Arizona WRF Discussion: 20160628

Previous Day
Most activity was restricted to SE Arizona and areas north of Phoenix. A few weak storms managed to sneak into the east valley of Phoenix.

Model forecasts were pretty good in general and the weak outflow through Phoenix did verify. They weren't quite strong enough with the activity north of Phoenix during the afternoon.

Initializations
For the first time in many days, Arizona is mostly clear and the model initializations have no problems with clouds. IPW was initialized well by all three of the 12Z model initializations. Note that there are now no operational GPSMET IPW stations in the Phoenix area or in SE Arizona. I haven't talked much about the Rapid Refresh this year as I am back to using the operational version's initial conditions, which at times, are quite poor. Last year, I had access to the developmental version which is no longer the case this year. Operational RR is supposed to be upgraded to the new version 'any day now'. Very warm air is in the mid levels as seen at El Paso where it is -3C. Also, the west Texas trough has sheared out and can no longer be identified. Some of it may of sheared out to the SW across northern Mexico. There is an inverted trough over the central Gulf of California in the initializations of all three 12Z models and an accurate initialization of this feature is critical for Arizona over the next few days. The problem is the lack of a sounding at Guaymas which would be very helpful in this situation. Satellite imagery does show some cyclonic circulation in that area along with an area of early morning storms so it does look like the feature is real. Overall, initializations all look good with no favorite and model confidence is high.

Day 1
Impressive early season moisture continues across much of the state extending all the way north to Las Vegas. Easterly low level flow has become established across eastern Arizona with dry air over NE Arizona while SE Arizona remains wet. By mid-day, the edge of the easterly flow is north-south of a line from Flagstaff to Tucson and will act as a focus for afternoon convection.

Warm air is present across southeastern Arizona and along with low level easterly flow, will restrict convection there. Central and western Arizona are a bit cooler thus less hostile and along with moderate SE flow, storms that do form will be steered off of the higher terrain.

As usual, the WRFGFS has somewhat higher CAPE forecast for the afternoon. Both runs have sufficient CAPE to support deep convection from SE Arizona up towards Flagstaff thus areas west of the windshift line should be quite active this afternoon.

By early afternoon, storms have developed from Nogales northward with some very strong/severe storms in the Flagstaff area. The WRFGFS and WRFNAM are similar except the WRFGFS storms develop an hour or two later. By late afternoon storms are winding down.

The WRFGFS diverges from the WRFNAM and WRFRR as the later two redevelop storms over eastern Arizona during the evening while the WRFGFS waits until later. The question is if these storms continue and move into the lower elevations around Tucson and Phoenix later as was forecast by yesterday's runs.

Looking at the forecast Skew-T plot for Phoenix tonight, it certainly looks like the atmosphere will support big storms if they can propagate into the valley. CAPE and moisture are high, much like the previous forecasts.

Tucson is also primed for late night activity as CAPE sufficient to support deep convection.

All of the 12 runs move/develop storms between Tucson and Phoenix during the late night and early morning. There is quite a bit of uncertainty with timing, location, and intensity with the WRFRR have very strong storms in and around Tucson while the WRFGFS has storms around Phoenix after midnight and the WRFNAM has storms mostly in Pinal county. In general, intensity has backed off compared to previous runs. Still, some storms could be very strong producing isolated damaging winds, lightning, and heavy rain.

WRFRR

WRFNAM

WRFGFS

Day 2
There is the potential for a widespread strong/severe weather outbreak for many parts of the lower elevations during the late afternoon and evening. Very wet air is present by early afternoon with most desert locations in the mid to upper 40mm range! The low level easterly flow continues with the backdoor dryline/windshift front located again from about Flagstaff to Nogales.

WRFNAM

CAPE is forecast to be in the 1500 J/Kg range across much of Arizona which will support strong/severe storms.

There is disagreement between the WRFGFS and WRFNAM where the NW Mexico IT is located. The WRFNAM moves it into far southern Arizona producing somewhat more favorable mid level winds while the WRFGFS keeps it stationary over the central GofC with weaker winds over the state.

WRFNAM

WRFGFS

One issue is going to be how much overnight activity and morning clouds reduce heating. If it's quite active, the atmosphere may not recover sufficiently to support widespread severe storms and we'll have to wait and see about that until the morning. Both model runs develop strong storms by mid-afternoon over the higher terrain of southern Arizona and around Flagstaff. The WRFNAM has storms farther east (in and around Tucson by late afternoon) as it did not move the backdoor front as far west as the WRFGFS. What a complicated situation!

WRFNAM

A classic Phoenix outflow intersection/convergence situation is forecast for Phoenix as late afternoon thunderstorms to the south and north send strong outflows into the Phoenix area during the late afternoon and early evening. CAPE is forecast to be in the 1100-1500 range which will result in strong/severe storms.