Unfortunately, a strong arctic high still looks like it’ll descend into the upper Mid West Friday before moving east over the Great Lakes (Saturday) and into the northeast (Sunday).  This will help shove a cold front south to the upper TN Valley Friday and dense, cold air will bleed south to encompass central Indiana as we wrap up the work week.  As we progress into the weekend, warm moist air will override the shallow cold air locked in place at the surface.  Ripples of energy will move along the boundary and periods of more concentrated, steadier precipitation will fall.  Significant ice accumulations (greater than one quarter inch) will be possible for portions of central Indiana.

GFS ensemble members above show the overall good agreement on a central IN ice set-up for portions of the weekend.

Timing:  As of now, I think most of Friday is dry and cold before moisture overspreads the region late Friday night into Saturday.  Additional waves of moisture will push through the region during the second half of the weekend, as well.

Confidence:  We have very high confidence on at least light to moderate icing in the Friday night – Saturday time frame, but confidence on additional icing thereafter begins to drop, thanks to disagreement in modeling.  The GFS is warmer for the second half of the weekend and would reduce the threat of significant ice build-up as some brief thawing would be in place in between waves of moisture thanks to temperatures rising into the middle 30s.  However, the European model is much colder and keeps IND below freezing Saturday and Sunday, with nearly half an inch of liquid during that time frame.  That’s downright concerning and would result in significant issues with potentially downed tree limbs and power lines.

We do have concern the European could have a better handle on things right now.  Modeling is notorious for underestimating the strength and depth of the cold air with these arctic highs and similar overrunning events of the past.  Stay tuned.

Impacts:  Greatest concern right now is for icing on exposed and elevated surfaces (bridges, tree limbs, power lines, etc.).  With the milder air of midweek, along with marginally cold air, it’s possible crews will be able to keep roads passable during this event.  Additionally, something else to consider is the rate of precipitation.  While bad for elevated ice build-up, if precipitation rates are heavy enough, this can help reduce ice build-up on roadways.

Summary:  We still have concern for the potential of an impactful ice event this weekend through central Indiana.  Winter Storm Watches (and potentially Ice Storm Warnings) may be hoisted by the National Weather Service later this week for this event.  Despite an overall high confidence in at least some icing impacting the region, questions do remain in regards to the temperature profile later in the forecast period this weekend, and caution the slighted deviation in surface temperature can make all the difference to impacts.  At the very least, low pressure should pull out of the southern Plains early next week and this will serve to push enough warm air northeast to change everything over to plain ole rain early next week as we rise into the 50s.