July 13, 2013: Hot, Humid Week Ahead

Forecast Highlights:

A wave of low pressure affected the region yesterday with widespread heavy rain in the Mid Atlantic; rain totals were generally near or under 1/4 inch, although totals were locally higher, such as Islip, NY with 0.79". As the upper level low exits to the west, strong ridging will redevelop over the eastern half of the US with another relatively long stretch of hot and humid conditions throughout next week as temperatures approach the upper 90s.

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This Weekend: Warming Up, Scattered Storms

Yesterday, an upper level low temporarily slowed down over the region while over Pennsylvania, but has started to track to the southwest around the eastern edge of ridging in the central US. With the ULL moving southwest, then west into the central US, ridging from the central US and the western Atlantic will begin to connect this weekend and intensify, leading to Sunday when a strong ridge with 500mb heights up to 597 dm sits on top of the region.

At the surface, the ULL tracking southwest will suppress most of today's more widespread storm activity to the south of the area, although isolated afternoon storms are possible today with partly sunny skies and highs in the low to mid 80s. As ridging continues to build overhead, the surface high pressure will spread west into the region for Sunday, with mostly to partly sunny skies and highs in the mid 80s near the coast and upper 80s to low 90s for the rest of the area with a light SW wind.


Next Week: Hot, Humid

A relatively stable pattern is setting up for next week as the strong ridging sets up over the Ohio Valley region and remains stationary for the majority of the week, with a shortwave in southern Canada aiding in slowly flattening the flow through the mid to late week. This ridging, along with the westerly flow setting up aloft and at the surface with 850mb temperatures near 20C, will lead to another heat wave with hot and humid conditions lasting through the week.

Mostly sunny skies are expected throughout the first half of the week; while an isolated afternoon storm can't be ruled out, most of the region is generally expected to stay dry. Monday and Tuesday are expected to start the heat wave with highs in the upper 80s near the coast and low to mid 90s for the rest of the area; a light NW wind is expected, which will keep dew points mostly in the mid to upper 60s and preventing much higher heat index values. By Wednesday and Thursday, however, as the ridging starts to flatten, a more westerly flow will develop, bringing more heat and a more humid air mass into the region, with high temperatures expected to reach the mid to upper 90s away from the coast and heat index values likely reaching or exceeding 100 degrees.

The next cold front is expected to approach towards Friday or next weekend; while the exact timing is still subject to change, heat and humidity are expected to continue until the front passes through, with an increased risk of showers and thunderstorms with the frontal passage, as well as a risk of severe weather. Uncertainty increases beyond next weekend, although the overall expectation is for temperatures to return closer to average following the front. Stay tuned for more information on next week's heat wave over the next few days.