A NEW SEVERE WEATHER THREAT is being monitored, the second in just 3 days, and to take hold Tuesday afternoon and evening

National Weather Service storm survey teams are still in the field after a full weekend of work assessing damage from Friday and Friday night’s severe weather outbreak which has yielded 16 tornadoes—with the potential the investigation of additional areas of damage may yield more tornadoes. It wouldn’t be surprising to see the final tally of twister approach 20 making what happened Friday and Friday night historic in the Chicago area for a late March outbreak in terms of the number of tornadoes spawned.

The new SEVERE WEATHER RISK covers an area of more than 418,000 square miles—a region home to more than 37-million Americans revolves around another huge SPRING STORM SYSTEM.

As with Friday’s storms, warm, buoyant air is to ascend into a powerful wind field aloft. The t-storms which result may tap that wind energy and bring it down to the surface as potentially damaging t-storm winds. Dew points—in other words the moisture content of the air—will actually be higher tomorrow (Tuesday) than on Friday—and convering southerly and easterly winds along a northbound warm front may serve as a focusing mechanism for storm development. 

An atmospheric “WILD CARD” Tuesday afternoon and evening is the presence of a layer of warm air aloft—what’s known as a “cap”. The extent of severe storm development Friday afternoon and evening may be impacted. “Caps” have been known to thwart storm formation.  But if storms later Tuesday can “break” the cap, the atmospheric is primed for additional vigorous t-storm development.

The LEVEL OF RISK IS A “3” ON THE 5-LEVEL SCALE ASSESSED BY THE NWS STORM PREDICTION CENTER—an elevated level of risk. Risk levels run in the 2 to 3 range in northwest Indiana—but over 4 in northwest Illinois where the threat of tornadoes and damaging winds is highest. 

The period which appears most prone to strong t-storm development is to run from 3pm to 10pm Tuesday afternoon and night. 

HIGH NON T-STORM WINDS sweep into the Chicago area once a cold front passes Wednesday toward midday. Until then warm, humid air will take hold with nighttime temps remaining in the 60s Tuesday night.

A warmer, less frequently wet pattern appears in the offing longer range. Temps last week came in about a degree below normal. They’ll average 1 to 2-deg above normal this week—but over 8-deg above normal next week.  Only three of the coming 15 days are predicted to produce a below normal daytime average temp.


TONIGHT: Cloudy and cooler due to northeast winds off Lake Michigan. Sporadic showers—a few with thunder. Low 42.

TUESDAY (Election Day): Extensive cloudiness, breezy and cool in the city and areas north until winds shift southerly late in the day.

Scattered morning showers and a possible thunderstorm. More potent, downpour, wind and hail generating t-storms develop by mid or late afternoon—some potentially severe. Isolated tornadoes can’t be ruled out. High 69—even low 70s south. But lakeshore temps remain in the 40s and 50s North Shore.

TUESDAY NIGHT: Active, possibly severe t-storms through the evening. Then more scattered showers, breezy, warm and humid. Low 65.

WEDNESDAY: Warm and humid with some possible morning t-storms—then clearing, very windy and turning noticeably cooler in the afternoon and evening. High 71—falling to the 40s by evening. Wind gusts to 40 and 50 mph likely.

THURSDAY and FRIDAY: Mostly sunny with cooler, more seasonable temps. High Thursday 53. Friday’s high 54.

SATURDAY: Partly sunny, mildest inland. High 55—but cooler lakeshore.

SUNDAY: Increasing cloudiness. Breezy and milder. Growing prospects for showers and t-storms—especially Sunday night. High 70.

MONDAY: Partly cloudy, not quite as mild. High 64.