Wednesday night system brings record rain, strong winds to Mid-Columbia

While the Tri-Cities Airport is still reporting a deficit for rainfall thus far in 2018, Wednesday night’s rainfall helped to bring our numbers a little bit higher. Parts of the area received record rainfall values, while others are now above average for the month of April (and it’s only the 12th!).

For me, at least, the most interesting feature of this system was the squall line that formed near Fossil and impacted Heppner, Pendleton, Milton-Freewater, and Walla Walla. Intermittent lightning strikes occurred in this cell in southern Morrow County, but they increased significantly in frequency after it passed Pendleton. We even heard some thunder in Boardman.

Calmer weather is expected Thursday through Saturday, with just isolated showers expected. The Storm Prediction Center says a few lightning strikes are possible Thursday afternoon, with the highest chance being generally south of Highway 12. Another system moves in for the second half of the weekend, but there still isn’t a lot of confidence for how this next one will impact the area.

Beyond the middle of next week, the Climate Prediction Center is predicting slightly above average precipitation for the 8-14 day period (April 19-25). While this forecast is vague, it hints that our unsettled weather pattern could continue for a while. It’s important to remember that when considering forecasts that far out into the future, there is a chance that everything can change.

Now that we’ve covered the forecast, here’s a look at what happened yesterday in the Tri-Cities, Walla Walla, Pendleton, Hermiston, and Boardman. If you’re looking to read the whole thing, it will probably be repetitive. If you’re looking for your city, just scroll down.

Tri-Cities

Rainfall values varied around the Tri-Cities, but official records are taken at the airport in Pasco. After last night, the airport is up to 2.72 inches of rain for the year, but what I found to be more interesting than that is the fact that we’re already above the April rainfall average. At the end of last night, we reached a monthly total of 0.86 inches, with the monthly average being 0.65 inches.

Of course, none of us live at the Tri-Cities Airport, so here are the rainfall values at some different sites around town, including data from CoCoRaHS sites (cross streets are approximate):

Areas to the west in Benton County got less. Prosser looks to have gotten 0.24 inches of rain.

Walla Walla

If you like severe weather, Walla Walla was the winner last night, but if you’re all about breaking records Walla Walla was the loser (not because they got the least, but because they got so close). The airport turned in 0.70 inches of rain, just one-hundredth of an inch shy of tying the record for the day.

About half of the rain Wednesday fell during the thunderstorm between 10:30 pm and midnight. At the onset of the storm, winds gusted to 39 mph at the airport, but seven miles east of town an automated CWOP station reported a wind gust of 64 mph. To be considered a severe thunderstorm, a storm has to have either 58 mph winds, hail at least one-inch in diameter, or a tornado.

This wind gust was the only severe weather report that was received by the National Weather Service on Wednesday. It is important to note that this station is located at an elevation of 3,454 feet. This is significantly higher than Walla Walla (942 feet) and possibly contributed to the severity of the winds felt there.

Other observations around Walla Walla include the following (locations are approximate):

Pendleton

Pendleton broke their daily rainfall record by three-hundredths of an inch. A small amount of rain, 0.05 inches to be exact, fell after 4pm, but the heavy rain in the evening didn’t begin until just before 10pm. Winds there gusted to 37mph, just 2mph short of what Walla Walla’s airport registered. Rain didn’t end until around 1am.

Here some other observations from around Pendleton (and Meacham because I wanted to):

Hermiston

Hermiston not only broke their record, but based on data from the Western Regional Climate Center (archive), they shattered it. It looked as though heavy rain parked over Hermiston for about five hours or so, and from what it looked like while driving through town today, it produced some pretty decent puddles.

Despite this amount of rain, the Umatilla River hasn’t risen. Forecasts aren’t issued for the Umatilla River at Umatilla, but some of the gauges upstream are showing a small increase in the flow. That being said, even if the river does raise, it won’t be enough to cause any sort of concern.

Other rain totals around Hermiston (locations are approximate):

Boardman

Boardman got the least out of the five cities we’re looking at, with only 0.29 inches of rain. We had more than Prosser did, but not by much. We had some drizzle here during the day, but like everywhere else, most of our rain fell overnight. There was thunder here, but we missed out on the squall that tracked through Pendleton, and it was well to our south.

A second band of showers came in from the west, combining with the first one that came through. There was a short gap as it approached, but once it made it here that was when we saw our highest rainfall rates. Like the Tri-Cities, we are now above the monthly rainfall average for April.

Drought conditions are currently in place for much of eastern Oregon; generally south of Heppner. That is expected to continue into the near future, but further drought development is not expected in the Mid-Columbia.

The ongoing series of precipitation is also helping boost our snowpack this late in the season. Last night, nine inches of fresh snow fell at Timberline on the slopes of Mount Hood. All areas of Washington where we need snow to be are at or above average for the year.

Part of this article was written at the Hermiston Public Library.