Heat Dome Threatens 98 Million as 122F Forecast Spreads From Texas to California

Q: How exactly does a massive cloud of Saharan dust manage to choke off South Florida's much-needed cooling thunderstorms?

A Saharan dust plume suppresses South Florida thunderstorms mainly because it arrives as the Saharan Air Layer, a deep mass of very warm, very dry, dusty air that makes the atmosphere more stable. South Florida’s usual summer cooling storms depend on hot, humid surface air rising quickly, often helped by the sea breeze. When Saharan air moves in, it does two things that work against that process. The dry air mixes into growing clouds and causes droplets to evaporate. That evaporation cools and weakens the updrafts before they can build into tall thunderstorm towers. At the same time, the Saharan layer is warm aloft, which acts like a “cap” or lid on the atmosphere, making it harder for surface air to keep rising. The dust itself also helps filter sunlight and creates hazy skies, but the bigger storm-killing factor is the air mass that comes with it: dryness, warmth aloft and often stronger winds. Forecasters also noted high pressure and a weaker or less effective sea-breeze setup, which further reduced the triggers that normally spark afternoon storms across South Florida. The result is fewer showers and thunderstorms, less cloud cover and less rain-cooled air. With the normal afternoon storm relief choked off, more sunshine reaches the ground, heat builds longer into the day, and temperatures and heat indices climb faster. That is why Saharan dust outbreaks are often linked not just to hazy sunsets, but to hotter, drier and more oppressive conditions in Florida.

3 articles · Updated · The Washington Post · Aug 25

98 million people face major or extreme heat risk through the end of August as the heat dome broadens westward from Texas and Oklahoma toward New Mexico, Arizona and Southern California.
Dallas tied its hottest day on record Monday with a 97.5F average and a 109F high, while Oklahoma City hit a daily-record-tying 108F and areas near Chickasha reached 115F.
122F in Death Valley, 116F in Yuma, 115F in El Centro and 114F in Phoenix are forecast this week, with numerous records expected as the core of the heat shifts west.
70F-plus overnight lows across much of Southern California and predicted lows of 93F in Lake Havasu City and 89F in Palm Springs could outpace daytime records, limiting recovery and raising health risks.
Near-70F dew points along coastal Southern California—fueled by a Pacific marine heat wave—are adding tropical humidity, while NOAA data show about 21 U.S. high-temperature records this year for every monthly low-temperature record.