July 6, 2012: Excessive Heat Tomorrow

Forecast Highlights:


- Peak of heat wave tomorrow; 100 degrees for some
- Scattered strong storms in evening, night to end heat
- Average temperatures return early-mid week
- Warmth, storms to gradually return in longer range


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Today's Observations:

The heat once again continued across the region with temperatures still above 90 degrees from NYC and further north/west, making today the 4th day of the heat wave for most places from NYC and further north/west, except for Newark which is up to its 9th consecutive 90+ degree day. Newark again peaked at 98 degrees, while places north/west of NYC peaked generally in the mid 90s. Long Island/S CT were cooler due to more sea breeze influence, as expected, peaking in the mid to upper 80s with coastal areas staying below 85 degrees further east.

The long heat wave is finally approaching its end, as the last and hottest day of the heat is expected for Saturday with widespread highs in the mid-upper 90s away from the coast, even reaching the 100s in the Mid Atlantic up to Philadelphia and potentially up to NE NJ. The heat won't last for long, however, as a cold front moves through the region tomorrow night with scattered thunderstorms, some of them possibly strong. Following the cold front, a cooler air mass will move into the region with seasonable temperatures, although there are signs of increasing humidity and heat towards late next week.




Saturday's Outlook:


The final surge of heat with the heat wave will move into the region for Saturday, resulting in what will likely be one of, if not the hottest days of the year. The heat surge went through the central US today, producing widespread 100+ degree heat with widespread 850mb temperatures above 20-25C. A slightly modified version of this air mass will reach the region tomorrow with the area near the northern edge, which will spread the heat briefly into the region.

Mostly sunny skies are expected, although cloud cover could increase later in the day ahead of convection, discussed in more detail in the next paragraph. West winds are expected with 850mb temperatures around 22C, all of which are supportive of widespread heat. Temperatures are expected to quickly rise in the morning, reaching the mid 80s by 8 AM in the immediate NYC area and the mid 90s by 11 AM. Temperatures will peak in the mid 90s inland, mid to upper 90s in the immediate NYC area, and the lower to upper 90s across most of Long Island/S CT, slightly below 90 degrees in eastern coastal areas, due to less sea breeze influence and more of a west wind. As with the other very hot days observed this year, the potential is there for parts of NE NJ to reach 100 degrees but it is not certain; there is more support for this than the previous times, however, especially with warmer 850mb temperatures than the previous heat surges, as well as support from the ECM model as well, not only the NAM which was the case with the previous potentials. Humid conditions are expected as well, with heat index values reaching the mid 100s in the immediate NYC area and approaching 100 degrees inland and in parts of Long Island/S CT.

In addition to the heat, there is also the possibility for severe thunderstorms in parts of the region tomorrow evening/night. Originally, this appeared to be over New England, but the models have since trended towards a faster cold front, as well as shifting the core of the warm air mass further south than where it was modeled to be yesterday. Most of the day is expected to be dry, although scattered thunderstorms, some of them strong with isolated severe activity possible, are likely for the evening and early overnight hours for parts of the area, especially west of NYC. Stay tuned for an afternoon update on Saturday regarding the heat and the storm potential.


Next Week: Cooler Start; Stormier Finish?


Following the cold front, a cooler air mass will move into the region, although highs will still be warm at first, reaching the mid 80s to lower 90s on Sunday. A mostly dry first half of the week is expected as an area of showers and thunderstorms stalls over the Mid Atlantic. Partly sunny skies are generally expected with temperatures in the mid to upper 80s for most of the area, ending up cooler closer to the coast. By the end of the week into next weekend, however, weak ridging appears to build again into the region, which won't produce any extreme heat but will likely result in slightly hotter temperatures along with the potential for storm activity in parts of the region. Stay tuned for more information on next week's outlook.