Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 050541 AAB

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1141 PM CST Sun Dec 4 2016

Updated for 06Z aviation discussion


06Z TAF discussion:
Widespread IFR and LIFR conditions are anticipated throughout the TAF
period. Currently, low stratus encompass much of the area. -RA is
ongoing at SE terminals, though most of the area is seeing a break in
the rain. Rain coverage with embedded TS is expected to increase
significantly around and shortly after daybreak, with ceilings
remaining low through the day. A few severe storms are possible
Monday late afternoon and evening mainly over the southeast half of
the area with the potential for a 50 kt wind gust or tornado. /DL/


The inverted sfc trough and associated forcing and isentropic ascent
responsible for the first round of rain this weekend has gradually
pulled away from the region today. This allowed for the best rainfall
to be in the SE half of the CWA. Isentropic decsent has overspread
the NW portion of the CWA and has thus kept any sfc precip limited to
drizzle over the last few hours. There will be a brief lull in precip
through 6z as the current SW to NE oriented band of rain pulls out
and the next round of precip moves in. A strong shortwave trough
over Mexico will move NE towards the area overnight as upper level
divergence associated with the entrance region of a stout upper jet
overspreads the area. Thus, when combined with renewed isentropic
ascent and forcing will allow for precip to ramp up from SW to NE
through 9z with widespread rainfall expected across much of the area
by 12z. Areas of patchy fog also can`t be ruled across the region
overnight. Otherwise, as we head into tomorrow afternoon anamolous
PWs and enhanced WAA and moisture flux convergence ahead of a
developing sfc low will lead to a limited flash flood potential
across the area. In addition to the flash flooding potential, some
degree of severe weather is still expected late tomorrow afternoon
into the evening hours. Stay tuned and check back tomorrow morning
for the latest forecast package update regarding both threats. /TW/

Prior discussion below:

Tonight through Monday night,

Forecast thinking is generally the same with thunderstorms and the
potential for heavy rainfall to develop over the ArkLaMiss ahead of
a strong shortwave trough as we go through Monday into Monday
evening. Increasing low level flow beneath the entrance region of an
impressive upper jet should increase isentropic ascent and
associated light/moderate rain later tonight, especially over
southern portions of the area. Greater warm advection and moisture
flux ahead of a developing surface low will increase convective
instability and should allow for more intense rainfall rates by
Monday afternoon as precipitable water values rise an anomalous 1.75
inches, impressive for December. Given the soaking rainfall over
much of the area this weekend, a limited threat flash flooding still
looks reasonable in the HWO.

The biggest uncertainty concerns the severe weather threat as
boundary layer (BL) moisture return is much in question. Very rich
marine layer moisture with dewpoint temperatures in the mid 70s is
located just off the coast. This moisture is forecast by most
guidance to remain confined to near the coast, but there are
indications that we could see at least mid 60 dewpoints reach the
Pine Belt region tomorrow evening, and given the strong wind shear
and sufficient convective instability, we could see a greater severe
weather threat evolve there. For now, will keep the limited threat
going in concert with SPC and the bulk of guidance, but will need to
be wary of trends as we move into the near term.  In the least,
still expect some threat for damaging wind gusts up the
Jackson/Meridian corridor given such a shallow stable BL that
wouldn`t be impossible for more intense downdraft winds to
penetrate. In addition, 0-3km shear values/orientation look
sufficient for mesovortex generation if storms become more organized
late in the afternoon and evening along a NNW-SSE oriented line of
forcing. Guidance consensus indicate the severe/heavy rain threats
will late Monday night over southeast MS. Otherwise, cloudy
conditions with little range in temperature will be the general rule
in the near term. /EC/

Tuesday through next weekend...
Rain will begin to exit the region early Tuesday as the responsible
upper level disturbance exits to the northeast. Temperatures will be
near their seasonal averages on Tuesday and Wednesday as the upper
jet remains just north of the region. By late Wednesday, a cold
front associated with an upper trough crossing the Central U.S. will
being to approach the region. Models have come into better agreement
on the timing and precip associated with the front as it traverses
the ArkLaMiss. Precip chances will begin to increase from west to
east late Wednesday night. This fast progressing front will be well
east of the region by Thursday evening. However, before the moisture
associated with the front has the chance to exit, a deep cold arctic
airmass will begin to filter into the region. This could result in a
few snow flurries on the back end of the precip as it exits,
especially in the northernmost counties of the ArkLaMiss. At this
point, no accumulations or impacts are expected with any wintry
precip on Thursday.
Much cooler temperatures will exist behind the front as a cold dry
continental airmass with origins in the polar region of the
northern hemisphere filters into the central and eastern US.
Temperatures on Friday and Saturday mornings will fall into the
upper teens to lower 20`s, 12-18 degrees below average. PGF due to a
strong surface high building into the region will result in
increased winds on Friday night, thus resulting in wind chills in
the mid to lower teens Friday morning. Highs on Friday will be
nearly 20 degrees below average, struggling to reach 40 degrees. By
Saturday morning the center of surface high will be closer to the
ArkLaMiss allowing for prime radiational cooling conditions to set
up. Temperatures will begin to rebound on Saturday as upper flow
becomes zonal and low level flow becomes southerly as the surface
high pushes to the east. Long term models agree on a slow moving
frontal system approaching the region late next weekend.


Jackson       48  60  52  59 /  51  92  88  14
Meridian      49  62  55  61 /  72  87  92  17
Vicksburg     47  56  51  59 /  61  99  78  12
Hattiesburg   53  66  55  63 /  73  83  81  10
Natchez       49  58  50  60 /  64  97  65   9
Greenville    44  50  48  56 /   7  95  89  13
Greenwood     44  53  49  56 /  12  92  95  19





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