20170703

Previous Forecast

A very active afternoon and evening along the border and down into Sonora.  Strong/severe storms formed over the high terrain of far south central Arizona and moved southwest.  The Q2 QPE OU/NOAA product is no longer publically available thus I'm using the lightning data to estimate model performance.

The 12Z runs performed well as they developed storms over Arizona and then much stronger deep convection over Sonora later.  WRFNAM

Initializations

Moisture continues to increase over the state due to a combination of a Gulf Surge and thunderstorm outflow surges.  Surface dewpoints are in the mid 60's at Yuma and IPW values are around 30-35mm over much of the southern 1/2 of the state.  Unfortunately, a fair number of IPW sites are missing as well as any upper air data from NW Mexico.   Satellite imagery indicates an MCV and associated debris clouds are located near Hermosillo and is moving slowly west.  The clouds are remaining in Mexico.   The morning 500mb plot has the high center just west of Tucson with temperatures around -8C which is fairly cool.

Both the 12Z GFS and NAM initialize a weak vortex located in central Sonora and the GFS has cloud initialized well (for once).  The NAM has some clouds, but not enough.  Arizona is clear so no problem there with cloud initializations.   Most GPSMET IPW stations have minimal errors.  However, no sites except for Puerto Penasco reported in NW Sonora.  Overall, Both the WRFNAM and GFS initialized well and model confidence is high.

Day 1

Moisture continues to advect into much of southern Arizona due to the ongoing surge and IPW increases slightly during the day.

850mb dewpoint temperatures are above 10C over all the lower deserts so there is enough moisture to support deep convection.  However, as is typically the case with the first 24 hours of s surge, cooler air in the lower troposphere and warmer air above, stabilizes the atmosphere.

Both Tucson and Phoenix have significant CAPE by afternoon, but an inversion is present on top of the cool layer preventing deep convection.

1000 to nearly 2000 J/Kg are forecast for this afternoon.

Eventually, deep convection does initiate over the higher terrain of SE Arizona and the White Mountains.  Yesterday, the WRF was a few hours slow and that may be the case again so formation might be a little earlier.

Activity continues into the evening to the SE of Tucson.

The potential is there for Tucson, but the mixed layer remains shallow and will need some mesoscale lift to realize convection.  Outflows, while locally strong, are not strong enough once they reach Tucson as the PBL heights don't support very strong winds.  Storms also aren't moving that much due to the light and variable winds between 400 - 600mb.  A wasted opportunity!

Day 2

The surge weakens tomorrow, but enough moisture remains to support deep convection if there is enough heating and lift.

The low levels recover somewhat and by afternoon, Tucson becomes quite deeply mixed along with some CAPE.  Mid-level steering winds continue to be poor thus it's likely to see deep convection over the mountains, but not move into the lower elevations.

The WRFNAM and WRFGFS diverge as the WRFNAM is active in central Pima County while the WRFGFS has activity only in Cochise County.

By early evening, a few storms are possible close to the Tucson valley.  Not much activity expected, but perhaps some cooling from thunderstorm outflows.  I'll take anything at this point!