IT SCREAMS WINTER...

terryswails1
1 minute ago
6 min read

Significant changes are taking place that will result in a pattern realignment in roughly a week. This will bring significantly colder temperatures and set the stage for what should be a wintry start to December. More on today's developments in just a moment.

First, Steve Gottschalk, the Lowden climate guru, continues his reports on extreme November weather events. This one is a humdinger that involves all types of impactful weather and left the Midwest dazed and confused. Here's his report.

THE GREAT BLUE NORTHER OF 1911

On Nov. 11, 1911, a powerful cold front swept across most of the central U.S. producing unprecedented temperature falls that still stand to this day. The intense low pressure system and cold front moved across S.E. Iowa on the 11th, spawning severe thunderstorms and a tornado ahead of it and blizzard conditions behind it.

The first half of that fateful day, temperatures were May-like across the SE half of Iowa. Some of the warmer readings were Dubuque - 70, Cedar Rapids - 72, Iowa City - 75, Clinton and Davenport - 76, Burlington - 77 and Keokuk - 79. By midnight, a vicious cold front had dropped temperatures in Dubuque to 16 while Davenport had plummeted to 14.

At Keokuk, the cold front swept through before 2:00 p.m. with the temperature falling to 37 degrees during the first hour and 28 more degrees to 14 by midnight, a fall of 65 degrees in 10 hours. The rain changed to sleet with 1.0" falling during the afternoon and evening hours, and then to snow with blizzard conditions produced by the very strong N.W. winds. The next day, the high temperature was just 17 degrees.

At Keosauqua, the temperature fell from a high of 79 to a low of 9, a drop of 69 degrees in a matter of hours. Rain changed to snow

At Burlington, the temperature rose to 77 during the early afternoon but fell to 10 degrees by late evening.

Thunderstorms that erupted along the front produced hail, strong winds and a F2 tornado that was 20 yards wide and traveled 9 miles near Davenport, injuring one person. The tornado tracked from 1 mile west of Davenport, near Locust Street Road, moving N.E. to 1 mile east of Mount Joy. There was damage to homes, farm buildings, trees and wires.

The storm system also spawned two F2 tornadoes in Illinois, one in Cass County was 100 yards wide and was on the ground for 18 miles, injuring 12 persons. Another F2 tornado, in DuPage County, tracked for 4 miles. An F3 tornado in Mason County was on the ground for 11 miles, killing 2 persons and injuring another 9.

The deadliest tornado of the day was an F4, 400 yards wide that was on the ground for 18 miles near Janesville, Wisconsin, striking the city at 9:00 p.m., killing 9 persons and injuring another 50. One hour later, survivors were digging out of the rubble in blizzard conditions and temperatures approaching zero.

Behind the arctic front, strong winds resulted in injuries and damage to farm buildings, trees, and utility lines. The rain mixed with sleet and changed over to snow in most areas before ending. Over 100 years later, virtually all the record temperature falls set during this event, have never been equaled.

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WHAT'S THIS, COULD IT BE WINTER?

After a rather raw, ugly day Tuesday, guidance is consistent in showing another uptick in temperatures that would again meet the qualifications of Indian Summer. A couple of 60 degree days are even in the table, especially from I-80 south. Then, look what happens Thanksgiving. A dramatic reversal takes place that has the high in the Quad Cities December 4th at 20 following a low of 11.

Considering the MJO is headed into the holy grail of cold December phases (7, 8, and probably 1 the next 30 days), this is a trend that's been well teleconnected for over a week. The EURO enters phase 8 around December 15th.

The GEFS extended MJO is even more amplified, otherwise similar. As a rule, the more amplified the cycle is away from the diagram's center, the greater the chances of significant cold.

For those who have not been playing along, you can see how we depart the warmth of phase 6 and enter into the cold western hemispheric December analogs of 7, 8, and 1 by the end of November.

What allows the change is the flip that takes place in pressures, especially in Alaska. Below, mean pressures over Alaska and much of the western U.S. are shown to be low (in blue and green) through early next week.

By November 28th, look at the dramatic change. High pressure is ridging from the Arctic into Alaska and the Plains. The higher the pressure, especially in the cold season, the colder the air. That is a massive change that opens the door for cold to enter the lower 48.

Just look at what that does to temperature departures. They are way above normal over much of North America under the influence of low pressure.

Ten days from now with high pressure pushing, much of that same area has transitioned to below normal readings with the core of the cold relative to average perched over the center of the nation.

By watching the MJO, and convective trends in the western tropical Pacific, we could see there was potential for this change 10 days ago. Now the models are sensing the shift and picking up on it.

Aside from that, the AO (Arctic Oscillation) is forecast to go negative. Nick mentioned this in a weekend post. By the 25th, 10mb winds in the stratosphere are shown dramatically weakening. Normally these winds, associated with the Polar Vortex, are quite strong and restrict extreme cold from reaching the mid-latitudes where we abide. When they weaken, it allows the cold to descend to lower levels that extend into the U.S.

It's a complex topic, but when the stratosphere warms and zonal winds weaken at high latitudes, that goes hand in hand with a negative Arctic Oscillation. As shown below, the AO goes negative around the 23rd and stays there into early December.

Look at temperatures lower right associated with the -AO

With a weak to moderate La Niña and an -AO, temperature departures over the eastern 2/3rds of the nation are typically well below normal. See the box with the red X.

Not to be forgotten is the serious dip in the WPO (western Pacific Oscillation) that is forecast around the 24th. The WPO and EPO (eastern Pacific Oscillation) are negative in union, that is another strong teleconnection for cold in the lower 48 with a western ridge forcing cold southeast.

The EPO

Last but not least, the NAO (north Atlantic Oscillation) is also shown trending negative.

A -NAO implies an elongated block centered on Greenland. That's a set-up that forces arctic air and often storminess underneath the block. It can be an active stormy, even snowy pattern for much of the northern half of the country. The typical temperature departures for the -NAO and -AO is shown on the bottom left.

From a teleconnection standpoint, you can't draw it up any better for cold and potentially snowy weather than what I've seen today. Of course, small mesoscale details are impossible to see, such as individual storm tracks. It is also possible that the cold comes in stages, each push a little more potent than the previous. Whatever happens, confidence continues to grow that December could be quite interesting.

Over the past week, I've been showing what the EURO weeklies have been indicating for snowfall in the run-up to Christmas. This is the ensemble mean, an average of many solutions. It's been quite consistent for at least a week.

The control was an insane run with little chance of ending up as extreme as what's shown. However, the trend of a significant storm track over the heart of the Midwest gives me hope we could do all right in the snowfall department this December.