Complex Forecast: Plowable Snow Likely Tomorrow

8 02 2016

Hi all, hope everyone had a nice weekend. A complex and extremely difficult to forecast inverted trough will form tomorrow, creating snowy conditions tomorrow afternoon into Wednesday morning.

The setup:

As of Monday morning, an extremely powerful low pressure system is moving up the coast, affecting areas of New England. As this low pressure moves away, a clipper will enter the area late tonight and transfer it’s energy off the coast. As this transfer occurs, a rare phenomenon known as the Norlun Trough will form. The trough is an interaction between the weakening low pressure in Ohio and western PA and the strengthening one off the coast. The North American Model depicts this interaction in the 500mb image below:

nam_rapid-hgtprs--conus-33-C-001.pngReferring to the image above, the Norlun Trough will likely setup somewhere along the turquoise arrow I drew to illustrate the interaction between the lows.

Forecasting the Trough:

I will be completely honest here: the Norlun Trough is a forecaster’s nightmare. The models have been historically bad at determining the location of the trough, since we still do not completely understand the atmospheric factors that drive the transfer of energy between the low pressures. That being said, from the data and information I have, it is looking likely that the trough will setup a little south of Philadelphia.

Screen Shot 2016-02-08 at 11.13.27 AM.pngThe NAM 4KM is one of the better short range simulated radar models. As you can see in the above image, the trough parks itself over the area for a prolonged period of time tomorrow evening into early Wednesday morning. Even though the event is a little over 24 hours away, there is still lots of uncertainty to where the trough will setup. If the interaction occurs 100 miles south or north, no snow would fall in Philadelphia.

My forecast: 

For areas north of the city, less snow will fall: 2-4 inches

For areas West and South of the city, more substantial snowfall is likely: 4-8 inches

There will also be banding during this storm, meaning that there might be places that receive locally higher amounts in excess of 8 inches.

Stay tuned for updates.

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Final Forecast for the January Blizzard of 2016

22 01 2016

A major blizzard will affect most of the Eastern seaboard starting tonight into Sunday morning. This storm will rival the 1996 blizzard in terms of intensity and snow totals. Blizzard warnings have been posted by the national weather service for many areas, including Washington DC, Baltimore, Philadelphia, and New York City. This blog post will overview the storm in three sections: snow and timing, wind, and recommendations.

Snow:

Currently, our storm is gaining strength in the southeast. Snow is currently falling in Virginia, Tennessee, and Kentucky. The low pressure is moving northeast and will exit off the Atlantic coast sometime Saturday morning. Light snowfall should start at around 10 PM tonight and progressively become heavier by Saturday morning. The image below of the 4K NAM shows steady snow moving into the region late tonight and early Saturday morning. Screen Shot 2016-01-22 at 9.22.24 AM.pngAs the low pressure moves off of the coast, it will strengthen further and the the wind and snow will pick up during the day on Saturday. Snowfall rates of 1-2 inches an hour are very likely from 10 AM to 6 PM on Saturday as the storm moves into open water. The 4k NAM image below shows the snow in the area becoming heavy tomorrow morning:

Screen Shot 2016-01-22 at 9.24.16 AM.png

As we head through the day Saturday, a lull is likely as the storm’s initial precipitation shield moves off the coast. This lull will occur during the afternoon or early evening on Saturday. By nighttime, the snow will pickup again and blizzard conditions will prevail until early Sunday morning.

Screen Shot 2016-01-22 at 9.37.43 AM.pngBy Sunday morning, the snow should slow down and eventually end from west to east.

Totals: 

Forecast models have projected snowfall totals ranging from 1 foot to over 2 feet. My forecasted totals are a blend of multiple models and are shown below:

 

Screen Shot 2016-01-22 at 11.01.48 AM.png

As the snow map shows, we are in for a snowstorm of historic proportions. Areas in Virginia and Maryland will receive the most snow, with some totals approach 3 feet! Our area will likely see totals 1-2 feet with locally higher amounts.

Wind:

Heavy snow is not the only factor of this storm. As the storm moves offshore, it will strengthen and bring in strong winds from the northeast (that’s why they call it a nor’easter). These winds will be strong, cold, and straight out brutal. At the peak of the storm, winds will be 20-25 mph with gusts up to 40. Along with the snow, it will create whiteout conditions on Saturday and Saturday night. Visibilities will be almost 0 and temperatures in the upper 20s. Additionally, there will be blowing and drifting snow, which will make it extremely difficult to clear the roads on Sunday.

nam_rapid---usne-30-C-10mwindarrows_white.pngRecommendations:

Please do not drive during this storm. With visibilities extremely low and heavy snow falling, travel will be nearly impossible on Saturday and even into Sunday. If you go outside during the storm, wear layers and make sure any exposed skin is covered. Travel will likely be limited into Monday as drifting snow and refreeze will cause issues early into next week.

Thanks all and don’t hesitate to comment with questions or concerns!

 





We’re Back! Analysis of the Upcoming Nor’easter

19 01 2016

Hey everyone! I apologize for the scant number of posts during the past 9 months (zero as a matter of fact!), but Philaburbia is back for the rest of the winter season.

With a strong El Niño present, it’s been a very warm winter so far, with temperatures in Philadelphia running 13.7 degrees above normal in December. So far in January we are running around 2 degrees above normal. However, with El Niño beginning to weaken (see below) and arctic air starting to creep in, we are in for a stormy and colder February and March.

nino34Sea

Ocean Temperatures:

It’s been a very quiet winter so far with no major coastal system running up the coast. This, however, will change Friday and Saturday as a coastal system with abundant moisture will strengthen off of the Atlantic coast. I’ve explained to friends and colleagues, our warm December and January has resulted in extremely warm ocean temperatures off the coast. With warmer ocean temperatures, a low pressure system can strengthen quicker through sources of evaporation (this is why we primarily see hurricanes during the summer months, when the oceans are warm). As you can see from the map below, ocean temperatures have been nearly 3 degrees above normal:

atl_anom

Teleconnections:

Additionally, projected teleconnections have signaled the likelihood of a large disturbance. Both the NAO and AO (atlantic and arctic oscillations) are both headed toward a neutral position, with the AO doing so rapidly, following the storm.

Atmospheric Setup: 

The atmospheric setup is also favorable in the days leading up to the storm. All models are projecting a Canadian high moving in to provide cold air aloft while the low pressure moves into a benchmark position off the coast. Where the uncertainty lies so far is the location of the storm formation in the southeast. This aspect of forecasting is extremely difficult, since we do not possess the instruments necessarily to accurately predict the location of storm initialization. This brings us to our two scenarios:

Two Scenarios:

  1. GFS, Canadian: Storm moves exits coast at Virginia, follows up the benchmark and stays close to the coast. In this scenario, areas in Maryland would receive the most snow with other areas like Philly, NYC, and Boston all receiving over a foot of snow as well. This solution is shown below:

gfs---conus-90-C-mslpthkpcp_white

2. EUROPEAN: Instead of exiting the coast off of Virginia, the storm will slide further south and strengthen more quickly than anticipated before moving Northeast, away from land. While this scenario still projects a strong nor’easter, most of the heavy precipitation will be located off the coast. In the Philadelphia region, we would still receive a plowable snowfall, but nothing close to the 1-2 feet projected in scenario 1. The european is pictured below, courtesy of Accuweather:

ecmwfued---conus-108-C-mslpthkpcp6_white.png

Timing:

For both scenarios, the timing will be from Friday night into early Sunday morning. The major snowfall will occur during the day on Saturday. If scenario 1 plays out, we could see a prolonged period of 1-2 inch/hour snowfall rates Saturday afternoon. By midnight on Sunday, most of the snow should be finished with some scattered snow showers moving out by 3 AM on Sunday.

Regardless of which scenario is correct, this storm will be disruptive. I would advise against traveling at all from Friday night to Sunday morning until roads are cleared.

More updates coming with a final forecast on Thursday. It’s nice to be back.





Winter’s Last Stand: Significant Snowstorm on its Way

4 03 2015

Winter 2014-2015 will be ending with a bang.

I am currently tracking a disturbance associated with a stalled front which will pass through the region tonight into tomorrow. This system will be moisture-rich and will have plenty of cold air associated with it. While the event is less than 24 hours away, there is still some uncertainty concerning where the front will stall. If it stations itself further south, this means less snow for areas around I-95 and more snow for South Jersey and Delaware. If the front stalls further north, more of the Delaware Valley will receive significant snows.

The timeline of this storm will also be prolonged. Throughout the day today, it will be rainy and “warm”. As the front progresses south, temperatures will slowly fall to freezing. At this point, the rain should change to snow. The snow should start to fall by 1 AM tonight and continue throughout the day tomorrow until slowing down and ending by around 6-7 PM. Since snow will be falling for an extended period, totals will be significant.

GFS Model 8 AM Thursday

GFS Model 8 AM Thursday

Many models are projecting a general 6-9 inches falling for the immediate suburbs with slightly higher totals possible in South Jersey. The effects on the roads will be serious tonight and tomorrow. I would strongly recommend against driving tomorrow unless it is absolutely necessary.

Snow Map for Early March Snowstorm

Snow Map for Early March Snowstorm

That said, the snow will not last long after the storm ends. The March sun angle (equivalent to late September at this point) will quickly melt the snow. Roads should be fine by Friday and most of the snow could be melted by the end of next week.

A note about February: February was one of the coldest months we have seen on record. In Philadelphia temperatures were 10 degrees below normal. The last time we hit a high temperature above normal was on February 8th when we reached 51 degrees! The brutal February pattern should regress as we head into March, but will likely not completely disappear if long-range models are correct. Overall, I expect March to be around 3-4 degrees below normal, which is still an improvement over February.

Until next time…





48 Hours of Snow Coming! Forecasting the Nor’easter on Tuesday

25 01 2015

It is going to be an extremely eventful next 72 hours for the region and the northeast as a whole.

As a mentioned in my last post, a small clipper system will pass through the area late tonight and tomorrow. This storm has the stereotypical features of a clipper: plenty of cold air, fluffy snow, a general 2-4 inches for most. Precipitation will start falling late tonight and continue throughout the day tomorrow.

NAM Model Monday

NAM Model Monday

At this point, the situation gets complicated. After the clipper exits the coast, it will interact with a weak disturbance off the Atlantic coast and strengthen rapidly into a nor’easter. Plenty of moisture will be fed into the storm from the ocean, and plenty of cold air will be present as well. The question that remains is where and when this storm will strengthen. Models have been a little inconsistent with the timing of the phase and where it will occur. The further west the storm phases, the more snow we will receive in the Philadelphia area. In New York City and Boston, blizzard conditions will be likely.

Model Analysis:

European: The European has been the aggressive model for this storm. Most of the solutions it shows bring the storm close to the coast and drop 10-15 inches of snow with totals higher in New Jersey and areas closer to New York.

European Model

European Model

GFS: The GFS model has been the more conservative model, showing a slower phase further east than the European. It’s latest runs have been having convective feedback issues, however, which means it’s solution may not be accurate. Until these issues are resolved, I will not be favoring this model when making my forecast.

NAM: The North American Model is the middle ground between the two previous ones. It is projecting 8-12 inches falling by Wednesday morning. I am favoring this model the most out of the three because of its increased accuracy in the short run.

NAM Model

NAM Model

Timing :

12 AM-6 AM Monday: Snow will start west to east

6 AM- 6 PM Monday: Snow accumulating a general 2-4 inches during the day

6 PM Monday- 2 AM Tuesday: Light Snow as storm strengthens off of coast

2 AM – 5 PM Tuesday: Snow. Heavy at times. Accumulating 5-8 inches (or more depending on location of storm off coast)

5 PM Tuesday – 3 AM Wednesday: More snow, eventually tapering off late night on Tuesday

The official Forecast:

While the clipper forecast is fairly straight forward, the following nor’easter involves many dynamic components which need to be ideal for a major snowstorm to occur in the Delaware Valley. Even though these conditions are favorable, there is still some uncertainty in the exact amount of snow we will receive by Wednesday morning. Temperatures will be in mid-20s, which means a light fluffy snow will fall. These low temperatures also increase the snow to precipitation ratio, which means snow will accumulate faster than normal.

The snow map below shows totals from the clipper and the nor’easter combined. Depending on the formation of the low off the coast, the 10-14″ area is subject to shift in the next day or two. Overall, 6-10″ inches is good bet for the city and areas south and west. Totals will be higher closer to NYC and even higher near Boston, where blizzard conditions will likely occur.

Snow Map for the One Two Punch

Snow Map for the One Two Punch

Effects on travel will be significant on Monday and Tuesday. Businesses and schools will be shutdown on Tuesday, and I wouldn’t count out some cancellations on Monday as well. Stay off the roads and be safe. More

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updates coming.





Messy Saturday Coming. Snowy Monday as Well?

23 01 2015

Hey everyone. Quick post here.

We are looking at a very messy and slushy overnight and Saturday as a large storm system will ride the coast in the next 12-24 hours. While I was wrong with my initial thoughts of a plowable snow event, I was correct when I said there is just not enough cold air aloft to produce snow.

NAM Saturday Morning

NAM Saturday Morning

The precipitation will start in the next few hours and continue throughout the day tomorrow. Snow totals will likely be around 2-4 inches north of Philadelphia and 1-2 inches to the south. Precipitation will initially start as snow then switch over to rain sometime tomorrow morning before changing back to snow by tomorrow afternoon. The storm should be over by tomorrow night.

NAM Saturday Evening

NAM Saturday Evening

I am also tracking a clipper system which will ride through the area on Monday. Many of the models are keeping the storm suppressed to the south at this point, which would mean lower totals for the region. Regardless of the amount of snow, travel conditions on Monday will not be ideal. I would not rule out school cancellations and numerous travel delays. I will go more into detail for this storm in the coming day or two.

Euro Monday Morning

Euro Monday Morning

Other than that, drive slow tomorrow and enjoy the slushy mess!





Taking a Closer Look at the Upcoming Winter Storm on Saturday

21 01 2015

Hey everyone. It has been quite a while since my last post. Winter 2014-2015 has been fairly quiet and cold so far. According to reports, we have only received 1-2 inches of snow so far this winter. This is much lower than what we had at this time last year.

Temperatures this winter have been around average so far. December finished 4 degrees above normal, while January has been nearly 3 degrees below normal. This contradicts my original forecast, where I said January would be warmer than December. An explanation for this flip in temperatures lies in the El Niño strength over the past couple months. The Niño we’re currently experiencing decreased from December into January, this indicates why our temperatures have been colder in January compared.

Current El Nino

Current El Nino

In current news, I am currently tracking a winter storm during the day on Saturday. Analytical indicators have been favoring a large storm streaming up from the Gulf of Mexico and intensifying off of the Mid-Atlantic coast. While the setup for this storm is not perfect, I do believe a plowable amount of snow will fall north and west of Philadelphia.

The Setup

Current models have been showing less than ideal conditions for a major east coast snowstorm. The most major flaw in the pattern right now is the lack of a “Quebec high”, which tends to bring frigid Canadian air down and feed the cold side of the storm. There is also no indication of strong blocking ahead of the storm, which means that there is a chance that it could quickly run east of the benchmark. This ultimately means that we could have some mixing with this storm as well as a sharp cutoff in the amount of precipitation north and west of the city.

Let’s look at some of the models:

The European and North American Model (NAM) have been aggressive with the amount of moisture associated with the storm. They also forecast the storm further west than some of the other models. With both models, however, mixing will be an issue south and east of the city. While snow totals could be around 6-8 inches for Philadelphia north, in South Jersey snow totals may be limited to 2-3 inches at the most. This mixing issue, as I alluded to earlier, is from the lack of the Canadian high providing cold air for the strengthening storm.

European Major Snowstorm

European Major Snowstorm

The GFS model has been possibly underestimating the strength of the storm. As a result, it brings the track further out to sea, which diminishes snow totals throughout the region. A general 2-4 inches would be expected if the GFS solution was the correct one.

GFS Model

GFS Model

At this point, I am leaning toward the Euro and NAM solutions. The reason for this lies in the Arctic Oscillation teleconnection, which is one of the main indicators I use to determine the strength of a storm. As you can see from the graph below, the AO is projected to sharply become positive a day after our storm pulls through. Any time this happens, it tends to indicate a change in the upper atmosphere in the arctic circle, possibly caused by a major storm system. This metric has increased my confidence for a larger and stronger storm on Saturday.

Arctic Oscillation

Arctic Oscillation

I will have more updates as we get closer to Saturday. I will release my snow map Friday night.

Thanks everyone!








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