It has been five years /1997-98/ since the climatic event "El Niño"
last occurred in the Pacific. The event is nothing new and has been going on for centuries.
Reliable data to measure El Niño is available to scientists for interpretation. El Niños are
detected by a host of meteorological equipment and methods including weather satellites,
moored and drifting buoys, and sea-level temperature analysis. This data is used in computer
models of the oceans and atmosphere to help predict the evolution and dissipation of the
El Niño life cycle.
The term El Niño is Spanish for the "boy child" and refers to the Christ child because
the effect generally is associated with the month of December and Christmas. The term
was coined by the Peruvian fisherman as far back as the 1600's to describe the change in
the Pacific Ocean currents off the coast of South America. The phenomenon originates in
the western tropical Pacific Ocean and generally occurs every two to seven years. The
normal easterly trade winds relax and a westerly wind begins to dominate. As a result,
the warmer surface sea water of the tropics spreads east and northward toward the South
and North American continents. This causes a stronger atmospheric link to develop
between the Pacific tropics and the higher latitudes and thus, invokes a shift in mid-latitude
weather patterns including those of North America.
Along with the shift in the mid-latitude weather patterns, abnormally low pressure
develops over the tropics in the eastern Pacific, while unusually high pressure takes shape
over Indonesia and Australia. Normal global atmospheric circulation patterns are disrupted
and since the U.S. is generally downwind of El Niño, the effects can be quite noteworthy.
As a result of El Niño, the tropical connection or "pineapple express" increases across
mainly the southern U.S. in the winter bringing additional storminess and rainfall. At the
same time, the northern U.S. tends to see a more pleasant winter with relatively milder and
drier conditions. While this is the general accepted scenario, other factors along with the
El Niño "effect" must be examined and considered, particularly when a weaker El Niño
occurs.
As mentioned, five years ago /1997-98/, a strong El Niño occurred in the Pacific. The
resultant 1997-98 winter was abnormally warm with well below normal snowfall across
much of Southeast Lower Michigan. Note the closer to normal season snowfall, however,
at Saginaw which was closer to the dominant storm track. (Chart-1)
(Chart - 1)
WINTER OF 97-98
AVERAGE TEMPERATURES (97-98)
(Note: Old Norms 1961-1990)
_____________________________________________________________
December January February Winter Normal
-------------------------------------------------------------
Detroit 32.3 32.8 36.7 33.9 25.5
(Depart) (+4.0) (+9.9) (+11.3) (+8.4)
Flint 29.9 29.9 34.6 31.5 24.1
(Depart) (+2.7) (+8.4) (+11.1) (+7.4)
Saginaw 26.2 28.6 33.4 29.4
(Depart) (+4.9) (+8.0) (+10.9) (+6.2) 23.2
_____________________________________________________________
PRECIPITATION (97-98)
(Note: Old Norms 1961-1990)
-------------------------------------------------------------
December January February Winter Normal
-------------------------------------------------------------
Detroit 1.89 2.78 3.60 8.27 6.32
(Depart) (-.93) (+1.02) (+1.86) (+1.95)
Snow/Dpt 6.1/-4.8 8.3/-3.5 T/-9.2 22.5 41.2
Flint 1.06 3.16 1.65 5.87 4.78
(Depart) (-1.05) (+1.77) (+.37) (+1.09)
Snow/Dpt 6.9/-4.4 8.0/-4.3 0.4/-9.9 28.3 45.1
Saginaw 0.78 4.04 2.79 7.61 5.37
(Depart) (-1.59) (+2.41) (+1.42) (+2.24)
Snow/Dpt 6.7/ 14.4 0.6 40.1 46.0
_____________________________________________________________
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The Climate Prediction Center forecast models indicate that moderate El Niño conditions
are likely to continue through the Winter of 2002-03. 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.
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 is
in response to lower pressure over the Gulf of Alaska that extends south off the coast of
Western Canada, while higher pressure dominates across the central Pacific. 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. Last winter was very mild and this is reflected well by the positive phase
dominance of both, the NAO and EPO.
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 as 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 upcoming winter, sunspot maxima are expected to
continue to wane from the peaks attained during the past few years. Additional factors include,
current soil conditions (moisture and temperature) and autumn Great Lakes water temperatures.
The following winters were researched under weak to moderate El Niños:
SUMMER AND AUTUMN TRENDS
Temperatures:
In researching the above winters, the trends during the proceeding year (since the
winter of 2001-02) were noted and compared to the weather in the above winters
and their proceeding year. Any occasional or frequent recurring weather correlations
were noted between the years. This research was primarily based on the most complete
database of records at Detroit.
Several similarities were seen between this past year and a number of years in the list.
During several of the preceding summers and/or falls, notable dry spells or droughts
were ongoing across significant portions of the country especially in: 1881, 1913,
1931, 1953, 1963 and 1977.
Probably the most consistent trend noted in the summer into, at least, early fall
preceding these winters was the overall above normal temperatures. A good number of
these summers and/or falls averaged above normal. The years that saw this trend included:
1881, 1913, 1931, 1939, 1953, 1963, 1987, 1991 and 1994. So, out of the 13 winters
researched, an impressive nine were preceded by an overall warmer than average summer
and/or fall. The most notable (warmest) of the lot (and also in top 20 warmest summers
and/or falls lists for Detroit, Flint or Saginaw) included 1931, 1939, 1953, 1963, 1987,
1991 and 1994 (and while the summer of 1977 did not average above normal, that July
made the list of top 20 warmest Julys). This warm summer pattern matched very well with
our past summer, especially at Detroit and Flint, which both placed in the top 20 Warmest
Summers list.
During the autumns, the majority of Septembers through Novembers averaged normal to
above for temperatures, especially in early fall. All in all, there were some nice and warm
Septembers and/or Octobers in this study. Out of the 13 Septembers, eight averaged
normal to above (some significantly, not unlike this past September) and five averaged
below normal. It must be mentioned, however, that when a September did average below
normal, it was generally by just a small departure. Eight of 13 Octobers also averaged
normal to above (and as September, a few also by a large margin). In contrast to the
minor below normal departures found in September, it was observed that when October
averaged below normal, it was usually by a more notable departure. Unseasonably cool
Octobers occurred in 1972, 1977 and 1987 when temperatures averaged in the mid 40s
/normal 51.9/. Moving on into November, here too, eight of 13 Novembers averaged
normal to above. And, like October, when the below normal departures occurred, they
were generally more significant. Some cool Novembers occurred in 1939, 1972 and 1991
when temperatures averaged in the mid to upper 30s /normal 40.7/. Thus, in spite of the
generally warm falls, the chances of a cool October or November jumped, as evidenced
by the three cool Octobers and Novembers, all in different years (1939, 1972, 1977, 1987
and 1991). The only exception was 1972, when both October and November averaged
below normal.
In spite of the dominant early warm autumns, it was interesting to note that frost/freezes
were generally seen over much of the region at pretty much their normal time period
(early - mid October). These cold snaps tended to be aggressive and were quite a contrast
from the dominating mild fall weather. They were generally followed, at some point, by
Indian Summer weather (for more info) well into November with temperatures pushing
back up into the 50s, 60s and even 70s. Besides the aggressive cold snaps early-mid
October, distinctive pattern changes to colder weather sometimes occurred during the
month; this pattern change resulted in the aforementioned cool Octobers.
Precipitation (including snowfall):
A clear majority of the summer into, at least, mid fall periods contained drier than normal
conditions. Generally, the precipitation trend that dominated during the summer held on
into early to mid fall. Late fall into winter saw more mixed results and was dependant on
the strength of El Niño (and resultant storm tracks) and the EPO/NAO phase. Some periods
from late October through November became wetter (and snowier, see below), while others
remained dry. The years that the entire fall was wet and contained above normal rainfall were
limited to just two, 1881 and 1931. The above normal departure was very substantial, however,
in the autumn of 1881 when 13.74 inches fell in Detroit (normal, 8.16 inches). And maybe not
surprising, the autumn of 1881 still remains at the top of the list for wettest falls in Detroit. The
1931 above normal departure is much tamer at just +.80 of an inch with 8.96 inches falling.
While the chances of a frost/freeze occurring near the average dates were good,
the dates when the first snow flakes (trace) flew were more variable. While October
historically sees at least a trace of snow by the end of the month, the majority (eight)
of these particular Octobers did not see any snow. The five Octobers that did see
snow had just a trace. And, while below normal snow dominated the Novembers
at Detroit with eight of 13 having below normal snowfalls, out of the five that
did contain normal to above snowfall, two (1972, 1977) were significant with nearly
triple the normal /2.7/ at Detroit (more in "contrary
indicators" below).
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, NAO and upper air pattern this fall
that occurred in 1972 and 1977?
The winter of 1977-78 unfolded while a weak El Niño was in place. Since it was a
generally rough winter, it was not surprising to find that a negative phase dominated
both the EPO (1977 |
1978) and NAO (1977 | 1978) that winter. These
negative phases of the EPO and NAO
worked in conjunction to help deliver the polar and arctic air into the Great Lakes
region. This, in turn, more than offset any warming from El Niño. The summer and
early fall proceeding that winter were not unlike the majority in the study as far as above
normal temperature. Rainfall, however, was more plentiful than most of the summer-fall
periods in the study. 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 (mentioned above in the
frost/freeze data) 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. The subsequent
November averaged near normal in 1977 but below normal in 1972 while both contained
well above normal snowfall. While the current fall 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.
Negative phases of the EPO and NAO more often than not prevailed the remainder
of the 1977-78 winter, but to a lesser extent in 1972-73. Both winters displayed a
fairly active southern stream storm track (aided by El Niño). In fact, it would
be remiss if it wasn't mentioned that during the weak El Niño winters of 1885-86
and 1977-78 in this study, two very powerful snowstorms crippled much of the
Great Lakes. Many can recall the January 26th, 1978 Blizzard whose 25th anniversary
will come this winter (watch for the write-up mid winter) which brought the lowest
pressure reading on record to a number of weather stations with its visit (including
Detroit with 28.345 inches). The biggest snowstorm (in terms of amount) ever to
clobber the Detroit area since records began occurred in April (yes April) 1886
(see "Tale of Two Storms")
when 24.5 inches fell at Detroit! In the 1978 storm, a strong phasing of the subtropical
jet and an evolving negative EPO and NAO, help set the stage for the creation of that monster.
In addition, an intense upper level disturbance screamed southeast out of Canada and
phased with the subtropical jet, deeply intensifying the surface low pressure developing
over the Southeastern U.S. as it raced north northwest. This meteorological "bomb"
blossomed over the Upper Ohio Valley into the Great Lakes and Southern Ontario.
Temperatures:
While the temperatures during these winters did tend to average normal to above normal
overall, they were not without their arctic or polar plunges and occasional storms. These
polar blasts, however, tended to be more transitory in nature rather than a permanent
winter visitor and, when they visited, it tended to be more in mid to late winter. The
exceptions, however, were during the few years mentioned when the winter actually
"began" somewhat early in November. The majority of the remainder of the winters
researched began early to mid December, generally by way of a strong arctic plunge
(or again, an abrupt change from the earlier, milder dominant temperature pattern).
This was directly related to either the NAO or EPO (or both) becoming decidedly
negative and had little bearing on El Niño. The two unseasonably warm winters of
1881-82 and 1931-32 averaged 8-10 degrees above normal and snowfall was well below
normal. In both these abnormally warm winters (1881-82/1931-32), winter did not really
"begin" until January (what winter there was).
The month of December saw a clear majority (11) averaging normal to above normal
in temperatures. Monthly average temperatures ranging from the upper 20s to mid 30s
were commonplace at Detroit, Flint and Saginaw. The incredibly mild December of
1881 averaged 40.6 degrees at Detroit. Several of the Decembers in the research placed
in the top 20 warmest Decembers on record. At Detroit, five of the 13 Decembers placed
in the top 20 warmest, while in the Flint area (using co-operative data since 1893), four
placed in the top 20 warmest Decembers and likewise in Saginaw (since 1899).
January into February also saw more normal to above normal temperature departures
over below normal departures. While nine out of 13 Januaries averaged normal or
above, that number dropped to seven (above normal) in February. Therefore, a trend
was noted that while the chances were fairly good that while any given winter month
may average normal or above, those odds dropped as the winter evolved (remembering
that 11 out 13 Decembers averaged above normal). One possible explanation could be
that with time, the cold air that had stored up in Canada was able to break through
El Niño's warming affects (and more zonal flow), particularly if the El Niño effect was
weak enough to allow it. Also, it must be mentioned that in both January and February,
there were also some impressive below normal departures from bitter cold, though they
were in the minority. There was no strong trend seen in January and February in the
winters that started early in November. The chance of a warmer period mid or late winter
(ex:"January Thaw") in these minority of winters that started out cold, however, was
better than 50 percent.
Precipitation (including snowfall):
Generally, only the strongest of El Niños bring unseasonably mild and relatively dry
winters to Southeast lower Michigan. As mentioned above, the late fall into winter period
saw more variability in rain and snowfall totals. During the strong El Niño of 1982-83,
only 20 inches of snow fell in Detroit, 33.6 in Flint and just 23.8 in Saginaw. In the more
recent strong El Niño of 1997-98, Detroit saw just 22.5 inches of snow, 28.3 fell in Flint
and with Saginaw nearer the storm track, snowfall totaled 40.1 inches.
Snowfall totals, however, varied considerably with weak to moderate El Niños in place.
While overall snowfalls tended to average a bit below normal, only one of the years
/1881-82/ appears in Detroit's top 20 snowless winters. Interestingly, none of the
researched winters appear in Flint's top 20 snowless winters (even back to1883) and
only the winter of 1963-64 winter made the list at Saginaw. It was intriguing, however,
to find one of the years /1977-78/ made the top 20 snowiest winters at Detroit, while
1972-73, 1977-78 and 1991-92 each made Flint's snowiest list, with 1972-73 and
1977-78 both making Saginaw's snowiest winters list.
As mentioned earlier, these winters tended to contain the majority of their snow mid
to late winter, BUT NOT ALWAYS. It was the years mentioned above where a trend
to colder weather took hold in October (1972, 1977 and 1987) also saw above normal
snow in December (with 1972 and 1977 also containing above normal snow in
November). These were the aforementioned winters that "began" earlier than the rest
in November.
Storm tracks depended largely on the type of dominating weather. In the mildest of
winters, generally clippers frequently ushered pacific orientated air into the region
with just the infrequent polar intrusion. Southern stream low pressure systems tended
to stay well south of the Great Lakes or move west of the area with just the occasional
hit and thus, the lowest snowfall totals occurred. 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.
