FastCast--Thursday, May 30 to Tuesday, June 4:
A couple dry days are expected across the region to end the work week, after region-wide showers on Tuesday and Wednesday. On Thursday and Friday, expect partly sunny skies, with highs reaching the mid to upper 60s on Thursday and upper 60s to low 70s on Friday. Mostly cloudy conditions will return on Saturday, with highs in the mid 60s. There is also a chance of showers on Saturday, although no more than 0.2" of rain is likely (most from Everett northward). Lows from Thursday to Saturday will be in the mid 40s to low 50s. Then, on Sunday, a significant atmospheric river will move into the region. This will likely bring moderate to heavy rain at times from Sunday morning through Monday morning, heaviest later on Sunday. Precipitation totals across the lowlands will be quite heavy, likely between 1.25 and 1.75", with some areas getting upwards of 2" by Monday. However, some uncertainty remains as to precipitation totals, so stay tuned. A second potential atmospheric river looms for Tuesday, although this forecast is far less certain. With a strong atmospheric river bringing an influx of moist air, temperatures will remain steady from Sunday through Tuesday, with highs in the upper 50s to low 60s, and lows in the low to mid 50s. The impacts of this atmospheric river will likely include standing water, reduced visibility, and potential rises on area rivers.
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Continue reading the full blog below!
June will begin in abnormal fashion, with a significant atmospheric river likely to impact the region from Sunday to Monday. Let's take a look at the forecast!
We'll start with the forecast for precipitable water (amount of water vapor in the atmosphere) for Sunday afternoon, from the European model.
This forecast clearly shows that an atmospheric river is likely for the Northwest. Notice the large area of moisture moving directly into the region.
Let's compare this to the GFS forecast, showing the same thing, also for Sunday afternoon.
This forecast is nearly identical, with a large atmospheric river moving into the region, stretching across the Pacific Ocean.
The European and GFS forecasts being in such good agreement about this atmospheric river is a good indication of confidence in the forecast. With that in mind, let's take a look at possible rain totals, through Monday night.
We'll start with the European model, shown below.
The European model shows the lowlands receiving 0.9-1.75" of rain, with 1.5-2" on the coast, and 2-4" in the mountains. Eastern Washington gets 0.15-0.5", except up to 1.25" along the Idaho border. The high amount of rain in the Cascades and Olympics will bring the potential for rises on area rivers, so stay tuned for more on this possibility.
Next, let's take a look at the GFS forecast, also showing total rain through Monday night.
This forecast shows a couple different things. First off, it has higher precipitation amounts. Secondly, it has much more pronounced rain shadows, both NE of the Olympics and across Eastern Washington. The GFS shows 1.5-2" of rain across the lowlands, with a significant rain shadow from Seattle to the San Juans. In this forecast, the coast gets walloped with 2.5-3.5" of rain in 2 days, while the mountains receive 2.5-5". Eastern Washington is a whole different story, with a significant rain shadow for the western half, and 0.4-1.2" for the eastern half.
As you can see, there is some disagreement between the European and GFS forecasts. A good go-between is the NWS National Blend of Models (NWS NBM) high-resolution forecast, showing total rain through Monday night.
This forecast shows 1-1.5" for the lowlands, 2-3" for the coast, and 2-4" for the mountains. Eastern Washington gets 0.1-0.8", depending on location (least in the Columbia Basin, most along the Idaho border and in the Blue Mountains).
Regardless, this is likely to be a significant event, especially for early June, so stay tuned for updates as we get closer to the atmospheric river's arrival!
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