Monday, November 07, 2016

Another East Wind Event Arrives On Election Day

Before I finish off discussions of the proposed NWS restructuring, I need to discuss a significant east wind event that is looming for the next several days.

Significant 500 mb ridging occurs over the northern Rockies, while another closed low develops over northern Sonora from now through the 10th, setting up deep easterly flow over much of the Southwest. I have taken a quick look at the 06 UTC forecasts from the WRF-GFS model runs at Atmo last night.

Shown here are two WRF-GFS forecasts for 10-m winds in kt - above is valid tomorrow, the 8th, at 10 am MST and below is valid at 3:00 am on Thursday, November 10th. The panel above is for the hour that model forecasts strongest winds at the airport; however the windy period continues well into the morning hours of Thursday. The high-resolution grid forecast for TUS indicates a gust of 37 mph (32 kt) at 1:00 pm tomorrow, with gusts over 30 mph from 9 am to 9:00 pm tomorrow and then gusts to 34 mph from noon to 4:00 pm on Wednesday.

At both times shown, the strongest winds are forecast to occur around and downwind of the highest elevations, with relatively light winds atop the Sky Islands. Tomorrow morning the strongest winds are forecast on the west slopes of the Rincons and downwind of Redington Pass, but the grid-point wind-gust forecasts for these areas are several mph weaker than those forecast at the airport.

By early morning on Thursday (below) winds have weakened in lower elevations and only remain strong around and downwind of the mountains. The WRF model forecasts are indicating significant local scale structures in the wind fields during the next several days, which is relevant to the NWS restructuring discussions.

As all of the above occurs, an extended high wind event will likely impact the Mt. Hopkins RAWS station and the Whipple Observatory complex that is on the mountain. I've grabbed three forecast skewTs from the 06 UTC WRF-GFS forecast here - above is valid at 10:00 am MST tomorrow morning. The first below is for 3:00 am Wednesday morning, while that at the bottom is for 3:00 am on Thursday the 10th. The sounding location is upwind of the Santa Ritas, along Highway 83, a couple of miles north of Sonoita.

Based on recent events I've looked at (plus a 10-year climatology of high winds at the RAWS site that I'm putting together), it looks like the observatory complex will experience high wind gusts of 40 mph or great for an extended period, beginning early tomorrow morning and extending into Thursday morning. Strong easterlies extend up to mountain-top (Mt. Wrightson) through much of the period, with the forecast for tomorrow morning being quite impressive. If these forecast skewTs verify, I'd expect that the RAWS site will experience wind gusts early Wednesday that could exceed 60-70 mph. Winds at the Whipple complex begin to impact operations when they exceed 40 mph. Even smaller scale effects occur at the observatory, with winds usually stronger at the lower-elevation RAWS station than those observed up at the large Multiple Mirror Telescope (MMT). The orography of the Santa Ritas seems to result in a very complex, gap-wind situation that impacts the observatory.

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