Special Weather Statement, NWS Jackson, MS

Area Forecast Discussion...Amended for aviation discussion
National Weather Service Jackson MS
1059 AM CDT TUE JUL 5 2016

.UPDATE...

Thinking from the previous update generally applies with convective
activity having waned along the Highway 82 corridor and more evidence
in the NCAR ensemble, HRRR, and SPC SSEO that storms will redevelop
over southeast portions of the ArkLaMiss where relatively steep mid
level lapse rates and deeper moisture will coincide. We have opted to
reflect this potential with a limited severe threat in the
HWO/Graphic for this afternoon. It appears the window of time will be
small and any severe threat should end prior to sunset.

Otherwise, temperatures and corresponding heat indices are slightly
lower due to the greater cloud cover/convective coverage, but max
heat indices will manage to top out in the 100-105 range over a good
portion of the area so will keep the HWO heat threat going. /EC/

&&

.AVIATION...Morning IFR/MVFR conditions have given way to VFR with
still a combination of SCT/BKN skies and some activity over various
portions of the CWA. Look for convection to organized more by 1-2pm
and be focused mainly across central and southern sections with a
eastward movement. Will focus to time restrictions based off that
with the main time window being between 2-6pm. VFR conditions will
prevail much of the evening with a trend to some MVFR ceilings as we
approach 5am. /CME/

&&

.PREV DISCUSSION... /issued 845 AM CDT TUE JUL 5 2016/

UPDATE...

Primarily made adjustments to rain chances to account for current
convective trends with widespread showers and a few storms continuing
along the Highway 82 corridor. There has been some waning of the
intensity and expect this trend to continue as we go into the late
morning. And there are some differences among guidance with how
things will evolve this afternoon - some signals are showing up for
convective redevelopment mainly south of the I-20 corridor this
afternoon peaking along the Highway 84 corridor during the mid
afternoon hours. For now will show a tendency toward that direction.
If storms do develop, mid level lapse rates with 28 vertical totals
and fairly large CAPE and precipitable water would support a few
strong storms. /EC

PREV DISCUSSION... /issued 442 AM CDT TUE JUL 5 2016/

SHORT TERM...Today through Wednesday night...Another hot day is on
tap for the area today with high's climbing into the low/mid 90s for
most of the area. Although this is not quite as hot as yesterday,
heat indices will once again climb to near 105 degrees. Will continue
the limited area for heat in the HWO. PWATS are well above 2 inches
this morning across much of the area, and this combined with a short
wave that is moving across louisiana will kick of a round of storms
this morning. Isolated storms are already beginning to form over the
western portions of the area. Expect the main focus of this first
round of storms to be north of the I-20 corridor with isolated storms
further south. Another short wave will move across the area later
this afternoon and expect much of the area to see scattered storms
this afternoon into the early evening hours. All of the Hi-res models
are in pretty good agreement on this scenario. With mid level lapse
rates around 6.0, 20-25kts of low level flow, and afternoon heating
a couple of storms could be strong to possibly severe, but with the
abundant low level moisture, expect heavy rainfall to be the main
concern today.

Expect the showers and thunderstorms to dissipate quickly after
sunset this evening leaving mainly partly to mostly cloudy skies
overnight. Upper ridging will begin to increase across the area on
Wednesday, but expect mainly diurnal isolated to scattered afternoon
showers and thunderstorms to form once again. Afternoon heat indices
will once again range from 100 to 105 over much of the area.
Overnight lows will continue to be on the warm side tonight and
Wednesday night only falling into the mid 70s.

LONG TERM...Thursday through next Monday...The long term period is
still looking quite hot, but there is potential for at least subtle
relief for portions of the region this weekend into the start of
next week.

First off, local weather should be dominated by vast subtropical
ridging over the south-central to southeastern CONUS Thursday and
Friday. Decent low level southerly flow vectors these days could be
enough to bring at least isolated thunderstorms to far southern
zones in the afternoon hours, as a result of inland-cascading
seabreeze penetration. Otherwise, the air mass should remain rather
capped to convection with highs in the mid to upper 90s while heat
index values border on oppressive (peaking near 105 degrees).

By this weekend the previously-mentioned vast subtropical ridge
stretching latitudinally across the vicinity is showing signs in
model consensus of breaking down a bit, with perhaps the biggest
weakness extending down into the Lower Mississippi Valley (if the
latest operational European model is to be believed). Important to
point that model consensus does not suggest an impact of a large
disturbance or front in our region but enough lessening of
subsidence and capping to activate what should likely be high
diurnally-driven instability. Probability of precipitation in these
periods kept at tame levels (20-40 percent) owing to lack of major
inclement features, but confidence is increasing that there may be
enough afternoon storms about to blunt heat a bit late in the day.
However, before storms break out these days the combination of heat
and humidity could still easily push heat index values above 100
degrees at least briefly. If storms only achieve isolated coverage
these days then heat could be a larger concern. There also may be
some opportunity for some potent pulse storms considering lapse
rates could border on impressive.

For now there is enough uncertainty for this weekend into early next
week to refrain from mentioning anything in the HWO/graphics for
those time periods at this juncture. However, we will continue with
the limited heat mention in the HWO for Thursday and Friday, when
convective coverage is not such as question mark. Still can't rule
out that a heat advisory might not be needed for portions of the
area on one or both of these days. /BB/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       91  77  94  76 /  33  17  24   6
Meridian      90  75  94  75 /  52  26  29   9
Vicksburg     92  77  95  77 /  19  12  22   5
Hattiesburg   91  77  95  76 /  41  28  30   7
Natchez       91  77  94  77 /  26  12  26   5
Greenville    91  77  95  77 /  33  10  12   5
Greenwood     89  76  94  76 /  44  11  16   7

&&

.JAN Watches/Warnings/Advisories...
MS...None.
LA...None.
AR...None.

&&

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