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Snowfall forecast for DCA and Montgomery County

Very In-My-Back-Yard (IMBY) forecast, but since I’ve been out of town and not keeping up with the weather I can’t really make a nice snowfall forecast.

With so much uncertainty with the cut-off for the big snowfall totals, I will go with 3-6″ of snow for DCA and Montgomery County (65% confidence), with higher totals (including 10″+) in eastern MD and 2-4″ further west in places like Leesburg, VA. There is about a 25% chance that DCA and MoCo could see higher than 6 in., and about a 10% chance that they could see less than 3 in.

This will be an event that will have to be closely followed on radar to see where the significant snowfall line sets up. The difference of a few tens of miles could be all it takes to go from “meh” to “wow this is a lot of snow!”

Either way, it looks like this snow storm will put DCA in the above normal snowfall category for December (we’re only ~1.2″ short of normal at this point), which would be a great start to a La Niña winter in the Mid-Atlantic as they tend to have below normal snowfall totals for most of the region.

Keep a close eye on the forecast this weekend!

A big system with the potential to dump snow (we’re talking 8-12+ inches possible, but the location remains uncertain) along the East Coast along the I-95 corridor starting late on Christmas Day and going through the 27th. There is still a high uncertainty with the track of this storm, so snow forecasts won’t be that accurate up until within two days of the event.

So keep an eye on the forecast and adjust your travel plans as necessary. There is some potential for this to be a big storm, though I’m still about 50/50 on this event hitting the East Coast hard. As of now, my call for DC/MoCo is 2-4″, which could go up to 3-6″ tomorrow if the models converge on a snowier solution.

I might not get to update the blog until Saturday, as I will be traveling to NY tomorrow, and I’ll be coming back to MD to work on Christmas.

Merry Christmas! Enjoy the snow (if you get it)!

January 2011 Temperature Forecast Update

A look ahead into what the current status of the atmosphere and mid-range forecast has done to the long term outlook.

The updated January 2011 temperature anomaly forecast:

And for reference the old January forecast (issued 7 October):

The changes:

The lingering blocking pattern is what caused the great change in the temperature forecast. As we move into January, the -NAO/-WPO pattern still exists, but is forecast to weaken as the indices trend towards neutral values (the NAO more so than the WPO). Should this blocking pattern break down completely and transfer into a neutral PNA, neutral WPO and weak +NAO, we will see a much more progressive pattern that will allow the above normal temperatures to work back into the eastern U.S.

My original map included a fully progressive pattern throughout the month of January, with the primary storm track going from the Pac. Northwest into Canada as the subtropical ridge lingered over the Desert Southwest. The more persistent blocking along with the strong -WPO allows the cold air to seep further into the mid-continent, which with plenty of available cold air would lead to drastic changes in the forecast like those seen above.

I would expect to start seeing the effects of the more progressive pattern around mid-January, which is somewhat-aligned with the pattern that the latest Euro weeklies show.

There is a risk for a more persistent blocking pattern or reinvigorated blocking pattern heading further into January, which would result in a cooler eastern half of the nation.

—–
UPDATE: Analogs and weight for January:
1996 (4)
1951 (2)
2006 (1)

The “So Close” Storm of December 2010 (18th-20th)

As this potential snow storm begins to materialize in the Southeast, it’s time to take a serious look at snowfall predictions. This storm appeared to be going out to sea at the start of this week, then for a couple of days it looked like the I-95 corridor would land a rare epic La Niña snowstorm along the East Coast. Unfortunately for the snow lovers of the East, the models are converging on a system that heads out to sea (OTS), with a quick snow dump over southern Virginia and a wintry mix in the Carolinas before sweeping northeastwards tantalizingly-close to the coast. The coastal areas of New England also have a shot at some snow.

Most of the precipitation will be off the coast, giving the fish a good time while the snow lovers despair over what could have been. At one point, 6-12 inches along the I-95 corridor seemed like a possibility. Now they’ll be lucky to get a dusting. Northern New England could get some backlash snow from this system after the 20th when the system tries to retrograde back to the west.

Here’s an estimate of what this system will put down on the 18th through the 20th (Sat-Mon):



My winter forecast (temperature only for DJF)

Not your typical Nina scenario… anomalies are in degrees Fahrenheit.

EXPLANATION:
I’ll just start off by saying that I’m not big into long range forecasting. I do it as part of my job at work, so I figured since I put in the effort to do it there I may as well show you all the results. As an aside for verification, my analogs did fairly well in September (I finished at/near the top amongst the forecasters at work), and they also caught on to the October transition that we are currently seeing.

METHODOLOGY:
When finding my analog years, I like to keep things simple. I used years that went from Nino to Nina status and found the ones that had similar seasonal temperature anomalies to this year, particularly JJA. Better analogs were weighted more in order to match up the temperature patterns more closely.

ANALOGS:
in [year (weight)] format

2005 (more)
1995 (more)
1988 (normal)
1983 (normal)
1998 (less)

New weather pattern in the works?

After a long, long period of having a subtropical ridge anchored over the Southeast, it appears as though the long-wave pattern has finally shifted, with an upper-level ridge over the Desert Southwest and Plains and a trough over the Mid-Atlantic and Northeast. This will mean warmer weather for the Southwest and cooler, disturbed weather for the Mid-Atlantic and Northeast.

The next couple of weeks appear to be rather turbulent weather-wise as the Northern Hemisphere transitions into the winter weather pattern. Cut-off lows, blocking ridges, the potential for powerful low pressure systems and tropical systems near the U.S. are all possible as we head into October. With so many things possible in the future, forecasting anything beyond five days will be extremely difficult, so don’t be surprised if your extended forecast makes dramatic shifts this month.

The GFS model has been hinting at a powerful mid-latitude system in the 10-12 day range, which could mean some interesting weather and an awesome chase day for myself and Jason, but we’ll have to wait and see what pans out.