Yesterday’s dust before the storm

5:17 PM. Cu fractus and humilis with edge of the approaching rain band clouds starting to obscure the sun through a dust haze.
5:17 PM. Cu fractus and humilis with edge of the approaching rain band clouds starting to obscure the sun through a dust haze on the horizon.
5:18 PM. Close up of setting sun amid dust. Yellow sun means larger particles likely due to dust. Small aerosol particles, due to smoke, lead to a reddish sun.
5:18 PM. Close up of setting sun amid dust. Yellow sun means larger aerosol particles likely due to dust. Tiny aerosol particles, due to smoke, lead to a reddish sun.  Here there are likely dust and some smoke particles intermingled.  A purely dust haze, absent smoke particles, produces a sun whose color is little altered at low elevations (see below).
May 2012. Example of a sunset only impacted by dust, little or no smoke.
May 2012. Example of a sunset only impacted by dust, little or no smoke.  Dust generally has particles larger than one micron in diameter, much larger than the wavelengths of light from the sun, and so those particles don’t interfere with it much; don’t scatter out the incoming shorter wavelengths as smoke would, and this lack of scattering keeps the sun looking pretty whitish.  Pretty hard these days not to have some very fine smoke particles up there.

The storm: what about it?

Its here, such as it is. Stations upwind of Catalina and in the approaching rain band have been reporting about a quarter to one third of an inch this early morning in light to moderate rain.  Seems that’s the most likely total here now, though our best model, from the U of AZ, has been indicating over half an inch in Catalina, and about a half an inch in Tucson.   The rain may last only a few hours, but given our normal intensities, a quarter of an inch can pile up in a hurry (an hour) in these rain bands.  Moderate rain is falling right now, 5:19 AM!  Yay!  Com’on rain!

Update:  0.15 inches in the first half hour here in Sutherland Heights  Excellent.

BTW, this loop of rain areas every hour from the U of AZ shows that we here in Catalina will have the center of the upper level low pass directly over us!  We’ll be in the spin.  Pretty cool.  You MIGHT even be able to see, in the distance, showers moving in different directions if you watch closely late in the day when it passes by.

The weather way ahead

The latest run of the wrf-gfs model, our best,  and based on global data at 11 PM AST last night, has no precip here after today over the next 15 days, through January 4th.

Reason to be depressed?

Nope. This is where those crazy spaghetti (“Lorenz”) plots come in.  They’re still indicating in their overall “messing around” that troughs here are a strong possibility near the end of December and early January.  The ACTUAL model runs will vary from run to run tremendously in this regard, some showing nuttin’, then maybe the next one, having a big, cold trough near us.  Stay tuned,  “details at 11…”, aka, “later”.

The End.

By Art Rangno

Retiree from a group specializing in airborne measurements of clouds and aerosols at the University of Washington (Cloud and Aerosol Research Group). The projects in which I participated were in many countries; from the Arctic to Brazil, from the Marshall Islands to South Africa.