20190810

Previous Forecast
Another quiet day.  Both of the WRFRR runs were the best and were able to predict the isolated activity over western Arizona.  Just south of the border, it was very active due to the approach of the IT.

Initializations
The 500mb plot clearly shows the strong IT over Sonora.  As was predicted, strong southerly winds are present on the east side.  The 500mb ridge had been displaced far to the east with the center over Oklahoma due to a strong (for this time of year) closed lower near northern California.  The IT is clearly visible in satellite imagery with the center near the Hermosillo area.  A weak MCV is moving north over southwestern NM.  The IT  is initialized quite strong by the NAM with 40-knot winds on the east side, which may be too strong.  The RR is a bit weaker thus looks more accurate.  The GFS is also a bit weaker.  All three have a weak cyclonic circulation in SW NM.  It's kind of amazing such small scale features can get initialized correctly.

Cloud cover is quite thick from Sonora and into SW NM, but it's mainly clear west of there, including the Tucson area.  All three have initialized the clouds fairly accurately, which is another pleasant surprise.   The RR appears to not have thick enough clouds over far SE Arizona though.

PW initializations were only OK.  The NAM, of course, had some significant errors.  The RR also had a few areas with errors as high as 6-10mm.  Other than these errors, generally all three initializations look pretty good for such a complicated situation and model confidence is reasonably high.

Day 1
There were three different types of forecasts yesterday.  The first was ongoing morning showers and storms with widespread clouds, which resulted in a limited amount of afternoon activity.  That one is out as many areas in southeastern Arizona are clear.  The second was only limited clouds and huge CAPE, which resulted in a lot of heating and severe deep convection.  The third, and what seems to be on tap, is a moderate amount of morning clouds and moderate CAPE.  This appears to be the one as Tucson morning PW is around 40mm (instead of 47mm like the severe forecast) and observed CAPE of only about 500 J/kg. The strong and moist Gulf Surge predicted yesterday is delayed and not as moist.  Since  the12Z sounding, PW has increased to 42mm and has been increasing over the past 6 hours, so moisture advection is occuring.

 There is strong flow up the Gulf of California as Yuma is reporting a 74-degree dewpoint and winds 18G23, but it's shallow.   The surge shows up nicely on the surface plot with high dewpoints reported almost all the way to Tucson.  There sure are a lot of DOD weather stations out on the Goldwater Range now.

 By early afternoon strong flow continues into southwestern Arizona.  High PW is advecting into far south-central Arizona.

Very high CAPE is forecast for southwest and south-central Arizona.  Tucson is just on the edge.

Tucson is primed and ready to go as the PBL is mixed nearly to the LFC (~700mb).  Low-level shear is present, but steering winds are a bit funky with mainly northerly to northeasterly as the IT approaches.

It should become more northeasterly as the IT slowly approaches.

The WRFRR develops strong storms over the higher terrain of southeastern Arizona during the afternoon and with favorable steering flow, these move into the lower elevations of eastern Pima county.

Generally, outflow winds aren't very strong, but isolated severe winds from wet microburst are likely.  Very heavy rain is another bit threat.

Some storms could produce over 2.5" of rain.

Well, all that seemed pretty straightforward.  Too bad the WRFGFS is MUCH different.  It initially develops storm more to the east and then moves an MCS looking thing into the lower elevations of Pinal and eastern Pima this evening.

The 15Z WRFRR predicts something more like it's 12Z run with moving strong storms through the Tucson area during the afternoon hours.

Both WRFRR runs move storms across Pinal county and towards Phoenix by early evening.

What about Phoenix?  It appears that the highest CAPE airmass doesn't make it that far north as by late afternoon PW is only 36mm, and CAPE is around 600-1200 J/kg.  This may or may not be enough to support storms.  It probably will depend on outflow boundary intersections (luck).

A strong thunderstorm outflow boundary does roll through Pinal County, so it looks like a big dust storm is likely.

It's going to be close!  Some storms impact the far eastern and southern valley during the evening hours.

The IT moves over the eastern part of the state during the late evening hours.  This results in continued support for deep convection from around Tucson up to Phoenix during the early morning hours.

Day 2
Little or no activity for most of the state tomorrow.