Super Inversion

Normally, temperature decreases with height, and for good reason.  

The sun's rays warm the surface more than the atmosphere above; thus, air temperature tends to decline with elevation.

But infrequently, the opposite occurs when temperatures are cool near the surface, and warm air is found aloft.

Since this is the opposite of the normal situation, we call it an inversion.

Most of the time, low-level inversions are weak, with temperatures increasing by only a few degrees above the surface before falling aloft.

This week was something else. 

  A SUPERINVERSION formed in which temperature increased by approximately 20°F within the lowest few thousand feet.

Unbelievable.

Over SeaTac Airport this morning, temperature was around 48F near the surface and around 70F at 1800 ft.   

22F warmer!  Amazing 

At Forks, along the WA coast, temperature increased from 8 to 22°C in a similar distance (see below), 

What is 25F!!!    Wow.

Looking at the surface weather map, showing the lowest temperature this morning around the I-90 corridor from Issaquah to North Bend, indicates a temperature range from 65 at higher elevation to 40 F at lower elevation, such as near Carnation.

Why such an amazing inversion this morning?   

The skies were generally clear, allowing the surface to cool off by emitting infrared radiation to space.  Nights are getting longer as well, allowing more time for cooling

Furthermore, there is a strong ridge of high pressure overhead (see below),

which not only produces the clear skies, but also produces sinking motion aloft that produces warming aloft.

The inversion weakens greatly during the day tomorrow (Saturday) as solar radiation heats the surface.  And with the ridge of high pressure moving easterly, the sinking air that supports this crazy temperature structure will soon be history

The Meteorological Cliff 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.