and visibility
and gusty winds. Another area of storms may move into the GLH,
GWO, JAN, HKS and MEI areas during the evening then diminish
around midnight. Otherwise, mostly VFR conditions will prevail.
MVFR visibilities in fog will develop after midnight and linger
through mid morning Friday./26/

&&

.DISCUSSION...
Satellite imagery this morning showing prominent MCV over northeast
MS moving southeast across gradient of high 0-3km theta-e. Its
locally modified wind field has been responsible for the forcing
that has led to the active convection in that area already this
morning. While that localized convective area will move into AL
shortly, more convection should get going in the east during the
afternoon along the theta-e axis. Some of that convection may
become robust as checklist indicating some chance of microbursts
during peak heating. Modified JAN 12Z sounding highlighted by CAPE
of 4166 J/kg, LI of -9, 0-3 km lapse rate of 9.2C/km and surface
theta-e of 366K. /26/

Prior discussion below:

Today and Tonight...A stalled and washing out front currently
resides just to my north, as an outflow boundary loses momentum as
it drifts south across far southern portions of the CWA this
morning.  Both of these features could result in some showers and
isolated storms bubbling up over the CWA first thing this morning.
Otherwise, any low stratus or fog that developed across the CWA
during the overnight hours, will begin to erode after sunrise this
morning.

Strong high pressure centered over the Four Corners region will
shift east and deeper into the Lower Mississippi River Valley
through the period.  While chances for afternoon and evening showers
and storms will remain in the forecast, the best rain chances will
shift mainly over East and Southeast Mississippi today.  As has been
the case the past couple of days, a few strong storms can't be ruled
out, neither can a stray storm reaching severe limits.  However,
with continued low confidence and overall coverage of such activity,
I'll refrain from introducing such wording in the HWO.  Still, gusty
winds, frequent lightning, and torrential downpours can be expected
with any storms that develop during the period.

Activity will begin to dissipate during the evening hours as daytime
heating is lost, with much of the tonight period remaining quiet.
However, as the CWA remains under persistent northwest flow aloft,
we'll have to continually monitor upstream for any MCS or related
outflow activity that could approach or move into the CWA overnight
into early Friday morning.  Currently, given the diurnal minimum in
which this scenario would unfold, again after midnight and before
sunrise early Friday, any activity associated with either an MCS or
outflow boundary impeding upon the CWA is expected to be sub-severe.

The bigger story during the period will be the ensuing heat as the
aforementioned high aloft builds into the region from the west. This
combination of heat, as highs range from the mid 90s to around the
century mark, and humidity, dew points in the 70s, will result in
afternoon heat index values ranging from 105-110 across mainly
central and western portions of the CWA today.  Therefore, a Heat
Advisory will be in effect from 10 AM until 7 PM.  Conditions
tonight will remain mild and muggy with lows falling into the 70s
areawide. /19/

Friday through Wednesday...The primary concerns will be heat
stress and rain chances along with muggy conditions through
period.

The period will be characterized by anomalous mid to upper ridging
west to mid to upper troughing over eastern conus. This will bring
northwest flow to the region during the period. The ridging will
expant east to the region on Friday. This will set up the regime of
anomalous low to midlevel temps over the region through the weekend.
This will result in highs in the middle to upper 90s with some
triple digit numbers west of the MS River. This will bring heat
indices from the around 105 to 113. The warmest indices will be over
the western areas mainly Friday and Saturday,which will decrease in
coverage on Sunday. So will maintain the heat risk in the HWO for
Friday through Sunday. Models indicate that isolated strong storms
will be possible on Friday into Friday night with northwest flow
aloft. We will have 0-3km winds of around 35 knots, Vertical totals
in the lower 30s in the north,a frontal passage for lift, and good
lapse rates. CAM guidance shows a good line passing in the TN valley
to the north, however if future runs push that line farther south an
outflow boundary could definitely increase strong storm coverage in
our unstable airmass. For now will hold off on any marginal risk for
day 2. As we push through the weekend the axis of the upper trough
will spread over the remainder of the region by Sunday. An
associated upper low will with another frontal boundary will push
south across the Lower Mississippi Valley On Tuesday. The weak closed
low will push into the northern gulf by Wednesday. This will keep
rain chances across the region for the upcoming workweek with our
soupy airmass./17/

As far as temperatures are concern beyond this weekend with the
frontal passage readings will tone back to mainly the lower 90s.
Lows will be in the lower to middle 70s. /17/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       94  74  97  76 /  12  11  17  12
Meridian      90  73  97  77 /  38  14  28  24
Vicksburg     95  76  98  76 /   7  11   7   4
Hattiesburg   92  74  96  77 /  43  19  29  10
Natchez       95  76  97  77 /  11  11  12   2
Greenville    94  75  98  76 /  13  18  14  12
Greenwood     93  75  96  76 /  16  20  22  27

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Heat Advisory until 7 PM CDT this evening for MSZ018-019-025>027-
     034>036-040>043-047>049-053>055-059>063.

LA...Heat Advisory until 7 PM CDT this evening for LAZ007>009-015-016-
     023>026.

AR...Heat Advisory until 7 PM CDT this evening for ARZ074-075.

&&

Hazardous Weather Outlook...UPDATED
National Weather Service Jackson MS
918 AM CDT Thu Jul 19 2018

ARZ074-075-LAZ007>009-015-016-023>026-MSZ018-019-025-034>036-
040>042-047-048-053-054-059>062-201430-
Ashley-Chicot-Morehouse-West Carroll-East Carroll-Richland-
Madison LA-Franklin LA-Catahoula-Tensas-Concordia-Bolivar-
Sunflower-Leflore-Washington-Humphreys-Holmes-Issaquena-Sharkey-
Yazoo-Warren-Hinds-Claiborne-Copiah-Jefferson-Adams-Franklin MS-
Lincoln-
918 AM CDT Thu Jul 19 2018

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

.DAY ONE...Today and Tonight

EXCESSIVE HEAT
THREAT...Elevated
TIMING...Today

Temperatures warming into the mid 90 to near 100 will combine
with high humidity levels to produce heat indices from 105 to 110,
mainly during the afternoon today. Precautions should be taken to
avoid strenuous outdoor activities. Check on those vulnerable to
heat stress. Stay hydrated and wear light, loose fitted clothing.

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

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

High temperatures from the upper 90s to near 100 will combine
with high humidity levels to produce heat indices around 110 each
afternoon from Friday through Monday. Precautions should be taken
to avoid strenuous outdoor activities. Check on those vulnerable
to heat stress. Stay hydrated and wear light, loose fitted
clothing.

(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 is not expected through next Wednesday.

MSZ029>033-038-039-044>046-050>052-056>058-064>066-072>074-201430-
Webster-Clay-Lowndes-Choctaw-Oktibbeha-Winston-Noxubee-Leake-
Neshoba-Kemper-Scott-Newton-Lauderdale-Smith-Jasper-Clarke-
Jefferson Davis-Covington-Jones-Marion-Lamar-Forrest-
918 AM CDT Thu Jul 19 2018

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

.DAY ONE...Today and Tonight

SEVERE THUNDERSTORMS
THREAT...Marginal
TIMING...Today

EXCESSIVE HEAT
THREAT...Limited
TIMING...Today

Isolated severe thunderstorms will be possible this afternoon.
Damaging wind gusts up to 60 mph and hail up to the size of
quarters will be the primary severe weather threats.

(https://www.weather.gov/images/jan/graphicast/3.png)

Temperatures warming into the mid to upper 90s will combine with
high humidity levels to produce heat indices around 105 during
the afternoon today. Precautions should be taken to avoid
strenuous outdoor activities. Check on those vulnerable to heat
stress. Stay hydrated and wear light, loose fitted clothing.

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

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

High temperatures from the mid to upper 90s will combine with
high humidity levels to produce heat indices 105 to 110 each
afternoon from Friday through Monday. Precautions should be taken
to avoid strenuous outdoor activities. Check on those vulnerable
to heat stress. Stay hydrated and wear light, loose fitted
clothing.

(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 today.

MSZ026>028-037-043-049-055-063-201430-
Grenada-Carroll-Montgomery-Attala-Madison MS-Rankin-Simpson-
Lawrence-
918 AM CDT Thu Jul 19 2018

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

.DAY ONE...Today and Tonight

EXCESSIVE HEAT
THREAT...Limited
TIMING...Today

Temperatures warming into the mid to upper 90s will combine with
high humidity levels to produce heat indices around 105 during
the afternoon today. Precautions should be taken to avoid
strenuous outdoor activities. Check on those vulnerable to heat
stress. Stay hydrated and wear light, loose fitted clothing.

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

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

High temperatures from the mid to upper 90s will combine with
high humidity levels to produce heat indices 105 to 110 each
afternoon from Friday through Monday. Precautions should be taken
to avoid strenuous outdoor activities. Check on those vulnerable
to heat stress. Stay hydrated and wear light, loose fitted
clothing.

(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 is not expected through next Wednesday.

26

&&

...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.

*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.

...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/

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