Water Supply Summary

NORTHWEST RIVER FORECAST CENTER PORTLAND OR
PRECIPITATION, TEMPERATURE, SNOW, AND STREAMFLOW SUMMARIES
may 09


WEATHER SUMMARY

A LARGE SCALE UPPER LEVEL TROUGH BROUGHT COOL WET CONDITIONS TO THE REGION FOR MUCH OF THE FIRST
WEEK OF MAY. THIS TROUGH SHIFTED NORTH OVER THE SECOND WEEK...BRINGING CONTINUED COOL BUT DRIER
CONDITIONS TO MUCH OF THE REGION. BY MID MONTH A HIGH PRESSURE RIDGE BUILT OVER THE
NORTHWEST...BRING DRY AND WARM CONDITIONS TO THE REGION. HIGH PRESSURE DOMINATED THE WEATHER FOR
THE SECOND HALF OF MAY...ONLY INTERUPTED BY A STRONG COLD FRONT THAT MOVED THROUGH THE 19TH
THROUGH THE 21ST. BY THE END OF THE MONTH...MONSOONAL MOISTURE TRAINED OVER SOUTHERN
IDAHO AND OREGON...BRINGING SHOWERS AND THUNDERSTORMS TO THE REGION.

PRECIPITATION SUMMARY

May precipitation was: 82 percent of normal (1971-2000) at Columbia above
Coulee, 91 percent of normal at the Snake River above Ice Harbor, and 91
percent of normal at Columbia above the Dalles.


Seasonal (October through May) precipitation was: 91 percent of normal
(1971-2000) at Columbia above Coulee, 103 percent of normal at the Snake River
above Ice Harbor, and 97 percent of normal at Columbia above the Dalles.




TEMPERATURE SUMMARY

The 37 station temperature index for the Pacific Northwest departed
+1.4 degrees from normal relative to the 1971-2000 normals. Mean
temperature departures ranged from -1.2 to 5.5 degrees.

General Summary -

May was a month of contrasts, cool and wet for half a month and then warm
and dry as the month ended. May precipitation for areas east of the
Cascade Range was slightly above average. An above average high elevation
snowpack began to melt actively at month's end. Overall, in most northern
portions of the Columbia basin, streamflow forecasts improved slightly
while streamflow forecasts for most Snake river area decreased slightly.

Snow Summary -

At the end of May only high elevation snow remains-generally above 5000 to
6000 feet. The high elevation snowpack was at 100 to 130 percent of the
June 1st average. In the Canadian portion of the Colunbia river basin
snow water equivqlents (SWE's) continued to acccumulate until the middle
of May. The best June 1st SWE's are on the Clark Fork and Bitterroot
rivers at 110 to 140 percent of average. West of the Cascades an above
average high elevation snowpack produced some active snowmelt especially
in Western Washington.

Streamflow Summary -

May streamflow was above average for most areas of the Columbia basin
due to rainfall and snowmelt. The only areas with below average May
streamflow were the Columbia-Kootenai rivers at 60 to 70 percent, the East
slopes of the Cascade Range at 60 to 80 percent and South Central Idaho
and Southeast Oregon at 50 to 80 percent. The best May streamflow was on
the Clark Fork in Montana at 130 percent, the Yakima in Eastern Washington
at 120 to 130 percent,the Salmon-Clearwater rivers in Idaho at 110 to 120
percent and the Blue Mountain tributaries in Northeast Oregon ar 120 to
150 percent. Active snowmelt at the month's end brought flooding to the
Naches River on the Yakima system and on the Bitterroot river in Montana.

The forecast streamflow for June 1st is near the May 1st forecast levels
for the major forecast locations in the Columbia basin. Forecast values
improved on the Clark Fork river in Montana, on the Spokane river and the
Yakima rivers in Eastern Washington. In contrast, some Middle Snake
tributaries decreased in forecast streamflow. West of the Cascades
streamflow forecasts improved from May 1st due to rainfall and some
snowmelt runoff.

http://www.nwrfc.noaa.gov/water_supply/ws_fcst.cgi
has detailed water supply forecasts.



MONTHLY PRECIPITATION AND TEMPERATURE RECORDS


Partial list of record high and low temperatures in degrees (F) are listed below.
Precipitation is reported in inches.
Please see the complete list of records at the National Weather Service Field
Offices Climatology Web pages.


5/2 A RECORD RAINFALL OF 0.63 INCHES WAS SET AT BOISE ID.
A RECORD RAINFALL OF 0.36 INCHES WAS SET AT BURNS OR.

5/03 A RECORD RAINFALL OF 0.90 INCH(ES) WAS SET AT MEDFORD OR.
A RECORD RAINFALL OF 0.61 INCHES WAS SET AT BURLEY ID.

5/04 A RECORD RAINFALL OF 0.78 INCHES WAS SET AT OLYMPIA WA.

5/05 A RECORD RAINFALL OF 0.59 INCHES WAS SET AT SEATTLE-TACOMA WA.

5/06 A RECORD RAINFALL OF 1.01 INCHES WAS SET AT OLYMPIA WA.
A RECORD RAINFALL OF 0.89 INCHES WAS SET AT SEATTLE-TACOMA WA.
A RECORD RAINFALL OF 0.98 INCHES WAS SET AT ASTORIA OR.

5/08 A RECORD LOW TEMPERATURE OF 25 DEGREES WAS SET AT POCATELLO ID.
A RECORD LOW TEMPERATURE OF 24 DEGREES WAS SET AT IDAHO FALLS ID.

5/09 A RECORD LOW TEMPERATURE OF 16 DEGREES WAS REPORTED IN CHALLIS ID.
A RECORD LOW TEMPERATURE OF 16 DEGREES WAS REPORTED IN STANLEY ID.

5/13 A RECORD LOW TEMPERATURE OF 28 DEGREES WAS SET AT OMAK WA.
A RECORD LOW TEMPERATURE OF 36 DEGREES WAS SET AT THE DALLES OR.
A RECORD LOW TEMPERATURE OF 25 DEGREES WAS REPORTED IN IDAHO FALLS ID.
A RECORD LOW TEMPERATURE OF 18 DEGREES WAS SET AT MCCALL ID.
A RECORD RAINFALL OF 0.44 INCHES WAS SET AT SEATTLE-TACOMA WA
A RECORD RAINFALL OF 0.83 INCHES WAS SET AT OLYMPIA WA.

5/18 A RECORD HIGH TEMPERATURE OF 91 DEGREES WAS SET AT POCATELLO ID.
A RECORD HIGH TEMPERATURE OF 88 DEGREES WAS SET AT MISSOULA MT.
A RECORD HIGH TEMPERATURE OF 95 DEGREES WAS SET AT BOISE ID.

5/20 A RECORD LOW TEMPERATURE OF 25 DEGREES WAS SET AT BURNS OR.

5/21 A RECORD LOW TEMPERATURE OF 28 DEGREES WAS SET AT MISSOULA MT.

5/24 A RECORD RAINFALL OF 0.60 INCHES WAS SET AT POCATELLO ID.

5/29 A RECORD HIGH TEMPERATURE OF 92 DEGREES WAS SET AT OMAK WA.

5/30 A RECORD RAINFALL OF 1.01 INCHES WAS SET AT BURNS OR.

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US Dept of Commerce National Oceanic and Atmospheric Administration National Weather Service Northwest River Forecast Center (NWRFC) 5241 NE 122nd Avenue Portland, Oregon 97230-1089 Telephone: 503-326-7401 Last Modified: June 6, 2008

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