Tag Archives: thunderstorms

NYC Weather Update – Apr 21, 2014

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Brilliant start to the week this Monday with comfortable and seasonable high temperatures in the low-mid 60s.

HPC forecast

Tuesday – A cold front will rapidly approach the region from the west. Ahead of this cold front, warm, moist Gulf air will flow in, allowing for high temperatures to edge close to 70. Given the moisture content and warm temps, there is some potential for enough instability in the atmosphere to support the growth of thunderstorms later in the afternoon hours. Some of these storms could produce small hail. Thunderstorms, should they form, would be mostly limited to inland areas west of NYC as the marine layer near the coast tends to exert a stabilizing influence.

Wednesday and Thursday will be similar weather-wise with high temperatures suppressed in the upper 50s to low 60s due to the influence of strong winds from the north and northwest in the wake of the departing cold front. We should see clear and sunny skies both days. Excellent conditions for radiational cooling on both nights will allow lows to drop into the upper 30s and low 40s across the region.

The next chance for rain will be this Friday into the weekend with another cold front moving in from the middle of the country.

Cool gif – Severe Thunderstorms in the Plains, Apr 3, 2014

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Check out this satellite loop of a line of severe thunderstorms over eastern Oklahoma extending northeast into western Missouri. You can see the classic telltale signs of explosive thunderstorm growth here. Notice how at the outset, the line of clouds near the center of the frame are relatively thin, but then balloon out as time goes by. What’s happening here is that the cumulonimbus (thunderstorm) clouds along this line are growing so rapidly that they are hitting the top of the troposphere. Since water vapor has a difficult time penetrating into the stratosphere, it gets forced out laterally instead. Indeed, the Storm Prediction Center in Norman, OK has issued a mesoscale discussion, along with severe thunderstorm warnings and tornado watches for much of the area.

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NYC Weather, Relief for CA, A Stormy Monday for NY? – Feb 25, 2014

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Keeping eyes peeled on the forecast for Monday, when the next strong storm system is forecast to arrive.

First, there’s some good news for our friends out west. As you can see in this first image, the GFS model is showing a storm system originating in the Pacific bringing areas of moderate to heavy rain over the weekend for California, which is currently in the grips of an historic drought. As the storm center approaches the coast, a strong cold front will swing from south to north through the state. This frontal boundary will spark thunderstorm and rain which should bring mild relief, with 1-2″ of rain forecast for coastal and valley areas, and 2-4″ up to 6″ for south-facing mountain slopes. In addition, heavy snow could fall in the higher elevations of the coastal ranges and Sierra. Welcome news for an area of the country that’s in need of moisture.

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After the storm exits the western US, it is forecast to reorganize over the plains and Midwest, then track into our area. Right now, it’s still to early to say with certainty whether the intensity of the precipitation this storm brings, and whether it will be all snow, a mix, or even mostly rain. Will keep you all updated.

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NYC Weather Update, Looking Ahead & the Arctic Oscillation (AO) – Feb 20, 2014

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A strong frontal system that’s currently pushing its way into the Central Plains will be arriving in our area Friday, bringing showers, potential thunderstorms, and much warmer temps. Currently, the storm system is impacting a wide swath of terrain. Blizzard warnings up for most of the state of Iowa, and heavy snow is expected across Wisconsin and Minnesota.

Though this storm will weaken somewhat before it hits our area, it should nonetheless bring widespread rain showers with the possibility for a strong thunderstorm and wind gusts up to 50mph. Temps tomorrow will range in the mid 50s with a warm front passing over tonight and southwest winds pumping in warmer air ahead of the cold front tomorrow. Timing of the cold front passage looks to be in the late morning/early afternoon. Rain showers/thundershowers could band together and form a continuous line with some embedded stronger thunderstorms. Chances of  strong thunderstorms are slim, though. As you can see below, the Storm Prediction Center in Norman, OK, placed the far reaches of southern New Jersey in its outlook for severe weather.

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Once the cold front passes, temps will regress back to average over the weekend, with temps on Saturday expected to top out around 50 under mostly sunny skies, and highs on Sunday in the mid 40s. Our reprieve from the cold will be short, however, as a reinforcing cold front will pass on Sunday, opening the door to a longer term trend of colder and below average temperatures.

You might be wondering why this has been such a cold winter for the Northeast. Well, something called the Arctic Oscillation (AO) is a contributing factor. The AO is a measure of the strength of the arctic jet stream. When the AO is positive, it means the arctic jet is strengthening. When negative, the AO signals a weakening in the arctic jet. Negative readings on the AO index generally correspond with colder surface temperatures. Why? When the arctic jet is speeding up and growing stronger, it keeps the coldest air trapped around the polar regions. When the arctic jet slows down, it allows this colder air mass to move southward, shifting the jet along with it. In extreme cases, it can even allow polar vortexes to take unusual orientations.

If you take a look at the AO Index bar graph below, you can note that the AO index was indeed negative during the latest outbreaks of bitter cold temperatures in our region.
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I bring this up because the forecast for the next 7 days indicates a return to a negative AO regime, which should lead to colder temperatures through the week. This won’t be as bad as other cold spells, since the angle of the sun is about what it would be for early October, and the days are getting longer, allowing for more daytime heating. Currently forecast highs in the Monday-Wednesday timeframe are all just under freezing for NYC.

There are some slight chances for precipitation Tuesday, but the next significant storm system looks like it will impact the area around Wednesday. Given the temperature trend, this storm should fall as mostly snow, so we’ll see how subsequent forecasts turn out on storm track and available precipitable water.