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FXUS64 KJAN 181200 AAA
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
600 AM CST Fri Jan 18 2019

.UPDATE...
Updated for 12Z aviation discussion

&&

.AVIATION...
12Z TAF discussion:
With the exception of GLH where MVFR conds were observed at 1130Z,
widespread LIFR conds have developed across the area. Vsbys wl be
slow to improve but should be 6SM or greater by 16Z. However, IFR
cigs are not expected to improve to MVFR until mid afternoon. Cigs
wl decrease to IFR again this evng and southerly winds wl increase
and become gusty in the west ahead of an approaching low pressure
system. TSRA/SHRA activity wl increase over GLH and GWO Friday
evng then spread across the remainder of the area through Saturday
morning. /22/

&&

.DISCUSSION...
Today and tonight: Foggy this morning then a few severe storms will
be possible later tonight. Early morning surface analysis had a
nearly stationary cold front across the Delta region; from just west
of Greenwood, Mississippi to just south of Winnsboro, Louisiana.
Areas of dense fog have formed along and just south of the front.
This front is expected to stall and become nearly diffuse this
morning. A Dense Fog Advisory is in effect until 9 AM this morning
and has been expanded to include the area southeast of a line from
Bastrop, Louisiana to Greenwood, Mississippi. The fog is expected to
dissipate by mid morning but, plenty of clouds look to linger
through the day. Weak induced mid level ridging, downstream of a
shortwave that will deepen a trough going into the weekend, will
move over our CWA today while our surface winds gradually increase
from the south this afternoon into the evening. This will lead to
warmer than normal temperatures despite the foggy start and
lingering cloud cover. Afternoon highs will range form the lower 60s
north to the upper 60s south.

Models have continued to trend faster with the next storm system to
affect our CWA, including the potential for severe storms. As the
deepening upper level trough moves over the Southern Plains tonight,
a surface low will lift northeast across the Ozarks and to near the
Missouri bootheel by sunrise Saturday. Strengthening WAA this
evening ahead of the approaching system will work to increase
moisture back into our CWA. Although coverage of rainfall will
increase from the west through the evening, the potential for severe
storms is expected to occur after midnight in our western most zones
and shift as far as the Natchez Trace by sunrise. By midnight, lower
60F surface dew points and PWATs in excess of an inch and a third
are expected back across the northwest half of our CWA. The
environment looks to feature MLCAPE 500-700j/kg with 50-60kts of
deep layer shear including 50-55kt 850mb winds. Damaging wind gusts
will be the primary threat but a brief tornado or two cannot be
ruled out. Locally heavy rainfall will also occur with the strongest
storms but flash flooding is not currently anticipated. /22/

This weekend through late next week (Saturday through next Thursday):

Saturday: Expect storms to be ongoing across the ArkLaMiss Delta.
This is in response to a deep trough & polar jet digging through the
southern Plains & ArkLaTex, leading to strong forcing & height falls
across the area. Low-level moisture response will help dewpoints
climb to around 60-62 degrees & strong mid-deep layer wind fields to
respond (i.e. ~50-85kts+ @ 850mb & 500mb, respectively) & strong
shear (i.e. 0-3km & 0-6km bulk shear ~55-70kts). This is conjunction
with a strong surface low moving through Arkansas & somewhat
clockwise to gradually veering hodographs. Due to this, there
remains potential for severe storms, especially east of the
Mississippi River. Expect these storms to be near to just east of
the Mississippi River by daybreak, I-55 corridor around mid-morning
& moving through the Highway 45 corridor around early afternoon
(i.e. 2-4PM or so). Right now, there remains potential for some
isolated to scattered severe storms. This looks to be a combination
of broken QLCS/supercell structures, with some potential for
damaging winds & some tornadoes. Any bowing northeast segment of any
QLCS/LEWP structure will bring tornado potential. Due to that, SPC
increased the risk to "Slight" for areas east of the Mississippi
River & we brought the "Marginal" back over the Delta due to any
earlier storms in the morning. This will be adjusted in the graphics
& HWO. There remains some potential for some heavy downpours with a
quick 1-2+ inches or so, but with rivers on the way down & being
fairly progressive, held off any mention on anything for flash
flooding for now, as we should be able to handle some. In addition,
with such strong low-level winds, with such strong low-level flow,
there will be gradient wind potential. Right now, going to hold off
any mention but something to keep an eye on.

Sunday-Monday: As the trough swings through, expect the strong cold
front to quickly progress eastward, & mostly through the area by
Saturday evening. This will help quickly drive out the moisture &
rain chances. However, some residual low-level moisture may remain,
even with the global models struggling to handle how much. The best
deformation axis & snow band will remain well off to our north.
However, based on forecast soundings & cold air advection (CAA) over
the snowpack to the north, a mix of light rain transitioning to some
light snow flurries/grains & possibly freezing drizzle look possible
into Sunday morning. This will be possible Saturday evening but
mainly near or after midnight & lingering across the Highway 82
corridor through early Sunday morning. Expect this moisture to
gradually pull out into Sunday morning with temperatures falling
near or below freezing across most of the area. There will remain a
continued much colder than normal pattern late weekend & early next
week (i.e. Sunday-Monday) with CAA over snowpack to the north &
anomalously cold thermal profiles. With strong high pressure
settling in, expect good radiational cooling & temperatures falling
well into the mid-upper 20s Monday morning. Wind chills could also
fall into the low 20s to teens in the north as well but hard freeze
conditions are not expected.

Tuesday-Thursday: Expect moderating conditions with some rain
chances through mid-week as mid-level ridging & warming build into
the region. Expect rain chances to move back in on Tuesday-
Wednesday, with no destabilization for any thunder at this time.
There remains uncertainty but some new guidance, including the Euro,
shows some potential for some lagging southern stream energy &
precip to overrun some colder air Wednesday & into Thursday morning.
This typically isn't the best setup for winter weather. However, the
current colder, slower & suppressed southern stream trends in the
global consensus & continued indications in ensembles do bring some
potential. Right now not going to mention winter weather, but if
this trend continues, will be something to watch. Due to the
discrepancies, not going to cut highs just yet, but if this trend
continues, will need to cut highs around mid-week on Wednesday. Due
to the slower trend, kept some rain chances in through daybreak
Thursday. /DC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson 66 58 63 32 / 4 92 89 19
Meridian 63 56 66 33 / 4 75 93 16
Vicksburg 67 58 62 32 / 9 92 74 12
Hattiesburg 69 59 65 34 / 4 65 93 11
Natchez 68 59 61 32 / 11 92 76 8
Greenville 62 56 59 30 / 8 93 65 14
Greenwood 64 56 62 30 / 5 92 80 25

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Dense Fog Advisory until 9 AM CST this morning for MSZ025>033-
035>066-072>074.

LA...Dense Fog Advisory until 9 AM CST this morning for LAZ007>009-
015-016-023>026.

AR...None.

&&


$$

22/DC
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