acus02 kwns 250534
Storm Prediction Center ac 250533
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1233 am CDT Sat may 25 2013
Valid 261200z - 271200z
..there is a slight risk of severe thunderstorms for parts of the northern High
Plains into the middle MO River Valley...
A western U.S. Upper trough centrally located over the Pacific northwest will
move eastward during the day 2 period as the upper air pattern becomes
more progressive as a middle level low departs from New England into
the Canadian maritime provinces. Modest broad southwesterly middle level flow
will spill downstream over the High Plains as an upper ridge weakens
over the central U.S. A residual frontal zone over the Midwest southeastward
to the southern Appalachians will slowly advance northward while a surface low
and attendant dryline/surface trough extend north-south over the
..mid MO River Valley into the north-central and northern High Plains...
A moderate warm advection regime will likely be ongoing Sunday
morning over the north-Central Plains near a frontal zone located over the
middle MO River Valley. Steep middle level lapse rates in excess of 8 degree
c per km may facilitate a marginal hail threat with early morning
storms. The northward advance of the frontal zone over the middle MO valley
may be hampered by the early day convection acting to reinforce this
effective outflow/front in vicinity of the middle MO River Valley.
Later in the day...strong heating farther west over the High Plains
will likely coincide with gradual middle level height falls from Kansas/Nebraska
northward into eastern Montana in concert with perhaps a few weak impulses ejecting
into the central-northern High Plains. A plume of low level moisture
characterized by dewpoints in the 50s should advect nwwd into the
western Dakotas into central-eastern Montana while Richer moisture with dewpoints
ranging through the 60s remain farther southeast over Nebraska southward east of the
dryline. Forecast soundings show a marginal to moderately unstable
boundary layer over Montana with MLCAPES ranging from 500 j/kg west to
upwards of 2000 j/kg near the Dakotas borders. Orographic
lift/upslope flow and general cyclonic southwesterly upper flow would
seemingly be supportive of isolated-widely scattered storms by the late
afternoon/evening hours. Backed Ely flow north of the Central High plains
low from the western Dakotas westward into Montana/Wyoming will contribute sufficient
deep layer shear for organized isolated strong-severe
storms...including supercells by late afternoon-evening...capable of
mainly a large hail/severe wind gust threat.
Farther S in closer proximity to the surface low...greater heating
will be necessary to overcome a cap over neb/KS. Modest shear
profiles will generally be supportive of organized strong-severe
multicells and perhaps a few supercells by the afternoon-evening.
Storm mergers/cold pool consolidation and a strengthening low level jet after
dark may favor upscale growth and a lingering large hail/damaging wind
threat into the evening.
..wrn Kansas southward into West Texas...
A sharpening dryline during the day may lead to a few widely-spaced
storms in vicinity of the dryline as strong heating into the 90s near/west of
the dryline weaken and locally erode the cap by late afternoon.
Forecast soundings along the dryline show a very steep lapse rate
profile with dewpoints mixing into the 50s. Although effective
shear values will remain modest /aob 30 kt/...a few of the stronger
storms will potentially be capable of large hail/damaging winds before
weakening during the evening.