Tuesday, July 2, 2013

Spring pattern transitions back to summer (sort of)

There have been no complaints lately regarding the unseasonably cool weather for the start of July. Sure there have been some pesky isolated showers, but those are certainly worth the low 80s we’ve been experiencing! [You may recall that it was MUCH hotter last year.  In fact, 6 of the first 7 days of July featured temps in the 98-103 range!]

This recent weather has been due to an upper-level low pressure system that has stuck around the region, quite literally, being wedged in between two dominant high pressure systems in the western U.S. and western Atlantic.

The recent cool spell is due to the presence of blocking high pressure over the  western Atlantic and western U.S., while a large trough and upper level low pressure system dominated the Mississippi Valley region - literally with nowhere to go.
Ultimately the season of summer will prevail and begin to diminish this unusual pattern we've been experiencing. The pattern change will bring increased presence of the Bermuda high, by shifting it farther west (over the southeastern U.S.), which is the more typical summer pattern you would expect this time of year. This means a change in surface wind direction (from north to south), and thus increased humidity and slightly warmer temperatures. However, a large trough will remain to the west of the area which will keep temperatures from getting too hot and allowing chances of rain to continue in the forecast.

A slight, but important, pattern shift takes place the next few days, with more influence from the Bermuda high over the eastern seaboard, and a weaker trough that will also shift slightly west, resulting in more moisture, humidity, and warmth, as well as higher precip chances.

So what does this all mean for the 4th of July?

Wednesday into Wednesday night looks the best, with limited cloud cover, pleasant temperatures, and very low precipitation chances for an evening of fireworks. Heading into the 4th of July, clouds and chances for rain increase (slightly) as well as warmer temps and higher humidity. Looking ahead to the weekend, the summer-like pattern looks to stick around with more chances for rain throughout. The bright side is our temps should stay capped out near 90 on the days with the most sun - it certainly could be worse this time of year!

--William Churchill, MWN Intern

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