Overview

As if the really wet last half of December weren’t wet enough, along came January – one of the wettest and mildest Januaries ever. Some locations set all-time records for total wet days or consecutive wet days. Others set records for most monthly precipitation. The mountains saw rather amazing increases in snowpack. All this adds up to what has been a wet, windy, wild winter in Oregon.

Table 1 is a summary of monthly averages and totals at selected stations throughout the state. Table 2 lists daily temperatures and precipitation for most of the locations listed in Table 1. In Table 3, monthly and seasonal precipitation totals throughout the state are listed.

Basin Summary

Here is a summary of water indicators at the end of the month, by river basin:

n.a. Not available
(1) Percent of normal January precipitation, from NOAA Cooperative sites
(2) Percent of normal seasonal precipitation (since Oct. 1), from NOAA Cooperative sites
(3) Percent of normal seasonal precipitation, from Natural Resources Conservation Service (NRCS) SNOTEL sites
(4) Percent of normal snow water equivalent, from NRCS SNOTEL sites
(5) Percent of normal January stream flow, from U.S. Geological Survey (USGS)
(6) Percent of normal seasonal stream flow (since Oct. 1), from USGS
(7) Surface Water Supply Index, from NRCS (-4 = very dry, 0 = normal, +4 = very wet)

Forecasts

The Climate Prediction Center forecast for Feb-Apr suggests a higher than average chance of cooler than average temperatures, with equal chance of drier-, wetter-, or near-average precipitation. Oregon Climate Service continues to predict a warmer and drier than average spring following the end of winter (still a month or so off).

31 Days of Really Wet Weather

The National Weather Service released the following statement on January 18:

Public Information Statement
National Weather Service, Portland OR
225 pm (PST) Wednesday January 18 2006
...Significant precipitation falls across northwest Oregon and southwest Washington from December 18, 2005 through January 17, 2006...A persistent wet weather pattern has produced measurable rainfall for 30 of the past 31 days across northwest Oregon and southwest Washington (from December 18 through January 17). This weather pattern has frequently produced very heavy rainfall that caused flooding over a large portion of the area. Rainfall totals from some selected stations from December 18 through January 17 are listed below:

www.weather.gov/portland

Oregon Climate Service went back into our archives to determine if any of these were new records. We found that many of the 31-day totals listed above were new records, or nearly so. For example:

Monthly Precipitation Records for January
Kelsey Kuykendall, Undergraduate Assistant

January was a wet month and set a lot of new precipitation records. Below is a table of records set, the observed amounts, the monthly normal, and the old records with the year it was set.

A Big Snow Storm --- Not!

The single most anticipated weather event in the Willamette Valley is a snow storm. Snow is a rare event here, it allows many people time off from school or work, and it can lead to a lot of outdoor fun. Never mind that it can be dangerous, especially to drivers.

When I give public talks, the most-asked question is, “will it snow this winter?” I tend to be very coy about giving answers, because snow events are very hard to predict in advance. What happened in December underscored my hesitation

In December the National Weather Service issued a stern warning for most of Northwestern Oregon. Snow was imminent! The forecasts prompted plenty of action. Tire stores in the Portland area stayed open very late as motorists brought in cars for installation of snow tires. The Portland Metro ordered chains installed on all buses. Portland battened down the hatches in anticipation of a major snow event.

Six hours later the next shift of forecasters came in (the Weather Service rotates shifts every 8 hours around the clock).What they were seeing was quite a bit different from what the earlier shifts had anticipated. At 4:22 am Thursday they issued the following statement:

THE NATIONAL WEATHER SERVICE IN PORTLAND HAS ISSUED A SNOW
ADVISORY WHICH IS IN EFFECT UNTIL NOON PST TODAY. THE WINTER STORM WARNING HAS BEEN CANCELLED.

Oops! No low elevation snow after all! There simply wasn’t enough cold air, because the cold easterly winds expected to funnel the cold into the Valley through the Columbia Gorge didn’t blow. Instead, cold rain fell.
Lest you get the wrong impression, I am NOT trying to heap scorn on the Weather Service. Generally their forecasts are quite accurate. What this does remind us of is the very tenuous nature of snow events at low elevations in our area.

Most of the time it’s too mild to snow. There’s usually plenty of moisture, but the air isn’t cold enough. And usually when it’s cold enough to snow it’s too dry.

There are two situations that tend to provide snow. The first is what forecasters expected this week: cold air in the Valley (especially near the Gorge) meeting a rain storm from the west. The rain freezes as it falls and produces snow.

The second situation, more common in the mid-valley, occurs when cold air pours out of the Fraser River Valley near Vancouver, BC, loops out over the ocean long enough to pick up moisture (but not long enough to warm up much) and then moves back onshore. Our biggest snow storms tend to happen during such circumstances.

So here we are, getting lots of lowland rain, and plenty of high elevation snow. Some of you are hoping once again for a snow event in the Valley. You long for a day off for sledding or snowball fights. Will we get one this winter?

I don’t know. And after what happened in December, I’m even more reticent than usual to hazard a guess!