July 9, 2013: Stormy Wednesday, Thursday

Forecast Highlights:

Warm and humid conditions continued today across the region with temperatures in the mid-upper 80s for most of the area and the low 90s in NE NJ, with another round of isolated afternoon thunderstorms focusing mostly in Bronx/south Westchester, western NJ and Connecticut away from the coast. An approaching cold front will bring another round of more widespread storms on Wednesday and Thursday, which will be capable of producing heavy rain, followed by another gradual increase in warmth and humidity into next week.

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Tonight - Thursday: More Storms, Localized Heavy Rain

The scattered afternoon and evening storm activity that was present earlier has mostly dissipated, with partly cloudy skies expected tonight and low temperatures again falling into the upper 60s to mid 70s for most of the area. A trough currently in the Midwest region will continue to dive southeast into the region, with a surface cold front slowly approaching on Wednesday and Thursday. For Wednesday, the highest risk of severe weather will remain well to the west, near Ohio and western Pennsylvania, closer to the front where a more favorable environment for late afternoon-evening severe weather activity exists. Further east over the NYC area, instability is likely to be limited along with a lack of bulk shear and lower lapse rates, which are likely to limit the risk of severe weather, although the higher resolution models show a vort lobe moving through in the early-mid afternoon hours, mostly between 12-4 PM, which triggers thunderstorms over eastern PA into New Jersey and SE NY, weakening as they move into Long Island and CT. With plenty of moisture, these storms will be capable of producing heavy rainfall and localized flash flooding, and gusty winds may also be a risk with the stronger storms. Due to the cloud cover and storms, slightly cooler temperatures are expected, peaking in the mid 80s inland and the mid to upper 80s for the rest of the area.

A lower risk of rain is expected overnight, with possible scattered storm activity especially in the evening, although overnight lows will remain relatively mild as the cold front continues to approach the area. The cold front is expected to move through on Thursday, with scattered storms developing again in the early-mid afternoon, likely continuing through the evening before tapering off as the cold front moves offshore. As with Wednesday, storms will be capable of producing heavy rain and gusty winds, although a relative lack of instability and lower temperatures, peaking in the low to mid 80s for highs, appears at this time to prevent a higher risk of severe thunderstorms.


Friday - Next Week: Gradually Warming Up

As the cold front moves offshore and stalls to the east of the area, drying conditions are expected for Friday into the weekend; at this time, I kept the outlook dry, although an isolated thunderstorm can't be completely ruled out for Friday and Saturday. The cold front will remove the humid air mass currently over the region, with high temperatures slightly cooling into the mid 80s for most of the area but with noticeably lower humidity. By the weekend into early next week, however, ridging is expected to spread back into the region, resulting in warming temperatures and an increase in humidity, with temperatures likely returning into the mid 80s to low 90s range. While uncertainty exists regarding the long range track of tropical storm Chantal, currently in the eastern Caribbean approaching landfall in Haiti as a strong tropical storm, and assuming Chantal survives past the landfall without falling apart, the ridging is expected at this time to block Chantal from tracking up the East Coast, with the storm likely taking a west or NW track once making landfall in the southeast US. The increasingly warm and humid air mass is likely to persist through at least the middle of next week when the latest models signal the next cold front may approach. Stay tuned for more information on the longer range outlook.