Today, an unseasonably cool airmass is in place over Arizona. In fact, the Flagstaff area had unusually early season reports of 1-2” of snow on Sunday morning (with 6” reported at Snow Bowl). Lighter accumulations of snow and graupel in the mountains around the south side of Prescott were reported to me by a fellow Embry-Riddle meteorology professor, Dr. Ivanova, and graduate student Tabitha Kloss. Expect cool, partly cloudy conditions to persist through this evening, with a decreasing chance of additional precipitation. Snow levels will still get down to 7,000’ elevation in heavier showers.
Mostly clear and warmer but breezy conditions will prevail Tues – Wed, with another not-as-cold upper-level trough developing along the California coast and swinging across Arizona on Thursday - Sunday. In advance of the trough a subtropical jet will develop and direct dissipating Hurricane Sergio eastward into the west coast of Baja California as a tropical storm and possibly into southeastern Arizona as a tropical depression. It is a bit too early to be sure about Sergio’s track, and although it is likely that the center of the storm will skirt by us at a distance of at least a couple of hundred miles, expect partly cloudy to cloudy conditions Thursday – Saturday with at least a slight chance of showers or thunderstorms each day. When tropical cyclones approach coastlines, they bring very moist air with them, and some of this moisture could flow as far northward as Yavapai County, possibly fueling scattered thundershowers. The approaching upper-air trough will also help to enhance lifting and vertical wind shear with the remote threat for organized thunderstorms and local areas of flooding.
Meanwhile, Hurricane Michael has now formed in the Caribbean and is moving north into the Gulf of Mexico. With very warm sea surface temperatures and light vertical wind shear over the Gulf, conditions will be favorable for Michael to form into a major hurricane (at least Category 3) and barrel into the Gulf Coast. Michael’s landfall is expected somewhere along the Florida panhandle on Wednesday.
This has already been one of the wettest months of October on record for portions of Arizona, and we are only 7 days into the month. You may ask, “Is this because of El Niño?” The answer is actually no! According to the Climate Prediction Center (http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.php) there is a good likelihood that El Niño conditions will develop this fall and winter, but we are currently in ENSO neutral conditions. So, why has it been so wet? It is probably due to the cooler-than-normal ocean temperatures currently located off the California Coast, with warmer-than-normal sea surface temperatures over the subtropical Pacific. This contrast in ocean temperatures has apparently been fueling the subtropical jet over Arizona and helping to create troughing off the West Coast.
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