000
acus01 kwns 210101
swody1
Storm Prediction Center ac 210059
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0759 PM CDT Monday may 20 2013
Valid 210100z - 211200z
..there is a MDT risk of severe thunderstorms across parts of MO...Northwest Arkansas...eastern
OK...southern OK and North Texas...
..there is a slight risk of severe thunderstorms across parts of the Southern
Plains...Central Plains...Ozarks...mid-MS valley...upper MS valley and
Great Lakes...
..srn plains/Ozarks/mid-MS valley...
Latest water vapor imagery shows an upper-level trough over the
central and Southern Plains with southwest flow located from the trough
axis northeastward into the middle-MS valley. An mesoscale convective system is currently ongoing along
this corridor on the western edge of a 30 to 40 knots low-level jet. The
low-level jet will continue to strengthen early this evening helping
to maintain intense convection across the moderate risk area. Surface
dewpoints ahead of the mesoscale convective system are in the upper 60s to near 70 f and
objective analysis shows MLCAPE values in the 2500 to 3500 j/kg
range. This along with 35 to 45 knots of deep layer shear across the
moderate risk area due to a Central Plains middle-level jet...will
continue to support widespread severe thunderstorms this evening
with a severe threat lasting into the overnight period.
Regional WSR-88D vwps from St. Louis south-southwestward to Springfield MO into
north central Texas show directional turning in the lowest 2 km with
substantial speed shear resulting in 0-3 km storm relative
helicities in the 300 to 400 m2/s2 range. This along with moderate
to strong instability suggests that the threat for tornadic
supercells will exist across an area extending from central MO southwestward
into North Texas. As the low-level jet continues to strengthen...a
potential for strong tornadoes will exist across the moderate risk
area. Concerning the threat for large hail...the steepest middle-level
lapse rates exist across eastern OK and north central Texas where the more intense
supercell will be capable of producing hail greater than 2 inches in
diameter. Supercells should also be capable of producing swaths of
wind damage. The wind damage threat should become enhanced early
this evening as the mesoscale convective system becomes increasingly linear and as the
low-level jet intensifies. The severe threat is expected to continue
into part of the overnight period due to amount of instability that
is currently located ahead of the mesoscale convective system.
..upper MS valley/western Great Lakes...
An upper-level low is currently located across the northern plains
according to water vapor imagery. At the surface...a cold front is
moving through the northern and central pains with a corridor of low-level
moisture extending northward into the upper MS valley. Surface dewpoints
across the upper MS valley are in the upper 50s to lower 60s f with
middle 60s f located in lower Michigan. This is resulting in MLCAPE values
estimated in the 750 to 1250 j/kg range across much of the region.
In addition...objective analysis shows 0-6km shear values in the 40
to 50 knots range across the northern part of the slight risk area. As the
exit region of a 70 to 80 knots middle-level jet overspreads the region
early this evening...deep layer shear will be enhanced helping to
support severe thunderstorm development. Model forecasts suggest
that thunderstorm activity will increase in coverage this
evening...with storms moving northeastward across southern Minnesota...WI and northern Illinois. The
environment should support scattered severe storms capable of
producing wind damage and large hail. As low-level shear increases
this evening...a few tornadoes may also occur with the more intense
cells. The severe threat should become more isolated after midnight
due to the weaker instability that is in place compared to areas
further south.
.Broyles.. 05/21/2013
Mesoscale Discussion
000
acus11 kwns 210233
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 210233
iaz000-210330-
Mesoscale discussion 0740
National Weather Service Storm Prediction Center Norman OK
0933 PM CDT Monday may 20 2013
Areas affected...central and eastern Iowa
Concerning...Severe Thunderstorm Watch 194...
Valid 210233z - 210330z
The severe weather threat for Severe Thunderstorm Watch 194
continues.
Summary...the threat for damaging winds and severe hail continues in
the near term...but severe storm potential should begin to diminish
by 04z.
Discussion...a broken band of strong to severe thunderstorms continues from
near and NE of alo to just east of lwd as of 0220z with the most
intense storms located over Marshall...Tama...and Decatur counties.
Recent trends in surface observations indicate a steady cooling of
the inflow air mass to these storms...resulting in decreasing
instability and a gradual accumulation of convective inhibition.
Uplift along the existing storm-scale cold pools...and deeper-layer
forcing attendant to a vorticity maximum moving through the lower-MO
valley will likely sustain ongoing storms with a continued risk for
isolated severe weather. This threat should begin to diminish by
04z as the boundary layer further stabilizes.
.Mead.. 05/21/2013
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...dvn...dmx...
Latitude...Lon 40689369 41259344 42319302 42829270 42889232 42679213
42439218 42149171 42139154 41779155 41179142 40859161
40669240 40689369
