000
acus01 kwns 182002
swody1
Storm Prediction Center ac 182000
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0300 PM CDT Tuesday Jun 18 2013
Valid 182000z - 191200z
..there is a slight risk of severe thunderstorms this afternoon/evening across
central/southern Illinois and Indiana...
..there is a slight risk of severe thunderstorms across much of the High Plains
this afternoon/evening...
..there is a slight risk of severe thunderstorms across NE Idaho/northwest Montana this
afternoon/evening...
..ern Georgia into the Carolinas...
An extensive area of scattered storms has developed over Alabama/Georgia early this
afternoon with the area over the Carolina coastal plain largely void
of storms/cloud cover prior to 20z. Although moderate west-southwesterly middle
level flow has overspread the region ahead of a weak disturbance
moving across the Carolinas/Virginia this afternoon/evening...modest middle
level lapse rates observed on the morning area radiosonde observations have limited
the magnitude of destabilization despite temperatures rising to near 90 degree
f. 9 km cappi radar data indicates the updrafts have so far
remained tempered...and expecting this trend to continue into the
early evening hours as scattered storms eventually move into the Carolina
coastal plain...perhaps yielding a few pockets of wind damage. As a
result...have removed 15 percent wind probabilities given the
expected coverage of the severe wind threat.
Elsewhere...only minor modifications have been made to the outlook.
The most notable change includes a southward shift of the 10 percent
thunderstorm probability line over the southern Great Lakes and over the
northestern U.S. To reflect visible satellite trends and a confining of
severe hail/wind probabilities over the Ohio Valley where an agitated
cumulus field/cold front are located as of mid-afternoon.
.Smith/Kerr.. 06/18/2013
Previous discussion... /issued 1117 am CDT Tuesday Jun 18 2013/
..central and southern Illinois/Indiana this afternoon/evening...
Water vapor imagery shows an embedded shortwave trough moving east-southeastward
over Iowa...and this wave will cross Illinois/Indiana this
afternoon/evening. The midlevel wave coincides with a frontal zone
across central IL/Indiana...which will provide a focus for
thunderstorm development this afternoon. Modified 12z soundings
from dvn/ilx show the potential for MLCAPE of 1500-2000 j/kg...with
steep low-midlevel lapse rates and strong deep-layer vertical shear
which will support a risk for couple of supercells capable of
producing large hail and damaging winds.
..High Plains this afternoon/evening...
Falling pressures across the northern rockies...in advance of the deep
trough moving inland over the Pacific northwest...will induce southeasterly upslope flow
across the Central High plains. Deep-layer bulk shear will be
sufficient for supercells with modest westerly flow aloft above southeasterly
low-level flow...in a steep lapse rate environment with 1500-2000
j/kg MLCAPE. Expect thunderstorm initiation by early-middle afternoon
along the east slopes of the Big Horn and Laramie ranges in Wyoming...as
well as the Front Range of Colorado/NE nm...possibly aided by weak ascent
over northern Colorado/Wyoming in advance of a weak shortwave trough ejecting northeastward
from Utah. Storms will then spread eastward through the afternoon/evening
onto the High Plains...with an accompanying risk for large hail and
a few damaging gusts. Some of the convection could persist into
tonight across the Texas/OK panhandles in response to a developing low level jet
and increasing moisture flux from the southeast.
Additional storms could form this afternoon along a residual outflow
boundary across northwest/west central Kansas. Vertical shear will be at least
marginally favorable for supercells with the potential to produce
isolated hail/damaging gusts.
..NW Montana/NE Idaho this afternoon/evening...
Large scale ascent downstream from the deep Pacific northwest trough...and the
northern extent of a steep lapse rate plume...will combine with daytime
heating and boundary layer dewpoints in the upper 40s to lower 50s
to support moderate instability and thunderstorm development by middle
afternoon across NE Idaho/western Montana. Storms will then spread north-northeastward off
the higher terrain...and will be capable of producing at least
isolated damaging winds and large hail. The strongest vertical
shear...and greater potential for supercells...will be near the
baroclinic zone across northwest/north central Montana.
..ern Georgia into the eastern Carolinas this afternoon...
A midlevel shortwave trough and associated surface low over the southern
Appalachians will progress eastward to the Atlantic coast by tonight. A
wide swath of thick clouds/rain accompanies this trough from the middle
Atlantic southwestward to the southern Appalachians and Piedmont of the Carolinas.
Regional 12z soundings and recent vwp/S reveal somewhat enhanced
low-midlevel west-southwesterly flow of 30-40 knots...though the clouds and moist
profiles/poor lapse rates will tend to limit destabilization this
afternoon...aside from stronger surface heating across the coastal
plains where midlevel flow weakens. The net result is a marginal
situation for multicell clusters with damaging winds.
..E/southeast Texas into la/MS this afternoon...
A well-developed mesoscale convective vortex from overnight convection persists over north
central Texas as of middle-late morning. East-S of the mesoscale convective vortex and weak
associated surface low in NE Texas...daytime heating and convergence
along weak surface frontal boundaries will support thunderstorm
development. Deep-layer flow is relatively weak within the unstable
warm sector...and lapse rates aloft are not steep. Isolated wet
microbursts will be possible this afternoon...but severe storm
coverage should remain rather sparse.
Mesoscale Discussion
000
acus11 kwns 182004
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 182004
ksz000-nez000-182130-
Mesoscale discussion 1122
National Weather Service Storm Prediction Center Norman OK
0304 PM CDT Tuesday Jun 18 2013
Areas affected...northern Kansas
Concerning...severe potential...watch unlikely
Valid 182004z - 182130z
Probability of watch issuance...20 percent
Summary...storms developing over northern Kansas may pose a risk for isolated
large hail and strong wind gusts into early evening. Overall threat
does not appear sufficient for a ww...but trends will continue to be
monitored.
Discussion...this afternoon storms are developing along a northwest-southeast
oriented frontal boundary across northestern Kansas. Other storms are
developing over north central Kansas along a convective outflow boundary.
Middle-level lapse rates are not particularly steep /on the order of
6.5-7 c/km/. However...low-mid 60s surface dewpoints and strong diabatic
warming with steep low-level lapse rates are supporting 1500-2000
j/kg MLCAPE. Storms are developing south of stronger winds aloft
with effective bulk shear generally less than 30 knots suggesting
multicells should be the dominant Mode. Strongest storms are
currently developing where a southward moving convective outflow boundary
is intersecting the front over northestern Kansas. While a few strong storms
may produce hail and gusty winds...the overall environment parameter
space does not appear supportive of more than very isolated severe
events.
.Dial/Thompson.. 06/18/2013
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...eax...top...ict...Gid...gld...
Latitude...Lon 39899709 39539616 39169543 38539464 38259504 38959667
39289945 39869988 40019857 39899709
