Weekend Rain Update

Typically at this time of year, most of us are looking for some dry days to put up hay. But this year, rain will be a welcome sight. And it still looks like we will be blessed with some rain this weekend. So let’s look at some details. 

First, the timing. It still appears that the rain could start as early as Friday evening, but is a guaranteed done deal by Saturday afternoon. Here’s the rain probability for Deer Park. 


93% of the computers agree that it will be raining at 2pm on Saturday. It’s rare to get that much agreement on a forecast of rain, especially at this time of year.   You can see decent chances of rain throughout Sunday and even Monday as well before we dry out and warm up. But the extended forecast doesn’t look hot yet and may provide another chance of rain late next week. 

How much rain will we get this weekend?  That is typically the toughest part of the forecast. First I’ll show you the National Blend of Models (NBM). 



It expects the bulk of the rain to fall Saturday afternoon and evening, with a total of just over a half inch for the weekend in Deer Park. 

Here’s a graphic I’ve shown before. It displays the probability of various rainfall amounts. 0.01” on Saturday is a sure bet at 90%.  There’s a 57% chance of a quarter inch on Saturday, at 37% chance of a half inch, and even a 10% chance of over 1” of rain. 



Here’s a map showing the NBM forecast for all of Washington. 


0.4” for Spokane with higher amounts to the north.  This agrees pretty well with the average of the European computer forecasts shown below. 




The uncertainty from this storm isn’t due to hit or miss showers or thunderstorms. This storm is a widespread rain that we typically see in May (except for this year). The low passes slowly over the state. Even after the center of the low moves east of us, we can still get more “wrap-around” rain on the back side of the low.  But the exact track and speed of the low is still a bit unpredictable. If the low tracks across northern vs southern Washington, or if the low speeds up or slows down a bit, the rainfall amounts will vary accordingly. 

We’ll all get some rain this weekend. Someone is likely to get a lot of rain from this event. Most likely that will be in southern BC. But it could get displaced into the northeast mountains of Washington or perhaps the Palouse. 






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