20160927

Initializations

The mid and upper low responsible for all the wind and rain is slowly moving northward and is located somewhere over the far northern Gulf of California-the analysis may be too far to the west. Showers and storms have been active on the east side of the low with ongoing activity from west of Douglas up through Tucson. Already, this has thrown a monkey wrench into the forecasts from yesterday and this morning as heating was required to obtain 500 J/Kg or so of CAPE. The 6Z and 12Z WRFNAM had a bit of activity this morning while the rest of the model runs had little or no clouds or shower activity. Unless it clears up in the next few hours, all the forecasts from the last 24 hours or so are going to have much less activity this afternoon than predicted.

Day 1

Both the 6Z and 12Z WRFNAM dissipate clouds and showers throughout the morning. There is some decrease in activity south of the border so perhaps the sun may break through later this morning in SE Arizona.

The 6Z WRFNAM had some activity over Santa Cruz county, but not nearly enough.

By this afternoon, the 500mb low is forecast to be over the northern GofC. However, satellite imagery shows that the low is about 100 miles east of that position already at 15Z - another potentially significant error.

The wettest air is over SE Arizona this afternoon. However, with limited sun, not much heating occurs and CAPE is minimal.

Shear is about as good as it gets here with both directional and speed shear. The 6Z WRFNAM seems to have the best handle on the CAPE and it has only a few hundred J/Kg this afternoon.

The other extreme is the 12Z WRFNAM which has more heating, moisture, and CAPE. I find this to be less likely, but you never know as it might clear up later this morning.

All the runs continue to forecast deep convection developing over Pinal and Pima counties this afternoon. Areas that receive some heating will see scattered strong to isolated severe storms.  At this point, maybe areas of central Pima and western Pinal? It's really hard to say due to all the uncertainties in the model runs today (clouds, possible mid-level low position)

There is a chance of some activity in and around the Phoenix area as there is sufficient heating and moisture which results in 5-700 J/Kg of CAPE. The late afternoon wind profile isn’t quite as good as it is in SE Arizona but is still good enough to support some organized activity.

The models are split on activity around Phoenix. The WRFNAM is the most active and develops some showers and a few storms during the early evening.

As there is likely to be some big storms to the south of Phoenix, a haboob is also quite likely during the late afternoon. As seen in the above model sounding forecast, the PBL exhibits a decent inverted V profile.

A few storms develop during the early morning hours from Tucson northward.