Thick wildfire smoke can make for unique challenges as a forecaster, even if that smoke is many thousands of feet up with the actual fires thousands & thousands of miles away. Many times, models do not handle the reflective effects of sooty smoke very well. The result can be changes to forecasts needed that support decreases in temperature during the day or increases at night, t'storms & severe weather risk, pollution forecasts, heat index forecasts & even (in terms of distinct severe weather threats) tornado potential & intensity.
1. Smoke Can Impact Surface Temperature Day & Night
"It can impact temperature. The smoke acts as a cloud so it may not get as hot because not as much radiation from the sun reaches the surface and that has cascading effects, such as on wind speeds and thunderstorm development."
Depending on how heavy the smoke is, it could alter temperatures from a couple of degrees to maybe 10 degrees lower. "I'm ballparking it," he said. "It just depends on how thick it is," said Nick Nauslar, a graduate research assistant at the Desert Research Institute in Nevada.
We have seen that recently with temperatures affected by as much as 7 degrees by the thickest smoke during the day. At night, temperature has been impacted some, but thickest smoke has tended to be here during the day, resulted in less effect at night here recently.
2. Smoke Can Prevent Storm Development
From NASA Earth Observatory's study: “Fire-emitted particles crippled the atmosphere’s ability to build clouds and thunderstorms, and that ultimately caused a decrease in rainfall during what's already a seasonal drought,” Dr. Tosca said. “While this ‘smoky’ image just shows one day, remember that these conditions persist essentially unabated from December through February. Taken together, it represents a huge climate perturbation.”
Tosca says the diminished cloud cover and rainfall is tied to the "semi-direct aerosol effect". The sooty particles in smoke absorb incoming sunlight. This warms the trosophere or weather-making part of the atmosphere. This warming inhibits "the upward movement of moisture, which is crucial to the development of cumulus clouds".
Smoke can quell storms by this way or just prevent them from forming by cooling temperatures at the surface.
"You need rising heat during the day to help trigger the thunderstorms," he said. "It's rising air temperatures with enough moisture in the air to create a cloud and that can develop into a thunderstorm", explains Nausler of DRI.
3. Smoke Can Increase Rainfall Rates When Showers & Storms Do Occur
According to University of Arizona researcher, Prof. Daniel Rosenfeld, (who was one of many scientists from around the world), measurements of smoke from forest fires and its impact on the clouds and rainfall in the Amazon were documented. They showed that smoke from such fires "delays the release of water from clouds in the form of rain, thus preventing depletion of the water in the clouds as they grow. As these water-laden clouds reach great heights, they produce thunderstorms and hail instead of relatively moderate rain."
So, the smoke prevented or delayed storm development, but once the obstacles were overcome & storms DID develop, they produced much heavier rainfall with flash floods.
4. Smoke Can Decrease Storm Coverage & Intensity, But Also Make It More Humid & Polluted Near the Surface
Smoke can create a stout cap or warm, dry layer as the soot warms the air several thousand feet off the ground. This cap can actually create a meso-high of warm air aloft (as the air begins to sink with the warming) with a lack of any rainfall. This, in turn, can trap pollutants & concentrate them near the ground (ozone). It can also trap low-level moisture near the surface from transpiring vegetation, especially corn. This moisture can cause a big rise in dew points, making for very high heat indices, even though the smoke drops the surface temperature several degrees.
It seems that the trapping of this low-level moisture can also contribute to much higher rainfall rates when storms do occur & can overcome the detrimental effects of thick smoke aloft.
5. Smoke May Increase & Enhance Tornado Risk
Last week's impressive tornado outbreak (for the conditions present there) in Iowa shows evidence that the smoke in the lower levels helped the tornado development. Tornadoes up to EF3 strength (wind up to 145 mph) occurred & looked to have been helped by a bit of the smoke.
Similar results have been found with the April 2011 tornado outbreak in the South, which was one of the worst on record for the U.S.
From Popular Science: