George R. Kasica
Rapid City, South Dakota Climatology

The area around Rapid City, South Dakota in March and April (the period for which we were forecasting was from March 26 - April 6, 2007) typically experiences temperatures in the low 50's for high temperatures and in the upper 20's for lows during that time. Precipitation is quite low with the average day receiving about 0.04-0.05"" of liquid precipitation. Looking at the extremes for the high and low temperatures in the detailed table (provided courtesy of the National Weather Service Forecast Office in Rapid City, South Dakota  NowData resource.)  you can see however that temperatures have reached as high as a summer-like 84 for a high and as low as a bone chilling -5 degrees, so clearly a very wide range of temperatures are possible which is typical for a continental climate such as this in a relatively dry area. One feature of the city that does complicate temperature forecasting similar to Atlantic City is the "Chinook winds" which can occur when winds blow from a westerly direction down the slopes of the Black Hills just to the west of the city which reach elevations of up to 7,000 feet in a number of locations.. When this occurs rapid and dramatic increases in temperature are common for the area. For a world record example of how dramatic the effects of the Chinook wind can be on both the rise and then fall of the temperature once the wind ceases consider the following account courtesy of the Internet Wiki-Pedia:

"The Black Hills of South Dakota are home to the world's fastest recorded rise in temperature. On January 22, 1943, at about 7:30am MST, the temperature in Spearfish, SD was -4 F (-20 C). The chinook kicked in, and two minutes later the temperature was 45 F (7 C) above zero. The 49 degree (27 C) rise in two minutes set a world record that is still on the books. By 9:00am, the temperature had risen to 54 F (12 C). Suddenly, the chinook died down and the temperature tumbled back to -4 F. The 58 degree drop took only 27 minutes."


(Map of South Dakota provided courtesy of NOAA Earth Systems Research Laboratory)

Looking more closely at wind direction, below you can see the obvious prevalence of wind directions in the wind rose for March and April which clearly shows the prevailing northwest winds. In March and April these winds averaged speeds over 20 mph on many days.  Further, you'll notice that the direct westerly direction winds are rare in either month, hence chinook winds are not a common occurrence that would lead to the dramatic temperature fluctuation as shown above.

(March and April prevailing wind directions courtesy of the National Resources Conservation Service - click picture for full size image)

In terms of precipitation, March is the snowiest month for the area around Rapid City with it receiving about 9.1" in a normal month. The record amount for March is 30.7" in 1950. And although large single snowfall amounts are rare back in 1973 they received 14.9" in one 24 hour period in March. April however is somewhat lower in terms of snowfall with the normal being 6.2", however they do still receive large amounts of snow at times such as in 30.6" for the month in 1970, which also had a 24 hour amount of 16.0" of snow. Total liquid precipitation for the area in March and April is 1.03 and 1.86" respectively. As you can see, although March is the snowiest month of the year for the area, predicting a 6" snowfall is not at all out of the question for either month. (All of the above climatic statistical data was provided courtesy of the Rapid City, South Dakota National Weather Service Forecast Office climatic narrative).

Given the data above, you can see that making the forecasts for Rapid City, South Dakota will be a challenging process indeed with many variables to consider, most definitely one being the winds again, in terms of temperature and precipitation forecasts.

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