Winter Forecast

AshevilleWX 2020-2021 Winter Weather Outlook

AshevilleWX 2020-2021 Winter Weather Outlook

Each year here at AshevilleWX we do our best to put out a reasonable forecast about what you can expect during winter, based off of several factors. Most of this forecast is rooted in historical data and conclusions are reached through data comparison. Once we denote similarities of how a particular year is setting up, we can compare this data to data from years past to create a Winter Weather Outlook. This is merely a long range forecast though, and there is great uncertainty as usually with exactly how winter will unfold here in the mountains of WNC. Below you can find my 2020-2021 Winter Weather Outlook.

Graphic Produced By Evan Fisher

Seasonal Snowfall 20’-21’ Projections

Boone: 28”-35”

Asheville: 6”-8”

Charlotte: 2”-3”

Greensboro: 4”-6”

Raleigh: 3”-5”

Wilmington: 1”-2”

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Why Less Than Average Snowfall For WNC?

There are a couple of factors that have lead me to forecast less than average snowfall for WNC this year, but the main reason is due to a moderate to strong La Nina setting up. What is La Nina? This is when cooling happens in the Nino region of the Pacific Ocean. The Nino region is observed on a regular basis by multiple sensors that monitor water temperatures. This area is where weather is generated for portions of the United States. If this region is warmer than normal then El Nino is consider to be in place. If the region is cooler than normal then La Nina is considered to be occurring. Historically, we see wetter conditions during El Nino events here in WNC. This means that warmer than normal temperatures in the Nino 3.4 region equates to wetter winter conditions in the Mountains of WNC. On the other hand, a La Nina would mean that temperatures in the Nino 3.4 region of the Pacific Ocean are cooler compared to the average. Historically during La Nina years, less precipitation has moved through WNC during winter time frames. With less activity in the key region, storms and Gulf Lows will be limited around the South. Strong cold shots are also possible with La Nina season, but I am leaning more towards a mild winter compared to a bitter cold one. That still remains to be seen though.

Moderate To Strong La Nina Setting Up

We have a moderate to strong La Nina setting up in the key Nino region where observations are taken. That means that cold water is pooling up in this region, and sea surface temperatures are falling below average. Therefore, limited storm development is expected to occur along the Equator and that means less precipitation moving through the Southeast. This is strictly based off of historical data. Below you can see what a typical La Nina looks like when observing sea surface temperatures.

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What To Expect Here In WNC?

Evan Fisher has produced a great graphic that details out the amount of snowfall we received here in WNC each Moderate or Strong La Nina year. As you can see below, there is great variation among average snowfall each year during moderate & Strong La Nina years.

Map Produced By Evan Fisher

Here is also a map that shows the combined average of snowfall each year during Moderate & Strong La Nina Winters. As you can see, we are working with limit data to compare with only 11 data points of comparison. Moderate to Strong La Ninas are somewhat rare, which is why there is great uncertainty with this forecast.

Map Produced By Evan Fisher

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Forecast

I posted this map above, but it is worth revisiting. I believe that Northwest Flow Snowfall will dominate totals this year in the NC Mountains, with close to average yearly snowfall totals being possible. Throughout the years, Northwest Flow has been the most consistent with providing snow events to the border counties.. and during this La Nina event I believe that sweeping arctic fronts this winter will bring several chances for Northwest Flow. That is why I have place most elevations above 3500’ in WNC at 80%-100% of normal in my projection map. Moving into the valley areas of WNC where snowfall totals are typically achieved by strong Gulf Low pressures, I have placed 60%-80% of normal snowfall. With limited storms moving in from the Gulf region, I think chances will be limited for a large snowstorm across the Southeast. That of course does not mean that one is not possible, history just shows that WNC and NC in general receive less precipitation during La Nina years.

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Moving on to the Piedmont area, I am projecting 60%-80% of average snowfall for the areas like Greensboro & Charlotte. Each year these locations tend to receive their yearly snowfall totals from Gulf Lows, and I am of the opinion that those will be limited this year. Things like backdoor frontal passages will be where snowfall is picked up in the Piedmont, but the chances for Gulf Lows appear to be less compared to El Nino years.

The Raleigh area will be an area of transition in my opinion. I believe that we will see a strong cold shot or two this year, and this will be where locations along the Coast of NC see their chance for snow. During La Nina seasons, suppression of storms can lead to strong cold meeting with a meandering low pressure along the coast. It is my opinion that we will see one of these type storms develop this winter, and locations along the coast will receive 100%-120% normal snowfall. The Raleigh area, being on the fringe of these events, as well benefiting from backdoor cold fronts and placing that location in my 80%-100% yearly snow average zone.

Model Data

I have sourced a couple of long range models as well to illustrate the outlook on snowfall for this winter. Snow lovers will not like these maps, but they are a good indicator and were somewhat accurate last year when I made my forecast for below normal snowfall for the Asheville area. These maps were all provided by https://www.bennollweather.com.

Model Super Blend

European Model Snowfall Forecast By Month

UKMET Snowfall Forecast By Month

Conclusion

This year across WNC, snowfall averages will vary greatly. Based off of a super blend of knowledge, I forecast that WNC will see slightly below normal snowfall, with near average temperatures throughout the season. Conditions could be fairly dry at times with limited forcing from the Pacific, but one Gulf Low that threads the needle will be all it takes to bust my forecast. Please take this forecast with a grain of salt, and know that these forecast are mainly for fun and enjoyment. Know the winter weather is extremely unpredictable, and each year a new precedence can be set. Use this article for fun, but don’t use it as spoken word because no winter forecast should be taken as certainty.

-Meteorologist Hunter Ward

2019-2020 AshevilleWX Winter Weather Forecast-Volatile Winter Ahead

Volatile Winter Ahead With Average Precipitation & Large Temperature Swings In Store For WNC

Each year I try and put together a general idea of how I think winter could play out around WNC based off of history, and the use of long range forecast methods. This includes the observation of the state of Sea Surface Temperatures (SST), the QBO (stratospheric winds), Solar Max/Mins, ENSO (El Nino/La Nina), and other various atmospheric anomalies that play into the complicated equation of winter weather in the Southeast. These methods are not exact, and many variables must be accounted for.. therefore accuracy from time to time is limited, especially here in the mountains of WNC. So without further ado, below is my 2019-2020 Winter Forecast for NC.

AshevilleWX 2019-2020 Winter Forecast

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Large Temperature Swings Expected This Winter

For Western North Carolina this winter, I am expecting average to above average snowfall in locations above 3500’, and slightly below average to average snowfall for locations below 3500’. I am basing this off of the belief that Northwest Flow snow will be more often this year compared to some other previous years, and that we will receive one or two moderate to large snowfall that will satisfy averages around the area. Below is the average annual snowfall for WNC per the NWS in GSP. If you extrapolate my percentages, you will determine that I expect around 10”-11” of snow total for Asheville this year. That would not be a blockbuster winter, but would fall in line with the average over the past 30 years.

Courtesy of GSP NWS

Here is the average seasonal snowfall for the entire state of North Carolina per the National Weather Service. As I stated earlier, I expect one or two big storm for the Southeast, and that will likely satisfy or come close to satisfying many averages. It doesn’t take much for some locations! With a near natural ENSO (El Nino/LaNina Index), we will likely enter into what is considered a Modoki El Nino, which is rare. Only a few years previously have been Modoki El Nino years so we have very little to compare to.

Modoki El Nino

So what exactly is a Modoki El Nino or even El Nino? When long range forecasting, meteorologist will observe the sea surface temperatures anomalies (SST) in a particular region of the Pacific Ocean know as Nino 3.4 region. Depending on where the water is cooling and warming at, plays a huge part in where systems develop in winter, as well as the direction they move. The United States weather moves in from the Pacific Ocean, so where storms develop, and which path they take towards the US matters greatly. Below is a graph showing what a strong El Nino would look like in the Nino 3.4 region taken from the year 2015.

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La Nina on the other hand is a cooling of the 3.4 Nino region. You can see what that looks like on the graph below from the winter of 2010-2011.

La NinaGraphic.jpg

Currently the ENSO region is showing a near natural signal, and many experts believe that it will either stay neutral or move slightly positive through the winter. A modoki El Nino is a near netural El Nino where a large basis of the warm water is positioned in the eastern portion of the Nino 3.4 region. You can see below the current sea surface temps and in the Nino 3.4 region there is only slight warming. At the end though, notice how it is extending to the East. That is a sign that a Modoki El Nino could be on the horizon.

Source: CPC

Modoki El Nino History In WNC

Years of Occurrence:

Winter (Nov-Mar)1991-1992 Asheville Snowfall: 1.5” Asheville Total Precipitation: 18.46”

Winter (Nov-Mar)1994-1995 Asheville Snowfall: 3.4” Asheville Total Precipitation: 18.56”

Winter (Nov-Mar)2002-2003 Asheville Snowfall: 17.9” Asheville Total Precipitation: 20.63”

Winter (Nov-Mar)2004-2005 Asheville Snowfall: 6.6” Asheville Total Precipitation: 16.35”

Winter (Nov-Mar)2009-2010 Asheville Snowfall: 39.2” Asheville Total Precipitation: 28.95”


These are the only years that an east based natural Nino (Modoki El Nino) has been present. As you can see, it’s a relatively new phenomenon. With that east based warmth, comes ample amounts of moisture that move into the Southeast. So, based off the numbers provided, one can assume that if the temperatures in Nino Region 3.4 stay consistent.. 15”+ of precipitation around WNC will be likely this winter. But will the cold air be in place for snow? That is the question, and we will need to look more at the winters of 2002-2003 & 2009-2010. I will observe the winter of 1991-1992 more closely because we were also in a drought at this point in time during 1991. With 1.27” in September of 1991, & only .19” of rain in October of 1991, WNC was in a deeper drought compared to where we currently sit.. but there are comparisons to be made.


Temperature Data Leading Into Modoki Years For WNC

Average September Temperature For Asheville:

1991: 67.2 degrees

1994: 64.6 degrees

2002: 68.8 degrees

2004: 66.4 degrees

2009: 66.9 degrees

2019: 71.2 degrees

So this tells us that we are leading into a neutral east base El Nino as we come off of our warmest September of all comparison dates. I think that trend continues too, and that a several warm shots will be possible this winter. That doesn’t mean that there will not be cold, but as I stated earlier, I believe large temperature swings will be likely. There is some long range model data to also support this warm idea. Below you can see the European Model monthly temperature anomalies, and each period shows above average temperatures for the Southeast.

NOV/DEC/JAN Courtesy of Weathermodels.com

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DEC/JAN/FEB Courtesy of Weathermodels.com

JAN/FEB/MAR Courtesy of Weathermodels.com

Will It Actually Be As Warm As The Models Show?

A word of caution with the Euro monthly charts, they are great guidance.. but on average last winter they were only right about 20% of the time. That being said, there does appear to be an increasing likelihood that this winter will be above average temperature-wise. So, a smart/easy bet for a winter forecast would be to go with warm and wet… but there is a wildcard this year.

Solar Minimum=Wildcard

We are progressing deeper into a solar minimum, which mean that solar flare activity is trending down. With less sun spots (none in the last 200+ days) this is the least active the sun has been since 2009. Remember the winter of 2009-2010? Almost 40” of snow fell that year at the Asheville Airport. Here’s an excerpt from Whats Up With That regarding how low solar activity correlates to shots of cold.

Low solar activity has been well correlated with an atmospheric phenomenon known as “high-latitude blocking” and this could play an important role in the upcoming winter season; especially, across the eastern US. In addition, one of the natural impacts of decreasing solar activity is the weakening of the ambient solar wind and its magnetic field which, in turn, allows more cosmic rays to penetrate the solar system. The intensification of cosmic rays can have important consequences on such things as Earth’s cloud cover and climate, the safety of air travelers, and as a possible trigger mechanism for lightning.

From Whats Up With That

High-latitude blocking is the key to getting cold air down to the Southeast. When you hear me talk about indices like the NAO & the AO, these are all measures of the degree of high latitude blocking in place. The blocking effectively creates a wall that deflects cold air from the arctic, down into the United States. How strong this blocking is, and where exactly it comes from, will determine how cold it gets in the Southeast.. and across the rest of the East Coast.

So we are entering a period of solar minimum that could rival any other period in the last 100 years. Does that mean record cold is possible? Maybe, but it really just tells me that this will be a unique winter, with several variable that will need to be properly accounted for.

QBO (Quasi-Binary Oscillation)

The last bit of information I will discuss before my conclusion is the QBO. This is a daily observation of stratospheric winds along the equatorial area. Detected over 50 years ago, these winds are measure by radio signal at various points in the atmosphere. By tabulating this data over the past 50 years in an increasingly large area, we have been able to tie certain atmospherical outcomes to either a positive or negative QBO. What you need to know here is that a negative QBO is known to correlate with high-latitude blocking. As you learned a few minutes ago, high latitude blocking sends cold air down into the United States. If a negative QBO stays persistent as projected by many, then cold shots this year will be likely.

Conclusion

So I know that I have detailed out a lot of information, but what you really need to know is that I believe that an East based Modoki El Nino will provide ample moisture that moves through the Southeast. At some point in time this winter, the high-latitude blocking will get in place, and put enough cold air into WNC and other portions of NC as moisture moves in from the Southeast, and in turn snow will fall. How often that happens is of course an unknown, but there are signs that indicate that the players will be on the field for a snowstorm this winter. We will see exactly how the Solar Minimum plays in because many experts are calling for a very warm winter. If we end up cold, or below normal temperature-wise, the Solar Minimum will have to be taken seriously. So again, I expect 1-2 large storms that will put many locations across NC at or close to their average yearly snowfall. Temperature swings will be frequent, and record daily highs/ lows both cannot be ruled out. It will be volatile. With this volatility I believe will come the possibility of frequent Northwest Flow Snow for the higher elevations of WNC. This will push those areas above their normal yearly averages. Asheville should expect around average snowfall, and as you progress east, the chances for a significant snow decreases. This is my best guess, and is only a forecast. These forecast can easily be busted or made by 1 storm, so please stay tuned for my daily forecast to keep yourself up to date on the approaching weather!

-Meteorologist Hunter Ward