The last 8 months (October-May) have been the coolest in the United States since 1977-78 As you can see, much of the cold has been centered over the Plains and Midwest..
Another healthy shot of cool air arrives today as a stout late spring cold front streaks across the Midwest. Here's the deep trough that delivers the fresh air.
After scattered showers and highs in the 60s Wednesday, skies clear and temperatures tank come Thursday morning. Most of the high resolution models have lows in the low to mid 40s which will be close to records for the date. A few 30s are possible from NE Iowa into Minnesota and Wisconsin.
The prolonged period of cool weather might be showing some signs of easing later this month. The SOI (Southern Oscillation Index) has recently made a big jump into positive territory. Today it was measured at +19.61. Just a few days ago it was -17.57. This is also a major change from the 3 month average of -7.11.
The change in the SOI indicates that the MJO (Madden Julian Oscillation) is on the move. That should spur it into phase 5 in less than 10 days.
As you can see phase 5 in June is warm over the central U.S.
It stays warm into July as well.
The other thing to note about phases 4 and 5, are that they tend to be dry over the central Midwest.
In support of the warmer idea is the 500mb jet stream flow on the EURO ensembles June 25th. Notice the ridge building over the SE United States which would promote a feed of warm humid air into the mid-Mississippi River Valley.
That would bring some warmth but not necessarily dry conditions. In fact, this looks like an active and potentially wet set-up. In other words, I'm getting contradictory signals.
I've been thinking all along that this summer would end up wetter and cooler than normal across my area. What we may end up seeing here is a transitional pattern that hits and holds for only a week to 10 days. The warmth comes and goes as the pattern reverts to where its been much of the past few months. Something to keep an eye on in coming days.
Meantime the pools and parks will be quiet today as crisp showery weather takes a spin through the Midwest. Pay it no mind as sunny, cool, and pleasant conditions return for Thursday. Roll weather...TS