Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 180215 AAA

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
915 PM CDT Sat Mar 17 2018


Updated for evening discussion.



We had a few relatively potent storms south of the Highway 84
corridor late this afternoon into very early this evening along
a low level convergence zone just north of the coast. Atop this
zone the strong west to east upper jet ensured enough deep layer
wind shear for some storm organization with respectable
temperature lapse rates aloft delivering moderate instability. But
that convection is gone with only a few showers trying to
initiate along this northward-drifting convergence zone in an
environment where instability is decreasing (due to loss of
heating). Meanwhile, out to our west more robust and widespread
showers and thunderstorms are going on west of the Sabine River
where a nearby low pressure system and closer proximity to energy
influx from western trough is providing substantially more
atmospheric lift.

Through the remainder of the night, model consensus is rather good
that the northward lifting convergence zone will eventually get
co-located with a southward sagging "stalled" surface front (now
mostly to our north), especially in western zones. In these
western zones enhanced lift associated with this feature will also
be prone to better instability (mainly elevated above the surface)
and upward motion aloft as minor disturbances approach from out of
the mentioned western trough. The result should be a smattering of
showers and embedded thunderstorms in western zones after
midnight. Small hail cannot be ruled out with some storms late
tonight as shear and most-unstable CAPE is certainly more than
marginal. However, thinking is that overnight activity will not be
rooted at the surface and also not organized enough to warrant a
truly severe threat. Of course we will be watching things closely.
The other, more minor, concern is for patchy (perhaps briefly
dense) fog forming late tonight mainly across southeastern MS.

As for tomorrow, models are trending to show more cool influx near
the surface in northern zones through at least midday as the
mentioned sagging front tries to work toward the I-20 corridor.
Scattered showers and embedded thunderstorms will increase in
coverage over this time period with probably only a marginal risk
for any severe storms in the region through midday (and this risk
mainly south of I-20). The considerably better chances for severe
storms still looks to come in the afternoon to evening hours
tomorrow with the main risks being large hail and damaging winds,
although tornadoes certainly cannot be ruled out. /BB/

Prior discussion below:

Tonight and Sunday: Local radars had scattered thunderstorms
tracking east across our southeast most zones. This activity is
not expected to become severe and will dissipate early this
evening with the loss of daytime heating. Mid afternoon water
vapor imagery and surface analysis had a weakening shortwave
nearing the Ohio River valley and an associated surface low with a
trailing cold front back across the ArkLaTex. This cold front
will drift into our northwest most zones later this evening and
stall close to Highway 82. Model consensus suggests thunderstorms
will develop to our west along this stalling front and track east
toward our CWA. Mostly elevated severe storms capable of hail and
damaging winds may enter our southeast Arkansas counties and
northeast Louisiana Parishes before sunrise. This activity should
spread east of our CWA before noon but afternoon heating will
contribute to additional thunderstorm development. This
development will likely be surface based and capable of producing
damaging winds, large hail and a few tornadoes. In addition,
locally heavy rain will also be possible. Considering the current
river flooding and soil moisture across the area, flash flooding
may also occur. Late Sunday afternoon and evening, a closed low
developing tonight over the Sierra Nevadas will swing east over
the Central Plains and deepen a surface low. The strengthening WAA
in response may help enhance development along the old stalled
front prolonging the severe thunderstorm threat. /22/

Sunday night through Friday...The primary concerns for the period
will be the several rounds of severe weather for Sunday night into
Monday followed by another round of cool temps for the middle of
next week.

At the beginning of the period some strong to severe convection will
be occurring across portions the region as a closed low tracks
across the Southern Plains. A surface boundary will be across the
forecast area. Wind shear fields and instability will be favorable
for severe weather for most of the night. Latest Cam guidance shows
that some of the strongest storms will be across the north where
the better forcing will take place. There was also some discrete
strong cells across the southeast according to the NAM Cam
guidance. Any development at night is going to depend on how the
convective features develop during the day Sunday. Another round
of severe weather will be possible for Monday as the associated
cold front pushes across the region. It looks like the best chance
will be across the east where the best instability will occur
during the afternoon. The latest NAM Cam guidance did not look
very active on this model run. The primary risk for Sunday night
into Monday will be large hail, damaging winds and some tornadoes.
So will split the Sunday to Monday period with two severe
graphics. One for Sunday and Sunday night with the slight risk
graphic and then the slight risk across the northeast graphic for
Monday with the SPC day 3 outlook issued earlier today.

With pwats around 1.5 inches WPC is holding on the the slight risk
for Sunday into Sunday night. So with some of the backwater areas
and some of the rivers being up and moist soil conditions from
recent rainfall, will keep the current flood graphic of 1 to 3
inches for Sunday into Sunday night. WPC has gone down some on the
QPF for our area for Days 1 through 3.

The cold front will exit the region by Monday evening taking out the
strong thunderstorms with it. There may be some lingering isolated
showers in the evening in the wake of the front before they depart.
Another southern stream shortwave will bring some showers on
Tuesday which will exit by Tuesday evening. Cool high pressure will
build across the region for Wednesday into Thursday. This will occur
as we develop an amplified pattern with an upper ridge over the
plains to an upper trough over the eastern seaboard. Northwest flow
aloft will bring some rather cool nights to the region. Lows for
Wednesday and Thursday morning will dip into the middle 30s across
the east, which will cause some frost issues for tender vegetation.
On Friday the upper ridge will move over the Lower Mississippi
Valley with some low level return flow. Temperatures will start to
moderate back into the lower 70s during on Friday./17/


00Z TAF discussion:

Thunderstorms have cleared southeast of the PIB/HBG vicinity and
those stations should be largely dry through the night, although
MVFR to locally IFR ceiling and visibility issues should arise
there after midnight. Elsewhere, expect a few showers and maybe an
embedded thunderstorm to move toward HKS/JAN/GWO/GLH late tonight
into daybreak tomorrow. Those areas will likely also see
conditions trending to predominately MVFR by that time. Much the
same potential for late night MVFR exists around CBM/GTR/NMM/MEI,
although any chances for rain and thunderstorms should hold off
until later in the day tomorrow. By tomorrow afternoon into
tomorrow evening there will be a risk of potent thunderstorms in
the region along a stalled frontal zone running through the heart
of the region. Tonight through tomorrow winds in the vicinity of
this frontal zone will tend to be quite variable at times, and
also light (except near bigger thunderstorms). /BB/


Jackson       62  74  62  82 /  39  73  61  27
Meridian      61  72  61  83 /  11  72  72  41
Vicksburg     61  74  63  81 /  61  73  56  24
Hattiesburg   62  78  64  84 /  16  66  65  31
Natchez       64  77  65  82 /  31  71  48  23
Greenville    55  68  60  76 /  53  72  66  26
Greenwood     55  69  59  77 /  32  66  68  36





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