900
acus01 kwns 232002
swody1
Storm Prediction Center ac 232000
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0300 PM CDT Wednesday may 23 2012
Valid 232000z - 241200z
..there is a slight risk of severe thunderstorms from the Central High plains to
the upper MS valley through tonight...
..there is a slight risk of severe thunderstorms for eastern NC and northestern SC through
evening...
..upper Midwest into the Central Plains...
Previous forecast reasoning remains on track. Maintaining the
amplitude of severe probabilities with minor changes to spatial
extent based on recent observations and 19z cold front position from
southwestern Minnesota/eastern South Dakota S/south-southwestward into north-central Kansas. Still expecting thunderstorms to
develop southward along the front by early evening /ref mcds 0758 and 0759
for near-term discussion/. Significant hail threat appears to be
marginal/isolated in nature given the expected convective Mode and
only a moderately buoyant air mass.
..nern Colorado into Central High plains...
Will maintain slight risk here...although concerns do exist over the
degree of low-level moistening given surface dew points still in the
middle 30s to lower 40s. Primary severe risk may be delayed until
later this evening and predominately be hail.
..ern Carolinas into southeastern Virginia...
Removed southeastern Virginia from slight risk as ongoing strong to severe thunderstorms
should largely remain in eastern NC and northestern SC through about sunset.
.Grams/bunting.. 05/23/2012
Previous discussion... /issued 1128 am CDT Wednesday may 23 2012/
..upper Midwest into the Central Plains...
Upper low over southern Canadian prairies is forecast to remain
quasi-stationary through the period as several perturbations
progress eastward within the band of the strong middle/upper level winds
from the Great Basin into the plains. Water vapor imagery shows one
short wave trough from eastern Wyoming into northestern Utah...and this is expected to
move into the plains tonight and provide increasing support for
convective development. At the surface...a cold front from the eastern
Dakotas/Minnesota border southwestward into northwestern Kansas and central Colorado is expected to move
slowly eastward/southeastward as increasing southwesterly flow aloft becomes more parallel
to the frontal orientation.
12z soundings show a very well-defined eml over the plains with very
warm 700 mb temperatures of 15c at lbf...ddc and Ama. The eml is
likely to inhibit surface-based convective development ahead of the
front...with model guidance generally indicating that storms will
initiate along/behind the front later this afternoon from southwestern Minnesota
southwestward into eastern Nebraska. Moisture continues to be modest with precipitable water values
of 1.0-1.25 inches and surface dew points remaining in the 55-60f
range. Very steep lapse rates are expected to develop through a
deep layer ahead of the front as strong diabatic heating steepens
low level lapse rates resulting in a deep well-mixed boundary layer.
Strengthening middle/upper level winds will gradually overspread the
Central Plains into the upper Midwest...contributing to 40-50 knots
deep layer shear supportive of organized convective structures
including supercells. Very large hail and damaging wind gusts will
be the primary severe threats from late afternoon through the
evening hours...although an isolated tornado or two may also be
possible for storms that form close to the front. Activity is
expected to progress slowly eastward/southeastward tonight...but largely remaining
along/north of the front...enhanced by a strong nocturnal low level
jet over the plains/MO valley.
..nern Colorado into Central High plains...
Guidance indicates a surface low will develop over southeastern Colorado with a
strong east-northeasterly surface pressure gradient developing over eastern Colorado.
Resultant upslope flow will advect moisture westward toward the foothills
and contribute to destabilization this afternoon as strong heating
occurs east of the mountains. With surface dew points increasing
into the middle-upper 40s...MUCAPE is expected to reach 500-1000 j/kg.
Low level upslope winds coupled with divergence aloft associated
with the left exit region of the strong upper jet will enhance
thunderstorm potential this afternoon and evening. Strongly veering
wind profiles with height will enhance organization and intensity of
convection with strong/severe storms expected including a few
supercells. Large hail...damaging wind gusts and an isolated
tornado or two will be possible. Activity may grow upscale into an
eastward moving mesoscale convective system that moves into parts of the Central Plains later
tonight.
..ern Carolinas into southeastern Virginia...
Water vapor imagery indicates cold upper low /-16c at 500 mb/ is
lifting northeastward from SC toward eastern NC and is expected to enhance
thunderstorm activity again this afternoon. Visible imagery shows
clouds are clearing/thinning over parts of NC in advance of the
system...which is allowing strong heating/destabilization to occur.
Although winds aloft and vertical shear will remain marginally
supportive for organized convective structures...very favorable
thermodynamic environment suggests potential for severe storms to
develop this afternoon and evening capable of producing large hail
and localized damaging wind gusts.
... MS valley...
strong heating amidst a northeastward-advancing warm front will support
isolated to widely scattered thunderstorms. Boundary-layer dewpoints in the
60s near and SW of the front will support moderate to strong
destabilization...with steep low-level lapse rates likely yielding
dcape values in excess of 1000 j/kg. Very weak flow throughout the
troposphere will support a pulse convective Mode...and a low threat
for damaging wind gusts and perhaps marginally severe hail cannot be ruled
out with the strongest storms.
Mesoscale Discussion
179
acus11 kwns 231956
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 231956
iaz000-nez000-sdz000-ksz000-232130-
Mesoscale discussion 0879
National Weather Service Storm Prediction Center Norman OK
0256 PM CDT Wednesday may 23 2012
Areas affected...far southeastern South Dakota...western Iowa...cntrl/ern Nebraska
Concerning...severe potential...watch likely
Valid 231956z - 232130z
Probability of watch issuance...80 percent
Summary...thunderstorm development is forecast to occur by late
afternoon across portions of far southeastern South Dakota...western Iowa...and central/eastern
Nebraska. Large hail and damaging winds will be possible. Ww is likely.
Discussion...mesoanalysis at 19z showed a weak surface low pressure
center located in vicinity of southeastern South Dakota/northwestern Iowa/northestern Nebraska...with a cold front
extending southwestward from the low into north-central Kansas. Surface temperatures
ahead of the cold front are warming to around 90f...with dewpoints
in the 50s to near 60f. Given the presence of steep midlevel lapse
rates /near 7 c per km in the 700-500 mb layer/...MLCAPE values have
increased to 1500 j/kg. Surface heating along and ahead of the front
is also aiding in strong boundary layer destabilization...which is
resulting in the development of an expansive cumulus field over
central/eastern Nebraska. Combination of broad midlevel height falls and
embedded upper perturbations...as well as frontal convergence
enhanced within exit region of 30-50 knots low level jet should support
thunderstorm development by late afternoon...with coverage
increasing toward night. Most likely scenario is for storms to
remain anchored very close to the frontal boundary...with activity
posing a threat for large hail given the thermodynamic environment
coupled with effective bulk wind difference values from 30-50 knots. In
addition...upscale growth into a linear system suggests damaging
wind threat will also exist.
.Garner/Weiss.. 05/23/2012
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...dmx...fsd...oax...top...Gid...lbf...
Latitude...Lon 40589956 41879853 43449617 43109488 42119479 40709587
39909795 39989940 40589956
