Area Forecast Discussion
Issued by NWS Jackson, MS

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881
FXUS64 KJAN 170232
AFDJAN

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

.UPDATE...
Updated for evening discussion.

&&

.DISCUSSION...

The POPs have been shaped up for this evening update, mainly
focused a few showers to the east--near I-20 AL/MS border. Within
an hour everyone should be drying out across ARKLAMS region.

The latest run of the HRRR and the CONSShort is throwing in some
patchy fog down near Hwy 84 and Hwy 98. With clearing skies down
near the coast as dry air starts to seep in, low level moisture
from afternoon rain showers, & light winds, I expect a few
isolated areas to get a bit foggy. /12/


Prior discussion below:

Quick update for early evening...convection has been progressive
and has evolved in a manner where the main storm activity is
across east-central MS here to start the Tonight period. The
remainder of the forecast area is seeing lingering light rain due
to convective debris fallout from prev storms. The PoP forecast
was updated to show these trends here for early evening then have
values lower for the remainder of the night. Thunder wording was
drastically lower as well and only focused for a short period
across east-central. Temps were also lower to match the rain
cooled trends. Overnight lows were not changed. Graphics were
removed as late afternoon threats for heat/flooding have
diminished. /CME/

Prev discussion Thursday:


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...
00Z TAF discussion:
Afternoon convection is dissipating across most of the forecast
area with the exception being MEI where a solid TSRA is occurring.
Look for a brief period of IFR restrictions at MEI due to the
storm with improving conditions by 0020z or 0030z to VFR. The
remainder of the area will see the lingering -RA convective debris
but remain in VFR conditions. Much of the overnight period will be
VFR. However, low level flow and moist conditions will support
stratus developing by 10-11z across the NW and N half. A few of
the central/southern sites may see that as well, but it may start
later and occur in the 12-14z window. Overall, Thursday looks less
active for precip/storms with the NW sites having the better
chances during the afternoon. Surface winds may also be a tad
breezy across the north half as well. /CME/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       73  93  75  91 /  36  20  25  48
Meridian      73  93  75  90 /  60  18  14  49
Vicksburg     73  92  75  91 /  22  25  31  50
Hattiesburg   71  93  75  92 /  33  18   7  54
Natchez       72  91  75  90 /  23  24  16  48
Greenville    74  91  75  91 /  19  35  28  31
Greenwood     74  91  74  90 /  31  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.


&&


$$

12



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