After the Deluge, July 15

Late Sunday afternoon my place got three and a quarter inches of rain. This picture was taken just two hours after the most intense rainfall rate I've ever seen. The pot-of-gold is a couple of miles away in Bob Maddox's driveway.

Chartiers Hill

Last month I was visiting in Pennsylvania, and my cousin was kind enough to show me the way to Chartiers Hill. I must have been on that road as a kid. Back then, on hot humid summer evenings, after the supper dishes were done our family would go for a ride in the station wagon. We would cruise around until sunset, up, down and around the hills and hollows near the Mon River, trying to catch a cool breeze. At least one of those explorations would have gone through Chartiers Hill. At that time I didn't realize that two decades before then Chartiers Hill had been struck by one of the most powerful, long-lived and deadly tornadoes on record in Pennsylvania.

The scene above is viewed from near the top of the hill, standing in what had been the school playground. The left half of the scene faces north while the right half faces northeast. The path of the June 23, 1944 storm was from northwest to southeast, so the tornado was traveling from left to right in the scene above. The area in the foreground escaped. But along the lower part of the main road, from the curve to above where the young man is riding an ATV, it was total destruction. The company store (general store) stood there. Rows of houses extended off of that part of the main road, one row on the left and two rows on the right.

Chartiers Hill is a bluff of land standing between hollows that are more than 200 feet deep. Castile Hollow lies off to the left of the picture. Ahead as well as off to the right is the valley of the South Fork of Ten Mile Creek. The South Fork curves 90 degrees around Chartiers Hill, just as the road ahead in the picture curves sharply to the left. The road drops down to Castile Hollow, then turns right to meet the South Fork. Aerial surveys just after the storm showed a nearly continuous 80-mile path extending between the West Virginia and the Maryland panhandles. Naturally, emphasis was on the individual segments of structural damage and deaths. On this segment the starting point for death and destruction was Castile Hollow.

I grew up in Hiller, about 7 or 8 miles northeast of Chartiers Hill. At the end of my earlier post, there is a link to recollections from 1944 about how debris lifted by the tornado fell in my old neighborhood. I commented that it was only after reading about that I appreciated what must have been the large-supercell nature of the storm. Though the storm was moving from northwest to southeast, the fuel for the storm, the warm moist air, was entering from the southwest, traveling from lower left to upper right in the picture above.

Emerald Street branches diagonally off of the main road, toward the southeast, roughly parallel to the path of the tornado. There is no outlet because the street ends before it reaches the steep hill down to the South Fork. Before the tornado there were about 16 houses on this street, eight on each side.

The house farthest away, near the end of Emerald Street, is the size of the pre-tornado houses. That house was relatively lucky. The tornado only took it's roof. Perhaps the proximity and orientation of the South Fork valley gave some respite at the very end from the intensity of the tornado. The original version of the house next door was where Eileen Sullenbarger grew up. I was fortunate to meet and talk with Eileen's son, Art. In 1994, on the 50th anniversary of the tornado, Eileen's story of survival was reported in the Washington, Pa, Observer-Reporter. Looking at today's house, the outline of the original house can be seen in the wing that extends toward the street. From the other side, you can identify by the style of concrete block the part of the basement wall that stayed in place when Eileen's house was torn from its foundation.

When it comes to whether a storm might manage to produce a tornado, one of the key environmental parameters is high humidity. Southwest Pennsylvania and the adjacent parts of West Virginia and Maryland are often spared in the springtime; the dewpoint never quite gets high enough. But the summer can be a different story. There's less of a need in summer to transport moisture rapidly north from the Gulf of Mexico; often the high humidity has been in place for several days. Fortunately, having all of the other ingredients come together, as they did in 1944, is relatively rare. Today's Storm Prediction Center does a great job of anticipating the possibilities. Let's hope the threats continue to be rare.

November through March

Safe to say that we won't be getting any more rain in Tucson this month. That means that the total at the Tucson airport for these five winter months, November through March, will be 3.48 inches, which is about 4.5 times the total for the same period last year, and just a little below the average for those five months over the last 60 years. I had about an inch more than the airport. That plus the fact that we did not have a late freeze is making the plants look much better this year. In my previous post, I had suggested that there were two winters, 1974-1975 and 1999-2000, that would serve as good analogues for this past winter in Tucson. In fact this past winter's rainfall was much better than those earlier second-year-of-La-Niña-in-a-row winters.

Since chatter about La Niña has ceased, it might come as a surprise to learn that those conditions are still in place, although weakening. March will probably be close to the end for La Niña, so the ocean temperature anomaly will have averaged about -0.75 C over the five-month winter period. For much of the rest of the country, the last two winters, both La Niñas, have been about as far apart as winters can get. So much for a repeat of last winter.

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.