Thursday, March 30, 2017

Birding on the Fly

When I go birding, I typically walk or drive slowly, stopping frequently to allow the birds to adjust to my presence.  When one takes along a grandson, however, the pace must be quicker, lest boredom overtake enthusiasm.  And when your "check engine" light comes on, one is not inclined to dally.

For both of those reasons, my visit to Eagle Bluffs Conservation Area was rather brief this morning and I covered the 12-mile, roundtrip drive in record time.  Nevertheless, we encountered an excellent variety of waterfowl and raptors on this cool, cloudy morning, including five bald eagles, a northern harrier, a Cooper's hawk, a kestrel and a red-tailed hawk.  A large flock of American white pelicans graced the floodplain refuge and, among the waterfowl, blue-winged teal, northern shovelers and American coot were especially abundant.  Both greater and lesser yellowlegs foraged on the mudflats while red-winged blackbirds, as usual, dominated the fields and marshes.

While our visit to the fabulous refuge was far too short, the effort is always rewarded, whether by the diversity of its wildlife or the serenity of its landscape.  Since I will soon return to Colorado, this brief trip to the Missouri River floodplain will be my last for a while but it, like hundreds of others, will long be remembered.

Sunday, March 26, 2017

Weather for Ducks

Having returned to Missouri, I made plans to visit Eagle Bluffs Conservation Area southwest of Columbia, my favorite birding location in the State.  Fortunately, a fellow birdwatcher was available; unfortunately, the weather was not as cooperative, offering a low, gray overcast, light intermittent drizzle and chilly air.

As is often the case, such ugly conditions were especially attractive to waterfowl and a large variety of ducks filled the shallow pools and flooded fields of the Missouri River floodplain.  Mallards were most abundant, joined by sizable flocks of northern shovelers, blue-winged and green-winged teal, gadwall and American coot.  A small flock of lesser scaup were also encountered and a large number of lesser golden plovers foraged on the mudflats and sodden fields.  Other sightings included greater yellowlegs, pectoral sandpipers, killdeer, belted kingfishers, a few double-crested cormorants, a lone red-breasted merganser, a couple pied-billed grebes and two American white pelicans; three bald eagles (two on their nests) and two red-tailed hawks patrolled the refuge.

Known for its chilly, sloppy weather in the American Heartland, March is often more appealing to ducks than it is to humans.  But, for those of us who don't mind getting mud on our tires and boots, there is no better time to observe the spring tide of migrant waterfowl.

Friday, March 24, 2017

The Anti-Environment President

Though he calls himself an environmentalist, President Trump has demonstrated a disregard for the health of our environment with almost every major decision he has made to date.  Today, his Administration added to that dismal record, clearing the way for the Keystone Pipeline at a time when an oil glut has suppressed the price of crude and when countries across the globe are making a concerted effort to diminish their use of fossil fuels; the pipeline, if completed, will transport low-quality crude from the decimated Tar Sands region of Canada to refineries along the U.S. Gulf Coast.

Of course, both Trump and his Chief of the EPA are climate change deniers and have vowed to withdraw U.S. support for the Paris climate accord.  Meanwhile, hoping to redirect funds to the bloated Defense Department budget, the President and his Administration have proposed cutting funds to various environmental programs, including projects designed to augment the welfare of the Great Lakes and the Chesapeake Bay.  Support for clean, renewable sources of energy will be a low priority for an Administration promising to "bring back the coal industry."

Worst of all, Trump wants to "role back" environmental regulations, willing to accept potential damage to natural ecosystems in order to boost corporate profits.  One would think that the health of our environment, which is directly tied to the welfare of our species, would not be subject to politics.  But, when ignorance and mysticism are pervasive and counter the validity of science, Conservative Republicans retain a base large enough to support their anti-environment agenda.

Thursday, March 23, 2017

The End is Near

For more than a month, a ridge of high pressure has been sitting over the Four Corners Region and the Southern High Plains, deflecting Pacific storms and their cold fronts to the north.  As a result, the Front Range urban corridor has enjoyed warm, dry, sunny weather, with afternoon highs often reaching the seventies and low eighties (F).

This afternoon, gusty southwest winds have again brought mild, sunny weather to the area but the end is near.  By 2PM, clouds were building to the west and the Continental Divide began to disappear within an upslope haze of snow.  A broad atmospheric trough, which currently encompasses most of the Pacific Northwest and Intermountain West, is moving eastward, producing a surface low along its leading edge.

By this evening, that cold front will move across the Front Range urban corridor and our winds will shift from the northeast.  This upslope flow will initially produce rain showers but, as the atmosphere cools, wet snow is expected by early morning.  Fortunately, Colorado will be enveloped by the trough for the coming week and cool, showery weather should become the rule, bringing some relief from our recent drought.  Sometimes, The End is a good thing!

Tuesday, March 21, 2017

Battle of the Goldfinches

As I have reported throughout the winter, a flock of lesser goldfinches stayed on our Littleton farm, declining to head for the Desert Southwest as had been their long-established tradition.  During those months, which were generally mild and relatively snowless, these beautiful freeloaders had the thistle (niger) feeder to themselves, disturbed only by an occasional, brief visit from one of our abundant house finches.

Today, for the first time, a small flock of American goldfinches arrived to take advantage of the handouts.  Larger and bulkier than their lesser cousins (and especially intimidating due to the molting plumage of the males), these new opportunists were initially more aggressive, displacing the lesser goldfinches from the feeder; this pattern continued until the male lessers seemed to have had enough (after all, this had been their exclusive domain for the past several months).  Taking charge, they refused to be dislodged and the American goldfinches soon decided to give up the battle, feeding with the lessers in peaceful coexistence.

Such confrontations are common in nature, fueling natural selection through competition and "the survival of the fittest."  Sometimes, however, when resources are plentiful, cooperation makes more sense.  Humans should take note!

Monday, March 20, 2017

Memories of Jim & Rudy

Now and then, when I'm wandering through a nature preserve, I catch sight of something startling or unusual and I am reminded of NatureScene, a program produced by South Carolina Educational TV.  Initially broadcast to viewers in that State in 1978, highlighting the natural diversity of South Carolina, the popular program was syndicated nationally by 1985 and the adventures of host Jim Welch and naturalist Rudy Mancke took on an international reach.

Pleasant to watch, the shows followed Jim and Rudy as they wandered through a wide variety of habitats, from wilderness to urban parks, backed by a mellow soundtrack.  Their explorations would suddenly be interrupted by Rudy as he spotted a unique plant or animal and explained its features or behavior to both Jim and the viewing audience.  As a budding naturalist, I thoroughly enjoyed those episodes back in the eighties and have since learned that the broadcasts continued until 2003.

This morning, while birding at South Platte Park, my Jim and Rudy moment was provided by an osprey, the first of the season, suddenly entering the airspace above Eaglewatch Lake.  My thanks to Jim, Rudy and the producers of NatureScene for their lasting inspiration; check out their fine work on or YouTube!

Saturday, March 18, 2017

Warfare trumps Human Care

The Trump Administration rolled out its first budget proposal this week, indicating its intention to significantly increase the bloated Defense Budget; this at a time when the U.S. already spends more on defense than the next seven countries combined.  Determined to keep their promise to protect America, the money will go toward jet fighters, weapon systems, immigration curtailment and, of course, The Wall.

To balance this increase, Trump and his cohorts propose cutting funds to a wide range of social support systems, many of which service the population that put him in office; these include Planned Parenthood, mental health programs, Public Broadcasting, legal services for the poor, international aid, biomedical research, environmental protection, climate change abatement, job retraining programs and a host of community-based service projects.  Of course, the proposed Republican Healthcare Bill will save money as well, eliminating coverage for 24 million individuals over the next few years (according to the Congressional Budget Office).

There is little if any evidence that increased Defense spending will make us safer.  On the other hand, Trump's hostile relationship with immigrants and with the leaders of many foreign countries may serve to fuel the risk of terrorism or outright warfare.  One wonders why Trump and his Administration would place so much emphasis on defending our country from foreign threats while degrading human rights, social welfare and American culture from within.

Friday, March 17, 2017

First Summer Resident

In the lingo of Ornithology, a summer resident is a bird that breeds in your home region but leaves for warmer latitudes or lower elevations during the colder months of the year.  Generally speaking, the summer resident arrives in spring, nests and raises its young and then departs in late summer or autumn for their winter range.

Here along the Colorado Front Range (and, indeed, in much of the country) tree swallows are among the first summer residents to arrive, often by mid March.  Yesterday, while birding at South Platte Park, I encountered 13 of these agile birds, snaring insects above Redtail Lake.  Since they nest in cavities, these small but aggressive insectivores compete with bluebirds, Prothonotary warblers and other species for those nest sites and, since they often out-compete bluebirds for man-made nest boxes, they are not always welcomed by some members of the birding community.

Then again, all swallow species consume a prodigious number of nuisance insects and anyone who lives near ponds or lakes is sure to appreciate their presence.  After nesting and raising their young, tree swallows depart for the south before an autumn cold snap wipes out their prey; unlike most swallows, which winter in Central or South America, tree swallows are satisfied to stay along the Gulf Coast and thus get a head start for the spring migration.

Thursday, March 16, 2017

Glorious Weather spells Trouble

To date, March as been sunny, dry and exceptionally warm along the Colorado Front Range.  While periods of mild weather are not unusual here (during any season of the year), March and April typically bring most of our annual moisture, dumped on the urban corridor by upslope snowstorms.  If this glorious weather persists, it will increase the risk of wildfire across the region and prompt increased water usage in suburban and agricultural areas.

Of course, the water supply for Metro Denver and other Front Range cities is provided primarily by snowmelt west of the Continental Divide and from river systems that rise among the high peaks of the Front Range; fortunately, the mountain snowpack has been decent this year.  On the other hand, demand for that water has increased in concert with the rampant growth of the region's population and we cannot afford to use that precious liquid to maintain our parks, lawns, golf courses and lush suburban landscapes.

We can hope for a change in the weather pattern, bringing upslope precipitation to the Front Range; indeed, in some years, April is snowier than March.  Over the long run, we can certainly plant native shrubs and grasses that thrive in a semiarid climate and thus reduce the need for artificial irrigation.  We may also be bailed out by an early and stormy Southwest Monsoon.  But, if this sunny, dry weather persists, trouble is certain to follow.

Wednesday, March 15, 2017

Apricots in Bloom

The apricot trees on out Littleton farm are in bloom this week, attracting large numbers of honeybees.  Among the earliest fruit trees to bloom in the spring, they rarely produce fruit on our property since heavy frosts and sub-freezing nights are common here in March and April.  Nevertheless, they are festooned with numerous pink-white flowers, offering nectar for the bees.

Native to Armenia, apricot trees were cultivated across the Persian Empire and were later taken to many areas of the globe;  Spanish explorers brought them to California, where most of the apricot production now occurs in the United States (Washington and Utah are also large producers).  Like peaches, this "stone fruit" will only grow in areas that have winter seasons and are thus planted in Temperate latitudes.  While they do best in sunny areas with well-drained soil, apricot trees do not tolerate excessive heat.

Here along the Colorado Front Range, their late winter beauty is a welcome sight.  If our warm weather persists, we may even get apricots this year; since I'm not fond of their taste, I'll leave them for the wildlife.

Monday, March 13, 2017

Frisky Juncos

A large number of dark-eyed juncos winter on our Littleton, Colorado, farm, including members of the slate-gray, Oregon and gray-headed races.  Hanging out with house finches, black-capped chickadees, bushtits and, this year, lesser goldfinches, the juncos are relatively inconspicuous through most of the winter, feeding beneath shrubs and thickets.  At times they will join the other birds in our feeding area, searching for seed that has fallen (or was thrown) on the ground.

Over the past week, our visiting juncos have become highly conspicuous, the males singing from trees or chasing prospective mates, their outer white tail feathers flashing as they zig-zag across the clearings.  Highly territorial on their nesting grounds, the male juncos seem to be preparing for that duty, chasing robins, flickers and other much larger birds from their local winter haunts.

Most will leave by early April, heading for coniferous forests in the Rockies or Canada.  Until then, I'll be entertained by their hormone-driven antics, wondering if their seasonal obsession will blind them to the raids of sharp-shinned hawks that regularly patrol our farm.

Sunday, March 12, 2017

Clear Creek of the Front Range

Clear Creek rises along the Continental Divide at Loveland Pass, just south of the Eisenhower Tunnel.  It then tumbles eastward, paralleling Interstate 70 until it is east of Idaho Springs; there it curves northward, away from the highway, and descends through its spectacular canyon in the Front Range foothills, flowing onto the Colorado Piedmont at Golden.  From this historic town, Clear Creek snakes eastward to join the South Platte River north of Denver.

The South Fork of  Clear Creek rises along Guanella Pass, which connects the Mt. Evans massif with the Continental Divide (to its west).  This tributary then descends northward, entering the main channel at Georgetown.  The West Fork of Clear Creek rises along the Continental Divide west of Berthoud Pass and tumbles to the ESE, entering the main channel just west of Dumont.  Fall River rises along the Continental Divide northeast of Berthoud Pass and drops to the southeast, merging with Clear Creek west of Idaho Springs.  Finally, the North Fork rises along the Continental Divide near James Peak and descends to the southeast, joining Clear Creek within its granite-walled canyon.

Local naturalists know Clear Creek for its whitewater rapids, which attract dippers, for its spectacular canyon through the foothills and especially for the rich aquatic ecosystems along upper sections of its major tributaries.  There, beaver ponds slow the drainage and thick stands of willow attract a host of subalpine birds and mammals.  White-tailed ptarmigan are especially common at Guanella Pass and moose may be encountered along upper stretches of the western and northern forks.  As many travelers know, bighorn sheep are often observed along the main valley of Clear Creek, especially on the north side of Interstate 70 near Dumont and Georgetown.

Saturday, March 11, 2017

EPA Chief ignores Climate Science

Scott Pruitt, the former Attorney General of oil-rich Oklahoma (see A Seismic Shift in Oklahoma), was confirmed as Chief of the Environmental Protection Agency in the Trump Administration.  Long a climate change denier, Mr. Pruitt declared again this week that human-produced carbon dioxide has not been convincingly linked to global warming.

Toeing the Party line, Pruitt sides with the fossil fuel industry, casting doubt on the overwhelming scientific evidence that links global warming with human activity; this from the man who is charged with protecting our environment!  Like many Conservative Republicans, dedicated more to corporate profits and religious zealotry than to human rights and the welfare of our natural environment, Mr. Pruitt likely abhors science which attacks his agenda with evidence-based facts.

When threatened by the power of science, one declares that our information is incomplete; the EPA Chief says that more studies are needed.  In other words, he'll delay any meaningful action as long as he remains in charge.  After all, 97% of climate scientists might be wrong!

Friday, March 10, 2017

Regal Visitors

While reading outside this morning, my attention was diverted by a loud, repetitive call that I initially presumed to be coming from a northern flicker.  To my surprise, the sound arose from an adult northern goshawk, perched in a large cottonwood tree.  Within a few minutes, it was joined by an immature goshawk and the large accipiters flew off soon thereafter.

Permanent residents of mature forests across Alaska, Canada, the Western Mountains, the Upper Great Lakes and Northern New England, northern goshawks are known for their rapid, powerful flight, their fierce engagement with prey or competitors and an aggressive defense of their nesting territory.  Prey includes large birds (grouse, woodpeckers, jays) and small mammals (especially rabbits, hares and squirrels); they may also kill other raptors that invade their home area.

During the colder months, some goshawks descend to intermountain valleys or adjacent lowlands; it is then that they may turn up across the High Plains and Upper Midwest.  Today's sightings were the first (at least for me) on our Littleton, Colorado, farm and their brief visit was both welcome and inspiring.

Thursday, March 9, 2017

Mistaken Identity

As one who has been an avid birder for more than 40 years, I have seen hundreds, if not thousands, of bald eagles, primarily during my years in Missouri.  It was thus easy for me to identify an immature bald eagle as it flapped its way across the South Platte Valley this morning.

Heading for a large, barren cottonwood, west of Eaglewatch Lake, the young eagle joined another large raptor that occupied one of the limbs.  At first, I assumed that the other predator was a light colored red-tailed hawk that has visited the refuge throughout the winter; after all, its wings and back were brown in color and its head was dull white.  Zeroing in with my binoculars, I was surprised to find that it was another bald eagle, different in appearance from any that I had seen over my birding career.

Approaching on the lakeside trail, I got a close look at what appeared to be a dull, sooty adult bald eagle, its white head speckled with gray blotches.  It was, in fact, likely a three or four year old bird, having molted from its dark immature plumage but not quite festooned with the regal coat of a breeding adult.  Once fledged, young bald eagles retain their dark feathers, broken by a variable pattern of white markings on the wings for at least two years; a gradual transition to the mature adult plumage occurs during the third and/or fourth year.  An eagle with a bright white head and tail and dark wings and torso is thus at least four years old; breeding capability coincides with achieving mature plumage.  While both juvenile and adult bald eagles have yellow feet, juveniles have a thick gray bill that takes on a bright yellow color as they mature.

Wednesday, March 8, 2017

Monte Vista NWR

Upon entering the San Luis Valley (see previous post), I headed for the Monte Vista National Wildlife Refuge, in the southwest portion of that vast basin.  It is there that most of the sandhill cranes tend to congregate, resting and feeding in fields throughout the day and spending the night in shallow lakes, safe from predators.

According to the current refuge brochure, 23,000 to 27,000 cranes stop in the valley during their spring and fall migrations; the peak spring migration now occurs in early March, earlier than in the past (perhaps another sign of global warming).  During my two hour visit, I'm sure I encountered at least 5,000 cranes; while most were quiet and stationary, the mobile and vocal flocks were especially inspiring, their bugling one of nature's most stirring sounds.  Canada geese were also abundant but ducks were rather limited since many of the pools remained frozen.  Other sightings included a small number of snow geese, a golden eagle, several rough-legged hawks and northern harriers, a few American kestrels and a modest number of mountain bluebirds.

The refuge is located approximately 6 miles south of Monte Vista on Highway 15.  An auto tour road begins at the refuge entrance but other viewing areas are located along the highway itself and on county roads east of Route 15.  According to the U.S. Fish & Wildlife Service, the majority of cranes that migrate through the San Luis Valley are greater sandhill cranes though Canadian and lesser subspecies may also be observed.  From 1975 until 1989, the Rocky Mountain sandhill cranes were used as foster parents in an effort to expand the range of whooping cranes in North America; unfortunately, that program was not successful.

Tuesday, March 7, 2017

Valley of the Cranes

Since researching my book, Colorado's Year, over 20 years ago, I have not returned to the San Luis Valley, in south-central Colorado.  Tomorrow's journey to that beautiful and fascinating landscape, the largest of the State's intermountain parks, will thus be a special treat.

Hemmed in by the Sangre de Cristo Range to the east and the San Juan and La Garita Mountains to the west, this high, sun-scorched basin is perhaps best known to birders as the spring staging area for Rocky Mountain sandhill cranes.  Having wintered in New Mexico, especially at and near the Bosque del Apache NWR, the cranes stop to rest and feed in the San Luis Valley on their way to breeding grounds in Idaho, Montana and Wyoming.  The Valley's unique hydrology and high water table offer ideal feeding areas for these majestic birds, which feast on tubers, waste grain and a variety of invertebrates.  Cranes begin to arrive in late February, peaking in number (usually more than 20,000) in mid-late March.

My route from Denver will take me along U.S. 285, climbing through the Front Range foothills and then dropping into South Park beyond Kenosha Pass.  After skirting the northern and western edges of that Park, the highway crosses Trout Creek Pass at the southern end of the Mosquito Range, entering the scenic, upper valley of the Arkansas River where the massive Collegiate Peaks of the Sawatch Range rise along its western edge.  Angling south to Poncha Springs, U.S. 285 then crosses Poncha Pass, entering the San Luis Valley.  More details tomorrow!

Addendum:  The brochure at Monte Vista NWR reports that the peak population of sandhill cranes in the San Luis Valley (ranging from 23-27,000) now occurs in early March.  Perhaps this shift is just another sign of global warming.

Sunday, March 5, 2017

Waterfowl Exodus in the Valley

It was partly cloudy and pleasantly mild down at South Platte Park this morning but strong southerly winds raked the valley for the third straight day.  Waterfowl numbers had declined dramatically, suggesting that migrants may have taken advantage of strong tail winds and headed north.

On the positive side, buffleheads and common goldeneyes were still present in significant numbers and the male goldeneyes were performing their unique courtship displays.  Other sightings of note included an immature bald eagle, two red-tailed hawks, two kestrels and a lone male greater scaup.  The strong winds kept most of the songbirds in the shrubs and thickets, making them less conspicuous; indeed, I identified the song sparrows and a spotted towhee by their voices alone.

Veteran birders know that strong winds hamper birdwatching more than any other weather condition (with the possible exception of heavy rain).  It is certainly disappointing to head out on a warm, sunny morning, only to discover that a steady or gusty wind is keeping the birds in their secluded haunts.  Today, it may have also encouraged many of our wintering waterfowl to depart for their northern breeding grounds.

Saturday, March 4, 2017

Inspiration from the Dead

Most sports fans are familiar with the scenario.  An athlete loses a relative or close friend and then goes on to deliver an exceptional performance, stating that he/she felt the presence and heard the encouragement of the deceased loved one.  Of course, the media takes advantage of these emotional events, soothing both athlete and fans with the conviction that the dead individual is "looking down" with pride.

No doubt, those who experience such a loss often imagine that they receive communication from their dead friend or relative.  After all, we are emotional creatures and many retain hope that death is but a temporary separation.  As a naturalist, I believe that death is the final event of life and reject the mysticism that feeds these public stories.  Nevertheless, I do accept the fact that the advice, encouragement and emotional support offered during one's life has a lasting impact on those who survive them.

In my mind, this is the lesson to be learned from such stories.  During our own life, it is important that we express our love, acknowledge our pride, extend our kindness, offer our support and share our philosophy with family and friends.  Those gifts live on and will surface repeatedly after our death.

Friday, March 3, 2017

Lure of the West

Raised in the eastern suburbs of Cincinnati, I seemed to have a fascination with "the West" before I understood the function of a compass.  By the time I was 5 or 6, I had noticed castle-like buildings on the prominent ridge west of the Mill Creek Valley; in later years, I learned that one was a water tower and the other a retirement home.  Nevertheless, when my paternal grandparents eventually moved to the west side of town, I relished the lengthy excursions (probably an hour or less) to their new home; the fact that we sometimes stopped to ride horses at a roadside amusement park only added to the illusion that they lived in the exotic West.

Since my family always vacationed either at Lake Erie or in Florida and since high school field trips took us to history-laden cities of the East, the West remained a land of mystery, revealed only in nature documentaries, in films about the Wild West or on the colorful pages of calendars.  I would not cross the Mississippi until I attended a friend's wedding in St. Louis, in 1973, and would not see the Mountain West until my wife and I interviewed for residency programs in 1975.  It was this latter trip, which included a circuit through the Desert Southwest and Pacific Northwest, that cemented my attraction to the West.

Now, having lived in Colorado (at least part time) since 1982, I realize that the West begins with the High Plains; every city and landscape east of that high, dry corridor belongs to the East, a region I associate with my youth.  To me, despite its many spectacular ecosystems, the East is defined by greenery, humidity, history and tradition.  The West, on the other hand, is thin air, arid landscapes, lofty peaks and adventure.  My soul resides in the West.

Thursday, March 2, 2017

Denying Complexity

Anyone with even a modest science education would agree that the Universe is a complex place.  At least 13.7 billion years old, it contains billions of galaxies, each containing billions of stars, many if not most of which possess their own solar systems.  Our home planet is amazingly complex, composed of complex ecosystems that harbor a vast array of complex organisms.

We have just begun to understand the biochemistry of our own bodies, which are sustained by complex organ systems that carry out complex functions and are subject to complex diseases.  Our tremendously complex brains orchestrate a wide range of complex behaviors and dictate the very nature of our being.

Ironically, it is the human brain, the most complex structure in the animal kingdom, that leads many members of our species to deny complexity itself.  Our imagination has led to mysticism which offers simplistic answers to the mysteries of life and simplistic solutions to the problems faced by our society.  One need only look at the actions and platitudes of our new President to understand how the tendency to deny complexity can lead to rash decisions and produce far ranging consequences.  We cannot solve the problems of human civilization by denying that they exist or by waving the magic wand of executive orders.  Ignorance is no excuse and details matter; life is complex.

Wednesday, March 1, 2017

Denver's Snow Season

Those who have never spent much time along the Colorado Front Range often imagine that the region is snowbound for at least six months of the year.  But, while it may snow in Metro Denver during ten months of the year (July and August are generally the exceptions), the city enjoys mild, sunny weather most of the time, even during the winter season.

In fact, most of the snow along the Front Range urban corridor falls in March, April and November (in that order).  Since the Continental Divide "wrings out" moisture arriving from the Pacific Ocean, snowfall east of the mountains is primarily the product of Gulf of Mexico moisture, pulled northward and westward across the Great Plains.  As storm systems move eastward, counterclockwise winds around the central zone of low pressure sweep the moisture-laden air toward the Front Range, causing it to rise and cool; depending on the regional air temperature, the "upslope precipitation" falls as rain or snow.  Denver generally gets its heaviest upslope snowstorms when the surface low moves eastward along the Colorado-New Mexico line.

The upslope snowstorms of March, April and, yes, early May bring most of the annual snowfall (which averages 55 inches) to Metro Denver.  Fortunately, the intense spring sun usually melts the snow within a day or two and provides warm interludes between the storms.  After a mild, dry winter, many of us who live along the Front Range hope that spring storms bring plenty of moisture this year (even if the heavy, wet snow flattens the tulips).