Area Forecast Discussion
Issued by NWS Jackson, MS

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424
FXUS64 KJAN 211731 AAC
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1231 PM CDT Sat Apr 21 2018

.UPDATE...
Updated for 18Z aviation discussion

&&

.AVIATION...
18Z TAF discussion:
VFR conditions prevail across the region this afternoon, but as a
storm system approaches the area tonight, conditions will begin to
deteriorate with ceilings lowering to MVFR and in some areas IFR
range through the remainder of the TAF period. Showers and
thunderstorms will increase early Sunday morning through the
daytime hours, leading to occasional visibility reductions as
well. Southerly winds will be gusty at times especially across
East MS, with some gusts over 25 kt possible beginning overnight.
/DL/

&&

.DISCUSSION...
Mostly sunny conditions prevail across the majority of the area
this morning, though clouds are already on the increase west of
the MS River ahead of the next approaching storm system. Area 88Ds
are picking up some echos in that area, but a look at the ULM
radar suggests little of this is reaching the ground at this
stage, as dewpoints remain in the 40s in most locations. Steady
warm/moist advection will continue through the day, but in the
mean time, the drier conditions will enable us to warm up fairly
quickly. As a result, I nudged up today`s max temps in a few
areas. By late this afternoon, there are hints some light showers
could begin making it into the Delta, but given the antecedent low
level dryness, it is questionable whether this rain would be
measurable. /DL/

Prior discussion below:

Today and tonight:

Shortwave ridging will remain in place today but also slowly move to
the east through the day. This will occur as a trough and closed low
slowly track east across central Oklahoma. Ahead of this, moisture
will continue to return to the region and temperatures will run
warmer today than they did on Friday. Highs should reach into the
middle 70s under sunny skies initially. However, as moisture
increases and the next weather system approaches, clouds will be on
the increase through the afternoon and cloudy skies will prevail
tonight. The bulk of the rain is likely to hold off until late
tonight, but some showers will move in across the west through the
evening. As the upper low tracks east, a surface low looks to
develop and move north through Arkansas. After midnight, a broken
line of storms will move into my western counties and parishes.
There will be a limited risk for flooding as 1-2 inches of rain will
be possible with this line as it moves through. Given cloud cover
and rain, overnight lows will be mild in the upper 50s and lower
60s. /28/

Tomorrow (Sunday) through next Friday:

Expect an active start to the forecast period by the end of the
weekend on Sunday. Expect the synoptic pattern to consist of a
closed upper low & negatively tilted trough diving through Arkansas
and the lower Mississippi Valley. In addition, very favorable lift
and upper divergence/diffluence due to favorable front left entrance
region of nearly 70kt & 100kt jet (500mb and 300mb, respectively)
will be over the area. This will help a strong compact low pressure
system and warm front to continue to lift to the east-northeast
through the region. Due to strong height falls and increasing low-
mid level moisture (i.e. dewpoints in the low 60s and PWs around an
inch and a half which is around 90th percentile) expect widespread
showers and thunderstorm development, especially along the warm
front, baroclinic zone and deformation area right near the surface
low tracking through the ArkLaMiss Delta. This will continue Sunday
morning and progress east-northeast through the afternoon. Due to
some potential of any training convection and some recent heavy
rainfall within the last week, kept the "Limited" area for heavy
rain and flash flooding highlighted in the HWO/graphics areawide
as this propagates to the east. Overall 1-2" with locally higher
amounts are possible, potentially at most in the 3-4" range like
some CAM model solutions. Right now there isn`t enough confidence
on a better area for any higher swaths, so will keep the "Limited"
highlighted for now.

There will a better severe weather potential going into Sunday as
models have slowed slightly, keeping most of the rain and storm
chances more confined into Sunday and less in the overnight period.
Due to the slower movement, expect increasing moisture return along
and ahead of the lifting warm front. CAM guidance show various
solutions but there is potential for better destabilization due to
any storms being confined more into Sunday. Due to surface low
deepening over the ArkLaMiss Delta, expect low-mid level wind fields
to strengthen (~30-50kts effective bulk shear) and starting out
with clockwise curving hodographs. CAM guidance, such as the ARW,
show a decent potential for QLCS propagating east-northeastward
across the area. This would make sense as the Corfidi vectors
today in newer runs have more push to them. With them stronger and
0-3km bulk shear vectors oriented from the west-southwest
~30-35kts, this may help an organized QLCS to move across the
area. Regardless, any convective line or isolated storm has
potential to become strong to severe in this environment. If a
QLCS develops, any northeast surge would likely have the best
potential to take hold of any localized higher helicity levels
(~150-200 m2/s2) and bring potential for mesovortex tornadoes,
mainly before the wind field veers into the afternoon. CIPS
analogs seems to be hitting on the severe potential with
increasing probs of severe storms and CWASP has increased, with
the northernmost gradient along the I-20 corridor. Right now it
continues to look favorable for potential for damaging winds, some
hail, maybe up to quarter size (especially in any afternoon
convection that can linger) and a tornado or two are possible.
Continued the "Marginal" in the HWO/graphics but after coordination
with SPC, this area was expanded northwest towards I-55 and along
and southeast of the Natchez Trace corridor. There still remains
some uncertainty on any coastal convection as the Euro/GFS show
that solution but seeing less indications of it being far enough
east to limit moisture return. Continued to stay alert and check
back on later forecasts for updates.

As the upper low dives down early next week, expect northerly flow
and cold air advection to keep clouds locked in. This will lead to a
a drearier day Monday. With lingering low-level boundary layer
moisture, some light rain & drizzle is possible early next week
(Monday- Tuesday). Can`t rule temperatures possibly being even
cooler than advertised due to this setup but for now, consensus
seems pretty close for highs. Lows will be warmer due to
widespread clouds lingering through the area. Guidance seems to
keep our area locked in a somewhat wet pattern, albeit light QPF,
before a brief & weak shortwave ridging drying somewhat in mid-
week. Due to model uncertainties, kept PoPs slightly lower than
guidance. Expect a series of troughs in northwest flow mid-late
next week to bring a couple of weak fronts and few chances for
light drizzle & rain showers both mid-week and late week (Wednesday-
Friday). This could keep some clouds around and high temperatures
slightly below normals through the end of next week. /DC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       76  60  73  55 /  10  55  98  32
Meridian      76  58  72  56 /   5  33  92  54
Vicksburg     77  60  73  55 /   9  99  95  15
Hattiesburg   76  61  74  56 /  12  33  93  44
Natchez       75  62  74  55 /   4  99  89  11
Greenville    76  59  70  55 /  17  99  97  24
Greenwood     76  58  70  55 /  10  66 100  34

&&

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

&&


$$

DL/28/DC



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