Waterspout Hits Southern Puget Sound: First Tornado Warning Here in 17 Years

On Saturday around noon, several of you were startled to get a tornado warning on your smartphones.

The cause: a waterspout that developed near Anderson Island in the southern Sound and which remained intact for about a half-hour.   Here are some pics I found on the KOMO and KING-5 web sites.   An extremely well-formed funnel and you can see from the first that the winds reached the surface, kicking up lots of spray.  Beautiful pictures.

Waterspouts are the weaker cousins of the strong tornadoes one finds over the Midwest U.S.

According to the official Storm Prediction Center definition:

 A waterspout is a tornado over water--usually meaning non-supercell tornadoes over water. Waterspouts are common along the southeast U. S. coast--especially off southern Florida and the Keys--and can happen over seas, bays and lakes worldwide. Although waterspouts are always tornadoes by definition; they don't officially count in tornado records unless they hit land. They are smaller and weaker than the most intense Great Plains tornadoes, but still can be quite dangerous. Waterspouts can overturn boats, damage larger ships, do significant damage when hitting land, and kill people. 

This waterspot, and virtually all of our waterspouts/tornadoes around here, are associated with non-supercell thunderstorms.  Supercells are the big Kahunas of the thunderstorm world with very high tops (reaching 40-60K ft), intense rain, hail, and most importantly rotation.

This waterspout came out of a relatively wimply NW thunderstorm.  Let me show you.  We start with the composite reflectivity--a measure of the highest precipitation rate in the storm. Got some red...that is pouring rain, probably with some small hail in the south Sound. Impressive for around here.  But equally strong thunderstorms were hitting in the north Sound with no waterspouts. No sign of any hooked echoes...which indicate  supercell storms.

How high were the thunderstorm tops?....we have a radar-based diagnosis of this.  Only 20,000 ft!   Folks in the Midwest would laugh at such tops.

And since the National Weather Service radar is Dopplerized, it can show the radial winds toward or away from a radar.  Neither this shot from the Camano Island radar nor one from the Langley radar showed any hit of thunderstorm rotation as we would see in a supercell storm.  Rotation would be indicated by a pairing of warm (red,orange) and cool (green, blue) colors.  Nothing there.

Nearly all of the waterspouts and tornadoes in our area are from the non-superstorm type.   That usually involves a fairly strong thunderstorm passing/developing over a region where the wind changes rapidly with horizontal distance.   We call that horizontal wind shear.  Such wind shear is associated with some inherent rotation around a vertical axis that get spun up by the vertical motion of the thunderstorm.   A schematic of this effect is shown below and I have a whole section on this process in my book on Northwest weather (which is a good gift for the upcoming holidays by the way).

Looking at the surface map at noon on Saturday (see below), I wasn't impressed by the amount of shear, but clearly there was enough.  Perhaps we had 15 knots over southern Puget Sound and much weaker wind over land (Kitsap, Anderson Is.).

Most Puget Sound tornadoes seems to develop on the shear associated with a Puget Sound convergence zone or the strong wind shear near terrain.  This one appears to be an exception.

The last time a Tornado Warning was issued for the greater Seattle Metro was on  Dec. 12, 1969, so the younger folks reading this blog will never have experienced such excitement.

Dawg Dash:  Weather Looking Decent!

 One of my favorite events will occur Sunday morning at 9AM:  the UW Dawg Dash fun run.  For more information, check out their site: http://depts.washington.edu/alumni/blogs/dawgdash/  The latest forecast suggest no major storm at that time.  Little or no rain.

Wimpy El Nino

We are now close enough to the winter season to have a fairly clear idea of the El Nino situation ahead.  Remember that El Ninos are associated with warmer than normal water in the tropical Pacific and that such anomalies can influence Northwest weather (less storms, warmer, less snow).

Originally there was a lot of talk (last spring) of the potential for a Super El Nino, with some of the global warming "advocate" sites talking about its effects on the global temperature record (global temperatures can warm substantially with strong El Ninos).

However, the sea surface temperatures in the critical  central Pacific is only modestly warmer than normal and the atmospheric circulation has not reacted in a way to reinforce the warming and push us towards a moderate or stronger El Nino.

Let's start with one of the key measures:  the sea surface temperature in the Nino 3.4 area of the tropical Pacific.  The official definition of El Nino is an anomaly  there greater than .5C.  We are not there now and in fact the SST has declined recently.

A number of groups run statistical and full-physics models to simulate El Nino.  They suggest we will have an El Nino, but a weak one.  However, verifying these models for the forecasts started earlier in the year, suggest they have been pushing warming in an unrealistic way.

The National Weather Service Climate Forecast System (CFS) model is now going for an entirely marginal event, barely reaching the .5C criterion

And the official probabilities for El Nino are now only about 65%.

So we should not expect much more than a marginal El Nino during the upcoming fall and early winter months.  And amplitude matters.   Weak El Ninos have lesser impacts.

The correlation of our weather with El Nino is not perfect to start with.  And for weak El Nino years the relationship weakens further.

Let me illustrate this for you.

Here are the precipitation patterns across the U.S. for some STRONG El Nino years.  The most consistent implication is  the wetter southeast U.S.   There is a tendency for southern/central California to be wetter.  The Northwest is less consistent.

But for weak El Nino years, the precipitation patterns are all over the place.  I would not place bets on anything.  This is the story of our upcoming winter unless El Nino revs up unexpectedly.

So based on the correlation with El Nino, we have very little guidance for the upcoming winter. Sorry.

The latest NWS Climate Forecast System forecasts for December-January-February is for warmer than average over much of the U.S.  No hint of the feared "polar vortex."

What about precipitation?  Very little signal over the Northwest.  But wow...California is much wetter than normal.  This would really help the drought.  Fingers crossed.

And this week should be a shock to some.  Showers today.  Generally dry on Sunday and Monday day.  But they the celestial spigots will turn on.

Hopefully, the rain will be over by next Saturday.  Why?   Because one of my favorite events will occur Sunday morning at 9AM:  the UW Dawg Dash fun run.  For more information, check out their site: http://depts.washington.edu/alumni/blogs/dawgdash/