Wednesday, November 26, 2008

Hurricane Season Coming To Close, New Record Set

Here is a great article about the 2008 Atlantic Hurricane Season, which ends on November 30.

Click here for article.

You may have to scroll down the page a little to see the article once it opens.

Happy Thanksgiving!

Thank you so much for all you do for CoCoRaHS!

When you take a look at the daily US maps and see all the data points, it really makes you feel proud to be part of such a cool organization with so many great people!

Tuesday, November 25, 2008

Unsettled In New England, Hurricane Force Winds On Mt. Washington

Well they say some of the worst weather in the world happens on Mt. Washington!

Look at the live weather conditions from 11:30 am Tuesday!

A sustained wind of 86 MPH gusting to 109! And the air temperature is only 20 degrees!

Wow can you imagine?!?

Elsewhere in New England that windy, but it is cold, unsettled and blustery.

Heavy rain is falling at the coast and in lower valleys, while moderate to heavy snow is falling in the mountains!

Friday, November 21, 2008

Wrapping Up Fronts

There is another type of cold front sometimes mentioned during the weather report -- and that is the "back door" cold front.

It's no different than a typical cold front except it moves in from the east or northeast, where as most cold fronts approach from the north or northwest.

It can happen anywhere, but is most common on a large scale in the New England states.

On a smaller scale, we get a lot of back door cold fronts along the eastern side of the mountains here in Colorado.

Cold air from Nebraska will pool and spill down the South Platte River Valley and into the Denver/Front Range area.

We had that happen this week in fact!

When a back door cold front moves into the New England states, often the cold air hits the Appalachian Mountains and can't go any further.

This is because cold air is heavy and dense, and it can't rise up and over high barriers like a mountain range.

We call this cold air damming.

So the cold front stalls along the mountains (cold air damming) and will actually become a stationary front since it stops moving.

Back door cold fronts combined with the terrain barrier make for tricky forecasts -- because you just don't know how much "umph" the front will have to make it up and over the mountain barrier.

Thursday, November 20, 2008

Quiet For Most, And Some New Weather Lingo

Well it continues to be quiet for most today.

Heavy snows continue around favored areas of the Great Lakes. Winds continue to blow from a northerly direction over the warm, open waters -- picking up tons of moisture and dropping it in the form of snow at and just inland from the lakeshore on the south side.

Below normal temps continue in the southeast and will persist into the weekend.

And here in Denver, we dropped from the upper 70s to the 30s over the past 48 hours, and now we have a little light snow/freezing drizzle.

A new storm moving into the northwest will bring unsettled weather to Seattle and Portland to round-out the work week.

Here are some new weather terms to throw out at your next dinner party.

When a cold front weakens and the temperature gradient weakens (meaning with distance, the difference in temperature becomes less drastic) -- you call that frontolysis.

And when you have the opposite, and the temperature gradient strengthens, meaning the front and associated storm system (low pressure) is growing stronger, it is called frontogensis.

Wednesday, November 19, 2008

Quiet For Most, Now Let's Find That Cold Front

It's a quiet weather day for much of the country.

More heavy lake effect snow is expected today and over the next few days across portions of Michigan.

Marquette looks to pick up another 6-18 inches of snow depending on where you live in that region.

The terrain and exact orientation of the wind off the lake can bring a foot of snow to one spot and just an inch or two down to another.

Jacksonville, FL set a new record low last night of 28 degrees.

Denver set 2 new records on Tuesday. One was a high of 78 degrees. The other was the overnight low, which was only 47. That is a new record high low temperature for the date.

The map above will be very hard to read but I want to use it for today's lesson about cold fronts.

I believe the picture will get bigger if you click on it.

So if you were to take a weather analysis class, this is an exercise you would likely have.

It's called find and draw the cold front! This map is showing surface observations at major reporting stations around the US for 8 am Wednesday, Nov. 19.

It shows different weather parameters for each location, including temperature, dewpoint, wind direction and speed.

Actually reading and decoding the observation could be another entire lesson within itself, and we may do that at some point if there is any interest.

So if a meteorologist had this map, to find the cold front, he or she would...

  • Look for sharp temperature changes over a short distance (such as the pocket of 40s and 50s over southern Kansas versus the 30s not too far to the north over Nebraska, Iowa and points north.

  • Changes in moisture (or dewpoint)-- which is much harder on the map I provided you because much of the country is under a dry air mass. It's much easier to find a cold front using dewpoints in the warm season.

  • Shifts in wind direction -- look from Texas up to Kansas, winds are blowing from the south. But above that in to Nebraska and Iowa northward, winds are coming in from the north.

  • You can also look at pressure and pressure changes if you have maps that span a few hours, or you can also look at the clouds and precipitation patterns.

    So just in taking a quick glance at the surface map above from this morning, simply by checking the temperatures and wind, we could porbably draw in a cold front somewhere in the central plains states, likely across southern Nebraska and extending toward Michigan on the east and the Rockies on the west.

    Who knew finding the cold front could be so much fun!

    Now I should say if we pull a surface map from mid to late afternoon, it could be much easier to spot the cold front -- because we will be at maximum daytime heating and the atmosphere will be completely stirred up.

    The problem with the 8 am map above is overnight the atmosphere mixes out and settles down with no sunshine to act as the "oven burner" to cook things up.

    So although we clearly get an idea something is happening in the Nebraska/Iowa vicinity from the 8 am map above, if we looked at a 3 pm map this afternoon, the front may be a little more obvious.

    Then again -- it may not be any more clear than the map above.

    This front isn't terribly dynamic, meaning there is already some cool air in place over much of the country, so the clash of the air mass in front of and behind the cold front isn't as dramatic as it could be -- so the afternoon map may not be more obvious than the one above.

    That is why people get into weather -- it is always different from day to day, hour to hour and in many cases minute by minute.

    You just never know -- and you can never say for sure because there are so many variables involved that can shift ever so slightly and make all the difference in the world to the outcome.
  • Tuesday, November 18, 2008

    From Frosty Florida To Cookin' Colorado

    The lake effect snow machine has been cranking the past few days and a strong northwest flow of cold air pours out of Canada.

    Some places have picked up 1 to 2 feet in the favored area between Cleveland and Buffalo, as well as in portions of Michigan.

    Some flakes have been seen as far south as the Smoky Mountains of eastern Tennessee and western North Carolina.

    So while Denver is expected to set a new record high today, and possibly for the entire month, southern Georgia and much of northern Florida is bracing for overnight lows in the mid to upper 20s tonight.

    Over the past few days we've been discussing fronts. It's time to talk about the cold front.

    I found a great picture snapped as a cold front moved through the Memphis, Tennessee area.

    Click here to check it out.

    The cold front is the dividing line between a cold, dry and stable air mass versus one that is warmer, more moist and less stable.

    It is drawn as a solid blue line with the triangles pointing in the direction the front is traveling.

    Tomorrow we'll chat more about cold fronts.

    Monday, November 17, 2008

    Snowy Around The Lakes; More About Fronts

    Well if you want winter, head to the Great Lakes!

    A strong northwest flow is creating pockets of heavy lake effect snow today along the southern and eastern shores of all 5 lakes.

    Some places, especially in the upper peninsula of Michigan, could see 6-12 inches of the white stuff.

    Meanwhile here in the west we are having round 2 of Indian Summer, with Denver expecting upper 60s to mid 70s over the next couple of days.

    Ok on Friday we talked about the stationary cold front.

    The type of weather one would see along this type of front actually depends on the type of air mass on either side.

    Sometimes the weather along a stationary cold front is clear to partly cloudy and dry, with much colder air behind it.

    This happens when the air mass on either side of the front is dry.

    Other times, warm moist air may ride up and over the cold dry air, bringing widespread clouds and precip to a large area.

    An example of this: say you drive from Chicago to Milwaukee in clouds, drizzle and fog and experience a temperature of 45 in Milwaukee and 71 in Chicago.

    Once either of the two air masses begin to move, the stationary front will get erased off the weather map and either a cold or warm front will be drawn.

    It just depends on which air mass wins out.

    Friday, November 14, 2008

    Weather Fronts -- More Than You May Want To Know

    Well we've been discussing air masses over the past few blogs, and yesterday I told you a front is the "front-line" so to speak of these air masses.

    Today we'll start learning more about fronts.

    Cold fronts, stationary fronts, warm fronts, back door cold fronts, occluded may have never realized there are so many terms out there.

    It all just depends on what is happening at the boundary between two air masses.

    Let's start with a stationary front.

    This is just a front that has no movement. Neither air mass is strong enough to overtake the other.

    Waves of lower pressure, or disturbances, may ride along the front bringing unsettled weather to a region, sometimes for several days.

    Eventually either the two air masse kind of just equal out and blend into one another, sometimes described by a t.v. weatherman as the front "washing out".

    Or other times a new weather system may come along and give one air mass the strength it needs to push on and win the battle.

    On a colored weather map, the stationary front is drawn as an alternating red and blue line.

    The semicircles point toward the colder air on the red line.

    The triangles point toward the warmer air on the blue line.

    (Kind of opposite of what one might think -- welcome to meteorology!!)

    Winds at the surface tend to blow parallel to the stationary front, and in opposite direction on either side of it.

    Up above in the atmosphere, winds also tend to blow parallel to the front.

    (Remember you now have to think 3-D -- the cold front extends from the surface up into the atmosphere)

    Monday we will talk about the types of weather you can expect along a stationary front.

    Thursday, November 13, 2008

    The 3-Dimensional Front

    Over the past few days we have talked extensively about air masses.

    The leading edge of these air masses are often where you find a front.

    A front is simply a transition zone between two different air masses.

    More specifically, it is a transition zone between air masses with different densities.

    And since density differs between hot and cold air, we are talking air masses with different temperatures.

    Along with temperature, we often find a difference in moisture too.

    Now here is where things can get tricky. To wrap your brain around a full degree in meteorology, you eventually reach a point in the coursework where you have to start thinking in 3-D.

    So picture in your mind a big, cold air mass moving south from Canada.

    On the weather map you see on television, the leading edge of this air mass will be noted by a cold front.

    So now pretend you are standing in your yard looking north and you can actually see this cold front moving toward you, evident by the line of clouds and sometimes by the dust the winds kick up out ahead of it.

    Once it reaches you, look up -- the cold front also extends up into the atmosphere.

    This is why you have to picture weather in 3-D.

    This upward extension of the cold front is called a frontal surface, or frontal zone.

    The frontal system not only extends out horizontally along the surface, but also vertically up into the sky.

    Tomorrow we'll talk more about different types of fronts.

    Wednesday, November 12, 2008

    Maritime Polar Air Masses

    During the winter, cP (Continental Polar) air masses move east-southeast from Asia over the Pacific Ocean around the Aleutian low.

    The ocean water modifies this air mass by adding warmth and moisture to it.

    It gradually transitions from a cP air mass into a mP air mass.

    By the time it reaches the USA, it is cool, moist and unstable.

    You often hear the television weather folks call this a warm storm, and it usually brings a lot of rain to the Pacific Northwest with some high mountain snow.

    We can see mP air masses move into the New England states off the North Atlantic, but it isn't nearly as common due to the westerly winds that prevail up at the jet stream level.

    Maritime Tropical Air Masses (mT) originate from the tropics and move across oceans toward land.

    The best example of this is the "Pineapple Express" -- which is a flow of moisture from Hawaii toward the west coast of the US.

    This flow of moisture can be really powerful -- with the best example coming from January 1997.

    The "pineapple express" slammed central and northern California with tremendous flooding that sent thousands running for higher ground.

    Yosemite National Park was closed for 2 months due to flood damage after the storm event.

    In the eastern US, maritime tropical air masses that impact the weather mostly originate over the Gulf of Mexico or the Carribbean Sea.

    Finally, we have Continental Tropical Air Masses and these originate in the deserts of the southwestern US and northern Mexico.

    This is when we see an area of high pressure bring several days of 100+ degree heat to the center of the country, typically in late June to early August.

    Tuesday, November 11, 2008

    Air Masses And Your Weather

    Here in the lower 48 states of America, we typically see a few different types of air masses impact our weather.

    cP (Continental Polar) often visit during the winter. This air mass is sometimes called cA (Continental Arctic).

    They usually bring bitterly cold weather.

    These air masses originate over the ice and snow covered regions of northern Canada, Alaska and sometimes even Siberia.

    Once an air mass slides south along the Rockies and enters the plains, there are no barriers to stop it -- so it moves all the way to the Gulf of Mexico.

    Sometimes this is called a Texas norther.

    Cumulus clouds are rare -- even during the warmest, most unstable part of the day -- because these air masses are dry.

    At night, with clear skies and light winds, temperatures drop like a rock.

    These air masses can make heavy snow when they move over a warm, large body of water, such as the Great Salt Lake or the Great Lakes.

    These snow bands are common on the eastern shores typically when a large cP or cA air mass moves south and into the USA.

    The Rockies, Sierra Nevada and Cascade mountain ranges usually protect much of the west coast from these bitterly cold air masses.

    But if the right weather pattern sets up, they too can see the frigid air.

    One very memorable arctic outbreak in the US took place between December 21-24, 1989. There were over 350 record lows set east of the Rockies.

    $480 million dollars of damage was done to crops in Florida and Texas.

    That same week in 1990, a bitterly cold air mass settled into the west, causing over $300 million dollars of damage to crops in California.

    Lows dropped into the 20s all the down into the Los Angeles region. It was the coldest weather in over 50 years.

    During the summer we look forward to seeing a large cP air mass move south out of Canada because they cool us down and lower the humidity for a few days.

    Tomorrow we'll talk about maritime polar air masses. (mP)

    Monday, November 10, 2008

    More About Air Masses

    In my post last Tuesday, we talked about where air masses originate and 4 different classifications.

    They were cP, cT, mP, and mT.

    If you ever do any additional reading or want to "study-up" a little more on the subject, let me introduce two more letters you may find in the classification.

  • k
  • w

    If the air mass is colder than the surface it's over, the lowercase letter "k" is added.

    Just think of "k" meaning cold.

    And if the air mass is warmer than the surface below, the lowercase letter "w" is added.

    So adding this 3rd classification, you could potentially see an air mass described as cPk.

    That would be an air mass of continental (c) polar air (P) that is colder than the surface below it (k).

    I know, I know -- for some it may make sense and others it may have went right over your head.

    If the latter describes you, don't worry...

    When I was in meteorology school I could not wrap my brain around this concept to save my life!

    Now I totally get it.

    Unless you have taken a meteorology class, until reading this blog, you may have never heard of the concept where one can identify air masses based on origin and their temperature/moisture characteristics.

    Or have you?

    There are a lot of "nicknames" that describe some of these types of air masses...and they are often said by meteorologists on television.

  • Arctic Express or Siberian Express -- a large, bitterly cold and typically dry air mass that moves down from Siberia and into the lower 48 states during mid-winter. Well since this is an air mass that forms over land (Sibera) it is "continental (c)" and Siberia is located in a polar region (P) and depending on how far south if travels, it will either be colder or warmer than the surface it is above -- so let's assume colder (k). So this air mass is a "cPk" air mass.

  • Pineapple Express -- when a flow of air that feeds into the west coast of the US directly from Hawaii and brings ample moisture. Since it forms over an ocean (m) and is from a tropical location (T), it would be an air mass labeled "mT" -- and then if the air is warmer than the surface below, you would add "w" and if cooler "k". So this air mass would be either "mTk" or "mTw".

    We'll chat more tomorrow!
  • Sunday, November 9, 2008

    Back From Trip, Lots To Talk About

    Well I am home from my business trip -- had to work in Salt Lake City for a few days.

    We still have not seen our first flakes of snow in Denver (at the official reporting station).

    A few higher suburbs have -- including my house -- but it doesn't count until a trace or more of snow falls at Denver's snow measurement site.

    Salt Lake City, however, has seen it's first significant snow of the season -- I landed during a snow band off the lake and drove in it all day Wednesday.

    I had no idea they could see "lake-effect" snowfalls -- much like they do in the Great Lakes.

    Portions of the region were even under lake-effect snow warnings.

    As I drove from the airport south toward Sandy, the snow really picked up in intensity.

    And speaking of snow, my goodness -- the upper plains got whalloped this past week, esp. the Dakotas!

    I didn't get much time to follow the news story due to work, but have enjoyed seeing all the online reports.

    And the 2008 Atlantic Hurricane Season just doesn't wanna give up as Paloma churns across Cuba.

    The storm is weakening from major hurricane status, and is now a tropical storm.

    The remnant low is expected to linger off the coast of northern Cuba this week.

    That could mean unsettled weather for south Florida and the Bahamas.

    And if you haven't seen an episode of "Storm Chasers" on the Discovery Channel, check it out tonight at 10 pm ET/PT.

    I caught an episode on my flight back to Denver the other night. (That is why I fly Frontier, for the Direct TV at every seat!!)

    It is action packed and at times will have you sitting on the edge of your seat.

    Tuesday, November 4, 2008

    Where Do Air Masses Originate?

    There are basically 2 source regions for where air masses form, but 4 general categories to classify the source of an air mass.

    First, the two main source regions, each defined with a capital letter...

  • P -- air masses that originate in Polar latitudes
  • T -- ones that have warm Tropical origins

    Now the 4 general categories to classify an air mass.

    If the source region is over land, it will have a small letter "c" before the initial. If it is over water, there will be a small letter "m" before the main source region initial.

  • cP -- cold, dry and stable air throughout the air mass

  • cT -- hot, dry, stable air aloft with unstable air at the surface

  • mP -- cool, moist and unstable air throughout the air mass

  • mT -- warm, moist and usually unstable air found throughout the air mass

    There are a few other classifications, such as cA (continental Arctic air masses) but if you master the 4 main ones above you are in business!

    I am traveling on business out of state the next few days and will not have access to a computer.

    BUT -- when I return I will pick up with the air masses of North America in more detail.

    Get out and vote -- your voice could be the deciding one!

    Happy Election Day!
  • Monday, November 3, 2008

    Air Masses and Fronts

    I got away from the "daily lesson" in recent weeks just due to a hectic work life, but will attempt to get back in the grove.

    This week we're gonna talk about air masses and fronts.

    An air mass is an extremely large body of air where the temperature and humidity are similar as you increase with height or travel across the air mass.

    So let's take a large, winter air mass that moves down from Canada across the lower 48 states.

    It may have highs of -15 in Minneapolis with a dew point of -18, and in Little Rock it may have a high of +10 with a dew point of +7.

    Although those temperatures are not similar as you travel the 1,000 miles across the air mass, both are very cold and very dry for the respected locations, and would be associated with the same air mass.

    Now suppose Minneapolis is still -15 with a dewpoint of -18, but Little Rock has a high of 45 and a dew point of 38 -- the two locations would not be under the influence of the same air mass.

    Minneapolis would be very cold and very dry while Little Rock would be cool but moist in that scenario.

    Air masses originate in what we call source regions.

    These are places that are typically flat, have light surface winds and a uniform topography and other characteristics -- i.e. deserts, the frozen arctic

    Here in the much of the lower 48 where we live (also known as the middle latitudes (between 30 and 60°N on the globe) -- most locations are not good source regions because surface temperatures and moisture characteristics vary considerably.

    We live in what is known as a transition region -- a zone where air masses with different physical properties move in, clash, and produce an exciting gamma of weather.

    Tomorrow we will talk about the classification of air masses.

    Saturday, November 1, 2008

    Will November Be As Quiet As October?

    All in all, October was really a quiet weather month for the entire country.

    We had a few strong cold fronts move through that brought a taste of what is to come.

    There was some October snow, mostly in either the northern Rockies or New England.

    We also saw just a little bit of severe weather in the central states, but nothing like what some October's have brought.

    So what does this mean? Will the bottom drop out as we head into November?

    It's anybody's guess -- but I can tell you we will see the weather pattern become a little more active, at least for the northwest and northern tier of states over the next 5-7 days.

    The current national hazard outlook is calling for heavy rain and snow across eastern Wyoming, Montana, and the Dakotas around the middle of next week.

    Heavy rain is also forecast for the Pacific Northwest.

    This will all be courtesy of a few storm systems moving in from the Pacific.

    I know here in the Denver area, November is typically our cloudiest month of the year as we see frequent storm systems moving across the state this time of year.

    It will be fun to watch and see how all this plays out.

    If you have a thought or opinion on the subject, feel free to leave a comment for everyone to see.