An upper low, currently over southern Nevada, will move across Arizona today, bringing showers and isolated thunderstorms, cold temperatures and high elevation snow above 6,000 ft to northern Arizona today. Graupel (small hail) showers this afternoon are not out of the question. Dry, but windy conditions will develop Tuesday ahead of yet another low that is forecast to swing across our the area Wednesday, with another period of cool and showery weather through Thursday. More pleasant sunny, dry and seasonable conditions are forecast Friday through most of Memorial Day weekend, but with afternoon breezes each day.
Additional notes for the weather nuts out there:
Why are we getting this extended period of almost winter-like conditions this late into the spring? Part of the answer has to do with the location of the jet stream, the narrow band of strong wind near 35,000 ft. You can see the forecast location of the jet here. When the jet stream is to our south, conditions are cooler and less stable, favoring showers if there is sufficient moisture. The jet has been further south than normal this winter and spring, partly due to the presence of moderate El Nino conditions. In addition, the presence of the jet favors the formation of low pressure systems. As I noted a couple of weeks ago, whenever we are under an upper trough, conditions are cooler than normal, while an upper ridge favors warmer conditions. Based on this principle, the 500 mb anomaly (departure from normal) map shown here indicates regions expected to be warmer than normal in red and colder than normal in blue. Throughout more of the forecast period, Arizona is blue.
Have a great week, and enjoy the long weekend!
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Official National Weather Service forecast