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.
2.) Expanding Snowpack: 65.4% of the country is covered in snow this morning. The cold, arctic high suppressed the winter storm threat south as we alluded to in previous posts. Places across the Deep South that aren’t used to wintry precipitation are waking up to snowy and icy conditions this morning, including MS, AL, GA, SC, and into the Mid Atlantic. Heavier snowfall accumulated across east TN, including 5″-8″ in the high country. Heavy snow also fell through western and central NC and Blizzard Warnings are up in rare areas including VA Beach this morning.
3.) Moderating Temperatures: Our air flow will back around to the southwest and this will help temperatures begin to moderate early next week (around freezing Monday and all the way to around 50 Tuesday). As the moderating trend gets underway, we may have to deal with a brief period of freezing drizzle/ freezing rain Monday evening.
4.) Rainy Midweek: A more significant surge of moisture will arrive midweek and result in periods of moderate to heavy rain Wednesday PM into Thursday. Potential is present for 1″+ during this timeframe.
5.) Weekend Wintry “Fun And Games?” A tremendous battle will take place next weekend between a strong and sprawling arctic high pressure system and the southeast ridge. In between it’ll be fascinating to watch things unfold, and as you’d imagine, that includes Indiana. Despite the southeast ridge flexing it’s muscle, the concern here is that the shallow dense arctic air will “ooze” south and present an icy set-up for portions of the Ohio Valley and Mid West for the weekend. We still have some time to watch this, but the potential of significant icing is very much present for some and this will require a close eye through the week.
We note ensemble data is suggesting high latitude blocking tries to develop towards Day 10. Recall this was the missing ingredient in the bitterly cold blasts of air that occurred during the first few weeks of December. Both the GEFS and EPS agree on the increasingly blocky look to the pattern by Day 10. This would help drive a cold, stormy pattern by early January. Instead of storms cutting, we would see more suppression. With a “stubborn” southeast ridge, things could get interesting across the Ohio Valley from a wintry perspective….
We don’t want to jump the gun, but it the positives can “hook up” over the pole, we stand the chance of locking into a rather lengthy cold, snowy regime as we rumble deeper into the heart of winter.
Summary: A rather mild regime remains as we rumble through Christmas before trending more seasonable next week. From a wintry perspective we need to continue to keep an eye on the period around New Year’s Eve/ Day. Confidence continues to increase on the potential of a return of arctic air come early January.
We’ll open the work week with dry and cold conditions, but all eyes will be on the next arctic front by this time. It’ll blast through here the middle of the week with 
The overall set-up is certainly an intriguing one. Cross-polar flow seeds pressing arctic air into the pattern (again, it comes in “waves” over the next couple weeks, each subsequently stronger). What’s of particular interest is the battle that develops between a tag-team of ridges- SW and SE (at times these will put up more resistance than the other). Long-time Hoosiers know that when cross-polar flow gets involved it can “suppress” storms, but rest easy in knowing that the SE ridge will provide resistance. In fact, some across the lower Ohio and TN Valleys may eventually complain that the southeast ridge is providing too much resistance.
Since then, the European has begun to lock-in to a trend of bringing that SW energy out quicker and, in return, igniting a surface low to develop in the western Gulf of Mexico (GOM) Saturday before tracking northeast into the TN Valley (Sunday) and Great Lakes region (Monday).
Taken verbatim, this would spread a cold rain into central IN Sunday before colder air begins to change the rain over to a wet, heavy snow Sunday night into Monday morning across central IN. Heavy, wind-blown, snow amounts would result with such a solution for portions of central IN. Such a scenario would be a high-impact event. While the majority of model data (factoring in the GFS and Canadian, for example) is far from agreeing on such a solution, it’s important to note that a trend of such a scenario is beginning to develop within the powerful European forecast model. Furthermore, roughly half of the European’s (51) ensemble members agree on an impactful winter event in the Sunday-Monday time period for central Indiana.