Thursday, June 09, 2016

Look At WRF Forecasts For Today - June 9th

More things to consider today than I have time for this morning. Above graphic shows detected CG flashes for 12-hours ending at midnight last night (from Atmo and Vaisala). Most thunderstorm activity in Mexico was along and west of the Continental Divide, and the storms just south of Cochise County produced a weak outflow at Douglas. There were some thunderstorms in eastern Arizona.

This morning there is cool air at 500 mb over our region and PW values over an inch at TWC at 12 UTC. There is CAPE present this morning at low elevations, but the boundary layer (BL) has to mix out to above 600 mb and some lift is still required for BL air to reach its level of free convection. 

The main question for this afternoon and evening is whether thunderstorms will occur only over the higher elevations of Cochise and Santa Cruz Counties or will there will be some activity in eastern Pima County. The 06 UTC WRF forecasts at Atmo have fairly different outcomes.

The WRF-NAM forecast of composite radar echoes above is valid at 7:00 pm MST this evening and indicates very strong storms over parts of Cochise County but little further west. The forecast sounding from the NAM version shown below is valid at 5:00 pm for TWC. It is well-mixed to a bit above 700 mb, but would require lift to 500 mb for convection in low-levels. However, nearby mountain storms would seem possible. The steering winds are quite nice and from the east-northeast, so storms on the Catalinas and Galiuro Mountains would try to head our way. The BL mixing ratio is at about 7.5 g/kg which is high unless there is advection of more moist air into eastern Pima County.

The GFS version of the model forecasts much less activity in Cochise County and more activity in pasrt of Santa Cruz and Pima county - composite radar echoes forecast above is valid at 5:00 pm this afternoon. The PW forecast below indicates higher moisture from Sonora and also a moist outflow moving northward into the metro area - certainly more interesting forecast for Tucson than that of the NAM version. The forecast TWC sounding at bottom, however, shows that the GFS version has produced a BL mixing ratio of almost 10 g/kg - which appears very unlikely. So, watch for where the towers develop later today. I do feel that there will be more activity on the Pima County Sky Islands than either model forecasted from the 06 UTC runs. Thunderstorm bases will be very high due to depth of BL, and thus strong outflow winds and blowing dust are the main threat from today's storms.

Both versions of the model forecast a more active day for Pima County tomorrow - but when storms and outflows begin roaming around, it is often prudent to go day-by-day because of mesoscale impacts influencing the next day's forecast.

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