20180707

Previous Forecast

No storm activity was observed over the lower deserts yesterday but there was a lot of blowing dust between Tucson and Phoenix due to the strong easterly winds.  Storm activity was restricted to areas along the Rim and westward into Mohave county with some activity continuing this morning.

All three of the 12Z model runs had the right idea with the WRFNAM looking to be the best.

Initializations

The upper air pattern has not changed much since yesterday as a strong ridge continues over much of the western CONUS.  Cooler air and a weak shortwave are located over New Mexico and moving this way. The mid/upper circulation is located over far NE NM and is quite obvious in the WV imagery.  A closed upper low/IT is located over far southern Sinaloa and has been responsible for storms there that may eventually produce a Gulf Surge. Another weak IT is over NW Arizona and is responsible for the continuing activity there.  The RR (below) seems to have the best initialization of all the features but the NAM is also OK.

The RR also has the better initialization of PW with only minor errors observed.  The NAM was too dry in Mexico and too wet over northern NM, but errors are not large enough to cause any trouble with the PW correction routine.  The 12Z GFS was also too wet in Mexico. I received some more information about Empalme: the plan is to upgrade the equipment to a Vaisala system some time this summer so maybe this will help reliability.  The area of activity in NW Arizona was initialized well by the RR and NAM. Elsewhere, it’s mainly clear except for southern NM and this area of clouds was not initialized well. Overall, the RR seems to have the best initialization but the others are also good.

Day 1

I’m writing this from Paradise, AZ and unfortunately, the power has gone out.  I do have a small UPS as outages are common (one was 3 days long last summer!) so I can continue to work for awhile longer.  It’s windy here again so maybe that has something to do with the outage. It’s humid too, as dew-points are up into the mid 50’s here and into SW NM.  By early afternoon, easterly low level winds continue over SE Arizona while weak southerly flow is present over western Arizona and flow is advecting moisture in from both directions.  The question is if the flow has weakened enough in SE Arizona to decrease the downslope effect.

850mb Td does indicate that this is the case as SE Arizona is around 10C, which is the magic number in my book for widespread deep convection.

Finally, there is a bit of CAPE over SE Arizona and into SW NM.  The White Mountains and eastern Mogollon Rim have over 1000 J/kg so expect widespread activity there.  Also note the CAPE and moisture in central and western Pima county. Besides that, there is a low level convergence zone thus this is likely to be another area for significant deep convection.

500mb steering flow is excellent over the eastern ½ of the state. The slightly cooler mid-level air and associated weak IT are moving into SE Arizona by early afternoon.  Storms that form over the high elevations will be steered towards the lower deserts and there may be enough CAPE there for some lower elevation storms, mainly in SE Arizona.

By 21Z or so, scattered strong storms are active all along the high country and also developing over central/western Pima county.

Tucson is forecast to have around 500-700 J/kg of CAPE later this afternoon which may be enough to support storms in the lower elevations as they move in from the NE.  The mixed layer is fairly deep so strong winds are likely with the storms. The wind profile continues to lack the low level shear for really strong storms though.

Just as a curiosity, the 12Z Tucson sounding is below.  When I first looked at it, I thought it was the 0Z by mistake as the PBL looks like it is from a late afternoon sounding!

The general model consensus is for scattered storms to move into the Tucson area by around 4-6pm.

There is another possibility of a dust storm/haboob across Pinal county this evening.

CAPE is marginal (200-500 J/kg) for the Phoenix area but maybe a storm or two could develop as the outflows move through.

Isolated activity continues around Phoenix and Tucson into the evening.  All 12Z runs develop very strong storms over NE Arizona. This is likely in response to the upper trough which is located over central NM.

This area of deep convection moves towards the Phoenix area around midnight and the WRFRR and WRFNAM do have some scattered weak storms in southcentral during the early morning hours.

Day 2

SPC has a “Marginal” risk outlook for tomorrow.  I’m only going to be able to do a quick look as Day 1 has taken so long.  The mid/upper trough is over central NM tomorrow and puts much of southern Arizona under an area of upper difluence while mid levels continue to cool slightly.

One issue may be significant debris clouds left from the early morning activity reducing heating.  The model runs mostly burn off the clouds during the morning hours. CAPE continues to increase and is quite high in some areas while others, like around Phoenix are low due to clouds and cooling from the overnight activity.  However, most runs increase CAPE during the afternoon across central Arizona.

Low level easterly winds have finally quit thus Tucson has a bit of low-level shear plus excellent mid-level steering.  CAPE could be higher, but is enough, 400-800 J/kg.

Phoenix has 500-1000 J/kg of CAPE by late afternoon and an excellent vertical wind profile with low level shear and good mid-level steering winds.  Almost textbook for big organized tropical squall line like storms.

Big storms during the afternoon over eastern Arizona, NW Arizona, and down into Mexico.  Due to the complex nature of the weather overnight tonight, forecast confidence is low thus the model runs probably don’t have the location or timing quite right and will need to be fine tuned tomorrow.

Tucson is likely to be active during the late afternoon and early evening.

Phoenix might see some big storms during the evening if everything comes together.  Both the WRFRR and WRFNAM get storms going later in the afternoon NE of Phoenix and with the good steering, move these into the valley around 8-10pm.  Some storms are likely to be strong to severe. The WRFRR is between the WRFGFS which has only a little activity and the WRFNAM which has a lot. Phoenix needs the rain, Tucson needs the rain, we all need the rain!

20180706

Previous Forecast

Storms formed over the high country of east central Arizona and moved westward into Gila and eastern Pinal where they ejected a strong outflow that produced a big dust storm.  Scattered storms also developed in eastern Pima county during the afternoon.

The WRF runs during the 24 hours previous ranged in accuracy from excellent to poor.  Unfortunately, I went with the less active runs which were the 12Z runs from yesterday morning.  The previous day’s WRFGFS (below) and WRFNAM runs had the activity around the Tucson area and the outflow that caused the dust storm south of Phoenix.  This outflow cooled Phoenix down slightly thus no high low record. This is not the first time the previous day runs have been more accurate. It happened just a week ago Friday in Cochise county.  

Initializations

The heights at 500mb are 6000m at Grand Junction this morning.  Wow! The analysis shows a weak inverted trough over Sonora but I don’t see any cyclonic rotation in any of the morning satellite imagery.  I got word back from my contact in Mexico who called Servicio Meteorológico Nacional about Empalme and that they are out of helium for the balloon again and that they expected delivery in 2 weeks.  The same thing happened last year too and I don’t think they were resupplied until the very end of the monsoon season.  I’m going to talk with the people that are in charge of the upper air program at SNM next week and see if there is some way to assist them in keeping Empalme operational during the monsoon season.  

It is mostly clear over Arizona except for far SW Arizona and these clouds were missed by the initializations.  The NAM and GFS initialized a little too wet in NM while the RR had minimal errors. I’d give the nod to the WRFRR today.

Day 1

Moist advection continues due to southeasterly flow from New Mexico.  Western Arizona has become quite wet as some low-level moisture is also coming up from the Gulf of California.

Unfortunately, CAPE is nearly zero over much of the southern ½ of Arizona, but it’s sufficiently high to support some storms along the Rim and into Mohave county.

Deep convection initiates during the afternoon over these areas and by late afternoon a few storms are scattered about.

The forecast Skew-T for Phoenix has only minimal CAPE and unidirectional flow with no shear.

Day 2

The 500mb pattern remains about the same with the high centered in western Colorado and good mid-level north easterly steering flow over Arizona.  Note that there is some cooler air and possible shortwave moving to the SW over eastern CO and NM and is likely to be a factor for Arizona in a few days.

 

Low-level easterly flow continues over SE Arizona with unfavorable downslope conditions.  However, the strong easterly flow over central Arizona weakens while moisture continues to slowly increase from the south.

Sufficient CAPE is present over much of eastern Arizona to support scattered deep convection.  CAPE is quite high over far SW Arizona but it’s likely a strong cap exists there.

Quite a bit of activity is present by afternoon over the higher terrain of a large part of northern Arizona.

The lower deserts around Tucson and Phoenix don’t have enough CAPE to support widespread activity.  In addition, the wind profile is unidirectional with no good low-level shear to support propagation.  However, steering is excellent for moving storms down from the mountains towards Maricopa/Pinal and Pima counties.

The WRFNAM/WRFGFS and WRFRR are quite different as the WRFRR (below) does move a few storms into the lower elevations by early in the evening while the other two have minimal activity.

Both the WRFGFS and WRFNAM do have showers and storms continuing into the late evening over parts of eastern and northeastern Arizona.  Thus both Phoenix and Tucson may see some late night activity.

 

This nocturnal activity appears to be forced by the weak IT mentioned above which is approaching eastern Arizona by tomorrow night.

20180705

Initializations

It’s going to be a challenging year for evaluating the model initializations because UCAR is no longer supporting its Suominet GPS IPW network. The website has been broken since March.  We are still getting the binary IPW data most of the time, but there have been some extended outages plus many stations are missing, especially in NW Mexico.  I am unable to determine if the sites are down or if there is a processing problem. In April, the upper air site at Empalme began to take data again but that lasted for only a short time and now it has been missing for more than 2 months.  Mazatlan Is also missing at 0 and 12Z. Chihuahua appears to be sending up a sonde only at 0Z thus at 12Z there is no data for all of NW Mexico. This is the worst upper air coverage in Mexico since I started writing these discussions 5 years ago.

There is a weak trough moving north through northern Arizona with some associated clouds.  The 500mb strong (5980m) high center continues to be centered over Colorado and there is a large anticyclonic circulation from south Texas all the way across the Gulf of Mexico with a secondary circulation over NE Mexico.  Model initializations look good for all features. PW initializations are mainly good for all of the 12Z initializations.

Day 1

Moist air continues to move westward into Arizona on strong low-level easterly flow around the strong low/mid level ridge and some moisture makes its way into western Arizona from the south.  

Easy come easy go.  The higher CAPE that was forecast to move across SE Arizona during the afternoon yesterday now appears to be insufficient to support any significant deep convection.  

About all that is expected are some showers and maybe a weak storm or two over south-central Arizona and into parts of SE Arizona later this afternoon and into the early evening.

There may be enough weak activity just to the east of Phoenix to send a weak outflow through the valley this evening, with a little “cooling” of around 5 degrees.  

Both Tucson and Phoenix become windy overnight with winds out of the east/southeast at 20-25mph.  The wind will keep the atmosphere well mixed and result in very warm overnight low temperatures.

At one point, it looked like Phoenix may set an all-time high low temperature but now that looks less likely. It is still going to be very warm though as lows are forecast to be around 94-95.

Day 2

Moisture advection from the east continues and it is quite wet over western Arizona.  However, drier air is moving into SE Arizona.

This drier air and downslope winds results in only limited CAPE except for the higher terrain of the Rim/White mountains and over into northwestern Arizona.

Some storms do develop out that way during the afternoon hours while the rest of the state remains mainly quiet.

20180704

Day 1

Moisture has been increasing slowly over southern Arizona over the past day or so but continues to be insufficient for any deep convection across Arizona.

Day 2

The 500mb forecast has a high centered over Colorado with a ridge axis stretching to the SW over Arizona placing far southern Arizona in light easterly flow while a large trough is located west of WA/OR placing much of the western CONUS in southwesterly flow.

Low-level flow becomes easterly over much of the region with very wet air present over eastern NM.  This wet air advects into Arizona during the day with 850mb dew-points into the 10C range which is typically sufficient for deep convection.

A narrow band of 500-1000 J/kg of CAPE is forecast over SE Arizona with somewhat drier and more stable air over SW NM.  Typically, moderate to strong easterly flow results in drying and stabilization of the air mass due to downslope flow but there appears to be a period of time where some deep convection is possible before the drying kicks in.

By mid-afternoon, moisture increases to over 30mm over Tucson with 300-700 J/kg of CAPE.  Note that the CAPE calculation is too high in the forecast Skew-t below. Winds are unidirectional with 15-20 knots in the low levels while mid and upper-level winds are light thus shear is minimal and organization of storms is unlikely.  Of interest is the deep mixed layer which is favorable for strong dry microburst winds.

By later in the afternoon, a few storms are underway across eastern Pima and up into eastern Pinal counties along this narrow strip of higher CAPE.  It was interesting to see that all three of the 12Z runs plus the 6Z WRFNAM have a few storms in and around the Tucson area.

During the evening, wet air continues to advect into Arizona from NM on moderate to strong easterly flow, but CAPE is minimal so no activity is expected.

The other story is the heat.  Phoenix gets to around 112-114 tomorrow afternoon.  Easterly winds then develop during the evening and along with some clouds, resulting in low temperatures from 95-98 across the valley.  96F is the all-time record high low at KPHX.