Friday, August 26, 2016


Previous Day(s)/Daze
Will has been handling the discussions and forecasts the past few days as I had a hard disk crash in my head.  The restore process is going along and I’ve recovered most of my medium and long term memories, but there are still holes.  When I’m reminded of what I have forgotten, I usually remember.  Saturday to Monday is mostly blank.

Most precipitation was restricted to northern Arizona yesterday.  However, some late night/early morning showers and weak storms developed around both the Tucson and Phoenix areas.

Both the WRFNAM (below) and WRFGFS were pretty good and both had the late night activity.  As has been the case this summer, the WRFGFS was a little too widespread with precipitation coverage.

Thick clouds and embedded showers were present from near Yuma to east central Arizona.  The 12Z RR and NAM had the right idea, but not quite enough clouds.  

I was quite surprised once I started looking at the upper air maps again to see a large trough over the western US.  I think it was Bob who said the pattern looks like late September rather than late August.  Multiple short waves are dropping into the mean trough with one over UT/CO and another over the Pacific NW.  One interesting feature is a 700mb low located just west of San Diego and this may play an interesting role in the weather later today.  There is also an upper inverted trough located just south of Cabo San Lucas which is probably not a factor now that westerlies dominate, but my mind is still back in early August mode. The RR and NAM have these features initialized well.

This 700mb low seems to have played a part in increasing the IPW over Arizona the past 12 hours.  IPW is now in the mid 30mm range across southern Arizona. Most of Suominet is back and the IPW initialization errors are minimal.

Overall, initializations are OK with the main issue being not quite enough clouds.  However, the model runs’ heating rates haven’t been impacted that much.  Model confidence is medium.

Day 1
Upper-level winds continue to be strong with the 12Z 300mb map showing areas of upper divergence over the SW US.  The WRFNAM shows a few areas of upper divergence along with diffluence in the flow across Arizona which is likely to help enhance convection today.  It’s likely this feature is what is responsible for the AM activity across central Arizona.

The 850-700mb trough continues to pull up moisture from Mexico as 850mb dewpoints increase and become quite high, around 12C.

CAPE is forecast to be moderate over much of the state with high values over SE Arizona.  As this area is mostly sunny now, it’s likely to be the most active area today.

Impressive looking profile at Tucson as decent CAPE is present by early afternoon along with a fair amount of directional shear which should result in some organized convection.

The WRFNAM develops scattered deep convection over SE Arizona and around the Flagstaff areas by early afternoon.   As these areas are mainly clear, this looks likely to occur.  SE Arizona storms could be quite strong and produce very heavy rain with a risk of isolated damaging wet microburst winds.

Storms move fairly quickly to the NE and by late in the day, activity is winding down.

It’s hard to say if Phoenix will see another round of storms later this afternoon or evening as the model runs disagree on the amount of CAPE that will be present.  Even in the best case, it’s limited.  Like Tucson, the wind profile is fairly good.  My guess is limited or no activity as that area is not getting much heating.

It appears that NW Arizona will see activity overnight as sufficient moisture interacts with a shortwave dropping down into the mean trough position over Arizona.  Where was this pattern when we needed it back last winter/spring???

I started writing this before the WRFGFS was available because I knew I would need longer than usual and I wanted to get an early start. The WRFGFS is now running and is quite a bit less active than either the WRFRR or WRFNAM because it is a bit drier. Taking a quick look at the 14Z GPSIPW obs vs forecast, the WRFGFS looks slightly too dry. Reality might be between the WRFNAM and WRFGFS.

Day 2
An interesting pattern as a strong shortwave continues to move SE into Arizona.  Also, the upper IT is still present just south of Baja California Sur.

Dry air wraps around the 850-500mb low leaving only the eastern ⅓ of the state wet.

Moderate CAPE is present in this band of wet air and those are the only areas likely to see much activity.  

Little or no CAPE over Tucson or Phoenix thus no activity expected there.

The upper jet is position over northern Arizona and with the moderate amount of CAPE, it’s likely to be a very active day.  There are areas of strong upper divergence over that area which will result in some organized convection.

Storms restricted to far SE Arizona and over northern Arizona.

Wednesday, August 24, 2016



Relatively simple situation with clear skies over almost all of Arizona. The IPW errors are no larger than 2 mm, but unfortunately many of the SuomiNet sites didn’t make it into the data assimilation routine. We'll check on that later. Overall, confidence is high today.

12Z WRF GFS IPW initialization

Day 1

The Arizona is now on the back side of the trough and under northwesterly flow.

Storms form on the rim in the mid afternoon.

While northwesterly steering flow is generally not favorable for organized convection in the lower deserts, the storms are still somewhat able to “move” off the rim on outflow boundaries. Prime time in the deserts is between 4 and 6 PM today. Dust storms are likely in Pinal county.

The PBL is well mixed in Phoenix, 500 mb temperatures are a cool -11 C, and the vertical profile exhibits good directional shear. 12Z WRFNAM followed by 12Z WRFGFS.

Below, the 12Z WRF GFS shows a handful of isolated storms in the lower deserts around 6 PM.


It looks like it will be a little too dry in the lower levels and a little too warm in the mid levels for Tucson to see much activity.

Day 2

Isolated storms possible in southeastern AZ, mostly over higher terrain, with a few stronger storms in northern AZ.

Friday, August 19, 2016


Previous Day
As anticipated, the various runs of the RR were not very good. The WRFNAM struggled a bit too as it did not have activity far enough to the west. The WRFGFS was the best as it had the timing and locations down. There have been questions regarding the accuracy of the Q3 QPE product that I've been using for subjective verification. Bob Maddox suggested using Maricopa county's website to get QPE so here it is.

The upper trough continues over the SW US with multiple weak shortwaves rotating through. Why couldn't this split flow pattern have been like this in Febuary instead of now!?

One short wave or maybe a MCV is moving into east central Arizona. The various initializations have this feature more or less in the right location. Some clouds are over northern Arizona and associated with the MCV while much of the rest of the state is clear.  The NAM or GFS didn't have enough clouds over northern Arizona thus deep convection may form too early in the model runs.

IPW initializations look fine. However, I happened to take a look at the 850mb RR Td field and it was way too dry around the Tucson area. Overall, the initializations are OK. The WRFGFS and NAM should perform well today.

Day 1
As was being forecast yesterday, a moderate gulf surge gets underway this afternoon bringing in somewhat wetter air into SW Arizona.

A classic low-level surge flow pattern over southern Arizona at 850mb as the surge is quite strong.  However, moisture is lacking somewhat except for SW Arizona.

A weak mid-level trough is located over northern Arizona with a continued light flow and temperatures a cool -9 to -10 C.

Upper flow continues to be split with the jet moving off into the central US and only weak areas of divergence over central and northern Arizona.

Moderate to high CAPE across SW Arizona and as far east as Santa Cruz county.  This area is the most likely spot for strong deep convection today and this evening.

Deep convection develops this afternoon over higher elevations along the border in the WRFNAM.

The WRFGFS is more active late this afternoon as it has widespread storms west of Phoenix during the afternoon.  I believe this is unlikely as this area had a fair amount of activity yesterday and the model runs are too warm in this area.

CAPE continues to be limited at Tucson thus activity is also limited there. Along with that, the wind profile is more or less unidirectional and out of the west, which is not favorable for storms.

It looks like Phoenix has a better chance as somewhat more CAPE is present this evening. Winds are unfavorable as they are unidirectional with very little speed shear in the midlevels.

Is today the day that Yuma gets it's entire monsoon rainfall in 3 hours? Perhaps. All three of the runs have big storms at various locations around SW Arizona this evening. The locations and areal coverage differ across the models. The WRFGFS is most active and earlier with storms. It looks unlikely that storms will be this widespread and early, but if a big surge of moisture comes in as it forecasts, perhaps.

The WRFNAM has less activity over SW Arizona and later in the evening. Maybe reality is somewhere between the two?

The WRFRR slams the Yuma area.

Day 2
It looks like the WRFGFS has a better intensity forecast for TS Kay which is SSW of southern Baja today and moves WNW to a position SW of Baja tomorrow. It appears that it will be close enough to trigger a new surge/continue the old one. The wettest air remains far to the south, though.

Boundary layer moisture increases somewhat and the 850mb dewpoints increase to a decent 10-13C over much of southern Arizona.

A typical day 1 surge vertical profile at both Tucson and Phoenix with a cooler/wetter and somewhat shallow PBL. CAPE increases, but so does CIN. Mid level winds are very poor thus it looks like a day where big storms are possible over high terrain but don't propagate. The low elevations remain mostly quiet due to the lack of a trigger.

There are a few very weak shortwaves here and there, but I doubt they will able to provide any significant lift needed for deep convection around Tucson and Phoenix.

CAPE increases significantly over much of northern and western Arizona.

The high elevations of northern and eastern Arizona have widespread strong storms during the afternoon.

By early evening, some storms work their way south towards Phoenix while deep convection develops in the very high CAPE areas of SW Arizona.

By early evening, the PBL does become deeply mixed at Phoenix.  CAPE is also moderate.  If the convection to the north does eject halfway decent outflows, deep convection is certainly a possiblity.

Both the WRFGFS and WRFNAM are forecasting quite strong outflows into Phoenix from the north thus it looks possible for development.

Both runs do develop storms near the Phoenix area so there is some confidence in this forecast.