More unseasonably cool air to descend on eastern U.S. next week

Call it the return of the summer "polar vortex" if you want -- a mass of cool, dry air from the north is forecast to bring more unseasonably cool temperatures next week in Maryland and across the eastern United States.

The pattern is a similar one to what we saw much of the winter and again this spring and summer, with an area of warmth in the western third of the country but cold air spilling over the Canadian border across the rest of the country.

According to the National Weather Service, the shot of cool air (they call it a "well-advertised high-amplitude meridional event") will extend all the way to the Gulf of Mexico coast, with well below normal temperatures in Texas and Louisiana.

In the Baltimore area, while Friday's beautiful cool, dry weather won't last through the weekend, it should be back by Tuesday. Highs for the middle stretch of next week are forecast in the lower 80s, with dew points in the 50s doing little to make it feel like the last week of July.

This month is pacing to be the coolest July in Baltimore since 2009. The average temperature so far this month is 76.4 degrees through Thursday, about half a degree below normal. July 2009 averaged 74.7 degrees.

This summer has been somewhat remarkable for its lack of extreme heat in Baltimore, at least compared to recent years. Wednesday was this year's 10th day to hit the 90s, with a high of 94 degrees. That is five fewer 90+ degree days than we had tallied at the same time last year, and about a third of tallies from the previous three years.

The tallies of days to top 90 degrees in Baltimore as of July 24 in 2012, 2011 and 2010, respectively: 32, 27 and 38.

Twice this month, Baltimore has set new record lows, most recently on Friday. The low of 57 degrees at Baltimore-Washington International Thurgood Marshall Airport broke a record set in 2008, of 59 degrees. On July 18, a low of 57 broke a record dating to 1976.

But the cooling trend is somewhat unique to the eastern U.S. June was the third consecutive month to rank as the warmest on record for global average temperature.

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