March Nor’easter: Round 3??

Sunday Update:

Following days of model uncertainty, a consensus solution as finally been reached. At this point, it appears that the system will phase off the NC coast and strengthen 200 miles off the coast. With this solution, New England, including Boston, could receive over a foot of snow in areas. Philadelphia will likely only see a brief period of light snow on Monday before clearing Monday night. Little to no accumulation is expected.

Original Post

A third March nor’easter could impact our area Monday or Tuesday. However, the forecasting for this storm has been impossibly hard to nail down. The models have done a poor job handling this system, and it’s leaving meteorologists struggling to find an answer to this crucial question: will there be another March snowstorm in the Northeastern US?

First off, this post will NOT be a final forecast for this storm. There is too much uncertainty at this point and delivering a premature prediction is both reckless and shortsighted. Instead, I will focus on the meteorological factors at play and what’s necessary for this storm to become a significant nor’easter.

The Track

Later today, a small disturbance will form along the jet stream in northern Texas. As this low-pressure system moves east, it will interact with moisture from the Gulf of Mexico, strengthening and bringing severe thunderstorms to the southeastern states. Simultaneously, another disturbance in the Dakotas will flow down through the Midwest, bringing snow and rain to Iowa and Missouri:


As these systems move closer together, they will begin to interact, or phase:


This is where things get complicated. The models are having trouble predicting where and when this phase will occur. The NAM and GFS models have shown an earlier phase and amplifying the storm off the Atlantic coast. The first map below shows the NAM’s solution, which is a full phase off of the North Carolina coast. Once the storm heads over the Atlantic, it will move northeast and strengthen, bringing light snows to the coastal mid-Atlantic and heavier snowfall in New England.


The second map shows the GFS’ solution, which is also a full phase off of the NC coastline. The GFS, however, is having issues figuring out where to place the low once it’s in open water:


The map below shows the GFS feedback issue:

gfs_ptype_thick_east2_11 (1).png

While the GFS and NAM models show a phase into a nor’easter, the European model has consistently been showing a very late and southern phase, forcing the storm out to sea. This solution is very probable, with other models such as the UK and the Canadian consenting with the Euro’s track and timing.


The Situation

What I just outlined is the situation for this storm. There are three possible outcomes this storm could take:

  1. The Outlier Scenario: The northern and southern streams phase early, the storm strengthens and feeds cold air into the western side of the storm. This situation would create a significant nor’easter for the eastern seaboard with substantial snow totals from DC to Boston.
  2. GFS and NAM Scenario: The northern and southern streams phase later, but still close to the coast. The storm strengthens, but only enough to bring significant snows to New England and Atlantic Canada.
  3. The Foreign Scenario: The phase occurs very late, and the storm goes out to sea. Impacts from this scenario will be negligible apart from some high surf along the coast.

Based on what I’ve seen so far, the most likely scenario right now is #2. But, as we’ve seen before, weather is unpredictable, and things can change on a dime. That being said, please stay tuned to your local forecasts this weekend as a major nor’easter is still possible Monday or Tuesday. I will report any forecast updates at the top of this post later today or tomorrow.

Thanks, everyone!

High Impact Nor’easter: Round Two

This has been quite a pattern. Last Friday’s nor’easter had distinctive characteristics of a hurricane (see image below) with wind gusts of 60-70 mph across the Northeast. Millions of households lost power, and many remain in the dark. It could take weeks for crews to fully clear damage from fallen trees and power lines.28424504_1824455037855522_7931296027992448302_o.jpgSnow totals were significant in upstate NY, with some areas receiving over 30 inches of snow! In the Delaware Valley, totals were very isolated: Bryn Mawr received 9.5 inches of snow, but Wynnewood (4 miles away) reported only 4 inches and Philadelphia 3 inches. Boston experienced historic storm surge, and hurricane force winds were reported in Washington DC. After a historic storm like this, most people do not expect additional threats for at least a few weeks. Unfortunately, mother nature is relentless and an active pattern will provide at least two more nor’easter threats over the next week. Strap in, because it’ll be a wild ride into mid-March.

Nor’easter: Round Two

Only five days following the historic nor’easter last Friday, another coastal system will impact the Northeast with heavy snow and winds. While the meteorological setup is fairly similar to last week’s storm, there are a few differences. This system will move faster than the last one and will not produce the magnitude of wind we saw last week. There will also be more cold air in place as the nor’easter begins to strengthen. As a result, snow will be the primary precipitation type for our region (except for areas on the NJ coast). This combination of cold air and a strengthening coastal low-pressure system is a classic recipe for a major northeast US snowstorm.

Track and Timing

As with most nor’easters, the most prominent challenge for forecasters is determining the track. Currently, models are in decent agreement, with most showing a transfer of energy from a system moving east across the Ohio River Valley to a coastal disturbance off the Virginia coast. From there, the storm will begin to intensify and move northward, coming 50-100 miles from the NJ coastline:


The storm will continue to strengthen as it moves northeast, moving out toward Maine reasonably quickly:


From start to finish, this will be close to an 18-hour event, with the most intense precipitation falling from 7 AM Wednesday to 4 PM Wednesday. Snowfall rates will reach 1-2 inches per hour during this period, and winds will gust to 40-45 mph. The overall timing will look like this:

  • 10 PM Tuesday – 12 AM Wednesday: Light snow begins from South to North, mixing south of the Delaware River.
  • 12 AM Wednesday – 7 AM Wednesday: Light to moderate snow continues, accumulating 1-3 inches by daybreak on Wednesday.
  • 7 AM Wednesday – 4 PM Wednesday: Heavy snow moves in as storm intensifies, winds could reach 40-45 mph with visibilities near 0 at times.
  • 4 PM Wednesday – 8 PM Wednesday: Snow moves out south to north. Precipitation will end everywhere by 10 PM on Wednesday.

Final Snow Totals

This storm will bring significant snowfall accumulations to the I-95 corridor. While mixing concerns remain for areas south and east of the city, snow totals could be crippling in regions that stay all snow.

From a liquid equivalent perspective, forecast models have been showing 1.25-1.50 inches of “rainfall equivalent” falling from this storm:

nam_60hr_precip_ma_27 (1).png

Taking into account a 10:1 snow to rain ratio, this would calculate to a 12-15 inch snowfall in areas north of the city:


With this particular storm, however, the snow will be heavy, wet, and therefore, less fluffy. This will bring down snow-to-rain ratios to around 7-8:1, calculating to maximum 10-13 inch accumulations. Note that maximum is bolded; banding tends to occur during storms like these, creating isolated areas of maximum snowfall with most people reverting to the mean. Taking this into account, below is my official snowfall forecast:

North and Western Suburbs (Bucks, Montco, Chester County, Central NJ): 8-12 inches with isolated totals of 14+ inches. 

Philadelphia and immediate suburbs (Delco, Mercer Co., South Jersey): 4-8 inches, with pockets of 12+

Coastal Areas: 2-4 inches (mixing will suppress totals in areas close to the coast) 

Final Thoughts

With heavy snow and strong winds, travel will be nearly impossible on Wednesday. Only drive if you absolutely have to; it’s not worth risking being stranded or hurt in a storm like this. Stay safe and enjoy the snow!

In a few days, I will likely be posting about Nor’easter Round Three, which looks like it will occur Sunday into Monday of next week.




Significant Nor’easter Bringing Heavy Wind, Rain, Snow, and Storm Surge to the Northeast

This one is a doozy.

A low-pressure system originating in the Southwest is moving across the country tonight and will travel east before combining with a northern stream of energy and amplifying off of the Atlantic coast tomorrow evening. The pattern has been set with strong blocking high pressures in Quebec and Ontario, literally “blocking” the storm and allowing it to intensify quickly while remaining almost stationary. The following two maps show the phase of upper atmospheric vorticities beginning early Friday morning and completing by Friday afternoon:




The meteorological effects of this setup are extreme: high winds, significant storm surge, and heavy precipitation for an extended period. To provide complete coverage of this upcoming nor’easter, the post will be split into sections beginning with track and timing, then discussing the wind, storm surge, and precipitation impacts.


As I alluded to in the intro, the current atmospheric setup is prime for a massive, slow-moving coastal storm. As it moves off the coast, the storm will intensify and slowly travel northeast. The system will then slow down as it’s blocked by strong Canadian areas of high pressure to the north. This is where the forecast becomes difficult. Models are having a tough time tracking the storm and where the heaviest precipitation will fall. Precipitation type forecasting has been challenging as well, with warm surface temperatures during the onset of the storm, but dynamic cooling occurring as the storm strengthens. The maps below show the blocking, track, and strength of the nor’easter as it moves slowly eastward:


By Friday night, we have a full-fledged nor’easter on our hands:


Precipitation Type and Timing

Precipitation will start Thursday night initially as rain. Temperatures will be in the 50s, but will rapidly fall overnight Thursday into Friday morning. We will experience a short lull on Friday morning as the storm begins to gather strength. Round 2 will start by the afternoon as rain, then changing to snow reasonably quickly from north to south. By Friday evening, most of our region will experience accumulating snow accompanied by 50-60 mph wind gusts.


Precipitation should end early Saturday morning as the storm moves further off the coast. Based on forecast models and data, 2-4 inches of heavy snow could be on the ground by Saturday morning, with higher totals north of I-95, and lower ones closer to the coast. It is important to note that elevation could also play a key role in final snow totals, as surface temperatures could remain above freezing in areas near sea level.


The map below shows final snow predictions from the NAM model (note that these are overstated because of a 10:1 snow/rain ratio assumption; a 6:1 ratio is more likely with this storm):



The sheer strength of this storm will create powerful wind and wind gusts on Friday. Sustained winds will reach 30-35 mph with gusts of up to 60 mph in some places. Winds will be even higher along the Jersey shore. Damage will be significant, especially with wet soil and trees weighed down by heavy snow. Expect widespread power outages by Friday night, especially in rural areas.


Storm Surge

A combination of high tide and a coastal storm is never a good combination for coastal regions. Major storm surge will occur, especially in New England, with waters rising over 4 feet from normal high tide levels in Massachusetts. The NJ coastline will likely experience a storm surge of 2-3 feet, which will cause some coastal flooding during the height of the storm.

Concluding Thoughts

Regardless of the final forecast, we are looking at possibly a historically complex and prolonged event. Impacts from the storm will affect most of the Northeast, and damage from wind and storm surge will be significant. Areas in NY could receive 2-3 feet of snow, while Boston might experience a hurricane and blizzard on the same day! Philadelphia won’t be the hardest hit, but conditions will still be dangerous most of the day on Friday into Saturday. Enjoy the weather and stay safe out there, it’s going to be wild.




Tracking a President’s Day Weekend Snowstorm

The warm temperatures we experienced today will have a brief reprieve this weekend as a low-pressure system to our south impacts our region. A disturbance forming in the Midwest will amplify off of the mid-Atlantic coast on Saturday before moving northeast. Plenty of cold air aloft from a cold front combined with a coastal storm could bring widespread snowfall accumulation from Philadelphia to Boston.

While temperatures aloft will be cold enough to support snow, they will remain close to the freezing mark. As a result, the snow will be wet and heavy, sticking to both tree branches and power lines. Heavy precipitation will begin on Saturday night and end early Sunday morning. This is a quick mover, so a majority of the precipitation will fall within a 12-hour timeframe.

A major factor associated with this storm is the track. The further south the track, the higher chance that precipitation will fall as snow in the Delaware Valley. However, the models have been inconsistent. Shorter range models are showing colder solutions and the longer-range models are showing warmer ones. The map below is from short-range North American Model (the NAM):


If the NAM is correct, 4-6 inches of wet snow could accumulate along the I-95 corridor. As evidenced by the map, the rain/snow line is only 50-100 miles south of Philadelphia. Any slight shift northward of the track could have a significant impact on snow totals, especially south and east of the city.

The GFS model’s solution shows the possibility of mixing in Philadelphia and areas south:


With this solution, 1-2 inches of snow will fall with higher totals north and west of I-95.

Regardless of the precipitation type, expect a nasty Saturday night and Sunday morning, with frigid temperatures and heavy rain/snow (depending on the track of the storm).

In the longer term, a ridge in the jet stream will set up behind this system, bringing temperatures 25-30 degrees above average! A follow-up post reviewing this warmth and long-range forecast will be published this weekend.

An Active (and Warm) Pattern Ahead

Warmer Temperatures

February is opening to an active weather pattern for our region. Over the next 7 days, we will likely be impacted by three different storm systems. During this period, temperatures will be slightly above average as shown by the European anomaly map below:

Euro 7 Day Anomaly
Euro 7 Day Anomaly

As the anomaly shows, we are currently in a transition from a negative to positive PNA. What this means is that our reprieve from the cold is likely temporary.  Additionally, the Arctic Oscillation is forecast to go negative around the 10-day timeframe. This usually indicates a colder airmass entering the continental US:

AO Forecast
AO Forecast

7-Day Pattern

Until then, we have four storms to worry about! The first is arriving tonight into tomorrow. This is a system associated with a cold front moving across the Northeast. Temperatures were in the 40s today, but will rapidly drop tonight into tomorrow morning. I expect the rain to eventually change briefly over to snow overnight before moving off the NJ coast. The map below shows the high-resolution model forecast at 3 AM Friday:

NAM high-res 3 AM Friday
NAM high-res 3 AM Friday

Tomorrow morning’s commute could be slick as wet roads freeze over once the front pulls through. Temperatures will drop during the day on Friday before plunging into the teens with wind chills into the single digits:

Temperatures Early Saturday Morning

Storm #2 will quickly follow the first, forming rapidly during the day on Sunday. This system has characteristics of a coastal, phasing with a northern piece of energy over the great lakes. Models are currently projecting a quick phase, which would push the storm further west and keep our temperatures above freezing. Super Bowl Sunday will likely be a drencher as this storm barrels through the region Sunday evening. Any celebrations following the game (knock on wood!) will be cold and wet, with temperatures around 40 degrees.

Rainstorm Super Bowl Sunday
Rainstorm Super Bowl Sunday

Storm #3 is looking like a classic “Appalachian runner.” The storm will form over Missouri next Tuesday before moving Northeast along the Appalachian mountain range. This atmospheric setup will steer the storm to the west and warm up our region. Temperatures could reach the 50s on Wednesday as the storm pulls through.

Storm #3

Our pattern continues to be active following this storm, with another system impacting the region next Saturday.

Stay dry over the coming week! Go Eagles!

Quick Post on Tues/Wed Clipper Storm

Following a very short January thaw, winter is returning this week with both ample cold air and a storm.

Clipper/Coastal Forecast

An Alberta clipper is moving down through the great lakes region and will phase with a piece of energy off of the Atlantic coast late Tuesday night. As the clipper moves eastward, it will bring a period of snow tomorrow evening into Wednesday morning for much of the region. Depending on the timing of the coastal phase, areas north and west of Philadelphia could receive substantial snowfall from this system. The map below shows the radar tomorrow at 7 PM. According to this model (the NAM hi-res), as the clipper begins to phase with the coastal low, a broad swath of snow enhances over Central and Eastern Pennsylvania:

Clipper Phasing with Coastal
Clipper Phasing with Coastal

By early Wednesday morning, the phase is complete, with a full coastal storm strengthening off of New England. At this point, a wide area of heavy snow will form over New England and will extend down to Virginia:

Clipper Phased with Coastal
Clipper Phased with Coastal

As with many atmospheric phases, forecasting storms like this can be difficult. A slightly earlier or later phase would significantly alter the forecast for the I-95 corridor. Based on what I’ve observed from the forecast models, 5-8 inches will likely accumulate from the Poconos into New England. Most of the major cities, Philadelphia included, should receive 2-4 inches of light, fluffy snow.

Snow will likely begin after the evening rush on Tuesday in the Delaware Valley. In areas north or west of Allentown, I would advise preparing for a significant snowstorm tomorrow into Wednesday. Wednesday morning’s commute will likely be slick as the storm begins to move out.


Update on the Upcoming Nor’easter

Wednesday Afternoon Update

The storm appears to be taking a more western path, which means the heaviest of snow will push into the I-95 corridor late tonight into tomorrow afternoon. Storm totals will range from 4 inches NW of 95, 8 inches from Philly to NYC, and possibly over a foot near the coast. As with most nor’easters, there will be areas with locally higher snow amounts. The map below illustrates forecasted snow totals. Note that ratios will be higher than 10:1 in this storm, so a 10:1 snowfall map showing 5 inches will more likely be 6-7 inches with this storm:

NAM Snow Prediction
NAM Snow Prediction

Another concern with this storm is the wind. Wind speeds will approach 30 mph tomorrow morning as the storm bombs off the coast. There is a potential for scattered power outages from fallen tree branches.

Stay safe everyone and enjoy the snow!

Original Post

Happy New Year everyone! Hope your holidays were both relaxing and fulfilling.

In the weather…

We are currently in the middle of what will likely be the coldest late December/early January period in recent memory. The map below shows the temperature anomalies from last week. Apart from the west, the nation was at least 6 degrees below normal with northern areas exceeding 10 degrees below normal.

US surface temperature anomalies Dec 25-31

The cold isn’t going away anytime soon. After the nor’easter moves through on Thursday, a high-pressure system will settle to the northwest this weekend, bringing even colder temperatures. Based on forecasted anomalies, we could see low temperatures well below 0 in New England and close to 0 from Philadelphia to NYC.

Temperature anomaly Jan 7th
Temperature anomalies late Saturday night

Following the arctic blast this weekend, temperatures will likely return to normal or slightly above normal. However, more cold blasts are ahead, so stay warm over the next couple weeks!

Upcoming Nor’easter

The upcoming storm has all the features of a classic nor’easter. The actual system has actually already started to spin up in the Gulf of Mexico and will strengthen off the Atlantic coast tomorrow afternoon. Once the storm gathers strength, it will begin to move northeast and continue to strengthen.

There are a few factors that favor the development of a significant nor’easter. First, ocean temperatures in the Atlantic are above normal for this time of year. This promotes faster and stronger development. Below is a map showing the Atlantic warmth:

Above average ocean temperatures
Above Average Ocean Temperatures

Second, the current state of the teleconnections indicates conditions for storm development. The NAO will be transitioning to negative during the storm, the PNA remains strongly positive (trough in the east), and the EPO is negative. Finally, there is plenty of cold air feeding into the storm, creating blizzard conditions in some regions.

We know a storm is coming, but where and when? Right now, the nor’easter is projected to track up the coast late Wednesday and strengthen rapidly as it moves north on Thursday. The latest forecast models show the worst of the storm impacting New England with most of the heavy snow occurring east of the NJ coastline.

Thursday Morning Snow
Thursday Morning Storm Track

By Thursday evening, storm’s low pressure will be the equivalent of a category 3 hurricane. Blizzard conditions will be occurring in much of New England while the light snow ends in the Delaware Valley:

Nor'easter Peak Strength
Nor’easter Peak Strength

With all this being said, recent short term models have been trending slightly west. The ramifications for more westerly track could be significant in our region. As shown on the 3K NAM, a model that specializes in short range forecasting, a track even 75-100 miles west could bring heavy snows into the I-95 corridor:

3K NAM 7 AM Thursday
3K NAM 7 AM Thursday

It is apparent there is still uncertainty associated with this nor’easter. We are currently 36 hours before the beginning of the event, which means the next 12-18 hours are critical in determining the actual track of the storm.

Based on recent data, it would be reasonable to expect a disruptive storm on Thursday.  If the storm takes a more easterly track, 1-4 inches of snow should fall from this storm with more near the coast and less NW. If the storm takes a western path as shown in the 3k NAM above, 6-10 inches of snow would not be unreasonable.

If there are any changes overnight, I will post a quick update with a revised forecast tomorrow morning.