July 14, 2013: Heat Wave Starts Today

Forecast Highlights:


An upper level low over the region yesterday produced additional isolated showers and storms, especially in the evening hours near NYC. Since then, the ULL has drifted southwest into the central US region, with a broad, strong ridge forming on top of the region. This ridge will continue to drift west before stalling through the mid week, resulting in a week-long heat wave starting today with highs climbing well into the 90s, ending with potential severe weather by next weekend.


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Today – Friday: Hot, Humid


The initialized 500mb geopotential heights in decameters and absolute vorticity across North America from the 12z GFS is posted to the left. In this map, 500mb heights are outlined in black in intervals of 6 dm. A strong 594+ dm ridge is shown on top of the Northeast US, centered on top of New Jersey, with the upper level low that was nearby yesterday having ended up in Missouri as of this morning. The ULL will continue to be forced west as the ridge continues to expand west, covering the Great Lakes and Northeast region through Wednesday, when a shortwave moving through southern Canada will begin to gradually flatten the ridge. A more zonal flow will develop by the late week with a trough gradually sinking south by the weekend, bringing thunderstorms and potential severe weather into the region while slowly pushing the heat out. With 850mb temperatures approaching 20C and a westerly flow aloft and at the surface, widespread temperatures in the mid to upper 90s are expected along the I-95 corridor in the mid-late week time frame, with some locations approaching 100 degrees.

Mostly to partly sunny skies are expected today with highs in the upper 80s to low 90s away from the coast and the mid 80s near the coast with a light SW wind; an isolated interior storm can’t be ruled out in the evening. The hottest temperatures initially are expected on Monday, with mostly sunny skies, a light NW wind, and highs in the low to mid 90s inland and the mid to upper 90s for the rest of the area, excluding eastern coastal areas in LI/SE CT, which along with humid conditions will result in heat index values in the upper 90s to low 100s. Mostly sunny skies are expected again on Tuesday, but with slightly cooler temperatures and lower humidity with a NNW wind direction.

By Wednesday and Thursday, the wind direction will switch to the west, with a SW wind developing in coastal areas for the afternoon and evening hours. With mostly sunny skies expected to continue, highs will again reach the mid to upper 90s away from the coast and the upper 80s to mid 90s near the coast; heat index values are expected to reach the low 100s again. Similar temperatures are expected to continue again on Friday, possibly slightly cooler, as a cold front approaches from the north.

Next Weekend: Storms, Possible Severe Weather

By next weekend, a trough is expected to slowly sink southeast into the region from Canada, with a cold front gradually making its way southeast, from the Great Lakes on Thursday and Friday into the area on Saturday, although the exact timing is still subject to some changes. The air mass ahead of the front will be humid and unstable, with the latest models showing higher instability overlapped with higher bulk shear and sufficient lapse rates to result in widespread thunderstorms and the possibility of strong or severe storms with the frontal passage. Temperatures are likely to cool down behind the front to near or slightly above average, but with a decrease in humidity. Stay tuned for more information on next weekend’s outlook.

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