Late December through early January is a critical time period where most folks (even those maybe not normally interested in the weather) are glued in on the forecast. For some, they’re rooting for a white Christmas, while others are preparing for holiday travel to see loved ones. The idea here of a transitional pattern remains and this should promote active weather during the holidays this year.
Understanding things can change with respect to timing from this distance (in some cases 2+ weeks out), these are the dates we’re targeting for storm impacts across central Indiana:
- Dec. 20-21
- Dec. 24-25
- Dec. 27
- Dec. 30-31
Before we talk specifics, it’s important to look at some of the pattern drivers. Some of these drivers include teleconnections such as the NAO, AO, PNA, and MJO.
Forecast indices with respect to the AO, NAO, and PNA are expected to be more or less neutral through the late month period. This is what the respective teleconnection “state” would result in the temperature department across the country.
Arctic Oscillation
North Atlantic Oscillation
Pacific North American Pattern
The basis of our late-December forecast is built from the MJO, or Madden-Julian Oscillation. We note the MJO is expected to rumble through Phase 4 before heading into Phase 5 around Christmas. Phase 4 (image 2 below) is a warm phase and correlates well to what the week ahead will provide. However, Phase 5 (image 3 below) is a colder phase and could “up the ante” for the potential of wintry weather around Christmas.
If the MJO amplitude remains, it’ll roll into Phase 6 to close the month and open January. Here’s how that would correlate in the temperature department:
The upcoming week will run milder than normal- lining up perfectly with MJO Phase 4.
The first of our targeted holiday storm systems will come at the tail end of the warm Phase 4 and will likely deliver a wind-whipped rain in here as early as Wednesday night and Thursday morning. However, as the storm pulls northeast along the Ohio River, it’ll deepen on its journey into the eastern Great Lakes region. This will help pull colder air into the region, likely resulting in rain transitioning to snow Friday. Given the path of the storm, this doesn’t favor some sort of prolonged backlash snow event, but it could be enough to result in accumulating snow across eastern Ohio Valley sections and downwind of the snow belt regions of northern IN, OH, and MI.
The pattern, as a whole, appears to be one of transition to close the month and open January and it’s not really until we get to mid-January where we think all of the drivers “align” to create more of a lock and hold cold pattern. With that said, a stormy late December pattern can present problems, even in the midst of relatively mild times. We’ll be here to dissect the storms as they come throughout the holiday season…
Additional rainfall totals of 1″ to 2″ with locally heavier amounts are a good bet in that Monday night – Tuesday time frame.
While we’ll certainly turn colder behind this storm system, the true early season push of arctic air will wait a couple of days to arrive- Thursday afternoon into Friday. Not only will this be the coldest air of the season (lower-middle 20s Friday morning and likely colder next Saturday), but the first flakes of the season are also likely to fly across central Indiana to wrap up the work week. Furthermore, 
Don’t look now, but more “fun and games” await the following week…
II. Wet Halloween: A cold front will approach the state Tuesday evening into our Halloween. Widespread rain is expected Wednesday, BUT the silver lining may be that the bulk of precipitation will be shoved to our southeast before most trick-or-treaters take to the streets.
III. Chilly Open To November: Reinforcing chilly air will blow into town behind the cold front and set the stage for an unseasonably chilly open to November. Generally, lows will fall into the middle 30s and highs will top out in the upper 40s for the first few days of the month.
IV. Raw Saturday: It’s a “rinse and repeat” scenario as next weekend opens raw and wet thanks to a new storm system moving through the region. Gusty showers and unseasonably cool temperatures can be expected Saturday. Note the possibility of wet snow to fall on the northern periphery of the storm system through IA, MN, and WI. (Signs of the times).
V. Wet Pattern: After a long stretch of dry weather through the balance of October, a big shift in the pattern is taking place now and will continue to promote well above normal rainfall as we move through the first couple weeks of November. In some cases, the upcoming (10) days alone may yield 3″ to 4″ of rain in some areas of the region.
