Old Man Winter “Bringing the House?”

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Pardon the expression if you’re not a football fan, but Old Man Winter may be getting ready to “bring the house” across the Central and Eastern United States with some of the coldest weather in quite some time. One of the coldest Arctic blasts in the past two years (and maybe even the past 10 years) is charging up and getting set to move south.

CAUTION: What you are about to read is a discussion beyond the normal “forecast.” If all you want is the forecast itself, click over to WHNT.com/Weather for specific highs, lows, and rain chances for the next week.

I’ll start this by saying there is a lot of uncertainty in forecasting long-range specifics; in fact, take a look at this 500 millibar spaghetti plot of ensemble forecasts. Each individual set of red, light blue, and dark blue lines indicates a
possible position of particular 500 millibar height levels. (Click here to learn about what 500 millibar heights are and why they matter?)


The more variation you see in those lines means there is more uncertainty in the forecast. When they start to show more of a pattern, confidence grows that one particular solution is more accurate than the rest. Based on this run of the GFS model (12:00 AM today), there is a lot of uncertainty, but there is increasing consistency in the long-term showing those lines dipping south over the East. That indicates where a future deep trough will set up opening the door for some very cold air.

Another signal that some bitterly cold weather will come this way is starting to show up in an area that we don’t normally look for weather changes: the stratosphere. The vast majority of the weather that impacts us at the surface occurs in the lowest layer of the atmosphere: the troposphere. The stratosphere is the next layer up, and while storms don’t occur there, research has shown that temperature changes in the stratosphere often signal changes in the troposphere as well. They are opposite each other, though! Warming in the stratosphere can be a clue to significant cooling in the troposphere.

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Notice how we flip from a cold stratosphere to a warm one over the next 10 days? That is a model forecast, and it can be very, very wrong; however, you cannot ignore that kind of look in the guidance!

Another set of clues we can use comes from global signals: the NAO (North American Oscillation) and PNA (Pacific-North American Oscillation).

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These two seem to be in conflict over how the upper-air pattern will evolve if you base your forecast solely on the “usual” outcome. It does not always work the usual way, though! In fact, some of the coldest weather in North Alabama in the past 30 years happened when the NAO and PNA were in a state of change instead of being strongly positive or negative.

A cold outbreak in January 2003 featured a positive PNA and a neutral/slightly positive NAO.

Bitterly cold air in January 1994 (with a low of 3ยบ F in Huntsville on Jan. 19) featured a neutral/slightly positive NAO and a consistently negative PNA.

So, you cannot always bet the farm on the global oscillations/indicators! They are very good at picking out patterns, but sometimes individual weather events like cold surges, snow storms, etc. can happen even without the perfect set-up.

The Bottom Line:

  • The next week or so will feature chilly weather with a gradual moderation as you will see reflected in our Seven Day Forecast on WHNT.com/Weather.
  • Just beyond the seven day period, a significant flip to very cold weather is possible. The odds are better than 60% that we will see some of the coldest weather since January 2011. As we get closer to the cold period, we will be able to see more clearly if this could actually rival some of the January 2003 or 1994 cold weather when highs were in the 10s and lows were near zero.
  • A big rain event (probably no severe weather in the Tenn. Valley, but we will keep an eye out for it just to be certain) will occur as we make the change to the colder pattern. That rain will come between Thursday, Jan. 10th and Saturday, Jan. 12th.
  • Snow or No? Too early to know for sure, but snow-lovers will be on their tip toes looking at the pattern between Saturday, Jan. 12th and Tuesday, Jan. 16th. If we’re going to get any (and it’s a big “if”), that looks like about as good a set-up as we could get. It is a long way off, and I definitely would not go buy a sled or stock up on groceries just yet!
  • Just a suggestion – Like most families, my household lives on a budget that requires a certain amount of money be set aside for the normal monthly expenses…like the utility bill. As temperatures sit here in chilly territory right now, consider conserving a little power or natural gas in case we do get some serious cold weather. Wear a sweater or sweatshirt around the house and turn the heat down a little. Best-case scenario, your bill will be lower because it didn’t get brutally cold after-all. Worst-case scenario, conserving now keeps you from doubling your electric or gas bill by the end of January.

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