On Wednesday, sticky humidity will build toward evening and will lead to an uncomfortable overnight. Afternoon highs will range from the mid 80s near Lake Erie to 87-90 farther inland, particularly well northeast of Buffalo, writes Don Paul.

We had our little Tuesday respite, with a below average high of 75, and a seasonable Wednesday morning low of 61. That’s all over for now, as a south-southwest flow renews midsummer heat in the afternoon, with sticky humidity building toward evening and leading to an uncomfortable overnight. Afternoon highs will range from the mid 80s near Lake Erie to 87-90 farther inland, particularly well northeast of Buffalo.

The exceptionally high water vapor content of the atmosphere, to which meteorologists refer as “precipitable water,” or PWAT, will be drawing closer later Wednesday night, as modeled by the European ECMWF.

The presence of such high PWATs still requires atmospheric triggers, such as disturbances and frontal boundaries, to force the water vapor to converge into what will be convective cells. This convergence may begin to increase Thursday afternoon into Thursday night, based on upwind atmospheric soundings and model output. With that in mind, the Weather Prediction Center/WPC has placed our region into at least a 15% risk area for locally excessive rainfall Thursday afternoon and Thursday night.

In the big picture, this potential all seems to come together later Thursday with the very slow approach of a cold front edging into these high PWATs.

When you begin to look at the more detailed high resolution model output, however, you can see coverage for convective rainfall will be much spottier than implied by the broad dark green swath in the national graphic. After an overnight low of 72-74, a few thinly scattered showers may show up before dawn on Thursday, with a few more scattered showers and thundershowers during the morning. Later in the day, model support for widespread convection is unimpressive. The ECMWF holds off much of the activity until mid-late Thursday evening. 

When triggers are weak in very moist air, models can miss localized moisture convergence, as occurred late Monday evening in parts of the Buffalo area. With that in mind, the WPC projects locally heavier rainfall being wrung out of this moist atmosphere, though I expect the coverage to be spottier than implied by their graphic.

If a sufficiently organized trigger comes along, there will be a PWAT range of 1.5-2.2 inches of potential rainfall in a few locations. As of this writing, the models suggest doubt for much organization, keeping our risk for excessive rainfall in the slight category.

Thursday will also be quite muggy, with readings reaching the low-mid 80s if much sunshine breaks through, following a few scattered morning showers and thunderstorms. Such heating would further destabilize the atmosphere, as opposed to more persistent cloud cover reducing the risk of stronger convection. 

Friday, we’ll be facing a lower, 5% risk of excessive rainfall due to the slow movement of the frontal boundary.

The risk for heavier rainfall Friday will be greater toward the Southern Tier. The humidity will still be high, and temperatures will reach to near 80, with very little wind.

On the whole, however, the risk for heavy rainfall will be lessening during Friday. 

By Saturday and Sunday, sultry conditions will be returning under a partly sunny sky for both days. A southwest flow Saturday will boost the afternoon high well into the 80s, with dew points both weekend days from the upper 60s to truly uncomfortable low 70s. Highs in the mid 80s return on Sunday, as well. Most or all of Saturday will be rain free, though an isolated afternoon shower can’t be ruled out. With the slow approach of another cold front Sunday, the risk for scattered showers and thunderstorms will begin to increase in the afternoon. 

With the front settling into our region or just south of us by Monday, there will still be a risk of scattered showers, but temperatures should settle back toward a less sultry 80. Behind this front, a bit more cooling will filter in for Tuesday, with a reduced risk for a few showers and some partial sunshine. In general, it should begin to become more comfortable next week. 

Pattern change for the Great Lakes, Northeast, and Middle Atlantic

In my previous 2 Buffalo News articles, I’ve written about the projected retrogression of the heat dome dominating large parts of the nation back toward the west-central U.S. This trend is still showing today with good definition in the extended range upper air pattern ensembles. By around Aug. 8-10, this westward displacement is readily apparent.

This should not be taken to imply our region will be headed into an unseasonably cool pattern, even with the northwest flow aloft. But it will be shifting excessive heat back to the West, and away from the East. While Western New York has gotten off lightly from the heat, it has been oppressively hot in New York City, Philadelphia, Baltimore and Washington. 

This overall trend appears likely to persist past the month’s midpoint.

The trend I’ve described is also apparent in the Climate Prediction Center’s 8-14 day temperature anomaly outlook, which reflects the cooler troughing over the Northeast. 

A more robust monsoonal flow in the Southwest and the interior of the West may also be putting at least a temporary dent in the megadrought from southeast California (the desert region) eastward, as seen in the new seasonal drought outlook from the U.S. Drought Monitor. Numerous showers and thunderstorms are expected to make a difference in this stricken region.

On the other hand, drought is expected to develop and expand into large parts of our grain growing region, all the way into Iowa and southern Minnesota.

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On Wednesday, sticky humidity will build toward evening and will lead to an uncomfortable overnight. Afternoon highs will range from the mid 80s near Lake Erie to 87-90 farther inland, particularly well northeast of Buffalo, writes Don Paul.

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