Weather 101 - Eastern Two-thirds of the U.S. Is Now Locked in a Bitter Cold Wave

With nearly stationary intense low-pressure systems located at the northwest and northeast corners of the nation, a massive arctic high-pressure has developed across the Canadian and U.S. Plains states. This high, with a central pressure of 30.77 inches of mercury (1042 millibars), has sprawled across most of the area from the western High Plains to the mid-Atlantic and from central Canada to the Gulf Coast. For comparison, average sea level pressure is 30.12 inches of mercury (1012 millibars) and the central pressure in Hurricane Ike at landfall was 28.05 inches of mercury (950 millibars).

Due to the clockwise circulation around the high-pressure system, winds east of a line from the Minnesota-North Dakota border to Brownsville, TX almost all have a component from the north (Fig. 1). Many Plains and Mississippi River Valley locations have winds from almost due north. This is allowing cold air to funnel southward and eastward, intensifying the grip of the arctic air mass.

At midnight on January 2, temperatures across the northern Plains, the upper western Great Lakes and eastern Montana were already below zero. The eastern Dakotas and western Minnesota, under clear skies with an ample snowpack, had chilled to around minus 30 degrees Fahrenheit. Even places in the Deep South were in the 20's and 30's. Only Miami, FL and Key West, FL have escaped the bitter chill. Yet, the 56-degree morning reading in Key West on January 2 was 9 degrees below average and was quite unusual.

It's not just the temperature, it's the humidity

With the exception of extreme south Texas and southernmost Florida, the air mass has also brought very low dew points to the entire eastern two-thirds of the Nation. This has led to the issuance of red flag warnings (high risk of forest and grassland fire spread) across much of the Florida peninsula for daylight hours on Saturday, January 2 (Fig. 2). The low dew points will add to indoor and outdoor discomfort thanks to enhanced evaporative cooling from our skin. This means that you'll feel cooler than the temperature alone might indicate and you'll also suffer more from dry skin, chapped lips, and periodic static electricity shocks.

The thing to do is to start humidifying your home early. If you have a built in furnace humidifier you are well ahead of the game. If you don't, consider a belated Christmas present by buying a free-standing humidifier. Other actions you can do include boiling water, running a vaporizer and/or running the shower periodically. Another alternative is to fill a bathtub with warm water; if you have a Jacuzzi-style bathtub, run the jets. This allows for tiny water droplets to be expelled into the air. For any of these actions, exercise caution. You don't want a toddler going by the bathtub or allowing the water to completely boil out of a pot on the stove.

Freezing temperatures expected to reach far south in Florida

The low dew points are also allowing for greater radiational heat loss to space at night. That's why the National Weather Service (NWS) in Jacksonville posted hard freeze warnings for early Saturday morning and again for much of the night and early morning on Sunday. In their warning message, the NWS noted, "...temperatures will bottom out early Sunday morning in the lower 20's with long durations of sub-freezing temperatures expected."

Because freezing conditions are expected to spread as far south as inland northern and central Collier County during early morning hours on Sunday, a freeze warning is in place in these areas. A freeze watch (extended period of freezing temperatures are possible) has been issued for interior regions of Palm Beach, Broward and Miami-Dade counties for Sunday morning.

Sunday morning now appears to be at the greatest risk for low temperatures. This is tied, in part, to the additional period during which colder and dry air moves into the south Florida area and the fact that cooling tonight will start off from daytime highs in the lower 60's rather than the lower 70's observed on Friday.

While wind chills will be very low, and some areas will experience vegetation damage, especially in interior sections of central and northern Florida, freezing of indoor pipes poses a bigger problem for much of the Deep South. If your home is not as well insulated as it should be, and/or your pipes have frozen before, think about protective actions early. Keeping cabinets under sinks open and allowing indoor water faucets to drip, even slightly, may save you the grief associated with pipes that develop leaks after a freeze.

Record-keeping continues

This air mass has already started to set a few records. Many more are likely to be established as the cold wave remains locked in place and is reinforced by next weekend, except for a brief respite across Florida on Thursday (January 7).

Here are some of the weather records set on January 1, 2010 alone. The list only includes reports received through 6am EST on January 2, 2010.

...Jamestown, ND recorded a low of minus 28 degrees, tying a record set in 1919.

...Grand Forks International Airport, ND broke its record low temperature record of minus 30 degrees set in 1974. The new record for January 1 is now minus 33 degrees.

...Sissteon, SD set a record low temperature of minus 26. This broke the old record of minus 24 observed in 2001.

And looking ahead to January 2...

...Grand Forks International Airport, ND has already broken its record low temperature record of minus 27 degrees set in 1991. The new record for January 2 is now minus 34 degrees. The temperature was expected to drop further before sunrise.

...Some locations from southern Georgia to southern Florida are anticipating record or near record lows both on January 2 and/or January 3. These include Gainesville, FL where the temperature may dip as low as 25 on January 2 (record is 23 set in 1918); St. Simons Island, GA may drop to 28 degrees on January 2 (record was 27 in 1969); and Fort Myers, FL could touch 35 on the morning of January 2 (record of 37 in 1949). On the morning of January 3, La Belle, FL (east of Fort Myers) could reach a low of 29 (record of 30 set in 1979).

...Record low maximum temperatures in parts of southwest Florida are at risk of being broken, too. For example, the high temperature expected in Fort Myers on January 2 is only 62 (record is 62, which occurred back in 1958). Naples is only expected to reach 62 on January 2, with its low maximum temperature record of 60 (set in 2008).

For updates on this evolving story, please check out my examiner.com web site.