Another Chance of Rain

We have another potential opportunity for some rain later this week. But this will be very different from the rain last week. In that situation, the moisture was coming at us from the south, resulting in very muggy weather and heavy thunderstorms. In the case coming up, the storm is coming at us from the west. Typically this pattern in the summer yields very little if any rainfall for our side of the Cascades. But in this instance, the computer models beg to differ.  This is also not a good pattern for thunderstorms like we saw last week.

First I’ll start off with the National Blend of Models (NBM). Remember, this is a blend of over 100 computer forecasts plus bias adjustment. It expects the rain to start Wednesday night and continue through Thursday.




This pattern of rain looks pretty standard for this kind of storm and will probably verify the best.  But there are a few other ideas that the computers are throwing out, as usual.  First I’ll show you the US GFS model, zoomed in to the state of Washington.  A pretty standard forecast with about 0.10” forecast for the Spokane area, and a little more to the north.


The European model is an outlier with this event, giving the Spokane area over 1” of rain, which seems way overdone given this pattern. But even if you ignore that detail, it’s still a wetter forecast than the GFS or NBM.


Part of the discrepancy is that the European model sees a band of rain coming through on Wednesday, much earlier than any other model.  


Given all the uncertainty, it’s best to lean on the NBM in this situation.

So why are the computers giving us more rain than a normal summertime front?  The answer is that this system is bringing with it an impressive plume of moisture from the subtropical Pacific, which is somewhat unusual for this time of year.  You can see this plume on the image below, highlighted with the black arrow.


After this cool and wet spell, things will warm back up into the 90s by the weekend and last into next week.









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