Data released by the NOAA National Climatic Data Center indicate that Arizona, much like the capital of Phoenix, just went through the hottest August on record. The heat was not confined to just Arizona – Colorado, New Mexico, Texas, Oklahoma, and Louisiana also experienced their hottest August in 117 years of observations.
The family and I traveled back home to Minnesota today. What a day to arrive! Under a 500 mb ridge with a central height of 596 dm (over two standard deviations above normal, see above) temperatures have pushed well into the 90s. Minneapolis-St. Paul International Airport reached a peak temperature of 97 F, with the “worst” hour being 4 PMwhen the temperature was 95 F and the dew point was a record-setting 82 F degrees (see insert below). The heat index was an incredible of 119 F. That ties the highest heat index ever observed in Phoenix on June 26, 1990 when the all-time high of 122 F was observed (with a dew point of 54 F). For comparison, the high in Phoenix today was 109 and the highest heat index was 105 at 5 PM. Glad I can say I was back in Minnesota for what appears to the hottest day in recorded history.
PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE TWIN CITIES/CHANHASSEN MN 400 PM CDT TUE JUL 19 2011 ...UNOFFICIAL DEW POINT RECORD SET IN THE TWIN CITIES TODAY... THE DEW POINT TEMPERATURE AT THE MINNEAPOLIS ST PAUL INTERNATIONAL AIRPORT WAS 82 DEGREES ON THE 3 PM AND 4 PM OBSERVATION. THIS IS THE HIGHEST DEW POINT TEMPERATURE REPORTED ON AN HOURLY OBSERVATION AT THE MINNEAPOLIS ST PAUL INTERNATIONAL AIRPORT SINCE HOURLY DEW POINT RECORDS BEGAN IN 1945. THE PREVIOUS HOURLY DEW POINT RECORD WAS 81 DEGREES...WHICH WAS SET ON JULY 30TH 1999. A DEW POINT OF 81 DEGREES WAS ALSO REPORTED AT THE AIRPORT ON SUNDAY...MONDAY...AND EARLIER TODAY /JULY 17-19/. THE MINNESOTA STATE CLIMATOLOGY OFFICE IS THE OFFICIAL SOURCE OF DEW POINT RECORDS ACROSS THE STATE. THIS NEW RECORD WILL BE CONSIDERED UNOFFICIAL UNTIL IT IS CONFIRMED BY THE STAFF AT THE STATE CLIMATE OFFICE.
July is half way over and thus far the Phoenix area has received about 1/4″ of an inch of rain (nearly all of which was from a cluster of early morning thunderstorms on July 10). This isn’t horribly unusual – the average rainfall for Phoenix from June 15 – July 15 is 0.34″ so 2011 is just a bit behind schedule. Climatologically the most active period in Phoenix during the summer is late July through August.
The drier weather looks like it will continue though through the next several days. A southeasterly mid/upper level wind flow is in the process of becoming established today, and will do so tomorrow. It will then remain in place through about Wednesday before another trough dips into the Southwest and brushes the moisture back east. Not that moisture levels increase appreciably between now and Wednesday, with SREF guidance suggesting surface dew points only rising to near 50 and precipitable water near 1″ – barely high enough to support anything more than mountains storms across eastern Arizona. In fact, the total rainfall from this morning’s run of the GFS indicates a rather benign week ahead (see below) with barely 1/2″ over the eastern Arizona mountains.
Of more interest might be the incredibly oppressive heat wave setting in for the Upper Midwest. Just eyeballing it, appears that 15-20% of the country will be under a heat warning/advisory coming up as high temperatures range from the upper 80s to near 110 in the central U.S. In Minnesota (where the family and I are heading to on Tuesday, great timing) dew points will be near 80 and with air temperatures in the 94-98 range the heat index will peg into the 110 to 120 area – a higher apparent temperature than Phoenix typically sees at any time throughout the summer.
The NOAA National Climatic Data Center (NCDC) has pushed out the first batch of updates to our climate normals. “Normals” are simply a snapshot of the current state of the climate, based on the most recent 30 year period. In this case, the normals were updated from 1971-2000 to 1981-2010. For many areas of the country, the 00s were a warmer, in some cases much warmer, decade than the 70s. Therefore the normals increased in many areas. Some cooling did occur of course, but averaged out over the course of the full year every state warmed.
For Phoenix, there was actually some slight cooling of the high temperatures in the daily high temperatures (see below, note that the saw tooth look is because the 1981-2010 normals are calculated to the tenth of a degree while the 1971-2000 normals are in whole degrees) during the peak of the summer and in the winter, though that cooling was relatively minor. More noticeable is the increases in the spring and fall months. This shows that the intensity of our summer heat has not increased, but the length of our heat season is expanding – it is getting warmer earlier in the spring and staying warmer later into the fall.
Not surprising, low temperatures warmed through the entire year – reflective of the urban heat island phenomenon. The UHI intensity was really strengthening during the 70s, so to have that decade roll off the normals and the 00s to come one when the UHI was firmly established was completely expected to result in these changes. This (UHI) is a great example of how humans can change the climate. The pattern is similar to what we saw in the highs – not so much an increase in the intensity of the heat during the peak of the summer, rather an expansion of the heat into the spring and fall.
An upper level low lifted north across the Phoenix area during the early morning hours today (Monday). With a very moist airmass in place and elevated instability, a complex of showers and thunderstorms developed. The storms developed just south of Phoenix and went on to drop rain on nearly the entire Valley. From a post on July 5 I noted that it is relatively rare for the entire Phoenix area to get rain during the summer, on average occurring just once. Once the PRI is calculated at midnight I’m expecting this rain to to have 85-95% coverage. Rainfall amounts varied from around 1/10″ to nearly 1″. The CoCoRaHS reports (shown above) did a great job capturing this event. Consider joining CoCoRaHS if you want to report rainfall at your house!
Starting tonight already, deeper southwest/west winds will spread across Arizona, dragging much drier air with and pushing the big moisture plume that is emanating out of Mexico (and has been over Arizona for the past week) east into New Mexico. Rain chances will drop to ZERO for Phoenix Tuesday through at least Saturday, possibly longer. The image to the left is the forecast rainfall totals from the Global Forecasting System (GFS) model through Sunday morning – you’ll note the lack of substantial rain over Phoenix. Temperatures will increase as a result, with 110 °F likely by Friday.
Signs point to a relatively quiet weekend weather-wise ahead for the Phoenix area. Instability will remain limited today through Sunday (400-600 J/kg with moderate capping in place). Storm motion will keep thunderstorms that form over southeast Arizona heading east to north, likely sending weak to moderate outflow boundaries up our way. All-in-all a pretty typical summer pattern.
Added quite a bit of info to the dust storm event page at the NWS Phoenix office today, including some radar loops and a picture of my sweet ride. The media coverage of this event was really amazing. Our office handled well over 40 media interviews during the day. I did a live interview with BBC radio, was quoted in a Chilean newspaper, and was contacted (timing didn’t work out) by a TV station in Denmark! National news websites prominently featured the event, as did the national evening news (NBC Nightly News covered it as one of their top stories and interview local Jim Cantore Lite, Rob Carlmark from 12News). Very weird for a change to have the momentary focus of the intense media glare on you. At least in this weather event, it wasn’t because of widespread damage, destruction, and death.
Working the event was interesting as well. Of course we were aware that a dust storm would be possible with the severe storms near Tucson. I became more aggressive in my thinking once we saw the observed wind speeds at and north of Tucson of 70 MPH. Clearly there was going to be significant outflow heading our way – but the question is always “how bad is it going to be?”. Pretty bad was the obvious answer. At least we got some good heads up from spotters (actually former MIC Tony Haffer) just at our County Warning Area line that we got dust storm warnings out quickly and well ahead of it. But of course once it moved into the Valley everything went nuts. The spotter calls are appreciated, without doubt, but I think we got notified about the dust storm in Phoenix about one hundred times. Local media went wall-to-wall coverage…eventually. Interestingly enough only one channel went live early in the event, perhaps that had more to do with what programming was on or could be that the station met had a good grasp on what was about to happen. Kudos to them.
The social media aspect of the event was crazy to try and watch too. There are tons of photos and videos floating around all over the place. Would be a great project to try and archive a bunch of them and tie them into the meteorology at that time…maybe I’ll do that for a regional conference/workshop!
Picture I took at work (near Priest & Washington in Tempe) looking south toward South Mountain about two minutes before this thing engulfed us.
Well, I was wrong yesterday with how much activity there would be. Looks like that cooler mid-level air in Southeast Arizona was one of the key features as thunderstorms near the Tucson area went severe (measured wind gusts over 70 mph). The outflow from these storms then traveled all the way up from Pima County through Pinal and Maricopa Counties, picking up lots of dust on the way. The result was a massive dust storm that moved through Phoenix, garnering world-wide media coverage [1] [2] [3] [4]. Winds were still blowing over 60 mph as the dust storm hit the far southeast fringes of the Valley Tuesday evening, with near zero visibility and 40+ mph winds spreading across the entire Phoenix Metropolitan Area. While dust storms do happen a couple of times every summer around here, this one was noteworthy for its intensity and size. I’ll write up more of this at work through the coming days.
Despite the massive outflow boundary, and even a decaying outflow boundary moving south into Phoenix from the Wickenburg area, new thunderstorms did not develop. This likely was due to a combination of lower CAPE and higher CIN evident in the 00Z 6 July 2011 KPSR sounding (below). Some rain did fall, with the PRI coming in at a whopping 0.01″ and 27% coverage.
Looking quick at today, the boundary is even cooler than yesterday resulting in less CAPE. Convection appears to be much slower to get going across Southeast Arizona, though there is a bit more activity to the north and northeast, per visible satellite (below). Also, check out that leftover MCV from yesterday’s cluster of storms! The UA high-res models, which did show a large outflow coming up into Phoenix yesterday (though to be fair, I’ve seen that forecast many times in the high-res models not pan out), are showing a mix bag again today with potential for outflow coming into Phoenix but not pointing toward much rain in the Valley.
Overall little has changed in the synoptic weather pattern, thus again today we’ll have a 20% chance of storms in the Phoenix area, perhaps an outflow boundary coming in (from the northeast?) this evening. I would not anticipate a dust storm like yesterday (not to say blowing dust isn’t possible, yesterday was such an extreme event).
A line of storms formed over Eastern Pinal County yesterday evening and pushed WNW into the Phoenix area from 9-11 PM. Unfortunately the storms dissipated as the hit the East Valley, though the outflow did cause a few storms to regenerate over Central Phoenix (another good example blowing away the Heat Shield Theory – I’ll write up a post on that in the near future). The Phoenix Rainfall Index (PRI) came in at 0.00″ with just 11% coverage. Decidedly not a big day.
A note on what a “Big Day” might be. Using historical PRI data, on average there are only five days each summer where at least half of the Phoenix Metropolitan Area receives measurable rain and only one day where practically all (90% or more) of the Valley gets rain. By far, when it does rain the norm is to have hit-or-miss events (10-50% coverage) like the past few days – which happens on average 19 days each summer.
Turning to today…the mid-level anti-cyclone (sometimes referred to as the Monsoon High) is near the Four Corners this morning per RAOB data. One thing that jumps out at me right away is an area of cooler temperatures coming around the south side of the high (see below). Cooler mid-level temperatures promote steeper mid-level lapse rates and higher CAPE value.
Looking at the morning sounding, it is still very moist but there isn’t as much instability as was available yesterday (see below). One good thing though would be the incoming cooler mid-level temperatures, which would increase CAPE values. SPC Mesoanalysis page is showing good CAPE is already present though.
Satellite and radar images (below) this morning are showing convection has already developed, with the tops quickly blowing west. That may cut down on temperatures for the day (blocking the sun/solar insolation over the Valley) and inhibiting CAPE from developing.
A problem appears to be the continued influence of drier air over far Eastern Arizona and New Mexico which is inhibiting convection/thunderstorms from developing and reaching maturity during the afternoon hours. With all the moisture and instability over the deserts it just goes to waste if nothing can act on it. I’ll be watching upstream thunderstorm development through the day as I think that is a key missing feature right now.
High-resolution models run at the University of Arizona and other run by NOAA don’t point to an incredibly active day. SREF data also aren’t pointing to a big day. I’m going to go with a low activity (10% or less coverage) day as well due to the lack of upstream storms forming.
The 12Z 4 July 2011 KPSR sounding looks awfully unstable! Moisture levels have increased throughout the atmospheric column and with temperatures expected in the 105-110 range this afternoon, CAPE could easily be over 1,000 J/kg.
There is still that dry air coming in from New Mexico, but there is now a distinct curl/rotation seen in the water vapor imagery near El Paso heading west. With the strong moisture boundary in place a bit further east than anticipated yesterday, this forcing feature coming in, a moderately unstable airmass, and good steering flow from the ENE still…I think today is the day the Phoenix area sees some big thunderstorms! Convective towers are already developing quickly over the mountains of SE AZ (see below), the Rim and even into New Mexico. I expect that trend to continue, with the storms moving off the mountains this afternoon then going crazy once they hit the moisture. Watch out today!
