Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 042345

Area Forecast Discussion
National Weather Service Jackson MS
545 PM CST Sun Dec 4 2016

Updated for 00Z aviation discussion


00Z TAF discussion:
Widespread MVFR and IFR conditions are occurring this evening, with
some LIFR conditions as well in some of the heavier rain. This is due
to reduced ceilings and some reduced vis. The lowered categories will
continue through the evening and overnight though some of the rain
may taper off overnight. Some improved ceilings have occurred in the
Delta, thanks to the lack of rain. Rain and some storms will move in
again tomorrow with stronger storms possible tomorrow afternoon and
evening, especially affecting TAF sites south of I-20. Poor flying
conditions will continue until the cold front moves through late
Monday into early Tuesday. /28/



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       49  60  52  59 /  69  92  88  14
Meridian      50  62  55  61 /  76  86  92  17
Vicksburg     48  56  51  59 /  62  99  78  12
Hattiesburg   53  66  55  63 /  66  83  81  10
Natchez       49  58  50  60 /  77  97  65   9
Greenville    44  50  48  56 /  32  95  89  13
Greenwood     44  53  49  56 /  35  92  95  19





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