Special Weather Statement, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
340 PM CDT Wed Aug 16 2017

.DISCUSSION...
Tonight through Thursday:

Overall expect convection to gradually wind by early evening around
8-9PM overnight. There could be some lower clouds lingering
overnight, especially as some stratus could build after midnight (~3-
4AM) from west to east. This could hinder some cooling overnight but
as the surface & upper ridging build in from the east overnight
expect conditions to clear & winds to become lighter. This could
help us fall a few degrees above normal into the low-mid 70s
areawide, a few degrees above normal.

As that upper & surface ridge build east Thursday over the Florida
Panhandle & north-eastern Gulf of Mexico. As an upper jet
strengthens over the central Plains & ejects into the mid-northern
Mississippi Valley & into the Great Lakes by Thursday afternoon, a
surface low & attendant cold front will be diving through the
central Plains & towards the area. In addition as the upper low over
the western Gulf of Mexico today propagates eastward, flow aloft
will be be slightly different with less diffluent flow. Moisture
will lessen, with closer to one and three quarters to two inch PWs,
& 850mb Theta E only near 340K. Low level moisture will continue to
linger & not mix too much. With thermal profiles gradually warming,
especially with any compressional heating, expect highs to be
slightly warmer potentially around the 92-94 degree range. With
dewpoints hovering in the mid-upper 70s, we should be able to
maintain some high heat indices near & above 105 degrees across most
areas. Heat stress can be expected tomorrow, especially along & west
of the I-55 corridor. Updated the HWO/graphics to include an
elevated risk for heat while wrapping the limited risk down into the
Golden Triangle as well. Issued a heat advisory from 9AM through 7PM
Thursday.

Due to the changing jet dynamics & less moisture, PoPs will be lower
tomorrow, but some 2 inch PWs pooling in the Delta will help more
convection to be sparked in the ArkLaMiss Delta & Highway 82
corridor. Global models & CAM guidance (including ARW) indicate this
idea. Surface winds & low-mid level flow will be stronger due to an
increased gradient & there could be some potential for some stronger
storms due to 15-20kts of 0-2 & 0-3km bulk shear. Lapse rates are
meager but if we warm enough & dewpoints hold, we should be able to
get some better vertical total, which the GFS shows in Delta. Did
not introduce anything in the HWO/graphics for now but expect
scattered convection across the Delta & Highway 82 corridor with
more isolated convection elsewhere. Locally heavy downpours are
possible but storms should be moving enough to preclude mentioning
anything in the HWO/graphics. /DC/

Thursday night through next Wednesday:

The upper low over the Great Lakes will sink a weak frontal boundary
down through our region on Friday. Rain chances over the southern
half of the CWA will be a bit higher than previous days due to extra
lift along the boundary. However, still expect precip to be in the
form of scattered afternoon showers and storms, but not widespread.
This rainfall will help mitigate the heat stress just a bit. Still
expect heat indices on Friday to be near 100 though.

Over the weekend, the trough pushes to the east and low level
ridging builds in behind it. PWs will remain high, especially in the
southern half of the area, 2" and higher, thus this will be where
the best rain chances over the weekend will exist. Temps will creep
upwards just a bit through the weekend and heat stress will
therefore increase as well. Heat indices could approach 105 degrees
by Sunday again. Heights will continue to increase going into next
week as the upper ridge builds back over the Southeast. Expect the
typical diurnal showers and storms with average seasonal temps as
well. /10/

&&

.AVIATION...
18Z TAF discussion:
Widespread convection is developing across the region, especially
near JAN & HKS & just north of MEI & NMM. Overall expect
widespread convection this afternoon, with some potential for some
storms to move back into these areas from the southwest around
16/21-22Z. Some storms (TSRA) could bring some brief reductions in
ceilings &/or visibilities & brief gusty southwest winds up to
15-20+kts or so. These widespread storms will affect all TAF
sites this afternoon. Areas should remain VFR in between, other
than some brief MVFR lower ceilings from area cumulus field.
Otherwise expect convection to wind down around 17/01-02Z or so.
Winds are from the west-southwest around 6-10kts & will wind down
after sunset. Expect more IFR ceilings & brief MVFR visibilities
overnight at all TAF sites. These will move in the area around
17/09-10Z or so & lift by mid-morning around 17/14-15Z before more
scattered convection is possible again tomorrow./DC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       74  93  75  91 /  22  20  25  48
Meridian      74  93  75  90 /  26  18  14  49
Vicksburg     74  92  75  91 /  22  25  31  50
Hattiesburg   72  93  75  92 /  27  18   7  54
Natchez       73  91  75  90 /  25  24  16  48
Greenville    75  91  75  91 /  18  35  28  31
Greenwood     76  91  74  90 /  23  33  30  28

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Heat Advisory from 9 AM to 7 PM CDT Thursday for MSZ018-019-025-
     027-034>036-040>043-047>049-053>055-059>062.

LA...Heat Advisory from 9 AM to 7 PM CDT Thursday for LAZ007>009-015-
     016-023>026.

AR...Heat Advisory from 9 AM to 7 PM CDT Thursday for ARZ074-075.

&&

10/DC

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