Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 051732
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
1132 AM CST Mon Dec 5 2016

.UPDATE...
Updated for 18Z aviation discussion

&&

.AVIATION...
18Z TAF discussion:
Widespread IFR/LIFR conditions continue across all TAF sites this
morning. Mostly showers are moving across the area with some
embedded thunderstorms activity. These conditions will continue
through much of the period, with a few severe thunderstorms possible
mainly at MEI/HBG this evening. The heavier rains will end from west
to east overnight, but expect the MVFR/IFR conditions to continue
through the end of the period.

&&

.DISCUSSION...
Today/Tonight: An extensive stratus deck overlies most of the CWA
this morning. Though there has been a recess in the rain overnight,
showers are already beginning to fill back in across Louisiana as a
surface low spins up over the northwestern Gulf Coast. Upper
divergence will increase through the day as an upper jet streak
begins to shift eastward across the Ohio Valley and a shortwave
upper trough pivots toward the Lower MS Valley. In response, an
upper low over northern Mexico will eject eastward across the Deep
South as a strong disturbance and the coastal surface low will track
directly across the CWA overnight, deepening as it does so.

Showers are expected to quickly expand across the area through this
morning. The ongoing widespread stratus along with increasing
widespread rain and cool easterly surface flow will notably limit
diurnal heating today. MOS highs were undercut in most areas, except
for the southeast where the warm sector may surge far enough
northward by late afternoon. Embedded thunder will be possible
through the day as elevated instability increases. Surface vectors
will slowly veer toward the SE as the surface low approaches, but
forecast soundings indicate a shallow stable layer will persist
through the afternoon. This makes sense as most CAM guidance
signifies widespread rain to reinforce such conditions. 0-3 SRH will
increase during the afternoon time frame, but effective SRH will
remain near zero, so it`s possible by this afternoon there could be
elevated rotating storms mainly down around the Pine Belt.

By this evening, the low will track northeastward from the MissLou
area into northern MS. It is not until this time frame that surface
flow will become more southerly (east of the low track) and
increasingly warm/moist air will begin to surge into the area. As a
result, some areas in E/SE Mississippi will become warmer this
evening than they were during the day. It will take some time for
this flow to erode the low level stable layer. By the time it does
happen across S/E Mississippi (forecast soundings suggest after 3Z
in most areas), helicity will be on the decrease as the better upper
dynamics pull away from the area. Still there is potential for
severe storms, with damaging wind gusts as the primary concern. We
still cannot rule out a tornado or two given the impressive shear
that will accompany the system. Only minor tweaks will be made to
the limited severe threat in our graphics/HWO, mainly to focus
things more for this evening/tonight.

Over the past two days, rainfall totals across the area ranged from
around a half inch in the eastern part of the area to over 2" across
parts of the Delta. Another widespread 1" to 2" is expected today
and tonight, with locally higher amounts possible with convection.
Even with the recent rainfall, most of our CWA should be able to
handle these amounts. Localized flooding will be possible in areas
that receive higher-end amounts, and we will continue to advertise a
limited flooding threat across the area through tonight. /DL/

Tuesday through Sunday: Much colder temperatures still look in store
by the end of the week. Come Tuesday morning the light rain will
finally be ending from the southwest as the upper level disturbance
shifts east of our CWA. On its heals, a cold front associated with a
northern stream low over the upper Mississippi river valley will be
approaching our northwest zones. This dry cold front will drop into
the Highway 82 corridor and stall Tuesday evening as our winds aloft
back to the southwest in response to a deepening trough over the
western CONUS. A few models try to develop light precipitation along
the stalled front Wednesday but, model consensus is dry. The
deepening upper level trough will send a second cold front into our
CWA Wednesday evening that will push south of our area before noon
Thursday. The ECMWF generates some qpf with this front but lack of
moisture return and convergence along the front will limit
precipitation development as model consensus is mostly dry. However,
have accounted for the ECMWF and gone above guidance pops to carry
mention of rain. The main affect of this cold front will be to usher
in much colder and drier air. Highs will be held in the 40s at most
locations Thursday with a breezy north wind. The center of the cold
airmass, a 1040mb high will become centered over the central plains
by Friday morning. This will bring us some of the coldest
temperatures so far this season with morning lows in the low to mid
20s. Normal lows run in the upper 30s. The large surface high will
shift east across our CWA Friday becoming centered over the southern
Appalachians by Saturday morning. Coldest temperatures will be over
east Mississippi where lows will again be in the lower 20 with mid to
upper 20 west. The surface high will continue shifting east Saturday
resulting in return flow back across our region. Zonal flow aloft
Saturday will back slightly Sunday ahead of an approaching more
subtle shortwave. The GFS and ECMWF are is good agreement that rain
chances will return to the northwest half of our area Sunday ahead of
a weak surface low that will develop in response to the shortwave.
/22/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       57  51  59  41 / 100 100  14   7
Meridian      60  56  60  41 / 100 100  18   5
Vicksburg     54  50  58  40 / 100  94  12   8
Hattiesburg   65  56  63  44 / 100  82  13   4
Natchez       57  51  58  44 / 100  76  11   7
Greenville    49  48  57  41 /  89  95  16   9
Greenwood     52  49  57  39 /  98 100  23   9

&&

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

&&


$$

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