Wednesday, June 21, 2017


Previous Forecast
Not a good day for the model runs and I neglected to pick up on some clues that indicated they were going to be too active.  Stronger storms were mainly restricted to the higher terrain of parts of SE Arizona with very weak activity around Tucson.  Below is the lightning plot as the QPE product from NOAA/OU ( is no longer available.  For whatever reason, NOAA had decided to make those products internal and not available to anyone else.  I've tried to get access but have been denied.

As mentioned, there were quite a few clues that the forecasts were going to be bad.  The first was that Tucson area IPW started dropping during the late morning hours while the model held steady or even increased slightly.  Another problem was the IT the model runs had initialized south of Douglas was not there.  Later in the morning, I could find no evidence when looking at cloud motions and I should have looked harder when evaluating the initializations.  The area of clouds that moved through during the morning also restricted heating a little.  By late morning, it was clear there was too much forecast activity by just looking at the lack of development.  Not a good way to start the season.

No significant errors noted.

Day 1
500mb heights have come down a little so not quite as hot today but moisture has increased slightly.  Even a weak Gulf of California moisture surge is underway as dewpoints are in the 50's there.   Quite a bit of moisture is lurking just to our south over western Mexico and some of this continues to trickle into Arizona today.

In spite of this low-level increase, only far eastern and southeastern Arizona have sufficient CAPE to support deep convection.

 Scattered storms are present during the afternoon for this area.

 The Tucson forecast vertical profile has only minimal CAPE and unfavorable winds.  Mt Lemmon might see a quick afternoon storm though. A deep inverted v profile will again cause storms east of Tucson to have very strong winds associated with them.

By late afternoon, areas of EC and SE Arizona as well as into SW NM may experience very strong winds.

Day 2
No significant weather expected as moisture is limited over higher terrain.  A weak surge continues to advect low-level moisture which will increase dewpoints into the 50's in western and central Arizona.

Tuesday, June 20, 2017


Previous Forecast
The various model runs were quite good forecasting the strong outflows over far southeastern AZ and SW NM where there was a terrible accident where the freeway crosses the Lordsburg Playa.  I was driving back from Paradise on I-10 shortly after the dust storm and at that point, the freeway had been closed.  It was spooky driving on an empty I-10 except for occasional tow trucks and emergency vehicles going the other way towards NM.  WRF-GFS was the best and is below.

The WRF runs are not all configured for the summer convective season yet and may have some issues with forecasting convection correctly.  Most runs will be transitioned over the next few days.

Southern NM was very active last evening which resulted in debris clouds advecting in over southern Arizona.  The key for today is if these clouds will thin out enough to allow sufficient heating for afternoon convection as IPW has increased to 26mm at Tucson.   Unfortunately, far SE AZ and far SW NM do not have any functioning GPSMET IPW stations so it's hard to say what is immediately upstream from us.  Demming is 28mm so southern NM is wet.

Of course, the first day back is tough as no model run has enough clouds; even the one that uses the new setting that is supposed to improve cloud coverage.  Because of overnight warmth, we got a head start on heating so, in spite of clouds, we're pretty close to the models.   

Looking at upper level maps, there does seem to be a weak inverted trough between Tucson and El Paso which is either a leftover MCV or an inverted trough.  In any case, this trough should help organize convection.  The 12Z NAM has a fairly sharp 500mb trough located just south of Douglas which looks OK.  The 6Z GFS is similar.   The 6Z WRFGFS also had the best cloud coverage of the morning models, but still not enough.  Model confidence is quite high as the clouds over SC Arizona are burning off quick enough to not be a big factor.

Day 1
Moisture continues to slowly increase over eastern Pima and Santa Cruz during the morning hours and is more than enough for deep convection.

CAPE is also very high for this time of year in SE Arizona with some values exceeding 2500 J/Kg.  NM also have very high CAPE.  

Deep convection forms over the high terrain of Santa Cruz County by early afternoon.

As mentioned by Dan Henz this morning, the mixed/sub cloud layer is very deep, extending to nearly 500mb.  The lower/mid level wind profile is also very good with mid-level easterlies and low-level northwest winds.  CAPE is low in the Tucson area but may be enough to support storms even in the lower elevations.
Storms are present over eastern Pima County later this afternoon while storms over the White mountains are just getting started.

Winds are going to be very strong with gusts above 50 knots in eastern Pima County with these storms.  It appears storms will put the break on temperatures so perhaps Tucson won't have record highs. 

The rest of SE Arizona becomes very active by late afternoon as outflows converge across Cochise County, triggering new development.  The big story is the winds as it looks like a repeat of yesterday with very strong outflow winds. 

A few storms form in far eastern Pinal County and eject outflows into the Phoenix area this evening accompied by a dust storm.  Strong winds continue over SE Arizona.

Due to slightly cooler/wetter air, it looks like Phoenix won't make it to the 'magic' 120 mark.  It's going to be close and maybe KLUF can do it.

Looks like the outflows provide some cooling for Phoenix this evening.

A Day 2 update will follow later this morning.

Friday, October 7, 2016


Another round of strong to possibly severe thunderstorms are possible over parts of the state tomorrow as moisture pools in the vicinity of a backdoor front. Activity gets off to an early start as a blob of moisture is forecast to be present over the Phoenix area around sunrise with some CAPE present.

Showers and few storms may form around 6-10am in the Phoenix vicinity.

This activity is being forced by a weak trough over SW Arizona as upper divergence is quite strong along the trough axis.
By early afternoon, moisture continues to increase over SE Arizona/SW NM with impressive 850 dewpoint temperatures around 10C.
CAPE is also impressive with 1000 J/Kg and higher over SE Arizona.  CAPE is also present over the White Mountains up towards Flagstaff which will also support strong storms.
As Bob Maddox pointed out, the wind profile is excellent with strong directional shear and with 1000+ CAPE, strong to severe storms are likely with isolated strong wind and some hail possible.  This is one of the more impressive vertical profiles I’ve seen this transition season due to high CAPE and good directional shear.

Deep convection develops over the high terrain of the Rim/White Mountains during the afternoon.
Later in the afternoon, deep convection forms over the higher terrain of SE Arizona.  Some of these storms become severe with the main threat being hail.  All the runs over the past 24 hours have been quite consistent with this solution.  The big question is if Tucson will see storms and the answer is unclear as some runs have storms in the valley while others (WRFNAM below) keep them over the higher terrain.

The WRFGFS does have strong storms in the Tucson valley and up into Pinal county by late afternoon.  So, the message is that some strong to severe storms are likely around SE Arizona, but exactly where is unclear.

A few strong storms continue over far eastern Arizona into the early evening.

The concern, as it always seems to be, is if there will be clouds restricting heating during the morning hours.  This is definitely a possibility as morning storm activity is possible around Phoenix as well as a large area of clouds overnight.  These clouds are forecast to move out during the morning hours thus there is nearly full heating in the model.

Tuesday, September 27, 2016


The mid and upper low responsible for all the wind and rain is slowly moving northward and is located somewhere over the far northern Gulf of California-the analysis may be too far to the west. Showers and storms have been active on the east side of the low with ongoing activity from west of Douglas up through Tucson. Already, this has thrown a monkey wrench into the forecasts from yesterday and this morning as heating was required to obtain 500 J/Kg or so of CAPE. The 6Z and 12Z WRFNAM had a bit of activity this morning while the rest of the model runs had little or no clouds or shower activity. Unless it clears up in the next few hours, all the forecasts from the last 24 hours or so are going to have much less activity this afternoon than predicted.

Day 1
Both the 6Z and 12Z WRFNAM dissipate clouds and showers throughout the morning. There is some decrease in activity south of the border so perhaps the sun may break through later this morning in SE Arizona.

The 6Z WRFNAM had some activity over Santa Cruz county, but not nearly enough.

By this afternoon, the 500mb low is forecast to be over the northern GofC. However, satellite imagery shows that the low is about 100 miles east of that position already at 15Z - another potentially significant error.

The wettest air is over SE Arizona this afternoon. However, with limited sun, not much heating occurs and CAPE is minimal.

Shear is about as good as it gets here with both directional and speed shear. The 6Z WRFNAM seems to have the best handle on the CAPE and it has only a few hundred J/Kg this afternoon.
The other extreme is the 12Z WRFNAM which has more heating, moisture, and CAPE. I find this to be less likely, but you never know as it might clear up later this morning.skewt_1_14.gif
All the runs continue to forecast deep convection developing over Pinal and Pima counties this afternoon. Areas that receive some heating will see scattered strong to isolated severe storms.  At this point, maybe areas of central Pima and western Pinal? It's really hard to say due to all the uncertainties in the model runs today (clouds, possible mid-level low position)skewt_1_8.gif
There is a chance of some activity in and around the Phoenix area as there is sufficient heating and moisture which results in 5-700 J/Kg of CAPE. The late afternoon wind profile isn’t quite as good as it is in SE Arizona but is still good enough to support some organized activity.mdbz_11.gif

The models are split on activity around Phoenix. The WRFNAM is the most active and develops some showers and a few storms during the early evening.

As there is likely to be some big storms to the south of Phoenix, a haboob is also quite likely during the late afternoon. As seen in the above model sounding forecast, the PBL exhibits a decent inverted V profile.
A few storms develop during the early morning hours from Tucson northward.


Monday, September 26, 2016


This discussion will cover the potential for severe weather tomorrow.  An anomalous retrograding cut-off low has moved to a position over the Baja spur this morning. Guaymas is reporting a -12@ 500mb and the low was analyzed at 5760 m. There is a moderate amount of moisture to the south and east of the low in the range of 25-35 mm. Plus, there is a TS (Roslyn) at 119W, 17N moving slowly to the NE which may add additional moisture over the next few days.

By tomorrow, the low begins to eject to the north with quite cool mid level temperatures over southern Arizona of around -12 to -15C.

Some low level moisture is present over southern Arizona with 850mb dewpoints in the 7-10 C range, which is fairly high for this time of year.
CAPE isn’t all that impressive, but the wind profile certainly is with a Great Plains supercell type of directional shear. Speed shear isn’t as good as was being forecast the other day but is still fair. The PBL becomes deeply mixed by early afternoon thus strong to severe storms are likely from around 1-4pm in and around the Tucson area. There is a risk of large hail. Storms are likely to exhibit rotation with the possibility of funnel clouds or maybe a brief tornado. The 12Z WRF GFS and WRF NAM model runs are quite similar thus there is some confidence in this forecast. The RR is missing at 12Z. I’ll check to see if there is any data available and make a run if that is the case.850_32.gif

Deep convection initiates around 20Z over the higher terrain of central Pima and Santa Cruz counties. By mid-afternoon, a broken line of strong to severe storms moves to the NW and impacts Pinal, eastern Pima, and western Cochise counties. Again, both models are quite similar with location and timing. The WRFGFS, below, is about an hour faster than the WRFNAM and has strong storms in the Tucson area around 3-4pm.

Thunderstorm winds are expected to be strong with isolated areas of severe winds.

The broken line of storms continues to move to the north and northeast into the early evening.  At this point, the model runs diverge with the WRFGFS (below) moving the dissipating storms to the east of Phoenix and continuing strong storms over Cochise county plus another area of storms moving off of the White Mountains.

The WRFNAM is a few hours slower and has storms dissipating over Arizona by 8-9pm.

The storms move fairly quickly so rainfall isn’t extreme.  However, some locations could see over an inch or more.  Mode consistency has been remarkable as all the runs from that last 18 hours have nearly identical solutions.  Saying that, there are some issues that have to be monitored.  All model runs allow full heating tomorrow and as past history has shown, the model does have issues with insufficient clouds so if we wake up to clouds tomorrow, there may be much less activity than predicted.