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000 
FXUS64 KJAN 091103 AAA
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
503 AM CST Mon Dec 9 2019

.UPDATE...
Updated for 12Z aviation discussion

&&

.AVIATION...
12Z TAF discussion: 
Variable IFR/MVFR conditions early this morning will become
predominantly MVFR by mid morning and VFR this afternoon into the
early evening. Isolated showers will begin developing by late 
morning with more widespread rainfall developing during the 
evening and continuing through the end of the period as a cold 
front enters the region from the northwest. Just ahead and behind 
the front, IFR/MVFR conditions will develop during the evening and
overspread the area overnight with the southward movement of the 
front./GG/

&&

.DISCUSSION...
Through tonight: WV imagery this morning showing our next weather 
maker in the form of a mid level wave dropping south through 
southern CA into northwestern Mexico. In advance, a large swath of 
moisture has been tapped from west of Baja and is being funneled 
northeastward across the southern CONUS in increasingly southwest 
mid level flow. Already, mid/high level cloudiness has built into 
the region.

At the surface, high pressure remains centered off the east coast 
while a shallow cold front approaches the MS valley from the Plains. 
The tightening pressure gradient ahead of the boundary will allow 
low level winds to increase today, especially over the open areas of 
the ArkLaMiss Delta. As the southwest flow aloft continues and low 
level winds increase today, moisture levels will increase steadily 
in the column, enough so for showers to be possible by late 
morning/afternoon over the south and west. 

Coverage of showers will increase from the northwest tonight as 
convergence along the frontal boundary encounters increasing low 
level moisture. Some thunder looks possible over the south where 
model soundings are indicating 300-500 J/kg of skinny CAPE ahead of 
the boundary. With the mid level energy moving into the region after 
midnight, backing winds aloft will allow widespread isentropic rains 
to break out, especially overtop the passing boundary./GG/

Tuesday Night through Sunday: Really the only period of interest 
for the remainder of the week will be Tuesday into Tuesday night 
as the anticipated shortwave trough swings east over our region 
and a colder post-frontal air mass seeps in from the northwest. 
With the right entrance region of the upper-level jet positioned 
overhead into Wednesday night, frontogenesis through the mid-
levels should continue to support precipitation falling behind the
cold front. Drier air will gradually work in aloft and at the 
surface as the trough axis moves eastward, but there may be enough
of a window for a wintry mix to develop in the cooling air mass.

Looking at forecast soundings especially across northern Mississippi 
and southeast Arkansas, the column will be awfully close to the 
tipping point between all rain and all snow, with precipitation 
rates being increased due to dynamics aloft. Given the uncertainties 
of just how much of a warm layer will remain aloft, and if low-level 
temps can chill to near freezing, weather type has been set at a mix 
of rain or snow mixing into areas generally around the US Highway 82 
corridor and northwards. Have also included a light accumulation of 
snow up to around one quarter of an inch in those areas, but warmer 
ground temperatures and the likelihood of standing puddles, etc. 
before any kind of transition can occur will probably limit much if 
any accumulation. Will also include a "Limited" threat area for 
winter weather to the Hazardous Weather Outlook text and graphics 
for this potential. For areas to the south of this zone, a little 
light wintry mix cannot be ruled out as precip tapers off Tuesday 
night, but confidence in a change over is much lower to include in 
the weather grids at this time.

The rest of the forecast is relatively low key, with a gradual 
warming trend ahead of the next shortwave trough passage over the 
weekend. A chance for showers will return to parts of the forecast 
area Friday into Saturday as this system passes, but at this time do 
not anticipate thunderstorms or winter weather to be of any concern 
for the weekend. /NF/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       73  50  53  35 /  29  89 100  96 
Meridian      72  55  63  36 /  18  75 100  99 
Vicksburg     76  47  50  34 /  26  89 100  84 
Hattiesburg   74  60  69  40 /  20  60  98  98 
Natchez       76  52  54  36 /  28  89 100  93 
Greenville    72  41  43  30 /  21  84 100  55 
Greenwood     71  44  45  30 /  21  88 100  73 

&&

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

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