Active Weather Day on Monday

Monday will likely be an active and interesting weather day around Western Washington, with rain, wind, a big temperature drop, and potential snow all in the cards. Let's take a look!

Starting late Sunday night, rain will move into Western WA. This rain will continue through Monday evening. Below is NWS Seattle's forecast for total rain with this storm.

Expect 1-1.5 inches of rain. That's enough to cause localized urban flooding, ponding, and standing water. Rain will likely be moderate to heavy at times, especially on Monday.

Next is the wind. Since all of this mayhem is caused by a low pressure system, wind is in the cards. The cold front associated with this system will bring winds gusting 30-50 mph during the day on Monday.

The blend of 4 forecast models for Puyallup shows strong gusts of 30-50 mph prior to the cold front. Expect similar winds around the area. Be prepared for localized tree damage and isolated power outages.

Another aspect of this weather system will be the temperatures. Sunday was warmer than usual, with temperatures of 47-55 degrees most of the day. Temperatures will remain in the mid-40s overnight into Monday, before peaking at 52-57 degrees during the day on Monday. Then, a big swing takes place. Temperatures will drop from 52-57 to 33-43 degrees as the cold front moves through on Monday afternoon. This swing will take place within hours, and it will set the stage for what you've been wanting to know about...

There is a chance of lowland snow on Monday afternoon and into the evening. The graphic below from NWS Seattle communicates the uncertainty ahead.

I expect that snowflakes will fall, either as heavy rain/snow mix or as snow. Snow accumulations are unlikely, except for some grassy surfaces away from the water and above sea level. It is unlikely that roads will be impacted, due to ground temperatures being above freezing.

The reason that this is a very challenging snow forecast is that there is a lack of cold air, the track of the incoming low matters (it can come down to miles), and there is a chance of a Convergence Zone (when air flows around the Olympic Mtns. and converges over parts of the Puget Sound area) snow band dropping more snow in select areas. Additionally, the temperature matters. Too warm during the day, much less of a snow chance. If the temperature drops into the low-mid 30s, there's a "better" snow chance. 

Let's talk snow accumulation. Don't expect much. A trace or a bit more is possible on grassy surfaces, with the highest likelihood of this in the Cascade foothills or higher hills around the area. Snow, if any, will end by late Monday evening.

There's not enough accumulation expected (or enough confidence in that forecast) to bring out the snow maps, but don't be surprised to see snowflakes!

Congratulations! You made it to the end of this blog. There's enough going on to warrant a summary at the end:

• Rain, heavy at times, will last from Sunday night to Monday evening, totaling 1-1.5 inches
• This rain could cause ponding and standing water, along with possible urban flooding
• Due to the incoming cold front, winds gusting 30-50 mph are possible on Monday as well
• Temperatures on Monday will peak in the mid-50s, dropping to 33-45 degrees by Monday evening (a drop happening in a matter of hours)
• Due to incoming cold air, there is a chance of mostly non-accumulating lowland snow Monday afternoon and evening
• A heavy rain/snow mix or brief heavy snow is possible

Stay tuned! There is still a lot of uncertainty in the forecast.