Meteorology

Often in the weather reports we hear of tropical lows, subtropical lows, extratropical lows, and thermal lows. What distinguishes these various flavours of "lows" from one another?

Sep 1, 2005 - Keith C. Heidorn

If you've ever watched a spark of static electricity jump from an object like a doorknob to your finger, you perhaps noted that mini-bolt followed a fairly straight-line path from the object to your finger. Lightning bolts are essentially the granddaddy version of that static spark, so why do lightning bolts generally appear so jagged and forked? The answer for lightning's jaggedness arises in its size and formation process.

Aug 1, 2005 - Keith C. Heidorn

A frequent question we meteorologists get is: "If water drops are heavier than air, why do clouds float?" With lovely forms of cumulus clouds popping up all around me on this summer's day, that is the question I will tackle this month.

Jul 1, 2005 - Keith C. Heidorn

Large water bodies have major influences on the weather,impacting the weather and climate of their shoreline regions. But unless we are involved with the maritime industry or sport sailing, we tend to overlook the weather and climate over the water body itself. Herein, we look specifically at one aspect: on-lake condensation on Lake Superior.

Jun 1, 2005 - Keith C. Heidorn

For those who love weather in all its varied forms, extreme or rare weather events often hold great allure. Spawned by our love of statistics, one extreme event that catches our attention is the breaking of daily temperature records. Whether a record hot day or record cold day, it is sure make local news headlines. If today's weather set a record for either maximum or minimum temperature, you would likely respond with a modicum of interest. If I told you that this day broke both the daily maximum and minimum temperature record, you might exhibit degree of incredulity. I call such days: double record days.

May 1, 2005 - Keith C. Heidorn

A common adage expresses the belief that it is coldest just before dawn and begins to warm with the appearance of dawn's first light, but observations and physical theory show us that the coldest hour of the day is not before dawn but often an hour or so after sunrise. Why is this so?

Apr 1, 2005 - Keith C. Heidorn

The dawn brought clear sky But, in a few hours, the warm sun would break the morning chill, and by mid-morning the perfectly clear sky would begin to lose its fair complexion as small buds of whiteness pop up hither and yon. So started a day when cumulus humilis, the most basic of the cumulus cloud family, would fill the skyscape. This cloud type often is the forerunner to larger, more developed cumulus varieties that fill the afternoon sky. But today, these fair-weather cumuli dot the sky within the large high-pressure cell that sat over the region.

Mar 1, 2005 - Keith C. Heidorn

The snows of winter bring many hazards to humans and wildlife. In urban areas, these hazards are usually manifested as transportation- or power-transmission-related hazards. But in mountainous terrain, another danger arises: the avalanche.

Feb 1, 2005 - Keith C. Heidorn

Arctic Outbreaks. They happen in all months of the year and can rate headlines during spring, summer, or early autumn if they bring extreme drops in temperature or killing frost. But it is during the winter that they receive the most attention because arctic outbreaks can drop air temperatures to hazardous levels, increase demands for home heating fuels, produce lake/sea effect snows, or in their deepest southern penetration kill sensitive fruit and vegetable crops in the southern American states.

Jan 1, 2005 - Keith C. Heidorn

Neither rain nor snow, nor freezing rain, for that matter. That is how one must often characterize winter precipitation. Rain and snow are just the most common members of the winter precipitation congregation, but not the only ones. Others include: ice pellets, snow grains, graupel, ice crystals and ice needles and also known by local names in different regions such as sleet, hail, soft hail, snow pellets and diamond dust.

Dec 1, 2004 - Keith C. Heidorn

For most North Americans, the combination, known as 'thundersnow', is a very unusual event. Even where they are most common, thundersnow occurs no more than a few times per year, usually when winter storms with substantial warm and humid air sectors spawn thunderstorms along their fronts, or when air crosses a large lake or rises over a mountain range.

Nov 1, 2004 - Keith C. Heidorn

Walk around any city where buildings rise more than a few stories, and you will experience areas with stronger and gustier winds than felt outside the urban area, at airports, or on sports fields. The prime cause of such urban winds is the redirecting of the over-ridding wind field by the structures themselves.

Oct 1, 2004 - Keith C. Heidorn

The lengthening nights during the late summer and autumn bring noticeably colder minimum temperatures across most of North America. If such nights have clear skies and fairly calm regional winds, the potential for temperatures to fall below the freezing mark increases as the days move on toward winter. This is especially true in low-lying terrain, hollows and drainage bottoms where cold air can pool. Such areas are more susceptible to frost than the surrounding terrain and are therefore known as frost pockets.

Sep 1, 2004 - Keith C. Heidorn

When you hear the word thunderstorm in the daily weather forecast, you automatically think of thunder and lightning accompanied by rain, often as a drenching cloudburst, and wind, gusty at times. Not all thunderstorms are wet, however, and that worries those watching for or fighting wildfires. These thunderstorms are called dry thunderstorms.

Aug 1, 2004 - Keith C. Heidorn

Glories appear as a full circle, their coloured rings centered on the observer's shadow. Prior to the advent of regular high-altitude flight, the glory appeared only to those who ascended to high mountain elevations. Today, we can see glories regularly from aircraft flying in the sunlight above uniform cloud decks. A glory is only visible when sunlight is at the observer's back; therefore, they are always exactly opposite the sun.

Jul 1, 2004 - Keith C. Heidorn

Blue jets, red sprites, elves, sprite halos and trolls may sound like Tolkein characters, but these high-altitude entities comprise the newest members in the pantheon of atmospheric electrical phenomena, joining lightning and St Elmo's Fire.

Jun 1, 2004 - Keith C. Heidorn

Mountain ranges have a major impact on moist air moving over them. On the windward side, upsloping air leads to a region of heavy precipitation near the summits. But in the descent on the ridge lee, descending air and decreased precipitation forms what we term the rainshadow.

May 1, 2004 - Keith C. Heidorn

Terrain interacts with the atmosphere in many ways to alter the weather. If winds push through the terrain in spots, rather than going over it, another set of wind phenomena arises, the gap winds. Gap winds are high-speed winds associated with gaps or low elevation areas in mountainous terrain, and whose direction more or less parallels the gap axis.

Apr 1, 2004 - Keith C. Heidorn

Rainbows have been part of human mythology and culture for millennia and have fascinated scientists through the ages as well. From two simple ingredients water drops and light, we can form the beauty of a rainbow. Here's how.

Mar 1, 2004 - Keith C. Heidorn

Weather bombs or bomb cyclones undergo explosive changes in intensity,forming an intense winter storm over a short period when they moved off the land and into the warm Gulf Stream waters off Cape Hatteras. These storms may move up the East Coast to form major snowstorms along their path.

Feb 1, 2004 - Keith C. Heidorn

During the depths of winter cold, we often hear some weather sage observe, "It's too cold to snow." Truth is, it is never too cold to snow. At very cold temperatures, 40 below zero (C or F) and colder, snow can actually fall out of the clear blue sky without intervening clouds, a weather condition known appropriately enough as diamond dust.

Jan 1, 2004 - Keith C. Heidorn

While the media rush to call any severe or heavy snowstorm a blizzard, true blizzards have a strict definition according to meteorologists, and snow need not even fall in a blizzard. Blizzards take on different characteristics when they rage around North America, combining wind and temperature and snow into a variety of recipes, though they all start as low pressure systems.

Dec 1, 2003 - Keith C. Heidorn

The great tropical storms roaming the world's oceans and seas have earned the right for individual names. Extratropical cyclonic storms, those forming from the clash of polar and tropical air masses, have not yet been honoured with individual names. However, some extratropical storms take on such unique characteristics that they are often recognized with a unique name for the genre: the Nor'easter along the Atlantic coast, the Alberta Clipper that races across the continent our of the Alberta plains.

Nov 1, 2003 - Keith C. Heidorn

Storms move out of the Gulf of Alaska into the Pacific Northwest with great regularity, as many as three or four per week during the height of the winter storm season. Winter Gulf of Alaska storms typically sport winds in excess of 80 km/h (50 mph) with corresponding high waves. Some storms rival the strength of the great hurricanes/typhoons and would be considered as such if their origins were tropical rather than polar.

Oct 1, 2003 - Keith C. Heidorn

We generally think of weather processes as occurring from the surface upward into the atmosphere, but weather has its influences downward into the soil and water bodies as well. Seasonal weather interactions play major roles in the processes and ecology of even the smallest freshwater lakes. One of the more important is the semi-annual turnover of a lake's water mass.

Sep 1, 2003 - Keith C. Heidorn

Have you ever gone out for a long walk, run, or bike ride on a gorgeous summer day and been caught in a torrential cloudburst? Bad enough to be caught in the rain, but cloudbursts can leave you drenched to the bone. But have you ever watched the approach of a thunderstorm darken the sky and then been surprised at how bright the day became during the heaviest downpour?

Aug 1, 2003 - Keith C. Heidorn

Blowing dust and sand can grow into huge duststorms and sandstorms that can even slow a war. How does the dust get into the air?

Jul 1, 2003 - Keith C. Heidorn

I look at two very localized thunderstorm events: the microburst and the heretofore rare heatburst. Microbursts are strong, damaging winds which occur during intense thunderstorms and have been linked to several aviation disasters. Heatbursts, on the other hand, are more rare and likely will only make the news as a weather oddity due to the sudden rise in temperature that mark their occurrence. Both, however, have similar origins, downward moving air from a thunderstorm's core, and affect only a rather small area.

Jun 1, 2003 - Keith C. Heidorn

The derecho is a violent, widespread windstorm emanating from long-lived thunderstorm complexes. Derechos produce damaging, straight-line winds of 100 to 160 km/h (60 to 100 mph) that are strong enough to down trees and power lines. They rush across a region along paths tens of kilometres (miles) wide and hundreds of kilometres (miles) long. Derecho damage is continuous and non-random over a large area.

May 1, 2003 - Keith C. Heidorn

April showers bring May flowers. Rain showers are very common weather events during April across most of North America. Showers are a distinct form of precipitation, whether falling as rain or snow or ice pellets.

Apr 1, 2003 - Keith C. Heidorn

They flow off the mountain ridges, rushing winds that are very hot and very dry. Along the eastern slope of the Rocky Mountains, they have been called "Snow Eaters" but today are more commonly known by their native American name: Chinook.

Mar 1, 2003 - Keith C. Heidorn

Looking across the open, snow-covered cornfield, they appear, on first glance, as if someone started to build snowmen or a snow fort then left the rolled balls of snow randomly across the field. And, although they each have a distinct "roll-up" track, close inspection show no footprints in the surrounding snow. Are these the winter version of crop circles, the work of winter spirits, or a curious product of nature? Such naturally formed snowballs are called snowrollers,cylindrical rolls of snow produced by the wind and shaped like a muff, rolled carpet, or jellyroll.

Feb 1, 2003 - Keith C. Heidorn

Icicles are one of our strongest symbols of winter and often used to depict the cold depths of prolonged winter. In its basic form, an icicle is a tapered, hanging spike or cone of ice formed by the freezing of dripping or falling water.

Jan 1, 2003 - Keith C. Heidorn

We think snowflakes, or more correctly snow crystals, are six-sided, frilly stars and are fairly flat like a pizza. Snow-crystal structure, however, takes on many forms from flat hexagonal plates to three-dimensional small hexagonal pillars with hexagonal plates lying on each end.

Dec 1, 2002 - Keith C. Heidorn

The polar front and its associated jet stream have a major influence on the weather conditions surrounding it. Many storms form along the polar front in the vicinity of the jet stream's maximum winds. Because the jet stream is associated with the polar front, media weather maps often include the jet stream's position as a rough indicator of warm and cold air masses.

Nov 15, 2002 - Keith C. Heidorn

High above the Earth's surface, rivers of air rush their way around the globe in a high speed current that often spawns side eddies that we on the ground call cyclones. Knowledge of the position of these streams, known as the jet stream because of their speed, is vital to accurate general weather forecasts and severe storm predictions. Knowledge of the location of the jet stream is also important to airlines and other long-distant air transportation.

Nov 1, 2002 - Keith C. Heidorn

While you might think that clear skies are not conducive to skywatching — unless you look past the atmosphere to the moon, planets and stars — but there are subtle changes in the clear sunset/sunrise skies that are worth looking for. Under clear skies, the twilight period can provide subtle sky beauty with its softly changing colours, particularly in the sky regions known as the twilight and anti-twilight arches.

Oct 1, 2002 - Keith C. Heidorn

The lower atmosphere, where we stand to view the stars, is mottled with pockets of varying density. When the local air density changes rapidly with time, the light ray's path also alters rapidly. This slight but perceptible refraction bends the path one way, one moment, slightly different the next. This constant, but random shifting results in the star's image jiving and jiggling, fading in and out, and even changing colours before our eyes. This stellar dancing is what we call "twinkling."

Sep 1, 2002 - Keith C. Heidorn

On late spring and summer days when the temperature soars, a special wind system may form along the coastline of the Great Lakes or other large lakes. It is known as the lake breeze, a similar condition to the sea breeze known along ocean shores.

Aug 1, 2002 - Keith C. Heidorn

Heat lightning is not a unique form of lightning, but normal thunderstorm lightning that flashes too far away from the observer for its thunder to be heard.

Jul 1, 2002 - Keith C. Heidorn

We don't hear or know as much about the superior mirage, so many think it is a rare occurrence. However, one form is so common that most of us do not recognize it as a mirage. The superior mirage can make objects appear to be floating in the air or cause objects actually located below the horizon to appear above it.

Jun 1, 2002 - Keith C. Heidorn

When we think about raindrops, we often have a fixed image of how they look,their shape as they fall. Literature, poetry and song are filled with allusions to raindrops as heaven/sky tears. In truth, raindrops are spherical in shape initially. Then, unless they are very small, they take on shapes looking more like falling hamburger buns.

May 1, 2002 - Keith C. Heidorn

Low pressure areas are the centers of interest in many weather situations for they are the storms that move across the continent.

Apr 1, 2002 - Keith C. Heidorn

Among the most commonly recognized weather features are the roaming regions of high and low pressure, designated by H and L on media weather maps, respectively.

Mar 2, 2002 - Keith C. Heidorn

Last month, we defined what air masses were and looked at some of their basic properties. Those distinguishing properties derive from the birthplace of the individual air mass, the geographical region where they form.

Feb 1, 2002 - Keith C. Heidorn

An air mass is a large dome of air which has similar horizontal temperature and moisture characteristics. At any given time, about fifty distinct air masses are scattered across the Earth. Some are newly born entities and strongly reflect their place of birth. Others are old and travel-scarred with only the slightest hint of their place of origin remaining.

Jan 8, 2002 - Keith C. Heidorn

As the calendar year winds down, so too does our Northern Hemisphere solar year, except that the sun reaches its cycle's end, the Winter Solstice, nine days before the last page of 2001 is ripped from the wall. The Winter Solstice is the shortest day of the year, but ironically is not the date of either the earliest sunset or the latest sunrise.

Dec 21, 2001 - Keith C. Heidorn

Residents of the eastern United States and Canada may experience freezing rain any time between late October and early May. When freezing rain falls for a long period and covers and extensive area it is called an ice storms. While ice storms may be very destructive, they can leave scenes of great beauty in their wake.

Dec 7, 2001 - Keith C. Heidorn

During the cold season in the Great Lakes Basin, cold-front passage is often followed by a 24-36-hour period of blustery winds, falling temperatures and lake-effect snows. Such lake-effect snowstorms are of major economic significance in the Great Lakes Basin as snowfall accumulates to as much as 75 cm (30 inches) per day.

Nov 23, 2001 - Keith C. Heidorn

Our Weather Eye this month focuses on the Great Lakes region. Over the world's largest fresh water bodies, two storm tracks converge in November. When cyclonic systems reach the region, the jet stream above and the warm Great Lakes waters below often induce an even more deadly spin in these storms.

Nov 16, 2001 - Keith C. Heidorn

Short days and low sun angles enhance the dreariness of November skies frequently flushed with stratus clouds from dusk to dawn. But at times, November mornings dawn with a quiet, spectacularly brilliant beauty. These are the mornings touched by the brush of Jack Frost.

Oct 26, 2001 - Keith C. Heidorn

Fog is actually a cloud formed or lying on the ground -- even those patchy fogs which fill low spots or hollows in the terrain. Radiation fog forms when the air near the surface cools to its saturation temperature due to nocturnal radiation cooling.

Oct 20, 2001 - Keith C. Heidorn

Today's groundwork background topic looks at humidity, and from the questions I have received over the years, there seems to be a lot of confusion about humidity.

Oct 12, 2001 - Keith C. Heidorn

The radiation balance of solar and heat energy is important for many weather processes and climate.

Oct 7, 2001 - Keith C. Heidorn

Sunbeams appear as light or dark shafts that appear to radiate out from the sun. Although they can be seen anytime the sun is in the sky or just below the horizon, sunbeams are most commonly seen, and often their most beautiful, around sunrise and sunset. Indeed, their technical name "crepuscular rays" means "rays related to twilight."

Sep 28, 2001 - Keith C. Heidorn

On the day of the Equinox, the sunrise and sunset times are not twelve hours apart. What atmospheric phenomenon causes this to happen?

Sep 14, 2001 - Keith C. Heidorn

Driving down the highway on a recent hot day, I saw the pavement ahead of me appeared to be covered with water. I never ever reached that wet pavement because what I observed was a true mirage commonly known today as a highway mirage.

Aug 30, 2001 - Keith C. Heidorn

Sun dogs or mock suns appear on either side of the solar disk as bright bursts of light formed when sunlight passes through ice crystals at the proper angle.

Aug 17, 2001 - Keith C. Heidorn

Knowing how sound travels through the atmosphere allows us to "watch" thunder and deduce something about the lightning that causes it.

Aug 10, 2001 - Keith C. Heidorn

We all know the voice of thunder. But what causes it to sound so different at times?

Aug 3, 2001 - Keith C. Heidorn

A halo around the sun often means rain, but not all come full circle.

Jul 17, 2001 - Keith C. Heidorn