- Day Three
acus03 kwns 210647
Storm Prediction Center ac 210646
Day 3 convective outlook
National Weather Service Storm Prediction Center Norman OK
0146 am CDT Thu Sep 21 2017
Valid 231200z - 241200z
..no severe thunderstorm areas forecast...
a very low severe risk will exist across portions of the southern
and Central High plains northeastward to central Minnesota.
A longwave trough will continue to persist across the west while
only making slow eastward progress. Meanwhile, ridging will remain
in place across the Ohio Valley and Great Lakes region, and strong,
meridionally oriented flow will remain in place across the High
Plains and upper Mississippi Valley.
At the surface, a nearly stationary boundary will extend from
northwestern Minnesota south-southwestward to a surface low over
eastern Colorado. A surface trough will extend southward from the
low across eastern New Mexico. To the east of these features,
southerly low-level flow will maintain a modified maritime tropical
airmass across much of the plains and upper Mississippi River
valley. An anticyclone will remain nearly stationary across the
east, while surface ridging slowly builds into portions of the
Sustained convergence along the surface boundary and Lee trough
should Foster ongoing deep convection at the beginning of the
period, and these storms should increase in coverage and intensity
throughout the day in response to surface heating and attendant
destabilization. Although shear profiles in much of the plains
would support updraft organization (and perhaps a few instances of
rotation), marginal mid-level lapse rates will act to limit the
overall magnitude of the severe risk in most areas. Low (5%) severe
risk areas may be needed in later outlooks where late-day
destabilization can be maximized.