Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 030027

Area Forecast Discussion
National Weather Service Shreveport LA
627 PM CST Fri Dec 2 2016

For the ArkLaTex, increasing clouds with virga for a few hrs. Sfc
winds are E and extend to 5kft 10-15kts...veering to SE/S/SW at
10kts by 10kft, then increasing in speed 25-90KTS for flight
levels. Meanwhile, the low levels are very dry and will saturate
from the top down overnight giving way to daybreak MVFR trending
to IFR/VLIFR by this time on Sat and overnight with in/out rain.
May see a break off from this pineapple connection, but the upper
storm is digging S along Baja and will be overhead here at 05/00z.


.PREV DISCUSSION... /issued 412 PM CST Fri Dec 2 2016/

The elevated cloud cover continues to thicken across the region
this afternoon...with the mosaic radar imagery indicating areas of
-RA developing/rapidly spreading NE across Cntrl and SE TX as well
as Srn LA...well ahead of the developing closed low still digging
S into Nrn Baja. Some of this -RA is reaching the ground per
regional sfc obs...with the short term progs still in good
agreement with isentropic forcing along the 305-310K surfaces
quickly spreading NE into the region this evening/overnight...with
the current air mass gradually expect to saturate from the top
down supporting light QPF amounts overnight. Low level moisture
advection will also increase significantly late across SE and Deep
E TX/SW a 35-45kt Srly LLJ develops near and N of an
inverted sfc trough that will develop tonight just inland of the
SE TX coast...before advancing NNE into the Lower Toledo Bend
region by daybreak Saturday. Given this...have increased pops
tonight to high end categorical across E TX/Wrn and the Srn
sections of N LA...with this sfc trough expected to become
oriented across Deep E TX Ncntrl LA Saturday. Overrunning will
only increase after 12Z Saturday atop and N of this trough over E
TX near/S of I-20...much of N LA and possibly extreme Srn
AR...tapping a prolonged episode of moderate to at times locally
heavy rainfall over these areas. Given the abnormally high PW/s
near 1.5 inches and strong convergence near this sfc and attendant
H850 trough...have added locally heavy rainfall wording to these
areas Saturday...with the sfc trough expected to gradually begin
shifting SE back into SE TX/Cntrl LA by late Saturday night in
response to sfc pressure rises that should build SE ahead of sfc
ridging building SE into KS/OK. Overrunning atop the sfc trough
should gradually weaken as well Saturday night as this trough
shifts SE...thus tapering the heavy rainfall threat with time.
However...did extend the heavy rainfall wording in the forecast
for Deep E TX/Ncntrl LA Saturday night before dropping mention

QPF amounts should range from 1-3 inches through late Saturday
night...with isolated higher amounts up to 5 inches possible.
Since the FFG values remain high and antecedent soil moisture
conditions remain dry...have held off on a Flash Flood Watch as
these areas should be able to take this initial round of heavy
rainfall. Rainfall rates should diminish Sunday as dry slotting
aloft begins to entrain E into extreme NE TX/SE OK/SW AR
Sunday...and subsidence associated with low level height rises
begins to spill SE. Still could see more organized rains persist
along/ahead of the attendant H850 trough over Deep E TX/Srn
sections of Ncntrl LA...but this diminish with time as the trough
weakens during the afternoon.

The medium range progs remain in good agreement with the
aforementioned closed low over Nrn Baja this afternoon drifting E
across Nrn old MX this weekend before ejecting NE across the Big
Bend region across TX Monday. The progs are in better agreement
with sfc cyclogenesis developing along the retreating sfc trough
Sunday night just off of the middle TX coast...lifting NE into SW
and Cntrl LA/Wcntrl MS Monday. This would maintain the warm sector
just SSE of the region...although any more NW shift in this warm
sector/warm front may result in at least an isolated SVR threat
across the SE sections of Ncntrl LA Monday afternoon given the
strengthening shear/broad diffluence aloft ahead of the
approaching trough. May have to consider a Flash Flood Watch for
portions of the region Monday after the impacts/rainfall amounts
are known from the Saturday/Saturday night rain event...before dry
slotting aloft quickly spreads E into the region Monday event
just ahead of the trough. Total event QPF/s of 1-2 inches are
expected across NE TX/SE OK/SW AR...with amounts of 4-6 inches
with isolated higher amounts in excess of 7 inches are possible
mainly across lower E TX/N LA.

Near seasonal temps should return to the region Tuesday and
Wednesday as we begin to dry out...before colder/arctic air begins
to build S Wednesday night and Thursday as longwave troughing
dives SE across the Rockies and into the Plains/MS Valley. H850
temps of -5 to -10C should spill S into the region within this
post-frontal air mass...with the ECMWF still consistent in
developing sct -SHRA just ahead of the trough/front Wednesday
afternoon/night. The GFS and even Canadian remain mostly dry...but
have left low chance pops in the forecast but regardless...QPF
amounts should be light with the moisture clearing the region
ahead of the arctic air mass. A dry NW flow aloft will continue
through the end of the week resulting in dry conditions and
abnormally cold conditions with the coldest temps so far this late
fall season expected.

Prelims to follow below...


PREV DISCUSSION... /issued 1140 AM CST Fri Dec 2 2016/

VFR conditions to prevail through today and into the overnight
hours. However, cloud cover will continue to increase from sw to
ne throughout the pd, and cigs will gradually lower as well. Rain
will begin late this evening and continue to increase in coverage
and intensity, as it spreads from sw to ne. Flight categories will
deteriorate as cigs/vsbys lower and rain intensifies during the
latter half of the 18Z TAF pd. Otherwise, light e to sely winds
will gradually back to a more e to nely direction, with speeds
generally around 6-12 kts. /12/


SHV  48  49  48  50 / 100 100 100  80
MLU  47  49  48  51 /  80 100 100  90
DEQ  44  46  45  52 /  70 100  60  30
TXK  45  48  45  50 /  80 100  70  60
ELD  45  47  46  49 /  80 100 100  80
TYR  48  49  47  51 / 100 100  90  70
GGG  48  49  47  50 / 100 100 100  70
LFK  49  52  50  53 / 100 100 100  90




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