acus01 kwns 201959
Storm Prediction Center ac 201957
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0257 PM CDT Monday may 20 2013
Valid 202000z - 211200z
..there is a MDT risk of severe thunderstorms over north central
Texas...central/ern OK...extreme southeastern Kansas...southern MO...and northwestern Arkansas...
..there is a slight risk of severe thunderstorms from the Southern Plains into the
Great Lakes region...
..srn plains into the Ozarks...
Minor adjustments have been made to the outlook based on current
boundary locations and recent convective initiation.
Severe storms have developed along the dry line from the western part of
North Texas into central OK...with additional storms over southeastern Kansas
and southwestern MO. Special soundings at 17-18z from oun/sgf/fwd indicate
steep lapse rates are persisting above 850 mb that are associated
with the elevated mixed layer across the region. With surface
dewpoints in the upper 60s/lower 70s and temperatures warming into
the low/middle 80s in OK and near 90 in northern Texas...a very unstable
environment is present with SBCAPE ranging from 3500-5000 j/kg. Deep
layer shear of 40-50 knots will enhance storm organization and
intensity with potential for supercells and bowing line segments.
Very large hail...damaging wind and several strong tornadoes will be
possible through the evening as activity continues to develop and
Stronger storms appear most likely from southern Georgia and northern Florida into the
southwestern part of the Florida Peninsula...in association with an upper low
over southern Georgia/northern Florida. Isolated marginal hail and wet microbursts may
accompany a few of the cells but overall severe threat should be
Previous discussion... /issued 1130 am CDT Monday may 20 2013/
..srn plains to Ozark Plateau...
Overall forecast scenario remains similar to earlier outlooks with
only minor overall changes to individual hazard probabilities.
Middle-level speed maximum /65 knots at 500 mb in the 12z abq radiosonde observation/ attendant
to the shortwave impulse over the Lee of the southern rockies will
overspread most of OK to the lower MO valley by early evening.
Trailing portion of cold front has become slow-moving from southeastern Kansas
to southwestern OK...intersecting a dryline that will become well
established S/southwestward across the Texas Big Country to the eastern Edwards
Plateau by late afternoon. Scattered thunderstorms will initiate along these
boundaries by mid-afternoon. Morning convection-allowing model
guidance are insistent that this activity will rapidly grow upscale
into numerous line segments...surging eastward this evening within a
strongly unstable environment.
Initial thunderstorms will become supercelluar quickly with very large hail
likely as hodographs/instability will be quite favorable...along
with a few tornadoes. The greatest risk for a couple of strong
tornadoes should exist from S-central into east-central OK. But with
predominant southwesterly component to low-level flow and moderate 0-1 km
shear...overall tornado intensity/longevity may be
tempered...especially with convection expected to grow upscale so
quickly. Nevertheless...this growth should yield bowing linear
segments capable of swaths of widespread damaging winds...large hail
and a few tornadoes.
..mid/upper-MS valley to central Great Lakes...
Primary change has been to expand damaging wind probabilities east/northeastward
for this afternoon and evening. In the wake of convection
yesterday...low-level moisture plume has become confined from lower
Michigan S/sswd to the confluence of the MS/Ohio rivers. But plentiful
heating is occurring to the north of this plume will yield a recovering
air mass downstream of a thunderstorm cluster approaching central MO. This
activity should grow upscale along the edge of the instability
axis...with additional linear segments emanating east/northeastward from the
Ozark Plateau later today. Swaths of damaging winds...large hail and
a couple of tornadoes will be possible.
Farther N/NW...scattered thunderstorms are expected to form over lower Michigan
and in parts of the upper Midwest in association with an upper-level
low centered over eastern South Dakota. Buoyancy will be strongest over lower Michigan
within the low-level moisture plume characterized by middle to upper
60s surface dew points. In the upper Midwest...pockets of robust
surface heating will support at least modest instability and with
strong unidirectional wind profiles...setup could a few organized
thunderstorm clusters. A mix of isolated severe hail/wind should be the
acus11 kwns 202027
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 202027
Mesoscale discussion 0729
National Weather Service Storm Prediction Center Norman OK
0327 PM CDT Monday may 20 2013
Areas affected...northestern MO...central Illinois...W-cntrl ind
Concerning...severe potential...watch possible
Valid 202027z - 202130z
Probability of watch issuance...60 percent
Summary...prospects for thunderstorm development are somewhat uncertain
across west-central ind westward into northestern MO...but the environment is
favorable for damaging winds and hail given strong
heating/destabilization. Convective trends are being monitored for
a possible ww...particularly activity developing northeastward from southwestern MO
towards the middle-MS valley.
Discussion...radar/satellite trends show a decaying thunderstorm cluster/mesoscale convective vortex
moving across north-central Illinois...with an increase in shallow boundary
layer cumulus noted across east-central Illinois. This appears to be developing
within a weak confluence axis which extends from 30 southeast mmo to 20 south-southwest
spi. Both modified 12z radiosonde observations and 12z NAM forecast soundings suggest
MLCAPE values have increased to 1000-1500 j/kg. While there is still
some uncertainty to what degree thunderstorms will intensify/organize over
Illinois...a threat for damaging winds and large hail could develop given
steep low-level lapse rates and moderately strong deep-layer shear.
Additionally...thunderstorms currently developing over western MO should
expand/develop northeastward towards east-central MO through late afternoon. It is
uncertain whether a ww will be required within the next 1-2
hours...but convective trends continue to be monitored.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 39918754 39488867 39078960 38749051 38819154 39059224
39719220 40199029 40468932 40988874 41188822 41298728
41208691 40788656 40298664 39918754