Category: High-latitude Blocking

Updated 01.19.21 @ 7:58a

Another upper level disturbance will push into Indiana this evening, providing a renewed shot of snow showers after dark, continuing into the overnight hours. Before we look at this and other storm dates of interest, I wanted to review the upcoming couple of weeks from a temperature and precipitation perspective.

While there weren’t a lot of changes overnight with respect to the ensemble guidance from Week 1 to Week 2, it’s fair to say the GEFS and EPS are trending in 2 separate directions- at least across the Ohio Valley into the Northeast Week 2. The theory here is that the differences come from the way the modeling handles the EPO and subsequent downstream ridge resistance. At any rate, confidence remains lower than normal in the 7-14 day period and it’ll likely take another 48-72 hours for things to become clearer during this time frame.

Week 1

I would lean more on the European in the Week 1 timeframe (due to the precipitation pattern with forecasted trough/ ridge positions), though the solutions are similar, overall.

Week 2

Despite the subtle differences, I would lean heavier towards the European solution again (retrograding eastern trough idea).

Storm dates of note include the following:

Jan. 24th-25th

Jan. 27th-28th

Jan. 31st-Feb. 1st

Expect continued wild run-to-run swings on the operational guidance as the data tries to understand the battle between the high latitude blocking (courtesy of the negative AO) and maturing negative PNA (will lead to southern ridging and more resistance as this gets established). These combined ingredients will lead to more of a question of wet vs. white, as opposed to a non-storm “event” that we’re dealing with Thursday-Friday. With the blocking in place, it’ll be tough to drive lows to the Great Lakes and we’ll need to watch for southward trends on guidance the closer we get to these potential storm dates of note above.

In the meantime, we have one more clipper system that will dive into the region this evening. This will offer up yet another round (the last in the series going back to last week) of snow showers after dark into early Wednesday (snow should be out of here by mid to late morning tomorrow). Snowfall accumulations across central Indiana can be expected to fall within the dusting to half inch range.