Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 201451
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
951 AM CDT Thu Jul 20 2017

.UPDATE...
Updated for morning discussion.

&&

.DISCUSSION...
As of 1430z, latest RAP analysis indicates a 597dam ridge centered
over the Central Plains and extending south and east into the
ArkLaMiss. A closed upper low was also located just off the South
Carolina coast and is sliding south and west beneath the
aforementioned ridge along the southeast Coastal Plain. A weak
shortwave trough and associated vort max and potential vorticity
anomaly was noted over central Mississippi. This feature is
helping to support some scattered cloud cover over the northeast
portion of the area this morning. For the remainder of today, the
main headline will be increased heat stress for much of the
ArkLaMiss. Latest obs show quickly warming temps this morning with
dewpoints in the mid to upper 70s over much of the area. Some
members of guidance, especially raw guidance, are too aggressive
mixing out the dewpoints this afternoon compared to obs from
yesterday. Dewpoints remaining in the low to mid 70s and
temperatures climbing into the mid to upper 90s as the ridge
builds in over the area will lead to heat index values of 105-110
degrees over a large portion of the area. As such, the heat
advisory for today was expanded to include all but the far
southeast. While some locations may linger around the 105 degree
heat advisory threshold, the impacts from the heat will still be
present. Otherwise, a few isolated showers and/or thunderstorms
cannot be ruled out at any one location this afternoon with
uncapped tall skinny CAPE profiles, but overall coverage will be
isolated at best due to subsidence from the ridge, thus any
convection that does form should not have any major impacts on
the heat potential. /TW/

Prior discussion below:

Today and Tonight: Mid/upper level ridge will continue to dominate
the weather across the region for the most part today. However,
water vapor imagery and satellite PW are showing a pocket of
moisture over AR into north MS with PWs near 2 inches. Model data
is indicating a weak shortwave associated with this feature which
will drop south southwest around the periphery of the high this
afternoon. Even though raw model dewpoints are too low, GFS BUFR
soundings are still showing some skinny CAPE across the region and
less inhibition than yesterday. So, think there will be some
isolated convection across the forecast area today into early this
evening. The convection that does occur will not be sufficient to
dispel the expected heat. Highest heat indices look to remain
over the ArkLaMiss Delta region again today as upper 90
temperatures and mid 70 dewpoints push values to near 110.
Included another layer of counties to the east in the existing
advisory as criteria looks to be met over a wider area./26/

Friday through Wednesday...The hot conditions will continue on
Friday, but the upper ridge will begin to weaken over the area.
Moisture will also increase on Friday with PWATS around 2.0
inches. Isolated to scattered afternoon convection will keep
temps a little cooler than the previous couple of days, although
areas in the delta may still see heat indices around 105.

The upper ridge will continue weaken across the area on Saturday,
and this combined PWATS ranging from 1.8 to 2.0 inches and afternoon
heating, will allow for another round of thunderstorms. Mid-level
troughing over the eastern conus will allow for a weak boundary to
drop into the area Sunday into Monday, with a continued chance for
diurnal showers and thunderstorms. Models suggest the boundary will
become stationary over the central Mississippi on Tuesday with
showers and thunderstorms possible. Little will change on
Wednesday with a continued chance for isolated to scattered
diurnal thunderstorms, with highs around 90./15/

&&

.AVIATION...
12Z TAF discussion:
Patchy MVFR visibilities in fog will intermittently pass over most
TAF sites this morning, but conditions should improve by 20/14Z.
Thereafter, VFR conditions will prevail with light and variable
winds./26/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       96  76  94  75 /  18  12  37  24
Meridian      96  75  92  74 /  19  19  40  30
Vicksburg     97  75  94  75 /  16   7  26  22
Hattiesburg   96  76  91  74 /  19  12  47  27
Natchez       95  75  91  73 /  17   9  37  26
Greenville    96  77  95  76 /  15   3  13  13
Greenwood     96  77  95  76 /  15   3  21  19

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Heat Advisory until 7 PM CDT this evening for MSZ018-019-025>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.


&&


$$

TW/15/26



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