Overview

July was a warm month, and quite dry everywhere except northeast Oregon – where significant thunderstorms brought severe weather (see article on this page). A possible developing El Niño in the Pacific is causing some interest among climate folks.

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. Figure 1 shows the percentage of seasonal precipitation statewide.

Basin Summary

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

	Precipitation			Stream Flow		SWSI
BASIN	(1)	(2)	(3)	(4)	(5)	(6)
OWYHEE	11	84	100	65	63	-1.5
MALHEUR	63	100	100	98	39	-0.7
GRAND RONDE, POWDER, BURNT	143	111	99	75	84	-1.3
UMATILLA, WALLA WALLA, WILLOW	60	106	105	68	113	1.4
UPPER JOHN DAY	77	110	98	71	90	-0.2
UPPER DESCHUTES, CROOKED	22	106	93	43	56	-0.2
LOWER DESCHUTES, HOOD RIVER	40	97	90	77	75	-1.0
WILLAMETTE	11	92	75	93	84	-0.6
ROGUE, UMPQUA	8	97	92	85	82	-0.2
KLAMATH	13	96	92	67	64	-2.6
LAKE COUNTY, GOOSE LAKE	55	87	90	41	59	-0.9
HARNEY	21	80	84	68	74	-1.1
NORTH COAST	7	88	n.a	91	80	-0.9
SOUTH COAST	9	96	n.a	73	86	-2.3

n.a. Not available
(1) Percent of normal July 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 July 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 August-October appear below. Temperatures for all of Oregon are likely to be above normal. Precipitation probabilities suggest an increased chance of below-normal precipitation in southeast Oregon. CPC also says:

“ The SSTs in the central Pacific near the Date Line have drifted upward and are now over 1 degree C above normal along the Equator from 125W to just west of the Date Line. Equatorial SSTs in the eastern Pacific continue to average below normal from the South American coast to about 120 W. Tropical intraseasonal activity appears to be weaker than in early July. With a mixture of warmer and cooler than normal SSTs in the equatorial Pacific and weakening intraseasonal activity... there are no clear signals from the tropical Pacific influencing temperature and precipitation over the CONUS and Alaska.”

Oregon Climate Service predicts above-normal temperatures and normal precipitation for August. For the three-month period August through October we predict normal temperatures and below-normal precipitation.

Regarding ENSO, CPC says:

“ Synopsis: El Niño conditions are expected to develop during the next 3 months.

“ Sea surface temperature anomalies increased substantially in the central equatorial Pacific during July 2004, while anomalies greater than +0.5°C persisted in the Niño 4 region. The recent increase and eastward expansion of positive SST anomalies in the central equatorial Pacific indicate the possible early stages of a warm episode. SST anomalies greater than +0.5°C (~1°F) were found between 160°E and 120°W, with anomalies greater than +1°C extending from 180°W eastward to 125°W. In spite of the anomalous warmth in the central equatorial Pacific during July, there appears to be little or no reflection of that warmth in the pattern of deep convection (precipitation) over the region.

“ Based on the recent trends and observed oceanic and atmospheric patterns discussed above, there is about a 50% chance that the NOAA operational definition for El Niño will be satisfied for the period June-August 2004. It seems most likely that SST anomalies in the Niño 3.4 region will remain positive, at or above +0.5°C, through the end of 2004. At this time it is not clear what, if any, impacts this event will have on ocean temperatures in the classical El Niño region (Niño 1+2) along the west coast of South America.”

Severe Weather, July 19, Northeast Oregon
George Taylor, Melanie Mitchell, and Emily Gibson, Oregon Climate Service

Thunderstorms rumbled through Northeast Oregon on the afternoon of July 19, 2004, bringing strong winds, hail, heavy rain, and flooding. Some parts of the region received more than 2 inches of rain.

The storm total estimate from NWS Doppler radar appears below.

Below are NWS warnings and storm reports for the afternoon and evening.

• At 1244 pm PDT...National Weather Service Doppler radar continued to indicate a severe thunderstorm. This storm was located 10 miles southwest of Bates...or about 17 miles east of John Day...and moving northeast at 20 mph.
  
• This storm produced penny sized hail at 1236 pm.
  
• 80-90 mph winds were reported 2 miles east of Mitchell at 145 pm.
  
• ...A severe thunderstorm warning continues until 445 pm PDT for Union County...
  
• At 155 pm PDT a spotter at Sumpter reported marble-sized hail covering the ground to a depth of one inch.
  
• At 414 pm PDT...the public reported a severe thunderstorm producing golf ball size hail...and destructive winds in excess of 70 mph. This storm was located 10 miles southwest of Hilgard...or about 13 miles southwest of La Grande...moving northeast at 35 mph.
  
• At 500 pm PDT...local law enforcement reported a severe thunderstorm containing damaging winds...including overturned vehicles and modular buildings...and downed trees and power lines. This storm was located 8 miles east of Imbler...or about 17 miles northeast of La Grande...moving northeast at 35 mph.
  
• At 517 pm PDT National Weather Service Doppler radar indicated very heavy rain over Union County. Flooding has been reported in La Grande. Rain is expected to continue through at least 7 pm leading to additional flooding of mainly low lying and poor drainage areas.
  
• At 531 pm PDT...National Weather Service Doppler radar continued to indicate a cluster of severe thunderstorms between Wallowa and Enterprise...moving northeast at 30 mph.
  
• At 550 pm PDT...local law enforcement officials reported that flash flooding was continuing in Baker City. The thunderstorms responsible for producing the flash flooding are moving northeast away from Baker City into northeastern Baker County. Even though the heaviest rain is tapering off...small streams and low areas are likely to remain flooded for the next hour or two.
  

Oregon Climate Service

George H. Taylor, Oregon State Climatologist

Wayne P. Gibson, Programmer/GIS mngr.

Mandy Matzke, 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

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