All posts by Art Rangno

Seattle comes to Catalina

Yes, if you’re from Seattle or the west side of the Cascade Mountains of the Pacific Northwest, you are going to feel especially at home today.   Its dark, even with the sun up, low ceilings and visibility, steady light rain mixed with snow, temperatures in the mid 30s to low 40s, well, that’s home in January.  And, here is that “home” right here in Catalina, AZ, for us to experience again!  Cloud type? Nimbostratus, often with an underlay of….Stratocumulus and Stratus fractus clouds to kind of provide that ragged, dark and gloomy, splotchy look.

As you may have experienced this morning, an extremely sharp cold front came through with a spectacular drop in temperature and a windshift at  6:30 A. M.   The temperature dropped from the upper 40s down into then upper 30s in only about 20 minutes, which it pretty unusual.  Along with the that temperature drop, the rains came in the “frontal band”, now totaling 0.80 inches here since the first period of rain began late yesterday afternoon (local weather station data here).  (BTW, this station’s wind data are averaged over 10 min, and gusts are 1 min averages.  Multiply gusts by about 1.5 to estimate the velocity of the strongest, few second duration puffs.)

This storm, still in progress,  brings the Catalina rainfall for December up to 1.93 inches.  Normal, based on a 31 year record provided by the folks at Our Garden here in Catalina, is 1.44 inches.  So with this storm, we have exceeded the normal AND crushed the monthly NOAA prediction of well below normal precip this month.  Yay!  Such predictions are partly derived from the effects of the strong La Nina now in progress-note colder than normal water along the Equator in the eastern and central Pacific.  La Ninas normally hedge the climate of the SW toward drought, and so this has been a great December if droughty conditions materialize later in the winter.  The December US-wide precip prediction, FYI:   (I should acknowledge a  bias here: I am overjoyed when droughty forecasts fail but also overjoyed when wet ones verify.)

Colorful announcement of a storm

This glorious sunrise today about 7:30 AM announces in its way that a strong storm is on the way.

Why?

First of all the clouds, “altocumulus lenticularis” are the lower, rippled clouds, combined with a higher,  solid layer of altocumulus and altostratus clouds demonstrates that the air is moist to saturated over a great depth above those lowest clouds.

The lenticulars highlighted by the rising sun just above the Catalina Mountains generally occur when the wind speed at their level is at least 30-40kts.  Thus, lenticular clouds have always been a sign of being around and under strong upper level winds we sometimes call the “jet stream.” While lenticulars might hover over the same spot for minutes to hours, watching how fast the elements in it move, or other cloud movements can tell you something about how strong the jet stream is over you.  Today, the clouds were racing across the peaks, consistent with the very strong jet stream and storm systems that is about to pounce on us.  The NWS balloon sounding from Tucson this morning, a couple of hours before this shot, indicated the winds were 30-35 kts at the level of the Ac len clouds.

The second photo, kind of dull compared to our glorious sunrise, has something to say in it, too. The wind at cloud level is at the photographer and its strong,   What happens in these “pre-frontal” situations is that the air ahead of the cold front can be relatively stable, that is resistant to moving up and down, and in resisting doing that when hills and mountains are present in the path of the air movement, something akin to gigantic ocean swells are produced.  Here you see darker bases off in the distance that are PERPENDICULAR to the wind just like huge ocean swells might be.  A time lapse camera would show the movement of these “swells” beautifully as they peak and die, going through ridges and troughs, that is, slight rises and falls of the air in its movement toward the camera.

At the same time, those clouds, due to the Catalina Mountains and the higher terrain downwind from Catalina, also forces these cloouds to deepen, a process that will continue as the upper low pressure trough approaches.  As this happens, clouds such as these that are not precipitating now, start to precipitate.  The rain often doesn’t move in, but begins to fall from these deepening layer clouds overhead.  I think that is going to happen here in the next couple of hours (its about noon now).

Here in Catalina, AZ, the rainfall (17.5 inches per year) is considerably more than that in and around Tucson (12 inches per year), and this difference largely comes in winter storms like these that are subjected to the lift zone described above out ahead of the higher terrain here in Catalina,  and downwind of us.

Catalina-Smog before the storm

Those of us awaking this morning were literally a-palled by the amount of smoke around.  Not even Twin Peaks was visible, some 10 miles to the SW. See examples of smog in the photos below.

Where did it come from?  Back trajectories, ones that end in Tucson as of this morning at 5 AM shown below, suggest the smog came from the SE of us (red and blue lines.  The green line for air around 12,000 feet, represents where the air came from  that air came from the off the California coast ; it was too high to be involved in our smog episode.  Best guess, could be smog from El Paso and/or from burning in northern Mexico, that in the presence of light winds,  has kind of muddled around and drifted N into Tucson.

Note the pooling of smoke in the low valley ahead in the Golder Ranch area in the first photo.  Probably the result of wood-burning stoves used in the small housing development back there.  What it shows you is the persistent nighttime inversion that forms in that bowl, the flat top of the smoke indicating a temperature inversion. You then see a “clear slot” of little smog and then the overall deeper smog layer above that, also very laminar in appearance.   With the sun’s rise over the mountain, that kind of structure/separation is soon removed as bubbles of warmer surface air float upward and are replaced by downward moving blobs, mixing all the structure you see in the first photo out.   In the last photo, a few tiny cumulus fractus clouds composed of droplets have formed over the Catalina Mountains.  The droplets in those clouds are probably 10 microns in diameter (about 1/10 the size of a human hair).   These droplets are about 100-1000 times bigger than the aerosol particles making up the smog.   This makes the clouds to tell from transparent haze blobs because the smog particles are too small to scatter much light while the cloud particles even in small clouds, prevent you from seeing through them.  Well something like that.

Hang on to your hat tomorrow; windy, thinking momentary gusts here in “Catalina Heights” will hit 30-50 mph by late afternoon and overnight before a very strong cold front rolls through around dawn tomorrow.  This is an unusually strong upper level AND lower level system with a deep low expected to form over southern Nevada during the day tomorrow.   Looks like the rain could change to snow above  3,000 feet after the front goes through, too.  That would be terrific!  The clearing after the front goes by will probably be late in the day with passing light showers possible until early Friday morning.  The ones later in the day and overnight, are likely to be snow flurries above 3,000 feet .  Don’t expect the temperature to do much tomorrow. And, the amounts of precip are likely to be substantial putting us at or above normal for the month.  Yay!   Well, this what it looks like to me; check the NWS for the official forecast!


Welcome

Many of us here in SE Arizona will not be outside today no matter how nice it is because of historic sports emergencies that will require viewing of the TEEVEE at all times.  However, if we do go outside to BBQ some hot dogs or prepare other similar worthwhile foods common to “football day”, there will be LOTs of icy cirrus clouds to view,  such as those in the photos.

However, there is also likely to be the quite odious contamination of these clouds by aircraft contrails as we have seen over the past few days. Aircraft produce long contrails when the air is at or near “ice saturation” and the temperatures at flight level are below about -35 C. Flight levels over Arizona for aircraft traversing the state are typically between 32,000 and 38,000 feet and the temperatures at those levels are almost always low enough for contrails.   Its only the moisture that is usually missing to allow them to happen.  These flight levels may be tuned depending on headwinds.

Often over Catalina, AZ, we only see contrails to the N for the heavily traveled airways above Casa Grande to PHX or to the S of TUS.  Lately there seem to have been an abnormal of contrails.   Not sure why.  The TUS balloon soundings have suggested that it is damp up there from about 25,000 feet to more than 40,000 feet over the past couple of days, the highest levels of that moisture a bit high for wintertime.  Perhaps that extra height explains the abnormal number of contrails.

OK, second post, still testing.  1-2-3, 1-2-3.

Cirrus clouds overhead now

These clouds, the very first ones usually precursors of disturbances, are overhead now with the airways crossing Arizona evident in the “condensation trails” (contrails) showing their positions. FORTUNATELY (the writer despises contrails), there are few overhead of Catalina-Tucson area because there are few airways overhead. Most of our contrails are to the north of us, likely representing cross country flights to Los Angeles. As some may know, contrails are considered a sky contaminant over such national treasures as the Grand Canyon. Also, with air travel predicted to double in the next ten years, more of them are likely to spoil more and more skies. (OK, this is a first shot at writing anything on a web page, so if anyone sees this, please forgive errors in constructing proper sentences.) Expect to upload cloud photos with some discussion of what is being looked at before too much longer.