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Current conditions - Climate data - Special reports - Weather data

Currents: Special report

It appears this winter will be similar to last, or maybe a bit more harsh. Above normal snowfall is forecasted, with below normal temperatures. More Information coming this November in our Winter Center.

OVERALL  Rev: 10/27/01



I. Introduction

Predicting upcoming winter seasons a few months before it actually gets underway still remains fairly difficult. However, recent development of new computer models and constant monitoring of global warming and ocean temperature trends have significantly helped the weather forecasting sector to become progressively more accurate in long range predictions. While many may argue that these high-tech methods are in-accurate and that more traditional methods are more reliable, we partly get the drift of what you are saying. While we will definitely not exclude the high-tech ways, we will be more weary of the traditional signs as well, such as our furry animal friends. We are also inclined to let you know what others in the business are thinking, in addition to this forecaster.

As always, we work hard to bring you an accurate forecast, however, long range predictions such as this are tricky. Check back during the early weeks of the season for updates.

II. Part A. Oscillations

El Niņo, ENSO, La Niņa and the NAO may just seem like strange words or abbreviations to you, but it can mean the difference between a season of snow and a season of warmth. The oceans and their temperatures and surface weather patterns surrounding North America have such an incredible impact on how the winter in our region will fare. El Niņo ("the infant boy") and the ENSO effect is when the SST (sea surface temperature) of the Central and Eastern Pacific to Northern South America warms significantly to affect upper air weather patterns. Typically during an El Niņo season, a strong low pressure establishes itself south of Alaska significantly altering jet streams (upper air west to east highways of wind that storms often follow) and allowing for ultimately a wetter pattern for the southern part of the national and a warmer one for the northern part. La Niņa, as you can guess, is completely the opposite, with a blocking high south of Alaska. Jet streams are still altered, but ultimately stronger storms remain across the northern part of the country while the south is warm and dry, opposite the north. Now, also an important, and recently discovered factor for our region, specifically the Northeastern and Middle Atlantic United States is the North Atlantic Oscillation, NAO or Arctic Oscillation. This oscillation primary operates in two distinctive phases, positive or negative. During a positive NAO phase, low pressure establishes itself to the north of the Jet Stream in Canada and Greenland, while high pressure builds across the Eastern Atlantic. This ultimately allows for a zonal flow and warmer storms, if you will, for our region. However, when the NAO dips into the negative phase, strong high pressure builds over Greenland allowing the jet stream to dip to the Gulf coast spilling cold air into the eastern half of the country, often allowing for huge nor'easters or snow storms to develop along the east coast side of the stream for our region.

II. Part B. Oscillation Behavior this season

After learning about these impacting factors, how will those oscillations behave this winter season? Well, preliminary information suggests the Pacific and Atlantic oscillations will be in the phases that makes our region most susceptible to harsh conditions. First, in the Pacific, there are some signs of a return by El Niņo, however it will not be enough, at least this season, to impact our weather patterns significantly. Similar to last winter, it looks like a year with the absence of both El Niņo and La Niņa. This is know as neutral. Climatologically, neutral seasons have seen some pretty impressive snowstorms.

As far as the NAO, early indicators are still tricky to decipher, but show a period of predominately negative phases. This will likely mean colder air dipping into our region and the Great Lakes states, with a heightened threat of nor'easters.

III. Temperature

With a negative NAO forecasted for a good portion of the season, it looks as though temperatures will fare normal to even a good bit below normal. But some indications are that we could have wide temperature deviations from month to month, all depending on the orientation of the NAO. It will be very difficult to repeat last November and December's record breaking cold, not only in our region, but across a good portion of the country. Beginning in late November and December, look for the colder air with a negative tilt for the NAO. This, as also hinted in the Farmer's Almanac, tells us that their is an increased risk of a storm developing and riding up the jet stream on the East coast, therefore a nor'easter could be headlining the end of the year 2001. December will be a tricky month to forecast as we even see some indications of milder spikes working into the region. Cold air is forecasted to last through January and into February with the negative NAO. By March, a slow warming trend, as is normal, is expected, so we can probably expect a quieter March than last year, or potentially last year.

IV. Snowfall

Yes, I know every forecast that either you or I have read includes the mention of possibly a good deal of snow for the Mid Atlantic and Northeast, especially with a negative NAO expected. I have noticed some clues out in nature being that of the unusually early abundance of acorns (have yet to see a caterpillar though). The Farmer's Almanac is also predicting a "real" winter for our region, with heaps of snow beginning in late November. Suprisingly, computer guidance is agreeing with all these traditional forecasters. This could, I repeat, could be a good season for skiing, and I think business will be booming for those in that "industry." Seeing such a forecast of negative NAO, one must think of the increased threat of nor'easters or potentially blockbuster storms across our region. Climatology shows in seasons with conditions similar to what is expected this season, 1996, 1993, 1989, and so on, there have been at least one big storm. For this and other reasons outlined above, I will call for above normal seasonal snowfall. Average seasonal snowfall for the extended Philadelphia area ranges from 15 inches to about 40 far northwest. Some of the averages potentially could be shattered early in the season. As we saw this summer, tracks of storms are becoming more southerly, and with very early indications such of that of Tropical Storm Gabrielle in Florida, we could be seeing an intense storm or two this season. This appears likely from the period beginning in late November to mid February.

V. National Outlook

Across the nation for the 2001-02 winter season:

Southeast - Dry conditions are expected, however, there is a good chance of normal temperatures with spikes of below normal at times.

Midwest - Much colder than normal conditions are forecasted, possibly days with subzero conditions, however, snowfall will be limited compared to previous seasons.

Rockies and Great Plains - Normal to slightly below normal temperatures are expected with wetter or snowier weather, depending on location.

West Coast - Wet weather with shots of snow are expected for the Pacific Northwest, while the desert south

V. Conclusion

The acorns are abundant already, snow shovels and blowers are being investigated for use and the smell of winter is almost here. This year is a tricky one, but could and more likely will be busy.

Enjoy the snow!