December 16-31, 2005: Pattern Thoughts

[Jim Hughes]

Don,


Nice analysis as usual. Just a couple of tidbits. The Pacific has changed in December and this has had an effect upon the PDO. The negative phase has definitely weakened in December.

The recent warm swing in the El Nino 1+2 SST's was related to some weaker upwelling numbers. We saw some lower pressures in the eastern Pacific a while back. I would expect to see a turn around in the SST anomalies during next 1-2 weeks. There is plenty of cooler water available in the subsurface.

Here is something to ponder. One has to wonder if these recent changes aren't related to the QBO finally peaking. The extreme strength of this eastern QBO has been anything but the norm. I have seen weather patterns change when the QBO peaks as well as change direction.

The prior pattern will usually return about four weeks down the road so a mid January return would line up about right if you consider when we started to finally warm up. Things started to change around Washington DC around 12/16. So 1/12 looks about right if the pattern flips again....Have to wonder about a storm pulling down the cold air. That can happen.



Jim

[donsutherland1]

Jim,

The verification will be posted in a few days. I was a little late with the warmup and underestimated its magnitude. The failure of the NAO to go negative for a meaningful stretch and the rapid collapse of the PNA+ before it could reach levels progged by the ensembles contributed to these errors in timing and magnitude.

As you noted, the PDO- appears to have weakened. That would be a good sign for winter weather lovers in the East (but not good for those in the West). I'll be looking forward to the December figure.

Like you, I don't see the Region 1+2 anomalies continuing to warm, much less to El Niño-ish levels. I do expect the Region 3.4 cool anomalies (now -0.7°C) to bottom out and gradually increase in the weeks ahead.

In terms of the QBO, from looking at 100 mb to 200 mb, I'm cautiously optimistic that the QBO bottomed out earlier in December and is, in fact, now rising. The December figure will be interesting to see.

Like you, I'm thinking the colder pattern will return in the 1/12-15 timeframe. While I believe cities such as Boston and Providence might be able to tap into some colder air for some accumulating snowfall prior to 1/10, I believe NYC and southward will probably see little or no measurable snowfall during that period.

[donsutherland1]

Verification:

The NAO proved predominantly positive (albeit weakly positive) rather than negative and the PNA did not rise to the positive levels I had expected. As a result, the cold pattern broke somewhat earlier than I had thought and the warmth was more significant than I had expected. Overall, this was a bad outlook, especially in terms of temperature anomalies.

December 16-31 will see temperatures from Raleigh to Boston average below normal:

This aspect of the forecast was incorrect. Readings generally wound up averaging above normal due to a big warmup that took place beginning around December 23. Select anomalies follow:

Baltimore: +2.1°
Boston: +2.8°
New York City: +4.3°
Philadelphia: +2.8°
Providence: +3.9°
Raleigh: +0.4°
Richmond: +1.6°
Washington, DC (DCA): +2.1°

The first half of the period could see an episode of severe cold with the lowest temperatures possibly reaching the single digits in Providence and Boston, and possibly in such cities as Washington., DC, Philadelphia, and New York. Teens are likely:

The cold never reached the above magnitude. Some teens were recorded. Lowest temperatures:

Baltimore: 19°, 12/22
Boston: 20°, 12/20
New York City: 22°, 12/20
Philadelphia: 15°, 12/21
Providence: 20°, 12/21-22
Washington, DC: DCA: 24°, 12/20; IAD: 17°, 12/20

Washington, DC, Baltimore, Philadelphia, New York, Providence, and Boston will likely add to their seasonal snowfall totals and possibly by 4” or more some of these cities.

Total snowfall December 16-31:

Baltimore: None
Boston: 0.2”
New York City: 0.4”
Newark: 0.3”
Philadelphia: None
Providence: 2.2”
Washington, DC: None


Some moderation in the closing 3-5 days of December but probably no much above normal temperatures.

The cold pattern ended on December 22.