Be PREPARED: An Unusually Hot Summer in The Forecasts + A New Heat-Risk Mapping Tool for Related Health Impacts

 +  This summer, the National Weather Service will have an added weapon in its arsenal to try to combat the deadly health-related effects/impacts of extreme heat.

HEAT RISK MAPPING TOOL

OFFICIAL Forecasts

Jun-Jul-Aug 2024

A long, hot U.S. summer is looming, forecasters say

• Andrew Freedman
  , author of
  Axios Generate

Map showing the likelihood of above, average, and below average temperatures across the U.S. during June, July and August 2024. Photo: NOAA/CPC

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How to Read the 3-class Three-Month Outlook maps

The contours on the map show the total probability (%) of three categories, above, indicated by the letter "A", below, indicated by the letter "B", and the middle category, indicated by the letter "N". At any point on the map, the sum of the probabilities of these three categories is 100%. For any particular location, and season, these three categories are defined from the 30 observations from 1981-2010. The coldest or driest 1/3 (10 years) define the B category, the warmest or wettest 1/3 (10 years) define the A category, and the remaining 10 years in between define the middle (N) category. When the forecasters decide that one of the extreme categories, say above (A), is the most likely one, they assign probabilities which exceed 33.33% to that category, and label the map with an "A" in the center of the region of enhanced probabilities. To make it possible to display three categories on one map, we assume that, when either A, or B is the most likely category, the probability of the middle category remains at 33.33% for most situations. This means, for example, that when the probability of A (B) is 40%, the probability of N is 33.33%, and the probability of B (A) is 100% minus 40%+33.33%=26.67%. When probability values of the favored category reaches 70%, or higher, the probability of the opposite category is fixed at 3.3%, and the probability of the middle category is adjusted to values (less than 33.33%) which cause the sum of the three probabilities to equal 100%. When the middle category (N) is higher than 33.33%, the probabilities of the A and B categories decline by (equal) amounts required for the sum of the A, N, B probabilities to equal 100%. In regions where the forecasters have no forecast tools which favor the chance of either A, or B, the chance of these two categories is defined to be 33.33% each, and the region is labeled "EC", which stands for equal chances. Shading is used to indicate different levels of probability above 33.33%

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A hotter-than-usual summer is likely to occur in the U.S. and many other parts of the globe, according to new forecasts and scientific research.

Why it matters: Extreme heat is a major public health threat and plays a role in droughts and wildfires.

• Hot weather, particularly when it occurs during prolonged heat waves, also threatens the reliability of the nation's increasingly strained electricity grid.

The big picture: An ongoing El Niño event in the tropical Pacific Ocean is quickly fading, with cooling ocean temperatures at and beneath the surface.

• A La Niña climate cycle is expected to take shape, which features cooler-than-average tropical Pacific Ocean temperatures, later this summer.
• Some studies show that these transitions are associated with hotter-than-average summertime conditions across large parts of the U.S., centered across the Midwest.
• The transition will also influence conditions around the globe, as the planet nears its 11th straight month with record warm temperatures.

What they're saying: Michelle L'Heureux, who leads the forecasting unit that predicts El Niño and La Niña at NOAA's Climate Prediction Center in Maryland, told Axios that other climate trends — including human-caused climate change — may outrank the see-saw from El Niño to La Niña as the dominant driver of U.S. summer temperature anomalies.

• "Clearly, greenhouse gases are the #1 primary driver of climate trends over the U.S.," she told Axios in an email.
• She noted that El Niño and La Niña tend to have their greatest influence on U.S. weather patterns during the winter months in the Northern Hemisphere.

Zoom in: A recently released NOAA climate outlook for the June through August meteorological summer shows only one whole state — North Dakota — in the Lower 48 with equal chances of below-average, average or above-average temperatures.

• Everywhere else in the region is projected to be hotter than average, but with varying odds.
• The chances for hotter-than-average conditions are highest in the Northeast, and across a vast swath of land from Texas to the Rockies into the Pacific Northwest.
• The Plains and West are projected to see below-average rainfall, which could lead to higher wildfire risks, while the East stays soggy.

Threat level: The ways climate change is altering the character of American summers increasingly stands out, and is one reason to take note given the hotter-than-average outlook.

• During the past several decades, summers have been warming across the U.S., with Austin, Texas, now seeing an average of 47 additional 100°F or higher days than the city saw in 1970, for example.
• Many other cities have seen similar jumps in 90°F days, along with a tendency toward longer, hotter and more humid heat waves.

• Climate attribution studies have found that more heat waves are occurring currently. They would have been virtually impossible without the influence of human-caused climate change.

The intrigue: One wild card this summer will be exactly where persistent areas of high pressure, also known as heat domes, set up. That will determine the areas that see some of the hottest conditions.

• Some research suggests there may be a tendency for that to occur across the Central states and Midwest.

Yes, but: Anthony Artusa, a meteorologist at CPC, pushed back against recent media headlines suggesting the lower 48 could see its "hottest summer ever" in 2024.

• "Nevertheless, what [models] do support is an unusually hot summer this year, especially for the south-central and western areas of the contiguous U.S., and people should be prepared for this," he said.

Between the lines: This summer, the National Weather Service will have an added weapon in its arsenal to try to combat the deadly effects of extreme heat.

HEAT RISK MAPPING TOOL
National Weather Service Climate Prediction Center 

• Working with the Centers for Disease Control and Prevention, NWS expanded out a new heat forecast tool Monday.

The HeatRisk mapping tool from the NWS and CDC, rolling out to the country for this summer. Photo: NOAA

• The "HeatRisk" forecast has a color-coded scale that is aimed at communicating the health risks from heat exposure.
• It incorporates the rarity of the heat, its likely duration, and the chances for heat-related health impacts, based on CDC data.

This forecast product, still in an experimental phase, goes out to seven days in advance.

Go deeper: Summers are heating up fastest in these cities