Satellite Observations of a Heat Wave
Much of the time when we look at weather satellites, we’re using them to look at clouds: where are they, how fast are they moving, are they growing or dissipating, things like that. Right now, however, the dominant story across much of the continental United States is a persistent heat wave. In the past couple of days, several locations in the western US have broken their all time high temperature records, with multiple sites in Montana reporting temperatures in excess of 110 F (43 C).
Heat waves, of course, are often typified by a lack of clouds. After all, if there are clouds present, some of the sun’s incoming shortwave radiation is bounced back to space where it can’t heat the surface. Therefore, you might not think that satellites have a lot to see when you’re in the middle of a heat wave. However, there’s still much that our constellation of satellites can do to help diagnose what’s currently happening and how people are being affected by it.
First, let’s get a big picture view of southern Canada and the continental United States on the afternoon of 14 July 2026, as depicted by the True Color product from GOES-19 (GOES East). There’s lots to see here. Most of the central part of the US is clear except for further south, where Gulf-influenced dew points are sufficiently high to support the development of cumulus clouds; those will most likely dissipate as solar heating diminishes later in the day. Numerous fires in Ontario, Saskatchewan, and elsewhere are producing smoke that is joining with the output of Minnesota’s fires (which we discussed in a blog post yesterday). This smoke is forecasted to A large low pressure system east of Hudson Bay is drawing in flow to the northeast of this loop. We also see strong southerly flow over the western United States that takes a sharp turn to the east along the US/Canada border.
Of course, there’s also lots to see when you look at the infrared wavelengths, too. Here’s the Band 9 (6.9 micron) loop for the same scene. Now we start to see some interesting things. First off, we have a good view of the general upper level flow that clearly shows warm, moist Pacific ocean air from off the coast of California being advected northward into the Pacific Northwest and western provinces of Canada. We also see a strong plume of moisture penetrating the central US from the southeast, likely contributing to the development of the cumulus clouds we saw above. Much of the Great Plains appears dry, too.
It’s that ability to quickly identify the characteristics of the large scale flow that really makes a product like the water vapor loop useful on a day like today. This is especially true for the current observational environment in the United States, where many of the 1200 UTC radiosondes have disappeared from the central and western part of the country. Consider the 500 mb analysis from this morning. This chart is one of the most common tools that a forecaster uses for assessing the general state of the atmosphere and what the overall flow is going to be. And yet, there’s hardly any observations on the west side of this figure which really limits how much it can be trusted. The water vapor satellite loops help forecasters identify how the flow is behaving in the absence of the observations and fill in the gaps created by the change in radiosonde observation times.
Of course, we can also use the satellites to track the temperature of the surface itself. The MODIS land surface temperature product provides a global land surface temperature for both the daytime and nighttime overpasses. This image shows that the far western parts of South Dakota and northeastern Wyoming are approaching temperatures of around 116 F (47 C)! You can access this product at the NASA Worldview website, an excellent one-stop shop for polar orbiting level 2 products.
Of course, the standard Band 13 infrared can also tell us a good deal about how surface temperatures are distributed. Here’s a loop of that band displayed in AWIPS with surface weather conditions displayed. This is an alternative color scale designed to exploit the temperature characteristics and to lnot look so much like clouds. Note something interesting here: Iowa is further south than Minnesota, but the Land of 10,000 Lakes is actually a little warmer than the Hawkeye State. Some potential reasons for this: Iowa had some pop-up cumulus to help bring some intermittent relief from the sun, and the smoke from the Canadian fires has wrapped around and is infiltrating Iowa from the east while leaving Minnesota clear. Take another look at the water vapor loop to see the kind of flow pattern that can lead to such a result.
Despite the fact that much of the central United States is experiencing clear skies, there’s still lots to see from satellites. They’re an important part of understanding the weather, regardless of what type of weather there is.