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Fourth of July forecast takes ugly turn

Yesterday, our forecasters were debating whether or not clouds would be a significant issue on the Fourth of July. Today, we have bigger problems to deal with. Forecast models have trended farther north with a surface low pressure system, which is expected to move from the Mid Atlantic States to a position southeast of Long island on Saturday. This low pressure system, associated with a mid level atmospheric disturbance, will promote the development of showers and areas of steady rain, which will progress through the area on Saturday.

Models, still, are wildly inconsistent with the areas of steadiest rain and more focused development of showery activity. What we do know, at this point, is that the surface low pressure system will promote widespread clouds from Friday Night into Saturday morning. We’ll put it to you this way: You won’t exactly wake up on Independence Day ready to run outside in shorts and fire up the grill. East winds and low clouds will keep things feeling much cooler, and showers will be meandering around the area as well.

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Fourth Forecast: Clouds possible, but not a certainty

Summers most loved holiday is almost here — and most already have their American Flags and sparklers ready. The weather, however, may not be so eager to cooperate. We’ll start with the good news: Medium range forecast models which had been showing a total washout for Independence Day have since backed off. The bad news? It still looks like an onshore flow will promote the development of low clouds and the intrusion of a marine layer, at least early in the day.

What will become interesting is forecasting both the erosion of that marine layer by the afternoon and evening hours, and the potential for a weak coastal storm system to scoot on by to our south and east. This looks most likely to occur on the night of July 3rd (Friday) into Independence Day morning, as a low pressure system develops in the Ohio Valley and then transfer offshore to the Mid-Atlantic Coast. Sheesh — you’d almost think this were a mid-winter forecast!

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Visible satellite showing cumulus clouds developed across the area early this afternoon

Some Sunshine and Showers/T-Storms This Week

After some dismal weather this past weekend, the tri-state area enjoyed of lots of sunshine this morning with temperatures in the middle or upper 60s and low humidity. An upper-level trough to the north is causing more clouds to mix with sunshine this afternoon. A few isolated showers could pop late this afternoon and evening, well north and west of New York City. Most of the area will stay dry this afternoon. Temperatures will reach in the middle to upper 70s with light southwest winds. Tonight, skies should become mostly clear with low temperatures in the lower 60s and 50s inland.

A warm front will begin moving through region tomorrow and tomorrow night. Ahead of it, light winds will turn more out of south-southeast off the cooler Atlantic waters. However, partial sunshine and 850mb temperatures around 14 degrees celsius during the afternoon, will help temperatures reach the upper 70s to lower 80s for much of the area. Near the New Jersey shore and the south shores of Long Island and Connecticut, high temperatures will be slightly cooler– likely in the middle 70s. A few showers or thunderstorms are possible well north and west of New York City, late in the afternoon. But scattered showers and thunderstorms are more likely later tomorrow night for the rest of us. Model guidance shows low instability and high precipitable water values, or atmospheric moisture co tent. Any thunderstorm will capable of producing heavy rainfall and cloud to ground lightning. Despite this, we aren’t anticipating organized severe weather or hazards at this time. 

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Lightning strikes Hoboken. (Gary Hershorn @GaryHershorn)

The June 23rd Severe Weather Outbreak in Review

“Them’s the breaks”, my father often says when things don’t quite go as planned. While this grammatically errant statement may not seem immediately applicable to meteorology, most of our staff were thinking something similar on Tuesday afternoon. Our meteorologists had forecasted an organized — potentially significant — severe weather event days in advance. While this event did in fact occur over New England, Southern New Jersey, and the Mid Atlantic, the brunt of the severe storms curiously “skipped” over New York City and much of Northern New Jersey as well.

Severe thunderstorm events, inherently, are difficult to forecast. Not only for their technical aspects and intricacies, but for their often isolated nature. One town may see wind damage and hail, while the next one down the road only sees light rain — or in some cases, no rain at all. What this means for forecasters is that communicating the scattered nature of thunderstorms becomes very important.

This time, however, the storms weren’t necessarily scattered in nature. The atmospheric pattern favored widespread thunderstorm development, with lines and bowing segments of severe thunderstorms moving from northwest to southeast while affecting a large area. Hence, our verbiage “Widespread organized severe weather”.

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12z NAM model showing an amplified ridge over Western US and deep, closed upper-level low over the Eastern US.

Weekend Outlook: Heavy Rainfall Late Saturday, Better Weather on Sunday

High pressure will gradually shift to the northeast Friday night and Saturday. Clouds will increase on Friday night. An amplifying ridge over the Western United States will cause shortwave energy to dig and form into a closed upper-level low over the Ohio Valley/Great Lakes.  This will cause a double-barrel surface low-pressure system to organize over the Eastern US on Saturday. A deep southerly flow will transport a plume of moisture from the Gulf of Mexico and the Atlantic into our area. Most of the model guidance agrees on a widespread heavy rainfall throughout the area starting on Saturday and continuing into Saturday night.

Saturday will feature mostly cloudy skies with some intermittent rain and drizzle breaking out from southwest to northeast across the region. This will gradually occur during the morning and early-afternoon hours. A strengthening southerly low-level jet and precipitable water values approaching two inches will cause rain to become steadier and heavier at times, late in the afternoon and early Saturday night for the region.

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