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Note: Dark red and italicized text is taken directly from the 2002-03 Winter Outlook issued in October, 2002.
Although there is some uncertainty in the forecasts about the timing and intensity of El Niño, all of the climate models indicate that it will indeed be weaker than the strong El Niño experienced in 1997-98. At this time, it is anticipated that this winter's El Niño will, at best, remain in the moderate category.
While El Niño was projected to hold in the moderate category for the balance of the winter, by February El Niño was showing signs of weakening, especially near the South American Coast where water temperatures actually began falling. While researching previous weak to moderate EL Niño's, concern about not only El Niños strength but WHERE that strength (greatest above normal water temperatures) would eventually surface, would likely impact our winter. It was noted, at least since the early 1980s, that the warmer (or highest departures above normal) the Eastern Pacific water temperatures were just offshore of South America, the better chance our winter would be milder. This was most evident in the moderate to strong El Niños. Mid fall indications were that water temperatures off the immediate South American Coast were hovering close to normal levels, yet areas further west over the central and western Pacific were above normal. This was a concern for two reasons, first: It was expected El Niño was not going to be a strong El Niño to begin with (hence the title of the Winter Outlook) and second; just how much this area (Eastern Pacific) would actually warm, was questionable.
As important as the progress of El Niño will be the evolution of the North Atlantic Oscillation (NAO) and the Eastern Pacific Oscillation (EPO). The NAO, basically, is the dominant upper wind flow pattern over the North Atlantic influenced by the ocean. 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.
The Eastern Pacific Oscillation (EPO) is the upper wind flow over the Eastern Pacific influenced by the ocean. When in a positive phase, the EPO generally is reflected by dominant stronger zonal flow and/or troughing along the West Coast of the U.S. This combination, in turn, tends to funnel milder Pacific air well inland into the country and thus, limits arctic outbreaks by holding them at bay up in Canada. When the EPO is dominated by a negative phase (as with the NAO), more ridging develops along the West Coast as higher pressure extends from the Gulf of Alaska south along the West Coast of Canada (opposite of the positive phase). This, in turn, encourages a northwesterly flow from Canada into the middle and eastern sections of the US and thus, the delivery of polar or arctic air.
While researching the NAO and EPO in the previous winters in the study, an interesting item was noted that tended to be more relevant in the El Niño winters. It appears that the EPO was as much (and sometimes more) of a determining factor to the overall temperature trend of the winter than the NAO. In some El Niño winters, it was noted that if the winter was dominated by a negative EPO, even when accompanied by a predominantly neutral to occasionally positive NAO, temperatures over Southeast Lower Michigan were generally normal to below while snowfall was normal to above. Logically then, the coldest PERIODS of any of the winters in the study were when BOTH the EPO and NAO were in a negative phase. Therefore, the negative EPO circulation helped set up and "feed" the Arctic air into the circulation of the negative NAO by amplifying a ridge along/near the West Coasts of the U.S. and Canada. Subsequently, the building of ridge along the West Coast encouraged the troughing and cold air delivery over the eastern half of the country.
This past winter was indeed dominated by negative EPO that had its roots in the mid fall time frame. The EPO cycled to and held in a negative phase frequently during the winter with the only predominant positive phase only occurring from mid December into early January. This predominant positive phase coincided well with our "mildest" period of the winter months. Also, even though the EPO was positive during that period, the NAO was mainly NEGATIVE but this still had little effect on our temperatures as readings still averaged above normal. This bears out the findings stated earlier that the EPO was mainly in the "driver seat" this winter. Another strong player this past winter (and part of NAO) was the Arctic Oscillation /AO/. While being a part of the NAO (and for our concerns), the AO is the upper wind circulation from the Arctic, south into North America. The AO was impressively strongly negative for the balance of the winter and worked in conjunction with the EPO to deliver the winter Arctic intrusions.
Along with the aforementioned factors, other considerations are taken into account for this winter outlook. First are the weather trends of the last year and how well they relate to the weather trends proceeding the 13 winters in the study. Second, 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 sunspot cycles (timing/peak/intensity) of past winters in the study.
During the winter of 2002-03, sunspot maxima continued to wane from the peaks attained during the past few years and this trend was compared to the past winters in the study. Though a similar sunspot waning trend was noted in some of the researched winters, the end result was more variable than other factors researched and mentioned above. A bit more weight, however, was given to the overall weather pattern of the proceeding summer and autumn time periods.
While the majority of winters in the study proved to proved mild with normal to below normal snow, there were important exceptions. Perhaps no trend of some of Autumns was more noteworthy than the abrupt change in the upper wind pattern to a dominant northwesterly flow beginning in October. Interestingly, this trend also was a foreboding of things to come and was picked up on in the research and then, noted in the original outlook under "Contrary Indicators".
Perhaps none of the winters challenged the prevalent below normal snowfall trend (and above normal temperatures when looking at 1977-78) more than the winters of 1885-86, 1972-73 and 1977-78 when snowfall was significantly above normal at most locations. While the detailed EPO and NAO trends were not available for 1885-86, they were for the winters of 1972-73 and 1977-78. Also, in addition to the being snowy, why was the winter of 1977-78 so much colder than the rest in the study? Reviewing the earlier archives of the EPO and NAO, along with the 500 MB upper wind pattern, may help understand the differences between the harder winters of 1972-73, 1977-78 and the dominant milder ones. Is there some trend to watch for in the EPO and NAO (1972-73 | 1977-78) and upper air pattern this fall that occurred in 1972 and 1977?
An important change came in October (and again, one of the few cool Octobers in the study) when abnormally cold air surged into the region mid month. While the timing of the polar blast duplicated most in the study its strength and dominance was atypical. The monthly average temperature for October 1977 was a cool 47.9 degrees /normal 51.9/ at Detroit. Curiously, this same pattern was noted in the fall of 1972 and again, this abrupt change surfaced in October. October of 1972 not only turned out to average well below normal, but with nearly the same average temperature as October 1977 with 47.3 degrees.
While October 2002 remained warm until mid October, the recent abrupt change to a deep 500 MB trough over the eastern half of the country resulting in much colder weather bears watching, especially if it represents an intermediate trend change to the past several months. In addition, the near-term projections of the EPO and NAO both indicate, at least short term, negative phases and this too bears watching for any overall, longer term trend change.
October 2002 was much like the other notably cool Octobers mentioned in the research and ironically, October 2002's weather abruptly also changed from a balmy summer-like beginning to a late fall-like ending, changing in mid-month During the first half of the month, the temperature averaged 60.4 degrees at Detroit, but by the end of the month, the average temperature had dropped to 50 degrees at Detroit ( and 47.6 at Flint) or 1 « to 2 degrees below normal.
Like the two "1970s" winters mentioned above, this was a very significant pattern change that occurred October, that had pretty much dominated the region into mid April. As mentioned in Detroit's specific write up, the month's of October through March all averaged below normal. And, incredibly, six months in a row below normal has not been seen in Detroit since 1979. In addition, the recognition of this significant pattern change and its evolution was stated in the Winter Outlook and also noted in several of the Monthly Summaries this past winter.
These weak to moderate El Niño winters more often that not, also had a tendency to be back-end loaded. Meaning, the likelihood of snow and/or cold increased as the winter evolved. It was the years mentioned above where a trend to colder weather took hold in October (1972, 1977 and also in 1987) that saw above normal snow in December.
This pattern exhibited itself this past winter also, with the heaviest and lateness of the snow generally falling mid - late winter (February - April) along with the coldest temperatures being registered as late as early March. Earlier heavy snowfalls (similar to 1972, 78 and 87) were also noted in December over Extreme Southeast Lower Michigan.
In the more active winters, where temperatures averaged within a few degrees of normal or below (1977-78), clippers were busy draping pacific, polar or arctic air across the nation. The dominant southern stream lows aided by El Niño generally tracked across the Southern Plains into the Great Lakes ("Colorado" or "Texas Panhandle" Lows). A third path tracked across the Southern U.S. into eastern Texas, then moved northeast either into the Ohio Valley or up the East Coast.
The winter of 2002-03 will go down as a very active winter with its endless parade of southern stream low pressure systems. By far, the most dominant low pressure track that affected Southeast Lower Michigan rode from Eastern Texas, northeast up the Ohio Valley. This put Southeast Lower Michigan on the north (and cold) side of these storms bringing for most of us, our snowy winter. As one can see in the Chart-1, Detroit registered the most snow during the winter of the three main cities.
|Weak To Moderate Strength El Niño Winters Researched (Chart 1)|
|1881-82||37.0 -1-||-||-||13.2 -2-||-||-|
|1931-32||35.6 -2-||33.4*||33.2 -1-||26.2||28.4*||31.0|
|1953-54||31.1 -13-||28.1 -8-||27.2 -15-||40.0||48.7||46.1|
|1972-73||27.8||27.3||23.8||45.0||62.9 (6)||65.8 (8)|
|1977-78||20.4 (7)||19.1 (5)||17.9 (6)||61.7 (8)||50.6||55.6 (20)|
|1991-92||30.4 -17-||28.2 -6-||27.0 -17-||43.5||54.4 (13)||46.2|
( ) Coldest or Snowiest Ranking
- - Warmest or Snowless Ranking
*Not an Official Record and not in ranking (Official Records Began in 1942)
**Sample Incomplete and Therefore Not a reliable Snow Average
Checking the other winters in the study, 1977-78 is nearly a dead-ringer as far as snowfall totals for both Detroit and Flint and also distribution of that snow, with Detroit again posting the most snow. A nearly duplicate storm track is also well reflected in the 1977-78 winter and was the southern stream track mentioned in the outlook "A third path tracked across the Southern U.S. into eastern Texas, then moved northeast either into the Ohio Valley or up the East Coast". The numerous lows in the Ohio Valley either moved into Southern Ontario or to the East Coast, while others just moved up the East Coast and missed our area. It's interesting to note that the 1977-78 winter contained our Great Blizzard of '78 storm as an intense Arctic Jet and sub-tropical jet merged over the Northern Ohio Valley/Eastern Lakes Region. While there was no "Great Blizzard"during this past winter, there were in fact several snow storms that dumped better than six inches of snow in the snowiest areas. Most of the systems this past winter reached their maximum intensities east of the region over Ontario or off the East Coast (which is typical). Even while 1977-78 was colder than this past winter, that long cold TREND with extended periods of time below normal was certainly duplicated this past winter, though not as severe. Really, the only notable difference was Saginaw's higher snowfall than this past winter. This can be explained most likely with the following phase "Blizzard of 1978" which dumped considerably more snow up in the Saginaw Valley.
The Winter of 1972-73 overall was also a snowy winter and shows the same type of distribution as this past winter, but main storm track rode a bit further north into Southeast Lower Michigan and thus, Saginaw received the highest amount of snow. Somewhat reflective of a further north storm track would be somewhat milder temperatures as was the case that winter. So, overall 1972-73 averaged warmer than this past winter, while this past winter was warmer than 1977- 78. Therefore, it is noted that the Winter of 2002-03 contained the same basic characteristics of both 1970's winters in the study.
A third winter on the list for similarity but to a lesser extent (and ironically, also was proceeded by a cool October), was the Winter of 1987-88. The snowfall pattern of the higher amounts over Extreme Southeast Lower Michigan surfaced here too, though snowfalls were not nearly as high as 1972-73, 1977-78 and 2002-03. At the same time, however, average winter temperatures were closer to this past winter than in either of the other two winters.
Finally, the Winter's of 1885-86 and 1913-14 also share a few of the characteristics with this past winter. The winter of 1885-86 seems to contain that energetic storm track of the 1970s winters and 2002-03, but it was milder and no other data is available from the other cities to make a better comparison. The winter of 1913-14 also has a similar temperature trend to that of 1987-88 and 2002-03 (but mainly 1987-88 since it was warmer) but it lacked any obvious snowfall trend and amounts (since Flint's data may be unreliable)
One thing all the above similar winters do have in common is they reflect that dominant storm track that rode through the southern Great Lakes/Northern Ohio Valley.
Out of the 13 winter/spring seasons reviewed, a majority (8) contained below normal temperatures, two averaged within a half degree of normal, while three averaged above normal. Therefore, if one went with the majority (not always the thing to do considering the sited "contrary indicators" of this past winter), temperatures this spring should have averaged below normal. Since our winter temperature trend was pretty much in between (or an average) of the Winters of 1973-74 and 1977-78, what were the springs of 1973 and 1978 like? Somewhat amusing, both held their perspective winter temperature trends on into following spring. The Spring of '73 was also warmer than normal, while the Spring of '78 was cooler than normal. Therefore, since our winter temperature trend was roughly in between these two winters, our spring temperatures was projected to average around normal (or within a 1/2 degree of the norm). Therefore, both of these trends strongly indicated temperatures this spring would average normal to below normal the months of March, April and May, which was the case.Rainfall:
Rainfall was a little more generous during many of these 13 springs than it has been of late with three springs containing above normal rainfall, six (the majority) contained within a half inch of normal and four received less than adequate rainfall. Again, slanting toward the majority, this implied rainfall for the spring should average closer to normal rather than the dominant below normal seen since last summer. Reflecting again back to the Springs of '73 and '78, rainfall during the Spring of '73 averaged above normal, while in the Spring of '78 rainfall was below. Therefore, the median of the two springs, or near normal (within a 1/2''), was supported and again the way to go. Rainfall this spring did follow that trend of the majority with an increase in overall rainfall (but not necessarily above normal) not seen since Spring 2002.Severe Weather Season:
The severe weather seasons proved to be rather early/active in the majority of the springs checked, and especially in the 1970s (the two in the study, 1973 and 1978 and others). Like the past winter, this spring also followed the trend of the two "70s" winters with a rather active/early severe weather season. One explanation for this past spring (and in some of the researched springs) was the persistence and relative strength of the southern jet stream and subsequent storm track into Southern and Central Great Lakes.