299
acus01 kwns 241947
swody1
Storm Prediction Center ac 241945
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0245 PM CDT Thursday may 24 2012
Valid 242000z - 251200z
..there is a MDT risk of severe thunderstorms over far northestern Iowa and southeastern
Minnesota...much of central and northern WI...
..there is a slight risk of severe thunderstorms from Kansas and MO northeastward into Michigan...
..Upper MS valley/Great Lakes region...
surface analysis shows a surface low over southeastern Minnesota into far western WI as
of 19z...with a cold front extending southwestward across central Iowa. Extending
northeastward from the low over northwestern WI was a slow moving warm front. Storms
will continue to increase in coverage and intensity as the cold
front continues eastward. Given complex storm Mode as well as very large
boundary layer temperature dewpoints spreads over much of the warm
sector...have decreased tornado probabilities a bit. The main threat
will continue to be damaging winds with very strong wind shear
profiles in place. Still...a tornado or two may occur. Hail will be
possible as well but have decreased coverage of hail over eastern
portions of the area as storms will lose the benefit of daytime
heating after 00z.
For more information see mesoscale discussion 0889.
...
Removed the severe hail probabilities due to the warm profiles
aloft. An isolated strong or severe wind gust may still occur as new
cells develop inland with continued heating.
.Jewell.. 05/24/2012
Previous discussion... /issued 1130 am CDT Thursday may 24 2012/
..nern Iowa/extreme southeastern Minnesota/much of WI...
Water vapor imagery indicates a strong upper short wave trough
moving northeastward over eastern Nebraska. This system is expected to progress into
the upper MS valley by this evening and continue across the upper
Great Lakes tonight as an upstream low develops southward along the northern
Pacific coastal region. This trough will become more negatively
tilted with time as it lifts northeastward...providing increasing divergence
aloft. This will result in the surface low currently near Oma to
deepen as it moves north-northeastward...reaching Western Lake Superior this evening
and continuing into Ontario tonight. A surface cold front extending
southward from the low will accelerate into the upper MS valley this
afternoon before reaching lower Michigan late tonight.
Very strong winds aloft are associated with the Midwest
trough...with a 50 knots low level jet over the lower MO valley
forecast to strengthen as it moves northward into WI this
afternoon...while an 80-90 knots middle level jet streak currently over
the central rockies/High Plains lifts northeastward toward the upper MS
valley. This will create very strong low/middle level shear over the
warm sector ahead of the cold front supportive of severe storms.
The primary limiting factor remains low level moisture with surface
dew points likely reaching the 55-60f range prior to frontal
passage. A plume of moderately steep middle level lapse rates also
extends over the warm sector and is contributing to greater
instability given the somewhat limited low level moisture. Enhanced
diabatic heating ahead of the cloud shield over the upper MS valley
will aid in further destabilization with MLCAPE reaching 1000-1500
j/kg this afternoon.
Current elevated storms over northwestern WI are expected to move rapidly
northeastward and pose a risk of hail into early afternoon. These storms
will also be monitored for the potential to become surface based
this afternoon...which would increase the likelihood of strong wind
gusts. Additional storms are expected to develop near the cold
front from northestern Iowa into western WI by middle afternoon. The favorable wind
shear will promote development of fast moving supercells and Bow
echo structures capable of producing damaging wind gusts...large
hail...and tornadoes. The storms are likely to develop into one or
more bowing line segments by later afternoon or evening...with the
severe threat transitioning into primarily a wind damage scenario as
bowing segments move rapidly northeastward through the evening hours. The
activity is expected to slowly diminish in intensity after 03-6z.
..Central Plains late tonight...
South-southwesterly low level jet will strengthen over much of Kansas and western MO late tonight in
response to diurnal influences and to the continued east-southeast
advance of upper low into northern California and the northern Great Basin. This
strengthening will occur atop trailing...SW end of same frontal zone
that will cross the upper MS valley later today. Coupled with the
arrival of fairly substantial moisture return /p.W. At or above 1.25 inches/
and with the continued presence of 40-50 knots west-southwesterly shear above the
frontal surface...setup may support elevated thunderstorms after 06-09z with
hail and perhaps locally strong wind gusts.
..cntrl/S Florida...
Scattered thunderstorms expected this afternoon in zone of strong heating...high
precipitable water...and upper divergence beneath southwesterly high level jet streak. These may
yield a few instances of severe wind/hail...mainly along sea breeze
boundary intersections.
..mid Atlantic into parts of Carolinas...
Tropical moisture spreading northward/converging beneath residual axis of
relatively cool middle level temperatures may support a few diurnal storms/storm
clusters with locally severe wind/marginally severe hail. Convection will
be enhanced by weak upper vorticity maximum moving north-northeastward over the western
Carolinas.
Mesoscale Discussion
656
acus11 kwns 242006
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 242006
wiz000-ilz000-iaz000-mnz000-moz000-242200-
Mesoscale discussion 0890
National Weather Service Storm Prediction Center Norman OK
0306 PM CDT Thursday may 24 2012
Areas affected...portions eastern Iowa...extreme northern MO...southwestern
WI...extreme northwestern Illinois -- S of ww 295.
Concerning...severe potential...watch possible
Valid 242006z - 242200z
Probability of watch issuance...40 percent
Summary...convection is increasing in vicinity of surface cold front over
central/southwestern Iowa and over northwestern MO. Potential exists for thunderstorms to
evolve from some of this activity and move eastward across portions Iowa SW
of ww 295. Main threat will be damaging gusts...with isolated hail
also possible. Ww appears more probable in northestern Iowa/southwestern WI versus
elsewhere in discussion area.
Discussion...at 1945z..sfc cold front extended south-southwestward from southeastern Minnesota
low...across Boone County Iowa to Brown County Kansas. Front should move
eastward/southeastward across Iowa...impinging on warm sector that should continue
to destabilize for another couple of hours. Convection will impinge
on narrow corridor of at least marginally favorable warm-sector thetae
over central/southern Iowa and southwestern WI...sandwiched between cold front and
plume of relative low-level drying farther east that has been indicated
persistently in radiosonde observation analyses and satellite-derived total-precipitable water
imagery. Modified forecast soundings suggest MLCAPE 1000-1500 j/kg with
50-100 nm ahead of front...atop well-mixed/inverted-v thermodynamic
profile in boundary layer. This regime...set amidst 50-70 knots
effective shear magnitude and strong deep-layer winds aligned nearly
parallel to front...indicates quasi-linear convective Mode with
damaging wind possible. Strongest middle-upper level support and
low-level frontal ascent should remain north of MO through
afternoon...while cinh increases with southward extent. This indicates
any convection S of Iowa should remain relatively short-lived and not
as intense as farther North.
.Edwards/Weiss.. 05/24/2012
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...mkx...dvn...arx...dmx...eax...
Latitude...Lon 43578991 42629016 42349029 41389134 40669271 39929513
41179413 42489337 43519301 43489122 43578991
