Double La Niña, and Tucson Winter Rain

La Niña will probably be with us again, and so the mantra in many places has been that this winter will be a repeat of last winter. But rain is coming to Tucson tomorrow night, and perhaps again on Monday. That expectation has temporarily dampened the chatter here. Eventually we will dry out again for an extended period—that happens every winter regardless of ENSO status—and the La Niña buzz will return. I predict that the total rainfall at the Tucson airport over the next five months, November through March, will be two to four times what it was for the same period last year. That is an easy call, because last year was one of the driest over the last sixty years for that five-month winter period.

In my post a little over a year ago, I plotted Tucson total rainfall, November through March, versus the ocean temperature anomaly used to officially delineate ENSO phases (my plot, as detailed in that earlier post, displays an average of the ocean anomaly over the entire five months). My point about rainfall for this year's current and upcoming five winter months is the same as it was last year. That is, based on what happened in the past, a range of possibilities should be expected: from well below normal to just below normal. But what about the fact that this would be the second La Niña winter in a row?

In the table below are data for selected years from my earlier plot, limited to four (including this one) recent extended periods of cool ocean temperatures following moderate to strong El Niños (red). Two of those winters with cool ocean temperatures came close but did not quite qualify as La Niña (blue), and so the ocean temperature anomalies for those two years are unshaded. Both 12 and 37 years ago at this point we were in the middle of not only a double but a triple La Niña. (Officially, La Niña ended for a few months during the summer of 2000, as it just did during the summer of 2011, but then redeveloped the following winter.) So the two winters of 1974-1975 and 1999-2000, each having come two years after an El Niño, look like good analogues for this winter. The rainfall totals for those two winters, 2.58 inches and 1.22 inches, offer a little more hope for Tucson this year than just a repeat of last winter.

November through March, Ocean Temperature Anomaly and Tucson Rain

37 years ago			|	27 years ago			|	12 years ago			|	Now
Winter	Ocean	Rain	|	Winter	Ocean	Rain	|	Winter	Ocean	Rain	|	Winter	Ocean	Rain
72-73	+1.59	5.77	|	82-83	+2.08	6.81	|	97-98	+2.17	8.38	|	09-10	+1.59	4.94
73-74	-1.84	1.95	|	83-84	-0.49	2.94	|	98-99	-1.22	1.13	|	10-11	-1.25	0.73
74-75	-0.70	2.58	|	84-85	-0.90	6.74	|	99-00	-1.43	1.22	|	11-12	<-0.5?	?
75-76	-1.39	1.83	|	85-86	-0.37	4.51	|	00-01	-0.56	3.94	|	12-13	?	?

The winter of 1984-1985 is a different story. It, along with the winter of 1967-1968, was a La Niña outlier on my earlier plot. Both of those La Niña outliers occurred in the second year after an El Niño. But each of them also followed a winter that did not quite qualify as La Niña. For that reason, it may be appropriate to dismiss those years as completely irrelevant to this year's interactions over the Pacific, since last year was most definitely a La Niña winter. But I'm not so sure as I look upstream at storms over the Pacific these last few days evolving in a way that they tend to do more often in El Niño years. So I will hedge my prediction and say that there is a slight chance that this year could be another stray, errant La Niña winter that brings above normal precipitation to Tucson.

Two Comments About The NWS

The original title for this post was going to be Yet Another Complaint About The NWS. But I discovered something today that I like. So I'll start with that. The following is an excerpt from the aviation portion of today's Charleston, West Virginia, Area Forecast Discussion.

FORECAST CONFIDENCE AND ALTERNATE SCENARIOS THROUGH 18Z SATURDAY...

FORECAST CONFIDENCE: MEDIUM.

ALTERNATE SCENARIOS: POSITION AND TIMING OF IFR SNOW AREAS COULD
SHIFT FURTHER SOUTH AND WEST TO AFFECT OTHER AREAS TONIGHT.

It's possible that this is an initiative in other parts of the NWS. But it's the first I've seen it, i.e. an explicit communication of the uncertainty in a short term forecast. It is a recognition that confidence does not always converge to certainty as the forecast time shortens. Models usually converge, but realistic scenarios may remain outside the model envelope. I hope there will continue to be efforts to better communicate uncertainty.

Now for my complaint. It is an old peeve, and it is about topography as much as meteorology. But it is mostly about a lack of common-sense communication skills. The following is the header for one of the zones in today's forecast from the Pittsburgh National Weather Service.

PAZ076-282030-

FAYETTE RIDGES-

INCLUDING THE CITIES OF...NORMALVILLE...FARMINGTON...OHIOPYLE...
MARKLEYSBURG
1258 PM EDT FRI OCT 28 2011


...WINTER STORM WARNING IN EFFECT FROM 7 PM THIS EVENING TO 8 PM
EDT SATURDAY...
(it goes on)

Nobody in Fayette County, except perhaps the radio announcer reading the forecast, refers to that part of the county as The Ridges. It is simply The Mountains, or perhaps The Mountain Area. The mountain area is comprised of prominent ridges (the two closest to Pittsburgh being Chestnut Ridge and Laurel Ridge) which enclose relatively lower but still rugged terrain. The cities are in that in-between area.

And here is an excerpt from the Pittsburgh AFD

... A WINTER STORM WARNING IS NOW IN EFFECT FOR THE RIDGES, WITH
STORM TOTAL SNOWFALL AMOUNTS OF 5 TO 9 INCHES AND LOCALLY HIGHER
AMOUNTS ACROSS THE RIDGE-TOPS POSSIBLE BY LATE SATURDAY MORNING.
IN ADDITION, A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR THE
LOWLANDS JUST WEST OF THE RIDGES...

... just west of Chestnut Ridge. It's that easy to fix, once you replace Fayette Ridges with Fayette Mountains. Here is my dictionary's definition of ridge: a long narrow hilltop. The ridge-tops are the ridges! For comparison and contrast, here is the topographical wording from an adjacent area, my new favorite the Charleston AFD.

...BASED ON NAM12/WWD/AND LOCAL DENDRITE ZONE AND OMEGA TOOL...HEAVY
SNOW CAN BE EXPECTED MAINLY OVER NORTHEAST MOUNTAINS...RANGING FROM
4-8 INCHES OVER HIGHEST TERRAIN...TO 1-4 INCHES ALONG WESTERN SLOPES
AND CENTRAL MOUNTAINS...

The HUB

Last week in Pennsylvania I took a few days to revisit some old haunts and favorite places including, for the first time in decades, the main campus at Penn State. Once there there were only a few hours to spare, and it rained the whole time, which was fitting because I remember many days like that in State College. (That's why I live where I do now.) Having read about and seen pictures of the changes at University Park, I was curious about how it would feel in person. I was especially interested in the feel of the HUB, and was pleasantly surprised. Although much has changed, the HUB still feels like a nice place to walk by/through while traipsing across campus. One of the changes is a garage next door, with space reserved for visitors. So I was able to park and then walk around the outside of the building without getting too wet. Viewed from the front, along Pollock Road, the HUB looks much different outside on the right side. But on the left side, pictured below, except for the brick pavement not much has changed since I first saw it almost 40 years ago.

This is what used to be called the HUB Ballroom. Now it is known as Alumni Hall. In addition to me, taking the picture, the other odd character in this setting is the guy sitting inside looking out up against the window on the right. (The other images in the windows are reflections from the outside.) It is Alumni Hall, so I guess he is an alumnus.

I only remember being in the HUB Ballroom for one event, and it was when I was still in high school. On the last night of Boys State there was a banquet in the ballroom. It had been a heated week-long campaign. My county (dorm-floor) was mostly supportive of our favorite son candidate. My roommate was a really nice guy. But he and one or two other people on our floor supported the other candidate. From dawn to dusk he and I would join our separate camps. Then while others were sleeping we would continue our running conversation: How can you support this?; Well what about you, how can you support that? My candidate lost by a significant margin, portending the real national election that fall. To make things worse, the banquet speaker was a Nixon speechwriter.

Until the banquet, the Boys State activities had been confined to the east side of campus, far to the left of the picture above. I wasn't impressed. But on that last night, approaching along Pollock Road, then resting in the shade of the big trees that predated the original HUB, I was impressed with the look and feel of the campus. Our party had decided that during the speech it would be important to protest the blatant real campaign agenda in the choice of the speaker. (Some things never change.) Despite the tension in the ballroom, I was preoccuppied with enjoying the view looking back out the windows.

The original trees started disappearing before my freshman year, and additions to the original HUB started that year. But the new trees have filled in nicely, and there are still good views and reflections into and out of the entire building. It's nice that they've managed to retain some of the look and feel of the original HUB. It's also nice to know that it still rains in State College, so that the trees will keep growing.

Pittsburgh Radar, July 25

It happens that the Pittsburgh radar, as well as the Phoenix radar, is an early test site for dual polarization. Not long after the Pittsburgh upgrade there was flash flooding in an area about 30 miles southeast of the radar. There were no fatalities, unlike a later event in Pittsburgh.

The image above is at 12:35 PM local daylight time. Thunderstorms by then were organized along two lines: one old, the other newly developed. The older, solid line of thunderstorms was oriented east-west and had been moving slowly to the south, reaching a position generally along highway I-70 (the thin red line in the background map generated by NOAA/NCDC's Weather and Climate Toolkit). The brown lines in the background map crudely approximate county boundaries, with the meandering brown line segments being where the county boundaries coincide with the Monongahela River. The flood reports (Donora, Allens Crossroads, Fayette City) were within a few miles of the point where I-70 crosses the river/county boundary. By this time a new, broken line of thunderstorm cells had formed in an area elongated west-southwest to east-northeast (from the southwest quadrant of the image toward the middle), with cell movement toward just slightly north of east. The severe flooding occurred where cells of the new line met and merged with the older line.

The differential reflectivity was higher at the western end of the old line and for most of the cells in the new line. It was lower in the area affected by flooding. It would be nice to think that the new information available after the dual-polarization upgrade would contribute to improved automated estimates of rainfall. But it would also be nice to think that the new information would better enable human forecasters to confidently, quickly, precisely and accurately communicate a flood threat.

Dual Polarization, July 7

Many Tucsonans, including me, tend to keep in mind a typical monsoon day. The typical day begins with abundant sunshine, continuing at lower elevations through lunchtime. By that time isolated storms are maturing over the highest mountains. About mid-afternoon new storms assemble southeast of Tucson, then proceed to sweep across town in an organized line, providing most locations along the way with a brief period of moderate to heavy rain. In some monsoon years there might be ten or twenty days approximating that description. Other years there are only a handful. So far this year we have had a good share of reasonably typical days. One of those days was Thursday, July 7.

The rain started at my place just before 6 PM (a little late for a typical day). Over the next 25 minutes the rain rate averaged about 1.5 inches per hour. There was no hail at my house, not even the tiniest trace of slush. There were reports of at least pea-sized hail nearby in several directions. A lady who lives about three miles east told me that her hail was long-lasting. From her description it sounds like some of her hail must have measured at least half an inch.

The time for the two images above is within a minute of when the rain started at my place. In the southwest quadrant of the top image, there is a reflectivity radial which alternates between green and yellow pixels. Beside it is another radial alternating yellow and red. My place is along the gradient between those two radials. At this distance from the radar, about 75 miles southeast of KIWA, the pixels are about 1 km wide in the azimuthal direction. Not surprisingly, given the first-hand description of the hail, there is an area of high reflectivity 4 to 5 kilometers east of my house. For simplicity, I'll call that cell the hailstorm. Fifteen minutes earlier, when that cell had just developed, it was more or less surrounded by a ring of high differential reflectivity. By the time of these images the high differential reflectivities (second image) had consolidated into two arcs, one extending northwest from my house, while the other, smaller area is southeast of the hailstorm. The rain began abruptly at my house with a brief barrage of big drops (higher differential reflectivity). That quickly changed over to a mixture of large and small drops (lower differential reflectivity), all wind-driven from due east.

Looking at what others are saying about dual-polarization, it appears that the emphasis is on dual-pol being an improvement in the classification of precipitation type. Incorporated in that classification is a distinction between different drop size distributions, and that distinction contributes to improved estimates of rainfall rates, for which it is straightforward to quantify the estimated benefits. But in addition, I think that differential reflectivity by itself will provide new information that will contribute to improved nowcasts of storm evolution.

With the heavy rainfall rates and the diversity of hail reports on July 7, it would seem to have been a good day for the other two dual-polarization products, the correlation coefficient and the differential phase, to shine. My initial impression is that there are problems interpreting them, perhaps because my house is too far from the radar. The differential phase seems to be overwhelmed by non-meteorological spatial variability. For the correlation coefficient, there seems to be a stronger meteorological signal. Here is an image of the correlation coefficient at the same time as the previous images.

The correlation coefficient never dropped below 0.97 at my house. It was lower around the hailstorm.

Phoenix Dual-Pol Radar, June 30

I stumbled on how to access the dual-polarization radar data from the archive at NCDC. Their viewer, the Weather and Climate Toolkit (WCT), in its Moment: pull-down-list conveniently and automatically adds the available dual-pol products to the original three (single-pol) products.

Although there have been several exciting days over the past week and a half, my previous post explained what was interesting about June 30. The day started for me with loud drops falling on the skylight shortly after 4 AM (11 GMT). It was the first rain in a long time. To make the morning even more interesting, the local media thoroughly covered the first uprooted tree of the season.

The two radar images below, which are zoomed into the Tucson area, were saved from the WCT. The top image is reflectivity and the bottom is differential reflectivity. The time is eight minutes before the reported time of the tree uprooting, and it is about a half hour before the big drops woke me. The thin red lines, conveniently provided by the WCT, are the highways I-10 (extending NW-SE) and I-19 (extending to the south). The marker labeled J is my house. The marker labeled M is the corner of Mission and Drexel, near the report of the tree toppling. The distance between M and J is about 12 miles.

The markers labeled with T's are prominent peaks in the Tucson Mountains. I imagine that the heights of the cloud bases were well above those mountains. Yet when viewing animations of both the reflectivity and the differential reflectivity, it's apparent that the cells were feeling the effects of the underlying terrain. Most of them were moving from southwest to northeast, along paths approximately perpendicular to the Tucson Mountains. The cell at M was slow moving, giving the impression of being attached to the southeast end of the Tucson Mountains. It's interesting to notice that the M cell is flanked by an area of bigger drops (higher differential reflectivity) on its southwest side. Now shift attention to an area directly north of M, where there is a cell centered on I-10. Ten minutes later that cell had moved to near my house (point J). By then the reflectivity had decreased by a good 5 dBZ and the differential reflectivity to mostly 2 dBZ or less. A second cell, approaching the top of the Tucson Mountains in this image, was near my house a half hour later. It too had reduced reflectivity by then, and its differential reflectivities had decreased to either slightly above or slightly below 2 dBZ. Perhaps the radar is telling me that the big drops had just finished falling onto my skylight.

Coincidentally, the upper air flow that morning was similar to what is expected for Tucson this coming Tuesday morning. I can see that the models are driving dry air well south of San Diego, then across Baja. There certainly are going to be changes, but I'm suspicious that the break in the monsoon is being exaggerated.

Big Drops

I would not quibble with anyone who says that this year's monsoon in Tucson got off to an early start on Tuesday (two days ago). Although most of yesterday (Wednesday) fit my picture of a pre-monsoon westerly trough, there were times on Tuesday when things were moving from the southeast. Then this morning a little after 4 AM I awoke to big drops falling on the skylight in the bathroom. The windows were still shut and the air conditioner was running, so it would have been hard for the thunder to wake me. But those big drops sounded like someone pounding on a saucepan with a spoon. (There were a bunch of damp, long-dead bees in my rain gage. It must have been not more than a few hundredths.)

I once remarked to John Marwitz that big drops were the most fascinating things to me about monsoon thunderstorms. John pooh-poohed the notion: A thunderstorm is a thunderstorm. He's right of course. Still I can't help thinking that there's something special about the distribution of big drops in storms west of 105W longitude.

When I first heard about dual-polarization radar about 25 years ago, I would be thinking about those big drops. The electrical engineer, V. Bringi, would fill the blackboard with a fog of phasors. But I would be picturing the old analog scopes on the finicky magnetron-based radar at Davis-Monthan, imagining those scopes magically transformed to show differential reflectivity. I wasn't aware until reading about it on Bob Maddox's blog that the National Weather Service radar in Phoenix (the radar is actually at the old Williams AFB) recently had an upgrade to dual-polarization. Since then I've been trying to figure out if there's a way to access the data. (My house is about 75 miles southeast of their radar; and I'll probably be disappointed with digital vs. old-time analog right next door. Still I think there will be interesting things to see.) In the meantime, I'll be excited to read about the first impressions in Phoenix. Here's an example from last night's Phoenix forecast discussion (FXUS65 KPSR 30035):

ALSO INTERESTING WAS OUR FIRST BETA TEST OF THE PHOENIX DUAL
POLARIZATION RADAR WITH THE NEARBY STORMS. OUR OBSERVATIONS
WERE...NOT A LOT OF PRECIP WAS DETECTED IN THE CLOUD CORES...
MEANING PRECIPITATION WAS IN THE FORM OF LARGE UNIFORM DROPS IN LOW
CONCENTRATIONS. OR VERY LITTLE MIXED PHASED PRECIPITATION
CONCENTRATIONS. SINCE VERY LITTLE PRECIP WAS DETECTED...THERE WAS
NOT A WHOLE LOT OF EVAPORATIVE COOLING ...AND THUS ACCOUNTED FOR
THE LACK OF STRONG DOWNBURST WINDS WE USUALLY GET WITH LARGE
TEMP/DEWPOINT SPREADS...WHICH AT THE TIME WAS 111 DEG OVER 50 F.

Obama In Pittsburgh

President Obama made an appearance in Pittsburgh last Friday. He traveled there to kick off a public-private partnership intended to promote the application of innovative technologies for use in manufacturing. It's nice that the President used the trip to remind everyone that innovation is not confined to the East and West Coasts. As for its effect politically, I think that the partnership will be a wash. Supporters will say that at least he is trying to do something to help with jobs in manufacturing. Opponents will say that he is doing it the wrong way.

As a supporter, I am perturbed by the part of his speech where President Obama cited Andrew Carnegie. For one thing, there is the incongruity of using Carnegie's role^* in the early development of the steel industry as the vision for an Advanced Manufacturing Partnership. The more important problem was Obama's pronounciation of the name. He used the New York pronunciation, CAR-nuh-Gee, instead of the way almost every voter in Southwest Pennsylvania says it, Car-NEIGH-gee. It's like making an effort to be seen in Philadelphia ordering a cheesesteak, then asking for it with Swiss cheese. And this was not the first visit to Pittsburgh. Getting legislation passed may be hard, but it isn't that hard to make an effort to connect with the local flavor. I hope that The President and his staff will do a better job of connecting with the voters he will need next year.

^*Before Carnegie built his own steel mill, he resisted the use of steel components in his iron bridges. His bridge engineers insisted that some steel parts were necessary for safety, but Carnegie then saw steel only as an extra cost that cut into profit. Carnegie did not invent the Bessemer process. He saw the innovative process applied successfully on a large scale in England, then scaled it up even more for his new mill in Pittsburgh. He made the huge capital investment only because he calculated that he could sell a high volume of a superior product for little additional production cost (analogous to China's big foot in global manufacturing). Carnegie was known to criticize innovations by his competitors, suggesting to customers that his competitors' products were dangerous. Then after his competitors went bankrupt he adopted those very same money-saving processes. Carnegie today would echo Senator Casey in criticizing the administration's trade policy.

The Monsoon Onset: What Has Changed?

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 monsoon itself of course has not changed. There is still much year-to-year and week-to-week variability. The variability would make it difficult to detect long-term changes in the monsoon anyway. But there have been other changes over the past few decades.

One of those changes is that meteorologists across the country recognize the notion of a monsoon in this part of the country. That recognition is thanks to various publications that have established the use of the terms Southwest Monsoon or North American Monsoon to describe the circulation and rainfall changes in the broader region around Arizona. But those broader changes have always been recognized from Arizona. Even before there was an Arizona there were Tucsonans who enjoyed sitting on their patios, peering far into the southern horizon (almost as far as a radar beam can reach), watching thunderstorm anvils and distant lightning, and wondering when the rains would get to Tucson.

Another change over the past few decades is the development of a wider variety of remote sensing techniques for better discerning the distribution of moisture in the atmosphere. The old satellite standby, an image of water vapor, happens to focus on moisture in the middle layers of the atmosphere. It has been joined by extra satellite sensors and by other indirect techniques. All of the remote techniques have their uncertainties. Instead of trying to weigh the uncertainties myself, I rely on depictions of precipitable water (PW) as assimilated into numerical models. Specifically, I like the presentations at COLA's wxmaps.org. Their plots clearly identify key contour levels of PW. When those contours are viewed alongside the old-standby satellite water vapor image, you get some feeling for the vertical distribution of the moisture: whether it is confined mostly to the lower layers of the atmosphere, as is often the case at the very beginning of the monsoon, or whether thunderstorms on previous days have left considerable remnant moisture in the middle layers. If the moisture is mostly confined to the lower layers of the atmosphere, then 25 mm (1 inch) of PW corresponds to a daytime surface dewpoint in the mid-50's. The bottom line is that 25-30 mm of PW is the transition to the monsoon.

Although they are still far from perfect, the model assimilations and forecasts of PW are more reliable than they were a few decades ago, providing a picture of the advance of the monsoon well before it reaches the southern horizon. But once it reaches the International Border, I revert to remotely sensing out on the patio and enjoying the show.

It's Monsoonal Season

The monsoonal season has arrived in Tucson. No, not the two months or so of near daily thunderstorms; that's still about a month away. What's already in full force is the silly season of talk about the monsoon. For the next month Tucsonans will endure media and meteorologists making pronouncements regarding the monsoon in general and the upcoming season in particular.

My peeve is not with the general public. Anyone who has lived in Tucson for awhile understands what the monsoon is about, and when it arrives. It's always fun to talk about the monsoon, and to speculate about the exact date when it will start. Most years the monsoon can be relied on to start within a week of, and usually just after the 4th of July. It's fun to plan on a dry 4th, anticipating a wet 6th, 8th or 10th.

More often than not at least once before the 4th it rains enough to wet the ground in Tucson. Obviously that will be the case when the monsoon arrives early. But there are rare rain days in June or very early July caused by mid-latitude westerly troughs. Traditionally meteorologists in Tucson would emphasize that those days were not the beginning of the monsoon. Their emphasis would be based not only on a diagnosis—that the winds aloft did not come close to meeting the definition of a seasonal wind shift, but also on a forecast—that the rains would not persist right on into the monsoon.

How does the National Weather Service currently define the beginning of the monsoon? I've lost track of the changes. I think that the NWS missed an opportunity a few years ago to reestablish a distinction between the monsoon, when thunderstorms occur almost every day, versus the encompassing summer thunderstorm season, the early part of which is mostly dry but with infrequent and especially hazardous days of high-based thunderstorms.

Although it goes against tradition, there is a case to be made for counting non-persistent June thunderstorms, perhaps racing swiftly off to the east-northeast, as part of the monsoon. The argument would go like this. The associated westerly trough managed to temporarily capture part of the moisture that was pooling south of the subtropical ridge. Climatologically that ridge is in the process of moving north to it's July-August position in Arizona. Parts of Sonora, Mexico, may already be experiencing the effects of a monsoonal flow. Thunderstorms in Tucson during the mid- to late-June period are less rare than earlier in June, suggesting that the northward advance of the subtropical ridge is more relevant than the obstinacy of the westerlies. The case against: those storms are followed by extended periods with no rain.

Tucson is very different from Phoenix in a number of ways. With regard to temporary surges of moisture before the monsoon, the difference lies in the trajectories of air flowing from the west-southwest toward each city. Phoenix is more susceptible to dry air from above the cold waters of the Pacific, say just south of San Diego. Tucson has more exposure to moist air channelled through the central Gulf of California. Temporary surges of high humidity at Phoenix get scoured away within a few days. In contrast, after the initial surge, high daily-average dewpoints may linger for several days in Tucson. It might be argued that persistently high daily-average dewpoints in June, albeit not quite high enough for afternoon/evening rain in the city, should define the beginning of the monsoon. But that definition clashes with what would have been the traditional call (based in part, I re-emphasize, on forecasters making forecasts) as well as my impression of what most Tucsonans think of as "the monsoon". If the monsoon starts this year on July 6, it will not be late. It will be right on time.

It Was A Dry Winter

in Tucson. Last October I posted about the oncoming La Niña winter in Tucson. Included with that post was a plot meant to illustrate that, based on the previous sixty years, the then oncoming La Niña winter had a range of possibilities for total rainfall, from well-below average to just-below average. The vertical scale in that plot is the rainfall total for a five month period extending from November through March. It is now close to the end of March, so this 61st five-month winter period is almost over. We aren't going to get any more rain in the next two days. Tucson airport will have had a total of 0.73 inches for November 2010 through March 2011, making it the second lowest November-March period in the last 61 years. The lowest was just five years ago, and that winter did not quite qualify officially as a La Niña winter. This past winter's nearest dry neighbors in the moderate-to-strong La Niña category were 1970-1971, 1998-1999, and 1999-2000. You can identify those three previous winters in the plot by noting the color-coding for the decades. (Although the March sea surface temperature anomaly in the Niño 3.4 region is not yet available, the average over the five-month period should work out to about -1.25 °C.)

My rainfall total for this most recent five-month winter period was 1.64 inches, more than twice that of the airport. Five years ago, when the airport had it's driest November through March, I also had about twice what the airport had. (I don't get twice as much as the airport on average.) To some extent the driest winters at the airport are just dumb luck, with rare showers in an already dry year happening to miss the airport.

Fortunately, within a day's drive both west and north of Tucson it has been a wet winter. Colorado River water inflow to Arizona is expected above normal. The fact that demand exceeds long-term supply in Arizona won't have to be reckoned with for a few more years.

Good Chance of Snow in Tucson Sunday Morning

The last few times before this, over the last few years, when the prospect of accumulating snow in Tucson has been played up, I have been skeptical. The most likely scenario always was for drier air to arrive with the coldest air. This time is different. Before the arctic air turns east and moves rapidly toward Tucson overnight Saturday, it will have had a long time to pick up moisture from the Pacific while hugging the California coast from San Francisco (overnight Friday) to Los Angeles (Saturday evening). The system will be moving east through Tucson rapidly on Sunday, and drier air should sweep in well before noon (per the consistent run-to-run GFS 700 mb RH progs for 18Z). And the heaviest precipitation should be all rain both in the foothills and in the valley until almost sunrise on Sunday. But there could well be a few hours of light, wet snow either side of sunrise when about a half-inch, maybe an inch average accumulates.

Bougainvillea and Ice

I took this picture at 10 AM today, February 3, 2011. By sunset a little over half of the ice had melted. The high at TUS airport was 38F, about the same as here.

The bougainvillea looked great at Christmas. But then near the beginning of the year there were two hard freeze events that took their tolls on the leaves and flowers. So I wasn't trying to protect these branches. Instead, I have a hodgepodge of covers and wraps and Christmas lights to try to protect the lower parts of the plants. I watered them last night, and will again tonight. I'm not sure what happened to the one irrigation line. It must have frozen during the night, and began spraying a fine mist straight up. The wind carried the mist onto these branches. In the top middle of the picture, against the brick background, you can see streaks of the airborne droplets.

It looks like the brunt of the next arctic outbreak will stay east of the Continental Divide. At least I hope so. But next week once again I'll have a wary eye on the weather stations along the I-80 corridor in Southern Wyoming for the first confirmation of sure trouble.

My Thoughts

Reflecting on a trait that I admired in one of the Tucson victims with whom I was slightly acquainted, I keep reminding myself to work at trying to be respectful of everyone, all the time, no exceptions. That includes the people I agree with, people I disagree with, Christians, Muslims, atheists, good drivers, slow drivers, distracted drivers, sane people, and people who may be on the edge.

It's the nature of politicians to point out the absurdity in their opponent's position. There's no disrespect in that. Comedians and entertainers point out absurdities all the time; they have a lot of material to work with in the political discourse. The real disrespect starts when evil motivations are ascribed to an opposing position. That angle of attack could be seen merely as a humorous way of making a point, as long as everyone is laughing. But I don't think that is always the case. The rhetoric easily deteriorates into our side against the evil other side, with the other side undeserving of respect.

It's understandable that some prominent people have taken umbrage at the remarks by our Sheriff, Clarence Dupnik. If those people were to drop their me against evil shtick, they wouldn't have anything left. I hope most people will agree with the words of the President last night.