Monsoon Relief

Returning to our Littleton, Colorado, farm today, I found that early monsoon rains have revitalized the landscape.  Indeed, over the past few days, heavy rains have moved northward across the Front Range, bringing much needed rain to the tinder-dry mountain forests and welcome moisture to the urban corridor.  While some flooding, mudslides and sinkholes developed, the storms have reduced the wildfire risk to some degree and, so far, have not ignited any new fires.

The annual monsoon rains of the American Southwest result from a southerly flow that brings in moisture from both the Gulf of California and the Gulf of Mexico.  The engine for this wind pattern is high pressure over the Southern Plains that generally develops by early July and persists through much of August; winds move clockwise around that atmospheric ridge, sweeping moisture northward along its western rim.  Showers and thunderstorms are usually confined to the Desert Southwest and Four Corners Region early in the season, reaching the Colorado Front Range by late July and August.  Thanks to the dome of drought that has plagued the south-central and southeastern U.S. for several weeks, the Monsoon got an early start and Colorado, caught in its own drought after a mild, snow-starved winter and a warm, dry spring, has received an early and very welcome gift.

Unfortunately, the monsoon flow will be shut off for the rest of this week as high pressure builds in from the West, bringing another round of hot, dry weather to the State and blocking the southerly stream of moisture.  When the Southwest Monsoon might generate more relief is anyone's guess but its typical arrival date is still a week or two away.

A Stubborn Ridge

The dome of high pressure that has parked itself over the Heartland for the past two weeks shows no sign of abating.  Rather than drifting off to the east, it has backed into the Southern Plains; unfortunately, those of us in the lower Missouri and Mississippi Valleys remain within its grip.

Beneath this atmospheric ridge, the air is sinking and drying out, producing excessive heat and retarding cloud formation.  Storm systems are shunted along its outer rim, exacerbating drought within the dome while fueling violent weather at its periphery (as we saw in the Upper Midwest and Mid-Atlantic region last week).  On the positive side, this stubborn ridge may ignite the Monoon Season across the American Southwest, pulling in moisture from both the Gulf of California and the Gulf of Mexico as clockwise winds stream along its western rim.

Those of us caught within its boundaries can expect another week of hot, dry weather, with afternoon highs near 100 degrees F.  Beyond prolonging our personal discomfort, this dome of drought is taking a toll on forests and crop fields across the Heartland, stressing natural ecosystems and posing a serious challenge for farmers and ranchers.  Unless relief arrives in the form of a potent Canadian front, it may take a hurricane to dislodge this ridge.

Desert Heat in the Midwest

Records are falling across the American Midwest this week as the first major heat wave of the season invades our region.  High pressure over the Southern Plains, combined with a high pressure dome over the Southeast, has ushered in the hot, dry air; afternoon highs should top 100 degrees F in most areas.

In part, the extreme heat reflects the dryness of the air, as Gulf of Mexico moisture is kept at bay by the blocking high across the Southeast.  Dry air is more dense than humid air and is thus capable of reaching higher temperatures.  Indeed, winds are from the west-southwest and it feels more like Phoenix than Miami across the Heartland.

This heat wave will be slow to break as cloudless skies permit the intense sunshine to heat up the roofs and roadways in our towns and cities; this heat radiates into the air overnight, keeping the morning low well above average.  In addition, it will likely take a strong cold front to displace this high pressure ridge and none are forecast over the coming week.  For now, we'll confine our outdoor activities to the early morning and evening hours, hide from the afternoon sun and dream of October.

Dubious Debby

After forming in the eastern Gulf of Mexico over the past 48 hours, Tropical Storm Debby is going nowhere fast.  Parked west of Tampa and south of Panama City, she seems to be teasing the National Hurricane Center with her uncertain intentions.

The question is whether a weak cold front dropping through the Southeast will pick up the storm and shunt it northeastward, across Florida, or whether Debby will drift westward, gathering strength over the warm waters of the Gulf before impacting Texas.  Other computer models suggest that the storm might exit to the north, crossing Louisiana, Alabama or Mississippi.

Currently raking the western edge of Florida with heavy rains and high surf, Debby is a lopsided Tropical Storm, its center of circulation west of the rain bands.  This reflects the presence of upper level winds, crossing the storm from southwest to northeast and keeping the thunderstorms along its eastern and northern rim.  Should the storm remain in the Gulf and drift westward, it may escape this wind shear, allowing a closed system to develop (with thunderstorm bands circling the center of low pressure).  Such architecture is essential to the formation of hurricanes and it remains possible that this tropical storm could become Hurricane Debby in the western Gulf.  Time will tell but, for now, she has the forecasters baffled.

Denver's Monster Storm

Late yesterday afternoon, a line of thunderstorms developed across northeastern Colorado, a typical occurrence in early summer. One of these was a tornadic monster that stretched from Castle Rock to the area just east of Denver International Airport.

While such storms usually move rapidly off to the east, this storm, unaffected by steering winds, sat in place throughout the evening, dropping torrential rain, producing large hail and spawning several tornados. In fact, by 10 PM, the massive thunderstorm began to drift southwest and then northwest, eventually stretching along the foothills west of Denver. Though radiation cooling generally causes Front Range storms to dissipate after sunset, this one continued to intensify and, by midnight, was illuminating the sky with incessant cloud-to-cloud and cloud-to-ground lightening.

Its final push across Metro Denver triggered severe thunderstorm and flash flood warnings from the National Weather Service. Here in Littleton, we received heavy rain and an inch or two of pea-sized hail; some areas reported golf ball sized hail and the region south and east of Denver, impacted twice by the same storm, received up to five inches of rain. Exiting the Front Range by 2 AM, the massive storm had put a significant dent in our drought and had produced the most spectacular light show that I have ever witnessed. Of course, for those impacted by large hail, flooding and tornados, the memories of this unusual weather event will be less positive.

Front Range Drought

Following a lackluster snow season and spotty rain throughout the spring, Colorado's Front Range is tinder dry and wildfires have become a significant problem, especially for residents of foothill communities. Over the past two days, the fire risk has increased dramatically as hot, dry, southeast winds have raked the area; while the humidity has increased a bit with this upsloping wind flow, little precipitation has developed and "dry thunderstorms" threaten to ignite more fires.

Along the urban corridor, the winds are producing a welcome "wind-chill," making the mid afternoon heat feel less intense than it might on a calm day. A stroll along the South Platte revealed water levels lower than I have encountered in many years; with much of its flow diverted for irrigation and water supply, the shallow river attests to the ongoing drought in much of the State. On the positive side, the sluggish stream attracted a variety of birds from the parched fields and woodlands, including yellow warblers, belted kingfishers, spotted sandpipers, killdeer, swallows, great blue herons and mother ducks (mallards and wood ducks) with their broods in tow.

There is some hope that the gusty, upsloping winds will produce showers and thunderstorms overnight but, even if they do, a widespread, soaking rain is not expected. As often occurs along the Front Range, the precipitation will be spotty in nature, with some areas enjoying a cloudburst and others left in the windblown dust. In reality, a significant break from our ongoing drought will probably not occur until the late summer Monsoon pumps moisture up from the Desert Southwest. Let's hope that annual relief arrives early, rescuing the Front Range from what appears to be a destructive wildfire season.

High Plains Thunderstorms

Our trip from Missouri to Colorado today was almost entirely under sunny skies, with afternoon temperatures near 90 degrees F. The one, significant exception was an imposing wall of dark clouds, lightening and intense rain along the Kansas-Colorado border. Though our journey through the storms was brief and, thankfully, unaccompanied by large hail, the thunderstorms were training over Kit Carson County, including the city of Burlington, triggering a flash flood warning from the National Weather Service.

Encounters with severe weather can be unsettling in any location but they are especially terrifying on the Plains or on open water. In these areas, one gets both a broad view of the storm's size and ferocity and plenty of time to observe the approaching monster, wondering what it might do to your vehicle or boat. In addition, if caught in an open landscape, one experiences a sense of hopelessness, finding no means to escape the looming threat.

While some make their living chasing and photographing storms on the Great Plains, the rest of us are well advised to check weather forecasts prior to our journey and be willing to stop at a safe location if unexpected storms develop. Today's storms seemed to blow up before our eyes and we had no recourse but to slow down and hope for the best; fortunately, the major storms were well away from the highway as we passed through and we had only to contend with torrential rain and gusty wind. Once we were through this swath of fury, the clouds dispersed and we crossed dry, sun-drenched terrain all the way to Denver.

A Breath of Spring

After weeks of summerlike heat, cool, Canadian air has dropped into the Heartland. The jet stream is ushering in this fresh breath of spring, dipping east of the Rockies, across the Southern Plains and then northeastward above the Mississippi and Ohio Valleys.

Here in mid Missouri, we awoke to clear, dry air and a temperature of 48 degrees F, twenty degrees cooler than recent overnight lows. Our high is forecast to peak near 70 degrees this afternoon, a pleasant change from the oppressive air that enveloped our region through most of May. Indeed, on this first calendar day of summer, we will enjoy our first spring-like day in many weeks.

Of course, nature pays no heed to the human calendar and her unpredictable style demands our attention. While we are grateful for her refreshing gift today, the next round of heat and humidity sits on our doorstep and a long, hot summer may soon take hold. Hopefully, she'll appease us with occasional waves of cool, northern air until the invigorating chill of autumn invades the Midwest.

An Early July

On this Memorial Day weekend, July has made an early appearance in the Heartland. With afternoon highs in the 90s (F) and overnight lows in the 70s, it feels like mid summer; were it not for the plentiful moisture still in the soil, the vegetation would be wilting in the intense heat, but, in this case, the verdant face of May persists.

This early heat wave is courtesy of a high pressure ridge over the southeastern U.S.; beneath this dome, air is sinking and heating up, retarding cloud formation, while, along its outer edge, thunderstorms will ignite across the Upper Midwest. One crop of storms, off the coast of South Carolina, has developed into Tropical Storm Beryl, which will move WSW along the rim of the dome over the next 24 hours, bringing heavy, much-needed rain to southern Georgia and northern Florida.

The high pressure ridge should stay in place through the holiday weekend and will then drift to the east, allowing cooler and drier air to filter in from the northwest. Until then, we'll endure heat and humidity more typical of July and the Southeastern Coast will receive an early taste of the hurricane season (which officially begins on June 1). Here's hoping that a premature summer ushers in an early autumn!

From Tropical Heat to Upslope Chill

After wilting in central Missouri over the last two days, enveloped in tropical heat and humidity, I arrived along the Colorado Front Range late this afternoon under low clouds and scattered showers; the temperature was 45 degrees F. These two weather extremes were produced by the same Pacific storm system; ahead of the front, muggy air was pumped into the Midwest from the Gulf of Mexico while, behind it, a plume of moisture was swept westward through the cool air. Since this flow is counterclockwise around the storm's central low, the moisture arrived from the northeast, the classic upslope direction for Metro Denver. Cooling and condensing as it rose across the western landscape, the plume dumped its cargo of moisture across northeastern Colorado.

Over the past 24 hours, Metro Denver received a half inch of rain in most areas while higher elevations to the west and south collected .75 inch or more, a welcome respite from the recent drought. Checking the foothills as I arrived from the east, it was obvious that the upslope shroud was beginning to lift though jet traffic was still landing to the north and likely offering a bumpy descent through the showers and virga. Our Littleton farm clearly benefited from the moisture, having taken on the untidy overgrowth that promises plenty of yard work this week.

As the system continues to move eastward, the muggy air and thunderstorms will be confined to the Eastern Seaboard and high pressure will reclaim the Heartland, bestowing warmth and sunshine for the days ahead. Here along the Front Range, the wind will shift to the south-southwest, a downsloping direction for Metro Denver; we expect sunshine, mild temperatures and a chance to dry out.

Southern Soup

Hot, humid air has been flowing into Missouri for the past two days and will continue for at least another 24 hours. This muggy, southern soup is courtesy of both a broad high pressure ridge over the eastern half of the U.S. and a slowly approaching Pacific front that should ignite thunderstorms by tomorrow afternoon.

Riding this river of subtropical air, the first wave of common nighthawks appeared in our skies yesterday evening. Among the last migrants of spring, they are more cautious than swallows and swifts, waiting until plenty of insects are reliably available for their late-day feasts. They'll be with us until late summer and, perhaps, as late as early October, departing for the tropics before autumn's chill annihilates their prey.

Meanwhile, here in the Midwest, this summer-like heat in early May is not welcomed by those of us who prefer cool weather. Fortunately, a milder and drier air mass is expected to move in by early next week, bringing spring conditions back to the Heartland. By then, I'll be heading to our Colorado farm, guaranteed to escape the heat and humidity that common nighthawks relish.

Caught on the Track

For the past 24 hours, a stationary front has stretched from the Southern Plains to the Great Lakes, separating cool, drier air to its northwest from warm, humid air to its southeast. Bisecting Missouri from southwest to northeast, it passes across the Columbia area, bringing intermittent heavy rain and thunderstorms as pulses of atmospheric instability have moved along the front.

Since the front is not connected to a potent storm system, tornadoes are unlikely but intense lightening, hail and periods of torrential rain have occurred and are expected to persist through the day. Of course, when these thunderstorms train along a stationary front, flooding often develops beneath their path and our creeks will soon be bank-full if the storm track does not bow northward or shift to the south and east.

On the positive side, the copious precipitation will nourish the verdant tide of spring, triggering an explosion of insects for the warbler wave and our returning summer residents. With hot, humid weather expected for the coming week, this steady dose of rain will also fuel the seasonal intensity of plant growth, insuring a healthy start for our woodlands and plenty of yardwork for suburbanites.

Crossing the Storm

After stewing in the warm sector of our latest Pacific storm for 36 hours, enduring periods of heavy rain, intense thunderstorms and interludes of steamy sunshine, we left Columbia this morning, bound for our Littleton, Colorado farm. Having checked the Weather Channel before our departure, we noted that the storm system's upper level low was still centered over western Kansas and that its dry line, responsible for the wealth of tornadoes over the previous 24 hours, was about to reach Kansas City.

Fortunately, the severe weather was down in northeast Oklahoma and we left the balmy air of Missouri as we crossed through a modest band of rain showers and entered cooler, drier air in eastern Kansas. Sunny conditions persisted into central Kansas but once we reached the Smoky Hills Wind Farm, its massive turbines spinning in a strong south wind, a band of clouds appeared across the western horizon. We soon realized that the clouds represented the eastern wall of the storm's low pressure swirl; produced by uplift and rotating counterclockwise around the center of low pressure, the direction of cloud movement changed as we continued west along I-70. Moving northward in central Kansas, the clouds were coming from the west in western Kansas and were drifting southward in eastern Colorado. Finally, as we neared the Front Range, upslope showers developed as a northeast wind from the atmospheric swirl pushed humid air toward the Palmer Divide and Front Range foothills. Rising, cooling and condensing, this upslope flow produced snow showers above 7000 feet and sleety rain on the High Plains.

An eleven hour (800 mile) drive had taken us from balmy, 70 degree F air on the west edge of the storm system to chilly showers of rain and sleet on its western rim. En route, we crossed all of the storm's component air masses and directly witnessed the atmospheric swirl of its central low. What better way to appreciate the structure and power of these massive storm systems?

April Encore

April, last seen in central Missouri back in early March, has returned to the Heartland. Cool and showery weather, more typical for this time of year, has displaced the summer-like warmth that dominated the last few weeks. As I walked into a chilly east wind and misty air this morning, it was 47 degrees F; today's high should stay in the fifties and tonight's low is expected to dip into the thirties.

The culprit for this dose of reality is a potent upper level low, the same system that produced the Texas tornadoes and Front Range snow earlier this week. Now parked over the central Mississippi Valley, it is pulling down cool air from the Great Lakes region while also drawing moisture from the Gulf of Mexico and Atlantic Ocean. As a result, thunderstorms will rumple across the Deep South while the rest of the eastern U.S. will experience the seasonal invasion of chilly April showers.

After the exceptional heat of March, many in the Midwest and East likely anticipated an unbroken run through summer and may have packed away the sweaters and parkas. But the extended forecast suggests that April weather will hang on for at least another week, just in time for the Opening Day of baseball and the Masters Golf Tournament, cultural symbols of the American spring.

Urban Tornadoes

Most Americans over age 50 associate tornadoes with open country, posing a risk to cropfields, barns and small, rural communities. We long assumed that these spectacular storms could only develop over flat terrain and that the varied topography of cities would tear them apart.

However, in recent decades, as occurred yesterday in Dallas, we have witnessed an increasing impact of tornadoes on large, urban centers. Some surely see God's hand in this apparent turn of events, punishment for the decadence and sinful behavior of the urban elite; perhaps the storms are directed toward Planned Parenthood Centers or non-Christian communities.

In reality, this increased incidence of urban tornadoes reflects the same process that threatens the Florida panther and corrals prairie dogs into tiny plots across Metro Denver. Suburban sprawl and commercial development are eliminating vast tracts of open space, urban areas are merging with one another and natural habitat is rapidly disappearing. The tornadoes that once tore across prairie, forest and farmland are now cutting swaths of destruction through our ever-expanding cities. As a result, the cost imposed by these storms, both in terms of damage to structures and the loss of human life, will continue to rise.

Fooled by March

This may be April Fools Day but March did the fooling this year. April first is so thirty days ago!

Thanks to our exceptionally warm weather in late winter and early spring, April begins as many of its annual flowers have already come and gone. Here in central Missouri, it looks like May and feels like June. Were it not for the lack of summer birds, still waiting for their solar cue to come north, we'd have no April events to anticipate.

Whether or not winter will attempt a token return to the Heartland remains uncertain but our average last freeze is rapidly approaching. It appears that old man winter concentrated on the Eastern Hemisphere this year and that we might experience one of the longest frost-free periods on record, beginning back in February and, perhaps, lasting until October. Then again, the jet stream could shift and we might endure the coolest summer in recorded history; such possibilities fuel our interest in nature's fickle behavior and discourage complacency.

Double-Dip of Winter

Lest we forget it is still March, wintery weather lingers in the Pacific Northwest and, thanks to a Canadian front, has re-invaded the Great Lakes and Northeast. Cloudy skies, chilly rain and snow showers will dominate those areas for the next few days while, between the dips, summer warmth persists across the Heartland, from the Central Plains to the Gulf Coast.

Despite the proximity of winter's advance, current forecasts suggest that neither trough will affect the mild (if not hot) spring that is entrenched from the Southern Rockies to the Southeast. Rather, the high-riding jet stream is expected to remain in Canada and warm air will return to New England by the end of the week.

After almost two weeks of summer-like weather, many under the central ridge of high pressure are tempted to plant the tomatoes. Nevertheless, here in Missouri, the historical risk of frost runs through mid April and we may yet encounter winter's final gasp before the heat is here to stay.

More like March

After a week of summer-like weather across most of the U.S., cooler air has moved east of the Continental Divide. Nevertheless, sunny skies and minimal wind in Metro Denver sent me down to the South Platte Valley for a morning hike.

Not fooled by the recent mild conditions, buffleheads and common goldeneyes still joined the Canada geese, mallards, shovelers, gadwall and pied-billed grebes on the valley ponds and lakes. Other signs of March included the loud, seasonal calls and drumming of northern flickers and nest building by a pair of black-billed magpies; the latter couple took a break from their work to harass a red-tailed hawk that had perched in a nearby cottonwood.

Perhaps the most potent reminder that we are still in early spring is the forecast for snow flurries overnight. Indeed, March is the snowiest month along the Front Range urban corridor and, lest we get too anxious for an end to winter, we must remember that April snowfall ranks just behind that of March. Fortunately, such upslope snowstorms are interspersed with mild, sunny weather and, except for the damage to flower beds, spring snows are easy to take. There are truly no bad months for outdoor exploration along the Colorado Front Range.

Ground Turbulence

My regular trips between Missouri and Colorado are usually a bit tiring but today's journey was especially difficult. After leaving Columbia in a balmy haze this morning, I encountered a southwest wind in eastern Kansas which strengthened with every mile to the west, all the way to the Front Range. Though the skies were mostly sunny and I had neither supercells nor snow to complicate my travel, nine hours of bone-jarring turbulence was more than enough.

While the strong wind was my sole problem through eastern and central Kansas, dust plumes and tumbleweed armies posed additional distractions across the dry landscape of the High Plains. Fortunately, no trucks were overturned by the winds and few RV's ventured across the Great Plains today, a wise response to the high wind advisory. Though strong winds are common across this region, today's wind field is especially widespread and is posing a major fire threat from New Mexico and West Texas to Nebraska. Gusty winds along the Front Range have enveloped Denver in a pall of dust and a large wildfire is currently burning in northeast Colorado.

Today's strong winds are the product of a potent low over Wyoming (attached to a deep trough over the western U.S.) and a massive area of high pressure over the eastern States. Counterclockwise winds around the low are combining with clockwise winds at the edge of the high pressure dome, leading to a strong south-southwesterly flow over the Great Plains. The leading edge of the trough is forecast to cross the Rockies overnight and, here in Metro Denver, we'll experience cool, showery weather for the next few days. Meanwhile, as the front moves eastward, these strong winds will precede it, raking the Midwest and igniting thunderstorms as Gulf moisture enters the mix.

May in March

We awoke in Cincinnati this morning under clear skies and enveloped in balmy air; the temperature was 60 degrees F. By mid morning, as we prepared to return to Missouri, the leading edge of a storm system arrived with intense lightening, torrential rain and pea sized hail.

Taking the northern route through Indianapolis, we managed to dodge most of the severe weather, and continued west under puffy white clouds in a hazy, blue sky; stopping for gas in western Indiana, we stepped from our air-conditioned car into summer-like heat. All across the till plains, meadows were greening, barren fields shimmered with the purple of henbit and early fruit trees were in bloom. Canada geese were nesting along the farm ponds, killdeer raced along the shallow sloughs and mourning doves cuddled on the powerlines, swaying in a mild, south breeze.

After crossing another band of storms in eastern Missouri, we arrived in Columbia to find the magnolias and wild cherries in bloom and the community in full summer mode. Though only mid March, the foliage is typical of early April and the warm, humid air evokes the feel of May. Unless a few Canadian fronts invade the Heartland over the coming months, we'll be sick of summer by June.