A prolonged stretch of very dangerous heat is setting up across much of the western US into the southern Plains, beginning now and lasting likely through at least the end of July as a dominant upper-level ridge of high pressure sits over the region through the foreseeable future.
This all comes as a pattern change takes place, bringing cooler and stormy weather to much of the eastern US while hot and dry weather takes over across the western half of the nation associated with a large ridge in the jet stream. This upper-level ridge will allow for extreme heat and mostly dry conditions, which will worsen the drought conditions and will make the environment even more conducive for the growth or formation of wildfires. Isolated thunderstorms, some of which will produce dry lightning, will still remain possible across the Four Corners states.
This Wednesday, about a 598 decameter ridge will be situated over the southwestern US. A ridge of this magnitude represents a very hot air mass and often allows for temperatures well above-average or even record-breaking heat. High temperatures will generally rise into the 90s and 100s from eastern Washington southward through the Central Valley of California and into the desert Southwest. Interior areas will also experience heat of this magnitude, including across most of Nevada, Utah, and southern Idaho.
The east is where the heat will be the most dangerous because of how high the temperatures will be and for how long they will last. Widespread highs into the 100s are in the forecast across the southern Plains. Down towards the coast of Texas it will be a few degrees “cooler,” into the mid to perhaps upper 90s. The key difference is that inland areas will actually be experiencing dry air through at least this weekend thanks to a flow coming from the north and west, while the coast continues to deal with an extremely humid air mass thanks to its proximity to the Gulf of Mexico. It is worth noting that dew points (humidity) will waver from the dry 50s to the humid 70s across eastern Texas, so heat indices will vary depending on your exact location.
Now on Thursday, the heat dome will begin to drift to the east, toward the southern Plains. Not only will this allow for the heat to intensify in this region but it will also expand it a bit further to the north and east. About a dozen record daily high temperatures are expected to be broken in the US on Thursday, most of which will be in Texas. High temperatures will follow a similar profile as on Wednesday, except for the fact they will be a few degrees warmer. High temperatures in the central Plains and ArkLaTex will increase from the 80s and 90s on Wednesday, and up into the 100s on Thursday.
So, how how unusual is this heat? It’s definitely somewhat uncommon, with daily record high temperatures being broken in some locations, however this heat wave will definitely not end up being the most intense on record. In a city like Dallas, their longest streak of 100-plus degrees was back from the summer of 1980. Dallas ended up with 42 straight days of temperatures at or greater than the century mark. Our current forecast for this most recent heat wave is for highs into the 100s for about a week. It may hit 110 degrees Friday through Monday, however. If they hit 110 degrees, that would tie it for the 7th hottest day on record for the city (records date back to 1898). Also, if the city records a 4-day streak of highs at or greater than 110 degrees, that would beat the current record of 3 days from 1980.
On Friday, an upper-level disturbance passing near the Northwest will allow for temperatures to cool off by a few degrees mainly near the coast. Farther to the south and east, the heat will remain in place with widespread high temperatures in the 90s and 100s. Temperatures will begin to max out across the southern Plains with temperatures in some locales exceeding 110 degrees. If you’re looking to cool off, head to the immediate West Coast, where the sea breeze will keep high temperatures down into the 70s and 80s this week and weekend.
In terms of this weekend, not much will change. Temperatures will return closer to normal in the central Plains, while the southern Plains bakes for yet another day in the 100-plus degree heat. The coast will even heat up with a high temperature of around 100 degrees in Houston Friday through early-next week. Temperatures will hover around where they have been in the Southwest, while heat slowly creeps back up the West Coast and into the Northwest by the end of the weekend. Highs will be near 90 degrees in the valleys in Washington once again.
Next week, the heat will remain persistent. The model guidance does suggest that the near-600 decameter strong ridge of high pressure over the southern Plains will drift back toward the Southwest. This will allow for temperatures to cool off somewhat in the southern Plains, especially north of the Red River. To the west, the heat will continue to creep up the West Coast and become more significant. Temperatures will also increase in the desert region, with high temperatures possibly exceeding 120 degrees in locations like Death Valley by Tuesday.