Cold, blustery weather to close out 2012

NAM model forecasting very cold temperatures at 850mb (purple is -10 F and below) in the Northeast Tuesday Night.

NAM model showing very cold temperatures at 850mb (purple is -10 F and below) in the Northeast Tuesday Night.

It has been a bit of a wild weather year. Alright, that might be putting it lightly. It has been a wild, wild weather year. Our area has experienced some extremely strong, damaging storm systems with tremendous variance in weather over short periods of time. After making it through a snowstorm just a few days ago with only light snowfall accumulations (the bigger totals were relegated to New England), we’ll be able to end the year on a relatively calm, quiet note. The pattern in the wake of the storm system will feature colder than normal weather and some blustery winds, but for the most part doesn’t look to feature any strong storms or high precipitation events for the next week or so.

GFS model forecast 500mb height anomalies at 120 hours from 12/30/12 (Valid 1/4/12)

GFS model forecast 500mb height anomalies at 120 hours from 12/30/12 (Valid 1/4/12)

The main culprit will be a developing ridge out west, in tandem with a Polar Vortex to our north over Southeast Canada and extending into the Northwest Atlantic. The image to your left (GFS Ensemble 500mb height anomalies valid Friday 1/4/13) displays the pattern which models suggest will be in place for the near future. West coast ridge (+PNA), East coast trough and plenty of cold air in Southeast Canada.  At first glance, you might think the pattern could be favorable for cold (which it is) and potentially snow on parts of the East Coast and Northeast including the NYC Area. However, the main trough will remain in the Northwest Atlantic…which means that pieces of energy/atmospheric disturbances will race through our area…but won’t amplify and develop any storm systems until they are far off to our east. So, while there will be continued shots of cold air and the potential for light snow/snow showers at times…significant precipitation will avoid our area barring any unforeseen changes to the general pattern.

Here’s the forecast for the next few days, but you can check out the long range details through Day 7 in our Forecast Brief and Forecast Discussion. We wish you all a happy and healthy New Year!

Monday: Partly sunny, blustery. West winds continue gusting near 20 miles per hour at times, but won’t be nearly as strong as they were on Sunday.

New Years Eve (Monday Night/Tuesday Morning): Partly cloudy and cold with temperatures falling into the 20’s and low 30’s. A slight chance of snow showers throughout the area. No accumulation expected. Occasionally blustery winds.

Tuesday: Partly cloudy, a bit warmer with high temperatures in the 30’s to near 40 in urban locations and places near the coast. Blustery west winds continue especially during the afternoon.

Post-mortem on recent storm

If we’re looking at this like a medical disorder, we can examine the symptoms and the root of the problem with this storm.

The symptoms of the illness were the following:

1) Progressive, unorganized trough, in which some of the H5 vort energy ran out ahead of the energy rounding the base of the trough. As a result, the energy couldn’t congeal and acquire a negative tilt. Instead, the lead H5 vort energy remained fairly neutral tilted which screams fast-moving, late developing coastal low. These tend to favor eastern New England due to longitude help.

2) The progressive unorganized H5 energy within the trough and lack of neg tilt caused an energy transfer that was too little too late for us. The 925MB low was still transfering from PA as precip was wrapping up in NJ. This is no good. When I looked at 925 winds yesterday around 1pm, and they were still SELY into PA, I knew we were dead in the water. You simply can’t have any warm tongue contamination from the sfc-850mb in thr NYC/coast. It’s a reason why the interior has a higher avg snowfall than us. We need more stars to align for a SECS event. Some people elsewhere were talking about how 850’s were conducive for all snow, but this event was a perfect example of why short term soundings are important, especially in energy transfers, there’s bound to be p-type problems on the coastal plain.

Tracing the symptoms back to the ultimate illness…

A) The trough on the West Coast kept wavelengths rather short, and the central Plains mid level ridge was too far east of the ideal Boise ID position for an amplified/neg tilted nor’easter on the east coast. The trough there did teleconnect to a fast moving / progressive, late developer for the Northeast coast. The lack of a decent PNA ridge definitely hurt us, as more amplification in the Western US would have resulted in a slower downstream pattern, meaning a deeper / more amplified trough, more organized H5 energy, and thus a higher likelihood for negative tilting and bombing on the mid atlantic coast.

We’ve seen winters with snowy with a -PNA overall but it makes sense meteorologically that you would want a ridge in the Western US in order to get a deep trough and bombogenesis on the East Coast. Low amplitude or non existant Western ridging results mostly in SWF events, and late bloomers, favoring eastern New England due to longitude once again. A stronger -NAO probably would have helped slow the pattern down but we didn’t have that either.

Ultimately it’s the progressive nature of the pattern that killed us here, and that’s largely due to the upstream lack of ridging on the West Coast, which will be fixed in the coming days as the PNA spikes. Problem now is the polar vortex in SE Canada might crush everything south of us.

Light to moderate snowfall expected area-wide Saturday

NAM model showing snow overspreading the area beginning Saturday morning. Notice warmer temperatures causing a changeover to rain near the coast, but moderate snow continuing across much of the area with the storm still offshore.

NAM model showing snow overspreading the area beginning Saturday morning. Notice warmer temperatures causing a changeover to rain near the coast, but moderate snow continuing across much of the area with the storm still offshore.

Forecast models have come into better agreement on the track and intensity of a storm system, which will pass offshore this Saturday afternoon. A disturbance in the mid levels of the atmosphere will pass from the Mississippi Valley off the east coast, while a second disturbance swings down from Canada and eventually phases with it. As the phase occurs, a strengthening surface low will develop off the coast of New Jersey. Finally, the surface low will swing northeastward to a position southeast of Cape Cod by early Sunday morning.

For the most part, this forecast remains unchanged since the last update. However, with the storm now less than 24 hours away (around 12 hours from start time), we’ll break down the timing and snowfall amounts in an attempt to simplify the storm system for all.

Timing: Light to moderate snow is expected to overspread the area beginning early Saturday from southwest to northeast. The snow could be light at times, especially early on. More moderate snow is expected over Western NJ and Southwest NJ initially, while lighter precipitation rates will continue farther to the northeast. By Saturday afternoon, moderate snow is expected area-wide, and snow may even taper off for a time across western zones as the best forcing for precipitation transfers to the coastal storm. Saturday evening, moderate snow is expected to continue, especially across NJ, Southeast NY, and CT. There is the potential for snow to mix with or change to rain along the area beaches, the south shore of Long Island, and Southern New Jersey. Finally, by late Saturday evening, snow will begin to taper off from west to east.

stormtotalsnow_dec2812Snowfall Totals: Our latest snowfall map, attached to the left, details the expected accumulations in graphical form. Generally, 2 to 5 inches of snow is expected throughout the entire area, but these amounts will obviously vary depending upon location. The broad 2 to 5 area encompasses much of Northern New Jersey, Southeast New York, and Connecticut. Amounts near the higher end of this scale, with isolated totals near 6 inches, are most likely from Northeast NJ into Connecticut and Southeast Southern New England. Lower amounts, kept down by warmer temperatures and a potential change to rain, are expected near the shores and Southern New Jersey.

Hazards: This is expected to be a light to moderate snowfall event, of low to moderate impact. No strong winds are expected, and the snow will gradually accumulate leaving crews plenty of time to treat/clean the roads. Although the roads will be slippery and icy, widespread travel delays and accidents are not currently anticipated. Nevertheless, exercise extreme caution when driving through snow. Moderate to occasionally heavy snow is possible at times — so be careful if you are traveling.

Technical: Please view our forthcoming evening Forecast Discussion (left side menu) for information regarding potential precipitation shadowing and concerns regarding h85/h7 mid level centers as well as compact cold conveyor belt development. This discussion details our reasoning behind the snowfall forecast.

As usual, we encourage you to stay tuned for the latest on the storm system. We’ll be posting up to the minute details on Facebook and Twitter.

Active pattern continues, potential snowstorm looms this weekend

European forecast model forecast a significant low pressure system off the NJ Coast on Saturday evening. If the storm develops, it could bring snow to much of the area.

European forecast model forecast a significant low pressure system off the NJ Coast on Saturday evening. If the storm develops, it could bring snow to much of the area.

While a powerful storm was ongoing throughout the New York City area this Thursday Morning, medium to long range meteorologists were forced to also watch the latest modeling data for an upcoming system this weekend — one which could potentially bring a snowstorm to much of the area. A strong disturbance in the mid levels of the atmosphere will make its way towards the Mississippi Valley by the end of the week, while a second piece of energy from the northern jet stream begins to move southeast from Canada into the Ohio Valley. Forecast models are struggling with the interaction between these two features — and the exact details of how they interact will determine what occurs. We’ve laid out the scenarios below:

Scenario 1: Should the two pieces of energy interact (or “phase”), a strong surface low would likely develop off the Mid Atlantic and Northeast Coasts Saturday into Sunday. A rapidly developing cyclone would then bring the potential for moderate snows across most of New Jersey, New York, and Connecticut with the potential for heavier snows near the coast and on Long Island.

Scenario 2: If the two pieces of energy don’t interact, or do so later or in an unorganized fashion, a weaker storm system will likely develop. The later developing, weaker system will save the area from a strong storm system and heavy precipitation. Instead, light snow would be possible in many locations as the storm system passes by and then strengthens well off to our northeast.

The trend on the forecast guidance, over the last 24 to 36 hours, has been stronger and farther west as a result of more phasing between the two features and a better initial setup (including a stronger/more organized initial shortwave and trough and more robust northern stream shortwave). We’ll be watching carefully over the next day or so — and in that time we should begin to get more answers to the questions we have regarding this storm going forward. We’ll be keeping you updated along the way.