Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 030002 AAA
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
602 PM CST Fri Dec 2 2016

.UPDATE...
Updated for 00Z aviation discussion

&&

.AVIATION...
00Z TAF discussion:
VFR conditions will prevail at all TAF sites through the region as
mid-high clouds gradually increase across the area. Light rain will
begin to move in tonight affecting most TAF sites beginning after
03/12-15Z near GLH/GWO/HKS/JAN and later in eastern TAF sites.
Widespread MVFR ceilings are possible at most TAF sites after
03/18-20Z. Some ceilings could fall to IFR briefly in areas in the
west, towards GLH/GWO, where increasing rain Saturday may lower
flight categories. /DC/

&&

.DISCUSSION...
Tonight and Saturday, a wet weekend is shaping up for our CWA.
Despite the mostly sunny skies and dry conditions across the area
this afternoon, rain chances will begin to increase from the
southwest this evening. Mid afternoon surface analysis had a 1025mb
high centered over the mid Mississippi river valley resulting in a
dry northeast to east wind over our CWA. This high will strengthen
as it shifts a little east through Saturday limiting return flow.
However, water vapor imagery/RAP analysis showed a closed low
dropping south across southwest Arizona toward the Baja region. The
diffluent flow east of this feature was drawing a decent plume of
moisture across the southern plains this afternoon. As the closed
low shifts southeast over Mexico through Saturday that plume of
moisture will shift our way and lead to rain development.
Measurable rain looks to fall over the western portions of our CWA
before midnight tonight then continue to spread east and increase in
intensity over our CWA through Saturday. The heaviest rainfall of an
inch or two through Saturday afternoon is expected over our
northwest zones where WPC has highlighted this area in a Day 2
slight risk for excessive rainfall. Although this area received
beneficial rainfall earlier this week, drought conditions continue
and considering the expected low rainfall rates, we will continue to
hold off on mention of a flood threat in the HWO for Saturday. /22/

Saturday Night through Thursday

Per previous discussion the 12z models continue to indicate that the
next system to affect the region will come in two parts. The first
part will be waves of rainfall followed by some severe potential for
Monday afternoon and evening.

During the weekend a closed low will close off over Baja from an
upper trough extending from the northern Rockies to the western
Mexico. This will result in a strong upper jet providing good
divergence over the CWA.  It will also result in strong warm
advection with isentropic lift which will which bring the rain
across the region. The baroclinic zone will remain well south at the
coast. Models shows that this rainfall will come across as waves
which will add up to some heavy rainfall amounts of up to around
four to locally five inches in the delta region of northeast
Louisiana, northwest Mississippi and southeast Arkansas. WPC has put
our area in a slight risk of excessive rainfall on day 3. Anomalous
pwats of around 1.8 inches will be a factor and a strong low level
jet. So with a series of waves coming in southwest flow do not see
any major flash flooding issues with rainfall accumulating over a
period of time from Saturday night through Monday night. Since
moderate to occasionally heavy rainfall rates will be hard to pin
down during that time period for flash flooding, will hold off in
mentioning any flooding potential in the HWO with the antecedent
surface conditions and the good state of the rivers. There will be
some elevated instability for some occasional thunder for Saturday
night through Sunday night.

For Monday into Monday night the closed low will track northeastward
through the Southern Plains and become a negatively tilted shortwave
across the CWA. We will be in the right rear quad of the upper jet
which will bring more upper divergence. Given increasing shear and
significant height falls/steepening lapse rates, thunderstorms are
expected and some severe storms will be possible in the south. The
best midlevel heights look to be in the southeast. On the surface the
warm sector may have a hard time pushing north against all that rain
taking place. Models are sort of split on the issue. So have adjusted
the limited risk from around KHEZ to KMEI area.

For the rest of the period the system will quickly move out of the
region on Tuesday. Weak high pressure will build into the region
from the west. This will be followed by a mostly dry cold front per
GFS on Wednesday. The Euro slows this trough down long enough to
gather some gulf moisture for a chance of rain along the frontal
boundary. So will continue the previous shift compromise between the
two models. Models and ensembles agree that a cold airmass will push
into the region as we move into next weekend./17/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       44  55  49  57 /  34  92  76  86
Meridian      41  53  47  57 /  12  81  71  86
Vicksburg     44  54  49  54 /  50  95  82  88
Hattiesburg   46  56  51  65 /  22  64  56  75
Natchez       45  54  51  57 /  68  96  72  87
Greenville    43  52  46  51 /  32  93  91  86
Greenwood     41  54  46  52 /  19  89  89  87

&&

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

&&


$$

DC/22/17



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