Sky on fire; chance of rain still ahead for southern Arizona (but not much)

Chance of early Feb rain still ahead, and I can prove it.   This panel below is from last night’s 5 PM AST global data ingest into the WRF-GFS model, our best, as rendered here by IPS MeteoStar.  As you can see, there are quite a few acres of rain showing up in southern Arizona on the 5th at 11 AM AST.  I’ve added an arrow to help you find it.

Ann Feb 5th 18 2013020100_CON_GFS_SFC_SLP_THK_PRECIP_WINDS_114What’s gone wrong with the possibilities of a good rain?

A low center is positioning itself off Baja as we speak, in almost exactly the same spot as the one that gave us our drenching rains of a couple of weeks ago. But, like a raggedy-looking hitchhiker that no one picks up, there’s no interaction with this developing low center down there by a trough zipping by in the westerlies to the north of it, one that dips down to the south just that bit and scoots our promising low and all its water to Arizona.  Before that happens, that low wanders around and dies a quiet death down there.

When low centers are as far south as this one that is developing off Baja and over the warm waters out there,  it’s cool center gradually warms up due to all the Cumulonimbus clouds it spawns, that warm air shooting up into its center and around it,  and the circulation around it dies; it gradually just goes away.   This is because there is no longer any temperature contrast between the center and regions outside of it, that which drives the circulation: no temperature contrast, no circulation.

Valid at 11 AM AST, February 3rd. This is looking very good indeed at this point.
Valid at 11 AM AST, February 3rd. This is looking very good, indeed, at this point.

You can see  what happens to that low center in the panel above when no trough ejects it right away toward Arizona and it has to survive on its own in the next forecast map below.

Valid for 11 AST, Tuesday, February 5th. I thought I was going to cry when I saw what happened to our promising low and storm.
Valid for 11 AST, Tuesday, February 5th. I thought I was going to cry when I saw what happened to our promising low and storm.  That remnant passing south of Arizona means dense middle and high clouds with a lot of virga, sprinkles, and that’s what the models are seeing in that small area of rain in the first panel.  Could be some great sunsets, like yesterday.

Yesterday’s cloud sequence, a classic one we see over and over again

First the thin Cirrus or Cirrostratus. Then, as though a real storm was coming, the sky lowers and thickens up in Altotratus. It non-desert locations, this sequence to Altostratus leads to rain about 70% of the time, that number from ancient cloud observation studies conducted before satellites and models. Finally, the back of the “storm”, well, at 25,000 feet you would’ve have thought is was a “storm” with all the snow that fell on you. Here is the start, middle and end, the latter of our fabulous sunset:

SONY DSC
8:03 AM. Cirrostratus fibratus overspreads sky.
1:39 PM. Too thick, too much shading to be defined as Cirrus; its now Altostratus. CIrrus typically, from cloud radar studies, thickens downward to become Altostratus.
1:39 PM. Too thick, too much shading to be defined as Cirrus; its now Altostratus. CIrrus typically, from vertically-pointed cloud radar studies, thickens downward to become Altostratus, with cloud tops staying at the same height.

 

6:01 PM. The backside, the last of the Altostratus clouds, allows the sun to illuminate their undersides, and the light snow that falls from these clouds, only to evaporate here in Arizona.
6:01 PM. The backside, the last of the Altostratus clouds, allows the sun to illuminate their undersides, and the light snow that falls from these clouds, only to evaporate here in Arizona.

A look back at our end of January rainstorm

Radar-derived total precipitation for the week ending January 31st, 2013. The Tucson radar was down several times and so our local heavy rains are not shown. But look at what the mountains got SE of Flagstaff! So great in this droughtful winter.
Radar-derived total precipitation from WSI Intellicast for the week ending January 31st, 2013. The Tucson radar was down several times and so our local heavy rains are not shown. But look at what the mountains got SE of Flagstaff, 4-8 inches! So great in this droughtful winter.

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.