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fxus64 kjan 292343 aaa 
afdjan

Area forecast discussion...updated
National Weather Service Jackson MS
643 PM CDT Sat Apr 29 2017

Update...
updated for 00z aviation discussion

&&

Aviation...
00z taf discussion:
a very unsettled weather regime will setup for aviation interests
during this period. Scattered to numerous showers and
thunderstorms increasing from the west will lead to variable
flight rule categories, especially during the daytime Sunday.
Otherwise, abundant deep moisture will keep multi-layered cloud
cover in the forecast through the period. Shortly after 30/00z,
boundary layer cooling will result in MVFR ceilings quickly
increasing from the south once again tonight. The tight pressure
gradient will keep winds gusty with sustained winds of 15 to 20
knots and gusts around 30 knots./26/

&&

Discussion...

Today through tonight....

Temperatures continue to be well above their average late April
averages this afternoon noon as warm, moist tropical air continues
to filter into the region. Southerly winds have remained strong and
gusty throughout the day as surface pressure gradients have remained
tight ahead of an approaching deep upper level low that has begun to
make its trek across the plains.

An upper level shortwave rotating around the southeastern periphery
of the aforementioned deep upper low, has resulted in the
development of some severe thunderstorms over north central
Louisiana. Convective thunderstorms associated with this disturbance
will continue to move NE towards the arklamiss. With an unstable
airmass in place over the region, coupled with ample amounts of deep
layer shear, these storms could maintain their intensity and more
storms could form as the disturbance approaches the region. Even
though latest high res guidance keeps these storms west of most of
the Jan cwa, the best chances of storms will exist in eastern
Louisiana and southeast Arkansas. Main threats with storms this
afternoon and evening will be hail and wind. A tornado can't be
ruled out.

Non thunderstorm winds will remain high through at least midnight as
the tight gradient remains over the region, even tightening a bit
over the westernmost counties and parishes. The Wind Advisory
will be extended through 1am to account for these strong southerly
winds.

During the early morning hours, the attention will begin to center
on an approaching linear convective system associated with the deep
upper low as it begins to eject northward. Although all modes of
severe weather will be possible as this line of storms begins to
progress through the region, severe winds and flash flooding look to
be the most significant threats. Forecast soundings depict near
and above record pw's and substantial amounts of elevated
instability as this system advances. This should lead to intense
convective showers and storms producing high rates of rainfall as
the line advances across the region resulting in flash flooding
and even river/stream flooding as water levels could quickly rise.
A Flash Flood Watch has been issued beginning at 4am Sunday
morning. The threats associated with this line of storms will
slowly move eastward throughout the day tomorrow./Jpm3/

Sunday through next week...

A rather complex forecast continues to unfold this weekend. Gusty
southerly winds continue to pump anomalous moisture into the region.
Strong moisture transport will lead to record precipitable water
values for this time of year around 2.1-2.3 inches during the day
Sunday across the region. Ample instability will be present in the
atmosphere given such warm conditions in place. All of this will
combine with our next approaching weather system to bring the
potential for flooding and severe weather on Sunday. The overall
synoptic pattern depicts a large upper trough swinging east across
the Southern Plains today and Sunday. As this does, a surface low
will develop and intensify and track northeast across the mid-
Mississippi Valley region. As this occurs a squall line looks to be
on our doorstep in my western counties and parishes by daybreak
sunday(if not a little before). This line will progress east across
the region through the day, exiting the eastern part of the state
during the evening ahead of a cold front.

The primary concern with this weather system will be torrential
downpours and resultant flooding. Models continue to show widespread
2 to 3 inches of rain in our soupy, tropical airmass. However, given
the efficient nature of this rainfall, despite some of the more
progressive nature of the linear complex, there is potential for
some spots to receive multiple rounds of rain and some localized
higher amounts of 4 to 6 inches. Hi-res model guidance shows
additional storm development ahead of the front across areas east of
I-55, which could mean a few rounds of storms for these areas. Flash
flooding issues, as well as river flooding issues, are possible
during the day tomorrow. Given this, have continued to mention an
elevated risk in the severe weather potential statement and graphics and a Flash Flood Watch has
been issued for the entire area. Locations along and west of I-55
have an earlier start to the watch given the timing of the expected
line. The eastern area is delayed into the mid morning but given that
hi-res guidance suggests storms will linger into the evening, the
ending time lasts til midnight.

The other concern with this system will be from severe weather.
Given plenty of wind energy in the atmosphere, wind shear is ample
for organized storms as well as tornadoes and damaging winds.
Vertical totals will be around 27-30c which will suggest hail as a
threat as well. Any storm that can take on more of a northeast
motion will also have some potential for mesovortex tornadoes but
otherwise the angle of the 0-3km shear vectors isn't optimal for
such tornadoes. Think the main concern will be from damaging winds
but given the low LCLs and ample shear, tornadoes will also be
possible. As the line moves through, the threat will diminish from
west to east during the day.

The upper low will pull off to the north on Monday, leaving the
region dry and cooler. Highs on Monday will be in the 70s areawide
under broad troughing. Dry, but warmer, weather will continue on
Tuesday before another round of rain and storms enters the area
Wednesday through the rest of the week. This next round of weather
will also hold potential for not just severe storms but also flash
flooding, especially given already saturated grounds. Near 2 inch precipitable water
airmass looks to return, to at least southern locales per the GFS.
It is interesting to note that the GFS hints at the possibility of a
coastal complex for this system which will likely have an impact on
how much moisture and rain impacts out region. The upper trough will
cut off and spin over our area as an upper low. This will spin
across our region through the end of the week, bringing at least
some kind of chance for wraparound moisture and rain to the region.
The good news with this scenario is that it should eliminate 90s
from our temperature forecast for the rest of the week and pleasant,
cooler temperatures should occur in the latter parts of the week.
/28/

&&

Preliminary point temps/pops...
Jackson 72 77 51 76 / 28 99 35 1
Meridian 71 82 54 77 / 16 91 89 1
Vicksburg 71 75 52 77 / 55 100 12 1
Hattiesburg 72 80 54 79 / 62 91 89 1
Natchez 71 73 50 77 / 60 100 14 1
Greenville 71 73 52 75 / 76 100 12 1
Greenwood 72 75 52 74 / 26 100 23 1

&&

Jan watches/warnings/advisories...
MS...Wind Advisory until 7 PM CDT this evening for msz028>033-037>039-
043>046-048>052-054>058-061>066-072>074.

Flash Flood Watch from Sunday morning through Sunday evening for
msz030-031-033-038-039-044>046-050>052-056>058-064>066-
072>074.

Wind Advisory until 1 am CDT Sunday for msz018-019-025>027-
034>036-040>042-047-053-059-060.

Flash Flood Watch from 4 am CDT Sunday through Sunday evening
for msz018-019-025>029-032-034>037-040>043-047>049-053>055-
059>063.

La...Wind Advisory until 1 am CDT Sunday for laz007>009-015-016-
023>026.

Flash Flood Watch from 4 am CDT Sunday through Sunday evening
for laz007>009-015-016-023>026.

Arkansas...Wind Advisory until 1 am CDT Sunday for arz074-075.

Flash Flood Watch from 4 am CDT Sunday through Sunday evening
for arz074-075.

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