Expect temperatures to continue downward trend

There are about two and a half weeks of summer left, with the first day of fall occurring on Sept. 22 this year. September is usually a pretty dry month in Spokane, with average rainfall (.76 inches) on par with July (.76 inches). Coeur d’Alene sees more of an increase in precipitation, from an average of .96 inches in July to 1.58 inches in September. Average highs and lows continue their downward trend this month from the upper 70s and lower 50s, respectively, at the beginning of the month, to the upper 60s and lower 40s at the end of the month. Spokane has never seen measurable snow during September, but late-month cold storms may result in some graupel (soft hail) which many folks like to put in the same category as snowfall.

One of the events that has been noticeably missing so far this summer has been the dust storm. Though I don’t believe there are any statistics regarding how many dust storms we see each summer, or even what thresholds of dust and wind are required for a storm to be labeled as such, it seems like one always occurs sometime during mid or late summer.

Dust storms happen when relatively dry thunderstorms move into the area after long periods of dry weather. Though little rainfall reaches the ground with these thunderstorms, what precipitation does fall evaporates into the air – cooling it and causing it to sink. The sinking air accelerates as it falls, and then spreads out at sometimes dangerously high speeds once it hits the ground. These winds can then kick up what is literally a wall of dust which progresses ahead of the storm that caused it. Sometimes the storm itself collapses, leaving nothing but the fast-moving outflow boundary, which can actually be seen on Doppler radar. Severely reduced visibilities along with wind damage are often the result. The most interesting part of a dust storm with its advancing wall of dust, however, is probably its other name – the “haboob.” The word “haboob” comes from the Arabic word “habb” which means “strong wind” or “phenomenon.” They are commonly observed in the Sahara desert, the Arabian Peninsula, throughout Kuwait, and across the arid regions of Iraq. Across the U.S. these types of storms are also frequently observed in Arizona, occasionally seen in West Texas, but can occur any place where the right conditions are met.