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For approximately the next week, the Madden Julien Oscillation (MJO) is expected to journey through phase 5. That implies several more days of warm muggy weather for the central Midwest. You can watch the MJO progression by following the dotted green lines below. Note on the right the correlation of phase 5 to warmth in the north central United States during July.

The EURO is in agreement showing above normal temperature departures the next 5 days.

Beyond the 7 day period, the MJO depicts a slow transition through phases 6 and 7 into early August. This looks to be the beginnings of a cooler weather pattern that should prevail from mid July into much of August. You can see in the phase correlation diagram at the top how 6 and 7 bring below normal temperatures.

Sure enough, the EURO concurs forecasting departures in the 5-10 day period that look like this.

Followed by day 10-15 departures such as this.

That's in stark contrast to the last 14 days where warmth was widespread across the nation.

This overall change in the 500mb jet stream pattern is significant. The jet this Friday in a warm flow is forecast to remain well to the north. Upper ridging dominates the Midwest.

By July 19th the EURO shows a trough displacing the ridge allowing cooler and drier air a path into the central U.S. That's a major change with significant temperature implications.

Before we get to the pattern change, another surge of heat and humidity is on the way. By Thursday and Friday highs will be around 90 and dew points will surge into the mid to upper 70s. Heat index values could easily exceed 100 and heat advisories are a distinct possibility for some. More on that in my next post. Roll weather...TS

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