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Source: US National Oceanic and Atmospheric Administration

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Aug 11, 2019 1630 UTC Day 1 Convective Outlook
Updated: Sun Aug 11 16:30:40 UTC 2019 (Print Version |   |  )
Probabilistic to Categorical Outlook Conversion Table

 Forecast Discussion

SPC AC 111630

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Sun Aug 11 2019

Valid 111630Z – 121200Z

…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHERN
NE…NORTHERN KS…NORTHEAST CO…AND EAST-CENTRAL MT…

…SUMMARY…
Scattered to numerous severe thunderstorms are likely across
portions of the northern and central Great Plains. A few tornadoes,
damaging wind gusts, and large hail are possible, mainly through
this evening.

…Central High Plains to Mid-MS Valley…
A belt of somewhat enhanced mid-level flow extends from the southern
Rockies to the Lower MO Valley around the anticyclone centered near
the Red River. Within this belt, an MCV from a remnant overnight MCS
is sliding eastward near the IA/MO border. Some surface-based storm
development is possible near this MCV along the leading edge of the
residual cold pool and perhaps in the wake of the ongoing stratiform
if modest boundary-layer heating can occur. Weak mid-level lapse
rates and generally modest effective shear suggests the threat for
damaging winds should be localized.

Farther west, a low-level upslope regime has become established
north of the remnant outflow/effective front that is draped near the
I-70 corridor. Recovery of low-level moisture and surface heating
will yield large buoyancy north of the front with MLCAPE likely
reaching 2500-3500 J/kg by late afternoon. Thunderstorm development
is expected first immediately east of the Front Range in CO, while
the boundary layer should remain capped through much of the
afternoon in far northeast CO vicinity. Buoyancy and deep-layer
vertical shear will be sufficient for a mix of supercells and
multicell clusters with large hail/severe gusts possible with the
initial deep convection east of the Front Range. Wind profiles will
be more favorable for supercells farther east on the High Plains
where low-level easterly flow and hodograph curvature will be
greater, though there will be a tendency for cell interactions and
upscale growth later into the evening. Any semi-discrete supercells
will pose a threat for a couple of tornadoes and large hail, while
the severe wind threat will increase with storm clustering into the
evening. These clusters should form into a forward-propagating MCS
that may develop into a longer-lived bow along the KS/NE border
region tonight. Weak low-level lapse rates should be a limiting
factor, but the reservoir of large buoyancy along the nose of the
low-level jet lends credence to the possibility of a swath of severe
wind gusts into the early overnight.

…Northern High Plains…
A shortwave trough will eject from western ID to eastern MT.
Easterly low-level flow will be maintained ahead of this trough and
its associated cold front that will push east across MT. This flow
regime will maintain a broad plume of mid 50s to mid 60s surface dew
points from west to east. Rather steep mid-level lapse rates of 8-9
C/km across WY/eastern MT will contribute to a corridor of MLCAPE
reaching 2000-3000 J/kg where greater surface heating is underway
across southeast MT/northeast WY/western SD.

Episodic thunderstorm initiation is expected during the next few
hours over the high terrain of southwest MT and downstream of a
leading lobe of ascent approaching the WY/MT/Dakota border region,
as well as by late afternoon in an arc off the higher terrain of WY.
Effective bulk shear of 35-50 kt will favor several supercells
initially with large hail and a couple of tornadoes. Convection is
expected to grow upscale into multiple clusters/line segments across
MT into the western Dakotas with an increasing threat of severe
winds. The most likely corridor for a swath of severe gusts is
across parts of east-central MT along the northern periphery of the
buoyancy plume where large-scale ascent should be greatest ahead of
the shortwave trough.

..Grams/Dean.. 08/11/2019

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