Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 042151

Area Forecast Discussion
National Weather Service Shreveport LA
351 PM CST Sun Dec 4 2016

The areas of -RA continue to gradually erode this afternoon across
Deep E TX and the Srn sections of Ncntrl LA...indicative of the drier
mid and upper level dry air that has been able to entrain ESE ahead of
the shortwave now traversing the MS Valley. This should be short-lived
however as the H850 trough remains progged to pull up stationary this
evening in VC of the I-20 corridor of E TX/N LA...before slowly
beginning to lift back N to the I-30 corridor by daybreak Monday.
Meanwhile...the closed low over Wrn MX will continue to drift E
overnight...nearing or just W of the TX Big Bend Region by 12Z. Upper
diffluence ahead of the closed low will result in convection gradually
expanding NE into E TX/N LA late tonight...with the HRRR/Canadian
more aggressive in the SHRA expansion than the GFS/ECMWF. Have ignored
the 12Z run of the NAM once this model continues to suggest
wedging of dry air aloft much farther S across SE TX/N LA
Monday...thus focusing the heavier QPF over NE TX/SE OK/SW AR. Temps
once again tonight will not drop much more than the current
temps...although weak cold advection and the potential for brief
lifting of the stratus cigs across SE OK/adjacent SW AR may result in
colder temps before the cigs lower once again Monday. Have toned pops
down this evening to slight chance/chance along/S of the I-20 corridor
near and S of the H850 trough...before ramping pops back up to
likely/categorical after 06Z and the SHRA development expands NNE. Did
taper pops down to slight and low chance for extreme NE TX/Srn AR
after 06Z...before raising pops to high end categorical areawide

The afternoon sfc analysis depicts an inverted sfc trough over the NW
Gulf S of the LA coast before crossing Plaquemines Parish...with sfc
cyclogenesis expected to commence late tonight along this trough just
off the Middle TX Coast before lifting NE into S LA Monday
afternoon/evening. The GFS has trended about 6 hours slower than
earlier runs with the sfc low ejection...and prefer the ECMWF/Canadian
handling instead with the low tracking NE across Acadiana into SE
LA/SW and Cntrl MS late in the day/evening. This consensus would keep
the warm sector SE of the region...and also would maintain the best
forcing for locally heavy rainfall just S of the area as well. Still
could see additional rainfall totals of 0.50-1.50 inches with isolated
higher amounts across portions of Deep E TX across much of N LA
Monday...but given the placement of the sfc trough much farther S than
Saturday...and the fact that overrunning will be weaker in addition
to dry air aloft entraining NE ahead of the closed low Monday
afternoon...believe that the relatively high FFG values and hourly
rain rates will not be significant enough to warrant the issuance of a
Flash Flood Watch for these areas attm. However...can/t rule out
localized flash flooding and minor flooding of low lying....poor
drainage areas before this threat diminished from W to E Monday

The convection should diminish from SW to NE Monday evening...but
wrap-around low stratus will likely persist overnight through much of
Tuesday which should limit the extent of warming at least over the Nrn
half of the region. The progs continue to advertise longwave troughing
that will swing E across the Rockies into the Plains Wednesday...which
will usher the coldest temps so far this fall season behind an arctic
cold front that will quickly spill SE into the area Wednesday
night/Thursday morning. The ECMWF remains persistent /albeit a tad
slower/ with sct SHRA developing Wednesday afternoon mainly across E
TX/Wrn LA/SW AR...before quickly expanding E across the remainder of
the region Wednesday night. Have increased pops to mid chance
Wednesday night for the Ern half of the area...before much drier air
behind the front tapers the SHRA from W to E late. Afterwards...temps
will struggle to climb into the 40s Thursday afternoon under brisk NW
winds...with a widespread and long duration freeze expected areawide
Thursday night. In fact...temps may fall into the teens across SE
OK/adjacent SW AR with lower and mid 20s a good bet elsewhere.

This air mass will be slow to modify Friday with another freeze
expected Friday night...but temps should begin to gradually moderate
next weekend with a return srly low level flow. Can/t rule out
isolated -SHRA developing with the increasing low level theta-e
advection...but QPF amounts...much like Wednesday night/s
event...should be light.

Prelims to follow below...



.PREV DISCUSSION... /issued 1209 PM CST Sun Dec 4 2016/

For the 04/18z TAFs, IFR and patchy LIFR conditions persist across
the area along with patchy drizzle between Interstates 20 and 30.
The next major round of rainfall is moving northeast into the area
from the Interstate 10 corridor. The rain will likely increase in
coverage and intensity, but most of the precip should be south of
Interstate 20. Precip will likely diminish tonight, but yet
another round of rain will move into the area before sunrise as a
surface low lifts northeast across Texas and into Arkansas. This
final round of precip should affect all TAF sites and will persist
through the end of the period. Flight conditions will continue to
fluctuate and vary between MVFR and IFR, with isolated instances
of LIFR. Wind speeds will generally remain around 10 kts or less.



SHV  48  50  47  57 /  60 100  50  10
MLU  47  52  49  57 /  60 100  60  10
DEQ  42  49  43  54 /  10  90  70  10
TXK  44  48  44  56 /  30 100  70  10
ELD  45  49  45  55 /  30 100  70  10
TYR  46  50  46  57 /  60 100  50   5
GGG  47  50  46  57 /  60 100  50   5
LFK  48  53  47  63 /  90 100  30   5




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