The models forecast a significant increase in thunderstorm activity for southeastern Arizona this afternoon - that is the Atmo WRF-GFS early and the current NWS NAM. The NWS GFS ensembles are dry for southeastern Arizona (more on this later). The 500 mb anticyclone is still nearby, and the morning Tucson sounding is not impressive. However, the anticyclone is forecast to shift to northwestern Arizona by evening, with storm steering level winds becoming northeasterly during the afternoon at 15 to 25 kts. WRF-GFS forecast of composite radar echoes at 5 pm MST is shown above - the storms in southeastern Arizona have propagated into eastern Pima County from the White Mountains in the model forecast. Keep in mind that storm development has typically been occurring 2-3 hours later in the real world these last few days. The WRF-GFS forecast of 10-m winds for 5 pm is shown below. A significant outflow has moved through the Tucson area by this time in the model forecast. IF the storms develop as predicted by the WRF-GFS and the NAM, THEN they will produce some severe wind gusts because of the very hot and deep boundary layer ahead of the storms.
The WRF-GFS forecast of total rainfall through midnight is shown below, with most all of eastern Pima County forecast to receive some rain today. Quite a change compared to yesterday, at least in the model world. Finally, the NWS GFS ensembles are probably dry this afternoon because in that particular model the terrain slopes smoothly and continuously down from the White Mountains, without any of the complex terrain features between here and there represented within the model.
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