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 211835
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 211835
arz000-laz000-txz000-212030-
Mesoscale discussion 0753
National Weather Service Storm Prediction Center Norman OK
0135 PM CDT Tuesday may 21 2013
Areas affected...arklatex region
Concerning...severe potential...Tornado Watch likely
Valid 211835z - 212030z
Probability of watch issuance...95 percent
Summary...a conditional threat for tornadoes has arisen across the
arklatex region...and a watch will be issued shortly.
Discussion...heating has eroded capping over northestern Texas into southern Arkansas and
northern la where dewpoints are in the 68-72 f range...creating very
strong instability. Meanwhile...a few small cells have recently
formed just S of a southward advancing outflow boundary now into far northestern
Texas. Although the air north of this boundary is relatively
stable...conditions are favorable for tornadoes...perhaps even
strong...S of the boundary.
A confluence axis may be setting up across the area...and with
continued heating...this may be enough for isolated storms to
form...well ahead of the advancing cold front to the west.
.Jewell/Kerr.. 05/21/2013
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...shv...fwd...
Latitude...Lon 32319649 33239627 33599563 33569492 33539442 33569382
33299347 32529345 32239370 31959421 31819480 31849617
32319649
