December 02, 2022

Low Indoor Relative Humidity and the Next Snow Event

Is your skin getting dry and cracked?  Developed a dry cough?  Getting a bit of static discharge when you touch that door knob?

These are all symptoms of low relative humidities that develop when outdoor temperatures turn cold.     

To illustrate check out the indoor relative humidities around Seattle, courtesy of the PurpleAir network.  Many indoor locations have relative humidities below 30%, some lower.

Relative humidities are far higher outside.  How can that be?   All is explained in my podcast (see information below).

And in the first segment of the podcast, I talk about the weather forecast.  Another snow event will occur tonight and tomorrow morning, but it won't be the equal of two days ago.   

As shown by the predicted snowfall totals from the high-resolution UW WRF system, most of the snow will be over the Olympics and Kitsap Country, with northwest Washington (particularly Whatcom County) getting a piece of the snowy action.


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December 01, 2022

Another Snow Event Friday Night/Saturday Morning

 The forecast models did a good job on this morning's snow event, which was mainly to the southeast of Seattle and over southern Puget Sound country.    2-4 inches fell in places and the I-5 corridor near Tacoma looked like Alaska (see below)


But ANOTHER snow event is coming.   And I don't want to hype this...it is not going to be a major snow event.   It will be a complex, marginal event that tests our modeling systems' fidelity.

Tomorrow night, a low center will move off our coast, while cold air is in place over the region (the map below shows sea level pressure--solid lines--and low-level temperatures--color shading at 10 PM Friday).   A weak front will approach our coast, spreading some light precipitation inland.

Complicating the situation, there will be easterly (from the east) winds driven by a strong east-west pressure difference (higher pressure to the east)


The latest UW high-resolution forecast of 24-h total snowfall ending at 4 AM Saturday shows bountiful snow on the southeast side of the Olympics (see below).  

Strong uplift by the easterly flow hitting the Olympics will be a major contributor.  Kitsap will get snow.  And so will central/north Seattle and southern Snohomish County.


There is a lot of uncertainty with this forecast.  I know this because our high-resolution ensemble prediction system (in which we run the model many times, each with minor variations in initialization or physics) is all over the place (see snow prediction for Queen Anne, Seattle, below).   From zero to 7 inches! 


We will have a more confident forecast tomorrow.  

Finally, I can't help but mention the front page story in the Seattle Times today (see below), claiming that climate change is resulting in sea level rise on the northwest Olympic Peninsula.  



This is bogus and wrong.

Although global warming IS causing a slow rise in sea level around the world, sea level is actually dropping or not changing along the Olympic coast.

Why?  Because the Olympic Peninsula, and particularly its western side, is RISING.  Why rising?  

Two reasons.  First, the peninsula was pushed down by the great ice-age glaciers and is still rebounding after the glaciers retreated more than 15,000 years ago.  Second, there is a subduction zone off our coast, which causes the land to rise to the east.

Want some proof?   Here is the sea level at Tatoosh, on the NW corner of the Peninsula from a NOAA website.   Sea level is dropping there. 






Low Indoor Relative Humidity and the Next Snow Event

Is your skin getting dry and cracked?  Developed a dry cough?  Getting a bit of static discharge when you touch that door knob? These are al...