Winter 2006/2007 Outlook - Updated December 13 2006

The Updated Winter 2006/2007 Outlook

For eastern North Dakota and northwest Minnesota

The updated official Winter Outlook from the Climate Prediction Center (CPC), including  eastern North Dakota and northwestern Minnesota, for the winter of 2006/2007 calls for the likelihood that  temperature will average above the climatalogical normal, while precipitation and snowfall will fall within the normal climatic range.

What Is Normal?

The following table shows the 1971 to 2000 Climatic Normals of various winter parameters at several locations in eastern North Dakota and northwest Minnesota.

Note: In the table below, winter is considered the months of December through February.

Temperature: (Degrees F)(Dec. - Feb.)

Grand Forks NWS
Fargo
Devils Lake
Warroad
Detroit Lakes
Avg. High Degrees F (Dec. - Feb.)
19.8 / 14.9 / 22.8
20.8 / 15.9 / 22.8
19.8 / 15.5 / 22.8
17.9 / 12.7 / 21.1
20.7 / 17.1 / 24.7
Avg Low Degrees F (Dec. - Feb.)
3.6 / -2.7 / 4.9
4.5 / -2.3 / 5.2
3.5 /  -2.8 / 4.9
-0.8 /  -9.0 / -1.7
2.2 /  -4.8 /  2.5
Mean Degrees F(Dec. Jan. Feb.)
11.7 / 6.1 / 13.8
12.6 / 6.8 / 14.0
11.6 / 6.1 / 13.8
8.6 / 1.9 / 9.7
11.5 / 6.1 / 13.6
# of Days with Highs Below 32F
68 days
68 days
67 days
75 Days
69 Days
 # of Days with Lows Below 0F  41 Days
 39 Days
 40 Days
51 Days
43 Days
Precipitation total: (Dec. - Feb.)
1.99"
1.97"
1.64"
1.80"
2.00"
 Total Snowfall (Dec - Feb)  23.3"  22.6"  17.0" 34.3"
26.0"
Total Snowfall (Seasonal)
41.1"
39.0"
35.8"
67.1"
44.5"

Large Scale Climate Forcing Mechanisms

Madden-Julian Oscillation (MJO)

The Madden-Julian Oscillation is a relatively short term climatological event on the order of 45 to 60 days in length. An MJO is essentially a wave of relatively warm water that translates from the Indian Ocean, across the tropical Pacific to the west coast of South America. There is typically an upper level wave of energy associated with the MJO that has an effect on tropical weather in the Atlantic basin as well. Recent research indicates that these upper level waves dampen hurricane activity in the Atlantic Basin. For our weather, a strong MJO serves to modulate the strength of a preexisting El Nino or La Nina. At this time there is limited skill at predicting the MJO strength, therefore it does not have a significant impact on the seasonal outlooks. However, shorter term forecasts such as the 8 to 14 day outlook consider MJO influences.

El Nino Southern Oscillation

Fluctuations in sea surface temperatures (SST) across the tropical Pacific Ocean are part of the El Nino/Southern Oscillation (ENSO). The warm phase of the ENSO is called El Nino and the cool phase is called La Nina. During a strong El Nino, warmer than normal winter weather generally prevails across the northern plains, as the polar jet stream is displaced north into Canada, preventing incursions of arctic air. The primary storm track is across the southern states, resulting in drier than normal conditions across our region. During La Nina, the storm track is more variable, resulting in intervals of cold and warmth and the potential for significant winter storms. An important aspect of forecasting the winter weather in the northern plains region is having the ability to predict the location and magnitude of the largest SST anomalies in the tropical Pacific Ocean. Warm ocean water leads to thunderstorm formation (called convection) and large clusters of thunderstorms that form over the tropical Pacific have a major influence on the pattern of the jet stream. This can influence the location of the storm track and where the areas of warmer and colder weather will prevail across North America. If the most persistent convection in the western Pacific is close to the South American coast, this usually results in frequent and persistent cold air outbreaks over the upper plains. If the most persistent convection is closer to the International Date Line, warmer than normal weather usually prevails across our region. Last winter featured above normal sea surface temperatures west of the International Date Line and near to below normal sea surface temperatures east of the Date Line.

Since October, water temperatures west of the Date Line are a quite a bit above normal, indicative of a mature warm phase ENSO.Looking at figures 1 and 2, you can see that northern plains winters during moderate warm ENSO events tends strongly to warmer than average, and drier than average.

Pacific Decadal Oscillation (PDO)

The Pacific Decadal Oscillation (PDO) is a larger, longer time scale oscillation than ENSO. The PDO affects the ocean temperature anomalies over the Pacific Ocean, with a time span of decades.  Since the PDO affects most of the Pacific Ocean, and ENSO is primarily a tropical Pacific Ocean temperature anomaly, the PDO modulates the strength of ENSO.  When the PDO is in the positive phase, as it was from 1978 to 1998, El Nino conditions dominate the tropical Pacific Ocean and strong El Nino conditions like the 1982-83 and 1997-98 events are more likely. La Nina events, the negative phase of ENSO, are weaker and less frequent. During the negative phase of the PDO, the opposite is true. The PDO was in the negative phase from around 1947 until 1977.  During that time, the Valley Region saw generally colder than normal winters. Drier than normal weather is also more prevalent over the northern plains, with greater than 60% of our dry years occurring since 1950 occurring during the negative phase of the PDO. Given the 20 to 30 year cycle of the PDO, we would expect the PDO to trend towards the negative phase over the next decade.  The PDO was mostly in the negative phase from 1998 to 2002, but has been mostly in the positive phase since the fall of 2002. So what phase will it be in this winter?  Based on the current trend, the negative phase seems likely. Based on that alone, it would seem that a colder and drier than normal winter would be indicated for the Valley Region.

NAO

One of the most significant atmospheric variables to affect the winter weather over the northeast third of the United States is the phase of the North Atlantic Oscillation (NAO). The negative phase of the NAO results in cold and snowy weather, as was the case during December of 2000, when Grand Forks had 19 inches of snow and averaged 11.8F below normal. The following month the NAO went into the positive phase, which typically results in warm and dry weather over our region. January 2001 in Grand Forks was 9.1F above normal with only 3.3 inches of snow! Unfortunately, it is difficult to predict changes in the phase of the NAO, meaning that sharp changes in the winter weather pattern like those of December 2000 to January 2001 can occur without much warning. Recently the NAO has been strongly negative which favors colder than normal weather across the northern plains.

Sun Spot Cycle near minimum

Local research indicates that there is a modest correlation to the waning leg of the 11 year Sun Spot  Cycle and temperatures patterns in the northern plains. While not as strong a signal as the ENSO, it is more common to see the tendency for colder than normal winters in years when the cycle was nearing its minimum. According to the NOAA Space Environment Center, the current cycle (#23)  is about  1 to 4 months away from minimum. If sunspot cycle history is a guide, this winter would favor colder than seasonal temperatures.

Long Term Trends

Between about 1960 and 1997 there was a distinct warming trend in the average winter temperatures over the region. Between about 1998 and 2000 the trend slowed as winter temperatures were not warming as fast. Between 2000 and 2005 there was a period of generally cooler winter temperatures (Figure 3). During this same period winter time precipitation has been, overall, slowly increasing. Although weather is certainly not linear, the recent downward trend in temperature and uptake in winter precipitation are factors in the overall outlook. It is important to note that January 2006, which is not depicted in Figure 3, was the warmest January on record for both the Grand Forks Airport and the NWS / University of North Dakota climate weather station.

Putting it All Together

Since we are experiencing moderate warm ENSO conditions (El Nino), past correlations suggest there’s a 60 percent or greater chance the winter temperature will feature normal to above normal temperatures. Should the PDO indeed enter a negative phase, that would support colder and drier weather. The NAO, which has been positive, is showing signs that it will turn negative.  Should that happen, it would favor more normal or below normal temperatures. The trend of warmer than normal winters during the last ten years suggests a warmer than normal winter, although a weak reversal in that trend appears to have started several winters ago. The NCEP coupled ocean/atmosphere model, which successfully predicted the warmer than normal winter of 2000-2001, is forecasting normal temperatures this winter. Taken together, all of this suggests there is a significant signal for the temperature to average above normal across the northern plains this winter.

Average precipitation is indicated by the moderate warm ENSO conditions, but this is not conclusive. Overall, precipitation tends to show tremendous variability in warm phase ENSO winters, with the El Nino average running about 85% to 95% of climatology.

Based on local studies, the winter temperature for eastern North Dakota and northwestern Minnesota is expected to favor the warmer side of the normal climatic range. Precipitation should be close to normal.  Snowfall should be near to, or perhaps slightly below normal.

Moderate warm phase ENSO temperature patterns

Figure 1

Moderate warm ENSO Precipitation Patterns

Figure 2

Average Winter Temperatures from the UND / NWS weather station

Figure 3

For more information contact Mark Ewens, Climate Services Focal Point at 701-772-0720 x327 or email Mark at Mark.Ewens@noaa.gov



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