Precipitation Overdose

Two months ago we were asking where La Nina was and running some numbers to find out how much precipitation we needed to avoid having a sub-par year for water resources.  Oh, how things have changed.  Whether the amount of water from the sky, mud on your shoes or water flowing through our waterways, it’s been real wet. Local creeks including Paradise Creek that runs through Moscow, reached flood stage (highest gauge height since 1997, although cfs not as high per stream modifications) following the couple week onslaught on systems followed by a high-intensity precipitation event (at least for the region) that dropped over an inch of precipitation in 10 hours.

Just to show how wet the last two weeks have been, let’s take a look at a nice product from NOAA called the Advanced Hydrologic Prediction Service Precipitation Analysis. The last 14-day have showcased extremely wet conditions across much of the interior NW with most of the central mountain and Panhandle of Idaho receiving at least 5 inches of liquid equivalent in 14 days (or about 300-500% of “normal”).

Some of the most anomalous precipitation totals were observed along the WA/ID border.         Station          thru 3/28         “Average” March   Wettest March (year)

Lewiston, ID:       3.00″                    1.12″                     4.07 (1931)

Spokane, WA:    3.36″                    1.52″                     3.81 (1995)

Moscow, ID:       5.80″ *                  2.57″                      5.15 (2003)

Kellogg, ID:         6.43″                    2.95″                      6.45 (1916)

McCall, ID:          4.85″                    2.53″                      5.56  (1951)

* estimated using COOP data through 3/22 and 3-nearby cocorahs data from 3/22-3/27

This all thanks to a “march” of storms and associated storm track advecting moisture from the Pacific jet through central Oregon, the Columbia River gap into the inland northwest. This generalized east-northeasterly route avoids the more prominent topographic barriers in the Cascades that tend to reduce precipitation rates when we have a more zonal west-to-east storm track. With April 1 around the corner it appears like this La Nina year with an assist from the month of March will yield above normal snowpack when it counts for the northern parts of the Pacific Northwest.