Category Archives: Nowcast

NYC Nowcast – Strong to Severe Thunderstorms Approaching

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Severe thunderstorms are approaching the area from our west. Several distinct bowing segments of severe thunderstorms have been making their way steadily towards our area from Central Pennsylvania since earlier this afternoon.

These storms have a history of producing damaging wind gusts and even a few tornadoes. Sundown over some of the areas under the current Severe Thunderstorm Watch areas in our region may weaken these storms, however, overall atmospheric conditions are quite favorable to the forward propagation of this line.
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NYC Afternoon Weather Update – Severe Tstorms in Vicinty – Jul 2, 2014

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You may have already experienced it, but if you haven’t you’re probably seeing some huge clouds forming on the horizon. We’re in for some stormy weather this evening, as the Storm Prediction Center and our local forecast office have us under a Severe Thunderstorm Watch. The hot, humid atmosphere, along with ample sunshine earlier today, has made the atmosphere moderately unstable, with CAPE values in the 2000-3000 J/Kg. This, along with mid-upper unidirectional shear will supply ample energy for strong to severe storms, with the greatest threat being frequent cloud to ground lightning and damaging winds.

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As you see above, there are already strong storms in our vicinity. The storms north of the city have met severe thunderstorm criteria (wind gusts in excess of 58mph, hail greater than 1/4″ in diameter, or a tornado). More storms are forming to our southwest, so NYC itself should not be immune to the threat later on. Check out this image of a classic towering cumulonimbus (thundercloud) below!

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NYC Nowcast – Jun 13, 2014

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You’ve felt the air warm up and become more humid as the warm front that brought our first round of rain passed through earlier today. Now, we’re getting set for a second round of heavy showers and thunderstorms associated with a pre-frontal trough that’s slowly progressing east towards the area from Eastern Pennsylvania.

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Ahead of this line of showers and thunderstorms, the air has destabilized readily with the ample sunshine earlier this afternoon. CAPE (Convective Available Potential Energy – a measure of how much fuel there is for thunderstorms to feed off of) is between 1000-1500 J/Kg over Northeastern New Jersey and NYC. This should allow for this line of storms to hold up and perhaps strengthen before hitting NYC. In fact, a couple sever thunderstorm warnings have already been posted for cells over Northeastern New Jersey.

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NYC Nowcast – Afternoon Tstorms – May 22, 2014

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The Storm Prediction Center in Norman, OK has placed western portions of our region under a slight risk for severe weather this afternoon, with the primary threat being damaging winds and hail.

UntitledMid-upper level conditions are favorable for the development of thunderstorms with some rotating updrafts. Unidirectional winds at various levels, as well as wind speed shear, could impart enough rotation on storm cells to cause marginally severe wind damage and some hail. The highest potential will be over Eastern Pennsylvania and New Jersey where sufficient solar heating could produce CAPE (Convective Available Potential Energy, measured in joules per cubic kilogram) values of between 1000-1500 J/kg^3.

Storm Prediction Center in Norman, OK has placed western portions of our region in a slight risk area for severe weather this afternoon
Storm Prediction Center in Norman, OK has placed western portions of our region in a slight risk area for severe weather this afternoon

A small cluster of thunderstorms is already initiating along the western New York/Pennsylvania border ahead of a weak cold front. These storms should expand in coverage and increase in intensity as skies are clear ahead of the frontal boundary, allowing for a good influx of energy for storms to feed off of. The current thinking is that isolated severe thunderstorms reach our region by around the 4-6PM time frame. The chances of these storms remaining severe over NYC and coastal areas is low, since there will be a stabilizing influence from the cool marine layer offshore.
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NYC Nowcast – May 10 @ 2:40PM EST

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A batch of strong showers with some rumbles of thunder is approaching the NYC area. For the remainder of the afternoon and evening, strong to possibly marginally severe thunderstorms may pass through ahead of an advancing cold front. Damaging wind gusts and small hail are the primary threats.

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Otherwise, expect broken clouds to cloudy skies and nice warm afternoon in the upper 70s to low 80s across the area. A line of thunderstorms is likely to fire up again later this afternoon into the evening hours as the cold front actually approaches.

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Atmospheric instability is continuing to increase as we are in the warm sector ahead of the advancing cold front. Low level lapse rates and shear profiles are marginally conducive to the growth of some strong to severe thunderstorms.

NYC Afternoon Weather Update – Apr 22, 2014

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Altocumulus clouds over the Empire State Building
Altocumulus clouds, preceded by cirrus clouds (earlier today and yesterday) are indicative of approaching frontal boundaries

Just a quick afternoon update for you all. It’s been quite a warm afternoon as warm air continues streaming into the area ahead of an approaching cold front. The frontal boundary is still quite a ways off, however, you can already see increasing cloudiness in the form of these altocumulus over the city. Some precipitation is beginning to show up over portions of western NJ. The atmosphere right over NYC is still on the dry side, with humidity recorded at LaGuardia Airport recently only at 47%, and dewpoint temperatures only 44 degrees. This should serve to limit the potential for convective activity and thunderstorms later in the day. In fact, as the area of precipitation to our west enters the region, showers may break up or scatter upon entering the relatively drier airmass.

NYC Nowcast – Apr 8, 2014 @

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Quick update here: skies will gradually begin to clear as clouds associated with the rain storm last night move offshore. As you can see from the satellite image below, sunny skies are already entering portions of Northern NJ. Depending on the time we get under clear conditions, we could very well see high temps hit 70 except in Long Island and coastal CT, where an onshore southwest wind will keep things cooler.

Also of interest, check out the wave clouds out over Central PA! Just as objects in the path of a water can cause eddies and waves to form behind them, you can get the same effect with air flowing over mountain ranges. You can’t surf these (maybe with a glider?)
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