Valid 161630Z – 171200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS PORTIONS OF
EASTERN KS AND WESTERN MO…
…SUMMARY…
Scattered severe storms are expected from the central High Plains to
the Lower Missouri Valley with very large hail and damaging winds as
the primary threats. The central High Plains threat will increase by
late afternoon and spread across Kansas through the night, with the
Missouri portion beginning this evening and continuing through the
night.
…Central High Plains to the Lower MO Valley…
While outflow from morning convection has spread across the Ozarks
and northern OK, this should dissipate as convection further decays
with a period of weakened low-level warm advection this afternoon.
Primary surface front should become established by early evening
from east-central CO arcing across southern KS through central MO as
pronounced differential heating occurs across it. Warm 700-mb
temperatures of 12-16 C within an intensifying and expanding stout
elevated mixed layer, characterized by extremely steep 700-500 mb
lapse rates of 9-9.5 C/km, will overspread much of the baroclinic
zone and effectively cap surface-based storm development through
early evening east of the high terrain.
Initial storms should form near the Front Range within a weak
low-level upslope flow regime north of the front, likely focused
across northeast CO where more robust insolation is underway south
of morning stratus. The western extent of upper 50s to low 60s
surface dew points will coincide with the western periphery of
MLCAPE exceeding 2000 J/kg. On the southern periphery of a strong
mid-level jet centered on southeast WY to IA, a few supercells
should develop with primary risks of very large hail and severe wind
gusts. How this convection evolves through the evening and eastward
into the northwest/north-central KS vicinity is uncertain given
pronounced MLCIN. It is plausible that a sufficient cold pool might
develop with colliding outflows and a subsequent MCS could
expand/intensify eastward given broad strengthening of a southerly
low-level jet across the frontal zone. With the presence of extreme
mid-level lapse rates and strong to extreme buoyancy remaining
centered across eastern KS, potential exists for a swath of
significant severe wind and large hail continuing into early
morning.
Farther east across the Lower MO Valley, a separate zone of
low-level warm-advection driven convection should develop near dusk
and likely be regenerative through the night along the periphery of
stronger MLCIN. Initial updrafts should have the greatest potential
to produce significant severe hail. Convective mode should quickly
evolve into potentially multiple clusters that would have a mixed
risk of severe wind/hail given the ample buoyancy. The potential
upstream MCS across northern KS might eventually merge with these
clusters prior to dawn.
…Northeast to Great Lakes…
A low-amplitude upper trough crossing the Lower Great Lakes to the
Saint Lawrence Valley will foster scattered thunderstorm development
along and ahead of its attendant surface trough. Modest mid-level
lapse rates and weak lower-level flow will be limiting factors to a
greater severe threat. Mid to upper-level speed shear will support
small hail while a mixed boundary-layer yields potential for locally
damaging winds. Overall threat should be more subdued compared to
yesterday.
A separate corridor of marginal severe potential is also apparent
across eastern WI to western Lower MI along a cold front associated
with a low-amplitude shortwave trough shifting east from northwest
WI.
..Grams/Jirak.. 08/16/2019
$$