One recent commenter asked about this year's snowfall since January 1st through the current date (February 17th). You ask and you shall receive...here is this year's snowfall compared to the last 5 years from January 1st through February 17th. Obviously, well below last year. Yet 2008, we had even LESS SNOW through. Interesting...
Northeast Ohio weather and science blog covering severe storms, long term outlooks, climate, behavioral meteorology, technology and other observations
Thursday, February 16, 2012
Tuesday, February 14, 2012
Valentine's Day Update: Any Ice on Lake Erie?
Now that the winter weather patterns are becoming more in line with normal Februaries from past winters--more cold and frequent snows--I can't help but look out the newsroom window to survey Lake Erie. Still no sign of any ice along the south shore. 98% of the lake is still open for business.
Environment Canada has a great site that tracks ice concentrations over the Great Lakes and higher latitudes of North America. So far this winter, overall Great Lakes Ice Cover is at the second lowest level since 1973 when record keeping began.
How about Lake Erie? 2011-12 ice cover is also at the second lowest level since 1973 slightly behind the winter of 1997-98. This winter: 2.54% The winter of 1997-98: 2.38%
Here is the actual data is you like numbers! I highlighted the top 5 lowest Lake Erie ice winters.
What does this all mean? As we've mentioned before, as long as late winter colder periods develops, expect more late season lake effect snows for the rest of February and March.
Environment Canada has a great site that tracks ice concentrations over the Great Lakes and higher latitudes of North America. So far this winter, overall Great Lakes Ice Cover is at the second lowest level since 1973 when record keeping began.
How about Lake Erie? 2011-12 ice cover is also at the second lowest level since 1973 slightly behind the winter of 1997-98. This winter: 2.54% The winter of 1997-98: 2.38%
Here is the actual data is you like numbers! I highlighted the top 5 lowest Lake Erie ice winters.
What does this all mean? As we've mentioned before, as long as late winter colder periods develops, expect more late season lake effect snows for the rest of February and March.
I'm still projecting between 20 and 25 more inches of snow from Valentine's Day and the end of March!
Friday, February 10, 2012
Where Does This Winter Rank So Far?
I finally checked the numbers from the NCDC (National Climate Data Center) for January across all of Northeastern Ohio. After averaging November and December temperatures and comparing them to all of the winters since the 1895-96 winter, this is where 2011-12 stacks up in the top 10 warmest winters. Each winter's snowfall through January is also included. Its number 3!
How about the trends over the last 110+ winters? It seems according to the data that the trend is slightly upward in Northeastern Ohio.
What does this mean for the rest of winter?
Look at the February temperatures in these winters? Well above normal...
In actuality, the actual temperatures have been even warmer!
How about March in the past years?
Temps stayed above normal in Ohio but they cooled compared to February and January. Notice the below normal temps across the upper Great Plains. A sign of late season colder spells.
If these comparisons are even slightly close to this March, expect temperatures to run closer to normal to slightly above normal which range from 41 on March 1st to 53 on March 31st. As for snow? We will look at those numbers next week.
How about the trends over the last 110+ winters? It seems according to the data that the trend is slightly upward in Northeastern Ohio.
What does this mean for the rest of winter?
Look at the February temperatures in these winters? Well above normal...
In actuality, the actual temperatures have been even warmer!
How about March in the past years?
Temps stayed above normal in Ohio but they cooled compared to February and January. Notice the below normal temps across the upper Great Plains. A sign of late season colder spells.
If these comparisons are even slightly close to this March, expect temperatures to run closer to normal to slightly above normal which range from 41 on March 1st to 53 on March 31st. As for snow? We will look at those numbers next week.
Wednesday, February 08, 2012
Climate and Weather: Complete Reporting by the Media is Paramount
In recent weeks,
several articles have been published that reignite the anthropogenic (man made)
Global Warming debate. Several surveys including
one on climate knowledge to lists of scientists who are considered skeptics
have made their way online. At roughly the same time, a new website was
launched that aims to list all television meteorologists who have made their
opinions public against Anthropogenic Global Warming. All of this has run
congruent to the abnormally mild winter we've experienced in Cleveland and across most of the US.
People have started asking me again what I think of
these articles and what my stance is on global warming/climate change. While I
purposefully steer clear of this polarizing debate, I always try to give answers that
describe the meteorological drivers of our weather patterns. Often time after explaining
this year's pattern, I quickly get blank stares when I describe the arctic and
its behavior this winter even without using fancy science terminology. By no
means is this a way of tap-dancing around the question but rather an
opportunity to present additional information that might not be known in a comfortable,
conversational setting.
Most people don't
want to be “taught" subject matter when watching a news program. Viewers
become uneasy when the news feels more like school than an informative
telecast. Most people cringe at science even more. They want their news simple and easy
to understand. Unfortunately, the world of atmospheric science—science
in general--is anything but simple. I’ve found that the general public knows
the terms "El Nino" or "La Nina" but little else.
How do we combat this
lack of basic weather/climate science knowledge? The answer is easy. Educate your viewers with
reporting the COMPLETE story. Yet most media outlets won’t and don’t do it.
Why?
As a television
meteorologist, you are taught to “know your viewers”. So we have to cater our
weather casts to fit what viewers are comfortable with. Most don’t want to know “why
is this happening”. They want the “whens” and “how much”. This makes sense. Weather impacts every aspect of their lives in the short term.
Viewers are impatient. They want
quick, “to-the-point” news and weather. Unfortunately, when a major weather
events occurs, the media explains the events in a highly, over simplified
manner to fit what viewers are used to during ordinary forecast segments. Key
elements are either watered down or left out entirely. The “dumbing” down of weather
and climate science stories into "easy-to-digest“ bullet points only
perpetuates weather and climate science as simple disciplines and fails to
accurately AND COMPLETELY present the reasons why our weather and weather
patterns behave the way they do. I'm not advocating long, drawn out, convoluted
television "seminars" devoted to weather and science just more
complete reporting. Reporters still need
to do their due diligence by researching the drivers of these events and
include them in stories before defaulting to the "Its Global Warming or
Cooling" card. Worst of all, it wouldn't take long to find.
Here are some
examples:
- Alabama Tornado Outbreak
The Xenia tornado
outbreak in 1974 was also during a La Nina. The link above shows that there may
be a link to tornado outbreaks and La Nina episodes in early spring.
2. New York Hurricanes - Irene in 2011 et all
East coast landfall
hurricanes occur more when the Atlantic is in its "warm mode". This
mode is called the Atlantic Multidecadal Oscillation. Hurricane Irene last year tracked north into New England.
Back in 1938, a category
3 hurricane made landfall near Bellport, New York. The Atlantic was also in its warm
mode.
Historic east coast landfalls compared to the state of the AMO
3. Drought in Texas
Another extreme
associated with La Nina. 20 La Nina events over the last 120 years. 19 of those
resulted in below normal precipitation in Texas. Look back at 1918 and 1956. Major drought centered in Texas from the Great Plains occurred during a La Nina.
How about 2011?
For comparison sake, here is the dust bowl drought of 1934
4. Alaska extreme
cold
The long term Pacific
Ocean cold pattern called the PDO (Pacific Multidecadal Oscillation) has been
linked to colder than normal temperature regimes. This study outlines the PDO
and other influences like El Nino and La Nina
Here are the January
1971 average temps along the side January 2012 average temperatures. Both of
these months occurred during a negative PDO.
The PDO isn’t the
only driver but the comparisons are significant. Some links between the cold
PDO and the western trough along the west coast reinforcing the ridge which set
the stage for the above normal temperatures during the summer of 2011
5. Mild winter across
the eastern 2/3 of the US
The Arctic
Oscillation and North Atlantic Oscillation has been strongly positive. (NWS Chicago has an excellent write up here.
The last two winters, these indices have been
strongly negative. One PhD in atmospheric science recently told me that these
oscillations are "stochastic processes". In other words, they are random pattern
shifts that the computer models have a tough time predicting.
My previous blog post
on the winter pattern so far
Is this over
simplification in weather/climate science reporting more a reflection of
today’s impatient, “Youtube-ified” society?
Probably. Television news is far different than it was 15 or 20 years
ago. News is not a ½ hour event like the good old days. News is produced in
smaller increments to fit our fast paced lives.
Mobile devices and other information gathering technology further reinforces the need for quick, one to two minute news bits. But when it comes to complex science topics
like weather and climate reporting, this format doesn’t work nor should we
force science into this highly compact template. Let me be clear on this. I am not against
Climate Change reporting. My intention
is not to debate climate change. I'm not here to analyze temperature data or to
follow the political money trail. I just want COMPLETE REPORTING that isn’t
watered down.
Allow me to get a bit
defensive: If someone wants to label me as a member of one of the climate
groups that’s routinely talked about as either pro or anti-AGW, go ahead. If you do than you
are missing my point entirely. My goal isn't to refute arguments for or against.
My goal of this post
is to emphasize better quality and COMPLETE science reporting on weather and
climate related stories through some basic research by the media. We serve our
viewers better if we abandon the practice of watering down weather/climate science
stories and explain the short-term drivers of weather events/trends within the AGW
context. Does this mean that we shouldn’t explain AGW? Absolutely not. Yet continual pointing at AGW as the ONLY first
order mechanism in the place of other drivers easily obtained through basic
research by reporters through credible sources (NWS, NOAA or NCEP) doesn’t do the
science or the journalism justice.
Friday, January 27, 2012
Weather and the Human Condition...Meteorologists Can't Win This Battle
Weather predictions
have an ingrained psychological component. The weather conditions might say one
thing, Yet we will characterize the weather differently depending on who we are
and where we live. Just looking outside at the current weather in our corner of
the world in Northeastern Ohio can shape our way of thinking even if the
overall weather data says otherwise. This winter’s lack of cold, small snow falls
and "milder” stretches are a prime
example of how psychology plays a role in how we perceive the weather. First,
let’s set the stage meteorologically then we'll examine the psych.
This early winter
weather has been stuck in a fall pattern. A ridge of milder air has sat stagnant
over the eastern US. The persistent low over the southwest and a general trough
with colder air over the western US and Canada hasn’t budged. The persistent southwestlow has spawned many Texas panhandle/southern systems rich with moisture fromthe gulf of Mexico; a pattern that is not indicative of a typical December or
January. The tropical La Nina pattern (cooler Pacific Ocean sea surface
temperatures) and an historically strong arctic pattern over the last several
winter say Canadian clipper systems would dominate the early winter with
frequent 2-4 inch snows. Unfortunately,
that same arctic component—our cold air driver--has stayed conspicuously stable
and quiet.
One computer projection
since late November has relentlessly pointed at clippers developing in Canada.
A quick snow usually accompanies these clippers across northeast Ohio followed
by colder air. This year, once we get inside 48 hours of the forecasted clipper
event, the computer projection would quickly push the system back north
allowing milder conditions to prevail!
Crazy stuff to be sure. In this atypical pattern where computer
projections offer little consistent help in forecasting, we more than ever want
a forecast that's definitive. This winter
has been anything but definitive.
At the heart of these
computer projections are equations that have no exact solutions, just
increasingly better approximations. I tell high school students to imagine math
without numbers and no calculators. That description usually follows with a
look of horror. Any thoughts of a student in the room becoming a mathematics
major are immediately wisped out the window.
Yet weather
forecasting is just that: An approximation. Throw in a splash of day-to-day
randomness and you have a very tough recipe to replicate over increasingly long
time periods. Computers will get faster
and faster. The amount of weather data from satellites will increase. But the equations that are used in these
simulations will always yield approximations…ALWAYS! No one wants to hear this
but all simulations are highly detailed shades of "grey" of varying
degrees. So are the weather forecasts that we present on television each day.
In a Facebook post,
I've explained the "approximate" nature of weather forecasts in the
context of this early winter wackiness. I hope that most people are receptive
to them. Many are judging by people’s comments.
Yet in times like this where weather isn't matching the Decembers and Januaries
of the past (snow and cold), the human condition takes over. Our mind gets
thrown off. Our preconceived notion of Decembers and Januaries featuring snow
and cold have been replaced with rain and milder air. These changes don't sit
well. It makes us feel uneasy holding onto these conflicting ideas. Psychologists call this "Cognitive
Dissonance". How many times recently have you had a conversation with
someone and they said, “What is the deal with this 'mild' winter…what is going
on here?” The uneasiness in the question is palpable.
No one likes to feel
uncertain or conflicted. Weather most
times exists in a perpetual "grey" area. It’s this built in randomness
that causes frustration and conflict. Most of the time, we grossly
underestimate its significance. We all have a built in motivation to reduce
conflicting ideas by altering the existing conditions in our mind to create
consistency. In the case of understanding the weather, we do this by 1) either
believing the weather information which best fits our comfort level or 2) we
alter its importance in our mind or 3) we just plain criticize it. Sometimes,
it’s a blend of all three. This inclination to favor information that
reinforces our comfort level is called a "Confirmation Bias". The
problem is that by creating "consistency" through favoring
information , we create a new false interpretation of the weather which we
believe to be true. Rather than looking objectively at the reasons for the
change scientifically (science scares people), most people tend to use an
overly simplified and often inaccurate scientific explanation of the weather to
ultimately confirm their predispositions.
For example, I go on
the air and say we’ll see rain to wet snow with 1-3 inches of snow by midnight.
Many of us are already preconditioned to believe that this snow forecast will
either be too much or too little. The reasons can vary from a disbelief in
meteorologists in general--some have the "they never get it right!"
mentality—to believing “the mild weather will stay” or that "the big snow
is coming!" Regardless, the
preconception of inaccuracy is set from the get-go.
The rain slowly
changes over to snow but only for some areas. It takes a few hours of rain/wet
snow before finally going to all snow. The new weather conditions highlighting
a slower, back and forth transition to rain and snow present new information
that favors the preconception of inaccuracy already present in many peoples' minds.
I go on the air and explain that there is no well-defined line where rain goes
to snow. I explain that it takes a while for cold air to overwhelm the milder
air so the rain/wet snow mix would exist for a longer period of time.
Those who are
preconditioned to believe that the forecast would be inaccurate dismiss the
scientific explanation, ignore the random changes and replace them with their
own simplified, non-scientific explanation while criticizing the real
explanation from the meteorologist as hogwash. The countless emails and phone
calls are strong evidence. All of this stacks the deck confirming their bias
that weather forecasts and meteorologists are always wrong. For a meteorologist, you can't win even if
you present objective information to the contrary.
The psychology
happens involuntarily: We struggle with the randomness of the changing weather
conditions. We feel conflicted. We feel
frustrated. We dismiss the weather
information that we deem unnecessary to ease our conflict. We might blame Lake Erie. We often say "Its Cleveland." We
criticize. We simplify. We use “weather
myths” to explain weather events. We come to a new conclusion and now believe
we fully grasp the nature of the weather. The false interpretation we just created
we believe to be very accurate. We feel
much better about ourselves. Case closed.
This inconsistency
doesn't mesh well with every one's already highly simplified view of the
weather. A crazy, changeable 8day forecast, negative connotations of weather
forecasts and forecasters in general, coupled with a lack of general understanding
is a highly volatile psychological mixture which further drives more false
conclusions and irrational beliefs about the weather. All of which makes people
even more uncomfortable and irritable. The
vicious circle is hard to break.
Weather prediction is
just as much art and psychology as it is science. We try to tailor the 8day
forecast to match the viewers’ perceptions by smoothing out some of the
randomness so that it fits nicely on the 8day but it doesn’t always work out.
Let’s hope that the weather pattern returns to "normal" soon. As a television meteorologist, the forecasts
daily would become easier to handle. As
a television viewer, the forecast could become easier to digest perhaps
quelling some of our cognitive discomfort.
I realize that
shifting the weather back to “normal” won't change perceptions. It won't change
the human condition. It probably won't alter beliefs about weather forecasts,
meteorologists and weather patterns as much as I wish it would. I can guarantee this: Cold weather in early February will make most
of us feel more at ease about the winter. That is until the first snow over
spring break!
Tuesday, January 24, 2012
Cleveland Snow This Winter vs. Least Snowiest Winters
Temperatures have been well above normal since November 1st. Snowfall hasn't stuck around for more than 4 or 5 days at a time. The reasons for the mild winter outlined a few weeks back. You can read about it HERE.
So far this winter, we've received:
22.8" through January 25th
How does this winter's seasonal snowfall stack up through the end of January when compared to the least snowiest winters of years gone by?
This winter is 33rd all-time on the "least snowiest winters by January 31st" list! Here are the top 32 winters on the list working backward from the 2001-2002 winter.
Breaking down the list by decade:
2000s: 1
1990s: 1
1980s: 2
1970s: 4
1960s: 4
1950s: 3
1940s: 4
1930s: 4
1920s: 7
1910s: 3
So far this winter, we've received:
22.8" through January 25th
How does this winter's seasonal snowfall stack up through the end of January when compared to the least snowiest winters of years gone by?
This winter is 33rd all-time on the "least snowiest winters by January 31st" list! Here are the top 32 winters on the list working backward from the 2001-2002 winter.
Breaking down the list by decade:
2000s: 1
1990s: 1
1980s: 2
1970s: 4
1960s: 4
1950s: 3
1940s: 4
1930s: 4
1920s: 7
1910s: 3
Thursday, January 19, 2012
Does Warming Over the North Pole Lead to Colder Temps in Ohio?
Technical weather discussions aren't exactly front page material. When I try to explain the weather to my wife, the conversation abruptly ends of changes subjects. I get it. Its geeky.
Yet sometimes, we need the complex nature of the atmosphere to be explained so that the variables in a winter like this one can be handled a bit easier with ultimately better short and long term forecasts.
So indulge the geeky, scientist in me for a bit...the late winter forecast lurks at the end! :)
============================================================================
Most of our weather occurs in the lower 10 miles of atmosphere. This layer is called the troposphere. However, the behavior of the atmospheric layer above it--called the Stratosphere--plays a big role in major cold air outbreaks like the one in the winter of 2009.
The profile of the atmosphere that you may remember from middle school science class
Notice how the temperatures in the Stratosphere rise whereas the temperatures in the troposphere drop as you increase in height. When the temperatures in the stratosphere rise suddenly over the high latitude regions close to the north pole, often time this rise can result in a sharp drop in surface temperatures which can propagate south across the continent and into Ohio. Remember some of the below zero periods in our past winters? These warming events often enhance the cold outbreaks. I'll have examples of this later.
This sudden rise in temperature is called a SUDDEN STRATOSPHERIC WARMING EVENT.
There are several key components that go into identifying SSW events. 1. A sharp temperature rise of at least 50-70 degrees in a short time interval. And 2) is an abrupt reversal of the jet stream from west to east away from the pole. Since 1958, 31 Sudden Stratospheric Events have occurred according to this paper published in 2010.
http://independent.academia.edu/erikwkolstad/Papers/156437/The_association_between_stratospheric_weak_polar_vortex_events_and_cold_air_outbreaks_in_the_Northern_hemisphere
Why does the stratosphere warm? The physics get very complicated and so do the equations that describe it. Here is the technical description from a paper I just read:
"The SSW is caused by a rapid amplification of planetary waves propagating upward from the troposphere. Planetary waves deposit westward momentum and create a strong meridional circulation which produces a large warming in the polar stratosphere due to adiabatic heating (e.g., McIntyre 1982)"
To visualize these "planetary waves", imagine a stream with random ripples on the surface caused by leaves, rock, sticks or any random object that permiates the surface of the water.
Imagine the atmosphere is like that stream filled with ripples. The only difference--and its a big difference--is that the atmospheric ripples are created by the earth's rotation and changes in heat from the oceans and land. These waves propagate like ripples throughout the atmosphere.
When they travel up into the stratosphere (100,000 feet above the ground), they dissipate and give off heat as the flow decreases. This causes the warming described above.
Notice the warming that has taken place since December 15th
Here is where we are now...notice the sharp warming in the high latitude regions over the last week or so. The temperature graph is in KELVIN shown in the purple line. Last year's levels are in blue; the 30 year average is in black.
Also the change in the jet stream has begun but its not sharp...yet. If the purple line drops below zero, that will indicate sharp shift in the jet stream which might be enough to start pushing temperatures south.
I looked at several warming events of different intensities (not necessarily major events) to see how the different stratospheric warming events effects temperatures for us in northern Ohio and surrounding areas. The first year, 1987, didn't result in any cooling; the 2003 warming event lead to a much colder February.
2009 was a MAJOR warming event. Look at the sharp temperature jump and the abrupt "180 turns" in the jet stream. Did it result in a major cold air outbreak across the eastern US? Not really...cold air developed over the extreme southeast US
Each SSW event is very different and can yield different temperatures across the US and Ohio. Often times, the cold air that develops over the North Pole sinks over Europe or Asia. While cold air outbreaks aren't a foregone conclusion over Canada and the Great Lakes when a stratospheric warming occurs, the chances increase by more than 50% during and after an event according to the scientific paper I sighted earlier.
Can we use the ARCTIC OSCILLATION (a measure of the arctic's stability) to determine cold air outbreaks during a SSW event?
I plotted the AO levels for 1987 noting the SSW time period to see whether the AO reacted to it.
How about 2003?
And finally 2009, one of the largest warming events in recent memory...
While Stratospheric warming events do lead to drops in the ARCTIC LEVELS, the are not always sharp and sustainable. SSWs can lead to major cold air outbreaks but not always as indicated by the 2009 February temps
What does this technical weather stuff mean for our long term trends in Ohio?
The warming over the North Pole continues but is forecasted to bounce around a bit.
Take a look at the projections through January 21st.. Notice the colder than normal air building in Canada trying to push south and the above normal temperatures staying out west.
While I'm not jumping on the ARCTIC COLD bandwagon just yet, the trend given even a slight warming event would be for more frequent periods of colder temperatures in northern Ohio and more frequent Alberta Clipper type snows and more lake effect in February!
Yet sometimes, we need the complex nature of the atmosphere to be explained so that the variables in a winter like this one can be handled a bit easier with ultimately better short and long term forecasts.
So indulge the geeky, scientist in me for a bit...the late winter forecast lurks at the end! :)
============================================================================
Most of our weather occurs in the lower 10 miles of atmosphere. This layer is called the troposphere. However, the behavior of the atmospheric layer above it--called the Stratosphere--plays a big role in major cold air outbreaks like the one in the winter of 2009.
The profile of the atmosphere that you may remember from middle school science class
Notice how the temperatures in the Stratosphere rise whereas the temperatures in the troposphere drop as you increase in height. When the temperatures in the stratosphere rise suddenly over the high latitude regions close to the north pole, often time this rise can result in a sharp drop in surface temperatures which can propagate south across the continent and into Ohio. Remember some of the below zero periods in our past winters? These warming events often enhance the cold outbreaks. I'll have examples of this later.
This sudden rise in temperature is called a SUDDEN STRATOSPHERIC WARMING EVENT.
There are several key components that go into identifying SSW events. 1. A sharp temperature rise of at least 50-70 degrees in a short time interval. And 2) is an abrupt reversal of the jet stream from west to east away from the pole. Since 1958, 31 Sudden Stratospheric Events have occurred according to this paper published in 2010.
http://independent.academia.edu/erikwkolstad/Papers/156437/The_association_between_stratospheric_weak_polar_vortex_events_and_cold_air_outbreaks_in_the_Northern_hemisphere
Why does the stratosphere warm? The physics get very complicated and so do the equations that describe it. Here is the technical description from a paper I just read:
"The SSW is caused by a rapid amplification of planetary waves propagating upward from the troposphere. Planetary waves deposit westward momentum and create a strong meridional circulation which produces a large warming in the polar stratosphere due to adiabatic heating (e.g., McIntyre 1982)"
To visualize these "planetary waves", imagine a stream with random ripples on the surface caused by leaves, rock, sticks or any random object that permiates the surface of the water.
Imagine the atmosphere is like that stream filled with ripples. The only difference--and its a big difference--is that the atmospheric ripples are created by the earth's rotation and changes in heat from the oceans and land. These waves propagate like ripples throughout the atmosphere.
![]() |
| Courtesy: The COMET Program |
When they travel up into the stratosphere (100,000 feet above the ground), they dissipate and give off heat as the flow decreases. This causes the warming described above.
Notice the warming that has taken place since December 15th
Here is where we are now...notice the sharp warming in the high latitude regions over the last week or so. The temperature graph is in KELVIN shown in the purple line. Last year's levels are in blue; the 30 year average is in black.
Also the change in the jet stream has begun but its not sharp...yet. If the purple line drops below zero, that will indicate sharp shift in the jet stream which might be enough to start pushing temperatures south.
I looked at several warming events of different intensities (not necessarily major events) to see how the different stratospheric warming events effects temperatures for us in northern Ohio and surrounding areas. The first year, 1987, didn't result in any cooling; the 2003 warming event lead to a much colder February.
2009 was a MAJOR warming event. Look at the sharp temperature jump and the abrupt "180 turns" in the jet stream. Did it result in a major cold air outbreak across the eastern US? Not really...cold air developed over the extreme southeast US
Each SSW event is very different and can yield different temperatures across the US and Ohio. Often times, the cold air that develops over the North Pole sinks over Europe or Asia. While cold air outbreaks aren't a foregone conclusion over Canada and the Great Lakes when a stratospheric warming occurs, the chances increase by more than 50% during and after an event according to the scientific paper I sighted earlier.
Can we use the ARCTIC OSCILLATION (a measure of the arctic's stability) to determine cold air outbreaks during a SSW event?
I plotted the AO levels for 1987 noting the SSW time period to see whether the AO reacted to it.
How about 2003?
And finally 2009, one of the largest warming events in recent memory...
While Stratospheric warming events do lead to drops in the ARCTIC LEVELS, the are not always sharp and sustainable. SSWs can lead to major cold air outbreaks but not always as indicated by the 2009 February temps
What does this technical weather stuff mean for our long term trends in Ohio?
The warming over the North Pole continues but is forecasted to bounce around a bit.
Take a look at the projections through January 21st.. Notice the colder than normal air building in Canada trying to push south and the above normal temperatures staying out west.
While I'm not jumping on the ARCTIC COLD bandwagon just yet, the trend given even a slight warming event would be for more frequent periods of colder temperatures in northern Ohio and more frequent Alberta Clipper type snows and more lake effect in February!
Thursday, January 12, 2012
What is Driving Our Not-so-Cold Winter?
The answers lie within several regions of the northern hemisphere and the indices that describe their behavior. Here are the regions and their parent indices in no particular order. I'll explain what each index measures and describe the impact each index has on our weather here in northern Ohio.
ARCTIC (ARCTIC OSCILLATION) "AO"
NORTH ATLANTIC (NORTH ATLANTIC OSCILLATION) "NAO"
EASTERN PACIFIC (PACIFIC-NORTH AMERICAN OSCILLATION) "PNA"
TROPICAL PACIFIC (EL NINO OR LA NINA)
We'll describe each teleconnect and show how each plays a role in our weather patterns across the Great Lakes and northern Ohio. It gets complicated so I've tried to keep the technical explanations to a minimum.
====================================================================
The Arctic Oscillation (AO) is a measure of the opposing pressure patterns of the mid-latitudes (across Canada and US) and the polar north.
When the index is POSITIVE, high pressure over the US and Canada drive storm tracks farther north keeping temperatures above normal across the eastern US (see left side of graphic above). When it is NEGATIVE (see right), the pressure tends to be lower across the US and Canada with higher pressure over the polar region. This causes storm tracks to come from the northwest ushering in colder than normal air.
The North Atlantic Oscillation (NAO), the AO's cousin, describes the pressure changes between low pressure over Iceland and the semi-permanent high over the Azores (eastern Atlantic).
Both of these teleconnections play direct role in how much and to what degree the cold air/storm track and intensity becomes in winter across the eastern US and Ohio. The lower or more negative the AO and NAO levels, the more frequent and deeper the cold air.
The problem is that these pressure variations are incredibly random and very difficult to predict much further than a week ahead of time. This is why we refer to these as "wild cards".
I plotted the average AO and NAO levels for the Novembers and Decembers since 1991.
The last 3 winters had AO/NAO levels well below zero. See how the NAO and AO run hand in hand. When the AO goes down, the NAO follows. Notice below how many days (graph below) over the last two early winters the AO/NAO were well below zero
The pressures over the arctic were alot higher, the pressure/storm tracks across the Great Lakes were much lower, the cold air much colder. The shades of blue show temperatures below normal across Ohio and the eastern US.
The pattern resulted in snows like this...
This year, we count only 9 days with AO levels below zero! Not many at all.
I plotted the average November and December combined temperatures for each year since 1991 on the AO/NAO plot. Notice that the warmer periods match up well with the higher levels of the
AO/NAO; colder periods for the lower AO/NAO levels.
The Pacific Ocean has also played a pivotal role in our pattern this year. TWO OTHER INDICES were very good guides on this milder pattern. The first is the PACIFIC-NORTH AMERICAN OSCILLATION. Its the general pressure pattern over this area shaded in red.
The higher the pressure pattern, the stronger the ridge over the western US and Canada, the stronger the trough/cold air over the US. This, unlike the other indices, means that lower than average pressure was centered over the western US/Canada and higher than average pressure was over the eastern US.
This winter, the PNA has been mainly negative.
The ocean temperatures in the tropical Pacific have been below average since last fall. This below normal ocean sea surface temperature pattern is a classic LA NINA PATTERN.
This change in ocean temperatures buckels the jet stream across North America which alters the storm tracks so that they come from the northwest. Last winter, we had more than 9 cold front-type snows from Canada. This year, ONLY TWO!
How does this LA NINA compare to others that share similar characteristics (time of peak/length of duration)? Use like to use the MEI Index because it factors in PRESSURE DIFFERENCE, WINDS, AIR TEMPERATURE, CLOUD COVER and SEA SURFACE TEMPERATURES in the tropical Pacific Ocean. Here is a graph that plots this LA NINA event to the others that compare favorably. Notice that it is similar to the three year LA NINA back in the early/mid 1970s.
How can we summarize what has happened so far?
- While the LA NINA pattern was present last winter allowing for clipper snows from Canada, the ARCTIC/NORTH ATLANTIC PATTERN continued to drive the cold air south reinforcing the La Nina storm track.
- This year, the LA NINA is present yet the ARCTIC/NORTH ATLANTIC CONNECTION is noticably absent. So instead of reinforcing the colder air/northwesterly storm tracks, it shifted the storm track more south featuring above normal rain (7+ inches for Cleveland in November and December).The ridge over Ohio and the east coast pushed snow producing CLIPPER SYSTEMS north and the temperatures higher.
- The cooler than normal Pacific water temps off of the coast of California and Alaska kept the cold and storminess further west (NEGATIVE PNA SHOWN EARLIER) while further enhancing theridge of dry/milder weather across the Great Lakes
How about snow totals comparing this year through January 12th to the last two winter? MUCH LOWER
How will these TELECONNECTIONS change in the weeks ahead? More on that later after this rare round of snow moves through. :)
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