Category Archives: Spaghetti plots

The case of the spaghetti plots; an update

In our last episode, it was foreseen that a confidently predicted, “Joe Trough” , was going to bash the West Coast on the last day of this month with a strong storm, little doubt about it.  He had been tracked nicely by the computer.  Looked the same, “buff”, potent, day after day 4-5, ten days away as he crossed the Pacific Ocean.  But after entering the USA at the end of March, “Joe” lost control of himself, it was unpredictable about what he would do next.  At that time, displayed here on this blog, one computer guess was that he was going to break up into pieces, one piece over Arizona for days, sitting around, dawdling really, producing scattered showers in the first week of April thoughout Arizona.  It was an unusual pattern, but there it was on the model outputs.

Sadly, from the spaghetti factory at our NOAA Super Weather Computer weather center, and the wild fluctuations it showed, indicated  “Joe T” might do a lot of different things after he entered the USA.   We could see that this rainy Arizona forecast was just one of many possibilities for “JT”, he was “unreliable” after approaching the West Coast no matter how badly we wanted that forecast that came out to come true;  we just couldn’t count on it.

Now “JT” is only a few days away from crashing into the West Coast, still well predicted.  But how about after he enters the West Coast?  What will happen now?  Will Joe break up into pieces and dawdle over AZ?  Will there be rain? Or will we have just a dust storm and a dry cold front?

Let’s look in on the spaghetti factory and see what happens to Joe on the way in now, only few days from possibly affecting our weather.

From last evening’s spaghetti plots (“ensembles” in weather higher ordered weatherspeak) this 96 h forecast showing “Joe Trough” as it is about to hit the West Coast.  As you can PLAINLY see, the entire earth’s weather north of the equator is well predicted as far out as 96 h, valid the evening of March 30th, 5 PM AST.    In case you’ve forgotten, when all of the lines run almost on top of each other, things are well predicted, little chance of a busted forecast.  The southward bulge in the turquoise and red lines just off the West Coast is our incoming “Joe Trough.”


























The next panel, for later, valid for 5 PM AST, March 31st, shows that “Joe” is now in the Great Basin doing his thing, and the southern part of “Joe” is over us!  Yay!  Or not.

Remember the Red Zone, not in fubball, but in these plots?  The red lines represent pretty much the southern edge of the jet stream at this level, 500 millibars pressure, around 18,000 feet above sea level.  The turquoise lines represent pretty much the northern side of the jet stream at this level.

So, what’s wrong with this pretty picture (2nd panel)?  Joe’s Jet (sounds like a singer I’ve heard of), doesn’t pass south of us by all reasonable expectations.  Those little “perturbations” they put into the model at the beginning of the run to see how they might change the prediction, and thus get a handle on its reliability in case of errors, missing data, chaos in general, have the Red Zone (where the red lines are grouped) north of us.  Jet north of us, as these red lines indicate, means no precip no where ’round here.

Well, unless you count dust as precip, and it certainly will pile up some.

“Joe” is strong and cold, but passes too far to the north.  But as he does, a huge, intense low forms in the Great Basin, drawing dusty southwest winds across southern Arizona before the dry cold front goes through with quite a chill.

Now, for a little humor to end this blurb, a real laugher spaghetti plot, that for 15 days from now.  You’ll go into conniptions, burst out laughing,  like I did I am quite sure with your knowledge of spaghetti plots when you see this one and what  virtually “unforecastable” weather looks like in a spaghetti plot.  They should put these in the newspaper as kind of weather cartoon.

Actually, after 15 days, they mostly look like this.

Ending on humor, The End.





The End is at hand…

…of the superbly pleasant days, that is.  Sure today and tomorrow, and Friday, with the except of afternoon breeziness that last day, will be quite nice.  Probably some Cirrus or Altocumulus clouds at times to make the sky look interesting.  You will still be able to brag to your friends elsewhere during these days about how nice it is in Arizona in the wintertime.

Below, an example of the kinds of clouds that might float by, yesterday’s Altocumulus clouds that appeared at sunset.  I’m sure you saw them, and recorded the event in your weather journal.  After all, it might indicate something and then later, you would be able to tell your friends that you knew that something was coming because you saw that cloud. Now, if you really have good eyes, you will see in this photo, a veil of ice that formed in the little sliver cloud that is farther away and to the left.  You really need to know about ice if you are going to be a good cloud person.

But by Sunday, you may want to go to Buffalo, NY, or Ottawa, Canada, to get warm after the cold front goes by.   It’ll be raining, maybe even snowing at some point.  Ski Catalina!  Its THAT cold in this mammmmmmmoth system approaching Catland that we are probably going to at least see some flakes in the rain Sunday or Monday.  (That my friend, is NOT sleet, dammitall!  Don’t let some silly weather presenter convince you that its “sleet” when rain and snow are mixed together.  Sleet bounces off the pavement; its frozen raindrops, ones that fell into a sub-freezing layer near the ground–takes about 2,000 feet  or more of sub-freezing air for there to be enough time for those drops to freeze, and typically, temperatures below about 28 F.)  Now, where was I?

Right.  Expectations are supremely high for this storm at this keyboard.  May set some storm precip records here in Catalina for the amount in 1-2 days.  I am expecting an inch of precip by Wednesday mid-day, but it COULD be 2 inches (water equivalent), that’s how much potential this storm has.  Almost certainly some of the rain will be accompanied by electrical displays.

Why so much confidence and take the chance that you will look very foolish if you are wrong in these extreme weather pronouncements?

This storm is, and has been, well-progged.   Remember that discussion about “spaghetti” a few days ago?  Now, only a few days away, this mammmmmmmmoth storm is “in the bag”; don’t even think about it missing us, even though its still more than 72 h before rain even begins to fall (likely sometime overnight Saturday).  You’ll have to deal with it.  Get used to it,.  You’ve seen it before:  the dust , the strong winds (at some point, probably more than 50 mph in a brief puff) Saturday or Sunday night and then the cold air and rain/snow.

Here is a sample from one of the best models, from our friends to the north, for Sunday afternoon when the storm is well under way in AZ:

Then,  once here, it moves VERY slowly, so that the duration of rain and snow will be extended.  Hey, we’re due for a break in getting a great, drenching storm. Poor desert spring weeds looking pretty sad these days around Catalina, which makes me sad.  Why can’t it rain more in the desert?

And with a trough of this magnitude (upper left panel of prog map) bringing such cold air down here, ahead of it,  east of the Rockies, extremely warm air will rush northward.  While low temperature records are likely to be set in the West by early next week, high temperature records are likely to be set in the East and probably in eastern Canada as well.

The folks at the NWS, Tucson, will be, and are, very, very excited, stimulated, really, by this situation.  So many advisories to be issued, so little time, when its upon you.  This is what we weatherfolk live for!

May hunker down for a couple of days, daydreaming about how great it will be.

The End.


Coming to Arizona-Catalina on March 18-19th: wind and dust followed by RAIN!

Sounds more like something coming to your local googleplex movie compound…but I am pretty excited today to be able to report a great model prediction that the title alludes to, one that has a higher degree of reliability than we usually see for that far in advance.

Normally one would not fool with a forecast of rain here that far in advance, more than a week, with any rain at all!  How many times have we seen that predicted rain in the models that far and more in advance, evaporate as the predicted rain day gets closer?  Well, I have anyway.  Way too many times.

However, as it has been written, the reliability of a longer range forecast by the models, such as a week or two in advance,  is discernible in something we call “ensemble,” or more colloquially,  “spahgetti” plots.  (Skip to pictures if you don’t want to know about these…gets a little technical.)

Occasionally, there are patterns in the jet stream that have high predictability, and these patterns produce “ensemble” predictions that are pretty much the same for one to two weeks in advance, even though the initial conditions are perturbed-that is, deliberately changed on purpose (haha) to see how much difference there might be in those longer term predictions because of the little changes.

You might think of these “perturbations” as representing bad data, “bad balloon”, lack of data, etc.    These small changes are introduced at the very outset of the model run and the models are run completely over again out to one to two weeks or more, to see how differently they look as the predicted days days accumulate.  At first, a “bad balloon”, bad data point, won’t have much effect, and so model forecasts just a couple of days out usually change very little.

But, if the pattern looks pretty much the same after, say 10 days out AFTER these changes are put in, then such a prediction has high reliability, a strong signal; what will happen has a high confidence level.   When the pattern is changed drastically with these little changes, then there can be little confidence is what is predicted.

Now, why am I going into all this (maybe useless) detail?

The strength of today’s blog title is due to having one of those rare situations where a situation has such a strong “signal” in the data that the forecast of a very strong trough here eight days away, has is showing a LOT of reliability in those “spaghetti” plots (shown below).

Re-inforcing this prediction a bit, too, is that in our Catalina climo data, there was a suggestion of a higher chance of rain in the third week of March than in the second week.   There really could be something in the global circulation that “likes” to put a big trough in Arizona and the West in the third week of March.

Another factor is that troughs are more common in the interior of the West in the springtime than at any other time of the year.  In many locations in the West (e.g., Seattle, San Francisco, Grand Junction), because troughs are cold aloft, March is the coldest month of the year overhead!  So, we would expect these kinds of events, just based on our usual climatology.

OK, back to our Catalina rain prediction:

Finally, below, if you have made it this far,  is what we are REALLY interested in, the areas of rain being predicted for Arizona-Catalina on March 19th (see panel below from IPS Meteostar).

First the rain prediction in panel 1 and the configuration of the jet stream over this same domain in panel 2.  You can see a huge southward plunge of the jet stream along the West Coast toward Baja and then see that it curls to the northeast after passing overhead of Baja.

If you read this blog, you know it ain’t going to rain here in SE AZ without the maximum wind at 500 millibars being south of us, and so, when you see so much rain in all of AZ, as in panel 1, you could have already guessed what this jet stream configuration would look like!  You’re friends will be amazed.  And, voila, there it is, where the jet should be!  Unless you have a telescope handy, you’ll have to click on these to get a resolution that you can see what the HECK I am talking about.


Next, we go into the ethereal world of spaghetti plots, this last panel, from NOAA.  These lines, some representing perturbations in the models, are pretty darn compact over Arizona on March 19th, and that, in turn, means a pretty darn reliable forecast.

Some details on this assertion:  take a look at the red lines, indicating a contour height on a 500 millibar map of 5700 m.  Compare the spread of our red lines to those in the Atlantic, where in that domain, there can be little confidence in what is predicted eight days out.  That 5700 m line is pretty much near the edge of the jet stream here, and the 5520 m contour lines (turqoise lines) well within in it. So, we are nicely sandwiched by those contour lines, meaning there is high reliability that there is a jet here.   Also, the yellow lines and gray lines, indicating the times of different model runs, also converge over Arizona.  I am so happy!

Finally, if you can make out the green “climo” line, you will see that the long term climatology favors this “trough in the West” pattern at this time of year!  Its all good!

What else can be confidently predicted?  Cold in the West, but also likely record warmth in the East with this pattern on the 18th-19th.

It will be interesting to see if Mr. Cloud-maven person really knows what he is talking about in the week ahead.  Of course, nothing can be guaranteed, but it sure looks like a rain is coming, finally!  What’s really certain in this longer range prediction, is the dust and wind part, dammitall.

The End, at last!