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of January 3-5, 2005 Answer to Question 1 |
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1. Look at these four forecasts from local NWS forecast offices for the bordering counties of Hemphill (TX) and Roger Mills (OK). Forecasts valid for Tuesday, January 4 are highlighted in bold-blue. Forecasts valid for Wednesday, January 5 are highlighted in bold-green.
- For a given time, what differences do you notice between the two counties?
- For a given county, what differences do you notice from one forecast to the next?
- Why do you think two neighboring counties can get substantially different forecasts?
- Why do you think each county's forecast changes noticably from one forecast to the next?
Answer.
- The earlier forecasts show strong agreement in precipitation (rain Tuesday changing to freezing rain and snow by Wednesday), with some slight differences in the temperature forecast. However, the mid-afternoon and early-evening updates show differences for Wednesday's forecasts (morning snow for Hemphill and morning freezing rain for Roger Mills County). By Tuesday morning, both the Tuesday and Wednesday forecasts are significantly different. Hemphill mentions rain and thunderstorms with temperatures in the 40s, while Roger Mills mentions freezing rain and fog with temperatures near 30.
- From the first update to the last, the Roger Mills forecast for Wednesday changes from temperatures in the 40s to temperatures in the 30s, and the precipitation type changes from snow to freezing rain.
- These two counties can get different forecasts for a number of reasons:
- The forecasts come from different forcast offices and different forecasters, who may interpret observations and models guidance differently.
- The offices are not required or expected to come to agreement at their forecast area boundaires.
- Also, the actual text of the forecasts is generated by computer, based on each forecaster's regional assessment.
- Forecasts often change from one forecast to the next as forecasters update their information and re-interpret situations. Adjusting a front 50 miles or so or changing expected temperatures by five degrees may make little difference in most scenarios. However, winter weather scenarios can magnify small changes in forecasts.
- Simply moving the surface front by 50 miles or so (which is not that much in the atmospheric "big picture") can produce radically different impacts on the ground.
The Bottom Line.
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Winter weather forecasting is very difficult and is likely to change often. In winter weather scenarios, expect changing and even some conflicting forecasts.
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