- Day Three
acus02 kwns 221729
Storm Prediction Center ac 221728
Day 2 convective outlook
National Weather Service Storm Prediction Center Norman OK
1228 PM CDT Thu Mar 22 2018
Valid 231200z - 241200z
..there is a marginal risk of severe thunderstorms Friday evening
across parts of the north Central Plains into middle/lower Missouri
Strong thunderstorms may impact portions of the north Central Plains
into lower Missouri Valley late Friday afternoon into Friday night.
Some of these could be accompanied by a risk for severe hail.
Models indicate that the remnants of an elongated, deep mid/upper
low will begin to gradually shift inland of the Pacific coast during
this period. It appears that one emerging significant impulse will
pivot across the Pacific northwest through Alberta/Saskatchewan by
late Friday night, while another continues to dig off the Pacific
northwest coast. These developments are expected to contribute to
the evolution of positively tilted large-scale troughing across much
of much of the west, where split belts of mid-latitude westerlies
emerging from the Pacific may become more in phase.
Downstream, large-scale upper ridging is forecast to continue
developing east of the U.S. Rockies and Canadian prairies through
the upper Great Lakes region, the Mississippi Valley and parts of
the southeast, while troughing lingers across eastern Canada and
much of the northeast. It still appears that a significant impulse
within the southern branch of the mid-latitude westerlies, initially
in the vicinity of The Four Corners region at 12z Friday, will
progress through the broader scale anticyclonic flow across the
Colorado rockies into the middle/lower Missouri Valley region by 12z
In association with this latter short wave, models indicate that
modest surface cyclogenesis is possible across parts of eastern
Colorado into Kansas during the day Friday. This will probably be
accompanied by strengthening southerly low-level flow across the
southern and Central Plains into the mid/lower Missouri Valley.
Beneath a belt of strengthening mid-level flow on the southern
periphery of the impulse, a destabilizing environment within the
warm sector of the low, and along a developing warm frontal zone,
may become supportive of at least some risk for strong/severe storm
development late Friday afternoon into Friday night.
..Central Plains into mid/lower Missouri Valley...
A southerly return flow is already underway from portions of the
western Gulf of Mexico through the southern and Central Plains. By
late Friday afternoon, it appears that moisture characterized by
precipitable water in excess of 1 inch and surface dew points in the
lower 60s may reach the vicinity of the deepening surface low.
Models indicate that this will contribute to at least weak cape on
the order of 500-1000 j/kg.
It does appear that inhibition associated with warm elevated mixed
layer air may suppress thunderstorm development to the south of the
surface frontal zone. However, strong boundary layer
heating/mixing, coupled with forcing associated with the upper
impulse, may support the initiation of storms across the High Plains
of southeast Wyoming/northeast Colorado and western Nebraska late
Friday afternoon. Severe weather potential across this area remains
unclear, but at least a risk for small hail and locally strong gusts
appears to exist in stronger storms through early evening.
Somewhat better potential for vigorous thunderstorm development may
evolve Friday evening into Friday night farther to the east, across
parts of southern Nebraska into the Missouri Valley, as stronger
mid-level height falls shift eastward and a strengthening (50+ kt at
850 mb) low-level jet enhances/focuses lift associated with
lower/mid tropospheric warm advection. Activity should be rooted
above a pronounced near surface stable layer, but the environment
may become conducive to the risk for at least marginally severe