By Meteorologist Paul Merzlock
Theoretically, extensive Great lakes ice cover, particularly this late in the season, may influence Springtime temperatures in Chicago. Prolonged late-season ice melt delays the warming of lake water. However, a study of lake ice coverage, including data from 1973 to present, suggests there is little or no correlation between the maximum amount of lake ice and average Spring temps. This is simply due to the surface area of the Great lakes being very small compared to large-scale air flow across the continent. The brutal winter of 1976-77 produced 94% ice coverage, but the following Spring turned out to be the warmest on record at the time. Persistent SW flow across the U.S. quickly melted the ice. Temps this Spring are forecast to be below normal, mainly due to a recurring northwesterly jet stream.
Southwest winds on Friday brought the area its mildest air since February 20th. Temperatures reached the upper 40s across most of the area. Following a cold frontal passage late Friday evening, winds turned north, putting the area’s warm-up on a temporary hiatus. Satellite imagery confirmed that over 90 percent of lake Michigan remains covered by ice. As northeast winds increase on Saturday, air flow off the ice pack will limit daytime readings to the low and mid 30s. Sunshine, and lighter winds on Sunday are expected to allow temps to moderate to seasonable levels. Much stronger southwest winds are forecast to sweep across the area on Monday, negating any influence of lake Michigan. The area can expect its warmest air in more than 3 months as readings soar to the mid and upper 50s.
After 4 days of thawing temperatures and snow melt, winter is set to make a comeback. At Midway airport this past Tuesday, a snow depth of 14 inches was measured. Late Friday that snow pack had shrunk to 5 inches. Colder air, sweeping into the region on gusty west winds, sent temps into the 20s Friday night, ending the thaw. A weak disturbance moving across the Midwest on Saturday is forecast to deposit a swath of 1 to 3 inches of snow across portions of the Chicago area. Should this verify, February 22nd would mark the 6th consecutive Saturday with observed snowfall. At O’Hare airport, the season snowfall stands at 68.3 inches. It appears likely that Saturday’s snow system will bring the city the 2 tenths inch accumulation needed to officially make the winter of 2013-14 the 4th snowiest on record.
Through February 16th, 62.9 inches of snow has officially been recorded at O’Hare airport. This places the winter of 2013-2014 as 7th snowiest on record. As much as 6 inches of new snow is expected to accumulate across the area by Monday evening. Should this forecast verify, the winter snow total would move to 5th place in the record book. The season snow total at Midway airport currently stands at 67.0 inches, and is likely to top the 70” plateau by Monday evening. Since snow records began in the winter of 1884-1885, snowfall in Chicago has topped 70 inches only 3 times. Accumulating snow is forecast to overspread the area by late Monday morning. This snow system will likely produce bands of heavy snow, with accumulation rates of 1 inch or more per hour. The area snowpack is expected to shrink later this week as temps rise above freezing and rain moves through the region.
Another round of wintry weather is due to arrive on Monday. This system threatens to bring a significant snowfall, before thawing temperatures begin to melt the region’s snowpack. Snow is not forecast to begin until mid-morning, thus sparing much of the early commute. Accumulations of 3 to 5 inches are expected by the time the snow ends late in the afternoon. Temperatures during Monday’s snowfall will hover near freezing, making for a sticky, heavy accumulation. Mild weather will follow in the wake of the snow, with temperatures climbing into the 40s on Tuesday. Daytime readings are then forecast to remain above freezing through the remainder of the week. Strong southerly winds are expected to bring rain, and a spike in temps Thursday, with readings pushing well into the 40s.
After a 3-day break in accumulating snowfall, another weather system is organizing over the southwestern U.S. This disturbance is forecast to spread snow across central Illinois Tuesday afternoon, with precipitation then expected to spread north, across the Chicago metro area Tuesday evening. Present indications suggest heavy snow from this system will stay south of the area, impacting areas generally along, and about 100 miles north of Interstate 70. Lighter snow across northern Illinois is forecast to range from around 2 inches near the Wisconsin state line, to 4 inches along the I-80 corridor, and 6 or more inches south of the Kankakee river.
The above infra-red satellite image taken about 7:45 PM CST Monday evening shows enhanced, cooling clouds forming a distorted “S” shaped edge to the cloud system, from southern IA, through northwest KS, to far west TX. This indicates a disturbance in upper level wind flow that is to promote development of a storm system on Tuesday. Radar shows only spotty patches of light snow over the Plains, As Gulf of Mexico moisture is ingested into this system late tonight and Tuesday morning, snow is expected to increase rapidly in coverage and intensity.
Above is a surface weather analysis of the Midwest as of 5 A.M. Red numbers represent air temperatures.
Frigid air has settled across the Midwest. Temperatures across the Chicago area are at, or just below zero. Biting northwest winds of 20 to 30 mph have lowered wind chill readings into the minus 20 to minus 30 degree range.
Temperatures are expected to slowly fall through the morning hours, leveling off around 5 to 10 below zero through midday as polar air across Iowa and southern Minnesota continues to stream into the area.
Following are some Chicago area 6AM temperatures and wind chills:
Location Temp Wind Chill
O’Hare 1 -19
Midway 0 -19
Rockford -4 -26
DeKalb -5 -27
Rochelle -4 -24
Du Page -3 -23
Aurora -3 -25
Romeoville -2 -24
Ottawa -2 -24
Joliet -3 -20
Lansing -1 -20
Kankakee -1 -20
Pontiac 1 -20
Morris -2 -24
Northwest winds will continue to gust around 40 mph overnight. Considerable blowing snow will create blizzard conditions at times, especially in open country. Travel is highly discouraged the remainder of tonight. In addition to locally poor visibility and drifting snow across roadways, the strong winds are ushering arctic air across the region. By daybreak Monday, temps across the Chicago area are expected to range from 5 to 10 below zero, with dangerous wind chills of minus 30 degrees or lower. Little or no recovery in temperature is expected during the day Monday.