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One last shot of Canadian air before summer

By Skip Rigney

On Sunday residents of Pearl River County will be breathing air that earlier this week was high above the northern Rocky Mountains of British Columbia, Canada. Enjoy it, because this may be the last mild, low humidity air mass to visit us before summer locks in.

The cool front which marks the leading edge of the Canadian air is forecast to move through south Mississippi today. You will know the front has passed when the wind direction switches to the north. Any showers or thunderstorms near the front will be isolated and brief.

As the front continues southward into the Gulf, the northerly winds will usher in air that will make Sunday one of the most pleasant days we are likely to see until the fall. Forecasters at the National Weather Service office in Slidell expect temperatures in Pearl River County on both Sunday and Monday mornings to drop to near 60 degrees. Some of us might even see upper 50s, readings which are unlikely to recur for the next several months.

Even after a cool start, intense late May sunshine will cause it to warm up quickly. Temperatures will climb into the middle 80s on Sunday and back to near 90 on Monday afternoon, but low humidities, as evidenced by dew point temperatures in the upper 50s, will be comfortable compared to what is on the way later in the week.

The nice-feeling air that we’ll be breathing on Sunday has made quite a journey over the past five days. NOAA has a computer-based model called HYSPLIT that can estimate the trajectory of a parcel of air during recent days. HYSPLIT calculates that the air covering Pearl River County on Sunday afternoon will have traveled over 3000 miles from western Canada since Tuesday.

However, as is usual during the transition from spring to summer, Canadian air masses that make it to Mississippi don’t stay long. By Monday, winds will shift back to the south pumping humid air from the Gulf across the coastline.

It will take a couple of days, but by mid-week there will be much more water vapor in the air, and it will seem very much like summer, namely, warm and muggy with a chance of daytime showers and thunderstorms. High temperatures will be close to the historical average for early June, while overnight lows are forecast to run about five degrees warmer than average.