20200728

Previous Forecast

Thunderstorms were restricted to the higher terrain of the eastern 1/2 of the state, with some areas of heavy rain.  Tucson had storms all around and only brief showers managed to form when the outflows moved through.  The early morning activity mentioned yesterday did not materialize.   Later WRF runs backed off on this possibility.

The WRFNAM was the best run as it had the most activity.  I guess a broken clock can be right every now and then.  I did find a problem with the GPSIPW correction routine where it wasn't always being applied, so forecasts going forward should be a bit more accurate.

Discussion

More of the same.  Light and variable mid-level flow and warm air at 500mb, -4 to -6C around the southwest.  Northern Mexico is worse due to the warm core tropical cyclone remnants.  

Tucson has one of it's better-looking soundings in a little while as there is some 10 knot easterly steering flow, 500 J/kg of MLCAPE, and only one weak inversion at 400mb.  Just based on this, I'd say a bit more activity today/tonight.  Monsoon's "swan song"?  I always wondered where this saying came from. From Wikipedia: "The phrase refers to an ancient belief that swans sing a beautiful song just before their death, having been silent (or alternatively, not so musical) during most of their lifetime."

Initializations

It's a straightforward situation as no inverted troughs were seen and the few clouds that were present are dissipating.  As has been typical, the NAM is too wet over eastern Arizona and all of NM.  As the PW correction routine is working better now, errors will be reduced.  

Day 1

It is still moderately moist over the eastern 1/2 of Arizona as dew-points are in the low 60's and PW is in the mid 30mm range.  By mid-day, a higher band of moisture is present mostly north-south over central Arizona.  Very dry air is to the west, and drier air is moving in from the east out of southern NM.    There is weak low-level convergence in the vicinity of this band and might help with the development of storms.  

There appears to be sufficient CAPE over the east central mountains to support storms.  With the weak steering, they might be able to move off into lower elevations of Pima and Pinal Counties where some areas of moderate CAPE are forecast to be present.

Well, it's better than nothing.  

A few storms might drift into the lower elevations.

Day 2

Dry air advection is in place over all of Arizona and NM as the 500mb ridge builds over the state.  It is shocking to see that the long-range WRFGFS forecasts no activity at all for the next 7 days.  There are occasional intrusions of moisture into far southern Arizona, but not enough to support any activity.  Needless to say, this is the last discussion until significant activity returns.

7-day forecast.  Unbelievable, right at the climatological peak of the monsoon.