Severe Storm Outlook Narrative (AC)
Issued by NWS
ACUS01 KWNS 240100
SPC AC 240059
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0659 PM CST Thu Feb 23 2017
Valid 240100Z - 241200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
KANSAS AND SOUTHEAST NEBRASKA INTO IOWA AND NORTHERN MISSOURI...
Showers and thunderstorms -- a few of which may produce hail that
approaches or even reaches marginal severe levels -- are expected
from northeast Kansas and southeast Nebraska northeastward across
parts of northern Missouri and Iowa this evening and overnight.
Mid-level troughing will continue to shift gradually eastward across
the central Plains this evening/overnight, while an associated
surface low now over southwest Kansas moves east-northeast, reaching
the northeast Missouri/west-central Illinois vicinity by the end of
the period. A warm front extending east from the low will gradually
shift northward across the Midwest, while a trailing cold front
advances southeastward across the southern Plains overnight.
...Parts of northern Kansas and southeast Nebraska northeast across
Iowa and northern Missouri...
Latest radar loop shows widespread rain/rain showers from Nebraska
eastward into the upper Great Lakes region, with scattered/elevated
thunderstorms developing on the southern fringe of this area of
precipitation -- i.e. from north central Kansas and parts of
southeast Nebraska into Iowa. The convection is occurring in a zone
of strong quasi-geostrophic forcing for ascent ahead of the
advancing upper system and north of the surface warm front, where
several hundred J/kg elevated CAPE exists per model forecast
soundings and extrapolation of evening RAOBs.
Given the degree of elevated CAPE, in conjunction with strong
southwesterly flow at mid levels supporting favorable cloud-layer
shear, a few stronger storms will likely evolve from time to time
this evening and into the overnight hours. Small hail -- possibly
nearing or exceeding severe levels with a couple of the strongest
updrafts -- can be expected, with the risk area shifting
northeastward with time across the mid-Missouri valley area.
Showers and a few thunderstorms are forecast to persist across parts
of Ohio and Pennsylvania, and later into New York state. Weak
instability precludes any appreciable severe risk.