Friday a large ridge of high pressure slides overhead and we drop about 10 degrees under mostly sunny skies. A few fair weather cumulus clouds will develop along the lakefront by afternoon, but the weather will be quiet.
Saturday and Sunday will be the exact opposite with a large storm system approaching from the southwest U.S. We are under the risk of severe weather from Saturday morning through Sunday morning.
As a warm front passes Saturday morning we will see temperatures rise into the 70s with periods of strong storms possible. Any break in the clouds during the afternoon hours will help recharge the atmosphere and as the cold front approaches Saturday night into early Sunday we will face another round of possible severe weather.
The main threats will be damaging straight-line winds (Derecho) and isolated tornadoes. 1" - 2" of heavy rain is also possible especially north of I-88. Skies should clear as the front passes east by Sunday afternoon.
The worst of this weather is expected to be just north and west of the greater Chicago area, but that may change in the next 24 hours as the storm strengthens.
FRIDAY: Sunny and cool with highs in the upper 50s and lows in the mid 40s.
SATURDAY: Mostly cloudy and windy with a 80% chance of storms both in the morning and again in the evening. Some of the storms could be strong or severe. Highs in the low 70s. Lows in the mid 50s.
SUNDAY: Mostly cloudy and breezy with an 90% chance of storms mainly in the morning. Highs in the mid 60s and lows in the mid 40s.
MONDAY: Partly sunny and cooler with highs in the upper 50s and lows in the low 40s.
TUESDAY: Partly sunny with increasing clouds and a chance of rain in the evening.. Highs in the mid 60s and lows in the low 50s.