VIRGINIA WEATHER ACTION’S 8TH WINTER WEATHER OUTLOOK
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It’s time for our 8TH Winter Weather Outlook!
Unforatenely, a lot of things went wrong with last winter and winter decided to show up a few months late as it was quite cold and rainy right through the spring. Besides ONE snow in December, the rest of the winter was very warm and dry. Some of the things that went wrong last winter was a lack of ridging across the Western U.S., which would help to drive colder air across the east. We also had little blocking near Greenland. To get really good snowstorms, you’ve got to have blocking to keep the colder air locked into place.
As we get closer to winter, we’re noticing things that DID NOT happen last winter. We have some ridging across the Western U.S. (with a drought,) plus the North Atlantic Oscillation has leaned negative, which gave us a lot of our rain events late Summer into early Fall. We have a weak to moderate La Nina, which “usually” supports milder conditions, due to a Southeast Ridge that also develops. While that WILL be a factor and in play this winter, this La Nina is “quite different” from past La Nina’s.
Our Analog years are: 1955-56, 1956-57, 1964-65, 1974-75, 1983-84, 1995-96, 2000-01, 2005-06, 2008-09, 2010-11, 2011-12, 2016-17, and 2017-18. Some of these analog years go from one extreme to another, which is something I DO NOT like using. However, it was very important to not have a total cold or warm bias. We looked at analog years that featured a weak to moderate La Nina, and ocean temperatures and other factors that matched those years that paint us a picture of what the 2020-21 could look like.
- Slightly Below to Below Average Temperatures
- Near Average Precipitation
- 2 to 3 moderate snow events (3 to 6 inches per storm)
One thing that has happened thus far that DID NOT last fall and winter is BLOCKING across Greenland. It has been noticeable and ONE reason why we’ve experienced cooler than average temperatures. The cold air intrusions will help to push the storm track to the south across the Tennessee River Valley into the Lower Mid-Atlantic. IF the cold air is stronger, this would favor storms along the coast and a snowier outcome is likely.
- Near to Slightly Above Average Temperatures, Much warmer mid to late month
- Slightly Below Average Precipitation
- 1 to 2 moderate events (3-6″) to potentially heavy snow events in mountains and Valley (6-12″+) ; potential for ice storm
As the cold eases a bit, due to the strength and “peak” of La Nina, we expect milder conditions by mid to late January. It’s common to see a big storm system ahead of a big pattern change, and if the cold air is in place, a big snow is not out of the question, BUT could easily be ice as well. The jet stream will move well north and west of us as the flow off the Pacific turns “zonal” (winds west to east,) and the warmth floods much of the Central and Eastern U.S.
- Much above Above Average Temperatures
- Below Average Precipitation
- Very small chance for ice or snow
The zonal flow off the Pacific will continue to flood the Central and Eastern United States, which will push the storm track north and west of our area. One thing to watch will be some systems crashing into the West Coast and moving eastward bringing a lot of wind with a few cold shots with them, but very short-lived (one to two days) due to lack of blocking.
- A return to Below Average Temperatures
- Near Average Precipitation
- Some coastal storms may produce snow or mixed precipitation events
As La Nina weakens, this will allow colder air to move back into the Eastern U.S. This will once again push the storm track back to the south and opens the door for a few storms that may feature snow or a mix of snow and rain.
Snowfall Forecast Prediction (December 2020 – March 2021)
- We are predicting 85 to 110 percent of snowfall (or near average snowfall.)
- The “number” on each location is our prediction.
- Our “ranges” are for elevation and/or if winter turns out to hang on longer than expected, leading to more snow events.
La Nina is here and we expect it to linger through much of the winter. Normally, La Nina’s are warm with and dry across the Mid-Atlantic. However, this is looking more like a “East-Based” La Nina, meaning the colder pool of water is confined across the Eastern Pacific, closer to South America.
One thing that may help with this winter – believe it or not – is the drought across the Southwest, stretching into California and Oregon. Also, the sea surface temperatures across parts of the Central and North Pacific remain warm. This has helped to develop a ridge of high pressure at times off the coast of Alaska and push the jet stream far to the north, then sending the jet stream east of the Rockies and dipping across the Eastern United States. This is a pattern that may very well continue through early to perhaps mid-winter.
This would support the EPO “Eastern Pacific Oscillation” to go negative at times. A ridge of high pressure near the coast of Alaska, allowing the jet stream to drive far to the north, giving Alaska a pretty warm winter! The “opposite” can also happen at times, which is the POSITIVE Eastern Pacific Oscillation. This would mean low pressure near the Alaskan Coast and flooding much of the United States with warmth, which we saw quite a bit last winter.
When the “EPO” is negative, a cross-polar flow from Siberia can happen and very cold air pours into the Eastern United States. One main ingredient or “source” of this cold air is a connection with the snow cover across Eurasia (Europe and Asia.) As of October 8, we’re already seeing a very busy start and this will help to supply some pretty cold arctic air intrusions across the Northern Plains into the Midwest, and at times, making it into the Northeast and Mid-Atlantic.
We have mentioned the North Atlantic Oscillation a lot over the last few months. High pressure near Greenland keeps the colder air “locked in” across the Eastern U.S. As storms develop, depending on where the blocking is located, they often cannot escape out to sea and ride up the East Coast. While we won’t have much influence from the sub-tropical jet due to La Nina, many storms that dive east of the Rockies and into the Tennessee River Valley often transfer energy to a new low pressure system that develops off the Mid-Atlantic coast. These storms often bring a mix of snow and ice to our area — they typically are never “true” snow blockbuster type events, due to weak low pressure in the Ohio or Tennessee River Valley still present and pumping in milder air aloft. This is a situation that may very well occur throughout December, part of January, and again in March.
Conclusion: I DO NOT think this winter will be ANYTHING like last winter. Yes, there will be mild spells, but as it looks like now, we should have opportunities for snow and or icy conditions in December, early January, and March. In between, mild conditions will be likely. With some of these up and down temperature swings, severe weather is also not out of the question. This winter will feature a bit of everything, or as I like to call it, a “Weather Buffet” for everyone to sample at the VWN dinner table.