Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 161120
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
520 AM CST Tue Jan 16 2018

...ACCUMULATING SNOW THIS MORNING THROUGH LATE EVENING, DANGEROUS
COLD THROUGH MIDWEEK...

.DISCUSSION...

Today:

Arctic front is racing through the region, bringing increasingly
cold air and wintry precipitation quickly filtering into the Delta
area. Expect this pattern to only continue as cold air advection
(CAA) quickly overtakes the moisture ascent in the wake of the cold
front. The synoptic pattern consists of a deep longwave trough
digging through the central portions of the nation, mainly along and
east of the Rockies. This is helping to drive this arctic cold front
& anomalously strong 1045-1050mb surface high currently over the
northern to central Plains. This strong ridging extends well south
into ArkLaTex and ArkLaMiss, keeping cold air advection locked in.
On the northern side of the cold front, moisture ascent & favorable
jet dynamics in the right entrance region, in addition to nearly a
half inch to three quarters of an inch PWs, is helping light snow be
developing across the Delta region. The back side of the subsidence
in the wake of the cold front is moving into south-central Arkansas.
Overall, we are continuing to expect as the trough digs to the south
and isentropic/moisture ascent continues, moisture will quickly
begin to fill in from northwest to southeast through the day. For
the most part, temperatures will be falling into the afternoon in
the 20s while really only in Interstate 59 corridor where
temperatures could reach above freezing. Due to this, most of the
area should begin to develop as light snow & stay that way
throughout the event. Local ULM sounding to our west shows that any
limiting issues in the mid-levels (snow growth region ~ -12 to -18
deg C) is not as much of a problem as the forecast soundings were
indicating, which would have held down totals. Kept the official
forecast mostly all snow as it first shortwave progresses across,
while areas in the southeast could have a trend towards light
rain/sleet prior to changing over to snow, mainly in the Pine Belt.
However, wet-bulbing and evaporational cooling, due to CAA, should
help cool the column for all snow across the area by later today.
Expect as the first shortwave moves southeast, the snow band should
slowly weaken somewhat but still should make it into central
portions of the area, especially the I-20 corridor. In addition,
models continue to indicate there could be a secondary shortwave
that could help increased isentropic/moisture ascent and another
light band of snow that could move back over along and southeast of
a line from Natchez to Meridian, MS. Right now this can`t be ruled
out but for now don`t think it would have a significant enough
affect to modify the current thinking. But these trends will have to
be monitored, especially with higher travel impacts due to dry snow
in a sub-freezing environment. Overall this will be a dry snow and
expect ratios to be in the 10-12:1 ratio in central portions of the
area while closer to 15-17:1 ratios in the Delta. This should help
higher accumulations even with limited QPF forecasts (0.05-0.2
inches or so across the region).

Generally, the totals for the system have remained nearly the same,
maybe with a slight uptick in QPF and snow totals across the Delta.
These areas could see 2-3+ inches, maybe locally higher, while along
and northwest of a line from Noxubee to Lawrence County could see up
to a half inch to 2 inches closer to the Natchez Trace Corridor.
Areas southeast of that line could see up to a half inch of snow.
For now, our official forecast doesn`t reflect too much influence
from the secondary wave but if it has enough QPF, could potentially
add another half inch or so across the region. Due to these
adjustments, expanded the Winter Storm Warning to include Grenada &
Carroll County. Also expanded the "significant" area to include more
of the Delta. Rest of the area for the Winter Weather Advisory
remains the same, other than removing the two counties that were
part of the Winter Storm Warning that remains in effect through this
afternoon. With this being a drier snow & temperatures being in the
20s & us being in the 50s yesterday, significant travel impacts are
possible due to the melting & refreezing of the snow. Utility
impacts are much less likely than they were with our December winter
storm. Though they are possible, confidence in travel impacts in the
Pine Belt is lesser than areas to the northwest, unless the
secondary wave overachieves with snowfall early this afternoon.
Regardless, prepare for slick roads & difficult to dangerous travel
across the region.

The timing this remains mostly the same as it should be
in the Delta & Winter Storm Warning area through around noon,
towards the Natchez Trace corridor by daybreak & lasting through
around mid-afternoon (6am-3pm), southeast of Natchez Trace Corridor
from Natchez to Jackson Metro to Golden Triangle around mid-morning
& lasting through through late afternoon (8am-5pm) and southeast
Mississippi in the Highway 84 & I-59 corridors by early afternoon
through late evening (1pm-9pm). Expect the snow to slowly taper off
as we go into the evening as the snow moves off into southeast
Mississippi.

In addition to the snow, wind chills will be widespread in the low
teens to 20s over most of the area (except in the Pine Belt) while
gusty winds in the wake (upwards of 25-30mph in the Delta) could
bring wind chills only reaching the single digits this afternoon.
Due to that, added a "limited" in the HWO for wind chills today and
added a wind chill advisory for this area in the Delta. However,
even more dangerous cold & wind chills are expected tonight across
the entire area, where a Wind Chill Advisory already was in effect.
/DC/

Tonight through the first part of next week:

Still will probably be some light snow ongoing early this evening
across portions of southeastern MS (the Pinebelt) but all snow
should be gone by around 9 pm. Thereafter the big story tonight
will be the continually plummeting temperatures with lows expected
to be well down into the teens by daybreak Wednesday. We still
cannot rule out a few single digit actual air temperatures up
along and north of the Highway 82 corridor. Up in that neck of the
woods wind chill values late tonight should dip at least briefly
below zero in many areas with all locations seeing single digit
wind chills late tonight.

Wind chills may take until late morning on Wednesday to recover
out of the single digits but gradually slackening winds through
the day will help out with the improvement. Sunshine should
prevail through the bulk of the day but the Arctic air mass in
place will hold high temperatures into a range from the upper 20s
to lower 30s along and north of a line from Natchez to Meridian
with highs south of that line maybe sneaking a degree or two above
freezing for only an our or two in the afternoon. As the sun sets
Wednesday evening anticipate calming winds to allow the
temperatures to again plummet thanks to good radiational cooling.
Any snow cover that managed to stick around through the sunshine
Wednesday will only exacerbate quickness of cooling and ultimate
minimum temperatures. For now we expect another night of low
temperatures well down into the teens. If it turns out some
significant patches of snow cover remain into Wednesday night
there may be some single digit lows near that snow.

The brunt of the Arctic air mass will really be moving out
Thursday with some westerly flow above the surface offering
potential for good mixing and warming. However, we are thinking
the cold/frozen ground will work again efficient warming although
temperatures should get comfortably above freezing in the
afternoon (even in the Arklamiss Delta). We inherited a hard
freeze warning expiring in the late morning Thursday and our
forecast does not require an adjustment of that thinking. Despite
the warming trend we still expect a cold (just not quite as cold)
night Thursday night with lows well down into the 20s, especially
across eastern Mississippi.

The warming trend will fortunately continue Friday and into the
weekend as the larger scale pattern changes and trough energy
starts digging through the Four Corners region and into the
Plains. There is a slight chance for some rain showers entering
back into the picture in western zones with southerly flow picking
up Saturday into Saturday night. However, the bulk of big rain (and
even associated thunderstorm) chances will likely hold off until
later Sunday into Sunday night when the aforementioned progressive
trough brings a Pacific-type cold front into the region. There is
non-negligible potential for some heavy rain issues in this time
frame but we will watch it for another day or two to build
confidence before worrying about inclusion in the HWO/graphics.

Following the late weekend fropa the model consensus decreases,
but in all likelihood conditions should dry out for at least a few
days with the air mass coming in the wake of the cold front not at
all of Arctic origin. /BB/

&&

.AVIATION...
06Z TAF discussion:
Cold front has moved through the Delta and towards the I-20
corridor. Some lower ceilings are slowly moving in advance of this
front, with some MVFR ceilings moving into GLH. Expect lowering
ceilings & visibilities to slowly decrease down towards MVFR to
IFR as some light snow moves in overnight, mainly near GLH/GWO
before daybreak (09-12Z), GTR/HKS/JAN by just after daybreak to
mid-morning (13-16Z) and towards MEI/HKS by mid-day/early
afternoon (17-20Z). Expect lower ceilings &/or visibilities with
any areas of light snow. The front will continue south through the
area today, making it out of the area by mid-day, with some gusty
northerly winds around 25-30kts around GLH, while closer to
15-20kts+ further to the east & south. Expect light snow to
gradually taper off from northwest to southeast by mid-afternoon
after 16/18-20Z in the northwest Delta, while areas in the east
and south (MEI & HBG) will be just beginning to have light snow
moving in. These areas light snow & lower ceilings &/or
visibilities could linger into the early evening hours before
conditions improve. /DC/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       29  14  32  15 /  74   7   0   0
Meridian      33  14  33  15 /  64  20   0   0
Vicksburg     29  15  29  14 /  74   4   0   0
Hattiesburg   39  17  36  17 /  37  39   0   0
Natchez       30  15  31  16 /  71   8   0   0
Greenville    23  13  27  15 /  83   0   0   0
Greenwood     25  11  27  13 /  81   0   0   0

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Hard Freeze Warning until noon CST Thursday for MSZ018-019-
     025>057-059>064.

     Winter Weather Advisory until 6 PM CST this evening for
     MSZ028>033-035>050-053-054-059-060.

     Wind Chill Advisory from 6 PM this evening to 10 AM CST
     Wednesday for MSZ026>033-036>039-042>066-072>074.

     Winter Storm Warning until 3 PM CST this afternoon for MSZ018-
     019-025>027-034.

     Hard Freeze Warning from noon today to noon CST Thursday for
     MSZ058-065-066-072>074.

     Winter Weather Advisory from 9 AM this morning to midnight CST
     tonight for MSZ051-052-055>058-061>066-072>074.

     Wind Chill Advisory until 10 AM CST Wednesday for MSZ018-019-025-
     034-035-040-041.

LA...Hard Freeze Warning until noon CST Thursday for LAZ007>009-015-
     016-023>026.

     Winter Weather Advisory until 6 PM CST this evening for LAZ008-
     009-015-016-023>026.

     Wind Chill Advisory from 6 PM this evening to 10 AM CST
     Wednesday for LAZ007-015-016-023>026.

     Winter Storm Warning until 3 PM CST this afternoon for LAZ007.

     Wind Chill Advisory until 10 AM CST Wednesday for LAZ008-009.

AR...Hard Freeze Warning until noon CST Thursday for ARZ074-075.

     Wind Chill Advisory from 6 PM this evening to 10 AM CST
     Wednesday for ARZ074.

     Winter Storm Warning until 3 PM CST this afternoon for ARZ074-
     075.

     Wind Chill Advisory until 10 AM CST Wednesday for ARZ075.

&&

$$

DC/BB


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