Friday, April 7, 2017

My April, 2017 Atlantic Hurricane Outlook.


Back on March 26th I posted my thoughts on how the hurricane season looked to unfold.  Looking at everything, I really haven't changed my mind. As far as I can see, I was the first or just about the first to post numbers on the 2017 hurricane season. I wanted to post before the Annual National Tropical Weather Conference was held this year.  I also wanted to beat Colorado State University's April outlook. Why? Because I wanted to make it clear that my ideas are sound, and lay the groundwork , by getting my predictions out there first.

The Atlantic hurricane season runs from June 1st until November 30th. But that doesn't mean tropical cyclones can't form before or after those dates.

Back in March, I said my analog years were, 1951,1953,,1957,1972,1997,2015. Since then I looked at and added 1965, 1976, and 2002. All of these years had some similarities to 2017.


Teleconnections:

The North Atlantic Osculation as primarily been positive since January.  So the North Atlantic Sea Surface Temperature (SST) anomalies have been cold. The cooling off of the SST increased in March.  So now we have cool SST in the North Atlantic, cool tropical SST off the West Coast of Africa, with warm SST off the East Coast of the United States. This places the Atlantic Multidecadal Oscillation (AMO) in a basically negative phase.

The  El Nino-Southern Oscillation (ENSO) is currently neutral. I've been posting on My Facebook weather pages, and I also talked about it in my March 26th blog post. So I won't go into a lot of detail on that. But, the ENSO looks to head for El Nino conditions. During the 2016 hurricane season we were experiencing a strong El Nino. Then late in the fall we transitioned into La Nina. During winter 2016-2017 the La Nina stayed very weak. This is one of many reasons why the winter turned out the way it did.

This year I don't think we will see the return of a strong El Nino. Instead I think it will be weak to moderate.  I don't think we will see a El Nino until at least mid-summer. Right now, the atmosphere is still acting like we have a weak La Nina; it will take awhile for the atmosphere to catch up. So, there wouldn't be Atlantic influence until we get into the hurricane season. 

Predictions from other major weather outlets.

Colorado State University (CSU):

They issued there outlook on the 6th of April, 2017. The team from CSU said they expect 11 named storms, 4 hurricanes, 2 of them major Cat3 or higher.

Accuweather:

 Issued their hurricane forecast April 5th, 2017. They say 10 named storms will form, 5 will become hurricanes, 3 will become major.

Tropical Storm Risk, INC (TSR):

TSR a prestigious private hurricane forecasting company in Britain, issued their hurricane outlook on April 5th, 2017.  They say they expect, 12 named storms, 6 hurricanes, 2 of them major.  

Weatherbell:

They released their thoughts on numbers for the 2017 season, on 31 March, 2017. They have listed, 10-12 named storms, 4-6 hurricanes, 1-2 of them major.

The numbers I released on the 26th of March, 2017:

I said, my early thoughts were, 10-12 named storms, 3-4 hurricanes, with 1 major.

Last season's tropical cyclone numbers:

In 2016, there were 15 named storms, 7 of them became hurricanes, with 4 major hurricanes.


The bottom line:

The combination of a positive AMO and El Nino will increased trades winds over the Main Development Zone (MDZ) of the tropical Atlantic.  We also have those cool SSTs, in the eastern Atlantic.  All of this will severely curtail tropical development in the MDZ.  So the odds of Cape Verde tropical storms will be much lower than average.  This same thing happened in 2016.

Those warm SSTs off the East Coast of the U.S., and the warm waters in the Gulf of Mexico and Caribbean will set the stage, for tropical cyclone development in the western Atlantic Basin.  As was the case last year, most of the tropical development should develop closer to the U.S. main land.  The warm SSTs also, increased the odds of stronger hurricanes coming up the East Coast.

My Call based on right now, is 10-12 named storms, 4-5 hurricanes, with 1-2 of them major.
 

If I have to adjust anything, I will release an updated outlook, during the last half of May.
 
 

Thursday, April 6, 2017

Summer 2017 Outlook


Despite busting  my winter 2016-2017 temperature outlook, my snowfall outlook got it right for the most part. Which shows, you can get a lot of snow, even during a warm winter.  Summer outlooks are much harder to forecast,  than winter outlooks. For this reason this outlook is a little more limited in scope than my typical winter outlooks.
 

We have a developing El Nino in the Pacific. It won't be as strong as last summer's.  I do think it will act like the La Nina over the winter.  The 2017 El Nino will be short lived. It should be weakening as we head into the upcoming winter.  There is a good chance this will end up being a El Nino Modoki event. If this is the case late fall and the winter will see the greatest impacts in the Mid Atlantic and Northeast.






 

Looking at the sea level pressures in the Pacific, the SOI is looking to be negative over the next 6 weeks, This trend looks to continue into Summer 2017.  Those cold SSTs in the Indian Ocean and around Indonesia means this won't be a long lasting El Nino. The upcoming El Nino should end up being weak to moderate.
 

My analogs  were difficult to compare to this year. But the closest I could find were: 1959, 1960,1961, 1980, 1983, 2002, 2006, 2009. None of these were a exact match. But they were close enough to gather some insight.   (Note: NOAA has been readjusting the old data. This makes past events look cooler than they might have been. ) So that doesn't help.






 

Temperatures:

The summer will start off warm. But then we will cool off after midsummer.  Typically transitions from La Nina to El Nino lead to overall cooler summer, especially during the 2nd half of summer.  This is because the atmosphere takes a little time to move from one phase to the other.  Overall, this upcoming summer, looks to be average to very slightly above average in temperatures.  Part of the reason will be those very warm sea surface temperatures off the East Coast.

 


Precipitation:

On my Facebook weather pages, I've been talking about how I expect to see a active severe season in the Northeast.  Also the threat that I see from close to the East Coast forming tropical cyclones, again those warm SSTs off the East Coast, has to be taken into account.
 
We have an ongoing drought going on in New England down into eastern Pennsylvania , New Jersey, and the Mid Atlantic. This is especially true for Connecticut and Long Island; the rest of the region is doing OK.  There is also drought in the Southern U.S. I do expect to see the active pattern we're in erode quite a bit of this over the next couple of weeks. But these areas will have to be watched. As, they would have a part to play on where the heat sets up.

I don't anticipate this to be a typical dry El Nino.      

 


Severe:

The severe season  in the Northeast runs from June through August. The Plains will be cooler than average June July and August. This is typical for El Nino years.  With a trough setting up in the Plains. We would see slight ridging over the east coast, with an active storm track looking to be in the cards. Severe weather in the Northeast will ramp up. This should end up a fairly active year for severe weather, with perhaps several severe outbreaks over the region.

 

Bottom Line:

This Summer is going to see temperatures warmer temperatures in June into July .  Then we will start to see a change to cooler overall temperatures mid to end of July and August.  I expect the temperatures to end up over all average to slightly above average for New England and New York State into Western Pennsylvania. With temperatures  over the rest of Pennsylvania and the Mid Atlantic to be moderately above average.  But we won't have the sweltering heat we had in Summer 2016.
This Summer will see a wet June and July, with things starting to dry up a little in August.  Overall I think precipitation will be average to slightly above average.  The wild card will be severe season and tropical activity. But if these play out like I think this Summer and Fall could be wet.
 
I will have a separate post on the 2017 Atlantic Hurricane Season, and my thoughts on the Severe Weather Outlook for June through August.

Tuesday, March 28, 2017

Tropical Cyclone information graphics changes for the 2017 season.


The National Hurricane Center (NHC) is making several changes to its tropical cyclone graphics.

The 2017 hurricane season will be here before you know it. So I wanted to go over these changes before June 1st.

1)  The NHC will be issuing advisories even before a disturbance becomes a depression or a named storm.  Any potential tropical cyclones that threaten land area with tropical storm or hurricane force winds within 48 hours will be given advisories, with discussions and tracking maps.

2)  The NHC started posting experimental alerts for storm surge last season. For 2017 those alerts will be mandatory. The NHC will be issuing storm surge watches and warnings for the Gulf and Atlantic Coast, for any storm that has the risk for life threatening surge conditions during any stage of a subtropical or tropical cyclone, even potential tropical cyclones.  
 

3)  For the 2017 hurricane season, the NHC will be issuing approximate arrival times of tropical storm force winds. The new graphic will display the earliest reasonable arrival time of winds of at least 39 mph.  A probability scale will be used along with the arrival time. The scale will show the probability threshold for 39 mph, 58 mph, and 74 mph wind speed will be met in a particular location. 
 

4)  The size of the Cone Of Uncertainty will be smaller. The cone will be based on the tracking error over the last four hurricane seasons. The cone doesn't represent where impacts like storm surge, wind, flooding, or tornadoes will be felt.
The old Cone of Uncertainty
 
The updated Cone of Uncertainty
 


Table showing the circle radii size of the cone
 

5)  Advisory graphics will be greatly improved.  New bolder colors and easier to read font should make the carts easier to view and understand.  The new graphics will include tropical storm and hurricane force wind fields.
 

I hope you found this helpful. As always let me know what you think, or post any questions you might have.

Sunday, March 26, 2017

A first glimpse at the 2017 hurricane season.


With a possible subtropical system developing in the Caribbean, the system could become named, it could even become a full born tropical system . I thought I would post some thoughts I have on the upcoming  2017 Atlantic Hurricane season. This isn't going to go into a lot of detail. There is still a lot of data that has to come in before I can state how things look to go. My official tropical outlook will be released most likely at the end of April.

The first day of the Atlantic Hurricane Season begins on June 1st.  So there is plenty of time to look at the data and trends.

Even though there isn't a lot to go by yet, looking at the current Sea Surface Temperatures (SST)can give us a clue and a few answers.

Here is a look at SST as of 3/26/2017; in it we can see two things. First, is the developing El Nino. The second is the cool water west of Africa, and warm waters off the East Coast of the US. 
 
 

 
 
 
 

The analog years I've been looking at are 1951, 1953, 1957, 1972, 1997, and 2015. Number 1 was 1972 and number 2 was 1997.
 


 
 
The Pacific:

Looking at the tropical Pacific, we see warming in ENSO regions one and two. The current ENSO neutral conditions look to continue for the rest of Spring, then we will transition toward El Nino this Summer , and most likely be in an El Nino this Fall.

History tells us that El Nino's typically inhibit Atlantic tropical activity. The warm SST in the Pacific causes the air to rise over the tropical Pacific. Since weather in the Northern Hemisphere tends to go west to east, that  warm rising air in the Pacific sinks over the Atlantic; this helps stabilizes the atmosphere over the tropical Atlantic. More in the way of stable air leads to less in the way of thunder storm activity.  El Nino's  also tend to cause stronger winds to come off of Central America, these winds extend into the tropical development zone of the Atlantic. The winds shear the tops off of developing tropical cyclones, making it harder for hurricanes to develop. During El Nino years we also tend to see the Atlantic trade winds blow faster. This causes any thunderstorms that do develop to move faster , again leading to fewer hurricanes.

It is still uncertain if El Nino develops, or if it does if the atmosphere will respond quick enough to make a difference.

The Atlantic:

We have cool SSTs west of Africa in the prime development zone.  Tropical cyclones need warm SST's in order to develop. Cooler tropical waters lead to unfavorable hurricane conditions. This along with a developing El Nino means  long track Cape Verde tropical systems will have a hard time this year.

This time of year it's hard to make long term predictions. Why? Because this time of year is always a time of transition.  

 ACE:

It's becoming obvious that the upcoming season will have less ACE points than we saw in 2016.

An article by Weatherbell's Joe Bastardi was shared to me. Here is a few graphics from Bastardi's post. These will prove the point I'm making.
Image credit Joe Bastardi, Weatherbell Analytics
Mean sea level pressures of the 1950's
Image credit Joe Bastardi, Weatherbell Analytics
mean sea level pressure from 2006 to 2016
Image credit Joe Bastardi, Weatherbell Analytics
Image credit Joe Bastardi, Weatherbell Analytics
Image credit Joe Bastardi, Weatherbell Analytics

In the images you can see the warmer than normal SST off the Southeast U.S. and Caribbean

Colder than normal SST off the Northeast and North Atlantic.

So you have higher pressures in the north and lower pressures in the tropical development zone of the Atlantic .

Mean sea level pressures of the 1950's were higher than normal in the north, normal in the Atlantic, and lower than normal in the Caribbean. 

All of this causes tropical storms to  come close to the U.S. Southeast Coast and move up the coast.

SST and mean sea level pressure from 2006 to 2016. This period has seen no official major hurricane strikes on the East Coast, (But I personally count Sandy as a major hit, based on her impact).  
 

This year will have some similarities to last season.

The SST's are warmer off the East Coast into the Caribbean and Gulf. So, any tropical systems that do develop will develop on the western side of the Atlantic. The closer the storms form to the U.S. the greater the odds for landfalling tropical cyclones on the East and Gulf Coast of the U.S.

My early thoughts on the upcoming hurricane season  is for a average to slightly below average season. Something similar to1972, 1997, or 2015. So  I'm leaning toward 10-12 tropical systems, with 3-4 hurricanes with 1 major hurricane.

The warmer waters off the East Coast, would also help tropical systems retain strength or even intensify as they move up the coast. This would be worrisome, because the impacts could be similar to what we saw during the 1950's.   

That's it for now.


 


Monday, March 6, 2017

What the heck happened to Winter 2016-2017


When I posted my winter outlook last fall; I thought I was going to make a three pointer at the buzzer and win the game.  For some areas my outlook went well, for other areas so far it's been woefully wrong. While snowfall for Winter 2016 2017 isn't over yet. (Last fall I said snowflake to snowflake), we can see a huge disparity between New York State  and New England compared to the Mid Atlantic.   
 

Places like Syracuse, Boston, New York City, and Hartford saw above average snowfall (thru the 5th of March). But places like Washington DC,  Buffalo, Baltimore, and Atlantic City saw well below average. Many places on the Tug Hill saw a well above average snowfall...Redfield has seen over 300 inches.

So while New York State and New England (especially northern areas) saw snowfall more or less like my outlook showed. Those in Pennsylvania and the Mid Atlantic surely didn't. The Mid Atlantic fell well below what I thought would happen.

As I've been talking about the last few days on my Facebook Weather Pages. The 10 thru the 20th look to be cold with an active pattern. So there most likely will be more snow, perhaps even in the Mid Atlantic States, how much is yet unclear.

As far as overall temperatures for December to the 1st of March, that I didn't even come close to being right.
Overall temperature anomaly from December 1st to March 1st.
 
 

This post will touch on the important reasons winter 2016-2017 turned out like it did.

Why the wacky winter?

When I made my outlook, the teleconnection setup pointed toward ridging out west and stronger troughing in the East. I had thought that we would see more blocking near Greenland. The SST projections supported my thoughts back in Fall of 2016.

The QBO (Quasi-biennial Oscillation)

When I looked at the analog years, everything pointed toward a negative QBO on average for the winter months. But it turned out that the QBO stayed strongly positive for much of the time. I couldn't find anything in the historic record that showed a weak La Nina, lower solar activity, with a positive QBO. Not saying there haven't been, but I couldn't find one. At least until this winter.

The Polar Vortex didn't weaken like the analogs showed it should. This was because the +QBO allowed the westerlies to remain much stronger than average. The stronger PV keep a lot of the cold locked up in northern Canada, with only a few weaker surges of arctic air into the Northeast and Mid Atlantic.

The MJO (Madden-Julian Oscillation)

The MJO is one of if not the major cause of the way winter 2016-2017 went down. The MJO has eight phases some of these associate cold in the East, others associate warmth in the East. The MJO is difficult to use and forecast from, it only is fairly reliable for around two weeks. Because of that it can't really be used to make a seasonal outlook.
 

For winter 2016-2017 the MJO was very active. This effected  Great Lakes, Northeast, and Mid Atlantic climatology.  Weak to neutral La Nina's tend to be cold and snowy in the Northeast. The MJO was so active that it overruled how a weak la Nina typically impacts the Northeast and Mid Atlantic region.  So we ended up with a warmer and less snowy winter than was expected based on climatology.   

Blocking:

What blocking we did have largely stayed over eastern Canada instead of being farther east closer to Greenland. This aided the troughing in southwest Canada into the western CONUS.

The Pacific:

The ENSO (El Nino- La Nina Southern Oscillation)

Last fall everything in the Pacific looked to support my thoughts. We were heading into a La Nina. But then as we got toward January things started to change, as there seemed to be a transition to El Nino underway. The transition became very clear by February as warmer than average SST (Sea Surface Temperature) returned to the Pacific west of South America. This shift happened very quickly, much quicker than I thought it would. These warm SSTs helped ensure that there would be no locked pattern of cold in the Northeast. 

The EPO (Eastern Pacific Oscillation)

When winter 2016-2017 started the EPO was staying negative to neutral most of the time. This was one of the main reason the first three quarters of December 2016 was so cold. Then things changed, From around Christmas to the end of the month we blowtorched. The last quarter of the month was so warm, that it wiped out all the cold before it, making December above average overall in temperatures.  The Cold came back for the start of January. Then SOI spiked during the last week of December, so I knew a January thaw was on the way. But the thaw went a lot longer than I thought it would. The reason I thought it wouldn't last was the Sudden Stratospheric Warming event that occurred at roughly the same time.  However, when combined with the timing of the MJO going into the warm phases, made sure there just wasn't any cold for it to bring south into the Northeast and Great Lakes. 

The EPO stayed positive for a large part of winter 2017, this assisted the ENSO to keep the pattern transient, The Pacific and Northern Jet were allowed to stream too fast. This helps keep the cold to the north, and greatly reduces storminess along with making an unfavorable storm track for the Mid Atlantic into the Northeast. 

The PDO (Pacific Decadal Oscillation)

We had warmer that average SST in the north Pacific in the Gulf of Alaska and off the Northwest Coast during late fall 2016. As we got into winter 2016-2017 those warm SST cooled quite quickly. This allowed the Jet to keep the cold air bottled up in Western Canada and the Western U.S. If the pool of warm SST had remained, the trough would have come farther east, bringing cold into the Great Lakes and East Coast.

Winter tried to reverse things for the first 10-12 days of February, but the pattern being so transitory ensured nothing could lock in. Se we warmed and torched once again.

There are other minor reasons for the way winter has turned out. But the ones I listed above are the major ones.



Thursday, March 2, 2017

Spring 2017 outlook thoughts.


For about half of you, the winter of 2016-2017 didn't go quite as I outlined last fall. There are several reasons for this which I will outline in a blog post very soon. Winter 2016-2017 will be remembered as a winter with decent precipitation, but with sharp temperature contrast.

Anyway, some are asking for my thoughts on Spring and Summer 2017. So your wish is my command :)

Spring 2017:

We had a short lived La Nina, it is now neutral. But even if La Nina has ended it still going to exert an influence on the rest of March into the 1st week of April.
CFSv2 2 meter temperature outlook.

 

Past years that looked similar to the current pattern, 1998, 1999, 2002, 2008, 2009, 2011, 2012, 2013. The year that looks the closest to what I'm seeing was 2008 with 2013 a close second.  
 

March is going to see this battle between warmth and cold continue. But I do see a chance for a major arctic shot of cold air for the end of the 2nd week of March into the third week of March.  So March will see a slow build up to Spring like weather. Could there be a snowstorm during that time? Maybe, but it will depend on timing.  The last week of March into April should see this winters hold break on the Northeast, as the jet stream lifts the cold air north and west back into Canada.

April and May look to be very warm over the entire Northeast and especially so for Maryland Delaware, southern New Jersey, and points south.
 

The precipitation outlook is looking to be average to above average across the Northeast and Mid Atlantic. Those Sea Surface Temperatures (SST) are way above average. As the coming El Nino strengthens, as we head into Summer, there could be plenty of moisture. Those SST's along the East Coast and in the Gulf of Mexico will play a big role in this year's severe season. 
East Coast SST:
 
Gulf SST:
 


Severe outlook:

This year's severe weather season, got an early and deadly start. But years that had a similar setups responded similarly.  April and May could be quite active, with both severe thunderstorms and tornado threats. The Ozarks into the South and Southeast CONUS could see quite a few outbreaks.

Remember, reliable tornado records only go back to 1950. So there isn't a lot of data to look at.

Because the Mid Atlantic, Southeast and the southern states saw a very light winter; There was nothing to cool down the coastal waters. All of this warmth and moisture will be available fuel for severe weather. 2017 will most likely be the most active severe season we've seen in 6 years.

2008 and 2011 were very active. For the Northeast this could be a year more akin to 1998 and 1973, as that southern moisture and warmth move north and clash with the cooler dry air just to our north in Canada.
Summer 2017? 

A quick few thoughts about summer 2017. I think the pattern will allow for a warm and fairly wet Summer across the Northeast. As for hurricanes, it could be similar to last summer with most of the hurricane threats coming into or close to the United States, those dratted warm SST again.  As far as numbers of tropical systems maybe a little less than last year. I will come out with an official summer outlook and an Atlantic hurricane outlook sometime in April.

Images come from WeatherBELL Analytics and NOAA/NCDC. 
 
 
 
 

Sunday, February 26, 2017

Teleconnections what the heck are they part two


Here is part two of the teleconnection post. This post will cover four major teleconnections. This won't make you an expert. But it will give you an idea of what they are and how they work.
 
The Arctic Oscillation (AO)

Before I can talk about the AO. I have to talk about the Polar Vortex. Because the AO and PV are forever linked.

One other thing to remember, is the phrase geopotential deals with how much work it takes raise a parcel of air from sea level to a certain altitude against the pull of earth's gravity.  Something I show a lot in my weather outlines and outlooks is the 500mb geopotential height charts, to show the state of the atmosphere.

The PV is an area of low pressure circulation over the arctic. The PV is a normal part of the atmosphere and is around the entire year, but most of us only hear about it in the winter. The PV is stronger in the Summer and weaker in the winter.     The strength of the low pressure circulation is the process we call the AO.

The AO is a climate index on the state of the atmospheric circulation over the Arctic. Like all teleconnections it has a positive and a negative state.
 

Positive phase

During the positive phase the AO features below average geopotential heights, which means the PV is strong. The lower area of low pressure at the mid latitudes is higher (weaker), due to the air travels from areas of high pressure to low pressure.  This means the air flow is toward the arctic. Because of this the westerlies and northeasterly trade winds are flowing much stronger.  The stronger winds keep the cold corralled in the arctic.  So the air over the lower 48 is warmer.

Negative phase

In this phase there are above average geopotential heights, which means the PV is weaker. The higher area of low pressure at the mid latitudes is higher (weaker), due to the air travels from areas of high pressure to low pressure.  This means the air flow is away from the arctic.  The winds circling the arctic are weaker, allowing for the PV meander north and south, allowing colder arctic air to invade the mid and low latitudes.  So cold air overruns North America invading the lower 48.  

Impacts on the Eastern U.S.

  • AO+ is associated with above-average temperatures
  • AO- contributes to colder winters and an increase in nor’easters (coastal storms) for New England states

 

North Atlantic Oscillation (NAO)

The NAO is defined by the difference in surface pressure between two atmospheric centers of action, the Icelandic Low and the Azores High.

The NAO is one of the major players in the climate variability in the Northeast and North Atlantic. It's these east west oscillation motions, that represent a north/south swing in pressure across the North Atlantic, that control the strength and direction of the westerly winds and storm tracks.

When the NAO is in its positive phase, we see upper level ridging over the Eastern U.S. The ridge causes a predominant south-westerly flow which  brings warmer temperatures into the Eastern CONUS.

Impacts on the Eastern U.S.

  • NAO index is high (NAO+) it's associated with above-average temperatures.

The NAO is also believed to have an impact on the weather over much of eastern North America. During the winter, when the index is high (NAO+), the Icelandic low draws a stronger south-westerly circulation over the eastern half of the North American continent which prevents Arctic air from plunging southward. This effect can produce significantly warmer winters over the northeastern United States and southeastern Canada.

  • NAO index is low (NAO-) contributes to colder winters and an increase in nor’easters (coastal storms) for New England states

When the NAO index is low (NAO-), the northeastern United States and  even the southeastern United States can incur winter cold arctic outbreaks . A strong NAO- contributes to a weakened jet stream that normally pulls zonal systems into the Atlantic Basin, thus contributing to heat waves.

 


The Pacific North American (PNA)

Is one of the major teleconnections that controls weather for the entire northern Pacific to the Eastern Seaboard of the U.S.

The PNA effect the circulation pattern over the Pacific for every month, except June and July. This circulation moves east over North America. It consists of anomalies in the geopotential height field (normally at the 500 and 700 mb level) over North America.  The disruptions in the Pacific Jet Stream affect weather downstream here in North America.

The positive phase

The positive phase involves above normal geopotential heights of the western US. This typically causes ridging over the western U.S. and troughing over the eastern U.S. This allows Canadian cold air to drop southeastward into the eastern U.S. When the PNA is positive we typically see an increase in southeast and Mid Atlantic winter storminess.

The negative phase

During the negative phase we see the trough over the western U.S. and the ridge over the eastern U.S. This allows the warm moist air from the Gulf of Mexico to lift north and east into the Mid Atlantic and Northeast; so these areas see above normal temperatures and humid conditions. The PNA has a much bigger impact on temperatures during the winter than during the summer. 

Positive phase
 
Negative phase


The Madden-Julian Oscillation (MJO)

The MJO is a pattern of suppressed and enhanced rainfall that shifts eastward in the tropics.  Anomalous rainfall becomes evident at the start over the western Indian Ocean, moves eastward into the equatorial Pacific Ocean, and then into the western hemisphere where the anomalous rainfall pattern becomes less apparent. It takes about 30-60 days to make it completely make it around the equator. During the winter, the MJO can be correlated to enhanced precipitation along the east coast of the United States. 

In the enhanced convective phase, winds at the surface converge, and air is pushed up throughout the atmosphere. At the top of the atmosphere, the winds reverse (i.e., diverge). Such rising air motion in the atmosphere tends to increase condensation and rainfall.

The MJO is quite complicated. But, depending on the time of year each phase can have a different impact on temperature and precipitation across the U.S. The MJO consist of 8 phases. In general the MJO phase response is 12 days.  During the winter months , the MJO can be correlated to enhanced precipitation and cooler temperatures along the east coast of the United States. 

Here are a couple of charts that show on the MJO typically impacts the U.S. during January, February, and March, as well as for June, July, and August.


 
That's enough for part two. Part three will cover the El Nino Southern Oscillation, The Southern Oscillation and briefly cover the other major teleconnections.