000
acus01 kwns 210601
swody1
Storm Prediction Center ac 210559
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1259 am CDT Tuesday may 21 2013
Valid 211200z - 221200z
..there is a MDT risk of severe thunderstorms across parts of SW Arkansas...Southeast
OK...northwest la...central Texas and NE Texas...
..there is a slight risk of severe thunderstorms across parts of the Southern
Plains...Ozarks...mid MS valley...Ohio Valley and Great Lakes...
..srn plains/arklatex/mid-MS valley...
An upper-level trough will move eastward from the southern rockies into the
Southern Plains today. At the surface...a cold front will advance southeastward across
central OK and west-central Texas. Ahead of the front...surface dewpoints across
the warm sector should be in the middle to upper 60s f resulting in
moderate to strong instability by this afternoon. Thunderstorms are
forecast to be ongoing at the start of the period across eastern OK
where an isolated threat for hail and wind damage may exist this
morning. With surface heating...new thunderstorms are forecast to
initiate along and ahead of the cold front from western Arkansas southwestward into
North Texas around midday. The models quickly expand thunderstorm
coverage with an mesoscale convective system organizing and moving southeastward across the moderate
risk area. Strong instability...steep middle-level lapse rates and
moderate to strong deep layer shear should be supportive of
widespread severe thunderstorm development across the moderate risk
area where a significant severe weather event will be possible.
Forecast soundings at 00z/Wednesday from Little Rock southwestward to around the
Dallas Fort Worth metroplex show MLCAPE values of 2500 to 4000 j/kg
with 0-6km shear of 45 to 55 knots. This along with 850 to 500 mb lapse
rates around 7.5 c/km should result in a potential for supercells
with large hail. Hailstones of greater than 2 inches in diameter
will be possible with the more intense supercells. In addition...the
more dominant supercells should be capable of producing tornadoes as
the low-level jet strengthens. A few strong tornadoes could occur
near the low-level jet as boundary layer shear becomes more
favorable during the early evening. The models suggest cells may be
discrete at the start of the event with a transition to a
squall-line. This would make the wind damage threat increasingly
dominant as a linear mesoscale convective system organizes early this evening. For this
reason...an enhanced wind damage threat will be possible across the
moderate risk area.
..Great Lakes/Ohio Valley...
Southwest flow will be in place today from the middle-MS valley northeastward
into the Great Lakes region. At the surface...a low is forecast to move
eastward across the upper MS valley with a corridor of low-level moisture
extending north-northeastward from the lower Ohio Valley into lower Michigan. Surface
dewpoints across southern Illinois...northwest ind and lower Michigan should be in the middle
60s f resulting in moderate destabilization. Model forecasts
initiate storms by middle afternoon along the instability axis with
storms moving northeastward across the region. Forecast soundings along the
instability axis west of Detroit and north of Indianapolis at 21z
show MLCAPE values in the 1000 to 2000 j/kg range with steep
low-level lapse rates and unidirectional wind profiles. This
environment should be favorable for wind damage as cells increase in
coverage this afternoon. Several model forecasts show an enhanced
severe threat across lower Michigan to the southeast of the surface low and on
the nose of the low-level jet. For this reason...an enhanced wind
damage threat will be possible with bowing line-segments in lower Michigan
late this afternoon. Large hail and a few tornadoes may also occur
with the more intense cells.
..nrn Appalachian Mountains...
An upper-level ridge will be in place today across the Appalachian
Mountains in spite of the ridge...moderate instability is forecast to
develop from PA northeastward across central New York where surface dewpoints should be
in the lower to middle 60s f. The models appear to move a disturbance
over the top of the ridge which would help with convective
initiation this afternoon. If storms can develop in spite of the
weak large-scale ascent...then steep low-level lapse rates coupled
with moderate instability and sufficient deep layer shear could be
supportive of a marginal wind damage threat.
.Broyles/Mead.. 05/21/2013
Mesoscale Discussion
000
acus11 kwns 210921
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 210920
arz000-okz000-211015-
Mesoscale discussion 0745
National Weather Service Storm Prediction Center Norman OK
0420 am CDT Tuesday may 21 2013
Areas affected...part of southern/eastern OK into west central Arkansas
Concerning...Severe Thunderstorm Watch 199...
Valid 210920z - 211015z
The severe weather threat for Severe Thunderstorm Watch 199
continues.
Summary...an isolated hail threat continues across ww 199 into the
early morning...as new storms develop from Kiowa County OK through
central McClain/southern Cleveland counties to McIntosh County OK.
Discussion...a broad warm air advection zone extending into southern OK within the nose
of a 45-50 knots south-southwesterly low level jet combined with a northward influx of moderate
instability suggests thunderstorm development will continue from west-east across
ww 199. Effective bulk shear up to 50 knots supports storm
organization. These factors combined with steep midlevel lapse
rates of 7.5-8 c/km per objective analyses will favor a continued
potential for additional stronger storms to produce primarily a hail
threat.
Since 0840z...regional radar imagery indicated an increase in thunderstorm
development from central McClain County OK to central and eastern Kiowa
County OK. These storms appear to be forming along a cold front
advancing southward into central and southwestern OK where the inflow of moderate
instability is supporting this new development.
.Peters.. 05/21/2013
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...lzk...shv...tsa...oun...
Latitude...Lon 34109762 34319816 34829893 35009855 35159766 35369712
35369628 35869562 35769372 35299379 34669450 34539455
34119526 34049714 34109762
