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NYC Weekend Weather & West Coast Storm – Dec 2, 2014

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It’s been a up and down week for weather in NYC, with Monday starting out in the mid-60s, then a colder mid-week that featured some mixed precipitation and rain. The end of this week will feature rain and slightly warmer temperatures by Saturday, then a return to colder conditions Sunday into next week. I’m also going to point out some of the spectacular weather brought on by a huge Pacific storm that hit California this week.

Thursday – the remainder of today will be pleasant and sunny, though cold with high temps only in the low 40s.

Friday – clouds will begin to build overnight tonight ahead of the a storm system moving in from the Southern Plains to the Ohio Valley. There is a small chance for scattered showers, otherwise expecting a cloudy day with highs in the mid-40s.

Saturday – rain should overspread the area by Friday night into Saturday. This storm system will be drawing on energy and moisture from the Pacific storm that slammed California earlier this week (discussed below). Combined with influx of Gulf moisture, this setup favors a moderate to at times heavy rain event for Saturday. Temperatures will rise steadily ahead of this storm system as it pushes warm air up. High temperatures Saturday should reach into the mid-50s despite rain and clouds.

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GFS model output for overnight Friday into Saturday

Sunday – rain should end overnight Saturday, and high pressure from Canada should quickly build in behind this storm system. The positioning of this high pressure, along with the exiting low, will make for a tight pressure gradient, which should allow for stiff northwest winds perhaps in the 15-25mph range. Temperatures will drop back into the low 40s with the arrival the colder Canadian air.

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GFS model output for Sunday night

Monday – the storm system from Saturday will move offshore, but it appears from model runs that there’s some chance the storm lingers. As the high pressure from Sunday moves off to the northeast, the clockwise flow behind it may draw this offshore area of low pressure back into the area. This could lead to some rain on Monday. It’ll be a mostly cloudy day otherwise with highs in the low 40s.

Pacific Storm Slams California

Earlier this week, California got slammed by a very strong Pacific low. This storm brought on furious rains that dropped 1″+ in many areas of Northern California, with totals as high as 3-4″ in spots near the Coast Range and Sierra, as well as further south in the mountains east of San Diego. These totals represent more rainfall than had fallen in many of these areas all of last year.

You can see from the map below which overlays drought conditions (the deeper the red, the more extreme the drought, with the darkest red representing extreme/record-breaking drought) with rainfall totals from yesterday. You’ll see that much of the heaviest rain did fall over regions worst affected by drought. Sadly, though this is a case of too much of a good thing, as much of this desperately needed rainfall occurred so quickly, it will simply runoff back into the ocean.

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Map of California with drought condition layer (reds/oranges), and rainfall totals from yesterday

NYC Weather Update – Nov 11, 2014

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I hope you all took advantage of this gift of incredibly warm weather that coincided with a federal holiday, because that’s going the be the last gasp of mild weather for at least the next 7-10 days. As you probably heard, we are going to get walloped by an arctic airmass the latter half of the week that will bring an abrupt end to fall temperatures and make it feel like we jumped straight into winter – I’m talking high temperatures that won’t even get out of the low 40s by week’s end. Before you ask, no this is not a polar vortex – it will be damn cold nonetheless.

Wednesday – this will be the last day we get above 60 degrees for quite a while. We are currently in a warm sector in between a warm front that pushed through earlier this week and ahead of a cold front that will be open the door to an arctic airmass swinging down from Canada. High temperatures in the Central Plains and Intermountain West where this airmass has already taken hold are ranging from the teens to the 30s. But Wednesday, we’ll still be in the mid-60s, although it won’t be as pleasant as today with a foggy and cloudy start to the day. Once the cold front below passes, clouds should clear quickly and lead to excellent conditions for radiational cooling, with low temperatures dropping into the low 40s and into the 30s in the interior areas north and west.Screen Shot 2014-11-11 at 5.49.52 PM
Thursday – it won’t be that cold just yet, with high temperatures still expected to hit the low 50s. But clouds will again increase ahead of a second, quick-moving storm system that is expected to pass through Thursday night into Friday. This will be the real arctic sledgehammer that brings seriously cold air into the region. There will be enough energy and moisture in the atmosphere for the possibility of rain/snow mix on Thursday night and even all snow in the city Friday morning.

Friday – skies should clear quickly during the day Friday, but despite all the sun, temperatures will struggle to hit the mid-40s. Arctic air will be firmly entrenched from this point on until as long as Thanksgiving!

Saturday – High pressure will be in control Saturday, high temperatures will have a difficult time hitting 40 though, because the setup of the high will favor northerly winds. gfs_namer_096_1000_850_thickSunday – yet another storm system brings us the chance for some precipitation. Behind that system – you guessed it, more cold air and temperatures that will be two standard deviations below normal for this time of year, as per our local forecast office.

For those of you who are interested in the long-term outlook, based on forecast models and the arctic oscillation index forecast, it looks like this blast of cold air will be sticking around with us for at least the next 7-10 days, and may not break until Thanksgiving. The Arctic Oscillation measures the climate pattern of winds circulating at high latitudes close to the arctic. When it is in it’s negative phase (as is about to be the case, on the right end of all the charts below), higher pressure tends to dominate over the arctic while lower than normal pressure occurs in mid-latitudes (i.e. our area). Air tends to flow from areas of high pressure towards areas of low pressure, so this pattern sets up favorable conditions for the intrusion of bitterly cold air into our region.

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NYC Weekend Weather – Oct 18, 2014

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We get one last day of late summer-like temperatures today before autumn comes back with a vengeance. A cold front has already passed through the city and you can already notice the winds beginning to shift to the northwest. This will herald a much cooler temperature trend. For the remainder of today, we can expect temperatures near 70 with some clouds building behind the front. There could be a sprinkle or two but nothing serious.

Sunday forecast map
Sunday forecast map

Sunday will be noticeably more cold with high temperatures struggling to hit the mid-50s and with a gusty northwest wind. Gusts could top 30mph at times with sustained winds 15-25mph. Overnight lows into Sunday and Sunday night will be downright chilly in the 40s. Some interior areas could see frost Sunday night.

Monday the winds will abate as the pressure gradient between the departing cold front and high pressure to the west eases. Temperatures will remain cool at only around 60.

Tuesday and into later this week we will see the impact of a frontal system that moves through from the Great Lakes and develops as a coastal low off the Mid-Atlantic. Current models seem to suggest that this low will linger for a few days offshore, so we could see multiple rounds of rain as bands rotate around the storm center.

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Winter Climate Outlook

The Climate Prediction Center has released its 3 month temperature and precipitation long range outlooks for the months ahead. As you will see, CPC has the NYC area in a zone of 33% chance of seeing a wetter and warmer than average winter. Call it a hunch, but I still think we’ll get a couple nasty Nor’easter type blizzards. Warmer than average of course doesn’t imply we won’t get freezing temperatures. A slightly warmer atmosphere would allow for more moisture and energy for coastal storms to feed off.

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2014 Atlantic Hurricane Season Outlook – Jun 2, 2014

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Yesterday marked the official start to the 2014  Atlantic Hurricane season (June 1 – November 30), so this is as good a day as any to talk about the forecast for this season. The graphic below shows the National Hurricane Center’s official 2014 Hurricane Season Outlook that was released last month. This forecast is probabilistic, i.e. it gives a range of numbers and chances that this season will either exceed or fall below the forecast total.

National Weather Service National Hurricane Center's forecast summary for 2014
National Weather Service National Hurricane Center’s forecast summary for 2014

Explanation

In the NHC’s parlance, Named Storms refers to tropical or subtropical storms that produce sustained winds in excess of 39mph (this is the criteria for a tropical or subtropical storm) at any point in their life cycle. Hurricanes refer to the named storms that end up producing sustained winds in excess of 74mph, and Major Hurricanes refer to hurricanes that make it to Category 3 or higher on the Saffir-Simpson classification scale. Accumulated Cyclone Energy (ACE) is a rough measure for the overall intensity of a tropical cyclone and is calculated as follows:

The ACE of a season is calculated by summing the squares of the estimated maximum sustained velocity of every active tropical storm (wind speed 35 knots (65 km/h) or higher), at six-hour intervals. Since the calculation is sensitive to the starting point of the six-hour intervals, the convention is to use 0000, 0600, 1200, and 1800 UTC. If any storms of a season happen to cross years, the storm’s ACE counts for the previous year.[2] The numbers are usually divided by 10,000 to make them more manageable. The unit of ACE is 104kn2, and for use as an index the unit is assumed. Thus:

\text{ACE} = 10^{-4} \sum v_\max^2

where vmax is estimated sustained wind speed in knots. (Source – Wikipedia)

Hence, a high ACE number corresponds to a very intense storm or storm(s).

Outlook

As you can see from the above image, the NHC is calling for a normal to slightly below normal season for the Atlantic with 8-13 named storms, 3-6 hurricanes, and 1-2 major hurricanes. Despite the fact that the forecast calls for a normal to below normal season, it only takes one landfalling hurricane or major hurricane to inflict serious damage to a coastal area. Even with just tropical storms, huge amounts of rain can fall leading to major flooding.

El Niño’s Impact

One of the reasons why the forecast is calling for a normal to below normal season is that it appears an El Niño event is initiating and forecast to increase in intensity. El Niño refers to a phenomenon that occurs when the ocean surface of the Eastern Pacific Ocean becomes abnormally warm (La Niña refers to the opposite effect, when the Eastern Pacific cools abnormally).

This anomalous warming of the Eastern Pacific leads to all sorts of global climate impacts. Among these is a noticeable decrease in the incidence of Atlantic hurricanes, and an increase in the number of Eastern Pacific hurricanes. In fact, you can see in the same outlook, NHC is calling for a near normal to above normal hurricane season for both the Eastern and Central Pacific. The reason behind this is simple: hurricanes feed on heat to grow, so the warmer the water below a storm, the greater the potential for that storm to grow.

Map of sea surface temperature anomalies as of 6/2/2014
Map of sea surface temperature anomalies as of 6/2/2014

As you can see from the map above, there is a region of abnormally warm sea surface temperatures extending west into the Eastern Pacific from the coast of Ecuador and Peru (yellow & orange). At the same time, there is a large area of much cooler than normal sea surface temperatures extending from the west coast of Africa into the Central Atlantic (light and dark blue). Incidentally, these cool temperatures off the coast of Africa are in a region that is notable for spawning some of the strongest hurricanes, the Cape Verde type hurricane. Clearly, if this temperature anomaly keeps up, it will serve to inhibit the formation of tropical storms and hurricanes in that region.

Increased Pollution in Asia = Stronger Pacific Storms

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pollution in china
Buildings in Lianyungang, China, are shrouded in smog on December 8, 2013. Aerosol pollution from Asia is likely leading to stronger cyclones in the Pacific, more precipitation, and warming temperatures at the North Pole. – National Geographic

A recently published study a by a Texas A&M team led by professor of atmospheric sciences Renyi Zhang points to a possible link between increased air pollution from Asian sources and stronger Pacific storms. There are implications for global climate, including impacts on El Niño. Stronger Pacific storms would lead to increased precipitation in places like the Pacific Northwest.

At its most basic level, the theory behind this study is a fundamental to atmospheric science and is well understood. Water vapor that makes up clouds first need condensation nuclei, such as salt, dust, or in this case, pollutants in order to coalesce around and form clouds. An increase in the number of available condensation nuclei should in theory lead to more robust cloud growth, which allows for more energy to be released into the atmosphere through the latent heat of condensation. This in turn will allow for stronger convective clouds, thunderstorms, and cyclonic storms.

NYC Weather – Spring Climate Outlook – Mar 20, 2014

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Today is the vernal equinox and marks the first day of astronomical spring (because as next week will show, even though it is technically ‘spring’, it won’t feel that way from a weather or climatological perspective).

The equinox denotes the precise date when the sun is directly overhead of the equator at noon. Although it is popularly stated that the equinox is also the date when the length of day and night are equal, this is not necessarily true depending on where you are on the planet. For example, the exact length of daylight for NYC today is 12 hours and 8 minutes, according to astronomical data from Weather Underground. That means the actual equinox for NYC occurred a couple of days ago.

Spring Climate Outlook

This is a good time for us to look ahead towards the forecast climate trends for the United States. Below you’ll see a map showing the Climate Prediction Center’s three-month outlook for both temperature and precipitation. Note that the northern tier of the US is forecast to have anywhere between 33% and 40% chances of a cooler than average spring, while much of the southern and western US is forecast to have between 33% and 50% chances of a warmer than average spring. California in particular is forecast to have 50% chance of warmer than average spring, combined with 33%-40% chance of below normal precipitation, which will be conducive for the persistence of the severe drought in the region.

NYC and the surrounding region is in a zone of equal chances, meaning there’s no strong indication as to whether we’ll have an above, below, or normal spring in terms of both temperature and precipitation.

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NYC Midweek Weather Update – Mar 5, 2014

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Just a quick update on the weather for NYC for the rest of the work week into the weekend. It’s finally going to be a quiet weather week for us after what’s been an cold and snowy February.

Tonight, a slight chance of flurries, and a cold night with fairly good conditions for radiational cooling, lows dropping into the low 20s in the city and teens in the interior. Wind chills in the single digits for Thursday morning.

Thursday – high pressure will prevail and bring sunny skies, but still a cold day with highs in the low 30s. Clouds will increase during the day with another slight chance for snow during the night into Friday morning.

Friday – cloudy with temps warming to the low 40s. As the high pressure center moves offshore, winds will shift to the west.

Saturday – increasingly warm with temps near 50 especially in coastal areas due to a northeast wind off of the relatively warmer ocean waters. A storm system will pass well to our south and east, so no precipitation is expected.

Sunday – slightly cooler with highs in the low 40s and a increasing wind from the north.

Our local NWS forecast office put together a great graphic that shows how this past February stacks up climatologically. Check it out:

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Active Weather Pattern to Bring Relief to Drought Stricken West

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Weather Prediction Center’s medium range forecast

 

Over the past couple of months, exceptional drought conditions have developed over large portions of the western UnitedStates caused by prolonged periods without measurable precipitation. It was not long ago that parts of California were literally on fire.

This past week, West Coast folks finally got some relief as rain and snow fell over portions of the Pacific Northwest and California, including the Cascades and the Sierra. As of today, winter storm warnings and advisories are up for much of the same region. The snow will be critical especially for the Central Valley of California. Annual snowmelt from the Sierra feeds the rivers and streams that farmers depend on to grow the abundant veggies and fruits that we get to enjoy across the nation.

This active weather pattern will continue for the west coast, with another area of low pressure forecast to slide southeast from the northeastern Pacific Ocean by Tuesday (see above). However, the long-term drought outlook still calls for persistence or deterioration. Either way, people out on the west coast are probably happy to see any precipitation.