Following in the footsteps of the record-setting cool air mass in mid-July, a second blast of air with polar origins will invade the eastern U.S. to close July. Like the original, the sequel will be glorious.
This taste of September may not be quite as strong mid-July’s version, but should produce temperatures 10-20 degrees below normal across a large swath of the eastern U.S. by early Tuesday.
The jet stream will take a big southeastward dive on Sunday, with a cold front along its leading edge. Thunderstorms – some severe – are likely to erupt out ahead of it in the Ohio Valley and East Coast Sunday into Monday.
Once the storms are through, the gorgeous weather stretch commences and below average temperatures take hold for much of the work week. In Washington, D.C., this means highs mostly in the 80-85 degree range.
Tuesday may be D.C.’s coolest day, in which highs could struggle to reach 80.
Wednesday morning will likely be the coolest in D.C., in the 50s in the suburbs to near 60 downtown. Yes – that’s 40s you see in the mountains.
Humidity levels will also drop to low levels – so this deep summertime trough, on balance, will deliver quite delightful weather.
Like the mid-July cool episode, the origins of the air mass can be traced inside the Arctic circle and within the summer (mid-tropospheric circum)polar vortex. However, it’s a less well-defined case so I’ll refrain from calling it a polar vortex “event.”
On Monday, when I first discussed this upcoming weather pattern, I mentioned models showing it taking on a Rex Block configuration. Models have since gently backed off from this idea, but haven’t backed off on the idea of an extended period of well-timed cooler than normal weather.