The relentless ridge and its effect on 99L

When meteorologists looked at the medium range forecasts on the first of August, one thing was clear, it appeared: Troughiness would become more likely east of the Mississippi River by the tail end of the month. Brought on by a change in tropical forcing and an overall adjustment in the hemispheric wave pattern, this seemed like a moderate to high confidence forecast. Those ideas were wrong.

Instead, poor modeling and a changed pattern evolution has led to an entirely different outcome: The mid level ridging, which has become a staple of the East Coast weather pattern since early July, will return. Forecast model guidance has altered the hemispheric pattern evolution to support a -PNA (Pacific North American oscillation), or troughiness on the West Coast of the United States. This will only feed the development of a strong ridge from the Southeast United States into the Mid Atlantic.

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Surge of cooler air likely to begin the week

A strong cold front, with an impressive thermal gradient, will push from the Ohio Valley through the Northeast late on Sunday evening. This cold front is associated with a larger mid and upper level system, which features an organized and deep trough emanating from Canada. The cooler air associated with this trough will be most prevalent in the Plains and Mississippi River Valley, but will also be noticeable in our area for a day or two behind the front.

This will be most recognizable on Monday and Tuesday, as atmospheric temperatures significantly cooler than the past several weeks settle overhead. Daytime highs will be cooler — and dew points will be much lower. Overnight lows may fall into the 50’s in the interior and 60’s even in the city and near the coast.

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Weekend Overview: Warmth, scattered storm chances return

Worry not! When we say “warmth” we don’t mean the oppressive heat from last weekend. Instead, what will return this weekend are temperatures more typical of late summer. Highs in the upper 80’s will be commonplace throughout the area this weekend, especially away from the area shores. Showers and thunderstorms are possible on each day, most likely during the afternoon and evening, but aren’t expected to be severe. They’ll remain isolated to scattered throughout the area.

Winds will turn southeasterly by Saturday afternoon and evening, meaning the influence of the area waters will be felt a bit more near the beaches. A bit more of a breeze and cooler temperatures are likely near the coast on both Saturday and Sunday. This southeast flow comes ahead of a cold front, which is expected to bring a period of steady rain on Sunday Night. Here are your weekend weather highlights:

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Central US cooldown on the way, marking larger pattern change

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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