000
acus01 kwns 200550
swody1
Storm Prediction Center ac 200548
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1248 am CDT Thursday Jun 20 2013
Valid 201200z - 211200z
..there is a slight risk of severe thunderstorms for the northern/Central Plains and
upper MS valley...
...
A large upper trough will reside across the western Continental U.S. During the d1
forecast period...while downstream...an upper ridge will be present
from the MO valley into the upper MS valley. A shortwave trough
located over the northern rockies early this morning will lift northward around
the eastern edge of the larger-scale wave into Canada by late morning.
As this occurs...a surface low pressure system will occlude...with a
cold front/occluded front arcing nwwd from the Dakotas into southern
Alberta...and a warm front extending southeastward from central ND into east-central
Minnesota. The southern portion of the cold front will then trail southwestward into the
Central High plains...where a second area of low pressure is forecast
to reside later in the afternoon.
..nrn/Central Plains and upper MS valley...
A broad area of southerly low-level flow will aid in transporting middle 60s
dewpoints into the northern plains and upper MS valley ahead of the
surface occluded/cold front...with upper 60s dewpoints possible over
eastern Nebraska and western Iowa. By midday...an eml is forecast to spread across
the area...with steep midlevel lapse rates combined with surface
temperatures in the 80s and a moist boundary layer aiding in MLCAPE
values at or above 2000 j/kg.
Latest model guidance indicates upper forcing for ascent will be
nebulous through late afternoon...with weak/subtle midlevel
vorticity maxima ejecting northeastward from the western trough.
However...current thinking is an mesoscale convective vortex emanating from an mesoscale convective system over eastern
Montana early this morning will round the upper ridge and aid in renewed
thunderstorm development by afternoon along and north of the warm front
over eastern ND and northern/central Minnesota. This activity may quickly grow upscale
into another mesoscale convective system and move southeastward along the warm front. Damaging winds
and large hail will be the primary threats...but a couple of
tornadoes will also be possible. Mesoscale convective system maintenance will continue to be
supported into the night as a southwesterly low-level jet strengthens and
expands northward into the upper MS valley.
Elsewhere over South Dakota into neb/IA...afternoon destabilization will
support a chance for isolated thunderstorm development evolving off
the cold/occluded front eastward across the warm sector. Middle and
upper-level southwesterly flow near 30 knots will reside above low-level
sselys...which will yield vertical shear profiles favorable for
organized multicell clusters and a few supercells. Given moderate to
strong cape and steep midlevel lapse rates...damaging winds and
large hail will be possible.
..wrn Nebraska/Nebraska Panhandle...Far southeastern Wyoming...
low-level winds are forecast to be out of the east over western Nebraska as a
cold front stalls over the Central High plains. This will aid in
maintaining a moist low-level airmass over the Nebraska Panhandle/far
southeastern Wyoming...with surface dewpoints in the 50s...and will support weak
to moderate instability with the occurrence of daytime heating and
the presence of steep midlevel lapse rates. Thus...a few isolated
thunderstorms cannot be ruled out within the upslope flow regime. If
this occurs...shear profiles will be favorable for supercells posing
a threat for large hail and a tornado. However...this scenario is
uncertain at this time...which precludes a categorical upgrade. The more
likely scenario is for storms to develop overnight as an upper
impulse ejects eastward into the High Plains. These storms would likely
be elevated and pose an isolated threat for large hail.
..ern nm...West Texas/Texas Panhandle...
dewpoints in the 50s to near 60f are forecast to reside over the southern
High Plains this afternoon in the presence of strong surface heating
and steep lapse rates. This will yield moderate instability
supportive of thunderstorm clusters...with storm initiation possibly
aided by a weak upper impulse entering the region by evening.
Isolated damaging winds and large hail will be possible with this
environment.
.Garner/Mosier.. 06/20/2013
Mesoscale Discussion
000
acus11 kwns 200657
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 200657
ndz000-mtz000-200830-
Mesoscale discussion 1138
National Weather Service Storm Prediction Center Norman OK
0157 am CDT Thursday Jun 20 2013
Areas affected...eastern Montana into western ND
Concerning...Severe Thunderstorm Watch 330...
Valid 200657z - 200830z
The severe weather threat for Severe Thunderstorm Watch 330
continues.
Summary...a wind threat will continue across ww 330...but the threat
is not expected to warrant a need for another watch into ND.
Discussion...a line of strong to severe storms continues to progress
eastward across Montana...and will eventually move into northwestern ND. The strongest
storms currently exist over McCone County in closer proximity to
better moisture...and may contain large hail in addition to severe
wind gusts. A warm advection Wing has materialized recently in
response to lift over the cooler air mass to the north. While storm
coverage could increase...this could disrupt overall organization a
bit. While isolated severe wind gusts may persist into northwestern ND...the
overall threat should not be widespread enough for another watch.
.Jewell.. 06/20/2013
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...bis...ggw...
Latitude...Lon 47210507 48720591 49050618 49030200 48150195 47840234
47390417 47210507
