A wintry mess coming to central Indiana Sunday night

A “storm” is developing in the Rocky Mountains that will impact central Indiana Sunday night and Monday.

During the day Sunday it will remain dry.  Clouds will be streaming in ahead of the storm.  Moisture will begin to appear on radar by early evening.  Much of the initial radar returns will not reach the ground as there is dry air in place in the lowest 5,000 feet above the ground.  High resolution data suggests the atmospheric column should become saturated all the way to the ground by 7pm.  It is at this point moisture will be able to make it to the surface.

Computer model projection of radar imagery.

Our latest RPM computer model takes the moisture from west to east across the state.  I think we will see an initial burst of snow before the precipitation changes over to a mix of snow and freezing rain.

Computer model projection of ice accumulation through Monday morning.

Most computer models keep the amount of freezing rain (ice) accumulation to just a couple hundredths of an inch.  One computer model, the NAM, is much more bullish with the precipitation and puts down a couple tenths of an inch.  At this time, the NAM is an outlier.  It appears to be overly aggressive with the moisture.

One of the difficult parts of determining the precipitation type is a thin layer of warm air projected to move over central Indiana.  Computer models suggest “warm” air – approximately 0.5°F to 2°F – will move in between 2,000 and 5,000 feet above the ground.  How thick this layer will be will determine what precipitation falls as temperatures at the surface will remain below freezing (32°F).

Nonetheless, any freezing rain that accumulates will become a problem as it coats the ground and other surfaces.

One factor that will be interesting to watch is the amount of salt/chemical treatment on roads from recent snows.  This may help chemically “warm” the ground and keep some of the ice accumulation off main roads.  That’s a theory, so we will have to see how it plays out in reality.  Stay tuned!


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