Dry weather returns for extended period; cool through Tuesday, then modest warmup through Thursday, then cooler again Friday before gradual warming through following week while staying mostly dry and sunny with low humidity leading to worsening drought

Plain-language summary:

 

After rain over the past few days dented the drought slightly, the dry weather pattern has returned today. It also has turned much cooler and will stay cool through Tuesday. It will warm up modestly Wednesday and Thursday before a reinforcing cool shot arrives by Friday, with light showers possible immediately before the reinforcing cool shot. It will then likely warm up for a longer period of time afterward, but never getting truly hot, while remaining mostly dry and sunny with cool nights and the drought worsening again.

 

Meteorological discussion: 

 

Dry weather returns, unseasonably cool through Tuesday, then modest warmup through Thursday

 

After many areas received the most rain in over a month over the past few days, dry weather has returned today, except for isolated showers mostly over higher terrain. It is also unseasonably cool with an amplified pattern across North America consisting of a pronounced upper-level ridge bringing record high temperatures to western Canada and a deep upper-level trough in Quebec. The cold air is not be as pronounced in our region as in the Midwest U.S. due to the trajectory of the cold air first going into the Midwest U.S. and then getting modified as it moves east into our region, as opposed to coming directly from the north or northwest. However, on Monday, as the upper-level trough weakens as pulls to the northeast, a Canadian surface high-pressure system will approach, briefly turning the flow slightly more to the northwest for a more direct shot of cold air into our region, though the truly cold air will still stay to the north of our region. The clouds and isolated showers will also mostly go away by Monday as the surface high-pressure system takes over. It will then warm up modestly through Thursday while staying sunny and dry as the surface high-pressure system moves just to our south, allowing modest warm advection from the southwest.

 

Source: TropicalTidbits

 

 

Cooler again Friday, then gradual warming through following week while not getting truly hot and remaining dry and sunny with cool nights and worsening drought 

 

The weather pattern afterward looks to resemble that of August in many ways, with some upper-level troughing pushing into western North America leading to a downstream upper-level ridge in central and eastern North America, but with the ridge axis staying west of the East Coast. Like with the amplified weather pattern earlier this week, this new weather pattern will also be phase shifted from the typical PNA, NAO, and AO patterns, rendering only weak signals on those indices. This weather pattern will be characterized by repeated Canadian surface high-pressure systems moving into our region, with the associated dry air and descent precluding thunderstorms or even any rain and clouds for the most part, leading to the drought continuing to progress after the recent rains temporarily dented it a bit. There may be occasional rain chances associated with cold fronts coming from the north, but the deep west to northwesterly flow preventing any moisture from the Gulf of Mexico from entering into our region, and the generally unfavorable location east of the upper-level ridge axis and west of the upper-level trough axis. 

 

Source: Climate Prediction Center

 

 

One of these cold fronts will come late on Thursday, with a reinforcing cool shot afterward, but then the air mass will gradually warm as the upper-level ridge gets more firmly established over the central and eastern North America. There also won't be any strong westerly or southwesterly flow for strong warmth and moisture advection, and with the lowering sun angle in September, the warmup will be gradual, and it is unlikely to become truly hot again, even with the drought leading to more of the sun's energy going into warming the ground instead of evaporating moisture. Nights will also remain relatively cool with a larger than average day-to-night temperature difference, like in August, due to the clear skies, light winds, dry air, and lengthening nights allowing for good nighttime radiational cooling.

 

Source: TropicalTidbits

 

 

One possible caveat is that today, a few models (e.g. ECMWF, UKMET, and ICON) show a cut-off low diving southward underneath what would otherwise be broad upper-level ridging across central and eastern North America. This would lead to a couple of days of cloudier and more showery weather, at least delaying if not stopping most of the warmup. However, models tend to show this more than in reality, and other models are not on board with this.

 

Source: TropicalTidbits