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171
FXUS64 KSHV 161446
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
946 AM CDT Wed Aug 16 2017

.UPDATE...
Scattered showers noted just northwest of McCurtain county and
across southern LA are associated with upper air troughs across
the Central Plains and southeast LA/Gulf of Mexico respectively.
The aforementioned shower activity activity at this time is
struggling to maintain its intensity, as radar analysis showed
light echoes moving across Deep East TX but quickly diminishing.
However, the onset of daytime mixing later this morning/early aftn
will aid in additional development impinging on portions of
southeast OK, southwest AR, deep East TX and central LA, with
perhaps isolated convection affecting northwest LA. Have therefore
inserted slight chance POPs across Deep East TX, and chance POPs
across portions of southeast OK for the 12-18Z period. Otherwise,
forecast is largely on track with the spatial extent of the
precipitation diminishing after sunset, though a nearby frontal
boundary may


&&

.PREV DISCUSSION... /issued 645 AM CDT Wed Aug 16 2017/

AVIATION...
For the 16/12z TAFs, low stratus has developed across much of
Louisiana and Southern Arkansas and into some portions of East
Texas. These clouds have led to MVFR/IFR conditions, and even
some instances of LIFR conditions, at area terminals this
morning. Ceilings will be slow to lift, but all TAF sites should
improve back into the VFR range by 16/17z. Southwesterly surface
winds will also increase in speed to between 10 and 15 kts with
gusts near 20 kts during the daytime hours. Isolated to widely
scattered convection will be possible in two areas...along and
north of Interstate 30 and southeast of a line from KLFK to KELD.
KMLU is the TAF site most likely to be affected by showers and
storms this period. Wind speeds should diminish slightly after
sunset. However, the strong southerly flow will continue to stream
Gulf moisture northward, which will likely result in more
MVFR/IFR ceilings after 17/06z.

/09/

PREV DISCUSSION... /issued 512 AM CDT Wed Aug 16 2017/

DISCUSSION...
The GOES-R 12.3-10.4um imagery indicates extensive bands of low
stratus developing across E TX and much of N LA/Scntrl and SE AR,
along a 20-30kts Swrly low level jet that extends across much of
the Srn Plains and lower MS Valley. Meanwhile, the water vapor
imagery depicts a H500-300 low over the Srn Gulf, with its
attendant inverted trough extending NE into extreme SE LA/Srn MS
and AL. The short term progs have initialized on the associated
H500 shear axis over SE LA, with sct convection just beginning to
fire over the SE LA coast and its adjacent coastal waters, which
will set the stage for more sct convection that will develop by
mid to late morning over S LA as the H500-300 trough slowly
retrogrades W, with the steering winds on the wrn periphery of the
H850-500 ridge guiding this convection NE across the Srn and Ern
sections of Ncntrl LA and lower Toledo Bend Country of Deep E TX,
as was the case Tuesday afternoon. Have maintained low to mid
chance pops for these areas for the afternoon, with possibly a few
rogue -TSRA possible over NW LA into Scntrl AR. With the presence
of the mid level ridge well to our E over the Cntrl Gulf coast,
believe that max temps should be similar to what was observed
Tuesday, with readings in the lower to mid 90s. The main question
is the extent of mixing that will occur today, as dewpoints mixed
out a little better than anticipated Tuesday. The short term progs
do suggest that dewpoints may not mix out quite as well today
than Tuesday afternoon, although the slightly tighter pressure
gradient may yield a little better mixing. After coordinating with
adjacent WFO`s, have decided to hold off on the issuance of a Heat
Advisory as conditions may still be marginal, and will allow later
shifts to re-evaluate.

Meanwhile, isolated convection can`t be ruled out today mainly
over SE OK, in VC of a H700-500 theta-e axis over Wcntrl and N
TX/Cntrl and Ern OK, extending ahead of the upper trough noted
over Cntrl CO. The convection over the SE zones this afternoon is
expected to diminish by early evening with the loss of heating,
with the aforementioned Cntrl CO trough expected to traverse E
into the Plains this afternoon and evening, where it will
reinforce a weak sfc front SE into W TX/Wcntrl OK/SE KS. Sct
convection is expected to fire near the frontal zone late this
afternoon/evening where it will shift SE into extreme N TX/SE
OK/Wrn AR late tonight. Have continued mention of low to mid
chance pops late tonight NW of the I-30 corridor, with the
convection expected to diminish Thursday morning as the SWrly LLJ
veers and weakens. The sfc front remains progged to drift SE into
extreme SE OK/Scntrl AR Thursday afternoon/evening before becoming
stationary Friday morning from extreme Ern OK into Srn AR/Ncntrl
MS. To our SE, the mid level ridge will begin to deepen and
amplify Thursday across much of the Gulf coast from SE TX to the
FL Panhandle, with increased subsidence resulting in an increase
in max temps especially S of I-20. Mixing may be more limited
Thursday, which would result heat indices possibly exceeding
advisory criteria over more of E TX/N LA.

The next upper trough remains progged to drop SE across the
Plains/MS Valley Friday, which should interact with the stalled
front just to our NE and yield sct convection during peak heating
over all but the far Wrn and SW sections of E TX. Thus, have
continued mention of mid chance pops for much of the region, with
the upper troughing carving into the ridge and allowing it to
retrograde further W and flatten across TX/Srn LA. Additional
impulses in the NW flow aloft should continue to yield mainly
diurnal sct convection over the Ern 2/3rds of the area this
weekend, with max temps remaining near climo. Both the GFS/ECMWF
suggest a weak upper low/inverted trough aloft drifting W across
the Gulf early next week, which would act to enhance widely sct
convection from Deep E TX across Ncntrl LA through the end of the
extended (through at least midweek).

Prelims to follow below...

15

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  94  78  95  77 /  20  10  20  20
MLU  93  76  94  76 /  40  20  20  20
DEQ  91  75  90  74 /  20  40  40  20
TXK  93  77  92  76 /  20  20  40  20
ELD  93  76  93  76 /  20  10  30  20
TYR  94  78  94  77 /  10  10  20  20
GGG  94  78  94  77 /  20  10  20  20
LFK  95  77  95  76 /  20  10  20  10

&&

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

$$

29/09/15