Location: New York
Author: Weather 2000, Inc
Date: Monday, January 14, 2008
Winter gradually resumes.........
The chronology of January 2008 past, present and future, was already outlined weeks ago, and the cold-warm-cold-warm swings across the Nation are materializing on cue. However, it's physically much easier to achieve a +35¡ãF temperature anomaly than it is to achieve a -35¡ãF temperature anomaly in the Winter, so you shouldn't expect equal & opposite hemispheric undulations.
As we explained earlier this week: a "series of Continental Polar Air masses are scheduled to gradually drop down from Canada over the next 2 weeks, each one a little more thermally potent and geographically expansive than its predecessor. They will pivot around a mean Trough axis that will be positively tilted from Hudson Bay across to the Southern Plains." This obviously means the initial waves of colder air will be rather benign and contained, and get stronger & larger over time, as snow-pack gets rebuilt, and polar/arctic air deeper into Canada is tapped into. And "waves" mean short-wave ripples and Jet Stream buckling, so New York City could easily be +6 when Chicago is -6, and vice versa.
There is still no Greenland Blocking that we see setting up yet on the horizon, which reminds people to keep any cold magnitude and longevity with conservative expectations for now, as short-term forecasters can get giddy. This upcoming flow pattern is being driven by upstream (Pacific) Teleconnections and a +PNA regime, which can certainly produce Winter cold, but by no means has maxed out the Hemisphere's potential. Which also drives home the point that should definitive -AO/-NAO patterns start to develop down the road (and you'll hear from us first), Mother Nature can make things a whole lot worse.
The large commercial firms began to whistle a colder forecast tune this week, but why the sudden change of heart when the cold start to the month, the recent warm spell, and the upcoming colder patterns, were all known about weeks ago? The reason is that the large forecast outfits have a vested interest in defending their warm-everywhere Winter Outlooks to the very end, so they will be quick/eager to highlight the warm spells (which will be numerous) and be slow/reluctant to highlight the colder spells (which will also be numerous). There are 1,001 model runs, so (since Thanksgiving) whichever ones depicted the most warmth, became their favorites, and now that there is general model consensus they must acknowledge the return of more Polar Air from Canada . We will continue to try and set the record straight, keep the Seasonal boat on an even keel, and
address the popular "agenda forecasting" you bring to our attention.
A misconception that has prevailed for years is that the "blank" areas on the (6-10 Day, 8-14 Day, Multi-Month, etc.) NOAA/CPC Outlooks are indications of Normal Temperatures, which is incorrect. These are probabilistic, not deterministic, forecasts so blank areas (no contours) means that ANYTHING could happen in their view (i.e. a Non-Forecast), not near-normal. Furthermore, people often mistakenly interpret increasing number of contours as increasingly warm or increasingly cold. Again, as probabilistic forecasts they are only depicting that there are increasing
odds (in their view) that a location might end up warmer than normal or colder than normal, but that gives no indication of anomaly magnitude (i.e. there could be high odds that a region might be only +2¡ãF, or low odds that a region might be -8¡ãF).
Be aware that we're approaching the point in the Winter Season where psychological potholes become prevalent, and while "psychological forecasting" is not a meteorological prediction, it does use meteorology to its advantage. For example, if one was to predict a Warm February, it could appear that way in contrast to the historically frigid February of 2007. If one was to predict a Cold March, it could appear that way in contrast to the uneventful March of 2007. These are clever ways to spin perceived accuracy without verifying results. For some users, perceptions is in fact the name of the game, and for other users actual (objective) HDD tallies is the name of the game. Our site-specific predictions for month-by-month HDD's, precipitation, critical days, etc. were already made earlier in the Autumn upon request, so we'll continue to track verifications, forecast weather chronology, and call out important Winter developments that might be drowned out by spin.
* Under colder Winter regimes, a sort of 'Conservation of Degree Days' applies. If you see that a recent week trended 25 HDD's milder than you originally thought, there is a good chance it's because a past or a future week will come in with an extra 25 HDD's than predicted. Same goes for a Half-Month interval (recall January 2005 flip), or entire Months (recall January to February 2007 flip).
* Keep in mind that any of the cold waves we have witnessed the past 6 weeks, are just the tip of the iceberg when it comes to the long Winter Season still ahead of us. Note that within the past 12 years, 7 of the 8 coldest (Population/Gas weighted) November-December weeks were set way back in 1995-2000, but 6 of the 9 coldest January-February weeks were more recently set in 2002-2007 (in addition to some contemporary records in March & April).
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