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Area Forecast Discussion (AFD)

Issued by Shreveport, LA (SHV)

FXUS64 KSHV 202122

Area Forecast Discussion
National Weather Service Shreveport LA
422 PM CDT Tue Aug 20 2019

.SHORT TERM.../Tonight through Wednesday Night/

A weak upper trough drifting west near the mouth of the 
Mississippi River has combined with diurnal instability to 
initiate widely scattered convection across much of the area 
today. For the most part, coverage remains relatively spotty, but 
some of the storms have congealed ahead of an outflow boundary in 
Deep East Texas. No severe weather is expected, but some brief 
heavy rainfall and gusty winds will be possible with these 
thunderstorms. Any convection still in the forecast area should 
quickly dissipate shortly after sunset as diurnal instability 
wanes. A similar situation should unfold on Wednesday, but 
stronger subsidence is expected. Therefore, convection on 
Wednesday should be limited to areas southeast of a line from 
Lufkin TX to Monroe LA where ascent from the weak upper trough and
moisture levels will be highest.

Hot temperatures will also likely continue. The 12z KSHV upper air
observation indicated precipitable water values near 1.75 inches,
which provided a decent indication that dewpoints would not mix
out today, which has indeed occurred. This led to heat index
values well above advisory criteria, and in many locations above
110 degrees F. Very little change in conditions are expected for
Wednesday. Due to some uncertainty, the Heat Advisory was
maintained with no changes. However, later shifts may need to
consider upgrading some of the area to an Excessive Heat Warning
for Wednesday.


.LONG TERM.../Thursday through Tuesday/

The long dominant upper ridge will finally begin to flatten Thursday 
as weak shortwave troughing begins to gradually slide ESE across 
OK/AR. While this may temper max temps back a bit away from the 
triple digits, have trended temps some 2-4 degrees above guidance, 
given the dry topsoil moisture and very warm 4" soil temps. However, 
the short term guidance is in agreement with the remnants of a weak 
inverted trough drifting N into Ncntrl and NE LA around the Bermuda 
ridge that will expand W into the Cntrl Gulf. This weak bndry aloft 
should help focus sct convection mainly during the afternoon/early 
evening with heating, and have maintained mid chance pops for these 
areas, with low and slight chance pops farther W into extreme Ern 
TX/SW AR/SE OK. The remnants of this weak inverted trough may linger 
over the area Friday, and again help focus isolated to sct 
convection over the region, although our focus will turn to a weak 
tropical wave that will develop over the Wrn Gulf Thursday and drift 
NNE towards the Scntrl or SE LA coast by the middle part of the 
weekend. Given this NNE track, the influence on our region will be 
minimal, aside from possibly a weak enhancement to the convection 
over the far SE sections of Ncntrl LA. Otherwise, the presence of 
the weak troughing to the N may linger across SE OK/SW AR and help 
focus additional isolated to sct convection even through Friday 

Prefer the more consistent runs of the ECMWF for the latter portions 
of the extended, which suggests that upper ridging will again begin 
to expand E into the Srn Plains Saturday night and Sunday, allowing 
the weak remnants of the shortwave trough to slide SE into the Lower 
MS Valley, and again help focus sct convection mainly over the Ern 
half of the region. As this trough slide further SE by Monday, the 
potential for isolated to sct convection looks to shift SE across 
the SE zones, while diminishing across much of NE TX/SE OK/SW AR 
ahead of the rebuilding upper ridge. Thus, a return to above normal 
temps and isolated convection at best looks like a good bet as move 
into much of next week. 



.PREV DISCUSSION... /issued 106 PM CDT Tue Aug 20 2019/ 

For the 20/18z TAFs, isolated to widely scattered convection will
continue to slowly develop during the first few hours of the
period. Coverage will remain very spotty, and any impacts at the
TAF sites are highly uncertain. The showers and thunderstorms
should quickly dissipate after 21/00z as daytime instability
wanes. Otherwise, VFR conditions should prevail in most locations
for the entire period.



SHV  77  98  77  98 /  10  10  10  20 
MLU  73  95  75  94 /  20  30  10  40 
DEQ  75  97  74  97 /   0  10  10  20 
TXK  77  97  76  97 /  10  10  10  20 
ELD  76  96  75  94 /  10  10  10  30 
TYR  77  97  76  98 /  10  10  10  10 
GGG  77  97  76  98 /  10  10  10  10 
LFK  75  96  75  97 /  10  20  10  30 


AR...Heat Advisory until 7 PM CDT Wednesday for ARZ050-051-059>061-

LA...Heat Advisory until 7 PM CDT Wednesday for LAZ001>006-010>014-

OK...Heat Advisory until 7 PM CDT Wednesday for OKZ077.

TX...Heat Advisory until 7 PM CDT Wednesday for TXZ096-097-108>112-