December running -9 degrees now, refreshing candor on busted D.C. snow forecast

Tired of that perpetual sting on your face as you step outside? Still startled by unattractive squeals and groans from your car as you crank the ignition? Sick of weather wind chill babble?

You might be a Minnesotan.

One more Canadian infusion pours south of the border Wednesday. This one too will get your full attention, and leave you dreaming of a Sun Country flight to tropical climes. The good news? We may actually crack the double digits above zero within 48 hours.

Baby steps, but progress.

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Image: Twin Cities NWS

-9.1F temps vs. average so far this December at MSP Airport

-1.5F approximate temps vs. average in 2013 in Minnesota

+24F High temp in Nome, Alaska Tuesday

7th warmest year on record globally through October

One more day.

That's all we'll have to endure as far as the really cold sub zero temps and chills this week. Wednesday will feel Nordic. Macho. Our Saskatchewan breezes keep us in the deep freeze Wednesday. Here's a look at some barbaric wind chill values Wednesday morning.

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Image: NOAA

Anatomy of wind chill

What exactly is wind chill anyway? Why do we talk about it so much? What does it really mean? Does it affect my car?

Here's everything you never wanted to know about wind chill from the NWS.

The NWS Windchill Temperature (WCT) index uses advances in science, technology, and computer modeling to provide an accurate, understandable, and useful formula for calculating the dangers from winter winds and freezing temperatures. The index:

  • Calculates wind speed at an average height of five feet, typical height of an adult human face, based on readings from the national standard height of 33 feet, typical height of an anemometer

  • Is based on a human face model

  • Incorporates heat transfer theory, heat loss from the body to its surroundings, during cold and breezy/windy days

  • Lowers the calm wind threshold to 3 mph

  • Uses a consistent standard for skin tissue resistance

  •               Assumes no impact from the sun (i.e., clear night sky).

Here's a neat little history lesson on wind chill from the always excellent Capital Weather Gang.

A little history first. In 1945, Antarctic explorers Paul Siple and Charles Passel devised an index that attempted to compare how cold we feel at various temperatures and wind speeds with how cold we feel at the same temperatures in still air. This original wind chill index languished, more or less, until it gained great notoriety during the famous (or infamous) "Ice Bowl" Championship Game between the Dallas Cowboys and the Green Bay Packers in Green Bay in 1967. With a game-time temperature of -13F and a wind chill factor of -48F (according to the original index), it was one of the two coldest pro football outings ever staged. (The other was the 1981 AFC Championship Game between the San Diego Chargers and the Cincinnati Bengals, which was played in -9F weather with a wind chill of -59F (original index).

Want to calculate wind chill on your own? Here's the NWS chart and wind chill calculator.

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Image: NOAA

Want even more on wind chill FAQ's? Most of this stuff is drilled into us as children in Minnesota, sort of like 'duck and cover' and the Pledge of Allegiance.

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Image: NOAA

There. Hopefully I won't have to do that again the rest of the winter.

Moderation ahead

My dad had several good pieces of advice. One of his best was "everything in moderation." Here's a look at slowly moderating temps by Thursday and Friday. We may get another snowy dusting Wednesday night, with the potential for another inch or two Friday night into Saturday.

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NOAA GFS data via Weatherspark

White Christmas in the bag?

Two weeks until Christmas and I don't see any huge snow busting thaws ahead between now and when Santa's sleigh sails south. There's plenty of snow now across all of Minnesota and the Upper Midwest. Here's the latest data from NOAA's National Operational Hydrologic Remote Sensing Center (NOHRSC.)

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Image: NOAA

Temps between now and Christmas do show signs of moderation...but I think most of what snow is here will stick around. We'll get a couple more dustings this week, and I'm keeping an eye on a potentially bigger snow event late next week lurking around December 19-20th. The GFS is hinting at that in the latest runs. You can probably bank on a White Christmas this year.

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Image: NOAA GFS via IPS Meteostar

Overall odds of a white Christmas in Minnesota are historically good.

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Image: Minnesota Climate Working Group

Here's a great summary from the the Minnesota Climate Working Group.

Will we have a white Christmas? It's an age-old question that occurs to almost everyone this time of year. The chances of having a white Christmas vary even here in Minnesota. Having a white Christmas is loosely defined as having 1 inch of snow on the ground on Christmas Day. The snow depth at most sites is measured once a day, usually in the morning. The best chances of having a white Christmas is almost guaranteed in the Boundary Waters Canoe Area and a good part of the Arrowhead. The chances decrease to the south and west and the best chance for a "brown" Christmas is in far southwest Minnesota where chances are a little better than 60%. Northern Minnesota is one of the few non-alpine climates in the US where a white Christmas is almost a sure bet (U.S. White Christmas Probabilities).

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Image: NOAA

Refreshing candor on busted East Coast snow forecast

I've busted more than a few times in 30 years of snow forecasting. You may have heard big talk of 3" to 6" snowfall for Washington, D.C and New York this week. Turns out it was a bust for DC, and New York's Central Park picked up a whopping inch.

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Image: Washington D.C. NWS

Many of my meteorologist friends discuss how damaging it is when some in our profession issue forecasts with unrealistic certainty, blow our own horns early and often, and never seem to account when a forecast is busted. I cut my teeth in the weather business issuing snow and ice and other specialized forecasts in private sector meteorology, where we are immediately accountable to our customers. I get how those trying to make a buck in weather are prone to aggrandizement and constant self promotion. I just wonder if they ever really look at the results of their forecasts when they go awry...before they issue the next certainty-laced forecast? I feel for the weather consumer trying to decide who to believe, and when.

Here's a refreshing look at some all too rare accountability from The Capital Weather Gang's excellent meteorologist Jason Samenow on a (half) missed forecast for Washington D.C this week.

A half-right, half-wrong snow forecast, and how we can improve

North and west of the Beltway, our forecast for today’s storm of 2-5 inches of snow was spot on. But inside the Beltway and to the south and east, it failed for reasons that may sound familiar. 

In short, temperatures inside the Beltway and to the south and east were just a degree or two too warm for snow to accumulate and precipitation was modestly lighter than we expected.

We’ve seen these circumstances before – the most recent example being 9 months ago on March 6, aka the Snowquester debacle. Of course, today’s (half) bust was relatively minor by comparison. Whereas we forecast 6-10″ in Snowquester and the underachieving areas got 0-1 inch, this time we forecast 2-5″, and the the snow-challenged areas got 0-2 inches.

Relative to Snowquester – in which we became overconfident a dump of snow was coming – we took baby steps with this forecast in that we clearly laid out the bust scenario, assigning it a 20-25 percent likelihood. As late as 10:45 p.m. last night, CWG’s Ian Livingston wrote:

“…there is one scenario in which … temperatures don’t cool down enough and we end up with some sleet and closer to an inch of snow.”

Also, in an update yesterday afternoon, Wes Junker discussed about five different ways this forecast could wrong.

Despite these qualifiers, we can’t be satisfied that we forecast the possibility of disruptive snow when that failed to occur over a sizable chunk of the region – with consequences for people’s daily routines. When we make a similar mistake more than once, we need to try to identify the root cause. In my view, it relates to an over-reliance on models.

Way to go Jason. I hope I'm able to be this honest the next time my snow forecast goes horribly wrong!