Updated Late Winter and Spring 2009 Outlook

The 2008/2009 winter season has been fairly cold and snowy across the Devils Lake basin, Red River Valley and Minnesota Lakes Country. But what about the rest of the cold season? Below is the updated outlook for the remainder of the meteorological winter, on into the spring months of March, April and May 2009.

Previously, your NOAA's National Weather Service (NWS) indicated that several factors were expected to influence the winter season. One of them was the expectation that the equatorial Pacific Ocean would see normal, or slightly below normal temperatures, technically called "ENSO Neutral". However, in December a La Nina developed, which has helped to make the weather colder than expected. This La Nina is forecast to persist into the meteorological spring (March-May) of 2009, further impacting the weather across the northern plains.

Details on the techniques and procedures used to make the outlook are available here. For brevity sake, the revised outlook follows.

The Outlook: Essentially, we expect temperatures to remain generally colder than normal the next three months, with a great deal of variability that is typical of spring weather. Snowfall is, on balance, expected to be close to or above the long term average, with the usual variability across the region. The higher amounts are expected from the southern Red River Valley on east across the west and north central Minnesota lakes country, and possibly in the Devils Lake Basin. At the mid point of this winter season, it looks as though the winters of 1952/53, 1978/79 and 1992/93 are most similar to the current winter in temperature and precipitation. It is important to note that while every year is unique, large scale climate patterns do result in somewhat similar weather patterns, making the use of analog years feasible.

Tables of temperature, precipitation and snowfall are below. These tables are based on the years noted on the previous paragraphs.  The following tables are specific to the UND/NWS Grand Forks Climate Station.

February to April Averages*
         Climo          Composite Outlook
Max(F)   36.3            30.2 to 34.9
Min(F)   17.2            11.8 to 16.5
Pcpn(In)  2.7             2.7 to  4.1
Snow(In) 15.9            13.3 to 21.2

The following tables are specific to the Fargo Area

Fargo Area
February to April Averages*

         Climo          Composite Outlook
Max(F)   37.5            33.1 to 37.5
Min(F)   18.8            14.1 to 18.8
Pcpn(In)  3.2             3.3 to  5.6
Snow(In) 18.6            15.2 to 25.5

*Some data are rounded. These are expected ranges based on the above technique and should not be used as an explicit forecast.

Generally speaking, the remainder of the winter season on into the spring will encompass tremendous variability. The coldest months, that are the ones with the greatest departure from normal, are expected to be March and April. Total snow will be close to or above average. Statistically normal snowfall is between 15 and 20 inches, with March having the greatest climatological averages. As is often the case in weak La Nina signals, the March and April time frame tilts predominantly to the cold side of climatology. Looking at the individual winters, the heavier snowfalls were mainly across the south and central Red River Valley, east through the Lakes Country.

Spring 2009 Flood Implications. The development of the La Nina has the potential to affect the spring 2009 flood season. Historically, the months of March and April are a little cooler and wetter than the long term averages suggest. The snow-melt cycle is often drawn-out and delayed, in some instances by several weeks in a La Nina affected spring. Should that occur, the risk of receiving rain during or soon after the melt increases the threat for more significant flooding. See the latest AHPS forecasts for more information.

Your NOAA's NWS will closely monitor the conditions as they develop through the rest of this winter season, and right on into the start of the spring snow melt. Stay tuned to your favorite source of weather information, including NOAA Weather All-Hazards Radio, commercial radio and T.V., as well as Internet sources for later forecasts and possible watches or warnings.

For more information contact the Grand Forks National Weather Service at 701.795.5198, or visit us at www.crh.noaa.gov/fgf

Mark Ewens, Climate Services Focal Point  Mark.Ewens@noaa.gov

Updated February 4th 2009

Techniques:  There are several methods used to develop the NWS Grand Forks seasonal climate outlooks. These include: 1) simple pattern recognition, 2) comparing the antecedent conditions to current, 3) extrapolating those forward, 4) developing correlation's between the Low-Frequency Variability modes of the atmosphere and seasonal responses, and 5) developing a local climate forecast verification/bias correction model.

Simple Pattern Recognition: Analogous to short term forecasting, understanding how the large scale climate affects the local weather is critical. Developing and understanding long wave orientation and movement with the resultant ‘weather’ is one part. An understanding of how events literally on the other side of the globe affect the local weather is another. Finally, proper use to observational and diagnostic tools to analyze those forces is critical. The 4 primary forcings used are the Pacific Decadal Oscillation (PDO), Atlantic Multidecadal Oscillation (AMO), East Pacific/North Pacific (EP/NP) and the El Nino Southern Oscillation (ENSO). Other important signals that are significant, but have more of an intraseasonal impact are the Madden-Julian Oscillation (MJO) and the Arctic Oscillation (AO). The MJO and AO modulate the PNA and NAO which are, in the climate sense, short term oscillations, and much more difficult to predict their phase.

The East Pacific/North Pacific (EP/NP) oscillation tends to be quite variable within a season, but is useful in the longer term. As a rule, in the Red River Valley, large scale wet cycles/precipitation peaks tend to cycle with the EP/NP peaks. There was a peak in the EP/NP in the early to mid 90s, and again in the early part of this decade. Recently, the EP/NP has been on a downward trend, suggesting a decrease in precipitation frequency. However, based on this past spring-fall wet cycle, there may well be other forcings at work overpowering the EP/NP signal.

Techniques used in this outlook: There is a variety of research already available which goes into greater detail than I wish to do here. The basic principle involved includes: 1) to correctly ascertain the last 3 season's climate and the atmospheric mode(s) and forcing(s) responsible for the climate; 2) using tools available at the Earth System Research Lab (ESRL, formally Climate Diagnostics Center) to determine the primary, secondary and tertiary forcings; 3) develop analog years corollary to the mode(s) in step 1 and test for statistical relevance; and 4) obtain the base data and develop graphics and tables based on the years determined to be relevant.

Years chosen: Based on the technique described, we used the following years for input to the analog in the outlook: 1955/56, 1957/58, 1961/62, 1962/63, 1963/64, 1971/72, 1972/73, 1978/79, and 1989/90. Some of these years are based on the phase and tendency of the AMO, PDO and ENSO. The ESRL has statistical tools available to determine the relative correlation of each signal. Please note there are years prior to 1950 that also fall into the analog years, but were not chosen to keep the sample smaller and more contemporary. Finally, there was still a fair amount of variability in the individual winters chosen; removing the warm years resulted in a minor change, to a slightly cooler winter season outlook. As previously stated, at the mid point of this winter season it looks as though the winters of 1952/53, 1978/79 and 1992/93 are most similar to the current winter is temperature and precipitation.

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