Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 181103
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
503 AM CST Wed Jan 18 2017

.DISCUSSION...
Today and Tonight:

A combination of low clouds and fog will start off the day for most
locations in the forecast area today, thanks to moisture pooling
along a stalled frontal boundary. Some fog could be dense,
especially in low lying areas and near water through southern
portions of Mississippi and Louisiana. Fog and low clouds should
burn off and lift by the afternoon, allowing for temperatures to
warm back into the mid 70s for locations south of Interstate 20.
Looking at the synoptic situation, a deepening cutoff low will lift
from New Mexico towards Kansas today while a ridge persists over the
eastern CONUS. In response, a surface low will develop over East
Texas and lift our stalled frontal boundary north as a warm front by
this evening. Flow aloft will become increasingly meridional by
tonight, slowing the eastward push of an approaching cold front.

As warm, moist air is lifted east of the low pressure system, we
should see an increase in shower activity this afternoon into
tonight. PWAT values will increase to around 1.5 inches, which is
near the climatological max for mid-January. MUCAPE values near 500
J/kg with a saturated profile suggest steady moderate to heavy
rainfall will be possible as showers tap into this rich moisture
supply. Some thunder could mix in. It currently looks like the
greatest potential for any heavy rain in the overnight period will
be focused through northeast Louisiana and southeast Arkansas, near
the 850 mb jet axis and greatest instability. Will hold off on any
mention of flooding potential in the Hazardous Weather Outlook for
now, since those areas are running behind normal precip over the last
month or so. /NF/

Thursday through Tuesday,

It will continue to feel more like late March or early April than
mid January in the ArkLaMiss late this week into the weekend.
Anomalously warm and stormy weather will be the general rule as
strong Pacific jet energy interacts with unseasonably moist and
unstable airmass surging northward into our region. The most
impactful weather will center on Thursday, when there will be a
limited threat for flooding and severe weather, and this weekend
when there will be the potential for a more significant severe
threat.

The threat for heavy convective rainfall will shift east across the
forecast area Thursday with increasing deep layer shear and
instability supporting organized thunderstorm activity and the
possibility for a few strong to severe storms, mainly during the
morning for the Delta region and for areas farther east during the
afternoon. Forecasted low to mid level shear would be supportive of
mesovortex generation with any line segments, but the widespread
nature of clouds/precip will help to limit instability and the
overall severe threat. With precipitable water > 1.5 inches and
strongest low level moisture convergence anchoring over the area for
several hours, localized flooding concerns still look like a
reasonable possibility, and will continue to mention both this and
the severe threat in the HWO graphics. Have left the entire area
under these threats for now, but we should be able to focus them a
bit more in future outlooks as CAM guidance becomes more definitive.
The trough axis will sweep activity quickly east of the area late
Thursday bringing an end to the thunderstorm potential. Expect
another break in the action Friday into Friday night before things
pick up again late Friday night.

Global models continue to indicate that a more significant threat
for severe weather could evolve Saturday, but the very fast flow
associated with the southward displaced Pacific jet stream is making
it difficult to iron out specific details concerning convective
evolution. What we do know now is that strong low level warm
advection should begin late Friday night over southern portions of
the ArkLaMiss, and there is a trend now for convection to develop
even more quickly, before the airmass can destabilize to extreme
values.

The trend is also for a more pronounced elevated mixed layer and cap
in the wake of the early morning convection Saturday resulting in
very steep lapse rates > 8 deg C/km and mixed layer CAPE > 2000
j/kg, extreme values for January. Along with strong deep layer
shear, there is little doubt that the environment will be supportive
of significant severe weather...but the big question continues to
center on how much deep convection there will be given the capping
and low confidence in forcing mechanisms. Moreover, with height
falls spreading more quickly along the Gulf Coast, the severe threat
is beginning to shift almost entirely east of the ArkLaMiss by
Sunday morning. With the erratic QPF patterns suggestive of
supercell potential in what may be a volatile environment, will
continue to encourage close monitoring of the outlook for the entire
weekend, but we may be able to focus the threat more squarely on
from late Friday night through Saturday while leaving out Sunday if
the latest trends continue.

Looking ahead to early next week, with the upper low closing off as
it moves across the ArkLaMiss, expect cooler and showery conditions
to be the general rule before things dry out. /EC/

&&

.AVIATION...
06Z TAF discussion:

It is a tricky aviation forecast for the next 24 hours, as low clouds
and fog will be a concern along and south of a frontal boundary that
has stalled across the forecast area. Highest chances for FG will be
at KHBG through about 16Z to 17Z Wednesday. All other sites will
likely see at least some development of IFR to LIFR ceilings this
morning as low-level moisture pools along the front. Expect low
ceilings to erode and break up by around 18Z for these sites except
at KGLH and KGWO, where a greater likelihood of showers and
thunderstorms throughout the day will keep low ceilings in the
forecast. /NF/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       74  64  69  56 /  24  51  92  46
Meridian      73  63  70  57 /  12  27  83  72
Vicksburg     70  65  69  55 /  50  70  94  30
Hattiesburg   76  65  71  57 /  12  27  79  63
Natchez       76  67  69  57 /  41  68  94  28
Greenville    60  59  66  53 /  61  79  94  30
Greenwood     65  61  69  55 /  34  65  92  44

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Dense Fog Advisory until 10 AM CST this morning for MSZ056>058-
     061>066-072>074.

LA...None.
AR...None.

&&


$$

NF/EC



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