Big Drops

I would not quibble with anyone who says that this year's monsoon in Tucson got off to an early start on Tuesday (two days ago). Although most of yesterday (Wednesday) fit my picture of a pre-monsoon westerly trough, there were times on Tuesday when things were moving from the southeast. Then this morning a little after 4 AM I awoke to big drops falling on the skylight in the bathroom. The windows were still shut and the air conditioner was running, so it would have been hard for the thunder to wake me. But those big drops sounded like someone pounding on a saucepan with a spoon. (There were a bunch of damp, long-dead bees in my rain gage. It must have been not more than a few hundredths.)

I once remarked to John Marwitz that big drops were the most fascinating things to me about monsoon thunderstorms. John pooh-poohed the notion: A thunderstorm is a thunderstorm. He's right of course. Still I can't help thinking that there's something special about the distribution of big drops in storms west of 105W longitude.

When I first heard about dual-polarization radar about 25 years ago, I would be thinking about those big drops. The electrical engineer, V. Bringi, would fill the blackboard with a fog of phasors. But I would be picturing the old analog scopes on the finicky magnetron-based radar at Davis-Monthan, imagining those scopes magically transformed to show differential reflectivity. I wasn't aware until reading about it on Bob Maddox's blog that the National Weather Service radar in Phoenix (the radar is actually at the old Williams AFB) recently had an upgrade to dual-polarization. Since then I've been trying to figure out if there's a way to access the data. (My house is about 75 miles southeast of their radar; and I'll probably be disappointed with digital vs. old-time analog right next door. Still I think there will be interesting things to see.) In the meantime, I'll be excited to read about the first impressions in Phoenix. Here's an example from last night's Phoenix forecast discussion (FXUS65 KPSR 30035):

ALSO INTERESTING WAS OUR FIRST BETA TEST OF THE PHOENIX DUAL
POLARIZATION RADAR WITH THE NEARBY STORMS. OUR OBSERVATIONS
WERE...NOT A LOT OF PRECIP WAS DETECTED IN THE CLOUD CORES...
MEANING PRECIPITATION WAS IN THE FORM OF LARGE UNIFORM DROPS IN LOW
CONCENTRATIONS. OR VERY LITTLE MIXED PHASED PRECIPITATION
CONCENTRATIONS. SINCE VERY LITTLE PRECIP WAS DETECTED...THERE WAS
NOT A WHOLE LOT OF EVAPORATIVE COOLING ...AND THUS ACCOUNTED FOR
THE LACK OF STRONG DOWNBURST WINDS WE USUALLY GET WITH LARGE
TEMP/DEWPOINT SPREADS...WHICH AT THE TIME WAS 111 DEG OVER 50 F.