Did weather forecasting play a role in D-Day?

Posted on June 11, 2018 by WeatherGuys Editor

Had the Allies delayed the D-Day invasion of Europe that began June 6, 1944 with the landings on the beaches at Normandy, the combination of lunar cycle, tides and weather almost certainly would have postponed the invasion for more than a month likely costing the effort the tremendous advantage of secrecy. (Photo Credit: Associated Press Archives)

Wednesday was the 74th anniversary of the Allied invasion of Europe that began with the landings on the beaches at Normandy.

The combined land, air and sea assault of June 6, 1944, remains the largest such event in history. The success of the invasion was extraordinarily dependent on weather conditions.

More than three months before the invasion, a combined British and American forecasting team began rigorous forecast exercises designed to iron out the physical and logistical kinks of such a coordinated effort.

As June drew near, the nature of this collaboration was still problematic as the two groups employed vastly different methods in fashioning the requisite three- to five-day forecasts. The British were attempting to make such forecasts based upon the understanding of atmospheric dynamics that had grown substantially during the war. The Americans were employing a method based on a statistically based search through old weather data for historical analogues that could be used to guide the forecast.

To maintain secrecy, a large portion of the Allied fleet was squirreled far away in northern Scotland. Consequently, five days of lead time was required to mobilize these forces. Thus, Gen, Dwight D. Eisenhower needed to know by May 31 whether the first week of June, the prospective target for the invasion, would provide favorable weather.

The forecasters foresaw a break in that year’s unusually stormy late spring and suggested June 5 would work. As the day approached, the team realized that a one-day postponement would offer better conditions, prompting Eisenhower to make the fateful decision to invade on June 6, under barely acceptable conditions.

Had the Allies delayed, the combination of lunar cycle, tides and weather almost certainly would have postponed the invasion for more than a month — likely costing the effort the tremendous advantage of secrecy.

Category: Meteorology

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If we stopped emitting carbon dioxide right now, would Earth stop warming?

Posted on June 4, 2018 by WeatherGuys Editor

No. Objects, even the atmosphere, will warm as long as the energy gains exceed the energy losses to their environment.

When the energy gains balance the energy losses, the object’s temperature remains constant. If the carbon dioxide levels were to suddenly remain constant, the atmosphere would continue to warm.

The orange line in this graph shows committed warming if greenhouse gases were held constant from the year 2000, the other lines show warming with continued fossil fuel use.

Climate models estimate that it will take about 40 more years for the temperature to stabilize at a temperature higher than today’s global mean temperature. This decades-long lag is due in part to the long time it takes to heat the oceans.

The energy increases due to higher carbon dioxide concentrations does more than warm the air, it heats the ocean. It takes more energy to raise the temperature of water than air. Once the ocean temperature is elevated, it will release heat back to the air, and be measured as surface warming.

Once the carbon dioxide is released into the atmosphere, from the burning of fossil fuels as an example, it accumulates and will remain in the atmosphere for many decades. Carbon dioxide moves among the atmosphere, the oceans, the land and the biosphere. Eventually, after many millennia the carbon dioxide in the atmosphere may be stored in rocks and as part of marine organisms’ shells that settle to the bottom of the ocean. Of course it is more complicated than just the amount of carbon in the atmosphere, there are feedbacks that enhance warming. For example, melting ice and snow increases the amount of solar energy our planet absorbs, increasing our energy gains and warming. A warmer atmosphere results in more atmospheric water vapor, which, like carbon dioxide, is a greenhouse gas and further warms the atmosphere.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison Department of Atmospheric and Oceanic Sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.
Category: Climate, Meteorology

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Is this hot start to summer unusual?

Posted on May 29, 2018 by WeatherGuys Editor

Jet stream winds. Credit: Climate Reanalyzer

Beginning on Saturday, Madison has experienced two straight days in May at or above 90 degrees for the first time since 1991 and for only the third time in nearly the last half-century (the others were in 1975 and 1978).

What’s more, the forecast is for temperatures to soar into the mid-90s again Memorial Day and Tuesday which, if it happens, would be the first time since at least 1971 (and perhaps in its history) that Madison has had four consecutive May days at or above 90.

The underlying causes of this remarkable heat are circumstantial. First, and perhaps most importantly, the jet stream is well north of its normal position for this time of year. Currently located in central Canada, the jet is in a location more common for late July and August. Since the jet is tied to regions of large horizontal temperature contrast, its current position ensures that locations even as far north as Madison are on the warm, tropical side of the hemispheric flow.

In addition, a reasonably strong upper-level trough exists over southern California which has been promoting broad southerly and southwesterly air flow from the Desert Southwest to the High Plains. This has placed a wide expanse of exceptionally warm air just to our west and southwest, ensuring a prolonged period of very warm temperatures over the western Great Lakes states.

So, the warmth we are likely to continue experiencing for the next couple of days is quite unusual for this time of year. Such a warm start to our summer season does not, however, suggest anything at all about the remainder of the summer in terms of warmth. The circumstances of the hemispheric flow patterns that have conspired to create this heat wave may, or may not, conspire again this season.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison Department of Atmospheric and Oceanic Sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.
 
Category: Climate, Meteorology, Seasons

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Will the recent volcanic eruptions in Hawaii lead to a change in global weather patterns?

Posted on May 21, 2018 by WeatherGuys Editor

To impact global weather patterns, a volcano must eject debris into the stratosphere.
(Photo credit: Marco Garcia, Associated Press)

While the recent Hawaiian eruptions are impacting the weather and air quality of the immediate area, they are not likely to have a global impact nor to affect Wisconsin’s weather.

The reason is that the ash cloud debris, while reaching 30,000 feet, has remained in the troposphere, the layer where local weather occurs. To have a global impact, the volcano must eject debris into the stratosphere. There it can last for a couple of years and spread over the entire globe. By the ash reaching only into the troposphere, it can stay airborne for no more than a week due to precipitation processes, wind and gravity.

If volcanic eruptions that reach the stratosphere contain sulfur dioxide gas, they can have an important global impact. The gas can react chemically in the stratosphere to form tiny sulfuric acid droplets. These droplets can reside in the stratosphere for a few years and cause a cooling of global surface temperatures because they reflect solar energy back into space. This was the case with Mount Pinatubo in 1992, which lowered the global temperature about 1 degree over a two-year period.

Volcanic eruptions can lead to cooler temperatures in the mountain’s vicinity because of ash in the atmosphere. The amount of solar energy reaching the surface can be reduced by the ash plume, just like a cloud would do, resulting in a cooler temperature.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.
Category: Meteorology, Phenomena

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How do I prepare for severe weather?

Posted on May 21, 2018 by WeatherGuys Editor

Severe summer weather can happen at any time and anywhere. The three biggest severe weather killers in the United States today are tornadoes, lightning and flash floods. Your best protection is to be prepared.

Lightning strikes the Wisconsin Capitol reflected on Lake Monona in May 2018.
Photo credit: Kenton Fowler, Monona.

First, you need access to reliable weather information so you remain alert for potential weather hazards. Get a NOAA weather radio for weather updates. Subscribe to wireless emergency alerts, or WEAs, that provide free messages to your cell phone that will alert you about severe weather in your area. For more information on WEA Alerts, go to www.ready.gov/warning-systems-signals.

Tune in to local forecasters on radio or television to get additional information. Local forecasters are experts on regional weather and can interpret observations and conditions for you.

In the case of tornado, go into a tornado shelter or the basement or into a small interior room on the lowest floor of a building, such as a bathroom or closet. Protect yourself from flying debris and stay away from windows. If you are in a mobile home or car, leave it and go to a strong building.

As for lightning, the National Weather Service, or NWS, advocates the simple rule: “When thunder roars, go indoors!” Avoid flagpoles, metal fences, golf carts, baseball dugouts and farm equipment. If you are in a forest, seek shelter in a low area under a thick growth of bushes or small trees.

Move to high ground when threatened by flooding. Stay out of flooded areas. Never drive your car across a flooded road, even if you think the water is shallow. As the NWS says, “Turn around, don’t drown.”

The NWS provides information and ideas for preparing for severe weather and you can learn more safety tips, available at www.ready.gov/severe-weather.

Steve Ackerman and Jonathan Martin, professors in the UW-Madison department of atmospheric and oceanic sciences, are guests on WHA radio (970 AM) at 11:45 a.m. the last Monday of each month.
Category: Meteorology, Severe Weather

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