The Godzilla Ridge Returns

It is big, hard to get rid of, and persistent.  Scary for those who love fresh snow. 

Yes, it is the Godzilla Ridge.  One so powerful that is may be hanging around for 1-2 weeks.  Strong enough to give us sun in normally cloudy December.

A ridge is the term given to a high pressure area, and is usually applied when talking about upper level charts.  Here are a series of 500 hPa (about 18,000 ft) upper level forecast charts from NOAA/NWS. 

Monday at 4 PM...big ridge off our coast.  Godzilla is here.  And ridges bring descending air and warmer temperatures aloft.

 Wednesday at 4 PM.....EVEN STRONGER and closer to the coast.  A major trough on the East Coast, bringing colder weather there.

 Friday at 4 PM...a small shift eastward and slightly weaker.  Big cooling in the eastern U.S.

Sunday, December 13th...the ridge strengthens.  Unbelievable

The latest weather.com forecast for Seattle, shows lots of sun this week and the probability of precipitation stays at 10% or less through Tuesday Dec 12th.

An interesting aspect of all this is that temperatures will warm substantially aloft, while cold air  (and high pressure) moves into eastern Washington.  As a result, a very strong pressure difference will develop near the Cascades crest (see map at 1 PM Wednesday, with lines of constant pressure--solid lines--and temperatures---colors), with localized strong easterly winds.

The wind gust prediction at this time (below), shows some gusty winds along the Cascade crest, with stronger winds north of Mt. Rainier downstream of the Stampede Gap.   Strong easterly winds over the eastern Strait of Juan de Fuca.

With high pressure aloft and associated sinking air, the air above us will warm and dry.  Take a look at the sounding of temperature (red) and dew point (blue) for 4 AM on Thursday.   Temps and dew point are really separated, which means very dry air.  And the freezing level is above 10,000 ft (700 hPa is roughly that height).  Note the inversion (temp warming with height) near the surface.  Air quality will decline.

The Upcoming December "Drought" in the Northwest

A stunning transition is going to happen on Sunday.  

Precipitation over the Northwest will end. 

And we might not see another drop for over a week.  Maybe more.  An unusual occurrence in December.  You will see sun....but as we will note there is a threat:  low clouds and fog.

Let's take a look at the forecast upper level (500 hPa)  maps this week from the NOAA GFS model...and be prepared to have your jaw drop!

At 10 AM Sunday, a trough has moved passed us and a ridge of high pressure has started to build in the eastern Pacific.  The rain will be ending at this time.

One day later, the eastern Pacific ridge has amplified.   We are totally dry.

The ridging increases by Wednesday.... the ridge is HUGE and extends up to Alaska.

 Saturday at 10 AM.  The ridge is still there, but a bit weaker.    Plenty strong enough to keep us dry.

 It revs up even more on Sunday!

 And it is STILL THERE on Tuesday 12/12.

 And it continues after that for several more days.

Folks...we are talking about a total shut down of precipitation over us for 1-1.5 weeks.  In December.

OK, I know what you are saying.  What do the ensemble systems using many runs show?  Here is the anomaly (difference from normal) of 500 hPa heights for the mean of the NOAA GFS ensemble system for 4 PM Thursday.  Much higher heights than normal (high pressure) over the NE Pacific and our area.  BIG positive (high pressure) anomaly.

The forecast a week later IS THE SAME THING, just a little weaker.  Wow.

Next lets look at the precipitation forecasts from the vaunted European Center ensemble.  There are 51 different forecasts in this ensemble system.

No precipitation for virtually all of them for Dec 5-9th, and then nearly nothing through December 12th.  After that, a few members have some light rain--very light rain. And yes, some rain this weekend.

So we should be confidence in the forecast: after the rain stops Sunday morning it will be absent for a week, and maybe more.

There  will be sun ... plenty of it.  But after a few days of high pressure there is a good chance that low clouds and fog may form, at least in the mornings.  

Why?   Because clear skies from the high pressure will allow the earth to radiate into space, resulting in low-level cooling.  That cooling can bring the air near the surface down to saturation, producing fog/low-clouds.  The weak winds associated with the high pressure won't mix it out.  And the sun is so weak now, it will have a hard time burning off the low clouds.   We will see.

And a major tip:  if the low clouds form you can easily escape them and enjoy sun by going up...to an elevated park (e.g., Cougar Mt) or into the Cascades/Olympics.  Leaves will be nice and dry...making raking easy and fun.