Very Cold for Christmas Weekend

Snow should be on the light side

Dec.19, 2022  4:30 P.M.

When I started forecasting weather for the Louisville area in 1969, I had one major point of emphasis about weather forecasting:  Don’t ever believe a weather forecast for more than 3 days ahead.  Weather forecasting has improved significantly since then, so,maybe, that could be extended by a day or two.  But the point is, we do not have perfect forecast models.  Nor can we measure weather parameters – humidity, temperature, winds, etc – precisely.  And, to make matters worse, when we measure our weather data, it’s at random spots on the Earth.  Forecast models are set to run on a precise computer grid.  The data is seldom measured at the grid points, so sophisticated smoothing systems have  been created to fit the data to the grid.

Thus, before forecast models even begin computing, we have three significant areas of known error sources within the system.  I am amazed at how well the longer range forecast models perform…most of the time.  But as good as the modern models are, they are not perfect!

So why do professional forecasters continue to believe them?   Why so much hype 7 to 10 days before an event is due to happen?

I can’t answer those questions, even after 50 years of trying.

This week

We are currently in one of those major “hype” situations.  The major outbreak of arctic air set to arrive Thursday night has been predicted to arrive “in 7-10 days” since before Thanksgiving.  So after many misfires it’s actually going to happen.  Since last week, the models have been predicting some pretty dire weather for much of the nation east of the Rockies.  The local outlook was for 4″-6″ of snow, very strong winds and a possible flash freeze in addition to frigid temperatures.  Keep in mind, this forecast was for at least 7 days ahead,

No matter!  The hype machine jumped into full gear.  By the weekend all the talk centered around a massive pre-Christmas storm of legendary proportions right here in Louisville.  But, as should be expected, the forecast models slowly made “adjustments” to the forecast.  Those incremental changes have greatly altered the forecast and possible consequences for us.  Even the most extravagent hypists should have it figured out by now.

This being Monday and the actual event is likely Thursday night, I expect more changes to occur during the days ahead.  Nevertheless, here’s what I’m currently expecting later this week:

Slowing warming temperatures tomorrow through Thursday midday.  Rain should move in Thursday afternoon and change over to snow Thursday evening.  Snow will last 2-3 hours with accumulations around 1″ – 2″.  Very windy, with temperatures dropping into the single digits by Friday morning.  Friday remains cloudy, windy and cold with snow showers and flurries.  Additional accumulation up to an inch.  Temperatures will reach only the lower teens.

Note: the possibility of a Flash freeze Thursday is much lower now than earlier thought.

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