Area Forecast Discussion
Issued by NWS Shreveport, LA

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FXUS64 KSHV 180811

Area Forecast Discussion
National Weather Service Shreveport LA
311 AM CDT Wed Apr 18 2018

Strong pressure gradient remains in place across the Four State
Region this morning but a low level inversion has formed and
therefore, winds have decreased considerably over the last 3 hours
or so across our western zones. While some stronger gusts will
remain possible across the Middle Red River Valley of Northeast
Texas, Southeast Oklahoma and Southwest Arkansas this morning,
sustained wind speeds will likely not support the need to
continue the Lake Wind Advisory so that hazard has been cancelled
for this morning`s package.

Low level moisture, albeit very shallow, is quickly returning from
the south this morning and should encompass most of the region
by sunrise. This return is in response to an upper level trough
well north of the region, moving across the Central/Northern
Plains. A cold front is associated with this disturbance with the
frontal boundary as of 08z located across SE KS into Central OK
and just now moving into NC Texas. This cold front will continue
making good progress south and east this morning and should be
near or just south and east of the I-30 Corridor by 18z today and
through all but our southeast parishes by 00z this evening. Kept
slight chance pops in the forecast along and ahead of this
boundary through today but as mentioned above, moisture is very
shallow and thus, only isolated showers are expected if anything
throughout the day before any precipitation dissipates later this
afternoon with the southeastward moving frontal boundary. Descent
warmup is expected ahead of the boundary today but just shy of the
warm temperatures witnessed across the entire region yesterday.
Much drier dewpoints will infiltrate the region behind this
boundary today through tonight with overnight lows some 10 to 15
degrees colder than what we are seeing this morning.

Upper flow becomes rather zonal on Wed with slight upper ridging
forecast to move across the Plains during the day Thu into Friday
ahead of our next weather maker in the form of a closed upper low
taking up residence across the Four Corners region of the country
on Friday. Medium range progs are in pretty good agreement with
the ejection of this system into the Plains during the day Sat
into Sat Night with the latest run of the GFS outpacing the
operational ECMWF by just 6hrs or so with the Canadian being the
slow outlier. We will continue to follow the slightly slower ECMWF
for this forecast which keeps all but our extreme western zones
dry through mid day Sat with likely coverage pops moving into
those same western zones by Sat Aftn with chance pops as far east
as SC AR into NW LA and slight chance pops across our eastern
third. Categorical pops areawide are warranted for Sat Night as
the closed low moves out of the OK/TX Pnhdl and into eastern OK
by 12z Sun before rain tapers off from west to east during the day

Concerning our severe weather chances with this storm system Sat
into Saturday Night, we still have some moisture modification that
must happen first in order to see the kind of instability we need
for a severe storms. Dewpoints by 12z Sat will still be in the 40s
across all of our region but 60+ dewpoints should be located along
the S LA coast into SE TX. Both the operational GFS/ECMWF bring 60
degree dewpoints as far north as the I-20 Corridor of NE TX into
NW LA by 00z Sun with strong to severe dryline convection likely
ongoing near or just west of the I-35 Corridor of Central TX Sat
Aftn. Convection ahead of this dryline closer to our western most
zones should be becoming more widespread by this time which could
offset daytime heating despite the higher returning dewpoint
recovery. The dryline should not come any further east Sat Evening
but the cold front catches the dryline to our northwest Sat
Night. SPC continues to outlook a 15% (Slight Chance) of severe
storms Sat/Sat Evening across Central Texas south and west of our
region closer to where the dryline convection will setup and this
seems plausible as this is where the best instability will reside.
Across our region, instability is forecast to be very weak
despite the strong deep layer speed and low level directional
shear that will be present ahead of the upper level trough Sat/Sat
Night. We will continue to monitor the moisture return and
instability parameters that would be necessary for strong to
severe thunderstorm probabilities Sat/Sat Night nonetheless.

Prelims to follow...13.


SHV  80  51  73  45 /  20   0   0   0
MLU  81  51  69  43 /  20   0   0   0
DEQ  77  41  69  41 /  20   0   0   0
TXK  77  46  70  44 /  20   0   0   0
ELD  79  45  69  41 /  20   0   0   0
TYR  80  49  72  47 /  20   0   0   0
GGG  80  49  72  47 /  20   0   0   0
LFK  81  54  77  49 /  20  10   0   0




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