Category Archives: Thunderstorms

NYC Weather Update – Apr 15, 2014

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Wet, windy, and cold conditions will predominate our weather today. We’ve already hit our high temperature for the day and will see temperatures continue to plummet throughout the course of the day as rain and the attendant strong cold front moves in later this afternoon. Gusty winds in excess of 40mph, and some rumbles of thunder are possible in the stronger rain showers.

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The heaviest rain will be this afternoon/evening, ending gradually overnight. Behind the cold front responsible for this heavy rain, a biting northwest wind will drop temperatures down into the low-mid 30s! Again, there is some small potential for snow flurries across NYC during the tail end of this storm.

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We could be looking at rainfall totals up to 2″ in the area, crazy wet for this time of year. Now, Wednesday, you’ll feel the impact of the passage of that cold front, as northwest winds will persist around 15-20mph, suppressing high temperatures in the mid-40s, much below the seasonal average.

Thursday and Friday will both be dry days with high pressure moving over the region, but high temperatures will remain below normal with an onshore breeze blowing in from the east and northeast. Overnight lows both days will remain quite cold in the mid-upper 30s. You thought you didn’t need that winter weather gear anymore, eh?

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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Really Cool Graphic – All Reports of Severe Hail from 1950-2013

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Another neat graphic from Storm Prediction Center’s SVRGIS: all reports of severe hail over .25″ in diameter from 1950-2013! Again, note the relative scarcity of severe hail west of the Rockies, but look at the density of hail reports over Mississippi and Georgia. Also, check out the dense patch of hail reports just east of the Front Range in Colorado.
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Weather Update – Midweek Storm, Mar 11, 2014

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Wednesday is shaping up to be a stormy, rainy day. Low pressure center currently located over Nebraska and Oklahoma will slide to the northeast into the Ohio valley while continuing to strengthen.

Current forecasts point to the storm center tracking just north of the NYC area. This should ensure that most of the region receives all rain for this storm. As the storm center draws closer, a nearly stationary frontal boundary will slowly push through to just north of the NYC area. This will allow the area to be entrenched in the warm sector, this means temperatures will stay relatively mild with highs in the mid-50s. It also raises the possibility for some weak thunderstorms in the afternoon hours as the cold front trailing the storm center pushes through.

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In fact, the Storm Prediction Center has placed the DC-PHL metro areas as well as parts of southern Pennsylvania, northern Virginia, Maryland (see diagram below) under a slight risk for severe thunderstorms. The same cold front could trigger stronger storms down to the south due to the likelihood of warmer temperatures, more unstable air, and favorable conditions for thunderstorm initiation.

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Behind the cold front, temperatures will plummet during the evening and overnight hours. The departing low will continue to strengthen into Thursday, with increasing northwest winds ushering in this colder air as well as a chance for snow showers (negligible accumulation expected). Highs will only barely hit the mid-20s.

Conditions will improve later in Thursday and Friday as an area of high pressure moves over the region. Temps will climb back into the low 40s Friday just below average, and rise to near 50 Saturday. Next chance of significant precipitation looks to be Sunday into Sunday night – with the potential for a snow storm!

 

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.