If you think your rainfall is representative of that area…think again.
This June has had very contrasting rainfall.
Consider the cumulative rainfall from June 1 to yesterday (June 26 shown below).
Wow. The windward (west) side of the Olympics has received 5-7 inches so far in June. In contrast, only 1-1.5 inches fell on Puget Sound and less than half an inch in wet Sequim, northwest of the Olympics.
More than TEN INCHES at some locations on the western slopes of the Cascades, dropping to less than half an inch along the eastern slopes of the Cascades and into the Columbia Basin.
Here’s a closer look at the contrast between Seattle and the Cascades. From 0.79 inches west of Seattle to 11.30 inches across the terrain.
Rainfall west of the Cascades not only alleviated some of the spikes, but also caused river levels to clear. Below are the latest USGS river level plots. Most western Washington rivers are near normal (light blue) and some are above normal (dark blue). In contrast, several rivers on the eastern slopes of the Cascades had below-normal water levels.
Western Washington and especially the western slopes are wetter than normal while the eastern slopes of the Cascades are relatively dry. Why?
This month, the wind blows stronger than usual to this area. The wind is stronger than usual from the west. Such a wind field increases the uphill flow and thus increases the rainfall on the western slopes of the mountain.
Conversely, increased winds from the west create stronger shadows and rain falls on the east side of the barriers — creating a strong rain shadow.
What caused the strong westerly flow this month?
How is this month’s situation different from normal? That is shown below (850 hPa height anomaly – think pressure at 5000 ft). This month, we’ve seen a stronger-than-normal low pressure over the Gulf of Mexico, which has enhanced southwesterly flow and brought more moisture to the region.
