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.

NYC Midweek Weather – Feb 19, 2014

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Sorry about the lapse in posts! Tuesday ended up being a pretty active weather day with showers moving through the area (thank goodness temps were warm enough so that it wasn’t more snow).

Your weather forecast for this week: rain has already dissipated across the region. Thursday starts out as a mostly sunny day, and highs should top out in the low-mid 40s, slightly above average in the city. Clouds will build throughout the day as a frontal system approaches from the west. Overnight Thursday, chances of precipitation increase along with the passage of a warm front.

Friday, temps continue to increase to the mid 50s ahead of an approaching cold front. Expect a mostly cloudy day, with showers and the potential for a line of stronger thunderstorms accompanying the frontal boundary passing in the afternoon.

Things dry out this weekend, with temps falling back to the mid 40s Saturday and Sunday. Another reinforcing cold front passes through Sunday, dipping high temps in the beginning of next week into mid 30s, below the average of around 40. No major storms on the horizon past Friday!

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NYC Weekend Weather Update – Feb 15, 2014

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We will be feeling the impacts of yet another storm, in what seems like an endless winter. A low pressure system currently over Cape Hatteras will move offshore into the Atlantic shortly. Once it does so, it is forecast to strengthen rapidly as it moves northeast towards the 40N 70W benchmark, which is associated with prime conditions for growth of strong nor’easters and winter storms.

Currently, forecast models are showing the brunt of the storm hitting Southeastern Mass and New England. In areas, the NWS office in Taunton is confident that there could be up to 12-15″ of snow, in addition to strong winds in excess of 50mph that have led to blizzard warnings for east facing shores of Mass including the Cape.

Impact

For our area, eastern Long Island is expected to see enough of a heavy snow band forecast to rotate around this storm to have winter storm warnings issued. These areas could see 6-8″+ of snow from this storm. Projected snowfall totals drop significantly as you go west, with mid-Island and Central Connecticut forecast to see 4-8″, and points west (including NYC) receiving 2-4″. Wind will also be a factor with a tightening pressure gradient caused by the rapid intensification of the coastal low.

Timing

Light snow is already falling over the area now, but the worst of this storm should take place in the evening and overnight hours. Snow and wind should pick up in intensity from southeast to northwest throughout the day. If you have made plans to travel along the NYC-Providence-Boston corridor, expect travel conditions to become hazardous this evening/night. The most intense part of this storm will be ongoing from about 6PM-1AM, but accumulating snow will begin around 3PM.

Notes

As with most storms this winter, there is still uncertainty as to the final track of the storm. Should the storm track slightly westward, and the deformation axis determining where a heavy band of snow progresses further inland, then areas west of where current winter storm warnings exist could see significantly higher snow accumulation. There is also some indication that a norlun trough might form, leading to a intense snow band projecting west/northwest from the center the coastal low. If this feature does develop, areas that this trough sits over could see much higher than projected snowfall.

Satellite image of the incoming storm below:

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NYC Weekend Weather – Feb 14, 2014

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Check out this impressive satellite image of the nor’easter that hit us yesterday. It’s now offshore of southeast Maine, and has strengthened considerably, taking on a classic “comma head” structure that is a hallmark of strong surface low storm systems.

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Don’t shoot the messenger, but we are forecast to get even more snow Saturday. A clipper system to our northwest over Michigan will combine with another low pressure system moving into the Carolinas later today. Once this system moves offshore, it will begin strengthening and growing into another nor’easter. Luckily, forecast models are currently showing much lower amounts of available moisture (precipitable water) for this upcoming storm. In addition, even though the storm is forecast to pass near us, the bulk of the precipitation is currently forecast to remain over the open ocean. What this means is that we should only see light accumulations of snow, on the order of 1-3″. However, as with the previous storm, there is still a little uncertainty about the final track of this storm, and changes could lead to higher snowfall amounts.

Otherwise, expect milder temps today with windy and sunny conditions prevailing, temps in the low 40s. This should help some of the snow to melt. We should have clear skies for part of the evening to see the full moon on Valentine’s Day. Clouds move in overnight, with snow showers during the day Saturday and a high in the mid 30s. Another weaker clipper system moves in Sunday with another chance for light snow and high temps around freezing. Yet another system is forecast for Monday night into Tuesday, which looks to be snow to start and snow transitioning to rain on Tuesday. Monday’s high near freezing with a warm up Tuesday ahead of the frontal system moving in.

Here’s a graphic showing the snowfall totals from around the area from this last storm.

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Nor’easter Update – 7PM Feb 13, 2014

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We’ve enjoyed a period of relative calm as the dry slot (orange outlined in purple below) mentioned earlier pushed in over the area, leading to a lull in heavy precipitation and more of misty drizzle. However, these conditions will not last as the nor’easter will gain strength overnight.

The mid-upper level low that is responsible for bringing in this dry slot will gradually move over the surface low pressure center currently located offshore of central NJ. Once the low pressure systems stack up, the surface low will rapidly deepen. As this occurs, the warm front extending from the nor’easter’s core will rotate to the NW of the storm center.

This frontal boundary will push moist air (greens and yellows in this image below) ahead of it, leading to the formation of a new heavy band of snow – technically a “frontogenetically induced deformation band”. Within this band, snowfall rates may hit 1-2″ per hour, and an additional 4-8″ could accumulate across the region (except eastern Long Island). Interior areas where temps have remained cold could see an additional 8-12″ overnight.
Screen shot 2014-02-13 at 7.03You can already see in the radar image below that precipitation is already filling back in across southern NJ and the WAS-BAL-PHL corridor.

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Nor’easter Update – 12PM, Feb 13, 2014

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Satellite water vapor imagery clearly shows an area of drier air (in orange), known as a dry slot, working its way into the nor’easter currently impacting the NYC area. Intense bands of snow continue to push into the interior areas north and west of the city.

However, radar imagery from Mount Holly, NJ NWS office is already beginning to show a break in precipitation associated with this drier air. As this dry air works its way north, we can expect a break with lighter snow/rain for the area. This could work to lower overall snowfall totals in areas that see this break. At the surface, snow has transitioned to rain/sleet for most areas in NYC, Long Island, coastal NJ and southeastern CT. The rain/snow line should remain stable in its current position for the remainder of the afternoon.

Precipitation should transition back to all snow during the evening and overnight. Additional accumulation is expected with more large-scale banding features forecast to form on the backside of the nor’easter low pressure center as it intensifies and exits to the northeast. Another 3-5″ is possible overnight in the city. Snowfall totals in areas north and west should easily top 12″ by the end of this event.

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NYC Noreaster Update – 6PM Feb 12, 2014

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Everything is on track for this strong noreaster to begin moving into our area late tonight. NWS forecast office in Upton has upgraded all areas in the NYC metro to winter storm warnings ahead of the storm. The low pressure center responsible for this weather will move offshore of the Delmarva Peninsula and begin a process of rapid strengthening as its central pressure drops precipitously by 25mb.

Snow will begin falling over the area from south to north after midnight tonight. Heavy snowfall rates of 1-2″/hour are possible with a large scale snow band  forecast to develop due to the influence of a strengthening frontal boundary. By morning, NYC will pick up at least 3″ of heavy, wet snow, making for a messy commute. Snow will continue falling during the morning commute, heavily at times, limiting visibility. Snow transitions into sleet and possibly some rain around the coastal areas during midday. If rain mixes in, areas near the coast would see minimal additional snow accumulation during the day. If rain does not mix in, then another 6″ is possible.

Areas in the interior will see snow start later than NYC and the coast, but will continue to experience all snow or a sleet/snow mix during the day Thursday. These areas will pick up an additional 6″+ during the day Thursday, with another shot at picking up 6″ or more Thursday night as bands of snow continue to rotate around the center of the low.

As the storm departs to the east, it will continue to strengthen. The tightening pressure gradient will lead to stronger winds, with gusts as high as 40-50mph in some parts, leading to blowing and drifting snow. The heavy, wet snow associated with this storm has the potential to knock out power and collapse roofs already encumbered with accumulation from previous storms.

 

Nor’easter Update – Feb 12, 2014

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High impact nor’easter for the NYC metro area starting tonight. A low pressure system has formed southeast of New Orleans and will be tracking along the Carolina coast before moving offshore of NJ. Once over open water, the storm will begin rapidly strengthening (bombogenesis). Recent model runs have come in with a colder scenario, so less mixing in of rain is anticipated near the coast.

Timing

Moderate to heavy snow will overspread the NYC area in the overnight hours tonight. Accumulating snow will impact the morning commute, before a changeover to sleet near the coast and rain over portions of eastern Long Island. Interior regions will continue to see all snow. Precipitation will continue through the day Thursday, transitioning back to all snow for coastal areas overnight before dissipating early Friday morning.

Impact

Periods of snow, heavy at times overnight Wednesday into Thursday. A large-scale snow band(s) is forecast to form over portions of the NYC area, generally west of I-95 across the interior north and west. Areas under this banding feature will easily see snowfall totals over 12″, with snowfall rates up to 1-2″ per hour. Closer to the coast, snowfall totals generally forecast between 6-10″ of snow and sleet. By morning, we can expect around 2-4″ in the city making for a messy commute. Higher amounts north and west. Additional snow/sleet accumulation in the city of 2-4″ during the day, and ending off with 2-4″ overnight Thursday. Some power outages are possible with heavier snowfall on top of ice from previous storms.

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NYC Storm Update – Feb 11, 2014

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There is increasing confidence that NYC will be seeing a high-impact snow storm Wednesday night into Thursday night. However, there are still discrepancies between different forecast models that are leading forecasters to not place too much confidence in overall snowfall totals. There are two main scenarios that could unfold: 1) the storm center takes a track closer to the coast, or 2) the storm center tracks further offshore.

In the first scenario, warmer air would be able to enter into coastal areas and lead to more rain, thus cutting down snowfall totals in NYC, Long Island, and coastal NJ, CT. In the second scenario, warmer air does not flow in as much. This would lead to higher snowfall totals for all areas of the NYC metro. With snow:water ratios about 8:1, and as much as .75-1.5″ inches of precipitable water available (moisture that can fall as snow, rain, ice, etc.), any small change in forecast track and temperature could lead to significant changes in the forecast total snowfall.

Current forecast:

Timing: accumulating snow will begin falling over the area, spreading from south to north, beginning Wednesday night. During the overnight hours into early Thursday morning, widespread totals of 4-6″ are possible. If the track producing a warmer temps verifies, then snow will mix in with rain along coastal areas during the day Thursday, while remaining all snow inland. A return to all snow will occur Thursday night as temps drop below freezing and the storm system exits to the northeast.

Impact: NWS is forecasting 6-8″ total snowfall for areas along the coast including NYC, with 8-10″+ in areas immediately north and west of the city. This is a total for Wednesday night into Thursday night. Thursday morning commute will be messy, with accumulating snow transitioning to rain making for a slushy mess in coastal areas, and all snow in the interior.

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Historic Ice Storm to Hit GA, SC

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The storm system set to impact the Northeast will make its impact felt in the Southeast Wednesday and Thursday. An historic ice storm/winter storm is set to take shape and impact areas of the Atlanta metro, hard hit by the January 28th storm.

To quote National Weather Service in Atlanta:

HAVE GONE WITH THE MORE DIRE PREDICTIONS OF A HALF AND INCHOF ICE TO CLOSE TO AN INCH FOR EAST CENTRAL PORTIONS OF THE STATE.BIGGEST CHANGE PERHAPS IS THE SNOWFALL ACCUMULATIONS WITH NOW 4 TO 8 INCHES ACROSS THE NORTHERN TIER WITH 10 INCHES TO PERHAPS A FOOT POSSIBLE IN THE NE MOUNTAINS. WE ALSO INCREASE THE TOTALS FOR THE NORTH ATLANTA METRO WITH AN INCREDIBLY DANGEROUS COMBINATION OF OVER A QUARTER INCH OF ICE AND 2 TO 5 INCHES OF SNOW.

Ice accumulation on top of snow of this magnitude will almost certainly lead to widespread power outages from downed tree limbs and power lines, as well as deadly travel conditions. The governor of Georgia, Nathan Deal, wisely declared a state of emergency and shut down non-essential services across the state.

The areas of greatest impact for icing will lie along the I-20 corridor east of Atlanta, curving into central South Carolina, although ice storm warnings have not been posted yet in some areas of South Carolina. If you are living in this area, avoid any unnecessary travel, and make any necessary preparations immediately.