NWS Little Rock, AR - Winter Weather Awareness Week

Winter can bring a variety of conditions, including heavy snow, ice, and cold temperatures. These conditions can make driving conditions hazardous, with power outages occurring at times. In the end, you may become exposed to the elements...with your life threatened.

To help the citizens of Arkansas prepare for these conditions, a special week has been set aside to review safety rules and to understand the hazards of winter. This year, Winter Weather Awareness Week runs from December 1 to December 7, 2024.

The National Weather Service (NWS) will transmit winter weather safety information every day during this special week. You can acquire this information on NOAA Weather Radio All Hazards and the internet.

One of the most reliable long-range predictors deals with monitoring water temperatures along the equator in the Pacific Ocean. If the water cools, we trend toward La Niña. If warming occurs, then it's El Niño. Both variables have a say in how the weather behaves across the country, especially when they become dominant. In the coming months, it appears the pendulum will swing weakly toward La Niña, which favors colder/wetter than usual conditions across the northern states this winter, and a warmer/drier scenario farther south.

Confidence is swayed toward above average temperatures this winter locally. That does not mean it will be mild the entire three month period (December through February). Instead, it is implied that rounds of cold air will be fewer than in a typical winter.

The same rationale applies to the precipitation outlook. The forecast is leaning toward a drier than normal winter, especially in southern sections of the state. While there will be wet periods (and chances of wintry precipitation if cold air is in place), big slugs of moisture should be less than usual. As a side note, the degree of wetness will dictate how an ongoing drought improves or worsens moving forward. This will be evaluated more closely as winter progresses.

With La Niña taking charge, the largest tornado outbreak in Arkansas took place in January of 1999. There were 56 tornadoes spawned. In December of 2000, two crippling ice storms occurred, and remain one of the largest natural disasters in state history. In February of 2008, a tornado tracked 122 miles through seven counties in the north and west. This was a record long track in the state. Another devastating ice storm hit the north in January of 2009. Finally, one to two feet of snow buried the Ozark Mountains in February of 2011. In April and May, an astonishing 67 (of the yearly total of 75) tornadoes were counted. There was also record flooding along the Black and lower White Rivers.

During several of these historic events, La Niña was strong (water temperatures were more than 1.5°C below normal). Since early 2012, La Niña has largely been infrequent and weak.

Since 2000, the AO dropped below -1.5 (strongly negative) for two or more consecutive months only five times. Two of these instances were less than a year apart (December, 2009 to February, 2010 and December, 2010/January, 2011). The next time it happened was ten years later (December, 2020/January, 2021).

There was another Arctic intrusion in February, 2021. This time, the heaviest snow (more than twenty inches in places) was in central and southern Arkansas from the 14th through the 18th. In happened in less than a week, and was courtesy of two big storm systems traversing the southern United States. Temperatures during this time frame were twenty to more than thirty degrees below normal.

One other thing to consider is severe weather. Although most people associate the spring months with severe storms, Arkansas is no stranger to tornadoes in the fall and winter. In fact, almost four of ten tornadoes from 2000 to 2023 occurred between September and February. 

Have you noticed that it feels colder on a winter day when the wind is blowing? This is not your imagination. On a 30 degree afternoon, if there is a 20 mph sustained wind, it feels like 17 degrees to exposed skin. This apparent temperature is the Wind Chill Index, and it can be dangerous as values approach 0 degrees. What if the wind was removed? An ambient temperature of 0 degrees is just as dangerous given calm conditions.

When temperatures and/or wind chill index values (with a wind speed of at least 10 mph) reach 0 degrees for several hours over a fairly large area, the National Weather Service will usually issue a Cold Weather Advisory.

When temperatures and/or wind chill index values (with a wind speed of at least 10 mph) reach -15 degrees for one hour over a fairly large area, an Extreme Cold Warning may be posted.

These headlines replace Wind Chill Advisories and Wind Chill Warnings, and are made available so people can adequately prepare for the elements. This includes wearing several layers of loose-fitting, light-weight clothing. The layers actually trap warm air, and keep the cold air out. In addition to a coat and scarf, a hat and mittens are recommended (since more than half of your body's heat escapes through your head and hands).

Warning criteria thresholds for heavy snow have been updated and simplified nationwide (2023). The updates were made to improve decision support services, collaboration between NWS offices, and communication to customers and partners. Non-meteorological discontinuities were removed to facilitate consistent hazard messaging and headlines. In addition, the criteria is now event based (up to 48 hours) and not tied to 12 or 24 hour periods.

In Arkansas, heavy snow is defined as two inches of accumulation during an event toward the Louisiana border, three inches in southern, central, and eastern sections of the state, and four inches in the north and west (including the Ozark and Ouachita Mountains). 

The underlying basis of the new criteria is a climatological dataset used by the Winter Storm Severity Index (WSSI). This is a tool that enhances communication regarding an event's expected severity. The WSSI provides winter storm impact information out to 72 hours.

Over the last few years, Arkansas has experienced several elevation-dependent winter precipitation events, with larger sleet, snow, and ice accumulations in the higher terrain versus the remaining area. These accumulations have been a difference of Winter Warning and/or Advisory criteria being met and not being met within the same county.

To mitigate issues such as this, and to add more precision to text forecasts and long-fused watches, warnings and advisories, NWS Little Rock reconfigured eleven (11) forecast zones in the north and west (on April 5, 2022).

The configuration allows forecasters at the office to better address incoming weather systems, and issue more accurate products. This is the third winter the configuration will be used locally.

Most winters in Arkansas feature temperatures that fluctuate (sometimes wildly) and periodic rounds of precipitation. If cold air arrives, and sticks around as moisture increases, that is when big snow or ice storms often unfold. Major winter events have affected Arkansas in recent years. On Christmas in 2012, much of the region was buried under a thick blanket of heavy snow, with accumulations over a foot in some areas. At Little Rock (Pulaski County), 10.3 inches of snow piled up. The last time it snowed (more than a trace) in the city on Christmas was 1926! In late January, 2009, one to two inches of freezing rain (and locally more) accrued on trees and power lines in roughly the northern two rows of counties. More than 300,000 utility customers lost power. Tree damage was extensive, and at least 30,000 power poles were downed or snapped.

Forecasting precipitation types in Arkansas is challenging. When cold air dives southward from Canada, it is usually shallow by the time it reaches us. Think of it as an upside down bowl of subfreezing conditions, and we are toward the southern edge of the bowl. If temperatures are above freezing over the bowl, and there is precipitation falling, there will likely be melting followed by refreezing. This is a typical ice (freezing rain or sleet) scenario. If the edge of the bowl extends all the way into the clouds, and no warm layer exists, then melting would not occur and here comes the snow!