While arriving later than originally expected (recall we originally thought the cold, wintry pattern would start on the 18th), it sure appears as if this was a case of “delayed, but not denied.”
The latest GFS and European ensembles are keying in on a significant pattern change as we put a wrap on February and open March. (Looks like we were about a week early in jumping on the cold bandwagon).
First and foremost, there’s excellent overall agreement amongst data (increases confidence significantly during the medium to long range period).
Days 1-5: Southeast ridge continues to dominate during the short-term period and there’s no high-latitude blocking to speak of. This suggests storms will continue to “cut” northwest of the region and place central Indiana in the “warm” sector, with transient, backlash cold/ snow potential.
Days 6-10: Significant changes begin to take place as heights (ridging) builds across AK. This is important as it can help “dislodge” late season cold air (and send it southeast). The SE ridge is also in the process of getting squashed during this period. We’ll likely transition away from the moisture-laden storm systems and replace with faster, overall weaker, systems that will be more capable of producing wintry precipitation.
Days 12-16: A total transformation of the pattern has taken shape since the Day 1-5 period. The new ‘mean’ trough position takes up shop across the East with the AK ridge continuing to dislocate late season arctic air southeast. The GEFS also shows a reflection of a southwest ridge which can be helpful in the overall storm track that could potentially deliver more “meaningful” wintry systems across the OH and TN Valleys as we get into the first couple weeks of meteorological spring.
Side notes: We’ve reviewed the crashing SOI index and this increases our confidence in a much colder pattern developing (typically takes place around 10-12 days after the crash begins). We’ve noted the deeply negative values against the base state which would suggest the cold pattern should continue for some time. We still believe the pattern remains colder than average, overall, through the 1st half of March.
The latest deeply negative EPO adds fuel to the fire in the idea of a cold open to March.
Given this, there should be no surprise to see the cold anomalies showing up on the latest medium-long range ensemble guidance:
It sure appears March will come in like a lion; will it go out like a lamb?
II. A much stronger storm system will wrap up to our northwest Wednesday night and Thursday. We’ll notice an increasingly strong southerly breeze during this time period and rain will be on the increase as we progress through the day Thursday. The trade-off? Highs between 55° and 60° to close the week- though those temperatures may actually come Thursday evening before cooler air begins to slip in here during the day Friday.
III. All attention is squarely focused on a significant pattern change that takes shape as we head into the new year. As mentioned in previous posts and discussions, the transition is likely to be a stormy one, but it’s far too early to talk precipitation types. A combination of ingredients appears to be aligning to create a colder than normal (and potentially significantly so) pattern at the traditionally coldest time of year (mid-Jan).
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…