gfs_ptype_slp_neng_29_!

Significant Nor’Easter becoming increasingly likely next week

Forecast models have come into better agreement in regards to the evolution of a mid and upper level pattern during the upcoming week which will eventually lead to the development of a significant Nor’Easter on Wednesday. Although specific details, in regards to the storms track and intensity (as well as the resulting precipitation type and amounts in our area) remain uncertain, confidence is increasing fairly quickly that the significant storm will in fact develop. This means there is a high likelihood that travel will be significantly impacted by hazardous weather — on the busiest travel day(s) of the year.

While it is too early to speak about precipitation totals, accumulations, and timing, the likelihood of the storm system impacting the area with multiple facets of hazardous weather means that it is prudent to prepare and adjust your travel plans adequately. And, despite the increased confidence in the storm system, the evolution of the pattern and disturbances that are working to develop the storm system remains extremely intricate — with the forecast prone to major changes over the next few days.

How, and why, is the storm forming? 

The potential Nor’Easter finds its origins from three separate mid level disturbances, all originating from the Pacific Jet — but all of them already over the Continental United States as of Sunday morning. By later on Monday into Tuesday, they will be in prime position for forecast model data ingestion and we are anticipating much greater forecast confidence by that time. However, it doesn’t take forecast models to understand a pattern — that’s what meteorologists are for!

The two main pieces which force the development of the storm system are mid level disturbances which are traveling over the top of a East Pacific/West Coast USA ridge. The first drives southward into the Mississippi Valley on Monday, hanging back and slowing down over the Southeast States. The second, trailing disturbance races southeastward through the Plains states on Tuesday and Wednesday before attempting to phase with the initial disturbance.

imageControl.php-3

GFS model showing the mid level evolution which will help develop the NorEaster next week. Notice the two pieces of energy, one over Texas and another coming through the Plains states.

As this occurs, the mid level low on the East Coast of the United States amplifies. The two phasing disturbances help to form a low pressure system off the East Coast, which then travels north/northeastward and strengthens as a result of a favorable mid level jet orientation and the phasing energy.

But, as you can imagine — the intricate details regarding the phasing disturbances leave us with a very low confidence situation. Making matters worse? A third disturbance, over the Great Lakes, tries to phase into the system late in the game on Tuesday into Wednesday as well. Forecast models are struggling to discern between which features will phase, how they will behave, and what the result will be in terms of sensible weather in our area.

What makes you guys think the storm has a chance to impact us?

Typically, our forecasters err on the side of caution when it comes to forecasting impact from low-confidence storms at a 3-5 day lead time. But in this situation, our confidence has increased fairly rapidly that our area will experience at least some sort of impact from the storm. Beginning with the Eastern Pacific/West Coast USA ridge, the pattern in the mid and upper levels throughout the United States becomes quite amplified by Monday.

The multiple disturbances which we discussed earlier slide southeastward to a position in the Mississippi Valley and Southeast States that is fairly classic for the development of East Coast storm systems. And the wavelengths remain supportive of storm development off the coast of North Carolina — a classic spot for Nor’Easters to develop that impact our area.

But perhaps the biggest harbinger of a significant storm is the jet streak at 250-300mb, which shows a classic entrance-region orientation for a significant east coast storm system. In fact, the 210kt jet streak argues for a storm track near the coast, and one that could feature a significant amount of moisture and strengthen fairly impressively off the East Coast near our latitude and near the latitude of New England.

The GFS showing a very favorable 250mb jet streak position for the strengthening of a low pressure system close to the East Coast next week.

The GFS showing a very favorable 250mb jet streak position for the strengthening of a low pressure system close to the East Coast next week.

Obviously, jet streak orientation can change as forecast models continue to iron out the details in the mid and upper level height pattern evolution. But generally, these lend confidence to the fact that the forecast models aren’t totally out to lunch with their idea of a strong storm near the coast — and meteorologically, they tell us that a storm is more likely than not.

What uncertainties do you have moving forward? 

The greatest uncertainties currently stem from the exact track of the storm system, as a result of the exact interactions which occur in the mid levels of the atmosphere. Where the storm tracks, and when/how the mid level disturbances phase, will have a significant impact on the sensible weather that our area experiences. And, making matters worse, forecast models have varying opinions on how this will all shake down.

The GFS (Global Forecast System) for example, thinks the storm system will form as a result of a “psuedo-phase” in the mid levels, and track near the 40/70 Benchmark on Wednesday. We used the term pseudo-phase because the model doesn’t show a full-blown phase in the mid levels. But the storm strengthens and brings significant precipitation, while drawing in enough cold air to make a lot of that precipitation snow in our area. In this scenario, significant snow accumulations would be possible throughout much of the area on Wednesday into Thanksgiving morning — with major travel impacts.

GFS model showing the 700mb relative humidity and vertical velocity (dashed lines). This is a classic depiction for a snowstorm from a Nor'Easter in our area.

GFS model showing the 700mb relative humidity and vertical velocity (dashed lines). This is a classic depiction for a snowstorm from a Nor’Easter in our area.

Conversely, the ECMWF (European model) has a much different scenario. On the Euro, the mid level disturbances phase — and do so strongly and completely. As a result, the low pressure system is much stronger and it tucked in very close to the East Coast. In fact, the Euro takes the center of low pressure over Eastern Long Island on Wednesday Night!

This would lead to a much different situation in our area. Precipitation would start as snow, but would then changeover to rain near the coast and in the suburbs. Some accumulating snow would still be likely in the suburbs of NYC. But heavy snow would fall over much of the interior from Northwest NJ to Southeast New York — with significant accumulations possible there. In the city and near the coast, the heaviest precipitation would fall as rain.

What scenario do you favor currently? 

Our current idea is that the storm is more likely to track closer to the coast than not. Our confidence, however, is low. In addition to the aforementioned ideas (jet streak, phasing) contributing to our thoughts — one also must consider the lack of any high latitude blocking in this mid and upper level setup. High latitude blocking can serve to put a “cap” on how far west, or amplified, a storm can get on the East Coast.

Without any blocking, a phased system can tuck in close to the coast, and bring warmer air with it. Although we don’t currently favor widespread significant/major snowfall — the probabilities of significant accumulating snow is highest in the Interior of Northern NJ (higher elevations, as well), Southeast New York and Eastern Pennsylvania. Significant snowfall is also looking likely in the interior areas of Northeast PA and New England.

Our confidence, still, is increasing that at least a few inches of accumulating snow will fall in most of New Jersey and New York City. The most important aspect of our forecast is that our confidence is high that travel will be impacted, probably significantly, by this storm system. Over the next few days, we encourage you to stay tuned for additional information including timing updates, snowfall forecasts, and watch/warning information so that you can better plan on how to adjust your travel.

Comments

comments