Winter Storm Watch Sunday night thru Monday

Saturday, December 13 -- 4:00PM

Winter Storm Watch from Sunday 6PM to Monday 4PM...

All signs still pointing to a significant Ice Storm for our region for late Sunday night into Monday. To be honest, I have a hard time believing some of the numbers being thrown at us. For instance, tomorrow's high temperature will likely break 60 degrees, and then the cold front is supposed to pass, and the temperature will plunge into the 20s by Monday morning. A 40 degree drop? That's not exactly unprecedented, but we will need every last bit of that temperature drop to get the expected ice accumulations. If the temperature "only" drops 35 degrees instead of 40, then this will just be cold rain.

Predicting the effects of an Ice Storm is tricky business. Forecast models are pretty poor at anticipating how cold the air will REALLY be. To give you an idea, since Sunday's high temperature will be around 60 degrees, for us to get significant ice accumulations Monday morning, the temperature actually needs to fall into the lower 20s (say, 22F) during the rain event to overcome that prior warm air presence. Yes, yes, I realize water freezes at 32 degrees. But entropy is at work here. Ever notice that if you put a glass of water into a freezer it doesn't immediately freeze? Same thing.

Then again....

Interested if schools will be closed? My guess is the following scenario will play out:

• This Ice Storm scenario will "mostly" come true. Come early Monday morning, the temperature will be around 27, and freezing rain will be accumulating as ice on the ground. At 4AM or so, we will have a light glaze, and forecasts will be dire
• By 6AM, it will still be moderately raining, with the temperature around 25, grassy areas will be covered with ice, but streets will be only slightly bad. School district officials will envision kiddies standing at bus stops, covered in ice as if Frozone from The Incredibles had sprayed an Ice Ray their way. The school officials will hit the panic button, and there will be widespread school closings.
• By noon-time, most of those school officials will walk outside, see that there is no ice on the streets, scratch their heads and say, "We called off school for some cold RAIN?!?"

The margins for error are razor thin here. Just a few degrees either way will make a huge difference. But if I was a betting man, I would say there is a 60-70% chance of widespread school closings, and for a very short period of time Monday morning, those decisions to close schools will seem justified. What worries me is come mid-day Monday, a lot of school officials will be second guessing their decisions.

Remember, weather fans, there is nothing I want to see more than a thick sheet of ice covering everything, to the point that I need to break out my ice skates to take the dog outside. I am just not convinced we will get those extra 5 degrees.

-WD

Ice Storm Sunday into Monday?

Friday, December 12 -- 10:00AM

Greetings all! Here we are, back for another season of exciting Winter Weather events...

All weather sources point to a fairly significant Ice Storm threat to the STL region beginning Sunday night, and lasting into Monday mid-day. The National Weather Service (NWS) has been advertising this for the last couple of days.

Could it happen? Sure. The odds are in our favor. But before we break out the champagne, I am a little worried about a few of the details.

On the negative side:

• First off, this weekend is supposed to be mild, with temperatures in the upper 50s on Sunday afternoon. It would not shock me if we touch 60 due to the strong southerly winds predicted. This will thaw the ground to the point that it will take quite a bit of freezing precipitation to change the ground temperature.
• Second, with all of this warm air in place Sunday, I am a little worried about the accuracy of the Arctic air intrusion predicted by the models. Models commonly predict an Arctic "Express Train" of cold air, but in reality it usually turns out more to resemble the "Saint Louis Zoo train."
  
• Also, the timing of the onset of frozen precipitation has me concerned: the switchover from rain to freezing rain/sleet is not predicted to occur until after midnight early Monday morning.
• Forecast models have historically not done a good job predicting freezing rain/sleet events 3 days before onset, particularly in November/December.
  

On the positive side:

• That strong southerly flow Sunday will bring the necessary moisture to the Midwest for us. We won't have to overcome dry air before precip starts, as the air will already be saturated.
  
• My prediction that this will be a colder-than-average winter plays into our favor (take that, Global Warming)
  
• My prediction of a wetter-than-average also plays into our favor.

In the final analysis, I am not skeptical that we will get a lot of moisture, and therefore a lot of precipitation. I am just not yet convinced of the cold air intrusion. Three days out, it is simply too early to make that call.

But if you are interested in my prediction, stay tuned, and I will put out a prediction in the next 24-36 hours.

Keep your fingers crossed!

-WD