The last several weeks have been drier than normal over the West Coast, and based on the latest forecasts, February will almost certainly come in below normal over the western U.S. This after an extraordinarily wet autumn and early winter.
In this blog, I would like to provide some perspective on this dry month and take a look at some of the updated model runs for the remainder of February
A plot of the precipitation anomaly from normal for the past two weeks shows the issue: below-normal precipitation from the Bay Area through Washington State, with some locations 1.5 to 4 inches below normal. SeaTac has only received .21 inches this month, 1.12 inches below normal.
HUGE variations from around 9 inches to about a third of an inch! Large year-to-year variability, with the average amount (3.76 inches) the result of averaging extremes in both directions. There are a number of wet years, with totals around 8 inches, and many years with only about 2 inches in the rain gauge. It shows you that you have to take average values with a big grain of salt.
Some years get hit by one or more soggy atmospheric rivers, while others do not. Like this year.
So dry Februarys are nothing new...or unusual... a fact your need to keep in mind. And this month is associated with a highly persistent ridge of high pressure offshore.
Looking Forward
It actually rained this morning....some drizzle from low clouds...but that does not count for much.
The weekend will be completely dry, but on Monday a weak system comes through, followed by a few others next week. Take a look at the total predicted rain through next Thursday at 4 PM over the region (see below).
Nothing I would write home about. Perhaps a few tenths of an inch over the western lowlands. A bit more in the mountains.
The European Center cumulative precipitation at SEATAC through Sunday, Feb. 20th is about .6 inches, with more significant rain coming in at the end of next weekend. Enough to get us out of record dry territory.
But the big question is the final week of the month, with both European and U.S. models going back to a near-normal precipitation regime for the region, which might get SeaTac to a monthly total of around 2 inches, joining the large number of dry years shown in the figure above.
The good news is that even with the recent dry spell the water-year totals (since October 1) for the region are above normal and reservoirs are generally higher than normal. The water year chart for SeaTac below shows the story..... still WAY above normal after the sodden fall (dark green indicates above normal). So enjoy the dry conditions and upcoming sun: you earned if by all the misery last autumn.
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