I run several models in the morning from the College of DuPage Weather Lab, the NAM (North American Mesoscale Forecast System), GFS (Global Forecast System), ECMWF (European Center for Medium-Range Weather Forecasts), HRRR (High Resolution Rapid Refresh which I use for the forecast maps) and the CFSv2 (coupled forecast system model version 2).
Below is a model from the CFSv2 running through September 11 which provides a better view of north America and the cooler air transport from Canada. I slowed the animation speed so you could better see the date stamps in the upper right hand corner. The greens and blues are the cooler air – purple is cold. Reds and orange are warm. As August progresses into September you can see the blues moving south. This is a long range model so it has to be taken with a grain of salt. This would be a fairly normal transition to fall.
Short term mostly clear skies are expected through Thursday afternoon before a frontal system moving through the area brings an area of showers and a few thunderstorms into our area Thursday night into Friday morning. Temperatures will be close to normal for this time of year today and Thursday. Cooler and drier air will follow for the weekend.
HRRR and Futurecast models runs are for 12 hours beginning at 7am – a second model run begins at 3pm
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Overall a rather quiet weather pattern is expected for Southwest Lower Michigan into Thursday afternoon. It does look like there will be a band of showers and thunderstorms ahead of the cold front that comes through this area Friday morning.
Clearing should follow the frontal passage Friday during the day. We have the polar jet to our south through this event, so that means we get the weather typical of an occlude front passage Thursday night into Friday morning. That includes the dry slot clearing behind the front during the day time hours of Friday.
What this is, is a digging northern stream shortwave that on at least some of the models shows the 500 mb wave trying to close off an upper low just as it is moving into Michigan. This usually means the system should be developing as it moves through this area which will support widespread rainfall with this frontal passage. We have left exit region of the upper jet to help the cause.
That helps to develop a low level jet with aims directly at Southwest Lower Michigan toward midnight tomorrow night. There is some instability but it is not spectacular (300 to 800 j/kg). There is weak isentropic lift (assoicated with the occluded frontal process). The CIPS analogs show widespread rain for our CWA with this type of event at this time of year.
The negatives for this are the Gulf inflow is cut off by the polar jet being south of this area. That means we do not have a huge amount of moisture to work with, still there is decent lift and the mean 1000 to 500 mb rh is around 90 pct (good for rain to reach the ground here) around midnight with the frontal passage. So my spin on this is severe storms are not expected (see CPC outlooks).
The SPC SREF 3 hour SEVERE PROB is zero, the Craven severe is less than 10,000, and the effective bulk shear mean is less than 30 knots. So the bottom line is a band of showers and a few thunderstorms is likely to cross this area in the 10 pm to 5 am time frame.
As for today, like yesterday and for tomorrow afternoon there is some instability shown in the model sounding but the 800 mb to 300 mb rh is mostly less than 10 pct, which is not good for convection, so I have 10 pct pop over our eastern CWA to cover that potential. .
A dry extended period seems to be in store for the end of the week and into next week. Temps should be rather uniform, and generally a bit below normal. The overall pattern has an upper low over Eastern Canada which spins occasional upper troughs across the Great Lakes. This should result in temps below normal with a predominate northwest flow over the Great Lakes.
Despite the upper trough on Friday night, surface ridging will be building in, and it should largely be dry. The coolest temps will probably be over the region for the weekend. Another trough comes down in the northwest flow by Sunday night, but the surface high should keep us mainly dry.
The beat goes on into Monday/Tuesday as yet another upper trough is indicated to come through. But again the surface high remains in place with somewhat of a blocked pattern. We can not completely rule out isolated showers with each upper trough, but it largely appears dry. Temps should be slightly warmer by Monday/Tuesday with the surface high slowly drifting to our east.