acus02 kwns 240553
Storm Prediction Center ac 240551
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1251 am CDT Friday may 24 2013
Valid 251200z - 261200z
..there is a slight risk of severe thunderstorms for a portion of eastern Montana / far
northestern Wyoming / western Dakotas...
The upper air pattern will feature a western U.S. Trough/central U.S.
Ridge/eastern U.S. Trough. Downstream of the western states trough...a
broad belt of moderate southwesterly middle-level flow will overspread the northern
High Plains. A Lee surface trough over much of the High Plains will
serve as a focus for afternoon/evening storm development. Farther
east...a frontal zone will extend from the eastern Dakotas to the middle MS
valley to the west of surface high pressure centered over the Great
..nrn High Plains into the middle MO valley...
Northward moisture return into the central-northern plains on the backside of the
Midwest surface high will be ongoing at the start of the day 2
period as a closed middle-level low remains centered over southern British
Columbia. The Lee trough located over central Montana will act to draw 50s
dewpoints westward into eastern Montana and upper 50s dewpoints in vicinity of the
Black Hills...contributing to marginal-moderate instability. Strong
diurnal heating will seemingly lead to isolated to widely scattered storms
in the late afternoon-middle evening. Deeply veering wind profiles
/40+ knots effective shear/ would support storm
organization...including supercells with isolated large hail/wind gusts
being the primary hazards.
Farther southeast over the middle MO valley...the terminus of a Central Plains
30 knots low level jet will focus over the middle MO valley throughout the day.
Although this region is beneath the upper ridge axis...at least a
low risk for storms is supported by various operational models.
Given moderate instability depicted by model forecast soundings...a
conditional severe area has been included this forecast update.
..portion of the southern High Plains...
A southeasterly low level fetch of moisture located over the Southern Plains is
forecast to move westward into the southern High Plains in concert with
the Lee trough...abutting next to the higher terrain in West Texas and the
eastern plains of nm. Steep middle level lapse rates emanating from the west
and strong daytime heating will act to favor isolated storm development
by afternoon...initially favoring higher terrain. Despite only 20
knots westerly 500 mb flow...strongly veering wind profiles would support some
storm organization featuring mainly higher-based multicellular
storms capable of perhaps a few severe wind gusts and marginally
severe hail. This activity should weaken during the evening hours
coincident with a stabilizing boundary layer..