Area Forecast Discussion
Issued by NWS Shreveport, LA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS64 KSHV 291218
AFDSHV

Area Forecast Discussion
National Weather Service Shreveport LA
718 AM CDT Wed Mar 29 2017

.AVIATION...
For the 29/12z TAFs, a line of convection is moving across the
area, but will gradually diminish during the first few hours of
the TAF period. More strong convection will move into the area
from the southwest, and new development is possible during the
afternoon, mainly east of a line from KJSO to KDEQ. Some of the
storms could be severe, especially this afternoon through tonight.
Convection will be slow to exit the area and may still be
affecting KELD and KMLU at the end of the period. Flight
conditions will be quite variable due to the showers and
thunderstorms. However, VFR conditions are expected late in the
period in locations where the convection ends. Sustained southerly
winds near 15 kts with gusts near 25 kts can be expected across
much of the area. Speeds should diminish after sunset, and winds
will become westerly after 30/06z as a Pacific cold front moves
across the region.

CN

&&

.PREV DISCUSSION... /issued 601 AM CDT Wed Mar 29 2017/

DISCUSSION...
The squall line of Ecntrl TX/SE OK has finally begun to weaken as it
enters our Wrn zones this morning, with wind gusts of 30-40kts still
being recorded along the line, most recently at PSN as of 0935Z. This
weakening trend should continue this morning as the convection moves
into an area of lower instability, and further away from large scale
forcing associated ahead of the closed low over Cntrl NM. This low
will drift into the TX Panhandle later this morning before reaching
Wrn OK/SW KS later this afternoon.

There remains some uncertainty as to the areal extent of the
convection later this afternoon, given the unknown placement of the
mesoscale bndrys associated with the ongoing convection of E TX, and
the overturning of the air mass this morning as the line continues to
push E. The HRRR has initialized poorly with the existing convection,
having to play catchup all night and thus have low confidence in
timing of convection later today. The GFS remains rather bullish
(moreso than the NAM/ECMWF) with extensive convection rapidly
redeveloping this afternoon over extreme Ern TX into Wrn LA/SW AR, but
not quite buying this just yet given the consensus amongst the
NAM/ECMWF and even the slower HRRR. While the ongoing convection
should leave bndrys behind somewhere over SW AR/extreme Ern TX/Wrn LA
later this morning, will have to wait to see how far E the dryline is
able to mix later this afternoon over E TX, before it is eventually
overtaken by the attendant cold front by mid-evening. Have
concentrated categorical pops over the Wrn sections of E TX/SE OK this
morning while tapering pops off to likely/chance farther E into SW
AR/Wrn LA, but believe the more plausible scenario would be for
convection to fire late this afternoon and especially this evening
near the TX/LA/AR line where MLCapes climb to 1500-2000+ J/kg (in a
mostly unworked environment) and large scale forcing increases in
response to the split upper jet beneath the closed low over SE TX/NW
Gulf lifts NE. A Srly LLJ of 40-50kts should increase by early evening
over these areas, although SE low level winds look to veer more Srly
around initiation time with 0-1km SRH a bit lower than 24 hrs ago
ranging from 200-300 m2/s2 before increasing a bit this evening with
the onset of the LLJ. Will also contend with dry air aloft entraining
NE ahead of the trough this evening which may focus convection further
away from the approaching frontal system and moreso in the expanding
warm/moist sector farther E. However, storm organization should occur
this evening once the peak instability is realized with the onset of
the LLJ over SW AR/N LA. It`s possible that the initial development
may be discrete before consolidating into convective clusters. Should
that occur, damaging winds and large hail will be the primary threats,
although isolated tornadoes can`t be ruled out given the increasing
shear late in the day.

Have toned down pops for this evening as well, but still concentrated
likely/categorical pops for N LA/SW AR, with the convection exiting
our Ern zones around/shortly after 06Z Thursday. In addition, the
pressure gradient should tighten later this morning through the
afternoon ahead of the Cntrl OK sfc low, especially over much of E
TX/N LA. As a result, have expanded the current Lake Wind Advisory
farther E across the remainder of Deep E TX into Ncntrl LA through 00Z
Thursday, although E TX will take a little longer to gust to criteria
(if at all) given the convective overturning that will occur this
morning.

The short term progs are in agreement though with the front rapidly
mixing E across the region overnight, exiting our Ern zones by mid to
late morning. Given the faster frontal movement and the dry
entrainment over the region beneath the closed low, convective
and svr potential over the Ern zones has diminished, and have toned
down pops as well to chance pops Thursday morning, with enough dry air
eliminating pops all-together for the afternoon. The exception may be
across SE OK/Nrn sections of SW AR where wrap-around cu will round
the base the of H850 low. This will also result in cooler temps than
previously forecast as well, before they clear the area Thursday
evening with the departure of the low.

Flat ridging aloft will build E over the Srn Plains and Lower MS
Valley Friday, with srly winds expected to return with ample
insolation. Have raised max temps areawide, with mid 80s a good bet
over much of E TX/N LA. Low level moisture return will commence late
Friday night into Saturday as the Srly LLJ increases in response to
the next bowling ball closed low that will drift E across the Srn
Rockies. The GFS remains most aggressive with with convective
development by Saturday evening, quite a bit faster than its earlier
run 24 hrs ago. Given the closed nature of the low, prefer the slower
ECMWF, with isolated to sct convection developing Saturday night,
before becoming more widespread Sunday. Still can`t rule out the
potential for another round of svr convection Sunday, as a sfc low
develops over E TX and progressing NE across N LA/Srn AR enhancing the
spread of the warmer/more unstable air N across these areas.
Increasing shear may help to offset the instability which may be
hampered by the clouds/rain, but should result in widespread wetting
rains needed to ease the ongoing drought conditions. Have increased
pops to likely areawide Sunday/Sunday night, before the convection
gradually diminishes later Monday with the departure of this system.
Very warm and dry conditions return for the midweek timeframe, before
the prospects for isolated/sct convection possible increase again with
the approach of the next upper trough from the NW.

Prelims to follow below...

15

&&

.PRELIMINARY POINT TEMPS/POPS...
SHV  82  58  74  50 /  60  60  20   0
MLU  85  65  78  50 /  20  80  40  10
DEQ  76  50  64  43 /  70  40  20  10
TXK  78  53  67  49 /  60  50  20  10
ELD  82  59  72  49 /  50  80  30  10
TYR  80  52  72  53 /  80  30  10   0
GGG  80  54  72  51 /  80  30  10   0
LFK  80  57  78  54 /  80  40  10   0

&&

.SHV WATCHES/WARNINGS/ADVISORIES...
AR...Lake Wind Advisory from 10 AM this morning to 7 PM CDT this
     evening for ARZ070-071.

LA...Lake Wind Advisory from 10 AM this morning to 7 PM CDT this
     evening for LAZ001>003-010>013-017>022.

OK...None.
TX...Lake Wind Advisory from 10 AM this morning to 7 PM CDT this
     evening for TXZ096-097-108>112-124>126-136>138-149>153-
     165>167.

&&

$$

15/09



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.