Analyze The Cap

Tucson's weather this winter will be exceptionally boring—one beautiful sunny day after another—thanks to a La Niña that is as certain as a Joe Biden win, according to outlooks from the Climate Prediction Center and The Economist online. Hopefully we'll get a few inches of rain this winter, not too far below normal. But that likelihood will be only half of what Tucson received in each of the last two winters.

So I'll be spending this winter revisiting the few exciting monsoon days from this past summer, and preparing and hoping for more of those days next summer. My most recent previous post here was on July 8. Three days later on Saturday, July 11, the monsoon made a dramatic appearance around sunset. A line of thunderstorms moved from east to west and resulted in several reports of high winds and damage in the Tucson area, including a 60 mph wind gust at Davis-Monthan Air Force Base. But the days immediately before and after July 11 had a similar weather pattern, and those days were just hot.

The selection of a "forecast problem of the day" as practiced by the National Weather Service amounts to wearing blinders. Typically the problem stated in a NWS discussion is confined to one element, for example "will the high temperature be a degree above or below the record" or "will there be damaging thunderstorm winds?" My gripe is not just that wearing blinders is a poor practice for a forecaster analyzing and monitoring the weather situation, it's that the fixation on a single element carries over to the public forecast, a communications disservice. The problem selected for attention on most summer days should be the underlying feature affecting multiple elements, "what is/will be happening with the cap?"

The cap of concern in the Southwest summer sits around 400-500 mb, as noted in the previous post here, or in terms of dry isentropic levels around 326-336 K. It persists most of the summer, yet can vary—in thickness and/or in height—from day to day and even hour to hour, and the variation can be on small as well as large horizontal scales. Let that stable layer subside several hundred meters, with mixed layer moisture overshooting into dry air at the base of the cap, and suddenly there is space for a record high temperature. Conversely lift that layer several hundred meters, and suddenly thunderstorms. Over the next several months I'll be examining available products that might help with what should be the mantra, "Analyze the cap."

Wrong Drumbeat

The Tucson National Weather Service is yet again fascinated and fixated on forecasting days ahead of time record-breaking highs, confidently predicting that Sunday's high will be not just 4 degrees warmer than today's (Wednesday's) 107, but precisely 7 degrees warmer. Dismissed is the more important point that unlike the last several afternoons, which have been just hot, the next several afternoons will be both hot and humid.

I have become fascinated with the "Forecast Soundings" option on the National Weather Service Model Analyses and Guidance page. It's fascinating to watch—not just every 12 hours, but every 3 hours—Tucson's capping inversion at around 400-500 mb evolve diurnally, and from day to day. That inversion rules out nearby thunderstorms today. But the mid-level inhibition becomes much weaker possibly as early as tomorrow afternoon, more consistently by Friday afternoon, along with a flow that would steer isolated, high-based, borderline thunderstorms from the east or southeast. The odds of measurable precipitation reaching the ground any of the next several days are low. But the record or near record hot environment will enhance negative bouyancy of any downdraft. Maybe by the end of the weekend the surface parameter that will have been observed to break a record will not be temperature.

The continued inanity of June 15th

Nine years ago I railed, twice in the same month, about the silly season of talk about the monsoon. In the second of those June 2011 posts I wrote (misspelling site for sight):

Suppose that someone had lived in Tucson for a couple of decades, then fell into a Rip van Winkle sleep for another couple of decades, and finally awoke last week. Rip van Winkle would be bewildered to hear that the monsoon starts Wednesday, and that, alas, despite the approaching start date there's no rain in site (as if rain in site would be normal for this date in June). As terrible as the wildfires have been this year, and as good as it would be to get enough rain to relieve the situation, that's not a realistic hope this early.

The difference this year is that June 15th arrives on Monday, not Wednesday as it did in 2011. It's still silly to talk about the monsoon starting on June 15th, despite a decade of the National Weather Service pretending otherwise.

At this point it might be enough to say, "See previous posts." But following after this April's remininiscing post, this post goes back forty-some years to the weather station at Davis-Monthan Air Force Base here in Tucson. Since the stations's weather radar and human eyes both had a relatively clear line of sight to the south, at this time of year it would not be uncommon for the weather observer to include in a late afternoon or early evening hourly weather observation an uncannilly precise remark that a thunderstorm cloud was being visibly observed 95 miles to the south. So there was no ignorance about moisture pooling in Mexico. But when a trough in the westerlies would briefly pull some of that moisture north and generate a thunderstorm or two, customers would be briefed that, "That was not the monsoon." Emphasis was on the long-term correlation between the north-to-south transition from dry to moist air and the north-to-south transition from westerly to easterly upper-level winds. Thunderstorms, at least scattered coverage, moving generally from east to west, day after day (or at least most days)--like pornography, Tucsonans know what they expect from the monsoon. And until recent decades forecasters understood how to tailor and communicate their monsoon call for locals.

I have no qualms about a firefighter labeling the entire difficult month of June as a nebulous and agonizingly long period known as "at the start of the monsoon." But I doubt a firefighter would insist that the lightning strike on the evening of June 5, which sparked the Bighorn Fire, was "not the monsoon" while at the same time insisting that a lightning strike tomorrow evening would be "the monsoon." That would be just silly.

Earth Day, 50 Years Ago

Decided to jump into remembering the first Earth Day. In the spring of 1970 in ninth grade at Redstone Junior High School, our social studies teacher, Doug "Skip" Harbaugh, was 25 years old, energetic and innovative. About halfway through the school year Mr. Harbaugh had thrown out the standard curriculum, saying, "This isn't going to do you any good!" The first innovative unit was financial, and it's the most financially-valuable course I've ever taken. After that we moved on to environmental. We, the students in Mr. Harbaugh's class, became the Sincere Teenagers Opposing Pollution.

Some classmates specialized in manufacturing armbands; I'm sure that the neat printing with a magic marker was not mine. Doug was active in the Jaycees in Brownsville, and I suppose it was through those connections that he arranged an appearance on what was then the relatively new local radio station, WASP. The station manager had a weekday call-in talk program called Bob's Beeline. (I know, it sounds like a skit from Hee Haw.) There were four of us students selected to be on the program. Not sure if it was on Earth Day itself, could have been a day or two before or after.

The original studio was a small room in the Gallatin Bank Building in downtown Brownsville. Bob was a big guy, and the four of us sat around him--no social distancing. It was additionally uncomfortable for me because my Dad worked at a chemical plant a few miles downriver that manufactured, among other things, sulfuric acid for industrial use. The plant had recently installed pollution control equipment to capture gas that had previously been vented to the atmosphere. The control process had a side effect in that it generated a lot of steam with a fine mist of ammonium sulfate. It was probably better for the trees than sulfur dioxide gas. But unfortunately, though fog tends to accumulate anyway in the Monongahela River valley on clear cold nights, the portion of the fog bank connected to the plant often seemed to be a bit more dense and slower to dissipate. When a call would come in, "What about that cloud from that chemical plant?" I would frantically motion "Don't point that microphone at me!"

Another Wet Winter

The numbers are in for precipitation for this 5-month winter of 2019-2020, and it was another wet one. In fact this was the 13th wettest of the last 71 winters. Hopefully the trend of three good winters in the 2010's will continue for the 2020's. Though the January ONI was a bit into El Niño territory, there is a duration requirement which means that when all is said and done the winter as a whole will have been at the high end of neutral territory, not quite enough to be considered an El Niño winter.

This winter's precipitation was skewed toward the first month-and-a-half of the five months. November was 400% of average (1.74 inches above average), while December was 126% of average, most of that in the first half of December. January was 76% of average, while February and March were each close to average. Thus the total for December through March was close to average. But November was the wettest November of the last 71 years. So this winter's good performance was the result of a fast start during the last two weeks of November, combined with the last four months together keeping up not just with the median but with the mean.