|Winter 2001-02 outlook for Southeast Lower Michigan|
The neutral pattern in the Pacific that commenced the fall of 2000, remains in place this fall. A neutral pattern reflects near normal Pacific sea surface temperatures. When a neutral pattern dominates, the upcoming winter's weather pattern is less affected by any specific pacific weather pattern (La Nina or El Nino). A La Nina pattern indicates the Pacific sea surface temperatures are below normal, whereas in El nino, the temperatures are above normal.
This neutral pattern was partly responsible for last winter's (2000-2001) outlook for an earlier, harsher beginning that came to past with a vengeance in December. The combination of record cold and snow during the month was unprecedented for December across much of Southeast Lower Michigan. Temperatures moderated nicely in January and February with only light amounts of snow. Also, like the hard beginning predicted, previous winters studied also indicated this moderating trend after a rough beginning, temperatures late in the winter fell back closer to normal or below but with still lighter snows. A more thorough summary about last winter can be found at:
The same neutral pattern is expected to, more or less, remain in place through much of the winter. Sometime late in the winter or spring, however, a weak El Nino is expected to evolve (therefore, with the neutral pattern expected to fade this winter, the term "late-stage neutral winter" will be used when needed for clarification sake). The timing of this El Nino evolution will be one of the critical factors as to how this winter's weather will play out. Similar to last winter, and may be most important, will be the evolution of the North Atlantic Oscillation (NAO). The NAO, basically, is the dominant upper wind flow pattern over the North Atlantic. While in a negative phase, the NAO sometimes tends to act as a block (or dam) to the upper wind flow over the eastern half of North America. This blocking effect, in turn, tends to deliver the polar/arctic air into the eastern half of the country and Great Lakes more readily.
Along with the aforementioned factors, other considerations are taken into account. One, is the weather trends of the Summer and Fall that proceeded the previous winter's studied (winters that fall under the above criteria). These patterns are then, compared to this past summer and, so far, this season's fall pattern.
Another consideration made when making the winter outlook is a check of the solar activity during the years of the past winters studied. It is known that sunspot activity has an impact on climatic trends and patterns over the earth. The current sunspot cycle is then, compared with similar sunspot cycles (timing/peak/intensity) of past winters studied. While this upcoming winter sunspot maxima cycle will be on the wane, it will still be near the peak reached last winter. Additionally, some other factors include current soil conditions (moisture and temperature) and fall Great Lakes water temperatures (especially for early in the winter).
Like a carbon-copy of this past summer into autumn period, research shows the majority of summer - autumn periods oscillated between very wet and distinctly dry intervals. What was even more interesting to find was that out of the 12 (Detroit) summer - winter periods researched (table-1), eight had a distinctive very wet period during the early fall (Sep and/or Oct). This correlates well with the very wet period seen this fall and last (Aug-Oct 2000), both taking place before a neutral winter. This is in contrast to the majority of relatively nicer, drier falls seen more often than not, during much of the 1990's.
Like this Fall and last, the majority of neutral falls had more aggressive, earlier cold snaps. Ironically, one of the first really strong cold air outbreaks in both Falls, occurred not only early in October, but around the same dates (the 6th-8th). It was on October 8th, 2000, that some snow showers were officially observed at several locations in Southeast Lower Michigan (including both Detroit and Flint),and then on October 6th this year, a few locations in the Saginaw Valley and Thumb region reported a few flakes.
Despite the early cold snaps seen, the majority of fall periods were still interspersed with some nice Indian Summer weather, sometimes occurring well into November. The considerable fluctuation of the upper wind pattern during the fall into the Winter was the driving force here in past neutral periods and is expected to be again in the upcoming late-stage neutral Winter. Nearly all of the Fall-Winter periods analyzed indicated large monthly (sometimes weekly) fluctuations in temperatures. Many of these fluctuations were directly related to upper wind pattern changes influenced by, in part, the NAO (North Atlantic Oscillation) mentioned earlier. This resulted in a busy, amplified upper wind pattern (jet stream) and while mainly progressive, occasionally became blocked (noted above) or zonal (absence of notable troughs/ridges). A weaker amplified and progressive pattern even tended to show up during the Summer months (not unlike this past Summer).
It is interesting to note that the onset of El Nino, in conjunction with the NAO phase, had a fairly strong influence on our winter (and early Spring) weather. Generally, the earlier (and/or stronger) El Nino was during the Winter, the milder the Winter outcome. This was especially true if the NAO (North Atlantic Oscillation) was dominated by a positive phase. Generally the milder Winters (1930-31, 1968-69, 1986-87, 1990-91) were a result of a overall neutral pattern where El Nino began early winter and/or the NAO phase was mainly positive. In direct contrast to this, were the winters that remained neutral for much of the winter (or just a weak El Nino began late winter) and most important, the NAO remained negative, these types of winters generally were the rougher ones noted with more aggressive cold outbreaks and normal to above normal snow.
The worse neutral Winters in the study (combination of snow and cold) were, ironically enough, about 100 years apart (1880-81 and 1981-82). While the NAO remained mainly negative during the winter, just a weak El Nino evolved mid-late Winter, which kept the storm track active from the Pacific into Southern Plains/Texas area, then northeast into the Southern Great Lakes/Northern Ohio Valley. Also, while an upper trough still dominated the Lakes Region (to supply the cold), it occasionally phased with Pacific systems and carved out a new trough further west in the Central Plains and Midwest.
Still, a few other Winters in the research were very cold (ranking in the top ten coldest Winters) with frequent outbreaks of Polar or Arctic air due to the domination of a strong upper low/trough over the Great Lakes (1904-05, 1962-63, 1976-77). However, as a result of that dominant cold trough, major synoptic snow producing storms, more often than not, tracked further South and/or East of the Great Lakes. With clipper type systems and subsequent lake effect snows prevailing, and the lack of a good moisture source from the Gulf of Mexico for synoptic snowstorms, snowfall across Southeast Lower Michigan tended to be near normal to below.
According to the Climatic Prediction Center, the most likely scenario
for the upcoming winter 2001-02 is for the basic neutral pattern to remain
in place for much of the Winter, with a weak El Nino possibly beginning
late Winter or Spring. While the NAO is not reliably predictable for more
than a week or two, chances are, a negative phase will dominate. The
2001-02 winter (like its predecessor) is expected to make an appearance
early with mid November to early December the optimum time (or around
Thanksgiving into the first two weeks of December). This was generally the
time of the first significant snows (a couple of inches or better).
However, it should be noted that a few late stage neutral Winters did
contain significant snowfalls early - mid November. This December,
however, is not expected to be as severe as last December when combining
both snow and cold.
It was interesting to note that the snowfall patterns of the late-stage neutral Winters tended to be more variable than the front-end loaded initial neutral Winters. While some late-stage neutral Winters did indeed contain the heavier snows early, others received the heavier snows mid or late Winter. In addition, a few winters contained above normal snow each of the months that normally have snow, while a few others even contained below normal snow each of those same months. A glance at the season snowfalls (table-1) certainly attests to its snowfall variability. Therefore, late-stage neutral Winters were definitely more variable in regards to snowfall than initial neutral Winters.
Normal snowfall ranges around 40 inches from Detroit south to the Ohio border, to 45 to 50 inches across Detroit's northern suburbs into Flint and the Saginaw valley. Over Southeast Lower Michigan (and like any other winter),this will be strongly dependant on predominant storm tracks that are established during in the winter.
The most dominant storm track during the late-stage neutral winter was the Alberta clipper which ushered in Polar or Arctic air originating from western Canada or the Arctic. Two other storm tracks of somewhat lesser frequency were also noted. One was the Colorado or Texas low that hooked northeast into the Great Lakes and, the Gulf of Mexico low that tracked northeast into the Ohio Valley/Eastern Great Lakes or up the East Coast. The two storm tracks that most often bring the heaviest snow to Southeast Lower Michigan are the Gulf low and the Texas low.
So summarizing, the consensus of the researched Summer - Winter periods indicate that temperatures across Southeast Lower Michigan for the Winter 2001-02 should average below normal (like last winter and with considerable temperature fluctuations). While seasonal snowfall amounts and patterns were quite variable, the consensus still indicates snowfall will average around normal to above.