A looking pattern change this week will bring big adjustments to the contiguous United States as the heat shifts to the south and west while storms become more common across the Eastern Seaboard. This comes as numerous troughs of low pressure become common over the eastern US, allowing for cooler and stormy weather while a dome of high pressure builds over the Southwest, making for a very hot and dry regime.
Stormy and Cooler East:
A cold front tracking through the Midwest and Northeast early-week will usher in a round of heavy showers and thunderstorms. Behind that: cooler and drier air. Temperatures will adjust from being up to 10 degrees above average to as much as 10 degrees below average. That means high temperatures in the 70s and 80s will be more commonplace compared to the oppressive 80s and 90s. Along with the lower humidity with dew points generally in the 50s will make normally the hottest time of the year much more enjoyable.
Behind that front will be a large area of high pressure with pressures exceeding 1020 millibars once it arrives to the Northeast. Entering the northern Plains Monday night, it will traverse the Northern Tier of the US, ending up over the Northeast by Thursday. This Canadian high pressure indicates sinking air, and therefore dry and generally sunny weather.
Unfortunately, the high pressure won’t last forever over these areas. A new storm system will develop around the Wednesday time period over the Central Plains. It will then track to the north and east and into the Upper Midwest by Friday, ushering in a new round of showers and thunderstorms to northern and central Plains and Midwest during the latter half of the work week. Some of this precipitation will be heavy, so localized flash flooding will be a concern atop of the already saturated soil.
This low pressure will then likely stall out over the Great Lakes while a new area of low pressure slowly forms near the Mid-Atlantic coastline. This will make for a prolonged period of unsettled and wet weather from the Northeast down toward the Carolinas into the start of next week. This will put a lid of temperatures, keeping them several degrees below average. There will be the risk for flash flooding in these areas as well.
By mid-next week, the weather pattern should relax again but the northern Plains and Upper Midwest should remain active. Otherwise, the remainder of the eastern US should experience a break for the stormy weather while the cooler yet comfortable temperatures persist. The only exception is for the East Coast where temperatures will be close to average thanks to the Bermuda High. It’s the areas farther inland that will be feeling the ultimate relief.
Extreme Heat Across South and West:
Meanwhile across the western and southern US, it will become quite hot and dry as large heat dome builds over the southwestern US beginning midweek. Geopotential heights will approach and possibly exceed 600 decameters, which signifies a very warm atmosphere and often translates to near to record-breaking temperatures. Based on the model guidance, this upper-level ridge of high pressure may remain stagnant over this part of the nation for over a week, holding in place through the end of July.
The extreme, record-breaking heat will already be in place to begin the week in the Pacific Northwest with high temperatures in the 80s and 90s near the coast while it’s generally into the 90s and 100s inland. The coastal areas will then cool down starting Wednesday while the heat persist east of the Cascades.
It’s not until Wednesday when that heat will expand and takeover almost all of the western US with the exception of the immediate West Coast thanks to the chilly Pacific Ocean. This building dome of high pressure over the Southwest will shut off the monsoonal flow. Following scattered showers and thunderstorms across areas that have been dealing with these storms the past several weeks, they finally experience drier weather starting on Wednesday as well. Now while the risk for dry lightning diminishes, which is one of the reasons for the wildfires, it will not help the extreme drought conditions plaguing the region.
High temperatures for the second half of the week will generally be into 90s and 100s except for the higher elevations. The Red River Valley may even approach 110 degrees, which is very unusual for the region during any time of the year. In fact, a multi-day stretch of record-breaking heat may begin across the southern Plains on Thursday. According to the mean of the ensemble members from the European model (ECMWF), a city like Dallas is currently forecast to experience 6 days of high temperatures of at least 105 degrees. That is unprecedented.
Not only will high temperatures be dangerous but the low temperatures as well. Many cities across the Southwest and South will not experience much relief at night with low temperatures only in the 70s and 80s. This component of heat waves, like this one forecast, is what can make it deadly because the body can’t cool off as efficiently.
To sum this up, here’s the key points to know about this upcoming pattern change:
- A pattern change will take place across the contiguous US beginning Wednesday.
- Most of the eastern US will turn cooler and stormy with multiple rounds of storms and temperatures generally 5 to 10 degrees below average.
- The western and southern US will become very hot and dry with little rainfall. Temperatures will mainly be up to 10 degrees above average, but that will translate to high temperatures into the 90s and 100s for most.
- This pattern change will likely remain dominate through the end of July.