textproduct: Chicago

KEY MESSAGES

- Showers and thunderstorms will persist this evening. Some storms will be severe, particularly across central IL into northwestern IN through 9 PM this evening.

- Periods of accumulating snow and blowing snow will set the stage for Blizzard conditions across northwestern IL overnight into Monday morning. We have thus opted to upgrade to a Blizzard Warning across parts of northwestern IL. A Winter Weather Advisory remains in effect for areas along and northwest of the I-55 corridor overnight through Monday morning. - Wind-whipped snow showers may develop across the area Monday afternoon, leading to locally hazardous travel conditions.

- A period of cold temperatures is expected Monday and Tuesday, with overnight wind chills ranging from 5 to 10 below, especially Tuesday morning.

- A clipper system will likely bring a period of snow to the area Tuesday night into Wednesday. Thereafter, a warming trend will commence through the end of the week.

UPDATE

Issued at 722 PM CDT Sun Mar 15 2026

We just recently updated the forecast to upgrade our Winter Storm Warning to a Blizzard Warning. We also included Dekalb and McHenry counties in this warning. We also expanded the Winter Weather advisory anther row of counties southeastward along the I-55 corridor.

The storm system is tracking farther south then originally thought. Overall, this adds concern that snowfall amounts may end up a bit higher than previous forecasts, particularly across the warned area where several hours of wind gusts of 45 to 50 mph will combine with the snow overnight into Monday morning to produce blizzard conditions. With this in mind, and the fact that there are numerous upstream obs across IA and parts of MO that are reporting 1/4 or less VSBYs, felt the path of least regret was to pull the trigger on the upgrade.

The end times of the winter headlines run from mid to late this evening through early Monday afternoon.

KJB

DISCUSSION

Issued at 313 PM CDT Sun Mar 15 2026

Through Monday night...

A strong and very dynamic early Spring season storm system currently shifting into western IL this afternoon, will deepen to near 980 mb late tonight into Monday as it lifts northward across Lower Michigan.

Hazards associated with this system late this afternoon through Monday include: - Another round of showers and thunderstorms this afternoon through early evening in advance of an approaching cold front. Some of these storms could be severe, with damaging winds in excess of 60 mph the main threat. - Rain mixing with a brief period of sleet and freezing rain before transitioning to snow from west to east across the area Sunday evening and night. - Turning much colder and very windy tonight into Monday, with considerable blowing and drifting snow, with possible near blizzard conditions at times, particularly across northwestern IL late tonight into Monday morning. Storm and Severe Threat This afternoon and evening:

Showers and thunderstorms continue to track east-northeastward into northern IL this afternoon. Thus far, these storms have remained sub severe, likely owing to limited instability. We will have to continue to monitor the shallow convective activity farther to the southwest in advance of the approaching cold front. This activity is expected to shift eastward across the area into early this evening. Extensive cloud cover, and only modest dewpoints into the low 50s, will continue to curtail destabilization ahead of this activity. However, given the continued presence of strong southwesterly flow off the surface, the potential will exist for some localized strong wind gusts in excess of 60 mph with this shallow convection, particularly in areas south of I-80 across eastern IL into northwestern IN.

Winter Weather Threat tonight into Monday:

Rain will transition to the snow from west to east this evening as a much colder airmass quickly spills in across the area along the backside of the deepening surface low moving into Lower Michigan. The transition is likely to be accompanied by an hour or so period of a wintry mix of sleet and freezing rain, though the main story will be the accumulating and blowing snow expected tonight into Monday morning, particularly across northwestern IL (Rockford area), where a Winter Storm Warning is in effect. In this region, steepening low and mid-level lapse rates will support some higher rates of snow (up to an inch per hour) for a period late this evening into the overnight hours as the 700 mb low tracks northeastward into south central WI. While initially the snow will be wet, a rapidly cooling column will result in a transition towards a drier (more blowable) snowfall late tonight into Monday morning.

This is important, as northwesterly wind gusts will become progressively stronger overnight as the surface low deepens down around 980 mb across northern lower Michigan. With wind gusts of 45 to 50 mph likely by early Monday morning, there continues to be concern for a period of near blizzard conditions late tonight into Monday morning. The worst conditions across the warned area will be from roughly 11 PM tonight through 10 AM Monday morning. We continue to hit the wording for near blizzard conditions hard in the Winter Storm Warning, and we cannot rule out the need for a an upgrade to a Blizzard Warning.

East and southeast of the Winter Storm Warning, a Winter Weather Advisory is in effect as far southeast as areas near the I-55 corridor tonight through Monday morning for snow and blowing snow. Snowfall amounts in this area will be lighter, and will taper with southeastward extent. Accordingly, amounts are generally expected to range from 2 to 4 inches far northwest, to 1 to 3 inches across the southeastern part of the advisory area. Hazardous travel conditions will also be likely in the advisory area due to the snow and blowing snow on these increasing northwest winds.

As the surface low begins to move out of the area Monday afternoon, we will see the snow begin to taper off across northern IL. However, steep low-level lapse rates through the DGZ (Dendritic Growth Zone) will continue to support scattered snow showers and squalls into the mid to late afternoon hours, with flurries potentially even continuing into Monday night.

KJB

Tuesday through Saturday:

The unseasonably cold start to the day on Tuesday will lower the ceiling for the day's high temperatures, with temperatures presently favored to peak only in the 20s. With expansive surface high pressure shuffling its way eastward across the region, no precipitation is expected during the daytime hours.

A fast-moving clipper-type shortwave diving southeastward out of Alberta will arrive at our doorstep Tuesday night. Nearly all members of the 00Z EPS and GEFS output a modest amount of QPF across our forecast area Tuesday night into Wednesday morning, which would translate to measurable snowfall with air temperatures not expected to rise above freezing until sometime during the mid to late morning on Wednesday. Some ensemble spread remains with the strength of the inbound wave and how much moisture it will have to work with, but overall, this doesn't have the look of a blockbuster snowfall event.

A strong upper-level ridge initially centered off the California coast will reposition itself eastward over the Desert Southwest for the latter half of the week. This will kick off a warming trend here locally through the end of the workweek as the associated thermal ridge expands eastward, with highs in the 50s and 60s expected to make a return.

The jet stream draped around the ridge's northern periphery will also get nudged eastward, which will steer any subsequent clipper waves/systems emanating out of Canada more to our east. That said, one additional clipper shortwave may still get close enough to our area Wednesday night into Thursday for another round of precipitation to occur here. This outcome is reflected only in a minority of Grand Ensemble members at this time, so made no changes to the dry NBM forecast at this juncture.

Ogorek

AVIATION /00Z TAFS THROUGH 06Z TUESDAY/

Issued at 658 PM CDT Sun Mar 15 2026

- Rain, heavy at times, with some embedded thunder expected early this evening. - Rain will change to snow from northwest to southeast this evening into the early overnight hours. - Snow, heavy at times, is expected overnight into early Monday morning before tapering off to lighter snow showers/flurries. - Strong northwest winds will result in blowing and drifting snow and reduced visibilities overnight into Monday.

Powerful storm system will continue to produce a wide variety of inclement weather over the next 24 hours. For the immediate Chicago terminals, rain, heavy at times, with some embedded thunder will gradually taper off early this evening. Rain will gradually change to snow from northwest to southeast across the terminals this evening into the early overnight hours. The heaviest snowfall rates are expected overnight, perhaps lingering into the early morning hours Monday. Very strong northwest winds will result in blowing and drifting snow, especially late tonight into Monday morning as the snow type becomes less wet and more apt to be blown around.

Steadier accumulating snow is expected to end during the early- mid morning hours Monday, but some snow showers/flurries could linger through much of the day with much lesser threat for accumulations. Snow threat should end by early Monday evening with winds gradually decreasing Monday night.

- Izzi

LOT WATCHES/WARNINGS/ADVISORIES

IL...Blizzard Warning until 1 PM CDT Monday for ILZ003-ILZ004- ILZ005-ILZ008-ILZ010-ILZ011.

Winter Weather Advisory until 1 PM CDT Monday for ILZ006- ILZ012-ILZ013-ILZ019-ILZ020-ILZ103.

Winter Weather Advisory from 1 AM to 1 PM CDT Monday for ILZ021-ILZ032-ILZ104-ILZ105-ILZ106-ILZ107-ILZ108.

IN...None. LM...Gale Warning until 10 PM CDT Monday for the IL and IN nearshore waters.