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 211655
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 211654
nhz000-maz000-ctz000-vtz000-nyz000-211800-
Mesoscale discussion 0751
National Weather Service Storm Prediction Center Norman OK
1154 am CDT Tuesday may 21 2013
Areas affected...wrn/cntrl New York...southern New England
Concerning...severe potential...watch possible
Valid 211654z - 211800z
Probability of watch issuance...40 percent
Summary...thunderstorms should continue increasing in intensity...primarily
focused along/S of a quasi-stationary front...across portions of
western/central New York and into southern New England this afternoon. The primary
threats will be damaging wind gusts and large hail. A ww may be needed
if convective trends continue to increase.
Discussion...subjective surface analysis from 16z places a
quasi-stationary front from near roc-alb. A few storms have recently
initiated along this front...likely in response to weak low-level
convergence...weakening convective inhibition...and modest midlevel
moistening/ascent as noted on water vapor. Modified 12z soundings
from both buf and alb suggest ample instability for the development
of strong-severe thunderstorms...with MLCAPE values likely exceeding 2000
j/kg...given the presence of moderately steep midlevel lapse rates
and rich low-level moisture. Additionally...both sounding and recent
vwp data show nearly 30 kts of midlevel flow and modestly veering
winds with height...supportive for organized thunderstorm. Coverage of thunderstorms
is somewhat uncertain given relatively weak forcing for ascent...but
with the potential for large hail and damaging wind gusts...a ww may be
required should trends continue to increase.
.Rogers/Kerr.. 05/21/2013
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...box...aly...bgm...buf...
Latitude...Lon 41997433 42067611 42277755 42697790 43147756 43197706
43027555 42987423 42957307 42897266 42677229 42257234
41717280 41997433
