No Heatwaves for the Rest of the Month!

 Today may well be the warmest day for the rest of the month.  

Mid-May warmth is quite typical around here.  But so is a cool down at the end of May.

And yes, precipitation will return.

Let's start with the latest European Center 10-day forecast for Seattle (below). 73F high today, but then temperatures slide into the 60s and then 50s.  My tomatoes will not be happy.

The NOAA/NWS National Blend of Models (NBM), which combines many forecast models and is usually quite accurate, also keeps things cool, with highs in the lower 60s.

You will need your sweater again.

And what about precipitation?

Let's look at the latest forecasts of the European Center Model.  The forecast precipitation accumulation through Friday morning shows a regional dampening, with the North Cascades getting a good wetting.

But it does not end there.  By the following Saturday morning (May 25th), there will be relatively heavy accumulated rain in all the regional mountains.  Good for river levels and fish.

The UW model has a similar solution.

This cool/wet period will be very positive for regional crops.   By the way, it appears that the Northwest cherry crop is in very good shape (I like cherries).

So why are we cooling down?  Because the warmth-inducing, high-pressure ridge over our coast will rapidly weaken, replaced by a trough of lower pressure.

Consider the average over the next five days for the upper level (500 hPa, about 18,000 ft) heights (like pressure) shown below.   Blue indicated below normal heights (called roughing).

Troughing (low pressure) is dominant over the region, with ridging (high pressure) offshore.  It's not a warm pattern for the Northwest.

Next five days?   Even cooler, with the troughing pushing westward over the Northwest coast.  Expect cooler and wetter than normal conditions.

You won't need any AC this month.

_______________________________________

Massive Vandalism Around the UW

I will talk about it in more detail in my next blog, but there has been massive (and very expensive) vandalism around the UW, including spray painting both historic and new buildings (see below).

This is what happens when a college administration allows lawbreaking and vandalism to spread. 

Antisemitism, physical violence, property destruction, and illegal camping are endemic around the UW.  The UW administration should have closed down the illegal encampment weeks ago.  When lawbreaking is tolerated with no consequences, it simply increases.

A sad period for all Huskies.  We are going the way of Columbia and UCLA and it could have been avoided.

Why isn't aurora prediction as good as weather prediction?

 On Friday afternoon, the NOAA Space Weather Center forecasted a great aurora for the Northwest and it happened.  A tremendous event to watch.  At the same time, the Center predicted a substantial event for Saturday night, but it never happened.

Aurora forecasts a day or two ahead often fail, while weather predictions are generally nearly perfect a few days into the future.

Why the difference between weather and auroral prediction?  

To understand the auroral forecast problem, you must understand why auroras occur.

Auroras generally start with a disturbance on the surface of the sun, such as a solar flare or a coronal mass ejection (CME)---see below.  Note that the corona is the outermost layer of the sun.

Courtesy of NASA

These disturbances eject vast quantities of charged particles that move at vast speeds (such as a million miles per hour!) away from the sun.  Such ejections of charged particles can also alter the magnetic field around the sun.  I should note that even without disturbances on the sun this is a background amount of particles leaving the sun, known as the solar wind.

The sun has a magnetic field around it, and so does the Earth (see below, from Zappys).  Note how the magnetic field lines (light blue) approach and leave the polar regions.   

Now the key part.  As particles from the sun (the solar wind) approach the earth, they interact with the earth's magnetic field, so that solar particles can enter the earth's atmosphere near the poles...or actually a ring around the poles centered on the earth's magnetic poles (see below).

These solar particles can interact with various atoms/molecules in the atmosphere (like oxygen and nitrogen), causing them to glow (just like a neon light tube).    This is what causes the auroral colors.

During a solar storm, increased numbers of particles leave the sun, which can reach the Earth a day or two later.  This revs up the aurora. It also disturbs the earth's magnetic field.

The aurora prediction problem

Astronomers have little skill in predicting disturbances on the sun's surface.  Yes, we know that solar flares, sunspots, and CMEs are more frequent during the height of the 11-year sunspot cycle, but skill in predicting individual events--the ones that revved up the aurora on Friday-- is minimal at best.

But it is worse than that.  The speed and direction of the particle ejection vary by event and it is very difficult to observe such parameters from Earth.

Like predicting where a ball will go, not knowing its exact speed and direction.

But there is some useful information at very short time ranges.   NASA and others have spacecraft between the Earth and the sun at what is known as the L1 point, about a million miles towards the sun  (see below).

Such spacecraft can sense solar particles approaching the Earth and provide reliable observations of changes 30 minutes to an hour before they reach the Earth, providing highly accurate auroral prediction.   On Saturday afternoon, an L1 satellite gave the warming before the approaching solar particles and the incipient aurora.  When I saw that data, I called my friends for an aurora party.

Right now, the NOAA Space Weather Center has noted another CME on the sun's surface and predicts the potential for a minor aurora tomorrow night (see below).   So I will be watching the L1 satellite data, just in case the forecasts are wrong again.

cc