Tuesday, August 4, 2020

20200804

Previous Forecast
Another mostly quiet day for most of the state.  Astonishing, when you look at the high country, considering this is typically the peak of the monsoon.  Parts of Tucson got lucky as some weak storms moved through during the afternoon hours.
All the model runs were accurate with regards to locations, but they were a bit off on timing as they had most activity occurring during the late afternoon/early evening.

Discussion
On and on it goes.  The 500mb anticyclone is centered over west-central New Mexico, and a weak trough is over Arizona and up through the NW CONUS.  500mb temperatures have warmed to -3 to -6, which is not good at all for storms.
Yesterday, the model runs were looking promising for today, but that is no longer the case.  Drying has occurred for most areas, in spite of an enormous amount of storms over Sonora last night.  A shallow outflow driven surge is underway over southwestern Arizona as Yuma's dewpoint has risen to 70F, but PW has only increased slightly.  (Suominet is operational again)
The Tucson Skew-T has no CAPE and a PW of only 24mm. Dry advection continues in the 850 to 600mb layer due to westerly winds.  The situation is the same for Phoenix.

Initializations
All that deep convection in Sonora has left behind a large area of debris clouds and a weak MCV, near Hermosillo.  All initializations had some sort of cyclonic rotation approximately in the area.  The 6Z GFS had clouds too far north, over southern Arizona.   PW was generally initialized well in Arizona, but a bit too high by the NAM and GFS in Mexico.  Overall, there is nothing serious enough to disqualify any run.

Day 1
850mb moisture, at least in the morning hours, doesn't look too bad, right?  Around 10C can be sufficient for storms.

Well, the layers above 850mb quite dry and dominated by southwest winds.

Now look what happens with the CBL builds into this dry layer.

Almost no activity for today and tonight.

Day 2

A bit of moisture manages to move into far SE Arizona.

It is sufficient for scattered afternoon storms.  Day 2 accuracy has been very poor lately so don't bet the farm on this forecast.

The medium-range looks terrible.  Here's the Tucson area Td forecast.




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