Saturday, July 23, 2016
Very Suppressed Yesterday But Interesting Possibilities Today
Yesterday was the most suppressed day of the past few and was characterized locally by many orphan anvils with no associated precipitation by the time they were overhead. View above is from 6:00 pm MST last evening. The CG flash density plot below (from weather.graphics and Vaisala) shows the dearth of thunderstorms over most of southern half of Arizona yesterday and last night.
There was essentially zero percent coverage of rainfall at the ALERT sites during past 24-hours, as only 1 of 93 sites measured rainfall of 0.04".
However, the situation appears to be improving today. TS Frank is apparently going to pass close enough to southern end of Baja to push a surge of higher moisture into the Southwest - particularly tomorrow and Monday. The above graphic shows MIMIC PW analysis from Univ. of Wisconsin CIMSS for 6:00 am this morning. High values of PW are already into parts of Arizona, even though Frank is currently just south of 20 degrees north at 110 degrees west.
The morning sounding from NWS TWC on campus (below from NCAR RAP/RAL) has 39 mm of PW - up from yesterday's brief dry down. The steering winds are very good for organized storm events, as they would move storms toward the west-northwest, leaving the anvils trailing behind. Low-level moisture should continue increasing some during the day. If the boundary layer mixes out to a bit above 700 mb, I estimate CAPE at about 1000 J/kg, but with a layer of CIN requiring outflow help to get storms into lower elevations.
The WRF-GFS forecast from 06 UTC last night forecasts a large area of storms into the metro area around 8:00 pm (above). The GFS version did well picking up the nocturnal storms and near-severe outflow on Thursday night, so I'm showing that version here. The timing Thursday was too fast in the model forecast by 3 hours or so. The NAM version also forecasts nocturnal storms, but later than the GFS version and has them dissipate near the Pima/Cochise County line. The GFS versions 10-m wind forecast, below also valid at 8:00 pm, indicates the possibility of a very strong outflow impacting the metro area after dark.
Currently, the NWS forecast for TUS indicates a sunny, hot day followed by a 10% chance of thunderstorms after 5:00 pm through 5:00 am tomorrow. The forecast after that is for a 30% chance of rain at the airport every 12-hour period through the next six days. Seems like folks there couldn't decide which of the coming days will have a better chance of storms, thus the climatological type homogeneous forecast.
Posted by Bob Maddox at 10:12 AM