Convective Outlook

SPC 2000Z Day 1 Outlook
Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0253 PM CDT Mon Jul 16 2018

Valid 162000Z - 171200Z


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 MI
has been trimmed to account for the progression of the primary
convective band. See MCD 1058 for additional details regarding this
region. The Marginal Risk area across northeast OK/southeast KS into
the Ozarks has been adjusted to account for ongoing convective
trends. See MCD 1059 for more information regarding this area. 

Elsewhere, the previous forecast, including the Slight Risk over WY
into the central High Plains, remains unchanged. See the previous
discussion below for more details.

..Dean/Peters.. 07/16/2018

.PREV 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 SD 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
tree damage.

...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.

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Updated 16 July 2018 | 2:57 pm