July 4, 2011 Brief Update

The 5-Day Forecast was updated today for the immediate NYC area only. Tomorrow’s update will add the rest of the area as well.

Forecast Overview For This Week:

– Temperatures similar to those of today will continue through Tuesday and Wednesday. Wednesday will be the hottest day, with temperatures reaching the lower to mid 90s in the immediate NYC area, potentially making this an official heat wave in Newark, which reached the lower 90s today.

– An isolated storm is possible on Wednesday afternoon/evening, but the best risk of thunderstorms will be on Thursday. As with yesterday’s storms, most of these storms should stay below severe levels, but with high precipitable water values, heavy rainfall will be a risk with Thursday’s storms once again. Some storms may continue into Friday.

Next Weekend Into Next Week: More Heat?

Cooler temperatures will return by Friday/Saturday, with highs in the upper 70s to mid 80s across the area. By Sunday, however, the latest long range models are hinting at another surge of heat into the region. These models show a ridge covering the East with 850 mb temperatures near or over 20c spreading into the area, with the GGEM and DGEX going as far as showing a tropical cyclone not too far off the coast. The main key to this is the modeled transition of the NAO from negative to positive around July 10th, with no signs of any feature such as a trough or a cut off low pressure blocking the heat from moving in. Such a scenario would bring the potential for temperatures to reach the lower to mid 90s for several days starting around Sunday or Monday.

The scenario mentioned above is a possibility, but we have seen long range heat potentials many times so far this summer, such as this week, which have failed to live up to their potential. This week, we are seeing some heat, but the worst of the heat stayed to the west of the region as an upper level low last weekend helped to weaken the large ridge that was moving towards the area. We are seeing a -NAO along with low pressure stuck in the Davis Strait, between Greenland and Canada, and in the longer range when the GFS modeled this week’s heat, the low pressure there was either too weak/too far north to have a significant impact on the region, or it was not there at all, and the NAO was modeled to be positive, not negative. The latest models do not show a low pressure near the Davis Strait in this time frame, when widespread heat covers the region, and show a transition to a +NAO as well.

It is a reasonable possibility that the bigger and longer lasting heat does reach the area, and a transition to a positive NAO is possible, but the big models that the models show once again for early next week is questionable. It is likely to warm up once again with temperatures early next week potentially ending up similar to those we are currently seeing, and a big heat spell with temperatures warming up well into the 90s cannot be ruled out as well, but especially given this year’s history and trends, unless there is solid evidence for a transition to a +NAO with no feature to block the heat from spreading into the northeastern US, I’m going with a slightly more conservative scenario, expecting the heat to be weaker and shorter lasting than the models currently show, with temperatures ending up slightly above average. Stay tuned for more information on the longer range heat potential.

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