Dry model prediction WRONG! 0.02 inches falls in Catalina!

It’s great when models falter, and yesterday was one of those times that a human bean can exult.  The U of A model, crunched out on the Beowolf Cluster (I can’t even imagine how powerful such a computer would be with a name like that), said that Catalina would have NO RAIN yesterday, zero, nil, 40-love, zilch, etc. (though there was predicted “model” rain close by).

In fact, in the space of about three minutes, just after 12 noon yesterday, Catalina, right here, received 0.02 inches!!!!  I couldn’t believe how WRONG that model was! It was a tremendous victory for those of us predicting a little rain, like even a trace; those that rebelled against the “king” and won, 2-nil.  If in soccer, it would have been a real drubbing.

Here are the clouds what done it yesterday, small versions of Cumulonimbus clouds that arose from a widespread layer of clouds with shafts of rain that looked like weak versions of our summer thunderstorm shafts:

7:51 AM. A weak shaft of rain falls from a Cumulonimbus sprouting from this overhead layer. The sloping shaft of rain below the cloud indicates both strong wind shear and that the rain drops are pretty modest in size. No cloudburst here.
9:28 AM. Miniature Cumulonimbus cloud with a light rain shower approaches Catalina from the south. Note the lack of dense cauliflower turrets, and wispy, icy tops, no anvils, these obs suggesting weak updrafts. Tops like these yesterday probably only rose to somewhere below 25,000 feet above sea level, and around -20 C (-4 F).  In contrast our summer gully washers usually fall from clouds with tops above 50 KFT.  Still, it was a pretty day overall.  Hope you called in sick to enjoy the first measurable rain in almost a month.


4:45 PM. Our last hope for rain arose late in the day when a line of clouds approached from the SW. While no rain shafts were evident upwind of Catalina, this Cumulonimbus and rainshaft was agonizingly close. Why didn’t the clouds show ice and precip upwind (like the sunsetty ones below)? Too shallow, tops didn’t reach above -10 C (14 F) level, a general requirement for ice to form in our clouds here. Temperatures aloft cooled rapidly to the north late yesterday and will today as well, so tops in that direction will be taller and colder than over us. We will again be left with clouds having tops too warm to form ice/rain.


5:53 PM. Nice sunset, though, even if the clouds had no ice in them (which would have produced virga).


Harangue about those models we love and hate

We desert lifers have a love hate relationship with our mostly superb weather forecasting computers such as at the U of AZ, ones that no longer require us to think when making weather forecasts for the next day or two.  (please see the colloquium by Prof. Cliff Mass in Seattle that pointed out that the NWS was wasting its time putting man-power on forecasts for the next day and beyond;  the computers have largely won that battle.)

Where can we forecasters provide skill?  In the weather right now!  That which occurs in the next few to 12 hours. That’s because, like yesterday, the models don’t know exactly where those showers, ones they might have even predicted, are going to be EXACTLY, and we can fine tune those predictions.  Happens all the time in the chaos of our summer rain season, for example.

But we hate those models like now when they predict dry conditions week after week.  Why can’t a dry forecast day turn up wet, be WRONG?  But they excite us when forecasting rain, even in the fuzzy predictive days one to two weeks ahead.  We know for the most part, such predictions can’t be relied upon, but still we hope they WILL be correct, of course, me in particular (I’m from Seattle and am still adjusting to dry MONTHS).

And here in the desert, most of the rain days predicted in the week to two week range dry up in the models it seems, so there’s always a modicum of disappointment being handed out by them.  We have rain days again today out around the 22nd of Oct, but its not worth mentioning.


LA Nada/ “El Nina” update.

The link up there is for a huge technical presentation based on the Climate Prediction Center’s Oct 9 update.  You might be bored by it, or this blog, but then, maybe you wanted to take a nap anyway.

In sum, it looks less and less like an El Nino will form, the Climate Prediction Center losing confidence in their earlier prediction, darn.  But they haven’t bailed altogether.   El Ninos can often produce wetter winters here, so I’m a little bummed out, as you will be if you’re not sleeping, by this update.