Severe Thunderstorm Warning 199, NWS Jackson, MS

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1229 PM CDT Wed May 30 2018

.UPDATE...
Updated for 18Z aviation discussion

&&

.AVIATION...
18Z TAF discussion:
VFR flight categories will prevail at sites through much of this
forecast period. Due to isolated to scattered convection this
afternoon, a brief period of MVFR/IFR categories can't be ruled
out at sites where convection is observed. The same goes for
early Thursday morning. Some low stratus/patchy fog developing
around day break Thursday, could potentially reduce ceilings
and/or visibilities to MVFR status for a brief 1-2 hour period.
Southwest winds today will gradually become light from the south
this evening, with a light south to calm wind expected during the
overnight hours. 19/

&&

.DISCUSSION...
The forecast area will remain under northwest flow aloft as we sit
on the western side of an exiting trough, and weak high pressure at
the surface.  This northwest flow will keep dry air and cool
temperatures aloft over the region, but conditions in the lower
levels of the atmosphere are quickly recovering as warming and
moistening conditions have ensued and will continue.  This will
result in warm and increasingly humid conditions across the region
today, as highs climb into the low and middle 90s.  This, as dew
points generally sit around 70, will result in afternoon heat index
values climbing up around the century mark today.

Isolated to scattered thunderstorms are also expected to develop
across mainly northern and eastern portions of the forecast area
later this afternoon as well.  This activity could be furthered by
an outflow boundary currently propagating east southeast across the
Delta region this morning.  As this boundary reaches East Central
Mississippi during peak heating hours this afternoon, it could
become the focusing mechanism for thunderstorms there from mid-
afternoon through early this evening. This, in addition to ample
instability and steep lapse rates over this area, could yield some
strong to isolated severe storms capable of producing both gusty
winds and hail.  Therefore, I'll maintain the ongoing "Marginal
Risk" for isolated severe storms across the northeast portion of the
CWA this afternoon.

The ongoing forecast is in good shape.  Other than some minor
adjustments to hourly elements of the forecast to better account for
current trends, no major changes will be made to the forecast on
this update. /19/

Prior discussion below:

Today through Tonight: The primary focus will be for a possible MCS
to affect the northern and eastern counties for this afternoon.

Latest satellite imagery showed the remnants of the tropical
disturbance moving north over the Mid-Mississippi Valley. The region
will be under the influence of troughiness through early this
evening. A disturbance will come into the region in northwest flow.
It will be combine with daytime heating and instability. Mid to
upper level ridging will build in from the west late tonight. It
will be another warm day as instability and daytime heating will
bring a better coverage of thunderstorms, mainly east of Interstate
55. Pwats will be around 1.8 inches, surface Cape 3-4Kft, 27-28
vertical totals, and 0-3 km 20 knots. Some of the CAM guidance shows
some isolated severe storms affecting portions of the northern and
eastern counties for this afternoon into early this evening. As we
lose daytime heating expect the storms to diminish after sunset. So
with this in mind will keep the current marginal risk graphic for
this afternoon.

As far as temperatures are concerned highs will range from the
lower 90s east to the middle 90s west. Lows will range from the
lower to middle 70s. Will keep the best scattered convective
chances generally east of Interstate 55./17/

Thursday through Sunday: Heat will be the big story for the end of
the week into the weekend as a stout mid/upper ridge builds
eastward into the region. Mid level warming in association with
this feature will help suppress convection across most of the
forecast area Thursday and Friday, though we can't rule out a
shower or storm on the eastern periphery of the ridge slipping
into East MS. Daytime temps will soar into the mid/upper 90s
across much of the area, which when combined with considerable
lingering low level moisture will result in heat indices beginning
to surpass 100 during the daytime hours.

By this weekend, confidence in the ridge keeping rain out of the
area decreases as a series of more potent shortwaves swing
through the Mid Atlantic and Southeast US. These could bring
convective complexes along the eastern periphery of the ridge and
across at least some portion of our area. Absent such systems to
disrupt insolation, Saturday and Sunday have the potential to be
the warmest days of this stretch, with heat indices potentially
reaching advisory criteria over some portion of the forecast area.
Unfortunately at this stage, it is too soon to accurately
determine when and which of these disturbances will result in
storms and how much they might disrupt heating.

For this morning's HWO/graphics, we'll expand mention of
dangerous heat into Thursday for NE Louisiana, continue mentioning
it everywhere Friday and Saturday, and continue highlighting it
over the southern 2/3rds of the CWA on Sunday.

Monday and Tuesday: While there are still indications a weak
front bringing humidity relief will make it into the region
toward the end of the forecast period, timing remains a bit more
uncertain, with some model solutions now pushing this back into
Monday. Even with a drier airmass over much of the area, temps
could still push the mid 90s especially over southern and western
portions of the forecast area into early next week, albeit with
lower heat indices. /DL/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       93  73  93  73 /  18  12   7   2
Meridian      91  71  93  71 /  35  20  16   5
Vicksburg     94  73  94  73 /   9   6   3   2
Hattiesburg   91  72  93  72 /  38  13  16   4
Natchez       93  73  93  73 /   9   4   5   2
Greenville    93  74  93  74 /  17   7   3   3
Greenwood     92  73  92  73 /  23  11   5   4

&&

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

&&

19

Hazardous Weather Outlook...UPDATED
National Weather Service Jackson MS
1232 PM CDT Wed May 30 2018

ARZ074-075-LAZ007>009-015-016-023>026-MSZ018-019-034-035-040>043-
047>050-053>057-059>066-072>074-310000-
Ashley-Chicot-Morehouse-West Carroll-East Carroll-Richland-
Madison LA-Franklin LA-Catahoula-Tensas-Concordia-Bolivar-
Sunflower-Washington-Humphreys-Issaquena-Sharkey-Yazoo-Madison MS-
Warren-Hinds-Rankin-Scott-Claiborne-Copiah-Simpson-Smith-Jasper-
Jefferson-Adams-Franklin MS-Lincoln-Lawrence-Jefferson Davis-
Covington-Jones-Marion-Lamar-Forrest-
1232 PM CDT Wed May 30 2018

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

.DAY ONE...The rest of Today and Tonight...

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday...

Heat indices approaching 105 degrees will be possible across
northeast Louisiana on Thursday, areawide on Friday and Saturday,
and along and south of I-20 on Sunday. This will result in
increasing heat stress. Those who will be spending extended
amounts of time outdoors are encouraged to stay hydrated, avoid
strenuous activies, and take frequent breaks.

(https://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 is not expected through next Tuesday.

MSZ025>033-036>039-044>046-051-052-058-310000-
Leflore-Grenada-Carroll-Montgomery-Webster-Clay-Lowndes-Choctaw-
Oktibbeha-Holmes-Attala-Winston-Noxubee-Leake-Neshoba-Kemper-
Newton-Lauderdale-Clarke-
1232 PM CDT Wed May 30 2018

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

.DAY ONE...The rest of Today and Tonight...

SEVERE THUNDERSTORMS
THREAT...Marginal
TIMING...remainder of today

Isolated severe storms capable of producing damaging wind gusts
and hail up to quarter size are possible this afternoon.

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

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday...

Heat indices approaching 105 degrees will be possible across
northeast Louisiana on Thursday, areawide on Friday and Saturday,
and along and south of I-20 on Sunday. This will result in
increasing heat stress. Those who will be spending extended
amounts of time outdoors are encouraged to stay hydrated, avoid
strenuous activies, and take frequent breaks.

(https://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 the rest
of today.

19

&&

...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.

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