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| Earth | Human World on Dec 21, 2013

Big storm hitting U.S. this weekend

Holiday travelers east of U.S. Rockies, be weather aware. This storm has everything, including severe thunderstorms, flooding, snow, and ice.

A monster storm system will affect millions of people in the United States during the weekend of December 21-22, 2013. It’s expected to produce a wide range of nasty weather – including severe thunderstorms, flooding, snow, and ice. If you’re in the eastern half of the United States, you will feel the full force of this storm either at home or if you plan on traveling this weekend. A potential severe weather outbreak is also possible across the U.S. Southeast from Louisiana into Mississippi and Arkansas. Meanwhile, Oklahoma has already been hit hard with significant icing across Oklahoma City and into Tulsa.

The local National Weather Service offices have been busy issuing plenty of watches and warnings all across the United States. Flood watches extend from the U.S. mid-South all the way into the Ohio River Valley.

There are four threats with this storm system. One of those threats has already occurred overnight across parts of Oklahoma as freezing rain fell (and as of Saturday morning, continues to fall) across a large part of Oklahoma City and Tulsa.

Map showing all of the watches and warnings across the United States. Busy weather weekend! Image Credit: NOAA

Map showing all of the watches and warnings across the United States. Busy weather weekend! Image via NOAA

Image via Detroit Free Press

Image from November 2013, via Detroit Free Press

The environment is primed for severe weather to develop across the U.S. Southeast Saturday afternoon, evening, and into Sunday morning. A strong jet stream – a column of fast-moving air that helps steer storms and divides the cold air from the north and the warm air to the south – will be pushing across the Southeast. A strong area of low pressure will push along this jet, and will create plenty of wind shear and spin. The spin in the atmosphere, also known as helicity, is extremely high. The winds aloft in the atmosphere are blowing at 60-80 knots, which is more than sufficient for severe weather.

The weather across the U.S. Southeast will become more typical of that region’s weather in April than of the first day of winter. Temperatures will soar into the 70s with dew points climbing into the 60s. Winds will be coming from the southeast at the surface and changing in direction as you go up into the sky. These are conditions that are ripe for tornadoes to develop.

With all that said, there’s plenty of reason as to why the Storm Prediction Center out of Norman, Oklahoma is concerned about this overall setup. They have issued a moderate risk of severe thunderstorms across Louisiana, Mississippi, Arkansas, western Tennessee, and northwest Alabama. Over 35 million people are included in a severe weather risk area for Saturday. The threat shifts to the east across Alabama, Georgia, and into the Carolinas by Sunday. However, the threat decreases as the main energy pushes off to the north.

According to the Storm Prediction Center (SPC),

THE GREATEST RISK FOR SEMI-DISCRETE SUPERCELLS SHOULD EXIST ACROSS THIS LOWER MS VALLEY THIS AFTERNOON…WITH POTENTIAL FOR SEVERAL TORNADOES/SOME OF WHICH SHOULD BE STRONG.

Severe weather

Storm Prediction Center's severe weather outlook for the United States. Severe weather outbreak likely today on Saturday, December 21, 2013.

Storm Prediction Center’s severe weather outlook for the United States. Severe weather outbreak likely today – Saturday, December 21, 2013.

Heavy Rain

Rainfall totals for the next three days are impressive. Flooding a potential issue. Image Credit: Weather Prediction Center

Rainfall totals for the next three days are impressive. Flooding a potential issue. Image via Weather Prediction Center

Snow

GFS model showing decent snowfall totals across the Central and Northeast parts of the U.S. this weekend. Image Credit: Weatherbell

GFS model showing decent snowfall totals across the Central and Northeast parts of the U.S. this weekend. Image via Weatherbell

A huge stream of moisture is being pulled from the Gulf of Mexico and being pushed up into the eastern United States. With so much warm air in place, a large part of the U.S. East will experience very heavy rains. We could see rainfall totals as high as 5-6 inches in isolated spots. With that in mind, we are seeing a large swath of flash flood watches all across the Midwest for the threat of flooding.

Behind the area of low pressure, cold air and moisture will be present. What does that mean? It means we could see some decent snowfall from eastern Kansas, into Iowa and Illinois, and into Wisconsin. Snowfall totals could add up to 3-5 inches with higher totals as you go northward into Wisconsin. Some spots could see nearly 10-12 inches of snow before the event is over with. Regardless of what happens, this storm is going to create travel nightmares all across the United States. If you live on the East Coast, this system will push into your neck of the woods by Sunday. Gusty winds, heavy rain, and snow across New England is likely.

Bottom line: If you plan on traveling across the United States this weekend, you might get stuck. Ice and snow likely from Oklahoma into Wisconsin. Meanwhile, a severe weather outbreak looks likely Saturday into Sunday with damaging winds and tornadoes possible across the Southeast. This storm has everything, so be weather aware no matter where you live east of the Rockies.