A Very Strong Cold Front Will Cross the Northwest on Tuesday

The Northwest is known for its weak cold fronts, since the relatively warm Pacific Ocean warms, near-surface, cold Arctic air before it arrives in our region.

But sometimes conditions allow us to get a relatively strong cold front, with a sharp temperature decline and profound wind shift...and this will happen tomorrow afternoon and evening.

A strong cold front that will bring substantial snow to the mountains and further ease any drought worries.

Let me show you the latest forecasts!

The predicted sea-level pressure (brown lines), near-surface temperatures (colors), and winds (arrows) at 5 PM Tuesday are shown below.   A strong front (indicated by the red dashed lines) has reached the Washington coast.

A profound wind shift (from southwesterly to northwesterly) is associated with the front, with cold air (blue) behind.  Mama Mia!  This is a spicy front.

The front is even stronger aloft, as shown by the predicted temperatures at 850 hPa (about 5000 ft) the next day (the front is crossing eastern Oregon at this time).  Dark blue is cold air. Cold enough for snow in all the mountains!

A simulated radar image for Tuesday evening shows an intense line of precipitation with the front (look for the thin yellow line that crosses the coast near Hoquim and extends to near Bellingham).  Pro-tip:  You will not want to be outside when this line is over you.

The line will be associated not only with heavy precipitation, but also with a dramatic wind shift and temperature decline.

To illustrate, here are the predicted temperatures at Hoquiam, on the Washington Coast, for the next few days.   Frontal passage drops the temperature from 49F to 39°F- a substantial decline on the coast.  On the western slopes of the Cascades, the temperature drop will be roughly TWICE that amount.

All this means snow in the mountains.   Below is the predicted snowfall through Thursday at 5 PM.  A foot or more in some locations!  A huge benefit this time of the year.

This surge of cold air originated over the Arctic and pushed southward into Alaska and then across the Gulf of Alaska.   Interestingly, the Gulf of Alaska is substantially cooler than normal (see below, blue indicates cooler than normal), which allows the chilly air to reach us with less ocean warming.

Finally, here in Seattle, the strong front will bring blustery winds tomorrow afternoon (see plot from Seattle windwatch below at 11 AM).  With the new leaves on the trees, there could be some scattered power outages near the coast and Puget Sound.  

Enjoy the weather show tomorrow!