Winter 2002/2003 Outlook
---How cold and snowy will the winter of 02/03 be? That's the million dollar question for many investors, traders, energy companies, etc. Since no one reading this will fall into any of those categories, it's a five dollar question, so after I answer the question I expect a full payment by December 1st :) Just kidding. Anyhow, as you already may know last winter was predicted by most, including myself, to be generally cold with average precipitation even though the fall 2001 was EXTREMELY above average in terms of temperature and very dry! Starting in November people began looking into the future for the potential big one, and some models fairly consistantly showed it coming with a huge surge of arctic air preceding it. "It's just 8 days away," was a statement that was made frequently last winter. Two days later, it was another 8 or 9 days away. Yet two more days had passed and computer models had delayed the cold air surge another 2 days. This became a trend, which became a pattern, which became a reality. The cold never came, nor did the snow. Granted there was one major storm in VA/NC on January 3rd, that was essentially it. Temperatures were the warmest in recent memory in many locations. Some areas received as little as 25% of their normal snowfall!!
---Why was the winter forecast to be cold? Two words, El Niņo. Sea surface temperatures (SSTs) forecasting models suggested that the then 4 year old La Niņa would fade into a weak El Niņo by January. After this forecast was published meteorologists started looking for analog years and had correlated last winter with winters of long ago, based on SST assumptions. They came to an agreement that it was likely that the eastern US would experience normal to below normal temps with near normal precip. Boy were they wrong. And before you totally distrust the models, know that the SST initialization data for the SST models was incorrect or some of the data was actually missing. Also, the well known cold-bias possessed by one of the main forecasting models was supposedly corrected this fall. We'll see :)
---Factors in this winter season include: El Niņo/Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Pacific Decadal Oscillatiion (PDO), Pacific-North America Pattern (PNA), Solar Flux, volcanic ash, and finally snowcover. Yeah, I bet your head hurts doesn't it (if you're still reading at this point). I will explain as best I can what these factors are and how they affect our climate.
---First we'll begin with El Niņo and the Southern Oscillation.
What is El Niņo/Southern Oscillation?
Now many of us have heard of El Niņo after the record event of 97/98, but what most don't know is what El Niņo is and what role it plays in our weather. El Niņo is characterized by unusually warm water in the eastern Pacific ocean along the South American coast (Niņo region 1+2) and/or in the central Pacific ocean (Niņo regions 3.4 and 4). A phenomenon that relates to this anomaly is the Southern Oscillation. The SO is an anomaly of relative pressures in the south Pacific, measured near Tahiti and Darwin, Australia. When the SO is in its negative phase, pressures are lower near Tahiti than they are near Darwin. Subtracting the pressure of Darwin from that of Tahiti gives us an index number that is negative. As you may expect, a positive SO would correlate to a positive SOI. What is interesting is that there is a relationship between El Niņo and the Southern Oscialltion. When there is a tendency for warmer than normal waters in the equatorial Pacific, the SO is typically negative. Or one could say that when there is a tendency for the SO to be neagtive, then we typically have an El Niņo. Climatoligists refer to this as ENSO, since they are related.
How does ENSO affect our weather?
It really all depends on the strength of El Niņo. In a strong ENSO event the affect on our weather is VERY evident. The jet stream configuration splits with the polar jet stream staying well to the north, with the active subtropical jet stream plowing into the California coast. This floods the nation with warm Pacific air and brings flooding rains to much of the Southwest. The Deep South also recieves above average rainfall as well as the Gulf Coast, while areas to the north are unusually dry and warm. An amplified pattern is VERY unlikely and there isn't much hope for snow lovers in the Mid-Atlantic and Northeast. Lucky for us, this ENSO event is different from many in the fact that the warm water originated in the central Pacific and has had trouble spreading east. Waters are only slightly above normal in the eastern Pacific, and the SOI shows that ENSO may have actually peaked or will peak soon! What this could mean for us is that ENSO will be weak/moderate as opposed to moderate (as it is now) or moderate/strong. When there is a weak ENSO, things become very interesting for folks in the east. The nation isn't necessarily flooded by Pacific airmasses as it would almost certainly be in a stronger event. The ability for the longwave pattern to amplify makes things exciting when it does because of the ever active subtropical jet. When pieces of energy from both jet streams phase, what happens next can potentially be of historic proportions. If the energy phases in the bottom of a negative-tilt (SSE-NNW orientated) trough in the east, cyclogenisis (storm formation) can occur off of the coast of the Southeast, and ride north-northeasterly. If conditions are right and the system bombs out, then our area could possibly recieve high winds and heavy rains of 1-4" and/or heavy snow on the order of 1-2 feet. Now of course this is an extreme solution, but it's certainly possible and has happened before (Jan. 6-8, 1996 and Jan. 25-26, 2000 for example). So far this year ENSO hasn't has much of an adverse impact on the weather here, and that could be to the fact that El Niņo regions 1+2 aren't that warm. It could also be because of an unusally cool pool of water between southern California and Hawaii. All I know is that if ENSO strenthens then you can kiss the cold and snow goodbye. IF it holds as is now or weakens, then anything is fair game :)
[Sea Surface Anomalies]|[Current Status of ENSO]
---Now we will cover the North Atlantic Oscillation.
What is the NAO, and how does it impact us?
The NAO is an oscillation (obviously) between realtive pressures in the north Atlantic ocean. The positive or "warm" phase of the NAO is defined by high pressure located near the Azores islands with low pressure in the vicinity of Iceland. This usually results in a progressive, zonal flow across the nation which drains cold air off of the east coast of Canada. Last year featured a positive or neutral NAO on average, and we all know what that lead to. A negative NAO is defined by an area of low pressure displacing the high pressure near the Azores, and high pressure builing or moving into a position near Iceland and eventually Greenland. When the Greenland block is in place, cold air is allowed to filter into the eastern US as this block acts like a stone in a stream. It cause the longwave pattern to buckle, and this can flood the eastern US with cold air, sometimes even brutally cold air as it strengthens. The only time any appreciable snow fell along the east coast was when the NAO was strongly negative (≈December 27th - January 5th). Of course I predicted the storm before anyone else did, but we don't need to hear about that :)
How about this year, what will the NAO be?
So far this fall the NAO has averaged negative, and I believe that this will continue. Most ENSO events possess a +NAO but this ENSO is different. There are other factors that influence the NAO, and I will discuss those next. I will tell you though that the NAO is expected to be negative more frequently this year, but the Climate Prediction Center seems to think otherwise!
[CPC Winter forecast map]
---Onward to the Arctic Oscillation!
What the heck is the AO, and why do I care?
The AO is similar to the NAO in that relative pressures are involved. In the negative phase, low pressure can be found in the Gulf of Alaska and near Greenland while high pressure sets up shop near the pole. Why is this important? Because when the AO is negative, the NAO tends to be negative and we already know that this leads to an amplified pattern. We are lucky, the AO is negative and forecast to remain that way much of the winter. This is due in part to the PDO, which is next!
[Read how the AO has moderated the winters of the 80's and 90's]
---The Pacific Decadal Oscillation, OH NO!
PDO, that's a great band!!!
The Pacific Decadal oscillation deals with the temperatures of water in the north Pacific. Obviously this cycle is one of longer term than say ENSO, which typically only last for 12-18 months. The PDO has been found to operate on cycles that last as much as 20-30 years. As the other oscillations have a positive and a negative phase, this one does as well. The neagative or "cool" phase correlates to higher than average temperatures in the north pacific with lower than average temperatures in the Gulf of Alaska. Last winter displayed a negative PDO, which tends to favor a positive AO and NAO. Not good for the snow hounds! This winter should be different as there has been a switch to a positive or "warm" PDO. The waters right now off of the coast of British Columbia and in the Gulf of Alaska are well abover average, and the is an indicator of a +PDO. This leads to lower pressures in the Gulf of Alaska. The AO is responding by going negative this fall along with the NAO. If ENSO weakens a bit, the PDO could be a big help this winter!!
[More on the PDO]
---Other possible factors
Snow cover!!!
Did you know that fall snow cover in the northern hemisphere plays a role in how cold the winter will be? Yes, it's true. A persistant snow pack is essential in the generation of cold air for winter. The larger the snow field, the more area that can be cooled by a greater albedo. It also helps to have a nice depth to the snow, so that any changes in wind won't melt it away! So far this fall, the snow cover across the northern hemisphere has averaged greater than it has in decades. While the depth isn't all to impressive, the snow field has steadily expanded and seems like it's here to stay already in many places. Hopefully ENSO doesn't kill it.
[Current snow cover]
Volcanic Ash? Huh?
Volcanic ash has an impact on winter patters as well. Many abnormally cold periods can be traced back to times when the has been increased volcanic activity. It's logical when you think about it. The more ash there is in the upper atmosphere, the less the sun can warm to lower atmosphere. It's like the theory of the extinction of the dinosaurs where dust and debris is thrown into the atmosphere from an asteroid impact, which causes the atmosphere to drastically cool. This in turn with starvation kills nearly everything. While nothing of that scale is even remotely possible, you get the point! This year has seen an increase in volcanic activity, hence more ash :)
Solar Flux
Solar activity plays a role in the upper atmosphere patterns, which eventually translate to the surface, making this something worth noting. Last year we experienced a peak in solar activity. Satellite communications went off line on occasion as did radio networks in certain regions. If this impacts satellites in near-earth orbits, you can rest assured that it has an impact on climate as well. When the Solar Flux is high like it was last year the upper atmosphere (at about a 300mb height) becomes warmed and the polar jet lifts northward in response to this. Occasionally this will translate to the surface and have a great impact on our weather. The degree of it's effects aren't certain, especially to me, but it is a key reason as to why forecasts for last winter busted. Solar activity has died down a bit so there shouldn't be much of an effect on this winter season.... hopefully.
The way I see it, this winter should be average in terms of temperature, possibly slightly below in our area with above average precipitation. There is a 25% chance of below normal temps, 60% chance of average temps (within 2°F either way), and a 15% chance of above average temps. This based on my belief that El Niņo will weaken through the winter and that the NAO will frequently be negative or neutral. Now there is a 5% chance for below normal precipitation, 40% chance for average precipitation (within .5" either way), and a 55% chance for above normal precipitation. And snowfall? My best GUESTIMATE would be that Blacksburg should receive about 125% of normal snowfall, or about 25" of snow. I should also note that the records for snowfall in Blacksburg are 1.5" as a low and 71.9" as a high! That's a large range of possibilities so 40" isn't out of the question, but neither is 3".
Seasonal Snowfall Probabilities for Winter 02/03
| <1" | 0% |
| 1-3" | 0% |
| 4-7" | 3% |
| 8-12" | 13% |
| 13-17" | 18% |
| 18-22" | 24% |
| 23-29" | 27% |
| 30-40" | 13% |
| >40" | 2% |
Thank you so very much for stopping by, Good Luck this season!!
Links
VTWx
CPC 6-10 day forecast
CPC 8-14 day forecast
Email: KendrasMan@excite.com
