April 2012

April brought showers and flowers to much of the inland northwest, with well above normal precipitation for western Idaho and eastern Washington and Oregon. A few sites received nearly double their climatological April precipitation.

Water year precipitation to-date (Oct-Apr) includes a mix of regions above normal (20-30% above normal in the Idaho-Panhandle and extreme eastern WA) and below normal (20-30% below normal in central to eastern WA), adhering to the typical geographic patterns of a La Nina winter.

Temperatures in April were a couple degrees above normal across the inland northwest, with the warmest anomalies across southeastern Idaho and into Wyoming.

Of course, at the monthly timescale, such numbers are composed of taking daily maximum and minimum temperatures.  A monthly anomaly of +2.0F above normal thus could occur if every day is +2.0F warmer than normal, or if 5 days are +12.0F warmer than normal and the other 25 days exactly “normal”.  All hypothetical, but worth noting that there are several pathways to realize climate data at the monthly time scale.  This is particularly relevant for April, as an intense-but-short-lived spring heatwave associated with pronounced ridging brought very warm conditions to much of the inland northwest, including the earliest 90+ degree temperatures on record in Boise (91F on 22-23rd). By the way, 91F is the climatological high temperature for mid-July in Boise. The brief run of warm days acted like a capstone to signal vegetation to flower and insects to awaken from their winter slumber.  Boise also received over half of their precipitation last month on April 26th when over 1″ of precipitation fell in as the ridge propagated eastward and moist and unstable air  from an approaching trough provided the right mix of ingredients for record setting daily precipitation.

Finally, an interesting observation regarding total snowfall this past winter. Both Idaho Falls and Pocatello, Idaho had their lowest snowfall accumulation (Oct-Apr) on record.

While Idaho Falls received below normal precipitation over the last seven months, precipitation in Pocatello was spot-on to the 1981-2010 climatology.  Using the North American Freezing Level Tracker from the Western Regional Climate Center we find that the mean elevation of the freezing height was over 500 feet higher than normal over the last 6-months likely allowing more of the precipitation to fall as rain rather than snow. In a few months, we’ll know the impacts and potential consequences of that shift.  This is also reflected in current snow water equivalent values that depict lousy numbers across the southern tier of the state consistent with much of the rest of the western US outside of the Cascades and Idaho Panhandle/western Montana.

This entry was posted in Uncategorized by John Abatzoglou. Bookmark the permalink.

About John Abatzoglou

John is an associate professor of Geography at the University of Idaho. John's interests are centered around climate and weather of the American West and their impacts to people and natural resources of the West. John and his Applied Climate Science Lab at the University of Idaho have published nearly 100 papers and book chapters on climate science, meteorology, and applied climate science connecting climate to water resources, wildfire and agriculture. The research group also develops web-based climate services that connect climate data with decision makers to help improve climate readiness of societies and ecosystems.

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