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Area forecast discussion 
National Weather Service Jackson MS
1019 am CST Thursday Mar 5 2015

Update...

Infrared satellite data show inflection with approaching shortwave
trough now moving into western la. Extrapolation takes it to the
MS/Alabama border by around 21z. Lift associated with the trough is
enhancing precipitation along the baroclinic zone from central/NE la
across SW/central/NE portions of MS. This is occurring as cold
advection has pushed the freezing line southeast to a Brookhaven to
Forest to Philadelphia to Macon line. Recent hrrr guidance is
handling situation well and suggests the freezing line will push a
little farther southeast as we go through the late morning before
stabilizing this afternoon. It has heavier quantitative precipitation forecast late this morning with
lighter precipitation lingering through early to middle
afternoon...diminishing as the previously mentioned wave passes
across and much drier air surges in.

The precipitation type has been a big challenge with a big middle level
warm nose in the 12z kjan sounding (+11 degree c) that brought complete
melting...above a substantial cold layer (-4.5 and ~4000 feet deep)
which apparently was enough for complete refreezing as sleet fell at
about the time of the radiosonde observation. Since then...the freezing rain has mostly
transitioned to MDT/heavy sleet over most of the area northwest of the
freezing line. We assume there is still a narrow zone of freezing
rain...but this seems to be less of an issue now.

The current winter weather warning/advisory alignment is still OK but
will keep a close eye on further progression of the freezing line as
precipitation is forecast to linger over the Pine belt region through late
afternoon. Latest sref guidance keeps freezing rain probs just northwest of
the Hattiesburg area...and the sref has performed well having hit
sleet probs hard several days ago. Will make updates to the near
term forecast based on the latest hrrr guidance...mainly to adjust
temperatures and add some precipitation into the late afternoon over the southeast. Will
also place more emphasis on sleet with a changeover to light snow as
the atmospheric column cools further over northwest portions of the
arklamiss. /Ec/

Aviation...MVFR flight categories continue to be observed at taf
sites across the area this morning as a result of low ceilings
heights. A mix bag of precipitation...mainly that in the form of a
sleet and light snow mix...is also being observed at namely
khks...kjan...and kgtr. At kglh and kgwo...precipitation is coming
to an end. There will be a brief window at kmei...from 17z-20z
today...of a light freezing rain and sleet mix...but little
accumulation is expected. Precipitation type at khbg will remain
rain as temperatures hover in the upper 30s.

Any sites that indeed experience any wintry precipitation could see
a light icing on aircraft and other metal and elevated surfaces.
Again...this is and/or will be the case at all sites except khbg
where frozen precipitation is not expected. This activity is
currently expected to come to and end by 21z this afternoon.
However tonight and Friday morning...with lows falling into the
teens and 20s...any residual or standing water on aircraft...
runways...tarmacs...and ramps will freeze.

Winds today will be breezy from the north around 15 knots...gusting
at times around 25 knots. Winds will remain northerly overnight...
but will subside a bit and range between 7-10 knots. /19/

&&

Previous discussion... /issued 439 am CST Thursday Mar 5 2015/

Winter storm ongoing for portions of the region...

Short term...today through Friday night...at 4 am the freezing line
at the surface has sunk down to just northwest of the Natchez trace
corridor and this freezing line will continue to steadily advance
southeast through the remainder of the morning hours. Aloft the meat
of the upper level trough is starting to swing into the lower MS
valley presently with an impressive right entrance region of a
screaming high level jet streak helping to focus lift in our region.
Precipitation has a somewhat convective look right now across the
northwest two-thirds of the region with areas northwest of the
Natchez trace reporting mostly sleet. A focused band of moderate to
heavy precipitation is setting up back to our southwest and looks to move
across the Natchez trace corridor over the next 2-4 hours. Some
thunder occurring in this precipitation band (and even elsewhere) gives
confidence of locally heavy precipitation which will be mostly wintry
considering dropping temperatures.

Taking mesoscale evolutions into account we have decided to expand
the Winter Storm Warning a bit further into The Heart of central MS
and expand the Winter Weather Advisory a bit further into south central
MS. We will take a last look at things before daybreak and make
minor adjustments to warnings and advisories if necessary. One thing
to point out is that while sleet has been rather ubiquitous so
far this morning in the northwestern portion of the region the
potential for freezing rain will increase toward The Heart of
forecast area owing to slightly warmer temperatures aloft. That
said...most areas outside of far southeastern MS should see some of
combination of sleet and freezing rain this morning with more sleet
north of I-20 and more freezing rain south of I-20.

Precipitation really looks to be tapering off pretty quickly from
late morning through early afternoon and it is possible portions of
the advisory and warning in effect through 3 PM may be able to be
cancelled early. Despite ending precipitation later today the only chance
at sun should be in the extreme northwest arklamiss Delta zones with
temperatures this afternoon struggling to get out of the low to middle
30s in most areas. Clearing skies tonight will set the stage for
decent rad cooling late tonight after todays strong north winds
gradually die down. Remaining ice pack in northwestern zones will
help with cooling and allow for lows in the teens in northwestern
zones and well down in the 20s most other areas. Some record lows
will likely fall. Still looks like wind chills in the single digits
will be possible in the arklamiss Delta tonight and the coming day
shift will have to consider issuing a Wind Chill Advisory.

Friday will feature lots of sun and somewhat warmer
temperatures...but highs will remain way below normal with modifying
Arctic high pressure parked right overhead. This high pressure ridge
will be situation to bring rather perfect rad cooling conditions
after Sundown with plummeting temperatures and lows once again way below
normal. /Bb/

Long term...Saturday through Thursday...for the weekend surface
high pressure will be over the region on Saturday while the upper
flow becomes west southwesterly. Daily highs in the weekend will
push into mainly the 50s. Clouds will increase over the weekend as
the southern stream upper jet becomes more active with a series of
shortwaves that will move through the region during the period. The
Euro... Gem models had some differences with area precipitation
coverage associated with the short waves. The first one will bring
some rain to the region for Saturday night into Monday. A little
stronger short wave will bring more rain to the region for Tuesday
through Thursday. This active pattern will continue over the region
into next weekend. Expect a warming trend for the upcoming work
week. As highs GOES from the 50s to the 60s. This will bring
afternoon highs closer to normal for this time of the year. By the
time we get to Thursday it will be Spring like with highs pushing
toward the 70 degree mark in the south. Lows will gradually rise to
the 50s by Wednesday night. /17/

&&

Jan watches/warnings/advisories...
MS...Winter Weather Advisory until 3 PM CST this afternoon for msz039-
045-046-049>051-054-055-059>062.

Winter Storm Warning until 3 PM CST this afternoon for
msz029>033-036>038-042>044-047-048-053.

Winter Storm Warning until noon CST today for msz018-019-025>028-
034-035-040-041.

La...Winter Weather Advisory until 3 PM CST this afternoon for laz024-
026.

Winter Storm Warning until 3 PM CST this afternoon for laz016-
023-025.

Winter Storm Warning until noon CST today for laz007>009-015.

Arkansas...Winter Storm Warning until noon CST today for arz074-075.

&&

$$

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