WINTER AND A MODOKI EL NINO....

The first flakes of the season fell on parts of Iowa and Illinois Friday morning. Snow amounts in Des Moines reached .2" and the Quad Cities recorded a trace. It wasn't much but it was nearly 3 weeks ahead of schedule. The question I've already been asked is this a sign of things to come?

From what I've researched, not necessarily. I can't find any strong correlation linking early snows to snowy winters. What I have observed is that years in which El Nino's were present, snow and cold did indeed came early. However, following cold Novembers and in some cases early Decembers, warmth and below normal snowfall prevailed the rest of the winter.

There's always exceptions to the rules. For example, the lay-out of sea surface temperatures, jet stream blocking at the upper levels, the strength of the El Nino, or even solar activity can off-set the effects of the southern oscillation. It's a complicated puzzle but its proven that the stronger the El Nino the warmer the winter here in the Midwest.

By all accounts a late starting El Nino is gaining strength this year in the tropical Pacific. But, there's an important twist based on the location of the warmest water within the tropical Pacific. This year indications are that the greatest departures (warmest water) are likely to be in the central Pacific as opposed to western and eastern sections.This is known as a Modoki El Nino and it teleconnects to a more traditional winter than the weaker types associated with a full fledged El Nino.

Models currently predict the Modoki reaching weak to moderate status in November before gradually weakening towards spring.

In an El Nino year the polar and sub-tropical jets generally remain split during the winter over the Midwest. The lack of phasing limits cold air intrusions and keeps the heaviest precipitation events over the southern U.S. (mild and drier than average winters).

The Modoki on the other hand keeps a western ridge far enough west to allow the polar jet access to the Midwest. This opens the door to colder air masses. It also allows enough phasing to occasionally hook the polar and sub-tropical jets together. The further west this happens the colder the temperatures and the more potential there is for snow. How this critical development evolves dictates the severity of the winter.

Being the snow freak that I am I decided to look at Modoki winters and resulting snowfall in my area. Here are some of the winters that I came up with and their associated snowfall in Cedar Rapids.

1963-64...26.3

1964-65...41.8

1968-69...25.3

2002-03...22.1

2004-05...22.5

2009-10...42.5

2014-15...24.1

What I found is that 5 out of 7 years snowfall was below normal by 6-10", (Normal is about 32)

However, 1964-65 and 2009-10 were good snow producing winters with amounts near 42". (10" above normal).

If you're playing the odds based on the Modoki theory there's about a 70% chance the winter will see below normal snowfall. Something on the order of 25"

Averaging all 7 Modoki years the snowfall figure increases to 29.2", just a tad below normal.

Based on what I've seen I think the ridge may set up further west this winter which would give my area a shot at snow amounts more on the order of 30-35". It would also imply regular shots of cold air. To sum it up, the coming winter stands a good chance of seeing near normal snowfall and below normal temperatures. Fun with numbers! Roll weather...TS

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