Category: The weather ahead

Not much to report really.  Things aren’t going quite as I expectulated yesterday afternoon in a burst of excitement about a good rain here beginning as early as October 3rd, so maybe I won’t say anything further about that, kind of pretend like I never said anything like that.  I do still think it will rain in October, however; not giving up on anything quite yet.

Next, I will distract you, get your mind off that, by showing a NOAA “ensemble” (spaghetti) plot based on last evening’s global data and let you figure it out.  That should do it; this is lot better than Sudoku.  This one below is valid for 5 PM AST, Friday, October 5th.  You might think about what teams are very likely going to be playing in really cold air for early October based on this map, baseball or football.

Hint:  where the blue lines bunch up some and extrude toward the Equator is where colder than normal air will be.  The more they are bunched together, the more reliable is the forecast.  Where they are scattered around, like in the SW, the more dicey the forecast.

Maybe some summer rain season stats tomorrow.

The End.

I got pretty worked up yesterday about the best weather maps I have ever seen for Arizona, ones produced by our best numerical forecast model, the WRF-GFS, one that had so much rain here at the end of the month, based on billions and billions of calculations.  The rain in that model was due to a former hurricane (one that has not yet formed, but like me, is still merely a depressed area–in the eastern Pacific).  It subsequently develops in the model into a strong tropical storm and its remains were forecast to track right into Catalina and SE Arizona and produce as much as 1.5 to 2 inches of rain in 12 h.  I loved that forecast map so much!  Thinking about having it framed.

And, rain in various amounts, was forecast here for a couple of model runs, not just one, before going away lately.

This is what weatherfolk deal with all the time, these model vagaries in the longer forecast range of 7-15 days. In the two maps below, one from yesterday’s blog, and the one to the right of that, the model run rain map from last night’s run for the SAME time and day, the afternoon of Friday, September 28th:

Well, that “solution” is gone now (see map at right), the one having no rain at all in AZ for the same time as the flood shown in the map at left.  That remnant of a tropical storm off Baja shown on the right, just sits, spins lethargically, and dies, its moisture staying to the south of AZ now.  I guess Wildcat fans will be happy that the football game on the 29th here won’t be played in the mud with some leftover rain falling.

This rain disappearance was not surprising,  I guess, when “we” looked at the NOAA spaghetti plots and saw that the confidence level had to be low because of all the vagaries produced by “perturbing” the model with a little bad data at the outset of its run.

If I was a weather presenter, my 15th day would be stacked with the different forecasts produced by the model for that same day as it got closer in real time.  This would be the purpose of demonstrating to my TEEVEE watchers that the forecasts for the SAME day, such as September 28th, are changing drastically: “Sunny!” “Rainy, 2 inches!” “Partly cloudy!” “Rainy, a quarter of an inch!  “Sunny!”  “I don’t have a clue!”–the correct answer for display.

Don’t give up all hope for rain here, though, in the coming two weeks.

First, the unpredictablility of our current situation means that the models could calculate a rainy “solution” for us at the end of the month yet.  Second, another hurricane/topical storm comes marching up the coast of Baja at the end of the first week in October, heading in the direction of AZ.  So, all the rain potential here in our Arizona fall is not lost yet.

——————

BTW, the uncertainty here was NOT the case for the weather back East in the spaghetti plots, where a cold regime has been solidly predicted there with considerable confidence in the 7-15 day range (forecast contours lines were pretty bunched up in that region AFTER the errors were introduced).  Low temperature records are already falling in a few locations, and more will fall over the next two weeks.

Clouds?

The scattered showers foretold for late Sunday and Monday have evaporated from the model runs now, and so have been looking around for a computer model run SOMEWHERE that had rain foretold for us.  Once again, I could find a rain prediction for us near the end of a 15 day model prediction period.  If we got all the rain the models predict for us in the 10-15 day period, year after year as they seemingly do, we’d all be growing bananas and coffee.

Below is a model prediction that was, in a sense, painful to see, and then de-construct, in a manner of speaking.  A tropical storm/hurricane forms in the model, one that hasn’t even formed in real life yet (that’s how great our models are)!  Eventually it races up the Baja California coast then turns toward Tucson, even strengthening that bit as it moves over the Sea of Cortez/Gulf of California.  The map below is valid for 5 PM AST, Sept. 29th.

But the planets of the upper level steering flow are not aligned correctly; that storm takes a sudden right turn into Hermosillo and never makes it to AZ.  Dud number one last night’s in the model run, except maybe they need some rain around Hermosillo so its not a dud for them.  You can see this sequence here.

————-

Then, right after this missed tropical storm,  a trough from the lower latitudes, rich with moisture, comes barreling across the Southwest with major rains indicated in AZ two days later, in early October.  Great!

Except that this situation must be de-constructed by checking out the NOAA spaghetti factory outputs to see if the indication of a trough here in early October is a likely dud as well.  I really hate checking, though, when the model run shows something I want to have happen.

The first map below shows the postiion of an upper level trough at 500 millibars as it was projected for October 2nd at 5 PM AST.   Looks great over AZ doesn’t?  Below this map is the map of the rain in the 12 hour period prior to the same time as the upper air map,  denoted by the green area (of course).  Bring it on, baby!

Now, let’s check….as we must do as scientists and junior cloud mavens.  We can’t just take things at face value that far in advance,  as you already know.

Below that rain map is the “spaghetti” plot resulting from some bad starting data which is deliberately input into the model as it begins its calculations.  The model is run again and again with different bad data points at the outset several times over.  These bad data points produce slightly different forecasts over time, forecasts of jet streams and such that get more different as time marches on in the model run.  Often though,  a weather system is so strong, so powerful, that these slight errors that are put into the model make little difference, even 10-15 days out.  Other times, slight errors make huge differences.

Instead of,  “garbage in, garbage out”, we get some incredibly important information about our model runs doing this, though it seems counterintuitive.   Where the many lines from each model run are in chaos, that is, all over the place, forget whatever was predicted for that region; its very uncertain, “garbagy.”

But if those lines cluster your area, you’re real forecast, the single run produced by the model from, say, as in this case, from last night’s data for October 2nd, is much more likely to happen.

With these thoughts in mind, I then looked at the NOAA NWS spaghetti plots that tell us whether the ACTUAL model run showing a nice trough right over AZ is an outlier (read, is a “phony”).  When I looked at the spaghetti plot, the wild display of blue contour lines in the eastern Pacfic and western US told me that last night’s run, with that great trough was a “phony”, an outlier model run, and that outlier run is indicated by the yellow line.  You can see how that yellow line, dipping into AZ, is NOT accompanied by a bunch of blue lines also dipping to the south in this direction.  Instead, they’re all over the eastern Pac and West Coast.  So, no strong signal for a good rain on October 2nd, dang.

After this great explanation (hah!) you, too, will instantly see that the two maps produced from last night’s model run and shown here are not very likely to be observed, but then’s there’s probably going to be a college football game on TEEVEE somewhere anyway, so who care’s?!  :}

What can you do with this information?  Let’s say you’re watching TEEVEE again, and your favorite weather presenter comes on with his long range forecast and has rain for October 2nd.  You can then turn to your TEEVEE viewing mates and inform them, with great confidence, “That’s not gonna happen!”  They’ll be quite amazed that YOU could critique an honest-to-goodness, highly paid weather presenter, one that has fun everyday predicting weather and gets a huge salary for having that fun while I have fun but get nothing.  Your friends might ask how you know that rain won’t happen.  You answer, “I checked the spaghetti plots.  It ain’t gonna happen.  Let’s watch some fubball.”

Of course, that rain prediction could STILL happen, but the chances are very small.

The sad end.

¹though the blue lines are not exactly the same contour height level)