Foggy morning and closer look at Christmas temperatures

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Dense fog appears likely across central Indiana to start the work-week.

Computer models suggest low clouds – below 5,000 feet – will settle in overnight.

Computer model projection of clouds at various altitudes.

The image above reads from right to left (yes, opposite to conventional wisdom).  The areas of grey indicate cloud cover.  The horizontal dashed lines represent levels of altitude above the surface.

Visibility will drop as cloud bases get closer to the ground and fog develops.

Computer model projection of visibility – measured in miles – at 8am Monday.

The low clouds will likely hand around through the morning and begin lifting during the afternoon.  However, I don’t expect skies to clear.  I think they will remain cloudy much of the day.  Visibility may remain low in areas northeast of Indianapolis.


A lot of questions coming in about what we expect for Christmas.  At this point, Christmas day is eight days away, which is a long time from now by a forecasting standpoint.

For several days computer models have been suggesting a big push of cold air coming to the Midwest for this weekend in to early Christmas week.

Today, models are slowing down the arrival of cold air by about 24-hours.  That does look probably at this time.  Also, computer models are backing off the strength of cold air.  However, a closer look at the data suggests the models have not locked in on a solution.

Typically, we look at “operational” computer models.  Operational models are a single projection of what may happen at a given time.  When we look at an ensemble computer model, the forecast can vary.  An ensemble model looks at 30-50 different computer models and attempts to average them out to a single solution.

When we look at the ensemble range, you can get an idea of what possibilities may be possible.  Here is Sunday morning’s European computer model ensemble projection of air temperature in Indianapolis.

European computer model ensemble projection of temperatures December 23-26.

Basically, the different color blues show the range in temperature by percentile.  Look at the range for Christmas day at 1pm!  Models are projecting the air temperature is anywhere from 13° to 66°.  A range of 53°!  What I take from that… It doesn’t have a consistent idea of what will happen.

I have a feeling temperatures will be on the cooler side of the ensemble forecast.  Which means high temperatures in the low/mid 20°s for central Indiana.  Stay tuned over the coming week!

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