© 2019 Terry Swails

LAKE ENHANCED UGLINESS...THE BACK DOOR FRONT!...

March 24, 2017

 

By now you've all heard about a big storm that's advancing on the Midwest. As with most spring systems, it will have its share of forecast challenges, not the least of which is a lake enhanced boundary that promises some wild temperature swings.

 

Now Friday, most of my local area and points east and south will enjoy spring-like readings as the day starts with a mild southwest flow ahead of a front stretching from a low in SE Colorado to central Lake Michigan.

 

Here's the expected temperatures at 1:00pm as forecast by the EURO. Look at the 70s as far north as SE Iowa and the Chicago metro area. 

Nice as it will feel in those locations, a wall of cold is getting set to power its way south. Its chill is already being felt in NW Iowa, Minnesota, and Wisconsin much of Friday. When the cold comes from the E/NE (as it will in this case) instead of the W/NW as it usually does, we call it a back door cold front. As winds gradually turn to the east in my area late Friday and Friday night, the cold will rapidly surge in as the storm center moves into Missouri. You can see the brisk easterly flow at 1:00pm Saturday on the surface depiction below.

The cold will be enhanced at the surface by the open but still cold waters of the Great Lakes. As you can see water temperatures in the lakes are generally in the mid 30s to lower 40s.

 

Those stiff east winds coming off the cold water for an extended period of time will bring an eye opening drop in temperatures. In some spots Saturday's mid-day readings will be nearly 30 degrees cooler than Friday. Here's the 1:00pm temperatures the EURO forecasts on Saturday.

Notice how once you get south of Lake Michigan the cooling is substantially less. Those cold lake waters make a huge impact on temperatures. Just ask anybody from Chicago or Milwaukee who's experienced the power of a back door cold front as it slips in off Lake Michigan. 

 

Once the lake enhanced cold dome is in place, warm moist air circulating around the storm will ride over it and bring widespread rains of 1 to as much as 2 inches. Here's a simulated satellite of the big storm as it's expected to look like Friday night. Rain is falling under much of that cloud cover.

Here is what the GFS has for rainfall through Sunday. In spots, some of this has already fallen.

Several more systems with similar characteristics are expected in the next couple of weeks. The operational GFS has this for 16 day total precipitation. 

The active pattern is expected to last through much of April. The EURO weeklies just in have this for 46 day precipitation. Most of the Midwest is 1 to 4" above normal for the period.

Just for fun, here's the 46 day temperature departure. There's a pretty strong signal for much of the nation to experience above normal readings. 

If the weeklies are on track (and I like the general trends), I would expect severe weather to also become a factor as spring-like warmth makes its way further north into the Midwest. I fully believe this year will be the most active for severe storms since 2008 across the central Midwest. We're already off to a fast start in my local area. Time will tell. Until next time roll weather and enjoy your weekend...TS

 

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