Thursday, September 06, 2018

Activity Continues To decrease

View of Catalinas at 6:00 pm MST last evening is interesting because of the thick anvil over the metro area that came from storms off to the southwest. There was no precipitation across the ALERT network during the past 24-hours, except for 0.04" at Tumacacori (the most southern site in network).

The plot below of detected CG flashes for 24-hours ending at 1:00 am (from Atmo and Vaisala) is quite interesting as it relates to yesterday's 06 UTC WRF forecasts. There were a few mountain flashes over the Catalinas and Rincons, but eastern Pima County was essentially suppressed. The WRF-GFS had forecast storms to remain mostly south and east of here, and that generally played out well. However, the NAM version had forecast an unusual propagation of heavy storms from higher terrain northwestward across the metro area - that of course did not occur. BUT, storms from just west of Nogales did propagate northwestward across central Pima County (reaching about to Gila Bend and producing the heavy anvil that moved overhead here). The unusual propagation forecast by the NAM version did occur, but was shifted southwestward from the forecast. Thus, aspects of both forecasts did verify.

The next few days look to be very quiet, since we'll be under the domination of the Pacific lobe of the subtropical anticyclone - sinking and drying. Perhaps some Cbs over mountains today. The above forecast is from 06 UTC WRF-GFS (on the 5.4 km grid) and is of PW at 11:00 am MST on the 9th (Sunday). Model forecasts local drying, but with southwest parts of state holding on to about an inch of PW. However, very moist air continues nearby over southern portions of the GoC. The forecast below (from same run but on 1.8 km grid) is for total precipitation through 11:00  am on 9th.

The big weather interest over the weekend will be focused on Hurricane Florence in the Atlantic - how strong will this storm be and will it impact the east Coast? Some model forecasts make it a significant event for US, while others keep it well offshore. Current NHC forecast track for Florence is at bottom.


  1. Wow, I didn't see what the 6Z was doing yesterday and I took a look at the PW initialization and it was over 12mm too wet over SE Arizona. No wonder! I'm also scratching my head a little about why all the other runs missed out on the central Pima storms. I did see that the 18Z HRRR eventually came around and had some activity out there but that forecast isn't of much use only an hour or two in advance.

  2. FYI, the huge bias continues with the 6Z run from this morning too with a 13mm error at Hermosillo. Did I tell you that I talked to someone at NCEP about this? He admitted a problem as they no longer assimilate GPSPW into the NAM as there was a period where PW values were bad. The problem was fixed but now the NAM is "locked" and they are unable to turn the assimilation back on. Crazy.