Final 2013-2014 Winter Forecast (Blogspot version)

Verification of analog vs. actual temperatures

Verification of analog vs. actual precipitation

 

 

 

 

 

 

 

Weather Jargon and Terminology

Hi everyone. In this thread is the official L'Heureux's Weather 2013-2014 winter forecast. I have a better understanding of more weather/sea surface temperature patterns this year, and will use this increased understanding towards this forecast. In this thread, I will be giving brief summaries of each of these patterns and how these patterns will influence the overall weather pattern this winter.

El Nino/La Nina/La Nada

 The El Niño Southern Oscillation (ENSO) influences the global upper atmospheric winter circulation and cyclone tracks associated with them.  During a neutral phase, upwelling of cold water along the Peru-Humboldt current occurs off the west coast of South America.  Warmer water found in the western Pacific Ocean is normally about 8°C greater than the eastern Pacific Ocean.  A La Niña event is defined when the 5 month mean of SST anomalies is less than -.5°C and an El Niño event occurs when there is 6 months of above .5°C in the western and central Pacific. When this area is in a "normal" phase, we call this a "La Nada". The sea surface temperature patterns of a la nada event can be seen in figure 1 below.

During El Niño, the trade winds relax in the central and western Pacific and sometimes reverse leading to an area of low pressure in the eastern Pacific and an area of higher pressure in the western Pacific.  Upwelling of cooler water to the surface in the Humboldt Current slows down or cuts off completely. The sea surface temperature patterns of an el nino event can be seen in figure 2 below.

            In a La Niña event, the Eastern Pacific is cooler than usual, and the cool water extends farther westward than average.  More upwelling of cooler water occurs in the Humboldt Current.  This enhances the Walker circulation across the equatorial Pacific regions.  El Niño and La Niña are opposite phases of the El Niño-Southern Oscillation (ENSO) cycle, with La Niña sometimes referred to as the cold phase of ENSO and El Niño as the warm phase of ENSO. 

A La Nina has the effect of making the northern half of the United States colder and the southern half warmer. An El nino has the opposite effect. Strong la nina winters tend to favor warmer weather across the southeast, but not always. A La Nina will cause a greater deal of "buckling" of the jet stream, causing a larger temperature swing throughout winter and leaves for a more inconsistent winter. An El Nino has a split storm track; the polar jet stream and the subtropical jet stream. Strong El Nino winters have a very slight cooling effect on the Southeast and a warming trend for the northern half of the country. The cooling effect on the Southeast may be driven more by the higher degree of precipitation. Because of the buckling in a La Nina, warm periods tend to be warmer and cold blasts tend to be more intense when they come. El Nino winters have a "dampening" effect on this temperature swing!

A La nina sets up a wetter pattern across the Ohio River Valley and the Pacific Northwest, and leaves the southern tier of the United States (particularly the southeast) in a dry spell. An El Nino favors much wetter winter for us in the southeast. If a La Nina winter favors "quality over quantity" for storms: i.e, stronger but fewer storms, an El Nino winter favors a greater quantity of weaker storms.

A La Nada scenario has a diminished impact on the weather pattern, and leaves the door open for other patterns to dominate.

The Pacific Decadal Oscillation

The El Nino Modoki

The North Atlantic Oscillation

The Arctic Oscillation

The Pacific North American Connection

The Polar Vortex

The East Pacific Oscillation

The West Pacific Oscillation

The Madden-Julian Oscillation

The Atlantic Meridional Mode

Pair this with the Pacific Decadal Oscillation and you explain a big chunk of the global warming argument. 

The Quasi-Biennial Oscillation

The Indian Dipole Anomaly

The Snow Advance Index

Mountain Torque Events

Sunspot count/Solar activity

Sea surface temperature anomalies

Backing Upper Level Low

This is a very unusual track for a cutoff upper level low - due to an elongated ridge over the northern tier of the United States, this low will move along the southern periphery from the East Coast to the Pacific Basin. The Southeast (especially North and South Carolina) will be extremely warm next week due to this ridge. The largest positive temperature anomalies will be across the Ohio River Valley and the Northeast.  Florida may have a small upper level system bringing rainfall to the state next week. The "wrong way low" will bring much needed rainfall to western Texas, New Mexico, and Arizona.

8-day forecast for the 300mb level. Check out the upper level low's backing track and where the hot weather will be!

April - May Spring Forecast

 First things first - the April 1st - May 31st forecast for geopotential heights. Blue would suggest a cooler than usual atmosphere (from a lower 500mb level) and a red color would suggest a warmer than usual atmosphere (from a higher 500mb level). I ran a weighted average of my most similar years from my original November winter forecast (1952, 1960, and 1964) up through May 30th. Note, this is a 5-day running mean.

Sorry I don't have the large date title at the top - the mini dates above the color bar may help. Note the cool start to April followed by the persistent warmth from April 8th through May 1st.

This output is the CFS sub-monthly output (0-45 days out) coupled with the 3 most similar spring setups.

Spring and Summer 2013 Long Term Forecast

 First things first - the March 15th - April 15th forecast for geopotential heights. Blue would suggest a cooler than usual atmosphere (from a lower 500mb level) and a red color would suggest a warmer than usual atmosphere (from a higher 500mb level). I ran a weighted average of my most similar years from my original November winter forecast (1952, 1967, 1970, 1978, 1979, 2009) up through April 30th. After April 30th, I have gone with a new list of years.

This forecast for geopotential height anomalies is a monthly index running from May 2013 through October 2013. My confidence at this time is low however I believe the large scale patterns (Pacific Decadal Oscillation, El Nino Southern Oscillation) will pan out very much similar to last summer. The new years chosen for my spring/summer index on similarity are 1952, 1967, 1979, and 2012.

 

My early concern is this blocking pattern showing up towards September (green over Greenland) - this is a similar pattern to what showed up last hurricane season.

1952 hurricane season

1967 hurricane season

1979 hurricane season

2012 hurricane season

January 30th Flooding Event Assessment

Last weeks flooding event may not been of a "historical worst" for the High Country but it did have its own circumstances that exasperated the flooding in the High Country anyway. The historical records since 1970 go to the dynamic duo of Hurricanes' Frances and Ivan in 2004. But where does this rain event stand with historical records? 

Snow Forecast 2013/02/26

February Archived Model Precipitation

This is my archived model precipitation outlook for each day in February, along with the daily mean temperature freezing line (dark blue line). Since the line represents the mean temperature, this can still mean the high exceeds the freezing point. A good rule of thumb is to assume the high and the low are 10-15* F apart from one another. So, it is best to be behind the freezing line for a higher probability of snowfall. The winters used are 1952, 1967,1970,1978,1979, and 2009. Rainfall is in mm/day. The high end is 25.4mm, which is the equivalent of 1" of rainfall.

Note that this model run is not going to be perfect and will have considerable inaccuracies. As Matt Parker from North Carolina State University says "All models are wrong. Some are useful." This model gives a good indication of what it has done historically for the most similar winters to this one, but does not necessarily imply the same pattern will show up. Rather, the larger scale teleconnection patterns are captured and unless small amplitude/high frequency patterns show up in multiple years, the small patterns are frequently dampened, if not removed entirely. Therefore, some patterns may still occur but be 1-4 days off from the actual pattern.

2013-01-30 Forecast Update

***Please note the time stamp is incorrect. The time shown on the animations should have +1 hours added on (for example, 2PM is really 3PM).***

Radar composite reflectivity forcast

Estimated rainfall (inches per hour)

Expected wind gusts (in knots)

Maximum wind speed

Visibility. A gray area is more likely to be fog, especially along the eastern slopes of the mountains

Updraft helicity. Helicity is the growth of horizontally oriented spin (a corkscrew motion). Upward helicity is the corkscrew spin growth in the vertical. Areas that are pinged are more likely to have squall line induced vortices that have a damaging wind component.

2013/01/23 Snow Forecast (Originally 1/20 forecast)

NAM Model Run 18Z

 

ECMWF snow projections, with the freezing line

Historically most similar storms with snow accumulations

Here we go with another snow producing system for this Friday. Note that with the presence of a weak warm layer aloft, there is a slight chance of sleet mixing in. The warm layer doesn't seem to be strong enough for freezing rain (complete melting), and we will not have the warm ground issue like our last system. Instead, what falls will likely stick right away. I expect this week to remain cold however there will be a short mild trend for next week. Late next week we get a harsh burst of cold air. For good measure, check this out: the plot was used from data I calculated back in November!

2013/01/17 Snow Update

WRF Model snow water equivalent (SWE)

Total snow accumulation for Thursday afternoon - Friday morning

A model agrees with me! So I'm not alone!

2013/01/16 Snow Projections

What changed from yesterday? Yesterday, the upper level component from within the southern branch of the jet stream was being stretched out into oblivion by a much larger trough from the northern branch of the jet stream. Today, the system is maintaining integrity through the Carolinas. You can see the difference between yesterday and today below. Note in the newer animation I have kept the "freezing line" at the surface. Note the newer track has the upper level component traveling farther south, thus delaying the onset of the weakening of the southern trough carrying this disturbance.

Yesterday's 500mb winds

Today's 500mb winds (with freezing line at the surface)

The ECMWF snow projections, with the freezing line in blue. Note that it is picking up snowfall south of the freezing line - which is accurate for the near freezing temperatures located there. South of the line, I would take 50% of the snowfall that is showing up in the model run. For other locations, the first image there is snowfall, take off 1-1.5" from the total, to account for the warm ground that must be cooled first.

ECMWF Model Snow Output

Forecast 2013/01/15

500mb level winds. You can see the degeneration of the upper level trough through the animation. Note that it gets flatter and flatter with time.

Precipitation, with the rain/snow line in light blue. Note the orange polygon - this is where I expect a mix of wet snow and rainfall, leading to a slushy accumulation on grassy surfaces.

Snow accumulations for the Appalachian Mountains will be less than 1" - this system is moving too quickly and is weakening too rapidly to amount to much else. With a probable 8:1 snow ratio for the mountains, 7:1 for the foothills, and with the orange area, 6:1. Snow accumulations will be at maximum, 1-2"(southern Appalachian Mountains). I-85 northward will get a dusting to 1"