Valid 141200Z – 151200Z
…THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE MS VALLEY AND CENTRAL PLAINS AND OVER PARTS OF AZ…
A few strong-severe storms are possible across portions of the upper
Mississippi Valley, extending southwest into the central Plains.
Locally damaging winds are the primary risk along with marginally
severe hail. Gusty winds may also accompany storms in the lower
desert regions of AZ.
…Upper MS Valley to Central Plains…
Notable short-wave trough over the northern Rockies is forecast to
progress across the Dakotas into the upper MS Valley by 15/00z.
While southern extent of this feature should influence northern
portions of the MRGL Risk late this afternoon, large-scale height
rises are expected across much of the central US, including the
Plains and MS Valley. Partly in response to this feature, LLJ should
increase across the central Plains before veering into WI by early
evening. This will allow higher-PW air mass to advance north, then
east into southern MN/IA by peak heating. Even so, forecast
soundings suggest surface parcels will struggle to reach convective
temperatures and low-level warm advection may ultimately be the
primary forcing mechanism for potential robust convective
development. Latest models support this with most guidance
suggesting warm-sector convection struggling to organize in the
presence of height rises and marginal low-level lapse rates.
However, isentropic ascent across southern MN into southwest WI
should encourage slightly elevated convection along nose of LLJ.
Some of this activity could produce gusty winds and perhaps some
Farther southwest across KS, strong boundary-layer heating will be
noted across the High Plains where surface temperatures should soar
into the mid 90s. Forecast soundings suggest convective temperatures
will be breached by 23z and isolated high-based convection is
expected to develop across southwest KS which could spread/develop
northeast along the boundary into south-central NE. Gusty winds and
hail are the primary threats with the diurnally-driven activity.
A considerable amount of deep convection developed over the higher
terrain of northwestern Mexico ahead of what appears to be a weak
short-wave trough. This low-latitude wave should drift toward the
Gulf of California which will allow for more favorable trajectories
to transport moisture north of the international border into AZ.
With PWs expected to climb well above 1″, strong boundary-layer
heating should contribute to increasing buoyancy that will prove
supportive of robust convection. Forecast soundings suggest deep
convection will develop as early as 19z across southeast AZ, then
spread/develop west toward the lower deserts. A considerable amount
of convection may ultimately evolve across this region and gusty
winds are certainly possible given the increasingly wet downdrafts.