Flood Potential Outlook
Issued by NWS Pendleton, OR

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Hydrologic Outlook
National Weather Service Pendleton OR
255 PM PST Mon Jan 16 2017

...RAIN AND SNOWMELT MAY CAUSE LOCALIZED FLOODING ISSUES TOWARD
THE MIDDLE OF THE WEEK...

THE WEATHER PATTERN WILL CHANGE...BRINGING WARMER TEMPERATURES...RISING
SNOW LEVELS AND PERIODS OF RAIN TO MUCH OF THE AREA BEGINNING
TUESDAY NIGHT AND LASTING THROUGH AT LEAST THURSDAY. TOWARD THE
END OF THE WEEK AND NEXT WEEKEND WEATHER SYSTEMS WILL CONTINUE TO
BRING PERIODS OF LOWER ELEVATION RAIN AND MOUNTAIN SNOW TO THE
AREA.

SNOW LEVELS WILL RISE TO BETWEEN 6500 TO 8500 FEET TUESDAY NIGHT
THROUGH WEDNESDAY...EXCEPT 5500 TO 6500 FEET OVER THE BLUE
MOUNTAINS...WALLOWA COUNTY AND THE EAST SLOPES OF THE WASHINGTON
CASCADES. SNOW LEVELS THEN GRADUALLY FALL...REACHING 3500 TO 4000
FEET AREAWIDE DURING THE DAY THURSDAY. TOWARD THE END OF THE WEEK
AND INTO NEXT WEEKEND SNOW LEVELS SHOULD HOVER BETWEEN 2000 TO
3500 FEET MUCH OF THE TIME.

BELOW THESE SNOW LEVELS EXPECTED PERIODS OF RAIN...MODERATE AT
TIMES WITH THE FIRST BATCH MOVING THROUGH FROM TUESDAY NIGHT
THROUGH WEDNESDAY NIGHT. ANOTHER SYSTEM WILL BRING ADDITIONAL RAIN
AND HIGHER ELEVATION SNOW FROM LATE THURSDAY NIGHT THROUGH FRIDAY
NIGHT. PRECIPITATION AMOUNTS THROUGH THURSDAY ARE EXPECTED TO
RANGE FROM ONE QUARTER TO THREE QUARTERS OF AN INCH OVER THE LOWER
COLUMBIA BASIN...YAKIMA VALLEY...KITTITAS VALLEY AND THE LOWER
BASINS OF CENTRAL OREGON. PRECIPITATION AMOUNTS ARE EXPECTED TO
RANGE FROM 0.75 TO 1.5 INCHES IN THE SOUTHERN BLUE MOUNTAINS AND
THE GRANDE RONDE VALLEY. EXPECT BETWEEN 1 TO 2 INCHES...WITH
LOCALLY AS MUCH AS 3 INCHES OF PRECIPITATION ALONG THE EAST SLOPES
OF THE OREGON CASCADES...NORTHERN BLUE MOUNTAINS AND IN WALLOWA
COUNTY. THE EAST SLOPES OF THE WASHINGTON CASCADES CAN EXPECT
BETWEEN 2 TO 4 INCHES OF PRECIPITATION BY THURSDAY EVENING...WITH
THE HIGHEST AMOUNTS ALONG THE CASCADE CREST.

THESE PRECIPITATION AMOUNTS WILL COMBINE WITH THE AFOREMENTIONED
WARMER TEMPERATURES AND HIGH SNOW LEVELS TO CREATE SOME HYDROLOGIC
CONCERNS. MUCH OF THE RAIN SHOULD INITIALLY BE ABSORBED WITHIN
THE SNOW PACK...BUT EVENTUALLY THIS WILL BEGIN TO MELT...ESPECIALLY
IN THE LOWER ELEVATIONS. THIS RAIN ON SNOW SCENARIO WILL ADD
ADDITIONAL WEIGHT TO ALREADY STRESSED BUILDINGS AND ROOFS IN
LOCATIONS THAT CURRENTLY HAVE A DEEP SNOWPACK.

THE POTENTIAL IMPACTS FROM THE SNOWMELT AND RAINFALL RUNOFF
INCLUDE PONDING OF WATER WHERE STORM DRAINS OR DITCHES ARE CLOGGED
WITH SNOW AND ICE, PONDING OF WATER IN LOW LYING AREAS WITH POOR
DRAINAGE OR FROZEN GROUND, POSSIBLE ICE JAMS ON SMALL CREEKS AND
RIVERS THAT HAVE FROZEN OVER.

WHILE NO MAJOR RIVER FLOODING IS FORECAST AT THIS TIME, THIS IS AN
EVOLVING SITUATION AND SHOULD BE MONITORED REGULARLY FOR UPDATES.


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