Tuesday, August 17, 2010

NWS Tucson Suffers A Bout of WFZZ Syndrome


The 8 pm radar composite above provides an indication of what a down day it was yesterday in southeastern Arizona. Most significant thunderstorm activity was confined to the northern half of the state. Some heavy storms did try to plow southward into the lower Colorado River Basin, but decent steering flow apparently didn't setup out there. Here in southeastern Arizona, the day was a big down turn from Sunday. Only 3 of the 93 ALERT sites had any additional rainfall through the day and last night, once the early morning showers ended. During the afternoon there were some heavy, terrain-locked storms over the mountains to the east, but only Ft. Huachuca picked up a thunderstorm and 0.02". After dark, the area of showers in southeastern Arizona (see radar chart above) began moving slowly to the northeast, and RAWS sites Carr and Rucker had 0.42" and 0.77" respectively, during the nighttime.
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The NWS here in Tucson had considerably under forecast events on Sunday for Zone 33 (eastern Pima County including all the metro region). Yesterday, however, the 3 pm update indicated 40% POPs for the rest of the afternoon and 70% POPs with heavy rains highlighted for the night. A very large flash flood watch was issued for almost all of southern Arizona. So, this was a classic example of Weather Forecasting Zig Zag Syndrome - which of course is the often observed tendency in our profession to over (under) forecast one day, followed by an under (over) forecast the next day. I've been forecasting for more than four decades, so I've suffered my share of bouts of WFZZ Syndrome over the years.

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