- Day Three
acus03 kwns 180709
Storm Prediction Center ac 180708
Day 3 convective outlook
National Weather Service Storm Prediction Center Norman OK
0208 am CDT Wed Sep 18 2019
Valid 201200z - 211200z
..there is a slight risk of severe thunderstorms over the northern
Scattered severe storms are possible on Friday across the northern
plains, with isolated activity into the Central High plains.
An upper trough will move across The Rockies and into the plains,
with an upper low deepening over Montana. Modest south/southwest winds
aloft will exist during the day over the plains before a
strengthening wave pivots northeast out of Wyoming and Colorado overnight. Low
pressure will develop over the northern High Plains during the day,
shifting into Canada overnight. Southerly winds across the plains
will maintain 60s f dewpoints with areas of moderate instability
supporting strong to severe storms ahead of a cold front that will
sweep east across the Dakotas and Nebraska late.
A few storms may be ongoing Friday morning over ND in a warm
advection regime with hail possible. Continued height falls aloft as
well as a warming boundary layer will lead to an uncapped air mass
extending south along the surface trough/wind shift, with additional
scattered storms expected by 21z from the central Dakotas into
western NE. Subtle hodograph details/weaknesses aside, generally
veering and increasing winds with height combined with the strong
instability will generally support severe hail, wind, and perhaps a
couple tornadoes. Given the meridional winds aloft and front
orientation, storm Mode may become complex with merging cells as the
corridor of storms gradually translates east, possibly reaching
western Minnesota by Saturday morning.
To the South, Strong heating and sufficient convergence near the
surface trough may lead to isolated late-afternoon storms over
eastern Colorado and western Kansas. Ample deep-layer shear as well as 30+ kt
south/southeast winds at 850 mb will conditionally support a
supercell or two capable of large hail and perhaps a brief tornado.
At this time, storm coverage is uncertain but a slight risk may be
needed for parts of the Central High plains in later outlooks should
expected coverage increase.