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
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acus11 kwns 210154
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 210153
ilz000-moz000-210300-
Mesoscale discussion 0739
National Weather Service Storm Prediction Center Norman OK
0853 PM CDT Monday may 20 2013
Areas affected...northestern - east-central MO / west-central Illinois
Concerning...Tornado Watch 193...
Valid 210153z - 210300z
The severe weather threat for Tornado Watch 193 continues.
Summary...the risk for damaging winds...large hail...and perhaps a
tornado continues across the watch area.
Discussion...a mature mesoscale convective system has evolved this evening from west-central Illinois
to southwestern MO. Within this broader-scale convective system...a line
segment from just east of cou to near vih as of 0140z has shown signs
of acceleration with a forward speed of 40-45 knots currently being
observed. Additional more discrete convective elements are forming
immediately downshear from the primary convective band /from near
stl to near and north of spi/ where low-level warm air advection is likely being
enhanced.
Latest surface observations and objective analyses suggest that the
inflow air mass to these storms remains moist and moderately
unstable. Moreover...the stl VAD has shown a notable increase in
the southwesterly wind field below 4-5 km above ground level...which will sustain ongoing
storm structures. While damaging winds and large hail will remain
the primary severe weather hazards...a tornado or two remains
possible with any embedded supercells and/or qlcs-related
mesovortices.
.Mead.. 05/21/2013
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...ilx...lsx...dvn...
Latitude...Lon 39119215 40169209 40539086 40629043 40999023 41088979
40938923 40488852 39718897 38838902 38408976 37989078
37929115 39119215
