Overall, for the past two months, it’s been warm across south Florida and chilly in the southwest U.S. That’s come to an abrupt end, at least for a few days. Then, things return to the way they’ve been starting tomorrow along the California coast and working their way eastward as the week unfolds. This means chilly weather returns to the west and warmer weather makes a comeback in the east.
For example, during the past two months, Naples has been quite warm. In January, the mercury averaged more than seven degrees above average. In February, it wasn’t quite as warm; however, the temperature was almost 1.5 degrees warmer than would be expected at that time of year. Similar warmth was reported across almost all of south Florida.
Then, during the past few days, chilly weather returned. This should be the watchword during the entire weekend with an even further chilling by Monday morning. As skies clear and winds die down, freezing or near freezing temperature readings could occur in inland locations across southwest Florida.
By midweek, the mercury should return to near or slightly above seasonal readings.
Meanwhile, as is typically the case, when it is swarm in the east, it is cold in the west (vice versa). This is linked to the geographical size of the United States and the typical pattern of troughs and ridges in the upper levels of the atmosphere. Thus, when there is a ridge (warm weather) in the west, there is often a trough (colder weather) in the east (Fig. 1). Conversely, when there is a trough (cold weather) in the east, there is often a ridge (warmer weather) in the west (Fig. 2). Troughs are u-shaped and ridges are upside down u-shaped.
Not surprisingly, in the southwest, the exact opposite of the eastern weather regime has occurred. San Diego, CA has shivered the past two months. In February, for example, below average readings were reported on 20 of 28 days; in January, colder than average temperatures were observed on 19 of 31 days.
Phoenix, AZ averaged about 2.5 degrees below seasonal readings in each of January and February. Tucson, AZ was even colder with its February average some 4.5 degrees colder than expected climatologically.
Then, on February 20, snow fell across parts of Arizona (Fig. 3). Tucson Airport reported two inches of snow, a rather rare event. Flights at the airport were disrupted, some mountain roadways were closed and the first day of competition for the PGA’s Accenture Match Play Golf Tournament was cancelled. Although snow delays are a rarity in PGA circles, Stewart Williams, the PGA Tour’s meteorologist, noted in an Arizona Daily News interview, that snow had fallen during the same event back in 2011.
Now, slightly more than a week later, the mercury has reached near record levels in San Diego, where Friday’s high topped out at 80 degrees. In Phoenix, the temperature also reached 80 degrees, while it was only 73 in Tucson.
Still, for today, it will remain relatively warm across the southwest. Then on Sunday, the marine layer returns to San Diego and a cool down arrives Monday for the rest of the southwest.
The biggest news, however, is that an even more dramatic drop in temperature and the risk of more snow in Arizona mountain areas sets up later next week. Snow levels will lower dramatically as a major upper level weather system moves into the area. It is not out of the question for this weather system to drop significant mountain snows and also bring measureable snowfall close to the valley floor in both Phoenix and Tucson.
By early in the week of March 10, the system exits the southwest and should bring a significant risk of severe weather and heavy rainfall across much of the Deep South (Fig. 4).
© 2013 H. Michael Mogil
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