A storm responsible for a crippling Plains blizzard Friday while stoking
100-degree temperatures in south Texas, bears down on the Chicago area
Saturday afternoon. Air ascends so quickly in such a system, barometric
pressures plunge, encouraging winds to rush in from the periphery. The
process can lead to eye-catching wind velocities -- like the 45+ m.p.h. gusts
expected to sweep this area as cold rain moves in later Saturday. Lakeshore
flood warnings have been issued on the Indiana and Illinois shorelines,
likely to be lashed by 10-12 foot waves which may lead to minor flooding.
It’s what happens next which may define this system. Rising air in storms
moves to higher elevations where atmospheric pressures are lower. As this
happens, air expands and cools. The speed with which that process takes
place will dictate whether and how fast the cold rains of later today
transition to sleet then snow. Current indications suggest the switch is to
begin late Saturday in northwest suburbs then proceed southeastward into the
city during Sunday’s pre-dawn hours. Converging winds above the surface may
lead to embedded, precipitation-enhancing thunderstorms as well. With snow
and sleet expected to fall longest west of the city -- particularly from the
Fox Valley and McHenry County westward, snow accumulations may be heaviest
there. But the city isn’t likely to completely escape. The arrival of snow
and sleet -- and the real possibility of a period of fairly healthy snowfall
for a time Sunday morning -- could lay down 2-5” in the city, while 5 to 8”
can’t be ruled out in the far west and northwest suburbs. Chicago typically
sees a 6”+ snow later than March 28 approximately once every 10 years.
Up to 20” down in the Plains, drifts tower to 10 ft.
Powerful gusts to 50 m.p.h. in the western Plains piled up 10 ft. drifts
from western Kansas south to the Texas Panhandle with 19” accumulations
reported at Ulysses, Kan.
--Tom Skilling, Chief Meteorologist, WGN-TV/Chicago Tribune
