A couple days ago, Lisa informed me that Dr. Greg Forbes was forecasting severe storms Monday in eastern Iowa and northern Illinois. I thought, hmmm…a bit far out to be definitive, but maybe I ought to take a look. I’ve been following the models since, and after this morning’s 6Z runs, it looks like Forbes is onto something.

Both the NAM and GFS suggest that an area from far eastern Iowa through northern Illinois and southern Wisconsin may be under the gun in the afternoon or evening. Here are a couple of NAM maps that will give you an idea why (click on maps to enlarge). The bottom line is that a low pressure system is cranking unseasonably warm temperatures and dewpoints in the mid-50s or higher into the Great Lakes region. The potential exists for weak instability to coincide with stiff 850 and 500 mb jet cores.

The GFS paints a somewhat more aggressive picture than the NAM and wants to clip things along a few hours faster. If that pans out, then north-central Illinois and south-central Wisconsin may see the best play. But both models are calling for essentially the same thing. Note the bullseye of 500 SBCAPE and 75 J/kg 3km MLCAPE at Clinton, Iowa, coincident with a nose of Theta-E bulging into the area. The GFS depicts the same scenario, albeit at 18Z rather than 21Z.

Today, Sunday, temps are forecast to rise into the 50s here in Grand Rapids, and tomorrow they should make it into the low 60s along with a significant increase in moisture. We stand a chance for a few thunderstorms of our own, particularly when the cold front moves in Monday night. As the KGRR forecast discussion puts it, “GIVEN TEMPS IN THE LOWER 60S…IT MAY ACTUALLY FEEL A BIT HUMID MONDAY AFTERNOON. THE CURRENT MENTION OF SLGHT CHC TSRA STILL LOOKS GOOD.” The SPC day 2 outlook has even thrown in mention of isolated tornadoes from southern Michigan southward, but tomorrow’s models will give a better sense of whether that’s any real concern. Helicity should be adequate, but instability is weak, and a November night-time squall line in Michigan is not your typical tornado machine.

Right now, the bottom line looks like warmer-than-usual weather in our area today and especially tomorrow, with storms in the offing in northern Illinois and nearby areas. And behind that, setting the tone for Thanksgiving, colder weather. So enjoy this last spate of warmth, because winter is waiting in the wings.