Coming off of record heat and a scorcher of a month in the East for April, I believe May will have a bit of a different story to tell. With ENSO, NAO, AO and PNA values going into May tracking similarly to those that lead into April, one could think another warm month in the East would be expected. However, given the actual values of the various indices, one would assume the opposite, with warm anomalies in the West and cooler anomalies in the Northeast and Mid-Atlantic. So what happened?
Throughout this month, the Southwest Coast has been receiving a large amount of storms and heavy rain, which is downstream of a ridge that has been in place over the Central Pacific for awhile now. This caused a H-L-H pattern that stretched from the Central Pacific to the Eastern US. The ridge of high pressure across the eastern half of the nation brought in the anomalous warmth that gave 90s to almost the entirety of the Midwest, Mid-Atlantic and Southeast at some point in the beginning of April.
So why will May be different? While the start of May is looking to have a similar pattern to the start of April (with the anomalies being much less extreme in May), models are favoring less cut-off lows just off the California coast than what has happened in April, in order to favor a more northerly track through the Pacific Northwest. This would allow ridging to take a hold in the East Pacific and Western US, which would be the normal conditions for mid to late Spring. Coincidentally, this would also favor a trough in the Eastern US, dominated by storms dropping from the Pacific Northwest into the Central Plains, with a secondary low formation hot-spot in the Northern Gulf of Mexico. This could mean an active period of severe weather in May across the Central and Southern Plains and in the Southeast.
Forecast summary:
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