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SWA Meteorology: Thanks, Canada!

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weatherIt was just two weeks ago we were experiencing the “return of the Polar Vortex” in the middle of summer, a highly unusual occurrence, or so we thought.  Now another round of welcome cool air is bringing much needed relief for the eastern half of the nation.  Is it another Polar Vortex?  Nah, this time, it’s cool air from Canada. Listen to a forecast on TV or read a forecast online, and you’ll often hear or see the words “a cold front from Canada is responsible for this summer season cold blast.”  Our Canadian friends sometimes get a little miffed over that.  Certainly not all of our cold outbreaks originate in Canada.  The Polar Vortex cold originates—you guessed it—over the Polar Regions.  Sometimes our winter cold outbreaks originate over Siberia and are simply passing through Canada on their way to the states.  In the summer, most of us don’t really care where the cool air comes from, we’re just happy to see it bring some shortterm relief from typical summertime hot temperatures. During the summer, when a high pressure system stalls over the U.S.  for several days or even weeks, it usually means a heat wave will ensue in that region (this is obviously not true in the winter).  For the last several weeks,  a large high pressure system has been sitting over the Rockies, baking Phoenix, Las Vegas, Salt Lake City, Reno, Tucson, and even parts of Idaho and Oregon.  That’s not unusual for the desert southwest, but it is rather unusual for the northern Rockies. Last week, that hot dome of high pressure spread eastward, bringing triple-digit heat and heat advisories to Little Rock and Memphis, through Oklahoma, all the way down to south Texas, and along the Gulf Coast states.  Thanks to another blast of cool air, that heat wave-producing high pressure system has now weakened, and temperatures for a good part of the nation have once again cooled to below average levels.  For instance the Dallas/Fort Worth area will be around ten degrees below average the rest of the week, Chicago and much of the Great Lakes will likely have high temps in the 70s, and Baltimore and New York City barely make it into the 80s through week’s end.  Even as far south as Greenville, SC and Charlotte, NC highs will only reach into the low-mid 80s. Unlike the return of the Polar Vortex a few weeks back, this blast of cool air originates in Canada, right around the Northwest Territories and Nunavut, but not quite to the Polar Regions.  Some people might  blame our neighbors to the north for our cool blast, but the majority of us will thank them.  Either way, enjoy the second recent blast of cool air this summer, but don’t think this necessarily has any bearing on how cold next winter may be!