- Day Three
acus01 kwns 161955
Storm Prediction Center ac 161953
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0253 PM CDT Mon Jul 16 2018
Valid 162000z - 171200z
..there is a slight risk of severe thunderstorms across portions of
Wyoming and the Central High plains...
Scattered severe storms are expected across parts of Wyoming into
the Central High plains and Black Hills regions from late afternoon
into tonight. Large hail and strong to severe wind gusts should be
the main hazards.
Only minor changes have been made to the previous outlook. The
northern portion of the marginal risk area across northern lower Michigan
has been trimmed to account for the progression of the primary
convective band. See mesoscale discussion 1058 for additional details regarding this
region. The marginal risk area across northeast OK/southeast Kansas into
the Ozarks has been adjusted to account for ongoing convective
trends. See mesoscale discussion 1059 for more information regarding this area.
Elsewhere, the previous forecast, including the slight risk over Wyoming
into the Central High plains, remains unchanged. See the previous
discussion below for more details.
Previous discussion... /issued 1130 am CDT Mon Jul 16 2018/
..intermountain West/Wyoming to Central High plans...
A perturbation embedded within a low-amplitude shortwave trough over
the Pacific northwest will move east from southern Idaho towards the
Central High plains through this evening with a subtle disturbance
or two preceding this more discernible mid-level impulse. Related
weak large-scale ascent in conjunction with a moist air mass, with
prevalent 60s f surface dewpoints across the High Plains, will lead
to widely scattered storm development by mid/late afternoon. Such
development is likely to initially occur over the intermountain west
to interior Wyoming, and potentially as far east as the Black Hills
vicinity and southwest/south-central South Dakota by late afternoon.
Semi-elongated hodographs (aided by 40+ kt high-level winds at 7+ km
agl) are anticipated to overlap with the eastern periphery of the
elevated mixed-layer characterized by steep mid-level lapse rates. A
moderately buoyant air mass is expected mainly from east-central/far
southeast Wyoming into southern South Dakota and much of
west/central Nebraska. The setup should favor a few discrete
supercells, the most sustained of which may be those that move
south-southeast from western/southern South Dakota into the Nebraska Panhandle
and/or northern Nebraska. Large hail along with isolated severe wind
gusts should be the primary hazards.
During the evening, this activity will likely grow upscale as
moderate low-level southerlies strengthen to around 30 kt over the
Central High plains. This should result in a
south/southeastward-propagating cluster with mainly a strong to
isolated severe wind risk in western Nebraska before weakening
overnight in the northwest Kansas/northeast Colorado vicinity.
..eastern Great Lakes...
In advance of an eastward-moving front, scattered thunderstorm
development is expected this afternoon across lower Michigan to the
Lee of lakes Erie/Ontario. Convergence is generally weak and
stronger mid-level westerlies will lag behind the surface cold
front, although brief overlap of the warm sector with modest
effective shear values may support some sustained/briefly organized
storms. With weak mid-level lapse rates and unfavorable nocturnal
timing of frontal impingement east of the lower lakes, the overall
setup is expected to only yield localized strong gusts capable of
..southeast Kansas/northeast Oklahoma to the Ozarks...
Small-scale cold pools and zones of differential heating will likely
influence additional storm development and intensification across
the region within a very moist and diurnally destabilizing boundary
layer. Given the degree of heating/moisture and resultant buoyancy,
it is conceivable that a couple of the wet microbursts could produce
localized wind damage this afternoon.
acus11 kwns 162052
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 162052
Mesoscale discussion 1061
National Weather Service Storm Prediction Center Norman OK
0352 PM CDT Mon Jul 16 2018
Areas affected...parts of south-central and southwestern South
Dakota...Nebraska Panhandle into north-central Nebraska
Concerning...severe potential...watch possible
Valid 162052z - 162245z
Probability of watch issuance...60 percent
Summary...cumulus clouds have become increasingly agitated within
the discussion area. A conditional threat exists for large hail and
severe wind gusts, with storm initiation/evolution uncertain.
Convective trends will be monitored for a possible ww issuance later
Discussion...cumulus clouds across south-central and southwestern
South Dakota along and near a Theta-east gradient and over the Black
Hills. Afternoon heating across the area, with low- to mid-60s
dewpoints in place, has lead to MLCAPE values of 1500-2500 j/kg.
With continued heating and approaching mid-level ascent, some cams
develop a cluster of storms in South Dakota and move them
south/southeastward into Nebraska. However, given upstream mid-level
ridging, uncertainty exists with regard to if storms will initiate
and how much coverage there will be. The greatest threat for severe
hail will be with any initial storms, should they develop, in South
Dakota as effective bulk shear of 30-40 kts will favor storm
organization. Any storms that do develop will also pose a risk of
severe wind gusts given the steep low-level lapse rates and high
surface temperature/dewpoint spreads.
Additional storms may also move out of Wyoming into southwest South
Dakota and the Nebraska Panhandle later this evening. These storms
will primarily pose a severe wind gust risk given the expected
linear/cluster storm Mode. Given the overall uncertainty in the
exact evolution of this event, convective trends will continue to be
monitored for the possible issuance of a ww.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 44590375 44870285 44770180 44640107 44350068 43800030
42750006 41740010 40990137 41070214 41060327 42050367