Monday Night Storm Update

It has been a rainy day across Western Washington as the atmospheric river begins impacting us. 24 hour rain totals as of 8:45 PM Monday are below.

Totals range from 0.4-1.2 inches, and an additional 1-2.5 inches are possible through Wednesday. 

Monday’s satellite image was incredible, showing the atmospheric river (plume of moisture) impacting us. The atmospheric river stretches thousands of miles all the way across the Pacific Ocean!

Those arrows aren’t actually there...but they show the incredible plume of moisture aimed at us. The air moving in to our area has gone from Japan, through the subtropical Pacific, and to our shores. While it brings us dreary weather, it’s amazing to see weather in action.

Due to all this rain, a Flood Watch (posted below) is in effect through Wednesday night.

Now that we know some of the impacts of the rain, let’s talk forecasts. The UW forecast model below shows precipitation through 4 PM Wednesday. 

Expect an additional 0.5-2.5 inches of rain. This will prompt urban, small stream, and river flooding, landslides, high soil moisture, and avalanche danger in the mountains.

Additionally, gusty winds are possible as well. Two timeframes of gusty winds are possible...Tuesday morning and Tuesday night/Wednesday morning.

Expect winds gusting 20-40 mph Tuesday morning and 25-45 mph Tuesday night into Wednesday morning.

Elevated soil moisture (in turn a very saturated ground) will cause an increased possibility of tree damage. 

For those along Puget Sound, there is also a chance of tidal overflow (up to 1 foot) due to king tides and low atmospheric pressure. Peak tidal overflow will likely occur between 5 and 6 AM Tuesday.

The graphic below from NWS Seattle shows our Monday to Wednesday rain forecast with impacts on the side.

One more thing...the “subtropical” component of the atmospheric river will bring highs of 52-57 degrees on Tuesday.

Be safe and try your best to stay dry!! We should have a break by Thursday!

Atmospheric River Bringing Heavy Rain, Gusty Winds, Possible Flooding

The second full week of 2021 will start off quite wet, with an atmospheric river set to impact Western Washington during the first half of the week. Let's take a look at the details.

This 5-day outlook from NWS Seattle shows what to expect in the coming days.

The UW forecast model has some great tools to see the strength of atmospheric rivers that impact the Pacific Northwest.

Below is the integrated water vapor transport (IVT). This is basically the measure of water vapor being transported in the atmosphere. The forecast below is for 1 AM Tuesday.

Yellows, reds, and dark blues are higher values (key at bottom of image). At this time (1 AM Tuesday), a true atmospheric river is aimed at the Pacific Northwest. You can see the area of dense moisture stretching across the Pacific Ocean to our shores.

There will be two surges of strong and deep moisture. One is Monday night/Tuesday morning, with the second coming early Wednesday. They are both shown below.

These are potent atmospheric rivers that will bring a lot of rain to Western Washington. In addition, snow levels will rise above pass level on Monday night, leading to rain (5-10 inches), snowmelt, and avalanche danger in the mountains.

The GFS Model forecasts around 3 inches of rain for Western Washington through Wednesday evening. Expect the heaviest rain from Monday evening to Tuesday morning.

3-5 inches of rain in the lowlands by the end of this week is a good ballpark estimate. This will cause urban & small stream flooding, a high landslide threat, and possible river flooding.

In addition to the rain, gusty winds are possible as well. Expect wind gusts of 20-40 mph Monday night into Tuesday morning.

More wind, potentially stronger, is possible on Wednesday. It looks like we will have a drier day on Thursday.

Any winds will be worth watching due to the saturation of the soils producing a higher probability of tree damage.

Stay tuned & stay safe!

Relatively Calm Weekend Then Rain to Start Next Week

After localized gap winds and occasional rain on Friday, we will have a relatively calm weekend.

Saturday will start off chilly and foggy, with temperatures of 30-35 degrees and areas of fog around the region. (Graphic from NWS Seattle)

Due to the cold temperatures, there is also a chance of black ice and freezing fog on Saturday morning.

Where fog burns off, expect mostly sunny weather with highs in the 40s!

Another bout of easterly (from the east) gap winds in prone locations is expected Saturday through early Sunday morning. Expect the strongest winds in the outlined area (gusts 30-45 mph) and lesser winds (15-25 mph) in other foothill locations.

A system will bring occasional rain on Saturday night & Sunday morning. Expect only 0.05-0.2 inches of rain.

Sunday will be a day of scattered showers, with mostly cloudy conditions.

Starting Monday night, our next round of impactful rain will arrive. An atmospheric river (aka Pineapple Express) will bring heavy rain and higher snow levels to the Pacific Northwest. Due to this, a Hydrologic Outlook (below) has been issued by NWS Seattle.

The bottom line is that another round of rain that will elevate the landslide threat again and potentially bring flooding is on the way.

Details of rain amounts aren't yet certain, but a general idea is given by the Weather Underground forecast for Puyallup.

It looks like the heaviest rain (along with some possible gusty winds) will occur on Monday and Tuesday of next week. Temperatures will likely be mild (50s) all of next week.

Next week's forecast totals another 1-3 inches of rain in the lowlands, adding to the 2-5 inches of rain that has already fallen this month.