Thursday, August 09, 2018

Back From Wisconsin

We've been away on trip to Wisconsin since early Saturday am and returned early this morning. We had a late connection through Denver and that was delayed 2 1/2 hours - finally back here at house at 3:00 am MST. Many Southwest flights were seriously delayed yesterday, and there were a lot of grim travelers crowding the C-Concourse at Denver International (DIA). An airline employee told us that golf ball hail at DIA on Tuesday had taken 12 planes out of service, causing the flight chaos that continued yesterday. However, I see no severe report of hail right at DIA on Tuesday - so I'll investigate a bit further.

In Wisconsin our travels took us a number of places - Milwaukee, Waukesha, Madison, Mt. Horeb, Cross Plains, and Mineral Point. Weather was unsettled - showers and thunderstorms Sunday evening and night through mid-morning Monday, light showers and sprinkles Tuesday, and thick morning fog yesterday - very nice change.

Just a quick look at the local situation. There were severe thunderstorms in the Phoenix area yesterday with many reports of severe winds at and east of the airport. The radar above (from NCAR RAP - base scan only in the NCAR products) is for about 7:15 pm last evening. Scottsdale reported gusts to 59 mph, along with 0.54" of rain. Sky Harbor had gusts to 63 mph, blowing dust and low visibility, along with 0.08" of rain. Sounds like a real "mud storm" in parts of Phoenix.

Here at house there was 0.11" in the gauge this morning. After examining ALERT data and radar (below is also from NCAR at about 10:00 pm last night), my guess is that we had thunder and a Trace on Tuesday, and then a repeat last evening with the measurable rainfall.

This morning there is heavy residual cloudiness over southeast Arizona and northern Mexico - as per 7:00 am visible satellite image above. Obviously, BL heating will be a problem today.

The morning sounding from TWC (skew-T below from SPC) is very moist and with almost a thousand J/Kg of potential CAPE. The wind profile is excellent for organized thunderstorms moving into the deserts. However, there has been considerable cooling through multiple residual BLs, and that will also cause problems. Soundings like this have often been associated with severe storms in the metro area, but also as well with no-go donut hole type events. Since a new and relatively shallow BL will be trying to re-build today, significant outflows and storms from east will be needed to trigger storms later today.

My very quick look at 06 UTC WRF forecasts revealed that the NAM version forecasts a donut hole day, while the GFS version forecasts afternoon and evening storms, particularly in northern portions of eastern Pima County. Yet again, another difficult forecast situation.

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