Valid 151630Z – 161200Z
…THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS EASTERN KS…
…THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF
NORTHERN/CENTRAL GREAT PLAINS AND NORTHEAST STATES…
…SUMMARY…
Severe thunderstorms are most likely to be centered on eastern
Kansas during the late afternoon and evening. Severe hail and wind
gusts may be significant with a few tornadoes also possible.
…Central/eastern KS vicinity…
An MCS is ongoing across eastern NE with a trailing composite
outflow/cold front extending into far northwest KS. Waning low-level
warm advection through the next few hours should inhibit substantial
strengthening across the Lower MS Valley. The trailing outflow will
be the primary focus for late afternoon to early evening
redevelopment. Low-level convergence should support initial storms
from north-central into northeast KS. A plume of upper 60s surface
dew points at present across central KS will be maintained as richer
boundary-layer moisture advects north from OK, beneath the eastern
extent of the elevated mixed layer. Ample diabatic heating will
yield large buoyancy with MLCAPE likely reaching 2500-3500 J/kg. A
veering wind profile with height will support initial supercells,
with hodograph enlargement occurring through the evening as a
southwesterly low-level jet intensifies. The setup should foster a
risk for very large hail and a few tornadoes. However, the overall
mode may tend to grow upscale into clusters and an MCS relatively
quickly given the strengthening forcing for ascent during the
evening. This may result in the predominant threat becoming severe
wind gusts (a few of which may be significant) as an MCS develops
bowing structures across eastern KS towards western MO/northern OK.
Overall severe threat should subside overnight with the most likely
MCS track approaching the Ozark Plateau. 12Z non-HRRR HREF members
are more consistent with this overall scenario than recent HRRR
runs, with the parent RAP maintaining more pronounced MLCIN in much
of the warm sector. Nevertheless, an Enhanced Slight Risk appears
warranted given the potential for a higher-end intensity/coverage
scenario.
…SD vicinity…
A low-amplitude shortwave trough and attendant surface boundary will
move east across the Dakotas. Ample diabatic heating is underway
downstream across central to eastern SD north of the NE MCS.
Presence of upper 50s to low 60s boundary-layer dew points will
support MLCAPE of at least 1500-2000 J/kg. While low-level shear
will be weak, robust speed shear from 700 mb on up will foster an
elongated mid/upper-level hodograph favorable for mid-level rotation
and an eventual eastward-progressing MCS with potential for a brief
bow. Initial large hail transitioning to predominant severe wind
gusts should be the main threats before activity weakens in western
MN.
…Eastern WY and NE Panhandle…
Residual low-level moisture (corridor of upper 50s surface dew
points) within a weak upslope regime north of the trailing composite
outflow/cold front over northeast CO will support a conditional
supercell environment favorable for large hail. However, storm
coverage appears likely to be rather isolated at peak heating in the
wake of the shortwave trough crossing the Dakotas. Greater
confidence in storms exists early Friday morning ahead of the next
upstream shortwave impulse.
…Eastern OH and PA vicinity…
A low-amplitude upper trough from eastern Lake Superior to western
OH will gradually move east with an attendant weak surface cyclone
drifting across northern OH. Relatively cool temperatures aloft atop
a plume of mid to upper 60s surface dew points should result in
MLCAPE reaching 1500-2000 J/kg during the next few hours. Though
low-level flow/shear will be weak, there will be sufficient
deep-layer vertical shear for multiple mid-level rotating updrafts
as scattered storms develop from the Upper OH Valley/Lower Great
Lakes regions across the lee of the Appalachians. Convection should
remain predominantly discrete, yielding a risk for both severe hail
and damaging winds, with these threats waning after dusk.
..Grams/Gleason.. 08/15/2019
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