Overview

After a promising start to the Water Year, November was a big disappointment. A strong ridge of high pressure dominated the weather for the month, bringing generally dry conditions, very little snow, and plenty of valley fog (yuck!). While skiers wait impatiently for good snow conditions and water managers begin to worry, let us remind you: the rule of thumb is that the deepest snow pack occurs on or about April 1, so we have a lot of the snow buildup season ahead of us.

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 precipitation, water supply, and snow pack as of the end of the month, by river basin:

	Precipitation			Snow	Stream Flow		SWSI
BASIN	(1)	(2)	(3)	(4)	(5)	(6)	(7)
OWYHEE	108	199	103	65	73	71	-1.0
MALHEUR	83	166	68	0	137	102	-1.3
GRAND RONDE, POWDER, BURNT	45	95	66	48	71	82	-1.2
UMATILLA, WALLA WALLA, WILLOW	44	57	66	29	70	79	0.8
UPPER JOHN DAY	46	83	70	29	66	76	0.2
UPPER DESCHUTES, CROOKED	23	67	52	36	46	51	-0.4
LOWER DESCHUTES, HOOD RIVER	34	64	60	13	52	66	0.4
WILLAMETTE	35	63	54	22	51	66	0.0
ROGUE, UMPQUA	33	70	60	18	33	48	-0.4
KLAMATH	33	80	57	17	70	76	-2.4
LAKE COUNTY, GOOSE LAKE	53	117	94	109	48	60	-1.0
HARNEY	52	117	85	58	77	79	-0.2
NORTH COAST	41	70	48	0	42	60	0.4
SOUTH COAST	36	77	n.a	n.a.	15	32	0.7

n.a. Not available
(1) Percent of normal November 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 November 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’s (CPC) forecasts for December-February appear below. Temperatures for Oregon (and all of the West) are likely to be above normal, while precipitation probabilities are below normal.

Oregon Climate Service predicts above-normal temperatures and above-normal precipitation for the next three months.

ENSO Update (from the Australian Bureau of Meteorology, December 8, 2004)

With a drop in the Southern Oscillation Index (SOI) and a warming of the far eastern Pacific over the past month, the climate indicators are more in line with what is expected during an El Niño event. However, the typical El Niño patterns of Pacific wind and cloud have failed to materialise. Furthermore, there is no example in the historical record of an El Niño developing this late in the year, and even if one did, summer is the time of year when El Niño-related impacts on Australian rainfall begin to break down. However, central Pacific surface temperatures are persisting at levels characteristic of El Niño, and the situation will continue to be monitored closely.

Surface temperatures in the western to central Pacific have hovered near El Niño thresholds for about three to four months now, but subsurface temperatures are below the levels normally associated with El Niño. The far eastern Pacific is now about 0.8°C warmer than average.

The Trade Winds continue to fluctuate across the tropical Pacific, with below average values being observed in most parts of the basin during the past week. In response, surface temperatures warmed in the far eastern Pacific, but there was no change elsewhere. The past four to six months has seen a sequence of westerly wind bursts (WWB), each one of which has resulted in a temporary decline in the strength of the Trades. There has not been a persistent and significant decline in the Trade Winds as normally occurs during an El Niño.

Winter “Heat Wave”

After all that cold, gloomy fog, I was really ready for a “winter heat wave.” This week we finally got it. And today (Friday) I put on a Hawaiian shirt instead of a long-sleeved one, or a sweater. Ah yes, a winter heat wave! And a rainy, cloudy one at that! How can that be?

It turns out that most of our warmest winter periods occur during storms, NOT during “fair weather.” There are several reasons for this:
1. winds prior to the arrival of a storm are generally from the south, bringing relatively warm air from California or the Pacific
2. cloud cover keeps nighttime low temperatures from dropping very low
3. water vapor in the air during humid conditions holds in the heat (the “greenhouse effect”)
4. when water vapor condenses (as it does during rain storms), heat is released

And this week, as the parade of wet, windy storms invaded our area, we finally got rid of the cold, foggy weather that plagued us for much of November. Temperatures in the daytime have been in the 50s, and may hit 60 today. And look at the contrast in a week’s time:

December 3 – high 38, low 33, no rain (cold, damp, drizzly)
December 10 – high 58, low 48, .26 inches of rain (3.03 inches for the week)

There you have it – this morning’s low 10 degrees higher than last Friday’s high -- no wonder it felt so Hawaiian!

The interesting thing about these “heat waves” is that they can literally occur at any time of the day or night, since they’re not primarily the result of sunshine. Much depends on when the storm arrives, or when the winds are strongest.

I remember a favorite PBS show (no longer on the air, unfortunately) called “AM Weather.” Two National Weather Service meteorologists did an overview of weather conditions and forecasts nationwide. It was just a 15-minute show, so all they could do was an overview.

So here we were, in the middle of a raging storm, wind blowing, rain falling – and the fellow says, “At 9 a.m. eastern time the warmest spot in the country was Portland, Oregon at 65 degrees.” Warmer than Florida. Warmer than Arizona. Warmer than Death Valley! That’s when I realized that our winter heat waves were far from typical, compared with places that are normally much warmer.

The downside to these kinds of conditions is that snow levels get very high. This can cause rapid snow melt, which can lead to flooding (the dreaded “rain-on-snow” flood). It also plays havoc with ski conditions. The high freezing levels are caused by warmer low-level temperatures as well as a lower “lapse rate.”

The lapse rate is the rate at which temperature decreases with altitude. In dry conditions in the atmosphere the temperature drops an average of 5.5 degrees F for every 1,000 feet of altitude increase, so at 5,000 feet above the ground we could expect temperature to be about 27.5 degrees
lower than at sea level. If yesterday had been dry, we can estimate that the 58 degree high temperature would have only 30.5 degrees at 5,000 feet – a little below freezing.

But it was wet, so we use a different lapse rate, for moist air. Because of heat released by condensation, moist air drops by only 3.3 degrees F per thousand feet, so yesterday’s actually corresponds to a temperature of 41.5 degrees at 5,000 feet – well above freezing. One would have to go up to almost 8,000 feet to go below freezing.

Mind you, these figures are for the “free air” above us, not the ground in the mountains. But the principle remains the same: our “winter heat waves” could also be called “snow eaters” because of the effects they have on the snowpack.

Nonetheless, I’m not only wearing a Hawaiian shirt, but a smile as well – I LOVE these wet, windy winter heat waves!

Tye Parzybok, former OCS scientist, has published a book, “Weather Extremes of the West.” His publisher, Mountain Press, says “Parzybok highlights the West’s most notorious historical weather events in easily understood prose, with photographs, figures, and satellite images to explain the workings of the West’s most unique, and regularly occurring, weather phenomena. With a multitude of statistics and scientific information, he explains what is causing the Salt Lake basin’s “lake stink,” how wide-open spaces influence Texas’s fearsome windstorms called “Blue Northers,” and why Albuquerque’s “box effect” draws balloonists from around the world. Both meteorologists and weather junkies will find Weather Extremes illuminating and entertaining.” Good description; I’ve read it and I like it!

To order a copy of Weather Extremes of the West by Tye W. Parzybok

call 1-800-234-5308
or go to www.mountain-press.com

Oregon Climate Service

George H. Taylor, Oregon State Climatologist

Wayne P. Gibson, Programmer/GIS mngr.

Eileen Kaspar, Research Assistant/Manager of Data Services

Melanie Mitchell, Undergraduate Assistant

Wolf Read, Undergraduate Assistant

Emily Gibson, Student Assistant

Cadee Hale, Publications Assistant

Kelsey Kuykendall, Undergraduate Assistant

Sara Joos, Student Assistant

Sean Daly, Student Assistant

Oregon Climate Service, Strand 326,                             	     Phone: (541) 737-5705  
Oregon State University                                                      Fax: (541) 737-5710   
Corvallis, Oregon  97331                                                     E-mail: oregon@coas.orst.edu   
                                                                             Web: http://www.ocs.oregonstate.edu