Posts

Doug Simonian

La Nina Update: Moderate or Strong Event Unlikely This Year

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While we had been tracking heat and severe thunderstorms over the first few months of the summer, the atmosphere was still undergoing a major transition away from El Nino and towards a La Nina. This transition has already resulted in sensible weather changes across much of the country, with a huge heat ridge building in the Central US last month — typical of a La Nina. However, to the despair of some long range forecasters, certain aspects of the transition have not gone as smoothly, and more recent forecast models have trended weaker with the eventual strength of the La Nina over the next few months.

During last year’s El Nino conditions, the trade winds in the Equatorial Pacific were strongly weakened, allowing warm water near Australia to pool eastward. Those trade winds have strengthened over the last few months, which pushed that warm water back to the west, and allowed cooler water to upwell towards the surface. However, climatology favors trade winds remaining a persistent feature — in other words, we are supposed to have east-to-west trade winds blowing warm water towards Australia keeping cooler water near Peru. We can only have a La Nina when those trade winds are consistently stronger than average, and that has yet to be the case this year. For more background on what causes El Nino, La Nina, and the demise of an El Nino, refer to our article from late April.

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John Homenuk

Heat returns, scattered severe storms Saturday afternoon

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A transitional ridge will build into the area from Friday Night into Saturday, with warming temperatures and increasing moisture expected. While this ridge won’t be necessarily large, it will bring much warmer air in both the mid and lower levels of the atmosphere. This will lead to increasing instability late Friday into Saturday, ahead of an approaching cold front which will be lingering to our north over Southeast Canada.

This front will begin sagging southward on Saturday morning and afternoon, with showers and thunderstorms likely to develop near the area during the early afternoon. Moderate instability in the atmosphere is expected to juxtapose with favorable wind shear to support the development of these strong and severe storms, which will sink southeastward through NJ, NYC and Long Island.

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John Homenuk

Strong and severe thunderstorms possible Saturday

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While lower dew points have been very well received in our area over the past several days, a warming trend will be underway once again by Friday. Increasing temperatures and moisture will become notable as winds, which had been coming inland off the area waters for the past few days, with to a warmer southwesterly direction. A transient ridge building overhead will aid in the warming temperatures moving into the Northeast US on both Friday and Saturday.

To our north, meanwhile, an expansive disturbance over Southeast Canada will begin shifting southeastward through parts of the Northeast US. While forecast models don’t currently show a strong or robust area of vorticity with this disturbance, the very broad disturbance has expansive height falls of its own. These act to supplement lift in the atmosphere along a cold front, which will be dropping southeastward through the Northeast states on Saturday.

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John Homenuk

Perseid outburst expected to make 2016’s shower special

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The Perseid meteor shower is always a highlight of the astronomical year, frequently bringing one of the most consistent meteor showers to the night sky in late summer. The warm weather and often favorable moon phases mean the Perseid’s are also one of the most comfortable meteor showers to enjoy. 2016 is expected to be even better than usual: An outburst of meteors is forecasted, resulting in nearly double the typical rate of meteors per hour during the showers peak from August 11th to 12th.

The meteor shower occurs each year as Earth passes through the debris tail of Comet Swift-Tuttle, resulting in meteors for several days with a peak of 1-2 days typically in mid-August. Comet Swift-Tuttle is the largest known object to repeatedly pass by Earth, with a nucleus about 16 miles wide. It last passed by in 1992, and won’t pass again until 2126. Our respective orbits, however, mean that Earth passes through the debris trail of the comet every year.

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