Western Heat Wave

Intense heat is beginning to develop across the Desert Southwest and will spread northward through the Great Basin and Central Valley of California; before it's over, the Pacific Northwest will also be enveloped in the swath of hot air.

The culprit is an atmospheric ridge, a northward bowing of the jet stream along the outer rim of a high pressure dome.  Within the ridge (beneath the dome), sinking air heats up and dries out and cloud formation is impaired; Santa Ana winds may also develop in Southern California.  Triple-digit heat is forecast for much of the region, with upper 90s (F) expected in Oregon and Washington.  Meteorologists warn that the high pressure ridge will remain in place through the upcoming weekend.

As one might expect, the Western heat wave is tied (meteorologically) to the Texas floods.  East of the ridge, the jet stream dips southward and this trough has spawned an upper level low over central Texas.  Counterclockwise winds around the low are combining with clockwise winds around a high pressure dome over the Southeast, pulling copious Gulf moisture across East Texas, Louisiana and the lower Mississippi Valley.  Once this atmospheric pattern shifts eastward, the flooding rains in Texas will cease and the Western heat will abate.

Brazos River Flooding

The Brazos River forms on the Llano Estacado at the junction of its Salt and Double Mountain Forks, northwest of Rule, Texas; it then flows northeastward to Seymour before angling southeast toward the Gulf of Mexico.  En route to the Gulf, the river passes through three major reservoirs: Possum Kingdom Lake, Lake Granbury and Lake Whitney; it also flows through Waco, passes west of College Station and flows west of Houston before emptying into the Gulf of Mexico at Freeport, Texas.

While the Brazos itself is 840 miles long, its watershed stretches back to eastern New Mexico; from its most distant tributary to its mouth, the River's watershed is 1280 miles in length, making it the 11th longest stream in the United States.  Over the past few weeks, heavy rainfall across the Brazos watershed has led to severe flooding, especially below the above mentioned reservoirs.  Not designed for flood control, these lakes must be partly drained as they fill in order to prevent catastrophic dam collapse.

As of this morning, the Brazos crested at 54.6 feet in Richmond, Texas (southwest of Houston), shattering a Century-old record by almost 4.5 feet; unfortunately, more rain is forecast across the watershed in the coming days.  To date, at least 6 individuals have been killed by the flooding and 31 Texas Counties have been declared disaster areas.  See also Texas: Land of Drought & Flood.

Mammatus Clouds

As a line of thunderstorms approached Columbia this evening, our daughter called our attention to mammatus clouds above the city.  Indeed, a broad area of dipping lobes was observed overhead, the product of sinking air beneath the advancing cummulonimbus clouds.

Often associated with severe thunderstorms, mammatus clouds (named for their breast-like shape) have long been rumored to predict the development of tornadoes.  However, though their development indicates a potent updraft within the thunderstorm, mammatus clouds are actually most commonly associated with weakening storms.  Nevertheless, they do indicate the presence of wind shear, ice crystals and potent temperature gradients and weather-savvy pilots know to avoid these cloud formations.

For those of us on the ground, mammatus clouds offer a beautiful sight, especially when illuminated by a rising or setting sun; my thanks to Ally for the heads-up!  Fortunately (or unfortunately) we should have more opportunities to observe these clouds this weekend as a potent storm system moves in from the west.

A Formal Sendoff

Preparing to leave for Missouri this morning, I heard the distinctive call of an olive-sided flycatcher in the "backyard" of our Littleton, Colorado, farm.  Sure enough, the large-headed silhouette of that summer mountain resident occupied the end of a dead limb; he would intermittently dart out to snare a flying insect before returning to the same perch.  Though formally known as the olive-sided flycatcher, I have long thought he should be called the "tuxedo flycatcher" since his greenish-brown flanks part to reveal a vertical white band on his chest and abdomen.

Passing through the urban corridor on his way to the mountains, this insectivore will spend the summer near forest clearings or along the alpine timberline where he and his mate will aggressively defend their nest (usually placed in a conifer) from all intruders.  Olive-sided flycatchers breed from Alaska to eastern Canada and southward through the Western Mountains and higher stretches of the Appalachians; come September, they will head for wintering grounds in Central and South America.

As for ourselves, we left the farm by early afternoon and enjoyed sunny, mild weather as far east as central Kansas.  There, however, we encountered severe thunderstorms and stopped for the night in Hays, where tornado sirens sent us to the first floor hallway; fortunately, we escaped the brunt of the storms, receiving torrential rain and intense lightening.  Indeed, as I write this post, a spectacular light display continues to our east, promising more stormy weather when we reach Missouri.

Birding in Bad Weather

Since we are leaving on our California road trip tomorrow, I decided to get in one more visit to South Platte Park.  While recent visits to the preserve occurred on warm, sunny days, this morning promised a different experience; low clouds, chilly air and a steady northeast breeze greeted me at the parking lot.

Despite these conditions (and, indeed, because of them), birding was excellent at the floodplain refuge.  Violent-green swallows were especially abundant, strafing the lakes and the woodlands; other sightings of note included 55 yellow-rumped warblers, 17 yellow warblers, 6 yellow-breasted chats, 4 western tanagers, a few chipping sparrows and a lone great horned owl that stared at me from a lakeside tree.  In all, my two-mile walk turned up 33 species, better than my counts on the warm, sunny days.

A gray overcast produces lighting that mimics dawn and dusk, when many species tend to be most active.  In addition, the chilly air invigorates birds and mammals alike, stoking the drive to move and to feed.  As a consequence, birding is often most productive on days that are less appealing to birders; today's visit to South Platte Park reinforced that fact.

Deluge in Houston

The ongoing deluge in Houston, Texas, is the product of a stalled cold front in East Texas and a "blocking high" over the eastern U.S.  The latter dome of high pressure has caused the cold front to become stationary and, at the same time, is funneling a plume of Gulf moisture into the area.  In the Northern Hemisphere, winds flow clockwise around high pressure domes and, in this case, are sweeping across the Gulf of Mexico and into Metro Houston; there, the cold front lifts the moisture-laden air, producing copious precipitation.

In northwest Houston, more than 15 inches of rain have fallen, 5 inches more than the previous record for the entire month of April.  As one might expect, severe flooding is widespread, snarling traffic, damaging structures and threatening lives.  As I write this post, the dome and its moisture plume are slowly shifting eastward and rain is beginning to dissipate in the city.

Indeed, the western edge of the high pressure dome is now entering Louisiana and Gulf moisture is streaming northward along the cold front.  Here in central Missouri, the band of heavy rain and its imbedded thunderstorms are nearing Columbia and should arrive by early evening; two days of rain are forecast before the dome and the front move on to the east.

Dust Storms & Wildfires

It was mild and sunny along the Front Range urban corridor this morning but a dense band of clouds obscured the Continental Divide to our west.  Arriving just after noon, this cold front unleashed strong winds, gusting to 50 mph.

In many areas across Metro Denver, plumes of dust were generated by the winds, a common development in this semiarid region; quarries, construction sites and plowed fields often provide most of the particulates.  The winds themselves were the product of high pressure across the Pacific Northwest and low pressure over the Southern Plains (currently centered over southeastern Colorado); as the front pushed across the city, intense winds plummeted from the Front Range and scoured the Piedmont, dropping temperatures from the mid 60s F to the upper forties.

Far to our southeast, wildfires are burning across Oklahoma, aggravated by dry vegetation, air temperatures in the mid 80s F and potent winds ahead of the same cold front.  Since the atmosphere over the Great Plains is "moisture starved," little precipitation is expected with this Pacific storm system until it moves farther east, tapping into moisture from the Great Lakes, Gulf of Mexico and Atlantic Ocean.  A mild upslope behind the front may bring light showers to the Front Range this evening but there will be little relief across the Southern Plains where the wildfire risk is extreme.

Morning Sunshine, Afternoon Snow

Following thunderstorms last evening, we awoke to bright sunshine in Metro Denver this morning.  Radio broadcasters, responding to a forecast of rain and snow showers and presumably looking out their small studio windows, scoffed at the predictions of local meteorologists.

Had their window offered a broader view, however, they might have been less dubious.  While sunshine bathed the city, the peaks of the Continental Divide had disappeared within a dense band of clouds that extended eastward across the northern horizon.  By noon, the front was closing in on Denver but the warm sunshine had sent many locals to parks and outdoor cafes for their lunch.  But within another hour, the cold front swept through the Metro area, unleashing cold northerly winds and scattered snow showers.

As I write this post, the storm is centered over southern Nebraska, too far north for a classic upslope snowstorm in Denver; nevertheless, periods of snow are expected to persist through the evening hours.  As the storm moves farther east, igniting severe thunderstorms across the Great Plains and Midwest, our winds will shift from the northwest, obliterating the upslope flow and clearing the skies by morning.  Weather is all about wind direction in this part of the country.

Changing Seasons

While the calendar and waxing daylight indicate that we have just passed from winter into spring, the weather suggests otherwise.  Following two warm days, with afternoon highs in the 70s (F), a cold front approached last evening, igniting thunderstorms in central Missouri just before 11 PM.

Behind the front, temperatures have cooled dramatically; today, the afternoon high is forecast to be in the forties.  Though we escaped the snow that fell in a swath from Colorado to Ontario, we can expect a gray overcast with scattered showers and gusty winds as the storm pushes off to the northeast.  From a weather point of view, we have gone from late spring to late winter.

Of course, such episodes are not unusual in the course of a Midwestern spring.  A restless jet stream keeps weather patterns unsettled and the higher sun fuels powerful storms, especially as we move into April.  This rapid cool off will be followed by a less abrupt but steady warm up; tomorrow's high is expected to reach the sixties.  Then we wait for the next Pacific storm.

A Promise Seldom Kept

After a week of mild, sunny weather and a single episode of heavy rain, color has returned to the landscape of central Missouri.  The grays and browns of winter are giving way to greening lawns and flowering plants.  Among the early spring bloomers are red maples, wild cherries, forsythias and several species of magnolia; the flowers of periwinkle, crocuses, daffodils and hyacinths adorn the flower beds and, much to the chagrin of lawn masters, the first crop of dandelions glow from every patch of grass.

This burst of spring seems to promise that winter has retreated to the north, not to return until the waning daylight of November, and that our path to the balmy days of May will be a steady, carefree climb.  Time to get out the gardening tools and mothball the winter coats!

Of course, nature makes no such promise; she is fickle and erratic, especially in March and April.  The conviction that spring weather is here to stay is a human fabrication, the product of hope and denial; while acknowledging the April snowstorms in our past, we promise ourselves that this year will be different.  Such promises are seldom kept; after all, we are powerless when it comes to weather.

Prelude to Storms

As the storm system that brought rain and mountain snows to California dips southeastward, a deep atmospheric trough and upper level low are developing across the Western U.S.  Ahead of this system, warm, moist air is moving northward from the Gulf of Mexico, priming the Southern Plains and lower Mississippi Valley for thunderstorms and flooding rains.

Here in Missouri, we expect an afternoon high of 70 degrees F under cloudy skies.  Thunderstorms are forecast to arrive overnight though severe weather will likely remain to our south; indeed, a tornado watch has been posted for much of Texas and States to its north and east.

In addition to the severe weather, copious rainfall is expected in the south-central U.S. over the next few days as the upper level low stalls over Texas, directing a plume of Gulf moisture and imbedded thunderstorms across the region.  Up to a foot of rain is forecast for Louisiana and Arkansas before the system breaks down and moves off to the east.  Flood season is certainly progressing with a vengeance.

The Damp Chill of March

Here in the Midwest, the crisp, dry air of autumn is welcome after a long, hot summer and we take the frigid blasts of winter in stride, relishing the beautiful, snowy landscapes that they often produce.  But the damp chill of March, contrasting with periods of mild, spring weather, is perhaps the least appealing weather of the year.

Children of the Tropics, we humans love warm, sunny weather and welcome the rains of late spring and summer.  And we adapt well to invasions of cold, dry air, layering on clothes or retreating to our heated shelters.  But the cold rain and icy mist of early spring cut to the bone, discouraging outdoor activity.

Of course, it's our impatience for the colors, fragrance and mild conditions of late spring that most taints our image of March and its fickle weather.  Those of us who enjoy the waterfowl migrations of early spring more easily tolerate this sloppy period with its flooded landscapes and swollen streams; others take solace in March Madness, an entertaining escape from the outdoor gloom.  Like it or not, the gauntlet of March has begun; time to get out those waterproof parkas and boots!

A February Chinook

Raked by gusty southwest winds yesterday afternoon, the Front Range urban corridor enjoyed temperatures in the low to mid seventies (F); in Denver, an 86 year-old record high for the date (71F) was exceeded by two degrees.  It felt as if we had skipped late winter and early spring and had moved on to May.

In truth, such "chinook" events are common in this region and can occur during any month of the year, often mimicking a seasonal change in the course of a day.  Produced by high pressure west of the Front Range and low pressure over the High Plains, the intense, often damaging winds spill across the mountains, descending 5000 feet or more to the Colorado Piedmont.  As the air mass plummets, it compresses, heats up and dries out, bringing warm temperatures and low dew points to the urban corridor.  Any snow that might still coat the Piedmont rapidly vanishes (hence the mistaken belief that chinook means "snow-eater" when it actually refers to Native American tribes of the Pacific Northwest, a region from which the wind-producing storms often originate).

Generally short lived, the chinook winds are usually followed by a brief period of calm, mild weather.  However, depending on the movement of the storm system that produced them, winds may suddenly shift from a different direction and, if an upslope flow develops, winter chill and snow may return to the Front Range cities, changing the season once again.

Tale of Two Domes

This morning, an atmospheric dome of high pressure, centered over Minnesota, was bringing cold, Canadian air to most of the central and eastern U.S.; another high pressure dome sat over the Desert Southwest.  Beneath the center of atmospheric domes, air sinks while, along their rims, air flows in a clockwise direction; the eastern dome lies within a broad atmospheric trough (a dip in the jet stream which allows cold air to plunge southward) while the southwestern dome is the heart of an atmospheric ridge (a northward curve in the jet which allows warm air to flow northward).

Northwesterly winds created by the cold, eastern dome were producing lake-effect snows in the Great Lakes region and sweeping frigid air as far south as the Mid-Atlantic States.  The western edge of this dome had backed up against the Colorado Front Range, creating dense morning fog as cold air settled above relatively warm, moist ground.

As the Southwest dome expands eastward, warm conditions are returning to the Front Range and will spread across the Southern Plains, eventually pushing into the Heartland.  In concert, the eastern dome will also drift eastward, bringing the coldest air of the winter to New England, the Great Lakes States and the Mid Atlantic region.

Winter takes a Hit

Down at South Platte Park this morning, crunchy snow still covered the ground and a layer of ice coated the larger lakes.  Winter ducks congregated on the river and open pools; northern shovelers were most abundant, joined by buffleheads, common goldeneyes, lesser scaup, American coot, ring-necked ducks, common mergansers and a pair of redheads.

A great blue heron hunted in the shallows and red-winged blackbirds, sensing spring, called from the icy wetlands.  Red-tailed hawks and black-billed magpies basked in the bright Colorado sun while downy woodpeckers scoured dead limbs for hibernating insects.  Finally, a pair of belted kingfishers chattered above the river, seemingly in celebration of the mild, sunny weather.

Indeed, the extended forecast calls for highs in the fifties and sixties (F) over the next ten days, putting a significant dent in winter's handiwork.  Then again, March and April lie ahead, two of the snowiest months along the Colorado Front Range.

March in January

Were it March, today would be described as a raw day; showers are threatening, the afternoon temperature is hovering in the low-mid forties (F) and a gray overcast shrouds the landscape of central Missouri.  However, since it's late January and today's weather arrived on the heels of snow and frigid temperatures, this mid-winter thaw seems mild by comparison.

In fact, the relatively mild conditions coaxed us down to the Forum Nature Area in the Hinkson Creek Valley.  There we completed a two mile circuit through the preserve; unfortunately, pockets of residual ice on the muddy trail forced us to pay more attention to the path before us than to the surrounding winter landscape.  When we did stop to peruse the scene, little activity was noticed though the calls of blue jays, crows, flickers and Canada geese echoed through the Valley.

Nevertheless, this March-like interlude was more than welcome and, according to the current forecast, we can expect another by this coming weekend.  Of course, the battle between winter and summer will continue over the next few months and our definition of "warm spells" will change as the season advances.

Anatomy of an Eastern Snowstorm

This morning, a massive snowstorm is developing over the Eastern U.S., fueled by several atmospheric and geographic factors.  A potent area of low pressure, currently over western Alabama, is sweeping Gulf of Mexico moisture across the Southeast.  In concert, a high pressure dome over the Great Lakes region is funneling cold air down from Canada, spreading sub-freezing air across all but the southernmost States.

The clash zone between the warm, moist southerly flow and the cold, dry air to the north is currently producing snow across the Ohio and Tennessee Valleys; along the southern edge of this band, an ice storm (including sleet and freezing rain) is expected to develop.  Later today, as the low pressure moves to the Eastern Seaboard, energized by the subtropical jet stream, it will intensify, pulling in copious moisture from the Atlantic Ocean.

Rather than moving rapidly up the coast, the storm is forecast to creep northward, stalled by the high pressure dome to the north.  This "blocking high," combined with the potent low, is expected to produce a long-lasting blizzard in the Mid-Atlantic region, perhaps dropping more than two feet of snow (especially along the eastern flank of the Appalachians).  Major cities and their airports will likely shut down, affecting at least 45 million people in this heavily populated region of the country.

Update:  As of 1-23-16, the storm has spread farther north than initially expected, now affecting at least 85 million people.  Power outages and coastal flooding (especially in New Jersey and southern New York) have become major problems.  Forty inches of snow have fallen in some areas of Virginia.

North into Winter

Leaving Longboat Key before dawn yesterday morning, winter was already knocking on the door; it was 45 degrees F in southwest Florida.  As sunrise commenced near Tampa, flocks of wood storks streamed across the orange sherbet sky while farther north, near Ocala, sandhill cranes foraged in the chilly morning air.

Though sunny skies prevailed all the way to Chattanooga, the temperature remained near freezing for the rest of the day.  High, wispy clouds stretched above the north Georgia mountains and, west of Chattanooga, a gray overcast shrouded the Cumberland Plateau, signaling the change to come.  Indeed, we stopped in Nashville, Tennessee, for the night, where snow was expected by morning; unfortunately, we received sleet and freezing rain, coating our vehicle with ice.

Heading north from Nashville, we encountered the snow near Clarksville, where plows seemed to be out of service; crawling along on the snow-packed Interstate, we eventually reached clear pavement south of Paducah, Kentucky.  From then on, our journey through the snowy landscape was unimpaired and we reached Columbia my mid afternoon.  To be honest, after almost two weeks in Florida, I was glad to be back in the American Heartland, where four honest seasons unfold; I'll take my summer heat with the glorious colors of autumn, the invigorating snowstorms of winter and the slow, uneven recovery of spring.

A Night of Tornadoes

Awakened by tornado warnings on our cell phones last night (just before 3AM), we turned on the TV and watched as a twister raked Siesta Key and moved northeastward through Metro Sarasota; three others followed in its wake but were less intense than the first.

The severe weather developed ahead of a potent cold front and were fueled, in part, by a strong subtropical jet stream, an atmospheric feature associated with El Nino.  Indeed, while most Florida tornadoes occur during the annual hurricane season (June to November), the strongest tend to develop during the winter months, especially in El Nino years.

Here on Longboat Key, we received heavy rain last night and continue to experience strong northwesterly winds behind the cold front this morning.  Fortunately, we escaped the brunt of the storms and were treated to a spectacular light show across Sarasota Bay as they moved onshore.  Unfortunately, at least two individuals were killed by the tornadoes.

A Sleet Storm

Driving back from the Kansas City Airport this morning, I encountered a sleet storm along Interstate 70, having developed on the backside of this week's massive winter storm.  Stretching for more than 50 miles along the highway and driven by a strong north wind, the swath of heavy sleet decreased visibility and produced a slippery surface on the roadway.

Unlike hail, which forms in the cold upper layers of thunderstorms and eventually falls to earth when gravity overcomes the force of the updraft, sleet forms as rain or partially melted snowflakes fall through a cold layer of air near the ground, refreezing into small ice pellets that coat lawns, fields and roads.  Freezing rain, generally more common and destructive than sleet, refers to liquid rain drops that freeze when they contact cold objects or surfaces (tree limbs, fence posts, cars, roads, etc.).

Needless to say, driving was treacherous in the midst of the sleet storm.  Unfortunately, the greatest danger arose from drivers that did not heed the conditions, racing by in the passing lane; as usual, SUV owners and truck drivers were the primary offenders and many of them paid the price, their cars, jeeps and sixteen-wheelers soon littering the median and grassy margins of the highway.