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February AO/PNA Scenarios


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With respect to the 1800-01, 1801-02, 1804-05, 1805-06, 1818-19, and 1819-20 La Niña winters, here are the New Haven temperature anomalies for those winters:

1800-01: +2.6°

1801-02: +4.5°

1804-05: -1.1° (February was warmer than normal)

1805-06: +5.3°

1818-19: +0.7° (December was 4.8° below normal)

1819-20: -0.7° (December was normal and January was 4.2° below normal)

Source: David M. Ludlum's Early American Winters 1604-1820

Some famous hurricanes in that time period too ;)

The famous snowicane was in 1804 and there was another big hurricane in 1821.

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Don, I find it interesting that some of these cold winters are amongst the strongest la ninas on record (specifically 1892-93, 1916-17 and 1942-43). March 1893 was our former snowiest month on record.

I remember you mentioned 1892-93 and 1942-43 awhile back when making comparisons to how this winter has been unfolding.

The winter of 1892-93 was extraordinary. Seattle had 58 inches of snow that winter and a total of 45 inches from Jan 27 to Feb 5. I wish we could see more winters where everyone gets clobbered.

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The winter of 1892-93 was extraordinary. Seattle had 58 inches of snow that winter and a total of 45 inches from Jan 27 to Feb 5. I wish we could see more winters where everyone gets clobbered.

I totally agree. Back when we had a multidecade snow drought, I would be more interested in reading about old winters rather than following current weather. Historical weather annals seemed so much more exciting than anything I had personally experienced so I basically ignored current weather; I feel your pain there. The most wonderful kind of winter is the one in which everyone partakes of the snow and cold.

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The winter of 1892-93 was extraordinary. Seattle had 58 inches of snow that winter and a total of 45 inches from Jan 27 to Feb 5. I wish we could see more winters where everyone gets clobbered.

It's getting kind of old. I think we have maybe 2 of the past 10 winters (2003-2004?, 2008-2009) above the 30-yr mean, and just 1 (2008-2009) above the long-term mean here in Portland. This winter was supposed to be halfway decent, and I have yet to see more than a trace of snow. Don's analysis suggests the possibility of a warm February for us, and unless we can get that PNA block to retrograde, that's looking like a reasonable possibility.

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It's getting kind of old. I think we have maybe 2 of the past 10 winters (2003-2004?, 2008-2009) above the 30-yr mean, and just 1 (2008-2009) above the long-term mean here in Portland. This winter was supposed to be halfway decent, and I have yet to see more than a trace of snow. Don's analysis suggests the possibility of a warm February for us, and unless we can get that PNA block to retrograde, that's looking like a reasonable possibility.

I can't imagine how agonizing this winter has been for you. Even with the couple of snow events I've had I feel really cheated. Now we are forced to pray for a second year La Nina. The East rarely steals the show with those. The only one I can think of where they did was 1917-18. Given this winter is nothing like 1916-17 in our region I'm not too worried about that one.

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Latest AO forecast:

Now only one ensemble member barely breaks above +2. Most top out, not between +1 and +2 but between 0 and +1. The downward trend toward new AO blocking is also featured, with most of the ensemble members < 0 by sometime during the first week in February. Things are now moving nicely in line with what the historic experience concerning past severe/extreme AO blocks in December suggested.

AO01222011.jpg

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I would love to understand the significance of this if someone can explain for me! Thanks!

Often times, if the polar stratosphere warms suddenly, it causes the polar vortex in the troposphere to break down, leading to an extremely -AO. Watching for signals in the stratosphere can hint at what the polar troposphere will look like in 2-3 weeks.

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Often times, if the polar stratosphere warms suddenly, it causes the polar vortex in the troposphere to break down, leading to an extremely -AO. Watching for signals in the stratosphere can hint at what the polar troposphere will look like in 2-3 weeks.

It will be interesting to see how this plays out. I suspect that there will be signifcant blocking (AO -3 or below) in place by around mid-February +/- a few days, and this signal provides some confidence.

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It will be interesting to see how this plays out. I suspect that there will be signifcant blocking (AO -3 or below) in place by around mid-February +/- a few days, and this signal provides some confidence.

Perhaps that period where the AO shifts from + to - will be a window where the NW could score something. Our November cold snap happened as the AO was initially plunging. I was happy to see your PNA/AO post which points out this region can indeed have a great February with a negative AO.

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only a couple ensemble members now show the AO crash. are there performance stats for individual members?

.

Unfortunately, not. However, it should be noted that some steps "backward" with wild spreads among the various members of the ensembles often show up in advance of regime changes before a consensus emerges. One saw such spreads prior to the historic December 2009 and 2010 blocking episodes and also the start of the extreme late January-early February 2010 blocking. From the individual ensemble members, it does appear that a number of them seem to be trying to head for typical La Niña climatology near the end of their range. It will be interesting to see how things play out, especially if a major stratospheric warming occurs in the near-term.

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Unfortunately, not. However, it should be noted that some steps "backward" with wild spreads among the various members of the ensembles often show up in advance of regime changes before a consensus emerges. One saw such spreads prior to the historic December 2009 and 2010 blocking episodes and also the start of the extreme late January-early February 2010 blocking. From the individual ensemble members, it does appear that a number of them seem to be trying to head for typical La Niña climatology near the end of their range. It will be interesting to see how things play out, especially if a major stratospheric warming occurs in the near-term.

No question the index forecasts for today look awful for the whole country. I hope things change again. Has the stratospheric warming begun yet or is it just expected?

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I'm sure it will work out great for you guys.

Hey Snow Wiz, the new WSI outlook might give you some encouragement (at least for February, they have cold in the west, especially NW, back to a big NAO block for March though). See Don's other pinned thread for details.

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Hey Snow Wiz, the new WSI outlook might give you some encouragement (at least for February, they have cold in the west, especially NW, back to a big NAO block for March though). See Don's other pinned thread for details.

Thanks for letting me know. The GFS ensembles started looking a whole lot better today also. I would have thought it would be more likely for March to be the good month for us, but February would be much better. I would be very surprised to see March be warm here regardless.

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It will be interesting to see how this plays out. I suspect that there will be signifcant blocking (AO -3 or below) in place by around mid-February +/- a few days, and this signal provides some confidence.

All in all, in my entire liefetime and I have hit the big 60, I have never ever seen such persistence. Unbelievalble. I know there are all the scientific and physical reasons for it but it is truly amazing I must say. The pattern on the west coast with a ridge in place...on the coast...day after day after day seemingly locked in is not something any of us expected. I know, I know, there are a myriad of reasons. It looks so much like El Nino out here right now it is hard to believe it isn't January of 2010. Not to take away from what has been just as historic for the upper midwest and northeast but you can understand that were the situation reversed and you had temps 10+ degrees above normal with ALL your storms rain you would be very frustrated as well.

Which brings me to NEXT winter..as I am pretty sure this one is toast for the PNW(lol). The Pacific is expected to warm..but still stays in negative territory according the latest ENSO outlook this week. How much change does that mean for the country(if any) or will blocking and solar be the main driving forces with respect to winters in the future?

Now.....if ONLY we could have this ridge in place from May-Sept.

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Speaking of ridges - HPC's Preliminary Extended Forecast Discussion this morning discusses an upcoming southeast ridge:

THE LONGWAVE PATTERN IS EXPECTED TO GRADUALLY TRANSITION FROM A

MEAN RIDGE OVER THE WEST/TROUGH OVER THE EAST ON DAY 3 TOWARD A

MEAN TROUGH OVER THE ROCKIES/RIDGE OVER THE SOUTHEAST BY DAY 7.

...

THE MAIN DIFFERENCE WITH THE MEANS INVOLVES THE ORIENTATION AND

STRENGTH OF THE MEAN RIDGE OVER THE SOUTHEAST BY DAY 7...WITH THE

ECMWF ENSEMBLE MEAN MORE AMPLIFIED AND STRONGER THAN THE

GEFS/NAEFS.

However -

CONFIDENCE BELOW AVERAGE FOR THE ENTIRE PERIOD.

Something else to stir into the stew, I suppose.

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All in all, in my entire liefetime and I have hit the big 60, I have never ever seen such persistence. Unbelievalble. I know there are all the scientific and physical reasons for it but it is truly amazing I must say. The pattern on the west coast with a ridge in place...on the coast...day after day after day seemingly locked in is not something any of us expected. I know, I know, there are a myriad of reasons. It looks so much like El Nino out here right now it is hard to believe it isn't January of 2010. Not to take away from what has been just as historic for the upper midwest and northeast but you can understand that were the situation reversed and you had temps 10+ degrees above normal with ALL your storms rain you would be very frustrated as well.

Which brings me to NEXT winter..as I am pretty sure this one is toast for the PNW(lol). The Pacific is expected to warm..but still stays in negative territory according the latest ENSO outlook this week. How much change does that mean for the country(if any) or will blocking and solar be the main driving forces with respect to winters in the future?

Now.....if ONLY we could have this ridge in place from May-Sept.

We still have February and March left which are traditionally the highest chance to be cold in the NW during a Nina. There are a lot of forecasts out there saying things are going to change. As tempting as it is to give up, I haven't yet.

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