NWS UPDATE: La Niña Advisory, Warm/Dry Winter Expected

From: National Weather Service, Fort Worth
Date: Thursday, 24 September 2020 15:43 CDT

Bottom Line

A La Niña Advisory is in effect, increasing the likelihood that the upcoming winter will be warmer and drier than normal across North and Central Texas.

Overview

A La Niña Advisory is issued when La Niña conditions are in place and are expected to persist. La Niña is defined by cooler than normal sea surface temperatures in the equatorial Pacific, which can affect weather patterns worldwide. The pattern that tends to dominate North America during a La Niña winter (shown below) favors warmer than normal temperatures and below normal precipitation in the Lone Star State. This influence begins as early as the fall season and can linger into the following spring.

Typical wintertime La Niña pattern

Our long-range outlooks for the cold season demonstrate this, with an enhanced potential for warmer and drier weather throughout the southern tier of states.

3-month temperature outlooks

3-month temperature outlooks

3-month precipitation outlooks

3-month precipitation outlooks

September has been remarkably wet across the region, and the climatological peak of the fall rainy season is upcoming in October. However, the pattern during late September and early October is expected to mirror the typical La Niña setup, bringing an extended dry spell to North and Central Texas. There will continue to be interludes with rainfall, particularly during October, but this precipitation-limiting pattern will likely become more common as we move deeper into the cold season.

3-Month Averages vs. Extreme Events

La Niña is a powerful tool for seasonal outlooks, but there are other inputs that affect the weather on sub-seasonal time scales. In other words, the classic La Niña pattern may dominate the season, but the weather pattern will vary. Unfortunately, these sub-seasonal factors (like variations in the Arctic Oscillation that can enhance the potential for outbreaks of severe cold and winter weather) are poor predictors beyond a couple of weeks. As a result, they aren't considered for seasonal outlooks. However, these anomalies are an important part of our winter forecasts, and we will address their significance when these pattern changes arise.

It is important to emphasize that the 3-month averages that are the focus of our seasonal outlooks mask the extreme events that can and do occur. In other words, even if the upcoming winter is warmer than normal overall, there could still be an extreme arctic outbreak. Such an event may be accompanied by wintry precipitation with significant impacts. For example, during the otherwise mild and dry La Niña winter of 2010-2011, there were multiple memorable snow/ice events in early February 2011.

Similarly, a heavy rain event with flooding issues can occur during an otherwise protracted drought. Sometimes, a wet period can persist enough to reverse the seasonal trend. This is precisely what happened during our last La Niña event (2017-2018). North and Central Texas were quite dry from October 2017 to January 2018, but February 2018 was the wettest on record for many locations from the Ark-La-Tex to the Great Lakes (including Dallas/Fort Worth).

Drought and Fire Danger

The wet start to fall quickly erased the summer drought throughout the region.

U.S. Drought Monitor: August 27, 2020U.S. Drought Monitor: September 24, 2020

Click the images above to enlarge.

With the anticipated precipitation deficits during the upcoming cold season, the redevelopment of drought conditions is likely. This would be a short-term drought, primarily impacting agriculture and enhancing the wildfire potential. (With our already healthy water supply further fortified by recent rainfall, this drought would not be of hydrologic impact.)

Not all short-term droughts have equivalent fire danger. Our most intense fire seasons tend to occur after periods of abundant rainfall, the extensive vegetative growth from which serves as fuel for wildfires. With a wet spring and a wet fall this year, both enhancing the amount of vegetation available for fuel, our upcoming cold season is primed for significant fire concerns.

Previous La Ni±a Events with Historic Wildfires:

  • January 2006 - thousands evacuated in Montague Country, over 30 homes destroyed in Ringgold
  • April 2009 - massive wildfires from Eastland County to Montague County claimed four lives
  • April 2011 - fire consumed over 100,000 acres near Possum Kingdom, destroying 150 homes

What We Are Certain Of:

  • La Niña conditions are currently in place and will likely continue throughout the upcoming winter.
  • Warmer than normal temperatures are more likely than below normal temperatures.
  • Throughout the cold season, rainfall amounts are more likely to be below normal.
  • Drought is expected to redevelop this winter.
  • There is an enhanced threat of wildfires this winter.
  • There is a reduced risk of heavy rain and flooding events.
  • There is a reduced risk of winter weather events.

What We Are Less Certain Of:

  • We aren’t able to project how far above normal temperatures will be.
  • We also can’t say how far below normal monthly/seasonal precipitation totals will be.
  • The frequency and severity of arctic outbreaks this winter is difficult to predict.
  • The number and intensity of winter weather events also can’t be projected.
  • Sub-seasonal anomalies may reduce or reverse the warm/dry trend this winter, but these inputs can’t be well predicted beyond a couple of weeks.

FAQs

Will the entire winter be warm? While days with warmer than normal temperatures are expected to outnumber days with below normal temperatures, our temperatures are highly variable during the cold season, and periods of cold weather will likely occur.

Does this mean there won’t be any wintry precipitation this winter? Absolutely not! While La Niña winters tend to have fewer winter weather events, significant snow/ice events can occur during any winter. Believe it or not, there has never been a winter with no wintry precipitation in the Dallas/Fort Worth Metroplex (since records began in the late 1800s).

When should I be concerned about wildfires? The fire threat is greatest on warm, dry, windy days, particularly those that follow several days without significant precipitation.

Does La Niña impact the potential for severe weather? Although La Niña events tend to have reduced precipitation overall, the incidence of large hail and tornadoes is greater when La Niña conditions are in place.

Additional Resources

National Weather Service Fort Worth Homepage
NWS Fort Worth El Niño/La Niña Information
NWS Fort Worth Drought Information
NWSChat
Who’s eligible for NWSChat

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