000
acus01 kwns 211630
swody1
Storm Prediction Center ac 211628
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1128 am CDT Tuesday may 21 2013
Valid 211630z - 221200z
..there is a MDT risk of severe thunderstorms for N-cntrl/northestern Texas...Southern
Arkansas...northwestern la...far southeastern OK...
..there is a slight risk of severe thunderstorms from the Southern Plains to the
Tennessee/Ohio valleys and the lower Great Lakes/northeast...
..substantial severe weather expected across north-central Texas to the
arklatex this afternoon and evening...
.Srn plains to lower MS valley...
Significant severe weather episode initially unfolding across the
Red River with supercells producing large hail along and north of the
composite outflow/cold front pushing southward from the Big Country to far
southeastern OK ahead of a well-defined shortwave trough over the southern High
Plains. Air mass S of the boundary is becoming strongly unstable as
gradual surface heating continues amidst lowest 100 mb mean mixing
ratios of 14-17 g/kg and 700-500 mb lapse rates of 8 to 9.5 degree c/km
sampled in all regional 12z radiosonde observations. As mlcin is minimized along the
dryline mixing eastward across the Edwards Plateau...additional supercell
development is anticipated with southward extent.
A belt of 50-60 knots middle-level swlys attendant to the compact
shortwave trough will promote risks for all severe types /some of
which will be significant/. Morning convection-allowing WRF and hrrr
simulations are insistent that upscale growth will occur throughout
the afternoon. Given the degree of instability...buoyancy and
shear...setup may yield a derecho accelerating eastward towards the
arklatex region by early evening. Here too...the strongest low-level
S/swlys will remain...promoting embedded mesovortices capable of
producing a couple of significant tornadoes. Otherwise...potential
does exist for widespread/destructive damaging wind gusts.
..TN valley to the lower Great Lakes/northeast...
A broad area of organized severe potential is expected along the eastern
extent of the elevated mixed layer plume sampled in 12z radiosonde observations. With
robust heating...moderate to strong instability is anticipated...but
most of the region will remain on the fringe of sufficient
deep-layer shear for supercells. Three zones of focus for sustained
convection are apparent. One will be downstream of an ongoing
cluster across western Tennessee. The others should be along a quasi-stationary
front bisecting New York into southern New England and perhaps in association
with a weak mesoscale convective vortex moving into lower Michigan. Multicell clusters and a few
supercells will be primarily capable of isolated damaging winds and
severe hail.
.Grams/Rogers.. 05/21/2013
Mesoscale Discussion
000
acus11 kwns 211943
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 211942
alz000-tnz000-msz000-kyz000-moz000-arz000-212045-
Mesoscale discussion 0755
National Weather Service Storm Prediction Center Norman OK
0242 PM CDT Tuesday may 21 2013
Areas affected...eastern Arkansas...western Tennessee...northern MS...MO bootheel.
Concerning...severe potential...Tornado Watch likely
Valid 211942z - 212045z
Probability of watch issuance...95 percent
Summary...thunderstorms have rapidly increased in intensity across eastern Arkansas
and northern MS. The environment is becoming increasingly favorable for
damaging winds...large hail...and perhaps a few tornadoes. A ww will
likely be coordinated soon with local forecast offices.
Discussion...northern segment of mesoscale convective system moving across Arkansas has fragmented
across central Arkansas...and is progressing nearly due eastward across eastern Arkansas.
Additional more discrete storms have developed across northern MS. Vwp
data from nqa shows favorably backed surface winds with veering in the
0-1 km layer...resulting in 0-1 srh near 150 m^2 s^-2.
Additionally...breaks in cloudiness have resulted in temperatures
heating up into the upper 70s to lower 80s f...resulting in an
increasingly unstable environment. This will be favorable for large
hail and damaging winds...as well as tornadoes especially with discrete
storms. A ww will be coordinated soon.
.Rogers/Kerr.. 05/21/2013
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...ohx...hun...pah...Meg...Jan...lzk...
Latitude...Lon 34618819 34248842 33898919 33908975 34119067 34319105
35039136 35659128 36099119 36379068 36689007 36438903
36278799 34618819
