Wednesday, February 25, 2015

A Look At Dual-Polarization Data From Yesterday

I grabbed several graphics yesterday morning and never had a chance to discuss them - so here goes. Above is the abbreviated upper-air data plot for Tucson's morning 12 UTC sounding - note that there is low-level CAPE present that reaches up to a bit above 700 mb. Compare this observation to the forecast sounding (see post below that is titled Another Moisture-Starved...). The WRF-NAM forecast this structure quite well. The sounding indicates that the updrafts of showers would reach above 0 C but that showers building above the -10 C level would be unlikely (charge separation and electrification occurs efficiently within updrafts at temperatures of -10 to -20 C), unless the 700-500 mb layer cooled and moistened substantially (which it did - see 00 UTC sounding below). However, the lower layers dried significantly, so that there was only a sliver of CAPE locally during the mid-afternoon. So, thunderstorms stayed well off to the north and northeast yesterday - a couple of Cbs tried to develop over the Catalinas late, but surface heating was basically gone by then. 

The graphics above and below are from College of DuPage's radar page and are the Tucson NWS Doppler radar data from about 7:30 am MST. The reflectivity at 3.4 degree tilt is at the top, while the echo-tops product just above shows that the showers reached up to only a bit over 10,000 ft above the radar (well below 20,000 ft MSL). So the strong reflectivities (>40 dBZ) were likely due to graupel - which is what the co-incident hydrometeor product below indicated (hard to see but the GR color is there in echo cores). So it was an interesting situation yesterday, but one with the low-levels evolving out-of-sync with the middle-levels, and keeping thunderstorms well off to the north.

Finally, a brief summary of the event. At 6:00 pm MST about 80% of the ALERT stations had recorded 0.04" of precipitation or more and plot above is 12-hour precipitation from MesoWest at that time. So it was a fairly widespread, but light, rain event. The airport did quite well with 0.29" and Park Tank on Redington Pass came in with the highest amount I noticed at 0.39". Here at the house we had only 0.04" - which is now the total for February (we will have to hope that the next system manages to produce some rain here before the month ends). Coolest morning here of February also this morning with a low of 28 F.

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