20180831

Initializations

The 500mb and Vorticity plot from the 12Z NAM this morning shows a trough moving towards Arizona from CA and this will be a big influence on the weather of eastern Arizona over the next few days.  

Moisture has increased over much of the state over the past 36 hours mainly due to outflow from a large MCS the night before last.  Nearly all of the GPSPW sites are reporting including SW NM and SE Arizona. NAM PW is initialized fairly well except for a bit of a wet bias in NW Mexico and the RR and GFS are also good.  All three initializations look good as there are no obvious errors and model confidence is high.

Day 1

As mentioned above, moisture has returned to the state on southerly low-level flow which continues today.

CAPE is low over the higher elevations so not too much activity is expected there.  CAPE is a bit higher over central Arizona, but the Phoenix vertical profile forecast will be more informative if deep convection is possible in Phoenix.

The western trough inches closer to Arizona but most of the southern part of the state is quite warm aloft.  Cooler air isn’t far away though.

The Phoenix late afternoon profile doesn’t look too bad.  There is quite a bit of CAPE present but mid-level steering is poor and from the WSW so no higher elevation storms will make it into the valley.  There is also a weak inversion at the top of the PBL which will keep storms from forming unless there is a strong outflow or some other lifting mechanism.  The situation is more unfavorable in Tucson as the mid-levels are quite warm and CAPE is low, so little or no activity is expected there.

Only a few showers and weak storms are present over far SE Arizona later this afternoon.

The odd man out is the WRFGFS as it has quite a bit more CAPE later this afternoon and overnight for central Arizona.  Looking at the current PW vs the forecast, WRFGFS PW is running a few mm too wet thus CAPE is probably too high. While I find it unlikely, it’s not out of the question that a few strong storms could develop during the early morning hours somewhere over central to eastern Arizona as the trough begins to interact with moisture.

Day 2

The west coast trough begins to move into Arizona along with positive vorticity advection thus providing both synoptic scale lift and mid-level cooling.

Drying occurs over western Arizona but the SE part of the state continues to be quite wet.  

Woah Nellie!  CAPE is very high over much of SE Arizona which has the potential to support very strong to severe storms.  All three of the morning runs are quite similar so confidence is high for this CAPE forecast.

The nose of the upper jet is over southern Arizona with areas of upper divergence and difluence.  I’m not very good at predicting situations like this with strong upper jets but from what I remember, the left exit region is where the best upper divergence occurs and that the jet will force the trough to the south.

Under this favorable upper divergence, storms form during the morning hours and move rapidly to the NE.  The different models disagree on the exact location with the WRFGFS being as far west as the Phoenix area or eastern NM like the WRFNAM.  The WRFNAM is kind of between the two as it develops some storms over parts of SE Arizona during the morning hours.

Fortunately, I am plotting a Skew-T for San Simon in far SE Arizona and it has quite a bit of CAPE present as well as a deeply mixed PBL but quite a strong inversion just below 500mb.  The wind field isn’t that impressive for organization as winds are mainly unidirectional with little directional or speed shear (WRFNAM below). This is not the case with the WRFRR as it has more CAPE and more directional and vertical shear thus more likely storms would organize with possible mini-supercells, but who knows which is correct.

The Tucson Skew-T also exhibits a strong inversion just below 500mb as well as high CAPE.  The wind profile is better with both directional and vertical shear. The problem is Tucson is located right on the boundary between dry air to the west and moist to the east so it could go either way.

The 15Z WRFRR is the most active and has some storms in the Tucson area during the early afternoon.

The various runs develop a few organized storms over SE Arizona during the afternoon which will possibly be severe with the threat of hail and strong winds.  Exactly where or when is hard to nail down.

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

20180824

Previous Forecast

Phoenicians need to stop complaining about how Tucson gets all the storm action!  Check out the precipitation map below for a prime example. It seems to me that Phoenix has had significantly more organized convection this year.  Storms fired all around SE Arizona by 11am with many locations receiving very heavy rain. Other storms moved south towards the Phoenix area during the late afternoon and generated multiple gust fronts which intersected over the valley resulting in additional development.

The WRFNAM ended up being the best overall but was a bit too late in the day with the very heavy far southern Arizona precipitation.  The WRFRR was also pretty good but didn’t have enough activity in the Phoenix area.

Initializations

A large inverted trough is over NW Mexico and SW NM.  Multiple smaller scale areas of cyclonic rotation were apparent on morning satellite imagery with one in SW NM and another south of Douglas.

An upper trough is located over NW Mexico and the analysis shows it as an open wave but water vapor imagery clearly shows a closed circulation.  There is quite a bit of upper divergence analyzed over Sonora and into SE Arizona which is probably responsible for the widespread clouds. The RR and NAM have the large IT initialized OK but are both missing the NM wave.  The GFS does have the NM wave but it’s too far west.

Clouds.  There are lots of them over SE Arizona.  However, looking out the window indicates that they are slowly burning off so perhaps there will be decent heating after all.

Somewhat surprisingly, the clouds were initialized quite well by all the runs: NAM, RR, and GFS.   RR and GFS PW errors were minimal and even the NAM wasn’t as wet as it has been recently. Overall, the initializations look pretty good for such a complex situation and all the runs should perform well today.

Day 1

PW has come down somewhat since yesterday and is generally in the low 40mm range over the lower deserts.  Tucson is the wettest at 43mm. A shallow surge continues over western Arizona with Yuma reporting 15 knot SE winds with a Td of 74F.  The surge continues during the day and increased PW somewhat over central and SE Arizona so storms are again likely to produce very heavy rain.

CAPE is moderate to high over much of the state and very high along the border.

The early afternoon Tucson vertical profile is tropical looking with a nearly saturated profile along with quite high CAPE of around 1400 J/kg (WRFRR).  The wind profile is a bit better. Mid-level steering is still quite weak but at least there is some easterly component. Anvils may be an issue if deep convection forms to the SW of Tucson, but other than that, it looks like a very active day in and around Tucson.  The other two runs are similar except for less CAPE but still enough to support deep convection.

The Sonoran IT drifts slowly north thus placing parts of SE Arizona in very light NE flow which may be enough to push storms off into the lower elevations.  As flow is light, they won’t move too much thus the flash flood risk is high.

The morning clouds give way to partly sunny conditions which delays the initiation of deep convection until later in the afternoon but once storms get going, they are strong.  As would be expected, the model runs do not agree on timing or location very well as the WRFRR has widespread storms over southern Arizona.

The WRFNAM and GFS are mostly active to the east of Tucson.  Take your pick as who knows which is right.

Both the WRFNAM and GFS move storms into Tucson during the evening.

Phoenix is mixed deeply by early evening and with moderate CAPE of around 1000 J/kg, some storms in and around the valley are possible.  Like yesterday, it’s likely that outflows will be needed to kick off deep convection.

The runs from yesterday were forecasting some strong outflows into the Phoenix area but today they are much weaker.  Are they strong enough? Maybe, or maybe not.

The WRFRR does forecast a few storms for the Phoenix area this evening as it moved a stronger outflow into the valley.

If Phoenix doesn’t see activity during the evening, they may overnight as the IT moves slowly north and is over south central Arizona during the early morning hours.

CAPE remains high enough for early morning activity.

The runs vary on their timing but all have some amount of activity in/near Phoenix during the early morning hours.

Day 2

The trough seems to shear apart leaving the state under mainly light southerly flow so not much good for storm organization.

Moisture and CAPE remain quite high so areas that see some heating will again be quite active.  Where and when that will be is difficult to say due to the complexity of the situation today. Tucson should have widespread activity today which results in a  worked over with only minimal CAPE in the area.

Not much activity for the lower elevations tomorrow.

20180823

Previous Forecast

It was an active day over southern Arizona as scattered storms formed during the afternoon hours and produced some very heavy rain.  The WRF runs didn’t have enough activity especially west of Tucson. Early morning storms did develop over southern Arizona but not in the Phoenix area as some runs said they would.  

The WRFGFS did better during the day as it had a lot of activity west of Tucson but it didn’t have any of the early morning activity.

Initializations

Oh boy, another complex situation.  The 500mb map indicates that Arizona is under generally westerly flow with the center of the 500mb anticyclone over in central Texas.  Satellite imagery and mid and upper maps have an IT over Sinaloa and it is moving northwest towards Arizona. Satellite imagery indicates that there is an IT/MCV over far SE Arizona and another MCV over SW NM which looks to all be a part of a f broad weak trough.   The NCEP data feed is finally fixed so future runs will be more on time but the NAM is unavailable right now. The RR and 12Z GFS have initialized the upper features fairly well.

Both the RR and GFS have a fair amount of clouds over southern Arizona and while not quite in the right place, they are still pretty good.  Also, an area of storms has just popped up to the NW of Tucson and both the WRFRR and WRFGFS were able to forecast these storms. Both the RR and GFS have initialized PW well.  The 12Z WRFNAM is sitting in the queue waiting to run but I can see its PW errors. It isn’t too bad over Arizona but too wet in Mexico and over NM and CO. Overall, in spite of the complex nature, the RR and GFS initializations look quite good.  Still, forecasting in this extremely moist environment is challenging for the model (and humans!) so I’m not all that confident.

Day 1

PW is very high over much of southern Arizona and ranges from 43mm at Safford to 48mm around Phoenix.  Drying is underway over far western Arizona as it’s dropped to 35mm at Yuma. Weak southerly flow continues to advect moisture into the central and western part of the state, but dry air is moving in aloft over western Arizona.  850mb Td are very high thus many storms are going to have very heavy rain and wet microbursts.

The Tucson sounding has more than 1400 J/kg of CAPE so no wonder there are storms in the vicinity already.  Like yesterday, the vertical wind profile has no good (any?) steering flow so storms will randomly wander about and form just about anywhere there is good heating.

CAPE is forecast to be high over much of the state today.

I better hurry up and get this finished as it become quite active over much of SE Arizona by noon.  Outflow from the storms near Tucson may trigger additional storms in the Tucson area.

Activity continues over SE Arizona and the high country throughout the afternoon.

While the various model runs have no actual storms for Phoenix, it’s very unstable as CAPE is from 1300-2000 J/kg this afternoon, depending on the model run,  so it is certainly possible that a few storms could form, mainly on the higher terrain, and then drift into the valley. Steering flow is poor thus storms won’t move much and have the potential to produce very heavy rain.  

A few storms do get close to the north side this evening.

Day 2

Moisture decreases somewhat but low-level flow continues from the south into the state so there is again a threat of very heavy rain and wet microbursts with storms.

Of great interest is the Mexican IT I mentioned earlier as the WRFRR moves it to just south of the NM Bootheel by mid-day.  The WRFGFS keeps it farther to the south but does put SE Arizona in favorable upper difluence and divergence.

The 500mb pattern also has an interesting mid-level IT over SE Arizona and northern Sonora which results in more favorable easterly steering flow at around 10 to 15 knots.  From what I can tell, this is the leftover MCV/IT which is in the area today.

CAPE is again high over much of the eastern ½ of the state thus it appears it will be quite an active day tomorrow.  Of course, this is all dependent on how much heating occurs.

Both the WRFGFS and WRFNAM have an early start to deep convection and areas of SE Arizona and eastern Arizona are active during the afternoon.

The PBL at Tucson is mixed nearly to the LFC (assuming around 700mb) and along with high CAPE and at least a little easterly mid-level flow, it should be very active tomorrow afternoon.

Storms appear to be much more organized compared to recent days due to the more favorable upper and mid-level winds and by late afternoon, both runs have strong storms moving into Eastern Pima and Pinal Counties.

Phoenix becomes deeply mixed and with some easterly steering flow, it looks likely storms will be in and/or near the Phoenix area during the evening.