Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 012203
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
403 PM CST Thu Dec 1 2016

.DISCUSSION...
Rapid changes will be underway within the next 24 hrs...as deep lyr
moisture begins to increase from the WSW ahead of the upper trough
now diving S along the Srn CA coast. This trough is expected to become
closed off by Friday afternoon as it digs S into the Gulf of
CA...before briefly settling along the Wrn MX coast Saturday night.
Cirrus noted on the visible satellite loop this afternoon over NM/TX
Panhandle will only increase and begin to thicken across the area
after 12-18Z Friday...with an extensive band of cu now over Deep S TX
expected to surge N across the Hill Country Friday afternoon on the
backside of the retreating low level ridge that will build into the SE
CONUS. The short term progs are quite aggressive in developing areas
of -SHRA across the Hill Country into Wcntrl TX Friday afternoon with
the increase in elevated isentropic along the 305-310K
surfaces...possibly advancing NE into the SW sections of E TX late in
the afternoon. Given the very dry low level air mass that will remain
in place...the column will have to saturate from the top down...before
low level moisture advection is able to saturate the lower layers
Friday night/Saturday morning in the strong overrunning regime. Have
added slight chance pops Friday afternoon from the far SW sections of
E TX...and have continued the trend in ramping pops up to categorical
over much of the area Friday night.

The 12Z GFS/ECMWF are in reasonable agreement in developing an
inverted sfc trough along the SE TX/Srn LA coasts Saturday...with the
attendant H850 trough expected to lift N across E TX/N LA. PW/s will
increase to near 1.6+ inches across these areas Saturday...with
embedded shortwave energy in the SWrly flow aloft within this very
moist environment expected to focus the potential for slightly more
enhanced rain rates mainly across lower E TX /S of I-20/ into NW
LA/possibly extreme Srn AR. Elevated lapse rates will remain poor
through much of Saturday...thus have dropped mention of thunder until
H700-500 lapse rates increase to ~6.5C/km across Deep E TX/Cntrl LA
Saturday night.

The inverted sfc trough along the coasts may lift N a tad to near or
just N of the I-10 corridor Sunday...focusing more convection across
the Srn zones by afternoon that areas to our N...where dry slotting
aloft will commence as a shortwave progresses E across the Cntrl
Plains/MS Valley and entrains drier air aloft Ewd. As a result...have
lowered pops down to chance/slight chance along/N of the I-30 corridor
before the await the arrival of the MX closed low as it begins to
eject NE across the Big Bend region by 12Z Monday. This low remains
progged to take on a more negative tilt Monday as it translates NE
across the area by evening...which will induce low level cyclogenesis
along the residual inverted coastal sfc trough along the SE TX coast
before shifting NE across Srn and/or Cntrl LA. The 12Z ECMWF remains
farther S than the GFS with the track of the sfc low/associated warm
front...and thus maintains the best instability well to our S and SE
where strong shear profiles would help support organized severe
convection. This will have to be closely monitored as any NW migration
of this inverted sfc trough would expand the SVR potential farther N
into Ncntrl LA Monday. However...in the meantime...not expecting much
diurnal spread in max/min temps this weekend...with widespread QPF
amounts of 2-4 inches expected with isolated higher amounts nearing 6
inches possible mainly across Lower E TX/N LA. Attm...the rain will
remain spread out in duration this weekend through Monday...with much
of the area able to take the soaking rains given the ongoing dry
conditions still in place. However...autumn leaves and other debris
that has fallen may clog up storm drains and enhance the potential for
localized flooding...especially in low lying...poor drainage areas.

Afterwards...should see arctic air begin to spill S into the Srn
Plains/Lower MS Valley Tuesday night/Wednesday morning...which will
result in possibly the coldest temps so far this fall season by the
end of the week. The ECMWF remains the only medium range model
supporting an increase in convection ahead of this front Wednesday
afternoon/evening...and thus have maintained low chance pops areawide
before the moisture clears the region ahead of the colder air.

Prelims to follow below...

15

&&

.PREV DISCUSSION... /issued 1136 AM CST Thu Dec 1 2016/

AVIATION...
VFR SKC conditions areawide. Cirrus clouds will make a quick
comeback from the west after 02/12z into the area, along with lgt
winds becmg e-se around 5 kts by around 02/15z. For this aftn, ne
TX terminals winds vrbl from e-s around 5-10 kts, while winds
remaining lgt further east over LA/AR. /VII/

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  37  65  47  49 /   0   5  80  90
MLU  32  65  46  50 /   0   0  80  90
DEQ  31  63  43  46 /   0   0  70  90
TXK  36  63  45  48 /   0   0  80  90
ELD  31  63  43  47 /   0   0  70  90
TYR  41  65  47  49 /   0  20  80  90
GGG  38  65  47  49 /   0  10  80  90
LFK  38  67  49  52 /   0  20  80  90

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...None.
LA...None.
OK...None.
TX...None.
&&

$$

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