The Weather Guys

How low will temperature go?

Posted on January 28, 2019 by WeatherGuys Editor

Arctic air mass plunging into the Great Lakes Region. (Image credit: ClimateReanalyzer.org)

On Jan. 30, 1951, the morning low temperature in Madison fell to minus 37. Nearly 12 years later, on Jan. 15, 1963, the mercury dropped to precisely minus 30.

These two days remain the only dates in Madison’s recorded history with temperatures as cold as minus 30. On those record-setting days a number of characteristic meteorological conditions were in play to drive the temperature to such extremes.

A healthy blanket of fresh snow on the ground is one such condition. Snow has two properties that contribute to cooling. First, it insulates the ground, effectively keeping the vast reservoir of infrared (thermal) energy in the ground.

Second, snow is very good at emitting infra-red energy, so the top surface of the snow can cool rapidly over the course of a long winter night while energy from the underlying surface is kept from reaching the top of the snow. If the wind is light, the frigid air cooling on top of the snow tends to pool in low-lying areas, such as Truax Field at Dane County Regional Airport.

Finally, when the air in the lowest levels of the atmosphere is also very cold that ensures the air is very dry (has little water vapor in it). This lack of water vapor further enhances the cooling that can be accomplished by emission of infrared radiation.

With the exception of really light winds, all of these variables will be at historic levels early Wednesday morning. That leads us to think that we will make a run at the all-time lowest temperature in Madison that morning.

With slightly stronger winds likely to characterize that morning compared to the prior minus 30 mornings in our past, even if the temperature does not approach the record, the combination of cold and wind will bring wind chills down near or past minus 60 — extremely dangerous conditions.

Be very careful venturing outside during this coming week – we will be talking about its cold for years to come.

Category: Meteorology, Seasons, Severe Weather

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Is winter finally here?

Posted on January 22, 2019 by WeatherGuys Editor

January 21 Terra MODIS view of wintry Wisconsin (Photo credit: CIMSS)

Though we have enjoyed a remarkably warm December and first half of January in Madison this year, we are now entering deep winter.

The period from Dec. 1 through Jan. 17 has averaged 7.4 degrees above normal this year and has contributed to our breaking or approaching several obscure, but nonetheless, interesting records of prolonged warmth — provided courtesy of Jordan Gerth at the Space Science and Engineering Center at UW-Madison.

We have already broken the previous record for latest date with a low temperature of 10 degrees or colder, set on Jan. 11, 1914. This year, we made it to Saturday, when the overnight low was zero.

A related measure, the record for the number of consecutive days with a low temperature of 10 degrees or warmer, had already been broken this year. The prior record was 324 consecutive such days (Feb. 10, 1997, to Dec. 30, 1997). The streak that began Feb. 14, 2018, ended Saturday, meaning we set a new record of 339 days.

As of Monday, we will likely edge up to the fifth spot in the latest first day (after July 1) for a low temperature below zero. The all-time latest occurred on March 3, 2002 — nearly a full month later than its nearest competitor.

Similarly, the number of consecutive days with a low temperature warmer than zero ended Sunday at 341 days. The all-time record in this category is 378, set between Feb. 18, 2001, and March 2, 2002.

So, even as you are cursing the cold in the last week of January, remember it has been a remarkably long run of unseasonably warm weather.

Category: Meteorology, Seasons, Severe Weather

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What is the status of Antarctica’s ice sheets?

Posted on January 15, 2019 by WeatherGuys Editor

The Antarctic Meteorological Research Center (AMRC) at the UW-Madison’s Space Science and Engineering Center (SSEC) maintains 57 Automated Weather Stations (AWS) in Antarctica. In the photo, Elina Valkonen and David Mikolajczyk travel by Twin Otter aircraft to service a remote weather station.
(Photo credit: AMRC)

Most of Antarctica is covered by ice.

The ice sheet is over 2 miles thick in places and in some places the ice sheet bottom is almost a mile below sea level. This massive ice covers mountain ranges, and volcanoes exist underneath the sheets.

The Antarctic Ice Sheet is categorized as three ice sheets: the Antarctic Peninsula Ice Sheet, the West Antarctic Ice Sheet and the East Antarctic Ice Sheet.

The Antarctic Ice Sheet currently discharges 90 percent of ice and sediment through corridors of fast-flowing ice within an ice sheet known as ice streams. Ice streams are typically large features, greater than 25 miles in width, and longer than 90 miles. Today, ice streams drain the Antarctic continent, with tributary glaciers reaching hundreds of miles inland.

Overall, recent estimates indicate that over a 19-year survey, Antarctic’s net ice mass is decreasing. Satellite observations measured a widespread enhanced flow toward the ocean, with tributary glaciers reaching deep into Antarctica’s interior.

Antarctica drains more than 80 percent of its ice sheet through floating ice shelves. In recent years we have seen the collapse and melting of these ice shelves. In 2002, satellite imagery captured the collapse of the entire 1,250-square-mile Larsen B Ice Shelf. The disintegration of this Antarctic Peninsula ice sheet was rapid.

New observations indicate that glaciers in East Antarctic have begun to melt. Scientists have long considered these glaciers to be more stable than those in West Antarctica. Glaciers around the West Antarctic Ice Sheet are currently thinning. The Antarctic Peninsula Ice Sheet is changing most rapidly.

Category: Climate, Meteorology, Seasons

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Can weather in the stratosphere affect us near the ground?

Posted on January 7, 2019 by WeatherGuys Editor

Thus far the winter has been relatively mild around the Northern Hemisphere. This December was the 14th-warmest December, and the period from Sept. 1 through Dec. 31 was the eighth-warmest since 1948.

Such a prolonged delay to the onset of winter makes one wonder if it will ever arrive this year. Though there is no clear way to be sure about the answer to that question, one potential phenomenon that can encourage a winter-like cold air outbreak is a sudden warming of the lower stratosphere, the layer of the atmosphere between 6 and 20 miles above the surface.

Every year, as the sun heads toward the horizon in polar regions at the autumnal equinox, a strong wind maximum develops on the edge of the cold, stratospheric air that is left in the expanding polar night. This jet is known as the polar night jet (PNJ). It is usually fairly east-west oriented with few undulations in it, and it provides dynamical support for containing cold air in the lower troposphere at high latitudes.

The PNJ can weaken rapidly when it is showered with wave energy that emanates from a parade of storms occurring in the underlying troposphere. Rapid weakening of the PNJ is often associated with lower stratospheric temperature increases of as much as 50 degrees in one day — sudden stratospheric warmings (SSWs).

With a weaker PNJ, the containment of cold polar air at lower altitudes is also weakened and so locations in the middle latitudes (where we live) are suddenly more susceptible to dramatic cold air outbreaks, often delayed by a few weeks from when the SSW occurs. At the turn of the new year, an SSW occurred and so some place in the Northern Hemisphere may be a couple of weeks away from a rude winter awakening.

Category: Meteorology, Phenomena, Seasons

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What were the top weather events for 2018?

Posted on January 3, 2019 by WeatherGuys Editor

The Yahara River overflowed its banks on the east side of Madison in late August after the rainiest day ever recorded in the city. (Photo credit: Wisconsin Air Coordination Group and Wisconsin Drone Network)

The year began with frigid temperatures across Wisconsin. The average temperatures for the first seven days of January were well below normal across southern Wisconsin with most areas at least 15 degrees below normal.

The end of 2018 saw temperatures several degrees warmer than normal, including a record high temperature of 50 F on Dec. 27, tying a record high for the date, last set in 2003, and previously set in 1936 and 1946.

The year-to-date temperature across the globe was more than 1 degree above the 20th-century average of 57.2 F. That may turn out to be the fourth-highest global mean temperature in the 139-year record,

Southern Wisconsin experienced a rainy summer. The August precipitation that fell over the region was about 200 percent of normal. Total precipitation was also above normal for June and July. By the end of summer, we were about 6 inches above normal.

On Aug. 19, 2.74 inches fell on Madison, setting a daily record rain amount, beating the old record of 2.13 inches set in 2007. In particular, August has been exceptionally rainy compared to the prior five Augusts as the only above-normal August in that stretch occurred in 2014 (+1.14 inches).

The United States had a below-average number of tornadoes. There were no tornadoes in the U.S. rated above EF3, making 2018 the first year there were no violent tornadoes in the U.S.

There were 17 confirmed tornadoes in Wisconsin on Aug. 28 with the strongest rated as EF-2 on the enhanced Fujita scale. Damage to trees and agriculture was widespread on that day, but there were no reported fatalities or injuries.