Final Forecast and Snow Map for The Pre-Thanksgiving Storm of 2014

25 11 2014

After a quick warmup on Monday, winter is back with a vengeance tomorrow with our first snowstorm of the season. There have been a few changes since I posted yesterday Morning.

Firstly, surface temperatures will be hovering at or a little above freezing for most of the day tomorrow. This, combined with warm upper air temperatures, will cause the snow to mix with rain initially before changing to snow later in the day. Areas further north should expect an earlier changeover, while most of South Jersey may not see a complete changeover to snow during the storm.

2m temperatures Wed afternoon

2m temperatures Wed afternoon

Since it is still November, forecasting snow totals for this storm is extremely difficult.  The most recent short-run models have been favoring a more west track. This means less snow for the region than originally expected. My snow map shows 2-4 inches falling in the city with 3-5 inches in the immediate northern and western suburbs. If the storm takes a more westerly track like the short-run models are showing, these totals could fall substantially.

This map below shows an example of how a small shift in the track could affect snow totals. A 10 mile shift west or east in the storm track is the difference between 8 inches of snow and none at all in Philadelphia.

RGEM model snow projection

RGEM model snow projection

Timeframe:

  • 4-6 AM Wednesday: Light Rain Enters from South to North.
  • 6-10 AM: Rain becomes heavier and turns to snow Philadelphia northward.
  • 10 AM-5PM: Becoming all snow from northwest to southeast. Heavy at times. Possible thundersnow in spots.
  • 5 PM-8 PM: Snow becoming lighter
  • 8PM-11 PM: Snow moves out from south to north

Finally, I will release my first snow map of the season. This map is based on a combination of multiple computer models I have analyzed over the past few days. If you have any questions or concerns regarding the map, please let me know in the comments.

Snow Map 11/26

Snow Map 11/26

Be safe everyone. Remember that this snow will be of the wet and heavy variety, which means sporadic power outages and downed trees around the region. Until next time…

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A pre-Thanksgiving Snowstorm Looking More and More Likely!

24 11 2014

Hey everyone.  What makes predicting the weather so interesting is the unpredictability of it.

This is what has happened with the latest forecast models projecting possible Thanksgiving snowstorm. Yep. Nor’ Easters in November.

Lets get to it!

1. Tomorrow will likely reach into the 70s with some rain ahead of a strong cold front which will pass through on Monday night. I wouldn’t be surprised if the sun peaked out sometime in the afternoon. After the front moves through, temperatures will plunge throughout the day on Tuesday. This is shown below, courtesy of the GFS:

GFS Monday at 2 PM

GFS Monday at 2 PM

2. After the front moves through, a blocking high will move into Atlantic Canada, forming the setup for a storm to form along the coast. Another small disturbance will also move in from the midwest, phasing with the budding coastal system. This will really begin the process of a large storm forming on early Wednesday morning.

GFS 5 AM Wednesday

GFS 5 AM Wednesday

So the setup is there for a large snowstorm, but will it happen?

At this point, most forecast models are showing some sort of storm riding up the coast Wednesday into Thanksgiving. Since we are in November, the problem lies in whether there will be mixing during the storm. Upper air temperatures could be above freezing during the storm, especially if it runs close to the coast. This would bring in some wintry mix to the region at the beginning of the storm before changing to all snow.

On the other side, some models are showing dynamic cooling at the surface, which could keep the precipitation type all snow for the duration of the event.

Model differences:

GFS:

The GFS is showing a solution which would go further to the east. This solution I am supporting right now.  In the end, the GFS projects a good 3-6 inches of heavy snow falling from DC to Boston. This will be enough snow to disrupt travel plans and create mass power outages (which is not good if you want to watch the Eagles game, like me). The maps below show the peak of the storm on Wednesday at 2 PM. Click the maps to see a larger version.

GFS 2 PM Wednesday

GFS 2 PM Wednesday

European:

The European model is projecting the storm to come further west near the coast. Since the storm is closer to the coast, temperatures at the surface will have trouble staying below or at 32 degrees. The upper air temperature will be above freezing as well, which could mean a mix of precipitation throughout the storm. Even though the Euro projects more total precipitation than the GFS, 3-6 inches would be a good estimate for final snow totals from this model. Below is the European model at 8 PM Wednesday night. Obviously it is a slower solution than the GFS, which means there is more time for the storm to strengthen.

European 8 PM Wed

European 8 PM Wed

So which solution is correct? Well the European ensembles show a solution more toward the GFS. The teleconnections are also marginal for a large nor’easter storm that retrogrades into the coast. As a result, my initial call is 3-6 inches for the I-95 corridor with totals lower by the coast and higher up in the Lehigh Valley. The timeframe is from Wednesday midday to Thursday early morning.

I will have more on the travel effects and my snow map either tomorrow night or Tuesday morning.

Stay tuned everyone! Let the winter of 2014-2015 begin!





Welcome Back: My Winter Forecast and a Cold November!

15 11 2014

Hey everyone. After a spring/summer hiatus, Philaburbia Weather is back for the 2014-2015 winter season!

I want to start this post off by thanking everyone for staying with Philaburbia through the years. We are heading into our 5th winter and I hope you are as excited as I am for the coming months ahead!

First on the agenda is the tropical outlook. The 2014 hurricane season in the Atlantic is about to officially end. With only 9 named storms, it has been a fairly unremarkable season in the tropics. A couple factors including cooler than normal ocean temperatures and a weak El Niño contributed to the lessened activity in the Atlantic.

Atlantic Temp Anomalies

Atlantic Temp Anomalies

My mention of the El Niño leads us into the next topic: What’s in store for the 2014-2015 winter season?

A couple of major factors will determine how cold and snowy our winter will be:

1. Strength of the El Niño: This parameter has been known to heavily influence our winters year in and year out. In a nutshell, an El Niño means that water temperatures off the coast of Peru are above normal. No one knows the exact reasons for El Niño’s effects on our winter weather, but research has been done to prove correlations between strength of the El Niño and meteorological averages in the continental United States.

El Nino

El Nino

 

We are currently headed into a weak El Niño from a weak La Niña last winter (see chart above). With El Niño winters, temperatures tend to be warmer than average in the Northeastern United States. Unfortunately, the magnitude of the El Niño this winter will be marginal at best, which makes it difficult to predict how warm this winter will be. I did, however, find a couple of analog winters. These could support a general trend for this winter.

Analog winter: 1990-1991. The first winter I chose to analyze was the winter of 1990-1991. This winter was one of the warmest on record for the Eastern United States. The El Niño recorded during this period was weak (see http://ggweather.com/enso/oni.htm for more), but was likely largely influential on the unusual warmth of this particular winter.

1990-1991 winter analog

1990-1991 winter analog

Analog Winter: 2002-2003: This winter was made famous from the Presidents Day Blizzard of 2003, where nearly 20 inches of snow fell in Philadelphia. Overall, the winter of 2002-2003 was remembered as being one of more snowy winters in recorded history. The El Niño during this winter was weakly moderate, and temperatures were actually below normal for the season!

Presidents Day Storm of 2003

Presidents Day Storm of 2003

These two analog winters had very different kinds of winters. This does not make it easy finding correlation and a pattern to base my forecast on. Luckily, other factors, like teleconnections, are important indicators during the winter that help forecasters fine-tune their predictions.

2. Teleconnection Strength: Multiple teleconnections, including the AO, NAO, and the PNA, will be crucial in determining the winter pattern. The Arctic Oscillation (AO), is an index which records the pressure anomaly in the arctic region. A positive AO usually means a warmer winter, while a negative AO usually signifies a colder one. Currently, the AO will stay negative over the next few weeks, which means the rest of November will be much colder than average.

The North American Oscillation teleconnection is an important indicator of the intensity of winter storms in the Northeast. Last year, we had a positive NAO, which limited the number of nor’ easters to just one. If the NAO turns negative this winter, there is a strong chance we will have a couple very large snowstorms, ones that will drop feet of snow.

The Philaburbia Weather Winter Forecast of 2014-2015:

After last year’s extremely cold and snowy winter, we will not get too much relief this year. Already, we are seeing temperatures way below normal for November and an AO that looks to be staying negative for the near future.

However, there are some indicators that the end of the winter could be warmer than last year’s. With a weak El Niño developing, there is a possibility that the Polar Vortex will retreat back north, which would cause our February and March to be much warmer.

In terms of snow, I think we are in for less frequent smaller storms and more large nor’easters than last year. I could easily see most of the snow falling this winter from 2 or 3 large nor’easters and nothing else. As a result, our area could see 30-40 inches of snow this year depending on how many nor’easters hit and how intense they end up being.

To recap:

1. Cold winter. February and March becoming warmer than average. Temperatures 2-3 below average in Dec and Jan. Temperatures 2-3 above average in Feb and March.

2. Snowy winter. Less smaller storms, more larger ones than last year. 30-40 inches of snow.

Thanks everyone! Stay tuned.

 








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