New Year's Potential Winter Storm

Potential is on the rise for a winter storm around December 30th into New Year's. Above is the ECMWF model's 500mb height anomaly forecast for the evening of December 28th. In areas of blues and greens, lower pressure is observed, hence the term of a low pressure system. Warm colors depict the presence of a high pressure system. The storm system we are watching is in Oklahoma/Texas at the moment.

Note the presence of a Rex Block in the West. A Rex Block involves high pressure in the Pacific Northwest and low pressure in the Southwest or just offshore of the region. When the Rex Block is in place, the southern jet stream amplifies, and high pressure will attempt to form in the East US in response to the increasing number of storm systems passing through the South Plains. In this forecast, the high pressure system is based in southern Canada, not the waters off of the Southeast, so a move into the Ohio Valley is not as likely as you may think.

On the evening of December 29th, we see the storm system has actually moved slightly to the northeast and has separated into two low pressure systems. One is based in Michigan, the other based in Missouri. If we count in the Fujiwhara Effect, these two systems should continue a motion to either the east northeast or plain northeast.

For those unfamiliar with the term, the Fujiwhara effect involves two cyclones that begin to orbit each other. This is not unlike the phenomenon of a binary solar system, but the two suns orbit each other rather than planets orbit the suns. If the Fujiwhara Effect does happen to evolve into this situation, I could see the Missouri system moving east northeast, and the Michigan system slightly retrograding or moving east to wait for the Missouri system to catch up.

The ECMWF Ensembles show a similar situation, but more to the north:

The ECMWF model shows snowfall as being confined to the Midwest (IL, WI, east IA, north MO) on the order of 3-6 inches. Do not use the heavy amounts in the Northeast or Ohio Valley here, that snow is for the Dec. 25-27 storm.

Those of you who have followed me for a while know how I use a pattern called the Lezak Recurring Cycle (LRC). This involves a pattern setting up every year that has repetitions, called cycles. Each cycle happens every 40-60 days.  The below image shows the observed 500mb height anomalies on November 7th, about 53 days from January 1st. This year's cycle length is 53 days, meaning that this system does fit into the pattern.

Andrew