Late morning cold slam

Its not a breakfast at a restaurant chain, but a sharp cold front passage later this morning, say between 10 AM and Noon.   Should be pretty interesting.  Temperature will drop about 10 F in an hour.   Expecting/hoping, too, for a little measurable rain with this “FROPA” (frontal passage in weatherspeak).  The brisk winds, as they always do,  have activated a lot of the nighttime wind detector lights in the neighborhood.

The usual post-frontal clearing in the afternoon and a pretty cool day, maybe 20 F cooler than yesterday afternoon which got to 88 F here in the Heights, the Sutherland ones, that is.  Of course, our media weather stars are all over this weather situation, so nothing much to be added here.

Still have plenty of higher ice clouds overhead right now at daybreak, but look for an invasion of Cumulus and Stratocumulus within the  couple of hours after daybreak.  They should appear first on the Lemmon, topping it, then fill in after that as the cold slam gets closer.

Yesterday’s clouds

The full complement of expected clouds was not really observed yesterday.  Missing in action for the most part locally were Altocumulus lenticulars downind of Ms. Lemmon.   Cirrocumulus clouds were also pretty much a no show.  You can see some of those high lenticular formations that did occur WAY downwind of Ms. Lemmon and the Catalinas if you view the U of AZ Weather Department time lapse movie for yesterday between 11 AM and 1 PM, then another pile of Ac len just at sunset (7:15 PM) in their movie.

Below, what we did see, various varieties of Cirrus, and eventually those thickening to Altostratus ice clouds.  And a hole was out there that allowed a brief colorized sunset rather than a gray one.

9:20 AM. Main feature is Cirrus spissatus, with Cirrus fibratus (lines at upper right) and some uncinus (center left) also present.
1:13 PM. Looking at incoming Cirrus to the WSW… More Cirrus spissatus (patches) in the distance with some hooked Cirrus (uncinus) upper center.
1:14 PM. Looking N at the traces of Altocumulus lenticularis clouds (e.g., sliver cloud above road in distance), possible Cirrocumulus top center of photo.
6:21 PM. By this time, the leaden look of Altostratus pretty much dominated the sky; dosen’t look good for sunset color at this point.
7:03 PM. Sunset bloom began as bottom of Altostratus got lit up.  Note how similar the cloud bottoms are in this photo compared to the one just above.
7:06 PM. Heavy line of Altostratus with a higher overcast of CIrrostratus adds interest to the fading sunset.


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.