20190731

Previous Forecast
It was a widespread light to moderate precipitation event for Arizona yesterday with some isolated areas receiving substantial rain.  About the only place that didn't see much rain was Tucson. It was suppressed much of the day due to the proximity of the MCV and later, anvils and cooling outflows.  Just now (16Z), it's finally raining here on campus.

The 12Z runs didn't have enough precipitation, especially around the Phoenix area.  The 15Z WRFRR turned out to be OK but didn't have quite enough activity over southwestern Arizona and too much for parts of SE Arizona, including Tucson.  It was a difficult day due to the uncertainty due to the MCV and the lack of its initialization.

Initializations
Model confidence isn't going to be any better today, that is for sure.  Morning clouds and scattered showers and storms are over most of the state except for the far eastern portions forced by some sort of cyclonic circulation.  I think it is an MCV, but I don't think it's the same one from yesterday.

The IT is over western Arizona and down towards the northern Gulf of California, which is resulting in moderate mid-level southerly to southeasterly winds over the state.

The NAM and RR have initialized the MCV well, but the GFS has it too far north in Yavapai County.  None of the 12Z initializations has the clouds and showers initialized correctly.  The RR is least bad, but it's missing all of the Tucson activity.  I'm afraid that the 12Z runs aren't going to be of much use today, except for far eastern Arizona where their initializations were best.  Maybe the 15Z RR will be better?  I'll include it later in this discussion.

Day 1
The airmass over Arizona is extremely moist with PW values from 45 to 50mm  over the low elevations.  High PW continues into the afternoon.

Moderate to high CAPE is present over much of southcentral and southeastern Arizona. It looks likely for strong storms with very heavy rain for areas that receive decent solar heating.

The WRFRR seems to have the right idea as it develops scattered storms by early afternoon over eastern Arizona.

It is a nice looking vertical profile at Tucson with some shear and good steering flow along with plenty of moisture and CAPE.  The PBL doesn't need to be mixed too deeply for deep convection, but that is going to be difficult as it's been cooled even more so than shown here.  Tucson is going to need some sunshine plus some outflows, and that is likely to not be sufficient.  Also, anvil shading may be a problem if convection forms first over the high terrain to the south.

Activity continues into the late afternoon over parts of southeastern Arizona.  Some of these storms are very strong and will produce very heavy rain.

Moderate mid-level flow pushes the storms along, so only a few spots have over 2 inches.

The 15Z WRFRR is now available, and it does have a bit better cloud initialization.    It looks similar to the 12Z run as it develops some strong storms over SE Arizona mainly over higher elevations. It looks like anvil shading from the south does occur over Tucson resulting in suppressed convection.  Most SE Arizona activity is over by this evening, and it seems like another goose egg for Tucson.

Day 2
Some drying takes place, but it's still plenty moist thus storms that do form are likely to produce very heavy rain.

A broad trough in the westerlies moves to the east which places most of the state in southerly flow.  500mb temperatures are a bit lower; thus, conditions may be a bit more favorable for deep convection.

CAPE continues to be quite good as some areas are around 1500 J/kg.

The bad news is that convection is typically suppressed on the backside of an ejecting IT and that seems to be the case tomorrow.  The model skew-t diagrams from Phoenix and Tucson both indicate only shallow afternoon PBLs and mid-level drying due to subsidence.

Only far eastern Arizona sees much activity tomorrow afternoon.

20190730

Previous Forecast
Showers and storms were present over much of southeastern Arizona yesterday and into the evening, much as was forecast by the WRF.  Strong storms formed over the Rincons during the late afternoon and looked like they were going to make a run for Tucson, but only the Marana area received any significant precipitation.  I don't know what the deal is with them receiving repeat big storm while most of the rest of the Tucson area has seen very little activity.

All the runs turned out to be pretty good for southeastern Arizona except they didn't have enough activity for Yavapai County.  The WRFGFS was the best of the bunch.  Showers and a few storms continued into the morning hours with some activity around Phoenix.  Both the WRFGFS and WRFRR had some weak activity in the general vicinity.

Initializations
While reviewing the satellite imagery, I noticed a swirl in the area of cloudiness over far SE Arizona. Looking back at the last 36 hours of imagery, it was the MCV mentioned yesterday that formed the night before last.   The area of clouds are present in the initializations, but the circulation is not, which isn't surprising.  A large IT is located over the northern Gulf of California with small areas of cyclonic flow moving around the periphery.  The models have initialized the large feature well, but the small scale circulations are missing. Clouds are initialized well in both the GFS and RR.    All initializations have some significant PW errors over Arizona and down into Mexico.  The NAM and GFS are pretty bad while the RR is the least bad; thus it's the favored initialization today. 

Day 1
Both the morning soundings from Tucson and Phoenix had almost no CAPE. Tucson had a strong inversion at 850mb due to rain-cooled air near the surface. I was surprised to see a flash flood watch from the Tucson NWS for this afternoon and evening.

It is plenty moist as most lower elevation locations have 40-50mm of PW today.  Low-level easterly flow has strengthened in New Mexico, and fortunately, the southern 1/2 of the state is still pretty wet; thus, there is no drying from the east.

850mb dew-points are relatively high, but nothing too extreme (>15C).  Southeasterly flow in NM is moderate even at 850mb.

The CAPE measured by the soundings at 12Z looked pitiful, but by early afternoon, it increases to a decent 500 to 1500 J/kg over much of southern Arizona.

All three 12Z runs are consistent in developing widespread storms over southeastern Arizona this afternoon.

By early afternoon, Tucson is well mixed, 6-900 J/kg of CAPE, and a favorable wind profile with good mid-level steering flow.  Just based on the forecast Skew-T, it looks likely for storms in parts of town this afternoon.

However, as is so frequently the case, the strongest storms skirt around the valley.  WRF QPF generally has less than 1.5" of rain, but there could be a storm or two the produce more.   Does the forecast warrant a flash flood watch?

Scattered weak storms move into Pinal County during the late afternoon.  Based on the amount of forecast CAPE, this looks about right.

The Phoenix late afternoon Skew-T forecast plot has only limited CAPE, but winds are favorable, and the PBL is mixed quite deeply.  My guess is that like last evening that a few showers/weak storms develop when the outflow boundaries move through.

Stop the presses!  The 15Z WRFRR is now available, and it is quite a bit more active.  It has slightly more CAPE and stronger outflow boundaries that move into the Phoenix area during the early evening. 

They are sufficiently strong for some storm formation in parts of the Phoenix valley.  The 15Z WRFRR has frequently been the best run of the morning suite but can sometimes be too active so we'll have to wait and see.

The Mexican IT move slowly to the NW and is over the far northern Gulf of California overnight.  This is close enough to keep some activity going into the early morning hours.

Day 2
The Mexican IT begins to lift out over western Arizona as a west coast trough moves closer.  This results in quite strong mid-level flow over the state.

PW continues to increase and is very high by morning.  With the influence of the trough plus the extreme moisture, showers and storms could occur just about any time.  Flash flooding looks much more likely than today.

The 15Z does have morning activity over parts of southern Arizona, which is certainly possible.  As no other runs have nearly this much activity, I don't think it's too likely.

If the above happens, it will negatively impact later development and results in only scattered storms.  If not, it could be a very active day as even the most conservative run has areas of moderate to high CAPE for much of the state.

Impressive CAPE is forecast by early afternoon for Tucson with around 1600 J/kg with relatively strong mid-level flow and some low-level shear.  Flash Flooding is likely with a PW of 47mm, that's for sure.  Storm motion will be moderately fast (for the monsoon season) thus I don't expect any extreme rain amounts.

Assuming it's sunny and early morning activity is limited, strong storms develop early and are widespread over southeastern Arizona by early afternoon.  Some areas may see over 2" of rain.

It is possible Phoenix may see some storms later in the afternoon, but forecast confidence is low.

20190729

Initializations
The last two nights have seen large nocturnal mesoscale convective systems form over Sonora. This has resulted in a slight increase of moisture for southern Arizona as PW is now in the mid-thirties.  The MCS from last night is still going over far southern Sonora this morning resulting in widespread clouds all through Sonora.  Southern Arizona is also experiencing broken to overcast conditions.  Cloud initializations are reasonably accurate, but the WRFNAM does burn the clouds off two quickly.  The other two runs hold onto the overcast a bit long but eventually clouds burn off too.

 A large inverted trough/MCV combination can be seen over much of Sonora.  A second, energetic MCV is located east of El Paso.  The Sonora IT was resolved in the 500mb data, but the El Paso MCV was not.  The mid-level anticyclone is one again near the Four Corners, and temperatures near the center are quite high, around -4C.

All three of the 12Z initializations did a good job initializing these features, including the El Paso MCV.  I was a bit concerned about the high wind speeds that were initialized at 600mb as the RR had 30 knot easterly winds just south of Nogales.  Satellite imagery does indicate rapid westward movement of the mid-level clouds, so 20-30 knot winds are probably accurate.

The GFS and RR had some moderate PW errors of around 3-5mm over southern Arizona and into Mexico.  The NAM was worse with 4-10mm errors.  The GFS and RR initialized the situation quite well, especially considering the complexity and those are the favored runs today.

Day 1
A gulf surge is underway over southwestern Arizona which continues into the early afternoon bringing moist air into much of the southern part of the state. PW slowly increases and may be as high at the low 40's.  The various runs disagree with the amount of PW with the GFS being the wettest. Weak low-level easterly flow is also present over New Mexico with quite a moisture gradient from north to south.  This sets up another low-level convergence zone over southeastern Arizona, so storms are more likely there.

As with the PW, model runs have varying amounts of CAPE, but none of them are that high.  The somewhat drier WRFRR has only limited CAPE over most of the state this afternoon.

The wetter WRFGFS has more CAPE for parts of southern Arizona which is likely to result in more activity there but it hard to say which one is right. 

Storms take their time getting underway this afternoon and the only active areas are the higher elevations of eastern Arizona, even in the wetter WRFGFS.

The WRFGFS late afternoon Skew-T forecast plot has a deeply mixed PBL and good mid-level steering flow of around 20 knots.  CAPE isn't very impressive with only 5-800 J/kg. 

Activity picks up over much of SE Arizona this evening, and the area of storms generally moves westward towards the lower elevations. 

A few storms and associated outflows move into the Tucson area this evening. 

While the Phoenix vertical wind profile looks good, there is only limited CAPE forecast, so it's unlikely that any activity will make it into the Phoenix area.

The model forecasts are all consistent with the lack of any activity near Phoenix, but some continue storms over far southern and/or southeastern Arizona well into the night. It appears another MCS forms over far northern Sonora aided by the Sonoran IT.

Day 2
All runs are consistent with placing the IT over the far northern Gulf of California which puts much of southern Arizona in favorable southeasterly 15-20 knot flow.

Very moist air is present over much of the state with PW over 50mm in places.  Drying is underway over far eastern Arizona due to dry air advection from New Mexico.

CAPE also increases and is the highest in the WRFGFS.  The big question will be how much heating with occur as extensive debris clouds are likely, especially over southern Arizona.  Confidence in the Day 2 forecasts is low because of all the uncertainties.

The WRFGFS and WRFRR generally agree on developing storms over the higher terrain near Tucson and Phoenix by late afternoon.

The wetter WRGFS has plenty of CAPE to support deep convection for both Tucson and Phoenix as well as favorable mid-level steering.

Storms continue into the evening near both Tucson and Phoenix with some activity possible for both cities.