It can get mighty hot in July, even here in the mountains of Central Pennsylvania. This most recent hot spell pales in comparison, though, to a couple blistering hot summers eight decades ago. Eighty years ago on July 9 and 10, 1936 the thermometer hit 98 and 99 degrees, the peak of a heat wave that lasted nearly three weeks in the Northeast United States. During that spell we went two full weeks without a drop of rain. The highest temperature every recorded in Pennsylvania, 111 degrees, was reached in Phoenixville, just north of Philadelphia, on those same days.
Altoona's 98 and 99 degree readings on those two dates was the second hottest two day spell on record. August 3 and 4, 1930 were 100 and 102, August 4th being the second hottest day ever in Altoona. (For you trivia hounds, the hottest temperature recorded was 103 on July 22, 2011.) Only a dozen days have ever gotten to 99 or higher in Altoona and seven were during the Thirties. The most extreme heat nationwide occurred two Julys before the '36 hot spell on July 21, 1934 when 43 states recorded temperatures over 90 degrees. (That was the first time that had happened since widespread temperature statistics had begun being recorded.) When it hit 103 in Carlisle that day many likely thought it couldn't get any hotter. Four days later it reached 104, yet that wasn't the hottest place in the state. Tamaqua took the prize at 108 that afternoon.
That was during one of the worst hot and dry spells of the Dust Bowl and the heat and drought spread across a large portion of the country. The disaster and its accompanying dust storms were at their worst in Texas and Oklahoma. While not so horrid as the Southern Plains, the heat and lack of rain cursed a much larger area, ultimately bankrupting farmers from one end of the country to the other. "Extreme" and "Severe" drought covered an area from Central Texas north to the Southern Plains of Canada, west to Central Washington and Oregon and east to the Western New York in July 1934. Our own Juniata River watershed was included in the severe drought area.
Already in the economic nightmare of the Great Depression, the catastrophic drought, heat and resulting windstorms produced perhaps the worst environmental disaster in the nation's history. Such large scale dryness perpetuates and magnifies the existing heat and drought conditions. Higher temperatures increase water evaporation from soils and places that are already relatively dry are pushed over the edge. Seeds sometimes never even sprout and native grasses struggle to hang on. Despite great improvements in soil conservation efforts, some climate scientists fear that global warming could set these same developments into motion here in the 2010s.
Drought puts greater pressure on groundwater extractions for irrigation, even in places like Pennsylvania. Concerns over the long-term depletion of the massive Ogallala Aquifer underneath much of the Great Plains remains a source of anxiety for farmers and geologists in that part of the country. Yet groundwater pressures exist even here in the Keystone State during particularly dry summers like this one, especially as growing populations and suburban sprawl gobble up an ever-increasing portion of those water resources.
Learn more about that decade in two award winning books:
The Worst Hard Time by Timothy Egan and The Dust Bowl by Donald Worster.
Summer 2016 was the warmest summer season since world-wide records began in 1880. The hottest three month spell ever recorded was this June, July and August 2016. The last eleven months have been the hottest on record and August tied July for the warmest month ever worldwide (the average of 6,300 weather stations across the globe). August was the 11th consecutive month the monthly global temperature record was broken. Amidst this sobering climatic news is the anniversary of one of the coldest summers since weather data compilation began. The "Year Without a Summer," 1816, wasn't just chilly, it was so extreme that widespread crop failures cursed all of North America and large regions across Europe.
A half foot of snow fell throughout Upstate New York and towns in New England endured 18 inches during a bizarre snowstorm on June 6th and 7th. But it was the persistently frigid weather throughout the summer that most profoundly impacted people. The passage of two brutal cold fronts brought widespread killing frosts in early July and again in mid-August. (Remember this was long before even railroads existed, making it impossible to ship many foodstuffs from other parts of the country.) Crop failures were widespread not only in North America but much of Asia and Europe. The loss of a large portion of the rice crop in China resulted in catastrophic famine. Still recovering from the destruction and economic upheaval of the Napoleonic Wars, food riots broke out in France and the United Kingdom. A three year-long typhus epidemic began in famine-stricken Ireland, killing about 100,000.
The July 17, 1816 edition of the Brattleborough Reporter wrote that "no man living can furnish a parallel to this present season." The Vermont newspaper continued, "From every part of the United States, north of the Potomac, as well as from Canada, we have accounts of the remarkable coldness of the weather, and of vegetation retarded or destroyed by untimely frosts." Those that lived called 1816 "eighteen hundred and froze to death."
The primary cause of the disaster was the eruption of Mount Tambora in Indonesia. It blew massive amounts of volcanic material (estimated to be nearly 20 cubic miles of pyroclastic debris) into the atmosphere. Washington State's Mount Saint Helens, by contrast, produced only a quarter of a cubic mile of material during its 1980 eruption. The pre-eruption height of Tambora was over 14,000 feet; the caldera crater that was left was over 2,000 feet high. Much of that material became airborne and the finer dust and ash remained in the stratosphere for months, some for several years. This blocked sunlight and altered weather throughout the following year. The material that ended up in the stratosphere persisted, too, since it was above the altitude where rain could wash it back to the surface.
Eighteen-sixteen might seem like an interesting climatic oddity 200 years later, but we might also look at it as a cautionary tale. Sudden climatic change, no matter why it's happened, can cause disastrous environmental change with serious social and economic repercussions.
More on the long streak of record warmth can be found at NASA.
Eighty years is a drop in the proverbial bucket of geologic time. But it seems to be a long spell in human terms. Two very different winters, eighty years apart, might provide a cautionary tale and speak to the profound climatic changes which have occurred in just one human lifespan. The winters of 1936 and 2016 were as different as two winters can be, especially here in the Northeastern United States. This February was not just the warmest worldwide February on record; it was a staggering 2.43 degrees Fahrenheit above the average (based on the period from 1951-1980). It marked the tenth straight month that the monthly record for the planet was broken. Records date back to 1880.
Climatologists were taken back by the unprecedented margin of the record. Prior to these recent record-breaking temperatures, such records were typically broken by a few hundredths of a degree. (Keep in mind this is a worldwide average and even .05 degrees across the entire planet is notable.) Each of the last five months have been 1.85 degrees Fahrenheit or more above average. It was the 372nd consecutive month at or above average worldwide, dating back 31 years, when February 1985 was colder than normal. Last year was the warmest since records began being compiled. Fifteen of the sixteen warmest years on record have occurred since 2000. The sixteenth was in 1998.
Ironically, the announcement of the record by NASA, the National Oceanic and Atmospheric Administration (NOAA) and the Japanese Meteorological Agency coincided with the 80th anniversary of the Saint Patrick's Day Flood and the end of the infamous winter of 1936. The Saint Patrick's Day Flood of 1936 marked the end of a winter of record cold, heavy snow and overwhelming spring floods. When comparing 1936 to 2016, it would seem that we were in two different climatic zones. Despite the blizzard in mid-winter, many parts of Pennsylvania experienced one of the least snowy winters on record. Williamsport missed every notable snow and had less than six inches this winter. Philadelphia set a record for most winter days over both 50 (48 days) and 60 degrees (23 days). Such mild and snowless weather is typically reserved for places at the latitude of North Carolina.
Beyond the impact of global warming, those two contrasting years were different for another reason. A strong El Niño has added an exclamation point to an already record-breaking streak here in 2016. El Niños are uncommonly warm ocean waters in the equatorial Pacific and are made stronger by a warming planet. El Niños come and go periodically and generate warmer temperatures by themselves. This also speaks to several important points connected with unusual temperatures. Weather changes often and a single unusual day or week does not constitute climate change. But longer term change can be an indication of bigger things amiss. This is why scientists are especially concerned about both this string of extraordinarily warm months and long spell of very warm years.
For more visit National Oceanic and Atmospheric Administration's State of the Climate Report.
The January 2016 snowstorm that shattered snowfall records across the southern tier of Pennsylvania left the traditionally snowy northern tier of the state untouched. What is it that powers such potent storms and how can such sharp differences in snowfall amounts occur? Such unusual weather doesn't just fascinate meteorologists, but intrigues all of us. The scientific details of such weather can be complicated but the general concepts are not so difficult to understand. Snow happens when the atmosphere is below freezing from the highest levels down to the surface. Drops of freezing rain, pellets of sleet and hailstones, by contrast, go through warm air at some point and spend part of their life as liquid water.
In places like Pennsylvania, that have moderate climates and are below 3,000 feet in elevation, widespread heavy snowfalls are unusual. That's because our coldest air comes from Canada and is moisture starved since it originates on dry land. The relatively small bands of "lake-effect" snow happen because the Great Lakes provide moisture that Canada can't. Lake-effect snow peters out by the time it gets to Blair County and rarely does such a storm bring more than three inches of snow to us. Our juiciest wintertime air masses come from the Gulf of Mexico, but they often produce rain rather than snow. Gulf air is not just moist, but warm as well.
Most readers can recall two other similar storms, one in March 1993 and the other in January 1996. Truly monstrous storms like these need both cold air from Canada and moist air from the Gulf of Mexico. This happens when the northern and southern branches of the Jet Stream (the strongest upper winds moving weather systems about) meet. Meteorologists call this confluence and it doesn't happen to this extreme all that often in these parts. Violent weather of all kinds is enhanced by large differences in atmospheric pressure and this, too, happened with our recent storm. High pressure parked over Canada not only provided the cold air we needed, it also brought the pressure contrasts that big storms thrive upon. When the pressure difference is large between the low pressure of the storm and the high to the north, it enables more moist Atlantic air to be sucked into the system from the east.
It was also this high pressure that helped cause the unusually abrupt differences in snowfall at the edge of the storm. The dry air and position of the blocking high pressure system meant that the juicy air in the storm ended suddenly, making for nearly snowless weather only fifty or so miles from areas of very heavy snowfall. These crazy differences over short distances could be seen here in Blair County and were typical of what happened throughout central Pennsylvania. Areas of Morrison Cove surpassed 30 inches, Altoona got less than 20 and Bellwood got only 11. Folks at the northern end of the county got less than ten inches, Bellefonte had only four and there was nothing more than flurries in Williamsport. Whether you welcomed or cursed the storm, it certainly proved to be a rare and interesting meteorological experience.
In a world full of conflict, it is notable when nearly 200 countries can agree, at least in principle, on a matter of great importance to the entire planet. The accords reached in the recent United Nations climate summit in Paris finally brought widespread recognition of the problem of global climate change and agreement that action must be taken to address it. However, some are frustrated that many important changes were postponed until 2030.
Basking in the unusual warmth of our late fall and early winter, it is easy for us to discount the problems caused by global warming. Looking at the bigger global picture, though, many throughout the world are not so pleased. About 25,000 islands are spread throughout the Pacific and Indian Oceans and nearly 2.5 million people live there. A large portion of them are currently endangered by rising sea levels. This is not something that might happen in the next few decades; it's happening now. And it's not just a handful of little islands with a few hundred people.
The Republic of Kiribati, so concerned about rising sea level, has endorsed a plan to buy land in Fiji with the intention of relocating its 103,000 people from 32 atolls and one island. A large portion of the 400,000 people that inhabit the Maldives' 1,100 islands are similarly endangered, their president at the time being one of the people that spoke of nations' plights at the Copenhagen Climate Summit in 2009. The overwhelming portion of Micronesia's 107,000 people live within a few feet of sea level on the island nation's 607 islands. Their ambassador to the United Nations, Masao Nakayama, has passionately appealed to the world about their plight. "Even a small rise of one meter...would already have a devastating effect," he said. "If it gets to a meter or higher, the islands would get uninhabitable."
In just these three island nations it seems likely that about a half million people will be permanently dislocated. Those three countries alone are home to about the same number of people as Blair and its surrounding counties. It begs the question of how we would feel if these six counties were slowly inundated with water over the next quarter century. Where would we go? How would we pay for our relocation? How would our new home handle the flood of refugees? These are questions being asked today in many parts of the world and it's much harder to ignore them when we realize that these are real people, not abstract statistics. Some of the dangers in other places are more subtle but every bit as serious, for the poorest places in the world impacted by both rising sea level and climate change are the least equipped to deal with the changes.
Nations like our own will likely find the resources to deal with many of the changes. Even here, though, those costs will be significant. Replacing water in the Southwest when winter snow packs shrink and keeping flood waters out of low lying coastal communities from higher sea levels may cost trillions. But for many of us, it will be only inconvenience and expense. For many others, it will be much more.
The New York Times did an extensive series of articles about the summit.
Mother Nature News highlighted endangered pacific island nations.
I began watching the weather forecast with my mother before I even went to school. A stay-at-home mom in the days when most moms were, Mom enjoyed watching Dr. Charles Hosler's weather forecast from Penn State on public television's "Farm, Home and Garden" when we finally got our five channel cable television in the early sixties. His first telecasts were actually on WFBG (now WTAJ) Television in 1957. Hosler was in the early stages of a distinguished career and was prompted to start such a show when he was overwhelmed by the ineptitude of "weathermen" in those early days of television. Those early years were in black and white and even predated satellite images.
Weather forecasting in general and Penn State's show in particular have come a long way since those days. When longtime co-host Paul Knight retired last week, another era in the storied history of the show came to an end. It was Knight that was asked to co-host the show in its present format, Weather World, in 1983 with fellow Penn State Meteorologist Fred Gadomski. During my days as a high school Earth Science, we often watched videos of the previous night's Weather World in my class, for the show's fifteen minute format and educational elements made it an exceptional teaching tool.
The only university-based television production of its kind in the country, I have always believed that the show's teaching value went beyond the classroom, though. For Weather World and its predecessor shows also attempted to bring atmospheric science education to the masses. Even regular viewers that did not have science backgrounds became well-versed in what made the weather what it was and found interest in the research and special topics discussed on the show. Knight, Gadomski and the other outstanding Penn State meteorologists have bought into Hosler's original goals of educating while raising the bar of expectations for television weather forecasts.
"It has been our goal from the beginning to both inform and educate our viewers and the fifteen format has allowed us to do so," Knight affirmed. Knight also reinforced the idea that the quality of local news forecasts have come to value that instructional element that helps everyone better understand what makes the weather machine work. "Our colleagues at the commercial stations have much less air-time to do so, but a number of them in this region do their best to educate as well," Knight notes. Having perhaps the most highly respected meteorology academic programs in the nation, Penn State meteorologists are spread across the country and have risen to the top of the weather industry in government, the private sector and on television. So this "inform and educate" philosophy has spread across not only our region but across the country in no small part because of Penn State's influence.
Coincidentally, one of Knight's vivid forecasting memories celebrated its thirtieth anniversary the same week he retired. Knight recalled that he and the crew successfully predicted the outbreak of tornadoes that swept across eastern Ohio and north central Pennsylvania the day before they devastated nearby Parker Dam State Park. Not surprisingly, Weather World didn't just predict the outbreak but explained why it happened. Weather World airs on PBS and PCN every weekday evening at 5:30 and 5:45 p.m. and is replayed on PBS World at 6:00 and 6:45 p.m.
Even if you spent most of June 2015 in a cave, it was difficult to miss that it was a very wet month. Blair County's resident meteorologist Joe Murgo recently noted that it was the second wettest June on record. The wettest was in 1972 when we were inundated with more than fifteen inches of rain, nearly half of that from Hurricane Agnes. While riverside communities like Johnstown and Harrisburg expect problems during such events, even places at the headwaters of the Susquehanna and Ohio rivers were swamped. It was one of the worst floods in Altoona's history.
Agnes became a tropical depression near the Yucatan Peninsula and went northward through the Gulf of Mexico. Had it stayed on land it would have just been another rain storm by the time it hit the Northeast. But it wandered back into the western Atlantic off the coast of South Carolina and intensified before turning westward into Pennsylvania. Parts of northeastern Pennsylvania were especially hard hit, part of Schuylkill County getting more than fifteen inches of rain, washing away a cemetery in the town of Forty Fort, dumping caskets and body parts in people's yards downstream.
While the remnants of Hurricane Bill brought some heavy rain in this second wettest June of all time, Bill was on dry land for several days before arriving in Pennsylvania. While it still brought a rainy day, Bill was not the reason we had such a wet June. What brought so much precipitation this June was the persistence of the rainy weather. Some parts of Blair County got rain on twenty of June's thirty days. (An average June has six rainy days.) Yet surprisingly, flooding was not as widespread this June as one might have expected for a record-breaking month.
Rain in Pennsylvania typically comes from two sources in the summer, frontal lifting and thermal convection. Frontal lifting (more often associated with steady, widespread rain) occurs when warm air is forced up colder, denser air. Moisture in that air condenses when the air cools as it is lifted into cold air higher up in the atmosphere. Thermal convection brings the pop-up storms we experience when air is very warm and moisture laden (usually when we are under the influence of air from the sultry Gulf of Mexico).
This June had a bit of both of these and we didn't go long between the rainy spells brought about by either rain-producing mechanism. Both kinds of rain storms can bring flooding and that flooding can be as different as the rain storms that make them. The typical heavy showers and thunderstorms of summer usually cause flash flooding, while long periods of steady rain bring larger scale river flooding. Both types of floods are made worse by paving and building over large expanses of land that previously absorbed rain water. While most county conservation districts require and oversee larger scale storm water management efforts, much can be done collectively by homeowners and other small scale property owners.
E-mail firstname.lastname@example.org or call 814-696-0877 x 113 for more information on their programs.
The winter of 2015 was a very cold one for Central Pennsylvania. When a rare warm day finally occurred in late March, it was the first day above sixty degrees for many of us since the last week of November. That was 151 days. They don't usually keep records for meteorological persistence, but this one ranks up there with some of our most persistently cold winters in half a century. Not since 1971 has the first sixty degree day of the year come this late. Not even the record breaking winters of 1977 and 1978 could match this year.
An ungodly cold winter, we had only two days warmer than normal from January 9 to March 13, 1978 and nine nights hit zero or below. (Many years we have no below zero nights at all.) An aspiring young bike racer at Penn State, I was eager to get in some early season training miles and the frigid winter and cold early spring frustrated me greatly. Yet even that frigid year, the first warm day of early spring arrived almost a week earlier than it did this year.
Like 1978, we had seven below zero nights in the Altoona area this winter. The below zero night of March 6th was an all-time record low for the entire month many places in the Northeastern United States. February was the coldest on record for much of north central Pennsylvania and northeastern Ohio. Records date back to 1895. As so often happens in North America, though, record cold in the east often coincides with record warmth in the west. Nearly all of California and Arizona, most of Nevada, southwestern Idaho and northwestern Oregon experienced their hottest February on record.
An upper air ridge persisted for much of the winter, pulling unusually warm air from the tropics into the western states. These same high level winds turned from the north and sucked frigid air into the eastern states from the arctic. Often, this air came across the meteorological north pole (in what is commonly called cross-polar flow). This is further testimony that weather is complicated and ever-changing. Whether the planet is warming as quickly as is feared or not, it's important to remember that the weather can vary a great deal from day to day and year to year. This is why we look at worldwide trends and keep track of long-term records in individual places.
After a record-breaking winter like this one in Pennsylvania, there is a temptation to discount global warming. After all, climate change deniers will argue, when it's this cold, the planet cannot possibly be warming. But one region of the world in one single season, is only one small piece of a very large and ever-expanding puzzle. World-wide average temperatures help us to better understand the big picture, rather than a tiny, short-lived piece like a single winter in one corner of a single country. Long-time records of particular places remain important, too, because recognizing those averages and extremes helps us, among other things, to better understand what plants, animals or pests can survive or thrive. Whatever extremes we must deal with, if they are changing profoundly over the long term, we would be well served to think about how we might deal with their consequences.
Rising sea level doesn't seem too important to those of us here in central Pennsylvania. Those closer to the ocean are a bit more concerned. When ice melts, water rises. No matter what you believe to be the cause of global warming, it's difficult to deny that the change is happening. Numbers don't lie. The ten warmest years on record globally have all occurred since 1998, the warmest three being 2014, 2005 and 2010.
The numbers are not just seen in rising temperatures. New York City's subway system is now twenty times more likely to flood than it was in the late nineteenth century, according to the conclusions of a study by the American Meteorological Society (AMS). Though the average annual increase might seem small, the cumulative rise makes a difference, especially during storms. "By raising the water level, sea level rise provides storms with a higher launching pad for storm surges," explains Climate Central's Andrew Freeman. Places like New York City are not just inconvenienced; it can result in damages and restoration costs that are staggering. Widespread subway flooding that was rare five decades ago happens every few years now. And it's not uncommon for a single storm to cause hundreds of millions in damage.
Though the Netherlands has lived with the ocean on its literal doorstep for centuries, much of the rest of the world has been presented with new and expensive challenges trying to keep the ocean at bay. "Today's coastal infrastructure is steadily losing ground due to relative sea level rise," said co-author of the AMS study, William Sweet, an oceanographer at the National Oceanic and Atmospheric Administration.
A recent report from the National Research Council also confirms the serious problems confronting the Atlantic and Gulf Coasts' barrier islands. Most of our popular beach communities set on these skinny islands. Running from Cape Cod to the tip of Florida and west to Texas, barrier islands are just what the name implies. They are relatively narrow islands (that are best described as over-gown sandbars) that set between the open ocean and the actual mainland. Much like the floodplains of large rivers, the constant erosional force of the water alters the shoreline every day.
The population of these coastal areas has grown rapidly in the last fifty years and, even though we should know better, we have built resorts, hotels, condos and a host of other tourism-related developments almost up to the shoreline. Protected naturally by a mound of sand called a back dune, these islands are sheltered from the worst stormy weather if we don't build in front of the protective dune. Most seaside communities have ignored the importance of that natural protection, cents overwhelming common sense. While inconvenient and often expensive, rising sea level presents some island nations with a much more serious problem. Two of the most endangered island systems, the Maldive Islands and the nation of Tuvalu are fighting for survival. Beyond the chronic flooding and accelerated erosion, salt water intrusion is ruining both their fresh ground water and their agricultural areas. Tuvala, New York and Ocean City, three very different places, share one notable similarity – an uncertain future.
The last part of July is statistically the hottest time of the year and we have seen what that can mean both here in Pennsylvania and across the continent in Southern California. In the midst of an overwhelming heat wave in the desert southwest this summer, we also marked the one hundredth anniversary of the highest official air temperature ever recorded on the planet. The thermometer hit 134 degrees Fahrenheit in the shade on July 10, 1913 at Death Valley, a record that still survives a century later.
The record was set at the appropriately-named Furnace Creek, two decades before Death Valley even became a National Monument. Like so many high temperature records, that hotter-than-blazes day was preceded by a hot night. The low during the night of July 9 and 10, 1913 was 93 degrees. This is true even here in Pennsylvania. The last time it went over 100 on my home weather station, July 22, 2011, the low the night before was only 82. Though those of us from the greener, wetter climate of Pennsylvania might find Death Valley a desolate place, it is one of the most unique places in America. The valley is nearly 300 feet below sea level, magnifying the very dry, frequently cloud-free and low latitude climate so common in southern California and Arizona. Many of us have experienced the influences of elevation when passing through snow on Cresson Mountain when it's raining in Altoona. This same principle makes Death Valley the most extraordinary of the blistering extremes of the desert southwest.
Beyond Death Valley, the region has suffered through some of the hottest weather ever this summer, June 2013 setting records far and wide in the entire Southwest. Las Vegas set its all-time record for June when the thermometer hit 117 on June 30th. Especially in the Southwest, this sort of hot and dry weather presents the perfect environment for fires and it has been a dreadful summer throughout much of the region. The death of 19 firefighters in Yarnell, Arizona on the same day Las Vegas set their temperature record was the tragic culmination of the persistent rash of fires. The danger presented by wildfires, in the Southwest especially, seems to have been exacerbated by two unrelated environmental issues. Regardless of whether you think it's been caused by man's contribution of greenhouse gasses or not, warming temperatures and longer droughts have made wildfire problems worse.
Related to that problem, High Country News reports that 45 million homes now set on what has become known as the wildland-urban interface, where the risk of wildfires damaging homes is greatest. This border, where the flammable rural lands meet the suburbs and exurbs, is only nine percent of the nation's land area. But the runaway suburbanization of America has profoundly changed where people live. Almost 40 percent of the housing units in America are now in these high risk areas. The Granite Mountain Hotshots were trying to save a 40 house subdivision built in just such a location. This is another in a long list of challenges confronting us, as we continue to build in places prone to natural hazards.
English poet William Cowper told us two centuries ago that "Variety is the very spice of life that gives it all its flavour." If we apply that premise to the weather, Pennsylvania is among some of the world's zestiest meteorological places. Beyond considerable seasonal variation, there is an amazing variability from place to place in the Commonwealth as well. It is not uncommon for Philadelphia and Bradford to have temperature differences approaching twenty degrees. Average annual snowfall is five times greater in the northwestern part of the state than in the southeast.
Differences in elevation contribute to this profound variability in Pennsylvania. A difference of over 2,500 feet from the lowest to highest elevations can understandably bring wildly different weather. Yet it is the variability from year to year that is sometimes most difficult to comprehend and explain. The anniversary of one of the world's most extreme rain events brings to mind one such example. In the midst of one of the worst regional droughts in the last half century, we commemorated the 70th anniversary of one of the world's most extreme rain events this past week. The Smethport/Port Allegheny Flood of 1947 took place on July 17 and 18, 1947. An almost incomprehensible thirty inches of rain fell in less than five hours in the town of Port Allegheny, not far from the New York border.
Three mechanisms can produce rain in these parts and all three showed up in McKean County on that fateful day post-World War II. When air is lifted, it is cooled and water vapor condenses on dust particles in the air. When that air is moist those clouds will have enough moisture in them to produced not just clouds, but rain-producing clouds. Warm, moist air being pumped northward from the Gulf of Mexico provided the moisture. A stationary front was hanging around the Pennsylvania/New York border and this provided an opportunity for something called "frontal lifting." This happens along fronts where cold and warm air meet. Since cold air is denser, the warmer air is lifted upward, cooling and producing clouds and rain in the process.
Since there was very warm, moist air also present, there was an excellent opportunity for lifting of the air by thermal convection. In simpler English, that means that heating of the earth's surface allows air to rise and produce clouds and rain. McKean County is part of an old deeply eroded plateau and the topography of the region is rough. This provides the possibility of something called "orographic lifting." That is to say that air can be lifted up and over mountains, again allowing cooling and cloud and rain formation. One final element turned it into a record-setting deluge. As thunderstorms formed, they did something called "training" along the stationary front. Training occurs when the rainstorms run or "train" along the front. When a front passes through, the associated rain passes through with it, but when the front doesn't move much the rain can stay in one place a very long time.
So though July can be very dry, like 2012, the great flood of 1947 reminds us that it can be mighty wet, too.
Applied Weather Associates did an excellent report on the 1947 storm.
Anytime it snows it reminds us what a curious and complicated thing snow can be. And as with so many other things, a little bit of knowledge about snow can be a bad thing. When political pundits start making long-term predictions about climate trends based on a month of snowy weather, I think it's time for the cooler and wiser heads to step in. A good place to start is by understanding the things that influence snow.
A great place to look at these factors is right here in Pennsylvania. The range of snowfall in the Commonwealth is astounding, Philadelphia averaging only 20 inches while the snow belt in the lee of Lake Erie gets 100 inches annually. While we here in Central Pennsylvania seldom get a big snow before Christmas, the Northwest can be pounded by lake-effect snow that gathers moisture from the still-liquid lakes starting as early as mid-October.
Elevation's impact on snowfall totals can be seen right here in Blair and Cambria Counties. Average snowfall in the valleys near Altoona's elevation is about 40 inches per year, while places just west of us on the Allegheny Plateau in Cambria County get nearly 80. This talk about averages, however, ignores the fact that many winters depart from the norm a great deal. In light of this year's above average snowfall, it is fun to look at the biggest snowfalls we've ever had. The total snowpack, drifting and road conditions can warp our perception of how much snow we really have.
It turns out that in the 75 years from 1926 to 2000, Altoona has officially had only 45 snow events of ten inches or more. (I defined a snowstorm as any one, two or three day period with ten inches or more of snow accumulation.) Five times (1941, 1964, 1970, 1971, 1972) we had two such storms in one winter. Twice (1978 and 1994) we had three in the same snow season. That means more than half our winters have not had a double digit storm.
Our recent twenty inch storm was only the ninth storm of such magnitude since 1925. Only one was officially over two feet, the March 6-7 blizzard of 1962 that brought us 26 inches. Our second biggest was perhaps our most unlikely, a 23 inch fiasco on April 27-29, 1928. One of the worst weeks of snow in our local weather annals came during my senior year in college when 35 inches fell from three separate storms January 14-21, 1978. The seventies, in fact, had more double digit snowstorms of any decade on record.
As you might have expected, well over half our biggest storms were in January and February. March, however, nearly matches the colder months. As a battleground of winter and spring weather, March can provide everything you need for a potent storm - abundant moisture from the Gulf and the Atlantic, coupled with the last gasp of cold winter air. That does not necessarily mean that our snowy winter will become a snowy March. After all, the one thing we can say for sure about snow is that we don't know what to expect.
Climate and Weather
Understanding Pennsylvania Snow
The Flood of 1947
The Hottest Day
Rising Sea Level
Cold Winters & Big Pictures
Rainy Junes: 1972 & 2015
Penn State's Weather World
The Paris Accord
2016's Peculiar Snowstorm
Two Different Winters: 1936 & 2016
The Year Without A Summer
Pennsylvania's Hottest Summer