Thursday, April 27, 2017

Can You Say "Pattern Change"?

Most of this spring east of the Rockies has been warm, coming on the heels of a mild winter. The growing season is running two to three weeks ahead of normal, but now Mother Nature is messing with us.

This week saw a lot of snow in the Rockies, not all that unusual even this late in spring. This morning flakes were flying in Minnesota and Wisconsin in the wake of a strong low and associated cold front.

Surface weather map at 1:00 p.m. CDT April 27. 2017

More snow is expected throughout the Rockies this weekend as cold air plunges south behind an intensifying low pressure system in the central Plains. This storm will be associated with an upper level closed low over the central U.S., one that will move very slowly over the weekend and early next week.

500  millibar level chart for 7:00 a.m. CDT Sunday, April 30, 2017

Heavy rain is expected this weekend from the Missouri Ozarks northeast through Illinois and Indiana. Severe weather is also likely from the southern Plains northeast into the Ohio River Valley. Flash flood watches are already in effect

Watches, warnings, and advisories in effect as of 9:00 p.m. April 27, 2017.

For the next week to ten days, and perhaps longer, the overall upper level pattern will be characterized by high pressure ridges off the west coast and the east coast, and a broad trough in the middle part of the country. That sets the stage for a cold, wet period for most of the U.S. east of the Mississippi River.

6-10 day temperature (left) and precipitation (right) outlooks from the Climate Prediction Center.

The next week is going to be a challenging one with heavy rainfall expected in the central U.S. CoCoRaHS rain gauges will get quite a workout from Oklahoma to Michigan and Nebraska east to Ohio. One thing to keep in mind when looking at these QPF maps is that this is a broad generalization of precipitation. The heavy amounts aren't uniformly distributed as these maps might indicate. "Precipitation doesn't fall the same on all."  (CoCoRaHS proverb). It certainly conveys the potential, however.

Quantitative Precipitation Forecast for the 7-day period ending 7:00 p.m. Thursday, May 4

After this weekend's system lifts out, another closed low is forecast to develop in the central U.S. late next week by one model.

500  millibar level chart for 7:00 a.m. CDT Friday, May 5, 2017

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