| Derechos |
Lee
E. Frelich |
| Nov
22, 2004 12:30 PST |
Bob et al.:
Lightning on the other hand, is restricted to thunderstorms,
most of which
occur during the afternoon and night time hours of summer. Two
of our
recent supercell derechos (also called Packwash derechos) had
cloud to
ground lightning frequencies of 3000 per hour and 6000 per hour.
These big
storms can and do cause a lot of tree mortality from lightning
in addition
to that from wind. This is especially true for the tallest
species like
white pine and cottonwood.
The problem you face if caught in the field during one of these
storms is
that its safer from a lightning perspective to be in the car,
but from the
wind perspective its safer not to be in the car, since cars have
a tendency
to become airborne missiles in high winds. You don't want to
stand under a
tree either, and you can forget the fold-up cot, since you won't
be able to
hold it down. The solution is to be aware of the signs of an
approaching
derecho (neatly stacked shelf clouds, mammatus clouds, green
sky) and drive
out of its path, or get home before it hits.
If you want to see a derecho, come here between May 15 and July
15. If you
don't want to see one visit some other time, and I will still be
able to
show you some derecho and tornado tracks in the forest.
Lee
|
| Derechos |
John
Knuerr |
| Nov
22, 2004 15:28 PST |
| RE:
Lightning frequency |
Lee
E. Frelich |
| Nov
23, 2004 05:49 PST |
Bob:
The maps I have seen show that derechos are rare or nonexistent
from about
Denver westward. Derechos seem to need tropical humidity from
the gulf of
Mexico, and that only occurs in the east. An analysis I saw
recently from
the NSSL (National Severe Storms Lab) shows that high end
supercell
derechos are most common in the Upper Midwest (The Dakotas
through the
Great Lakes), although they can also occur in Nebraska, Kansas,
Oklahoma
and Texas. Bow echo derechos, which are generally less severe,
occur
throughout the eastern U.S., even in MA.
Out west they still occasionally get dry microbursts, but they
are not as
large and destructive as the derechos.
Lee
|
| Re:
More questions for Lee |
Lee
E. Frelich |
| Nov
23, 2004 08:43 PST |
Bob:
Derecho is defined in a meteorological dictionary:
derecho [Spanish: 'straight'] A damaging straight-line wind
(i.e. one not
associated with rotation as in a tornado), produced by organized
downdraughts
such as those found in a squall line or mesoscale convective
system. The areas affected may be hundreds of kilometers long
and up to 150 km in width.
|
| RE:
Lightning frequency |
Lee
E. Frelich |
| Nov
23, 2004 09:09 PST |
Bob and Gary:
We have had fewer than usual intense thunderstorms during 2003
and 2004 as
well, since the southern position of the jet stream did not
allow warm
humid air from the Gulf of Mexico that thunderstorms need to
penetrate this
far north.
The thunderstorm we had on July 1, 1997, had 3000 cloud to
ground strikes
in Minneapolis in about 30 minutes, and it created enough ozone
to cause
damage to leaves of sensitive species such as white pine and
petunias.
Most people in Minneapolis turn off the interior lights to
maximize the
impact of a good lightning display. In a year or two maybe I
will move
into one of the 50 new condo towers under construction in
downtown
Minneapolis. Wouldn't it be cool to live on the 50th floor and
have
lightning bolts originate right outside your window?
Lee
|
| RE:
derechos |
Lee
E. Frelich |
|
Nov
23, 2004 12:56 PST |
Gary:
I have experienced several derechos. In one of them the roof was
blown off
of my brother's printing company, during a 2nd one a barn flew
across the
highway and landed on his house, in a 3rd derecho the country
club a block
from my parents house was smashed into thousands of pieces and
distributed
over the golf course, in a 4th one 20,000 large elm trees came
down across
the streets in Minneapolis and crushed many cars. A 40 foot tall
spruce
tree in my neighborhood park was found 100 feet from where it
had been rooted.
Here is what happens during a supercell derecho:
The distant approach. One sees a uniform light gray cloud on the
horizon
that gradually darkens over a period of an hour or more. This is
the anvil
cloud that is stretched out many miles ahead of the storm by
strong winds
at the top of the thunderstorm cells. This anvil may or may not
have have
small round pouches that project downward from it called mammata.
The near approach. When the western sky is almost solid black,
then a shelf
cloud becomes visible, which is lighter in color, low to the
ground, and
may have several layers that look like several huge wafers
stacked on top
of each other. Just before the shelf cloud arrives the sky may
turn dark
green, it is usually almost dead calm, and a faint roar can be
heard. When
the edge of the shelf cloud goes overhead, the wind speed
increases to
perhaps 20 or 30 mph for a short time, and light rain may begin
to
fall. If you live in an area with sirens, they go off at about
this time.
Under the storm. A very loud roar is heard and trees in the
distance
disappear one by one behind a gray curtain which marks the edge
of the wind
and very heavy rain. When that curtain arrives the wind
increases abruptly
to the full speed, perhaps 80 or 100 mph or more, and trees that
were
swaying gently in the 20 mph wind suddenly snap-to like a flag,
with all
the branches pointing the same direction. Visibility is limited
to 50-100
feet by a gray veil, and it will be as dark as it normally is 30
minutes
after sunset. The silhouettes of nearby trees can be seen waving
wildly at
impossible angles, a continuous roar of wind and thunder is
heard (too loud
for conversation), ripping and snapping sounds of breaking trees
punctuate
the continuous roar, and the lightning refracting through all
that rain
highlights the black and green base of the thunderstorm cell.
Great
splashes, thuds and booms can be heard and felt as trees and
buildings
break off, fall into the water, and hit the ground. This
continues for
15-30 minutes.
After the storm. The rain gradually stops. The streets will be
flooded 1-2
feet deep with rapidly rushing water. When the water recedes
enough one
can go out and explore. Thousands of leaves, twigs, seeds, etc.
will be
stuck to the sidewalk and walls of buildings. Mounds of red mush
on the
sidewalk with feathers stuck in them are the remains of birds
that failed
to reach a safe place in time. People will be walking around,
trying to
assess whether their car has been totaled, removing fallen
trees and
roofing materials so the streets can be reopened, figuring out
how long it
will be until electricity comes back on, etc. etc.
Lee
|
| RE:
derechos |
Paul
Jost |
| Nov
23, 2004 13:26 PST |
Lee,
I've been through that a few times, too. However, you forgot a
few
parts:
When you live on high, flat ground, it is always amazing to see
8-12"
of water in your back yard. Then, it's even more amazing to
realize
that the windows in your basement's window wells aren't
watertight as
you rush to clear the basement in paths from your basement
windows to
the sump pump pit so that you can squeegee the water to the exit
at the
sump, hopefully as fast as the water comes in...
When you explore the flooded streets immediately after the
storm, while
driving your truck through 15-25" of water on what you
thought were
streets on high flat ground, the police will try to chase after
you in
their cars to tell you that it isn't safe to drive your truck in
the
flooded water, but it is too deep for their cars which conk out
and get
stuck in the flood...
Then, there's the fun of cutting up all the fallen trees in your
yard,
including your neighbor's trees which are now also in your yard,
and
then dragging the branches to the curb side for pick up. And
then
noticing that everyone else has done the same and the street is
lined
with "snow drifts" of trees and branches 7-10' tall so
that you can't
see any of the houses as you drive down the street except for
brief
glimpses in the tree branch pile "windows" of
driveways that had been
cleared.
It's amazing how clear the skies become immediately after the
passage
of the storm!
By the way, I am always amazed that people from outside the
midwest
actually fear thunderstorms. When my wife and I were dating, we
would
drive out in the storms, head for more rural areas, and chase
the
lightning to get close-up views and sounds. It was a lot of fun.
It
was usually a light show that put the 4th of July fireworks
displays to
shame. We still open the shades/blinds and turn off the house
lights
to watch night-time thunder storms...
Regards,
Paul Jost |
| Re:
Kaaterskill Falls-Catskills-NY |
fores-@earthlink.net |
| Nov
23, 2004 13:52 PST |
Even for
the Northeast, 10 species sounds like quite a lot. Also, if we
are
truly interested in growth potential, once you past the first
4-5 species,
it would seem that there might be a number of tracts where the
remaining 5-6
trees would be hangers on and less adapted to the particular
microsite?
Maybe a RI10 and RI4 should be kept for everything (where
possible), along
with the HRI. (And while I'm at it, just to make a complete
complicated
mess of everything, fat diameters trees are also very impressive
and seem
to me as important as purely tall ones, perhaps a fatness index
should be
kept along with the Rucker height index, restricted to count
only in forest
(no field) grown trees having single trunks to say 20' or
greater above
ground, and just to add even more, something like the American
forest great
trees list, except with the restriction that the trees be tall,
columnar,
forest grown types, and that crown spread counts for nothing,
frnt yard and
field trees can be very nice, but there are much different breed
than
forest grown trees, which I think should have there own list.)
An
Appalachian mixed mesophyetic forest might easily have 10 solid
species,
but otherwise, it seems perhaps a stretch. I can think of some
fabulous
old-growth tracts in the Adirondacks that are so sugar maple
dominated,
that beyond some scattered white ash and yellow birch I don't
recall seeing
all that much else, and yet the tract was tall and impressive,
clearly OG,
but I'm not sure if it could qualify for the 10 species rucker,
perhaps
there are 10 species there, but I have my doubts, and even if
so, it would
surely have its index unfairly cut down quite drastically. Then
again my
tree identification skills are weak, and I haven't really paid
enough
attention, perhaps. Even my backyard tract back in NJ, which has
some nice
trees, quite well grown back and significant pit and mound
topography, I
can think of sugar maple, two oaks, white ash, tulip, ironwood,
hemlock (1
single tree), beech and maybe one other. That's 9. I'm not sure
if there is
a 10th species in the tract, and yet its quite a nice tract,
although the
older part is quite small in acreage, which is the only part I
was
counting, it would go beyond 10 species if I extended it to
encompass the
extensive surrounding woods (some parts of which are also quite
mature), so
perhaps it is simply too small a tract to make a fair test out
of, although
the additional species would be picked up from areas with
different growing
conditions. |
| RE:
derechos |
Lee
Frelich |
| Nov
23, 2004 17:19 PST |
Gary:
Yes I have been at ground zero for 3 of the 4 derechos I
mentioned before,
and it was a great experience. I was in a tent for one, in the
car for
another, and in a building for another.
You don't grab onto a tree. You get as far as possible from any
tree,
since trees might shed branches or tip over and conk you on the
head.
Lee
|
| Derechos |
Edward
Frank |
| Nov
23, 2004 21:45 PST |
Derechos
http://snrs.unl.edu/amet451/miriovsky/what.html
The word "derecho" is of Spanish origin, and means
straight ahead. The
strict translation of this word leads to the general public's
understanding
of a derecho: any straight-line wind associated with a
thunderstorm. While
correct to a certain extent, a more technical definition of
derecho is a
widespread convectively produced wind event resulting from the
outflow
boundary of a mesoscale convective system (MCS, see below).
Thus, derecho
producing mesoscale convective systems are referred to as DMCSs.
The winds
associated with derechos blow straight ahead, or are
straight-line. The
term straight-line is meant to be a contrast to the rotating
winds
associated with tornadoes. Johns and Hirt (1987) distinguished
between two
types of derechos, progressive and serial, differing in the
mechanism of
formation.
-------------
Hinrichs, G., 1888: Tornadoes and derechos. Amer. Meteor. J., 5,
306-317,
341-349.
-------------
Storm Event Summary and Preliminary Analysis of the Derecho that
struck the
Adirondacks in July of 1995.
http://cstar.cestm.albany.edu:7773/research/derecho.html
-------------
Ed Frank
|
| RE:
derechos |
Don
Bragg |
| Nov
24, 2004 06:08 PST |
Great description, Lee! I had the experience of sitting through
the July 4, 1977 derecho in northern Wisconsin. Much of the
energy of this storm had been spent by the time it reached our
home in Rhinelander, WI, but I remember eating supper and
watching tops snap out of the balsams (we eventually retreated
to our basement). We had some windthrown pine, but largely
escaped the major damage other parts of the state experienced.
One of the most vivid memories from this storm was our utter
disappointment that they canceled the fireworks show for that
night (hey, I wasn't quite 7 years old when it happened).
A number of years later, my father and I made a trip to the
Flambeau River State Forest to the area where an apparently
impressive old-growth hemlock stand had been virtually
eliminated. The area had since started to reforest with
hardwoods, but the extent of the damage was apparent. I was very
impressed that a single old white pine had survived virtually
unscathed as everything else fell around it. I don't remember
the exact dimensions of this tree, but it was probably 10+' CBH
and 130+' tall (after the storm). A couple years ago, my wife
and I drove past this tree, and I was dismayed to see it in a
state of rapid decline, and I suspect it is dead by now.
Don
p.s. A couple of my brothers were camping in northern Minnesota
during the July 1999 storm, but they weren't impacted by the
wind (too far south, I think).
|
| RE:
derechos, big Flambeau pine |
Paul
Jost |
| Nov
24, 2004 11:23 PST |
Don,
I know the big Flambeau River State Forest white pine that you
are
talking about. It was off Hawkins Road a few miles south of the
Connors Lake Fire Tower. It was dying when the S.F. management
declared that it would be cut down. Before the state foresters
could
cut it down, some locals cut it down in the middle of the night,
probably just to watch it fall. It was just over 130' tall and
14'8"
in girth with the first branches at least 90' from the ground. I
am
told that a piece of the trunk is now on display at the forest
headquarters/visitor center on Hwy W.
Paul Jost
|
| Another
derecho page |
Ernie
Ostuno |
| Feb
18, 2005 10:24 PST |
| Re:
Another derecho page |
John
Eichholz |
| Feb
18, 2005 16:33 PST |
Ernie:
After viewing this page I realize I was in that Derecho.
[Boundary Waters- Canadian Derecho- eff] A group
of my
friends and I were staying in some cabins on a lake in Harmony,
Maine
north of Waterville. The cabins were the only active part of an
old
campground. Early in the morning, we awoke to a howling in the
distance. The dawn was near, but the sky was a yellow color
rather than
the usual grey or blue, with a very dark horizon. The storm hit
soon
after, with winds and rain so severe we had the windows shut and
locked
but rain was still spraying in. The storm lasted a half hour or
so. In
the aftermath, we saw a corridor perhaps 60' wide of old white
pine
together with every other tree blown down. Literally nothing
bigger
than a bush was left standing in the blowdown path. Outside of
the
path, which began perhaps 200' from our cabin, there was
relatively
little destruction. We saw 2' diameter pines laying across the
center
of several campsites. I can only imagine the scene should they
have
been occupied. Luckily, they were not. The cleanup was a
limber's
nightmare, as a tangle of pine trunks in places 3 or 4 trunks
and 10'
high was typical, over a path at least a quarter mile long,
running from
the field by the cabins to the lake shore. There were widespread
power
outages, and nothing seemed to return to normal for a few days.
I guess
we were at the tail end of a massive trail of destruction, which
I
thought at the time was limited to that part of central Maine.
John
|
| RE:
Another derecho page |
Ernie
Ostuno |
| Feb
18, 2005 19:37 PST |
| Re:
Another derecho page |
Lee
Frelich |
| Feb
19, 2005 15:20 PST |
John:
Congratulations for surviving a derecho. Neat experience.
The Weather Channel has made an episode of their series 'Storm
Stories'
about some campers who were injured in the Boundary Waters in
northern MN
when the storm hit there. They show Storm Stories at 8:00 PM
Eastern Time.
They rotate through the available episodes, so this one will
probably come
up again during March.
In northern MN the storm developed a rotating head supercell
derecho, which
causes the biggest forest blowdowns we know of. About 10 by 40
miles of
forest was levelled by this rotating supercell, which
disappeared as the
storm moved east and became a bow-echo derecho. As you observed,
bow echo
derechos are characterized by scattered smaller blowdowns
embedded within a
large area of minor damage.
Lee
|
| Re:
Another derecho page |
Holly
Post |
| Feb
19, 2005 17:14 PST |
My house in Woodstock was hit by a similar occurrence
in 1998, probably during that Labor Day event. I lost
17 trees on my small .7 acre lot. All the felled
trees were laying in the same direction. Luckily my
house just missed being hit by any of the trees.
They called it a "wind shear" and said it travels in a
straight line instead of rotating. The crew literally
had to cut the way into to my house with chain saws so
we could get to my husband who was disabled and sick
at the time.
I was told that my road was the epicenter in the area.
The wind kind of bounced on the ground causing damage
and then would raise up off the ground only to bounce
back down further along its path.
|
| derecho |
Lee
E. Frelich |
| Jun
08, 2005 06:22 PDT |
ENTS:
A bow echo derecho crashed through Minneapolis last night at
4:00 am. This
was not a high end event, the storm was only moving at 40 mph
and wind
gusts only peaked at 60-70 mph with 1.5-3 inches of rain.
Nevertheless,
there were a few trees down in the neighborhood and over 100,000
houses
were without electricity this morning. I saw it begin to form on
the
weather channel radar last night at 9:00 near rapid city South
Dakota, and
made a note to myself to wake up at 4:00 am, and sure enough
that is just
when it arrived.
It is amazing how much stuff these storms bring down. The
sidewalks are
packed with debris that includes millions of tree seeds of all
sorts. These
storms must play a big role in seed dispersal of trees. I wonder
how far a
rain soaked elm or maple seed will go in a 60 mph wind, starting
from a
trajectory 60 feet above the ground? The
literature on seed dispersal
only examines dispersal of dry seeds in open fields on days with
low
windspeeds.
Lee |
| Another
derecho |
Lee
Frelich |
| Jun
20, 2005 19:57 PDT |
ENTS:
For the second time in two weeks, a bow echo derecho sliced
across
Minnesota today. It started in Ottertail County northwest of
Minneapolis
this morning, where thousands of trees were uprooted, houses
were 'blown
through' (a term that indicates windows blew in on the windward
side and
the house's contents disgorged through windows on the lee side),
and
hundreds of boats blown out of the water, some landing in piles
100 feet
inland. At 2:00 pm the sky over the University of Minnesota
turned light
green, with a dark gray shelf cloud underneath, as the storm cut
through
the Twin Cities. The storm just went through DesMoines Iowa in
the last few
minutes, at about 9:30 pm.
When the storm hit, horizontal sheets of water began flying
across the
campus and within a few minutes all of the streets and sidewalks
were
rivers with rapids. About 3 inches of rain fell during the 30
minute
storm. A giant cottonwood tree, as large in diameter as the
reporter
covering the story on TV is tall (about 5.5-6 feet), crushed the
garages of
two houses, and pulled down the power grid of the neighborhood.
Winds in Ottertail County were up to 100 mph, while we got by in
Minneapolis with rather wimpy 60 mph winds.
These storms usually come in sets of three. I can't wait to
experience the
third one.
Lee |
| Re:
Back to Dale |
Lee
E. Frelich |
| Jun
21, 2005 12:50 PDT |
Bob:
We do have a gazillion golf courses in MN (I believe the highest
per capita
number of golf holes in the U.S.), which are useful for sledding
and cross
country skiing during the other half of the year. A typical golf
course
hit by a high end derecho, such as the ones of July 1, 1997, and
May 30,
1998, loses about 1000 trees per hit, so they are continually
replanting. If they would just use bur oak, each tree would last
for 300
years, regardless of derechos.
We have a lot of local media devoted to the weather, so we can
keep up on
which streets are closed due to fallen trees or flash floods,
and specific
minute by minute forecasts for each neighborhood that give
people a 10 time
window during which they should 'take shelter' as a storm
crosses the Twin
Cities ('To take shelter' can be complicated since a supercell
derecho
could flash flood your basement at the same time as it sends
shards of
broken glass flying through your living room, and outside you
will be hit
by falling trees, struck by lightning or conked in the head by a
flying boat).
Then there are The Twister Sisters, videographers in MN who
manage to
capture every tornado and derecho in the state on film for the
evening news.
Lee
|
| The
third derecho |
Lee
Frelich |
| Jul
24, 2005 09:38 PDT |
ENTS:
The third derecho of the season that I expected, hit the Twin
Cities
yesterday at about 10:45 am. It had formed in North Dakota at
3:00 am, and
raced across North Dakota, Minnesota and Wisconsin, causing
winds up to 85
mph, in a damage swath 30 miles wide and 300 miles long. The
storm itself
was propelled at a speed of 55 mph by its rear inflow jet. I was
leading a
hiking group through Wood-Rill Natural area when it hit. We had
been
examining the effect of European earthworm damage and the trees
that fell
in the previous derecho about 4 weeks ago, as well as an old
tornado track
with crooked trees from 1965, when several F4 tornadoes hit the
Twin
Cities. Suddenly it was as dark as it would normally be around
10:00 PM,
and heavy rain and high winds began along with frequent cloud to
ground
lightning. Fortunately the part of the storm with the highest
winds missed
Wood-Rill, and since I had been tipped off as to the approaching
storm
earlier in the day, I chose a path that allowed us to escape
back to the
cars within a few minutes.
Wood-Rill did not lose any more trees in this storm; all the
susceptible
ones fell in the last derecho. The 300-400 year old sugar maples
were still
standing. These old trees have very deformed crowns from their
life-long
encounters with derechos. They shed branches, and become
relatively short
trees, and live a long time as a result.
We have had typical derecho weather for the last month, with
humid heat
that only the Midwest could possibly produce, and a large high
located to
the south. Last weekend the high was 97 Saturday and Sunday, and
it will be
about 97 again today. This coming week, the jet stream is
predicted to
change its path, leading to a return to temperatures that are
about
average. Although the derecho limited yesterdays high to the
upper 80s, it
only added to the humidity. My brother and I went to the
fireworks shown
over the Mississippi River last night, and with a dew point of
81 degrees,
several people were taken away from the crowd with heat stroke.
After a
long walk home through the incredibly packed sidewalks of
downtown
Minneapolis, with its dozens of nightclubs, numerous sidewalk
cafes, red
light district (no, we didn't stop there), broadway theater
district, and
the summer music festival in and around Orchestra Hall, we got
back to my
place at midnight, and at that point the air temperature of 88
combined
with a dewpoint of 78, gave a heat index of 100 degrees. I
believe this
was the first time we have had a heat index of 100 at midnight
since July
1995. We expect another derecho today or tomorrow, but this time
it will be
accompanied by a jet stream change, change of air mass and
return of more
normal 65 degree dew points--just in time for Bob's drive
through the Midwest.
Lee |
|