The Other Radar Gap: The Eastern Slopes of the Cascades

For over a decade, a group of Northwest meteorologists and weather-affected groups lobbied incessantly to fill a huge gap in the National Weather Service radar network over  the Washington coast and coastal waters.  With a lot of hard work, the strong support of Senator Cantwell and the rest of the Washington delegation, and the cooperation of the National Weather Service, a powerful radar was installed on September 2011 at Langley Hill, near Hoquiam.  And it has not disappointed, proving its worth on many occasions.

But although filling the coastal radar gap was the first order of business, we knew there was another important hole in National Weather Service radar coverage, on the eastern slopes of Cascades--extending from the crest down to the Okanagan, Wenatchee, Yakima, and Bend.

The NWS radar coverage map shows that western Washington is well covered at low levels, but that there is a distinct gap east of the Cascade crest.  Large gaps are found in eastern Oregon and along the central and southern Oregon coast.  I contacted the Oregon Congressional delegation and they were not interested in dealing with this.

There are two big issues here.  First, the Cascades block the view over the eastern slopes from the west-side radars (e.g., Camano Island, Portland, and Langley Hill).  Second, the east-side radars (Spokane, Pendleton) are too far away, with the radar beams far above the surface by the time they reach the eastern slopes....over 8,000 ft above sea level.

Why do we care about radar coverage east of the Cascade crest?   Here are some good reasons:

1.   There is little coverage of precipitation on the upper eastern slopes of the Cascades, which can be substantial.  This impedes hydrological prediction on eastern slope rivers like the Yakima.

2,  We can't use radars to track the beginning stages of thunderstorms along the eastern slopes.

3.  We can't use radar to get accurate precipitation amounts on the eastern slopes from thunderstorms, which is very important today, with so many unstable burn scar areas.

4.  We can't use the radar to track small to moderate fires (fire plumes do show in radar imagery)

5.  Folks in Yakima, Wenatchee, Winthrop and other eastern slope towns, and the varied agricultural interests in the region, don't have ability to do what we west-siders take for granted...the ability to know where it is raining and what will happen during the next hour.

6.  The Yakima Training Center, an important military facility, lacks radar coverage that would facilitate expensive maneuvers and weapon's testing.

Recently, a group of east-side folks have begun to discuss the eastern-slope radar gap under the leadership of Katherine Rowden and Ronald Miller of the National Weather Service Spokane office. I am hopeful that they and others can organize an effective effort to secure some additional radars to fill the gaps.

Yesterday was a good example of the problem.  A frontal band oriented east-west moved northward over Oregon.   Here is the visible satellite picture at 11:30 AM Thursday.

The 12-h precipitation totals ending about the same time showed precipitation on both sides of the Oregon Cascades (I suspect the larger east side amount of several inches are in error).  In any case, several locations got .5-1 inch on the eastern side of the Oregon Cascades.

Map covering the northern Oregon Cascades.  The Willamette Valley is on the left side.

The Portland radar "storm total" product shows plenty on the western slopes, but way less east of the Cascades...clearly less than observed on the ground.

The problem is even larger looking westward using the Pendleton radar.

I could give  you a dozen other examples of  poor eastern-slope weather radar coverage.  The solution is probably to secure 2 or 3 modest "C" band radars, each with a range of a few hundred km.  This will take substantial resources (perhaps as much as a million dollars ) and funds for maintenance and installation.  But I suspect the cost-benefit analysis for the region would be very favorable and the expenses could be shared by local, state, and Federal entities.   I wish the new group luck in their endeavor.