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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 NiƱa 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.

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.

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.

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.

T.D. Sixteen forms south of Cuba, takes aim at the East Coast

This post might have to be updated if the NHC decides to upgrade Tropical Depression Sixteen to Tropical Storm Nicole later today.

Massive rains are in store for the East Coast tomorrow through Friday as T.D. 16 organizes just south of Cuba and heads towards the U.S. This storm is likely to be sub-tropical when it impacts areas from the Carolinas northward as it interacts with a stationary front just off the East Coast, but it could still pack tropical storm force winds as it progresses up the East Coast. One thing to expect with this system is heavy rain, on the order or 2-5+ inches, to cut a path up the interior East Coast along the eastern slopes of the Appalachians. Impressive wind shear associated with the right-front quadrant of this system will bring the risk of strong to severe winds and isolated tornadoes to the East Coast, but limited thermal instability caused by cold air damming will limit the severe potential with this system.

The significant rain totals will be mostly the result of large-scale forcing along a preexisting boundary when the tropical/sub-tropical system interacts with the stationary front within an atmosphere primed with moisture as P-WAT values are forecast to be in the 2-2.5″ range. Widespread flooding will be a big concern with this event, as the short-term drought conditions will cause the soil to struggle to absorb the rainfall. The past few day’s rain will help alleviate this effect, but not to a great extent.

I will be missing most of this event, as I have travel plans which has me driving north Thursday morning. *UPDATE: It looks like it will progress a bit faster than I anticipated… I’ll be driving through it almost the entire way.* Hopefully Jason will be able to cover the event and keep you all informed. Stay safe, and be sure to go over your flood preparedness and stay tuned!

(click to enlarge)