Friday, May 01, 2015

May Day Miscellany

We are now into May, one of our two driest months here in the Sonoran Desert, as the heat builds in the run up to the summer thunderstorm season. April closed out with little to report. There was one precipitation event that produced only 0.18" here at the house - so conditions along the Rillito Wash are basically bone-dry with dusty ground awaiting gusty winds. Temperatures here were relatively mild - there were 9 mornings with lows in the 30s F and only 1 morning with a below freezing reading of 28 F. The forecast models continue to indicate at least some chance of showers early next week, so we will wait to see how that situation actually evolves. Other miscellany to start May.

Jack Diebolt sent along some interesting graphics this morning. Above is April precipitation across the Southwest, showing Arizona and southern California very dry. Amounts over an inch in Arizona occurred mainly up in the Rim Country. Most widespread heavy rains were up in southeast Wyoming and northeast Colorado. Unfortunately, this heavy precipitation fell mostly within the Platte River drainage. Headlines here in Arizona this week reported that Lake Mead has fallen to a new record- low level since the dam was completed back in 1935.

Graphic below shows the Pacific SST anomalies as we start out May. The area of unusually warm surface water over the eastern Pacific is just huge. Would be nice to know how the current situation will feedback and impact both tropical storm activity and summer rainfall this year.

There is a bit of a curiosity in the long-range, global model forecasts from 00 UTC last evening. The ECMWF (above, valid at 00 UTC on May 8th) forecasts a broad trough over the central U.S., with a somewhat disorganized structure due to the lingering southern branch of the flow. However, the GFS (below, valid same time) forecasts a quite strong, cold closed-low centered over California/Nevada, within the southern branch of the flow. Somewhat unusual for the GFS to be so much stronger and further south with features over the West, versus ECMWF. 

This will be a situation to watch during the coming week. Both models forecast the weak, almost tropical-looking, closed low off the southeast U.S.

Finally, the nighthawks (below) made their usual spring appearance here, circling and hunting insects during the evening just above the trees and houses here on our circle. They are about 10 days later than they were last year.

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