Valid 191200Z – 201200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE CENTRAL AND NORTHERN PLAINS…
…SUMMARY…
Isolated thunderstorms capable of hail and marginally severe wind
gusts will be possible in parts of the northern and central Plains
later this afternoon and evening.
…Northern/Central Plains…
Upper ridging will be shunted into the MS Valley later today as a
strong upper trough shifts across the northern Rockies/Great Basin.
While the primary corridor of height falls will spread across the
Great Basin during the day, modest 500mb flow should extend across
WY into MT with substantially weaker flow expected south of I-70
across CO/KS. As a result, large-scale forcing for ascent will be
negligible/weak across the High Plains through the period.
Early this morning, convection is beginning to expand in areal
coverage from northeast NE into northern IA. An upward evolving
cluster/MCS should be noted through sunrise and this would reinforce
a boundary that will drape itself across NE – arcing northwest into
southeast MT. The early-day MCS is not expected to be particularly
strong and its primary influence should be to reinforce the front
across the central Plains. Latest model guidance aggressively warms
the boundary layer across the central High Plains and convective
temperatures will likely be breached between 20-22z along the CO/KS
border into southwest NE. Latest thinking is isolated thunderstorms
should evolve across the High Plains driven primarily by diurnal
heating along western fringe of moist plume. CAMs support this
scenario and robust convection could produce some hail and wind.
Farther north across eastern WY into southeast MT, moisture will be
notably lower but forecast wind profiles substantially stronger,
more than adequate for sustaining organized updrafts. In the absence
of large-scale support, diurnal heating and orographic influences
will prove instrumental in convective development. Isolated severe
thunderstorms appear possible by late afternoon as surface
temperatures warm into the mid 80s – effectively removing minimal
inhibition expected across this region. This activity could linger
into the late evening as LLJ strengthens across western SD after
sunset.
..Darrow/Bentley.. 09/19/2019
$$