Download Nor`easters and Alberta Clippers

Nor'easters, Alberta Clippers, Water Spouts
The great tropical storms roaming the world's oceans and seas have earned the right for individual
names: Andrew and Katrina, Keli and Jelawat. Extratropical cyclonic storms, those forming from the
clash of polar and tropical air masses, have not yet been honored 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 Gulf of Alaska storms fit within this category as do the Colorado Lows. But for
two North American groups of cyclonic entities, their names are more descriptive: the Nor'easter
along the Atlantic coast, the Alberta Clipper that races across the continent our of the Alberta plains.
The Nor'easter
In a cyclonic flow pattern, winds spiral around the low pressure centre in a push-and-pull struggle
between pressure gradient, Coriolis and frictional forces. In a well-developed cyclonic storm with a
proper placement of surrounding high pressure cells, this flow regime develops sectors with strong
northeasterly, southwesterly and northwesterly winds. Therefore, any strong cyclonic storm has the
potential to be called a southwester, a northwester, or a northeaster. However, only along the North
American Atlantic coast, from Cape Hatteras northward to the Canadian Maritimes, can a storm truly
be called a Nor'easter. By accepted definition, a Nor'easter should have gale force or stronger winds
initially blowing from the northeast. These storms often bring heavy precipitation, falling as rain, snow,
or at times, freezing rain. Along the coastline, heavy surf generated by offshore storm winds may
cause extensive damage to the shoreline. Nor'easters are the most common, widespread severe
weather events to worry New Englanders and Maritimers.
The term Nor'easter arose in the colonial days before the concept of wind circulation around a low
pressure center was established. Storms were then considered to travel from the direction of the
wind. If a storm came with southwesterly winds, it originated from the southwest. A Nor'easter,
therefore, originated, and arrived, from the northeast of those feeling its fury. Those beliefs began to
change in the mid-eighteenth century, in part through the insights of Benjamin Franklin. Franklin had
looked forward to viewing a lunar eclipse but had been denied the visage by clouds associated with a
storm that rolled into Philadelphia that evening. Later, he was surprised to hear that his brother living
in Boston had seen it. Franklin had expected the obscuring clouds had moved over Philadelphia from the
northeast, around Boston, but Franklin's brother wrote the eclipse occurred before the clouds rolled
in. From this and other correspondence, Franklin began to suspect that, contrary to then-current
beliefs, large storms moved quite differently than indicated by their main wind direction. He reasoned
that his "eclipse storm" had come from the south or southwest rather than the northeast. While
Franklin never fully grasped the cyclonic flow pattern, he did realize that storms often moved in
directions other than that of their winds.
Nor'easters have become legendary along
the Atlantic Coast for their fury and
impacts. The Blizzard of '[18]88 and The
Perfect Storm are two prime examples.
Most nor'easters arise from cold-season
storm systems that first move through the
Ohio Valley or Gulf States to a position off
the Atlantic Coast. There, many receive a
regeneration of intensity when they encounter the warmer ocean waters, particularly if the Gulf
Stream waters are involved. When conditions are ideal, the storms become bomb cyclones, a term
relating to a sudden and dramatic deepening of the central pressure, at a rate equal to or exceeding 1
millibar per hour over a 24-hour period. The suddenness of a bomb cyclone's fury is matched only by
the resulting winds and precipitation. Nor'easters generally hug the coast as they move north. Their
northeast storm winds rush off the ocean with unbridled fury. The wind flow pattern also permits the
storm to pick up relatively warm and very moist air from the ocean which it drops when meeting colder
air on the western side of the system. If the air is cold enough, the precipitation falls as snow, at times
measured in feet rather than inches — merging blizzard with nor'easter.
The Alberta Clipper
While Nor'easters are creatures of the East Coast, many are born in
the lee of the Rocky Mountains. There are two prime mid-continent
spawning grounds for storm systems. One is around the State of
Colorado; the other the Province of Alberta. Those systems born
around Colorado are simply called Colorado Lows. Storms born in
Alberta possess unique characteristics that have led to the name
Alberta Clippers as they move swiftly out of the Canadian Prairies,
like the Clipper sailing ships of old, bringing frigid weather to the
east. Alberta Clippers form on Alberta's high plains east of the
Canadian Rockies. Once organized, they "sail" southeastward under
the push of a northwesterly jet stream into Montana and the
Dakotas, then turn across the Great Lakes basin headed toward the
Atlantic Coast. This track, however, leaves them far from the
moisture sources of the Pacific, Atlantic and Gulf of Mexico. As a result of their high forward speed and dryness,
the average Clipper rarely deposits huge snowfalls, dropping instead only a few centimeters of light, powdery snow
in its passing. At full maturity a Clipper's cold winds may reach 65 km/h with gusts to 100 km/h. Although the
amount of snowfall may be small, these strong, frigid winds produce severe blowing and drifting of any snow on
the ground, thus causing true blizzard conditions along the storm's track. When an Alberta Clipper passes, it often
ushers in bitter outbreaks of polar air, which continue the storm's wrath for days after the low itself has moved off.
Combine strong northerly winds and bitterly cold temperatures in the storm's wake, and you get severe ground
blizzards, days of white-outs (severe blowing and drifting snow that reduce near-surface visibility to zero), and
dangerous windchill factors.
Waterspouts
Waterspouts are tornadoes over water. But scientific work over
the last 30 or so years has led to a more complicated picture
with waterspouts differing in some ways from tornadoes over
land, especially large ones. Waterspouts and all the different
kinds of tornadoes have a similar basic structure with air
moving upward. At the ground or ocean surface, winds are
rushing faster and faster as they swirl into the vortex and then
upward. Often with both tornadoes and waterspouts, the
vortex is seen coming down from the cloud, but not obviously
touching the ground or ocean. Such vortices that don't seem to touch the ground are called "funnels" or
"funnel clouds." It's important to say "seems" not to touch because often, especially in the beginning,
the vortex is invisible along part of its path. We begin to see the vortex when its lower air pressure
cools the air enough to condense water vapor in the air into tiny water droplets. Beginning in the late
1960s when he investigated waterspouts in the Keys from a single-engine Cessna 172 piloted by a
friend, Joseph Golden, now a senior scientist at the National Oceanic and Atmospheric Administration,
documented the "what" of spouts and tried to puzzle out the "why." During 12 days in September
1974, Golden flew into 16 Florida Keys waterspouts — one of them 26 times — in a North American T-6
airplane that had been modified for weather research. The World War II era trainer was flown by a
professional weather research pilot. Golden recalls that flying into spouts with winds blowing faster
than 60 mph around the vortex and moving upwards at 20 mph or better "rattled my teeth." And, he
notes, these were "weak to moderate" strength waterspouts. Careful study of movies or videos of
waterspouts show speeds up to the 190 mph range. They are not to be taken lightly. In fact, Golden
speculates that "a significant fraction of the so-called Bermuda Triangle incidents are from
waterspouts."
How waterspouts form
The first sign, which can be seen from the air but usually not from a boat, is the formation of a dark
spot on the ocean. Smoke flares dropped in these areas show the air is moving in a circle and upward.
Many dark spots die out without progressing any further. But some begin to take on a spiral pattern of
dark and lighter water. Golden says at this second stage someone on a boat at the surface would
probably feel the wind shift and maybe increase. Also, if you looked upward, you might see a funnel
coming from a cloud overhead or off to one side. People on boats will see the third stage. Even though
it might be invisible, a vortex is reaching the ocean surface from the cloud. When the wind speeds
reach around 40 mph, the wind begins to kick up spray in a circular pattern — the spray vortex. At this
time you might see the funnel pointing down from the cloud toward the ring. The fourth, or mature,
stage is when the funnel reaches all the way from the cloud to the ocean. You can usually see through
the funnel - it's really a thin cloud of tiny water droplets. During this stage, small waves are being
kicked up and the spout leaves a bubbly wake behind as it moves across the ocean. These tiny bubbles
could be carbon dioxide and other gases that are dissolved in the water that are caused to effervesce
by the low air pressure in the spout's center - like a bottle of soda that's just opened. In the fifth,
and final stage, the spray vortex weakens and the funnel becomes shorter and maybe more tapered. It
often twists around and the bottom of the waterspout may move out from under the cloud. Scientists
say the waterspout's dissipation usually occurs when rain begins falling from the parent cloud. Cool air
brought down by the rain cuts off the supply of warm, humid air that's feeding into the waterspout to
keep it going.
Where waterspouts are most likely found
The Florida Keys "are the greatest, natural vortex lab in the world," says Golden. "Waterspouts probably
occur more frequently in the Florida Keys than anywhere in the world." Waters around the Keys, especially
from Marathon past Key West on westward to the Dry Tortugas, probably see 400 or 500 waterspouts a
year. Since they are so common, most go unreported unless they cause damage. Golden suspects so many
waterspouts hit the Florida Keys because the weather and geography supply two necessary ingredients.
First, the islands and the shallow water along them help heat the air. During the summer, waterspout season,
the air is extremely humid with temperatures in the mid-80s into the low 90s. The heat causes the air to
rise. As it rises, the air's humidity condenses into the tiny water droplets that make up clouds. As water
vapor condenses, it releases more heat that makes the air rise even faster. Rising air currents are needed
for waterspout formation. The second important waterspout ingredient in the Keys seems to be the regular
east or northeast "trade winds" that blow right down the islands. These winds help line up the clouds. Lines
of clouds encourage waterspouts. Exactly how is one of the questions researchers are trying to answer.
Clouds that spawn waterspouts in the Keys are generally from around to 18,000 to 22,000 feet high. Golden
says, waterspouts are likely to form when the clouds are growing upwards. In the Keys, waterspouts are
most likely to form between 4 and 7 p.m. with a secondary maximum from 11 a.m. to 1 p.m. A few waterspouts
form around sunrise.
After the Florida Keys, the next most active U.S. waterspout area is the southeast Florida Coast from
around Stuart south to Homestead. Tampa Bay has the greatest number of damaging waterspouts, probably
because the shores of the Bay are so built up. Places around the Gulf of Mexico along with the Atlantic
Coast northward to Chesapeake Bay are also likely to see waterspouts. Waterspouts have been reported on
the West Coast from Tatoosh Island, Wash., south to San Diego, but they tend to be weak and short lived.
Waterspouts also skip across the Great Lakes and Utah's Great Salt Lake from time to time.
Boater safety around waterspouts
Even though waterspouts are usually weaker than the strong tornadoes over land, they can be a real danger
to boaters. Waterspouts are most common in the Florida Keys and over other warm oceans, but they can
occur over just about any body of water. As with any kind of weather hazard, safety begins by staying
informed. One of the special radios that pick up weather broadcasts should always be aboard your boat.
And, you should listen to it regularly. Waterspouts tend to come from clouds with a dark, flat bottom when
there is just the first hint of rain. If one heads your way, try to escape by going at right angles to its
path. And if it's about to hit your boat, the best bet might be to dive overboard. Flying debris is the big
killer in tornadoes and waterspouts. How about diving underwater to escape? "If you dive before one hits,
I think you will be O.K.," says Golden. But no one really knows what the water is doing right under a
waterspout and such a dive should be a last-ditch attempt to avoid flying debris. I'm not prepared to say
it's safe to dive under a waterspout," Golden says.
Nor’easters, Alberta Clippers, and Waterspouts (answer on own paper)
1.
Where do Nor’easters come from?
2.
What causes the most extensive damage along a coastline during a nor’easter?
3.
How did Ben Franklin realize that these storms did not come from the NE?
4.
Do cyclones move clockwise or counterclockwise (see pict)?
5.
Where do nor’easters get the moisture that causes precipitation?
6.
What are the 2 non-coastal areas in N America where nor’easters form?
7.
Why are the storms that form in Alberta called “clippers”?
8.
Why do clippers NOT produce large amounts of precipitation?
9.
What are white-outs?
10. Why would it be dangerous to leave a pet outside during a nor’easter even if the temp
outside is above freezing?
11. What are waterspouts?
12. What is the name for vortices that do not reach the ground?
13. What are the highest wind speeds seen in videos of waterspouts?
14. What is the first sign of a waterspout?
15. At what wind speed does water start to “kick up” and form a spray?
16. What are the bubbles left in the wake of a waterspout?
17. What is a waterspout funnel made of?
18. Why do water spouts start to dissipate?
19. What area of the US has the highest concentration of waterspouts?
20. How many occur there in a year?
21. What 2 ingredients make this area perfect for waterspout formation?
22. While in FL, what time of the day would you expect to see waterspouts?
23. What area of the US has the most damaging waterspouts? Why?
24. What dangers threaten a boater during a waterspout?
25. What should you do if you are on a boat and a waterspout is approaching?