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Winter Weather Awareness Week
 
Introduction
 

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 1-6, 2019.

 

Important Information
 
Winter Weather Awareness Week is a joint effort between the National Weather Service and several partners across Arkansas including the Department of Emergency Management, the Department of Transportation, and the Department of Education.
In the picture: Winter Weather Awareness Week is a joint effort between the National Weather Service and several partners across Arkansas including the Department of Emergency Management, the Department of Transportation, and the Department of Education. Click to enlarge.
 

The NWS will transmit winter weather safety information on the NWS Weather Wire and on NOAA Weather Radio All Hazards during this week. You can also acquire weather information from NWS Little Rock on the Internet!

 

Information Sent During Winter Weather Awareness Week, 2019
 
Sunday, December 1, 2019...Introduction...click here.
Monday, December 2, 2019...Outlook for the Upcoming Winter...click here.
Tuesday, December 3, 2019...Winter Precipitation Types...click here.
Wednesday, December 4, 2019...Winter Weather Watches, Warnings and Advisories...click here.
Thursday, December 5, 2019...Winter Weather Safety Rules...click here.
Friday, December 6, 2019...The Cold of Winter...click here.

 

Winter Forecast
 
Confidence is highest in a warmer than normal winter (December, 2019 through February, 2020) across the southern United States and parts of New England. It should be wetter than average from the northern Rockies to the Ohio Valley, and drier than usual along parts of the Gulf Coast and California. The forecast closely resembles temperature and precipitation trends in 2019 (through mid-November). The outlook is courtesy of the Climate Prediction Center, and trend graphics are courtesy of the High Plains Regional Climate Center.
Temperature Outlook  |  Precipitation Outlook
Temperature Trends in 2019  |  Precipitation Trends in 2019
In the pictures: Confidence is highest in a warmer than normal winter (December, 2019 through February, 2020) across the southern United States and parts of New England. It should be wetter than average from the northern Rockies to the Ohio Valley, and drier than usual along parts of the Gulf Coast and California. The forecast closely resembles temperature and precipitation trends in 2019 (through mid-November). The outlook is courtesy of the Climate Prediction Center, and trend graphics are courtesy of the High Plains Regional Climate Center.
 

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, the pendulum will lie between El Niño and La Niña; that is, conditions will be neutral. When this happens, long-term trends become a key predictor of what may unfold during winter.

 

Beware La Niña

Interestingly, the most recent huge episodes of snow, ice, and severe thunderstorms occurred when La Niña conditions were dominant, or when water temperatures near the equator in the Pacific Ocean were colder than normal. Since early 2012, La Niña has been infrequent and weak.

With La Niña firmly in place, 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.

 

In 2019 (through mid-November), it was warmer than average across the southern United States and cooler than usual across parts of the north. The wettest conditions were from the northern Rockies to the Great Lakes, and it was dry in portions of the south and west. The forecast from the Climate Prediction Center for the upcoming winter is closely following these trends.

 

What It Means For Arkansas

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. Some forecast models are indicating that Arctic intrusions will be most likely in January and February, and not so much in December.

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 dryness will dictate the concern of a developing drought in the spring/early summer of 2020. This will be evaluated more closely as winter progresses.

 

Other than focusing on trends, the door is open for other variables such as Arctic Oscillation (AO). In its negative phase, pressure is higher toward the North Pole, and this sets up a blocking pattern. Cold air traversing Canada is forced to the south, and our temperatures drop.

 

One to two feet of snow piled up in northwest Arkansas on 02/09/2011. In the winter of 2010/2011, there was a long term negative AO, and that led to one cold blast after another. On February 9th, 2011, one to two feet of snow blanketed the Ozark Mountains. Six to eight inches of powder accumulated in the Little Rock (Pulaski County) area. It was a top ten snowy winter locally. Such a lengthy negative AO is rare. Usually, AO phases are of short duration (days to weeks), and are tricky to forecast compared to a much more stable El Niño/La Niña (months).
In the picture: One to two feet of snow piled up in northwest Arkansas on 02/09/2011.

 

 

Big Winter Events
 
There were ruts in a few neighborhood roads in Sherwood (Pulaski County) to start the morning on 12/26/2012. Otherwise, most roads were snow covered and hazardous.
In the picture: There were ruts in a few neighborhood roads in Sherwood (Pulaski County) to start the morning on 12/26/2012. Otherwise, most roads were snow covered and hazardous. Click to enlarge.
Along U.S. Highway 167 to the south of Cave City (Sharp County), there was ice on the lines and some snow on the ground on 01/28/2009.
In the picture: Along U.S. Highway 167 to the south of Cave City (Sharp County), there was ice on the lines and some snow on the ground on 01/28/2009. Click to enlarge.
 

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.

 

 

Precipitation Types
 
In Arkansas, it is not uncommon for subfreezing conditions to arrive from the north (provided by a large area of Arctic high pressure), and then warm/moist air tries to build into the state from the Gulf Coast (provided by low pressure to the southwest) before the cold air retreats. That is a recipe for a wintry mess. Clouds and precipitation often result, with snow where cold air is deepest, and rain where it is shallow. Sleet and freezing rain are found somewhere in-between.
Winter Precipitation Types (Part 1)  |  Winter Precipitation Types (Part 2)
In the pictures: In Arkansas, it is not uncommon for subfreezing conditions to arrive from the north (provided by a large area of Arctic high pressure), and then warm/moist air tries to build into the state from the Gulf Coast (provided by low pressure to the southwest) before the cold air retreats. That is a recipe for a wintry mess. Clouds and precipitation often result, with snow where cold air is deepest, and rain where it is shallow. Sleet and freezing rain are found somewhere in-between.
 

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!

 

Watches, Warnings, and Advisories
 
Winter weather headlines were posted across much of Arkansas in mid-January, 2018.
In the picture: Winter weather headlines were posted across much of Arkansas in mid-January, 2018.
 

When a winter event is on the horizon, the National Weather Service will usually have a headline in place. There could be a Watch followed by a Warning and/or Advisory, but what does it mean? 

If there is a possibility of heavy snow and/or ice, a Winter Storm Watch will be issued. In the Little Rock County Warning Area, this would be at least 4 inches of snow in 12 hours, 6 inches of snow in 24 hours, a quarter inch or more of freezing rain, and/or a half inch of sleet or more. If the heavy snow and/or ice becomes imminent, a Winter Storm Warning or Ice Storm Warning will be posted. On very rare occasions, it there is a lot of wind (at least 35 mph), and blowing/drifting snow creates very low visibility (less than a quarter mile), a Blizzard Warning will go out. Anything less than warning criteria will be a Winter Weather Advisory.

There is a short fuse warning (30 to 60 minute valid time) available starting this winter. A Snow Squall Warning will be issued when a brief period of intense snowfall (moderate to heavy in intensity) is expected, accompanied by gusty winds resulting in reduced visibility (a quarter mile or less). Ideally, road temperatures would be sub-freezing. It is thought this type of warning will seldom be disseminated.

 

Three day Winter Storm Severity Index (WSSI) through 1200 pm CST on 11/20/2019. Limted to minor impacts were expected in the northern and central Rockies, the northern Plains, and the upper Midwest.
In the picture: Three day Winter Storm Severity Index (WSSI) through 1200 pm CST on 11/20/2019. Limted to minor impacts were expected in the northern and central Rockies, the northern Plains, and the upper Midwest.
 

Another new item is the Winter Storm Severity Index (WSSI). This is an experimental tool that enhances communication regarding an event's expected severity. The WSSI provides winter storm impact information out to 72 hours.

 

 

Check the Roads
 
Roads were snow and slush covered in much of southern and eastern Arkansas at 900 am CST on 01/16/2018. The image is courtesy of IDriveArkansas.
In the picture: Roads were snow and slush covered in much of southern and eastern Arkansas at 900 am CST on 01/16/2018. The image is courtesy of IDriveArkansas.
 

Following a winter event, sometimes it is not a good idea to venture out onto the roads. From a safety standpoint, you are putting yourself at risk of having an accident. Also, you may get in the way of crews trying to treat and clear the roads. If you must drive, please slow down and take it easy! Before you start the vehicle, check the roads at IDriveArkansas. Maps are available to show the status of major thoroughfares; that is; what is on the pavement (such as snow, ice/ice patches, or slush) and how much (such as mostly clear, partly covered, or covered). This information is updated often, especially when there is wintry precipitation. 

 

Links of Interest
What is on the Road? (examples: clear, slush, ice patches, ice, snow)
Note: When there are issues on the roads, click on affected routes(s) for more information (such as extent of route covered by snow/ice).
Understanding Route Conditions (interpreting snow/ice coverage on roads)

 

Factoring in the Wind
 
WIND CHILL INDEX °F
  WIND SPEED (MPH)
TEMP (°F) 5 10 15 20 25 30 35 40
-25 -40 -47 -51 -55 -58 -60 -62 -64
-20 -34 -41 -45 -48 -51 -53 -55 -57
-15 -28 -35 -39 -42 -44 -46 -48 -50
-10 -22 -28 -32 -35 -37 -39 -41 -43
-5 -16 -22 -26 -29 -31 -33 -34 -36
0 -11 -16 -19 -22 -24 -26 -27 -29
5 -5 -10 -13 -15 -17 -19 -21 -22
10 1 -4 -7 -9 -11 -12 -14 -15
15 7 3 0 -2 -4 -5 -7 -8
20 13 9 6 4 3 1 0 -1
25 19 15 13 11 9 8 7 6
30 25 21 19 17 16 15 14 13
35 31 27 25 24 23 22 21 20
In the table: The wind chill index is determined by combining the temperature and wind speed. Given a temperature, the wind chill index will decrease as the wind strengthens.
 

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. Given such values, the National Weather Service will often issue a Wind Chill Advisory so that 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).

 

Link of Interest
More About the Wind Chill