Winter Outlook (Dec. 2003-Feb. 2004) November 20, 2003

[CaptinCrunch]

Winter Outlook (Dec. 2003-Feb. 2004)
8AM EST, November 20, 2003


Bitter cold and snowy weather arrived on
the scene in parts of the U.S. in October
and early November and attention is
turning to the outlook for the upcoming
winter.

Last winter featured a lopsided pattern
with very warm and dry conditions in
much of the west, with unusually wet and
cold in much of the south and northeast.
This winter is expected to be less extreme
with some relaxation of the drought in the
West and less severe winter conditions in
the East.

Several factors are expected to play a role
in the upcoming winter. The first factor, El
Nino, is very familiar to most people.

El Nino is defined as a periodic warming in the eastern and central Pacific near the equator. El Nino conditions usually favor a warm and dry winter in the northern U.S. with cool and wet conditions in the south and especially in California.

La Nina is a cooling in the eastern and central Pacific near the equator. Its
effects are typically opposite, cool and wet in the northern and western U.S. with warm and dry conditions in the southeast.

Meteorology researchers believe water temperatures in the Pacific have shifted back and forth between El Nino and La Nina conditions for centuries. As the link "Water Temperatures" to the right shows, water temperatures in the equatorial Pacific have crept above normal, especially in the central and western Pacific from the international dateline to Indonesia. Typically in an El Nino event, the warmest water temperatures versus normal concentrate close to coasts of Peru and Chile.

Since the waters in the Pacific are only likely to reach borderline El Nino
conditions and the warmest waters are unusually far west, the impact that the Pacific will have on this winter is quite uncertain. Based on patterns observed in past winters, the farther west the warmest waters remain, the better the chances of cooler conditions in the northeast and dry conditions in the eastern Gulf coast and Southwest.

With a weak El Nino versus a strong one, other factors such as snow cover, the strength of the Pacific jet stream, and an Atlantic pressure pattern called the North Atlantic Oscillation (NAO) will likely play more of a role. Over the last month, an unusually strong Pacific jet stream has been noted from East Asia to the coast of western North America. A pattern of abnormally cool water in the Gulf of Alaska and warmer water to the south is helping to fuel this jet stream. This strong jet is helping to bring surges of very mild air across much of the U.S. and also wet weather to the West Coast.

The strong Pacific jet stream is expected to remain in place through much of the winter, periodically flooding the country with mild air.
A second factor is snow cover. North American snow cover in the first week of November was the second highest since 1966, when records were first kept. Deep and early snow cover across Canada and Alaska typically serves as a refrigerator, helping to generate bitter cold air masses that can move into the U.S. However, given the predominant Pacific jet stream, this arctic air is not likely to make it deep into the U.S. on any regular basis. The northern states stand the best chances of being influenced by these bitter cold air masses.

Another factor to watch is the North Atlantic Oscillation (NAO). NAO is a
pressure anomaly (deviation from normal) that may be enhanced by water
temperature anomalies. When there is warm water in the high latitudes near Greenland and Iceland, high pressure tends to build.

These areas of high pressure near Greenland can become large and long
lasting and serve as a "block" in the atmosphere. When storms approach the eastern U.S., they are forced to dive underneath the block and track unusually far south. This often forces cold air masses into the East. Such was the case in 2002-03, when the NAO favored unusually strong blocking highs. On the other hand, when low pressure builds near Greenland it creates a strong westerly flow across the eastern U.S., forcing cold air masses out across eastern Canada into the Atlantic.

In any given winter, these blocks are an on/off feature, and cold episodes are often quickly replaced by mild Pacific flow. Overall, it appears that the NAO will not be as big a factor as last year. However, it should be noted that the NAO is much harder to predict several months in advance than is El Nino/La Nina.

Another area where water temperatures may have an influence is off the East Coast. During the fall there unusually cold water has built off along the immediate mid-Atlantic and northeast coasts with unusually warm water further offshore. The sharp boundary between the warm and cold water would encourage storms over land to redevelop off the mid-Atlantic and northeast coasts.

Our outlook for the winter indicates that mild surges will alternate with shots of arctic air. This is the reason why "normal" temperatures are indicated for much of the country. The area that will be most affected by the shots of arctic air is the northern Plains, so below normal temperatures are most likely there.

The jet stream is likely to surge northward into the western U.S., favoring
above normal temperatures from the Great Basin toward the West Coast.
The storm track is likely to run across the northern border of the U.S. with a second track from the southern Plains toward the Northeast. Just to the
northwest of the prevailing storm track, above normal precipitation is expected from the lower Mississippi Valley to the eastern Great Lakes and possibly the Appalachian Mountains. (Click here for graphic showing dominant storm tracks.)

The graphic in the upper right corner shows the details on the temperature and precipitation forecast. Since specific forecasts on amounts of precipitation and range of temperature are not possible, the images highlight the areas of the country that could see above normal, near normal and below normal temperature and precipitation. Click the enlarge link to see the image full size. (Click here for a forecast table of all states.)

It is difficult to make any specific prediction on snowfall amounts as even in a mild winter, one big snowstorm can produce nearly the normal snowfall for an entire winter season. Furthermore, a cold winter does not by any means guarantee a snowy one. Very cold winters are often dominated by arctic high pressure with storms starved for moisture.

[CaptinCrunch]

bummer my pics did not show up..

[JCT777]

That's a good read. Thanks for posting it, Chris.

[CaptinCrunch]

Thanks, JCT777

I just worked at getting it from Weatherbug and posting it here. I know allot of people don't use weatherbug so I just thought I would share. For those who do have it you can see the pics that didn't post.

I'm a weather nut and I have found this site to be the GREATEST thing since digital weather radar.

[Anonymous]

sounds like a boring..non passionate winter forecast....ill take a JB or intellicast or Wxrisk winterforecast read any day.

[CaptinCrunch]

All winter forecast are somewhat boring, but they do make for a good converstion among friends. I find each different forecast has something that another one didn't have and I try to read them all for the knowledge of the subject.

Happy Thanksgiving Everyone!!!!