Dickinson, ND is located in the Northern area of the Great Plains. It is surrounded by a vast area of grasslands, making it an iconic prairie environment.  As those who live there would attest the beauty of the grasslands speaks to the nostalgia of our pioneer past but when examining the climatic conditions it becomes clear that the forging settlers of this area faced many hardships.  

            Dickinson is located within the mid-latitude climatic region and as such experiences high seasonal temperature variations.    Solar exposure is also affected by the moderately high latitude of this area.  Day light length varies from less than 9 hours of daylight at the winter solstice to more than 16 hours of daylight during the summer solstice, partly accounting for the extremes seasonal temperature differences (USGS.)  The increased strength of the polar jet stream in the winter and increased sub-tropical lows in the Gulf of Mexico during the summer are also key factors to the sharp seasonal changes.

 

            The wide open space of these grasslands brings wind almost non-stop.  With the exception of only a few rising buttes, Dickinson lacks a local wind barrier and the dry low-lying grassland vegetation does little to slow the wind either (USGS.)  This can lead to a continuous breeze and severe winds that have caused several millions of dollars in damage in the past.  The winds come from the several air masses that are associated with this area but the foehn winds are most notable.  While it may not be visibly apparent, Dickinson sits just to the east of the lee side of the Rocky Mountains and as such can experience the high winds that are associated with the geographical feature (NOAA.)  The winds that are coming down from their orographic lift can be very strong, warm, and dry and at times can bring very high temperatures in the summer and brief warming periods in the winter.

          The average monthly temperature changes are very drastic in this dry, mid-latitude region.  Over the past 60 years the minimum temperature of June has been similar to the maximum high temperature of January.  With the polar jet stream at full strength little heat and insulating moisture are brought into the area, resulting in a very cold and dry January.  

            Comparing Dickinson, ND to Minneapolis, MN which are both located in the north central region of the United States we can see how much geographical features can affect a given locality.  While both areas experience similar seasonal temperature changes and solar exposure changes, Dickinson sees far less precipitation.  Minneapolis is located just to the southwest of the Great Lakes and experiences a climate with more maritime effects because of this.  Minneapolis may receive a few inches of rain in the summer months, whereas Dickinson on average receives less than 2/10 of an inch in even its rainiest month.  The increased precipitation in Minneapolis creates the opportunity for more plentiful vegetation.  This means that a greater amount of evapotranspiration can occur; therefore there is more latent heat capabilities in Minneapolis than in Dickinson.  The addition of moisture to the air also means that it takes more energy in Minneapolis to change the environmental temperatures so temperatures do not vary as much from diurnal changes.  Both places experience very cold periods during the winter, but Dickinson’s dryer air and higher albedo bring colder temperatures and more drastic changes.

 

This image from Google Earth indicates the proximity of Minneapolis, MN to both Dickinson, ND and to the Great Lakes

    The relatively high latitude, low moisture, lack of significant topographical features, and dry grasslands prevail as the dominant climatic controls of this region.  Drastic diurnal changes and the central continental location allowing for abundant cyclonic influences will always keep the weather interesting and quick to change in this sparsely populated area.  I spent one year living in this area and very much enjoyed the semi-humid summers with moderated temperatures and although my new truck grimaced at the thought of the severe thunderstorm hail potential, the lighting strikes were spectacular, especially on a night when the clouds cleared to display a wonderful showing of the Aurora Borealis.  The strength of the polar jet stream, however, was enough to convince me that one North Dakota winter, or as the locals call it NODAK, was enough.  Although I will never forget chipping the ice away from my door to get OUT of my house.

Several Air Masses can affect this area but most behave or have been modified to behave with Continental characteristics

Summer Air Mass Associations

·         Maritime Tropic(mT)- strengthened by the sub-tropic lows

·         Continental Polar(cP)- weaker than in winter but still causes frontal wedging in summer months

·         Maritime Polar(mP)- from the west coast, but orographic lift over the rocky mountains causes most moisture to be lost before it reaches North Dakota

Winter Air Mass Associations

·         Continental Polar- as the polar highs strengthen in winter this air mass dominates

·         Continental Arctic(cA)- this can bring subzero temperatures

·         Maritime Tropic- as fronts collide cyclones can be created bring warm fronts to the north

Pidwirny, M. (2006). Original Publication "Air Masses and Frontal Transitional Zones". Fundamentals of Physical Geography, 2nd Edition. Accessed via online post 10/01/12 http://www.physicalgeography.net/fundamentals/7r.html

Frontal air mass collisions regularly take place south of North Dakota as continental polar highs and maritime tropical lows seasonally weaken and strengthen. The high latitude of Dickinson, ND makes the continental polar air mass the most influential air mass association and as a result this area usually experiences extended periods of cold fronts.  This causes the typical cold and dry winters; however severe blizzards occur periodically as low pressure systems build to the south near Colorado or to the north near Alberta, Canada (Black, 38pg).  These mid-latitude cyclones can bring occluded warm fronts creating short durations of high precipitation. 

1Example of mid-latitude cyclone developing south of North Dakota that will eventually bring a warm front, Map Courtesy of meted.ucar.edu, Accessed 11/10/12

As the sub-tropic lows of the Gulf of Mexico strengthen in summer, warm maritime tropical fronts with moist air reach far enough north to cause the summers of Dickinson to be reported as semi-humid (currentresults.com).  While the sub-tropic highs have strengthened, the oscillating rossby waves periodically bring the continental polar air mass further south.  This wedges the warmer air upward and causes brief but severe thunderstorms with heavy precipitation.

2 A 1998 winter mid-latitude cyclone caused severe storms across the United States, this diagram shows the initiation of the cyclone.  Notice how Dickinson, indicated with the yellow circle, sits in the cold front.  From http://www.cmmap.org/scienceEd/summercourse/summerCourse11/docs/KateThursdayPM.pdf Accessed 11/14/12

This diagram shows the progression of the cyclone, and shows how the warm tropical air can be skewed to the north.  Dickinson still sits in the cold front but moist tropical air is being brought into this cold area, carrying heavy amounts of precipitation. http://www.cmmap.org/scienceEd/summercourse/summerCourse11/docs/KateThursdayPM.pdf Accessed 11/14/12

                                                                                                                             

This is a broader example of a high pressure cold front sweeping across the western United States, eventually occluding with a warm front.  Dickinson is again sitting in the cold front of this occlusion.  www.weatherchannel.com   

References

·         Black, R. E. 1971. A Synoptic Climatology of Blizzards on the North-

     Central Plains of the United States. NOAA Tech. Memo. NWS CR-39.

     38 p.