Upturn Yesterday But Downturn Likely Later Today

There was a considerable increase in thunderstorm activity yesterday, much as indicated by the morning NAM although not as widespread. The early WRF GFS was too suppressed. Strong thunderstorms developed over the mountains by 11 am MST (above image of Catalinas is at 11 am). Lightning strikes for 24-hours ending at 6 am this morning are shown below. CGs were mostly over mountains near and east of Tucson, but eventually some storms occurred at lower elevations west and north of Tucson. Some of these produced heavy rain, but they also spewed out widespread anvil cloud. Here at the house, after a sunrise sprinkle of 0.01", the day was mostly overcast with no storms at all. Across the ALERT network 46 sites (50%) had rainfall during the past 24-hours. Ten stations reported over 1/2" of rain and two in the Catalinas reported over 1".

Today will be a transition toward drier conditions over the weekend. Currently clouds and showers are widespread across southeastern and central Arizona - above is visible image at 6:45 am MST and below is Tucson composite radar a bit after 7 am.

The morning skew-T plot of the the TUS sounding (below) continues to show a very moist and unstable atmosphere. Winds are very light westerly through the sounding. Both the early WRF GFS and the new NAM forecasts indicate little storm activity this afternoon, after the current activity moves to the west and north. This is apparently due to subsidence produced by the consolidation of the western, 500 mb  anticyclone to be nearly overhead by this evening, although there continue to be two weak circulation centers with one located south of Tucson. The sinking air produces slow drying during the afternoon, followed by a more substantial dry out forecast by the models over the weekend, as the anticyclone is pushed southward into northern Mexico by an eastward progression of the trough west of California. I note that the early WRF GFS still forecasts an unstable atmosphere over Tucson at 6 pm this evening with PW of 39 mm and CAPE of >1600 j/kg. So, some caution is needed as well as a careful look at the new WRF forecasts later this morning.