John Homenuk

Heat returns to East, but active pattern awaits

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The remnants of Hermine are still hanging around, off the coast of New Jersey and south of Long Island this afternoon. The system, in fact, has drifted farther south today than it has been all week — much to the ire of meteorologists and forecasters up and down the East Coast. Nevertheless, the storm will begin to have a lessening impact on our areas weather as the days of this week go on. The system is vertically stacked, at all levels of the atmosphere, meaning it’s cut off from moisture and lift sources.

Accordingly, the storm will fade out slowly over the next 24 to 48 hours, with only momentum carrying its circulation. As it does so, a large mid level ridge will build across the East Coast and Western Atlantic, as we have seen several times already this summer. This pattern looks to remain in place through the weekend, when temperatures will again approach the 90’s in many areas.

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John Homenuk

Central US cooldown on the way, marking larger pattern change

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The establishment of a large ridge over the Central and Eastern United States has been well documented. Since July, multiple surges of ridging have kept above normal temperature anomalies rooted from the Plains states through the Mississippi and Ohio River Valleys to the Eastern Seaboard. With varying degrees of intensity and length, these above normal anomalies have slowly taken a hit, lessening in intensity from west to east. This will take on a larger meaning this weekend, as a large trough drives into the Plains and Mississippi River Valley, bringing a widespread area of below normal temperatures into the Central US amid a changing pattern.

While temperatures won’t necessarily be “cold” by sensible weather standards, they will be a few degrees below normal in many locations, and several degrees below normal in some. This is statistically significant for this time of year, especially considering overnight temperatures could fall into the 50’s in many locations. When one considers the change in temperature from the past week, the significance becomes apparent — a 30 degree temperature differential in some locations.

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Doug Simonian

La Nina Update: Moderate or Strong Event Unlikely This Year

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While we had been tracking heat and severe thunderstorms over the first few months of the summer, the atmosphere was still undergoing a major transition away from El Nino and towards a La Nina. This transition has already resulted in sensible weather changes across much of the country, with a huge heat ridge building in the Central US last month — typical of a La Nina. However, to the despair of some long range forecasters, certain aspects of the transition have not gone as smoothly, and more recent forecast models have trended weaker with the eventual strength of the La Nina over the next few months.

During last year’s El Nino conditions, the trade winds in the Equatorial Pacific were strongly weakened, allowing warm water near Australia to pool eastward. Those trade winds have strengthened over the last few months, which pushed that warm water back to the west, and allowed cooler water to upwell towards the surface. However, climatology favors trade winds remaining a persistent feature — in other words, we are supposed to have east-to-west trade winds blowing warm water towards Australia keeping cooler water near Peru. We can only have a La Nina when those trade winds are consistently stronger than average, and that has yet to be the case this year. For more background on what causes El Nino, La Nina, and the demise of an El Nino, refer to our article from late April.

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John Homenuk

Bouts of heat, multiple MCS threats to end July

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The hot weather is here — and as we have mentioned in our posts for the past week or so, it isn’t expected to go anywhere any time soon. While the pattern will remain somewhat transitional this weekend, a tremendous mid level ridge is forecast to build across the Central United States by the middle part of this upcoming week. This ridge will become the dominant feature in the jet stream and weather pattern throughout the Contiguous United States during this time frame.

The core of the ridge, and the center of the big-time heat, is likely to stay well to our west. The ridge center is expected to drift from the Mississippi River Valley westward toward the Plains states during the week ahead. However, the breadth of the ridge is likely to grow during this time frame, with rising mid level heights extending all the way to the Northeast United States.

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