U.S. Severe Weather Forecast (対流の概観)

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000 
acus01 kwns 292002 
swody1 
Storm Prediction Center ac 292000 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0300 PM CDT Wed Mar 29 2017 


Valid 292000z - 301200z 


..there is an enhanced risk of severe thunderstorms for the 
Missouri and Arkansas Ozarks... 


..there is an enhanced risk of severe thunderstorms for southeast 
Texas northeast into the lower Mississippi Valley... 


..there is a slight risk of severe thunderstorms for East Texas and 
lower Mississippi Valley and Ozark Plateau... 


..there is a marginal risk of severe thunderstorms surrounding the 
slight risk... 


... 
Severe thunderstorms are expected this afternoon into tonight from 
parts of East Texas, eastern Oklahoma, and southeast Kansas into the 
lower and middle Mississippi Valley. Large hail, tornadoes, and 
damaging winds will be possible especially later this afternoon and 
tonight. 


... 
The biggest substantial changes have been dictated in part to 
upper-air raob data from lzk (19z raob) and short-term model trends 
(time-lagged hrrr model). Have confined the 10-percent tornado to 
the Ozarks and in a corridor from the lower Sabine valley 
northeastward into northeastern la and far west-central MS. Have 
removed the significant tornado delineation based on instability 
concerns and prior convective overturning earlier today and recent 
surface analysis displaying a slower-than-expected recovery. 


.Smith.. 03/29/2017 


Previous discussion... /issued 1147 am CDT Wed Mar 29 2017/ 


..Ozarks/lower MO valley to arklatex/lower MS River Valley... 
The closed upper trough currently over the south-Central Plains at 
late morning will continue a slow-general-northeastward advance 
toward the lower MO River Valley through late tonight and early 
Thursday. Ahead of this system, 12z regional observed soundings 
reflected considerable lapse-rate-related impacts from the 
overnight/early morning squall line that continues to move generally 
east-northeastward and decay across the Ozarks and Ark-la-tex 
vicinity. This may have ramifications on the 
extensiveness/likelihood of significant hail potential, for 
instance, although the air mass will recover/gradually moisten and 
destabilize to the south of a northward-moving warm front across the 
Ozarks/lower MO valley, and ahead (east) of a slow-eastward-moving 
cold front. 


Latest thinking is that surface-based storms will develop as early 
as mid-afternoon near the eastern Kansas surface low southward along the 
front, including far eastern portions of Kansas/OK into western portions 
of MO/AR. Moderate low-level hodograph curvature (beneath strong but 
somewhat backed mid-level southwesterly winds) and resultant strong 
low-level shear/srh will support a tornado risk aside from large 
hail and evolving damaging wind risk into this evening. 


Farther south, storms may diurnally be a bit more isolated across 
the remainder of the arklatex vicinity, although an ongoing 
quasi-linear cluster across near-coastal southeast Texas may persist 
east-northeastward into la as it favors a zone of outflow-related 
weak boundary/zone of differential heating. This cluster and other 
peripheral development may pose a damaging wind/tornado risk through 
the afternoon and evening hours. 


Later tonight, storms should increase in coverage/intensity 
initially across portions of Arkansas/la as forcing for ascent/DPVA 
increases related to an east/northeastward-ejecting vorticity maxima 
within the base of the larger-scale trough. Related mass response 
should result in increasingly strong low-level winds/confluence. A 
mixed Mode of storms should be prevalent, with hail initially 
possible prior to a more common damaging wind/embedded tornado risk 
as storms toward/across the MS river late tonight. 


$$ 

Mesoscale Discussion


000 
acus11 kwns 292251 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 292250 
msz000-arz000-laz000-txz000-300045- 


Mesoscale discussion 0370 
National Weather Service Storm Prediction Center Norman OK 
0550 PM CDT Wed Mar 29 2017 


Areas affected...portions of la...western MS...southeast Arkansas 


Concerning...Tornado Watch 98... 


Valid 292250z - 300045z 


The severe weather threat for Tornado Watch 98 continues. 


Summary...the risk for severe thunderstorms and tornadoes continues 
across Tornado Watch 98, and will spread east-northeastward and 
northeastward through the evening and overnight hours. An additional 
watch will likely be required prior to the 02z expiration of watch 
98. 


Discussion...clusters of thunderstorms, including embedded rotating 
updrafts and bowing segments, continue in the vicinity of the lower 
Sabine valley. Inflow for this activity is characterized by around 
500-2000 j/kg of MLCAPE (higher buoyancy amid Richer moisture with 
southward extent), based on modifications to the 18z Lake Charles 
and Shreveport observed soundings. This activity lies within the 
warm sector of a broader extratropical cyclone, within which modest 
positive Theta-E advection will continue during the next several 
hours. 


As a result, convection will continue to spread east-northeastward 
and northeastward into the evening and overnight hours. This will 
occur while ascent attendant to the right-entrance region of a 
midlevel speed maximum encourages both (1) the maintenance of at 
least modest instability, and (2) a low-level mass response 
supporting moderate low-level shear and isentropic ascent. Moreover, 
with 40-55 kt of effective shear attendant to the speed maximum, 
organized convective modes will continue to be favored. 


While damaging winds and sporadic severe hail will be the primary 
concerns with this activity, tornado potential will exist with 
embedded supercell structures and meso-vortices. This would 
especially be the case as strengthening low-level shear juxtaposes 
increasing boundary-layer Theta-E through the night. Accordingly, a 
new watch will likely be issued from parts of southern la to the 
arklamiss region prior to the expiration of Tornado Watch 98. 


.Cohen/Edwards.. 03/29/2017 


..please see www.Spc.NOAA.Gov for graphic product... 


Attention...WFO...Jan...lix...lzk...lch...shv... 


Latitude...Lon 31839094 30869140 29849232 29729387 30009428 30459432 
31519353 33199273 33959204 34029100 33249064 31839094