A Meteorological Cliff is Ahead

We are about to descend a meteorological cliff, with little hope of return.

A transition to far cooler and wetter conditions, with no chance of reversal.

Even worse... this transition is perfectly normal for this time of the year.

Want proof?   Below are the latest temperature forecasts for several locations around our region.

In Seattle, temperatures will rise into the low 70s on Thursday and Friday before crashing down into the upper 50s next week.   And staying there.

On the coast at Hoquiaum?  Same thing.

At Snoqualmie Pass in the Cascades?    The big cooling takes them down into the 40s.

I find the October western transition in the Northwest fascinating-- and scary rapid.

Consider the climatological temperatures at Seattle (SeaTac) over the year (see below).  Red indicates the record highs, and brown shows the average temperature range (highs and lows).

Record temperatures reach into the 90s during the first half of the month, but after October 18 such warm temperatures simply don't occur.

This amazing transition around mid-October is made clearer by an expansion of the above figure for October.

Why such a rapid decline in temperatures in October?

Solar radiation reaching the surface declines rapidly during the month, and increasing weather system activity moves into the region as the jet stream strengthens and moves southward (see average color radiation below).

So enjoy the warmth of the next two days.  This may well be the last 70F+ highs you experience for many months.

First Frost of the Season is Revealing

Most of the region saw its first frost today.  

And it offers a lot to learn from.

Let's begin by looking at the surface low temperatures observed across the region (see below).  

Keep in mind that "surface" air temperatures reported at airports and other locations are NOT at ground level, but taken at 2 meters (about 6 feet) above the surface.

On cold nights, the temperature at the surface is usually colder than at 2 meters, often by 2-5 degrees F.  

Wow.  Substantial temperature range... from around 50F to below freezing!  

Warm near the water (around 50F near the coast), relatively warm near the Sound and the Strait (mid to upper 40s), but below freezing in the western interior (e.g., near Olympia Airport).    

30s in eastern Washington

Minimum temperatures were cooler at the surface than aloft (the opposite of the normal daytime situation), as shown by the temperature profiler at SeaTac Airport (see below at 8 AM).  

The warmest temperatures were at around 1600 ft.

The situation changes during the day, as the surface is warmed by the sun, as illustrated by the Seattle temperature profile at noon (see below).

As noted in previous blogs, the cold overnight temperatures are associated with longer nights and a lack of clouds aloft, which result in very effective cooling at the surface by the emission of infrared radiation from the surface (see below).

The visible satellite image from this morning shows the situation, with clear skies over much of the region and filaments of fog in a few valleys.

Now the problem.

 

In my "day job", I work to improve the skill of atmospheric forecast models.

A potent tool in doing so is comparing model simulations against observations. At Seattle-Tacoma Airport, the model simulation (colored lines) did a good job in matching reality (orange dots).

But at Olympia Airport, where temperatures got colder, the simulations were not as good, with models being too warm for the morning lows (but quite good for the daytime highs).

More work is needed, which is good. 😀