The following is a written synopsis of the Winter Outlook for the 2020-21 season. We would like to thank Habaneros Mexican Restaurant in Morganton for sponsoring the Winter Outlook.
The biggest player we see for the winter season is that a weak La Nina has developed in the equatorial Pacific Ocean. La Nina is depicted by the cooling of waters in the Pacific along the equator. The La Nina will build and become stronger as we get into the first quarter of 2021, by next Spring the La Nina could be classified in a moderate category. La Nina generally produces a dry and mild pattern across the Southeast US.
Looking at the teleconnections that are used to predict weather patterns over a 1-2 week span during the season, the MJO will likely be in an unfavorable phase at the start of Meteorological Winter (December 1) but could evolve into a favorable pattern before the month is over.
The NAO (North Atlantic Oscillation) is teleconnection we look at to help dictate how a storm track could develop over a period of time. Negative NAO signature including a blocking pattern over Greenland and a jet stream that sags further south across the US, meaning a colder pattern for many including the Carolinas.
The NAO will be slightly negative at the start of December but should average out in a neutral state for the entire month. There is a time fame of 10 days (early month) we are watching where the NAO goes negative and then quickly moves positive. History shows that the Eastern US usually gets a significant weather event as a result of the change in the metric.
The PNA (Pacific-North America Oscillation) looks to be in a generally unfavorable pattern for us this winter staying generally negative. That will result in a fast zonal-type flow off the Pacific and spreading across the Continuous US.
PRIMARY SYNOPTIC PATTERN:
The main jet stream configuration that we are predicting for the winter season will be a near zonal pattern across the Western and Central US and then a path through the Ohio Valley and Northeast. It’s those two regions of the country that may have an active winter. For us in the Carolinas, we will be south of the jet primarily and that should result in a mild pattern. Due to the La Nina, we will not have the assistance of the sub-tropical jet steam so it could help reduce precipitation amounts.
SECONDARY SYNOPTIC PATTERN:
We could see more of a dip in the jet stream across the Eastern US from time to time this winter season. Also note how the jet makes a due north movement into the North Atlantic, that would be a result of possible Greenland blocking at times, which is the -NAO signature. If we can get into 1 or 2 good -NAO regimes during the season it improves the chance of winter weather into the Carolinas.
WINTER TEMPERATURE FORECAST:
With the building La Nina and the jet being zonal, we expect temperatures this winter to be above average over the three-month period. Average high/low temperatures for the Foothills and Piedmont at the peak of the winter season (Late January) is 49/28.
WINTER PRECIPITATION FORECAST:
As we mentioned in the general analysis, La Nina is a drier pattern especially as the sub-tropical jet will not be as prevalent as compared to previous winters. You can actually look at the trends of the past 6-8 weeks that the Carolinas have seen extended dry stretches in the weather only to be interrupted by tropical features. Once we get into the winter the tropical influences will subside and we will have to rely solely on the jet stream. This La Nina influence could become even stronger by late winter and going next spring.
WINTER SNOWFALL FORECAST:
With all the negative factors to winter weather in play this winter, it does not eliminate the possibility of some winter storms and even big winter storms.
Looking back to history of weak La Nina’s over the past 40 years there are several examples of winters (1984-85, 1995-96, 2002-03, 2017-18) where the region has received snowfall amounts at or above normal. Other common characteristics of these years include early season snow events and multiple advisory level (3 inches of less) events to help reach climatological norms. So with that in play we feel optimistic that our coverage area can still reach normal snowfall amounts this winter. And for our friends in the North Carolina High Country, the chances of a high end northwest flow events go up slightly.
Due to all the factors we see coming into play this winter, our weather team is predicting a fairly dry and mild season overall but it does not necessarily preclude some fun and games of a winter variety. History has shown that some big winter weather events can occur in a weak La Nina so we cannot dismiss what history tells us.
The one big change we feel confident about going into winter and extending into spring is that our region could run into extended dry periods and the possibility of drought conditions developing by spring 2021 cannot be ruled out. Considering the anomalous wet weather our region has seen since 2018 it will be a definite reversal of patterns for Western North Carolina.