Fig. 10.28. Air Temperature (C) time-series plot comparing the Ames METAR and Ames RWIS observations to the RWFS forecasts

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RWIS observations quite well, but an hour or two before the light snow fell, the

observations actually rose while the forecasts kept declining (Fig. 10.28). This suggests

that there was a push of warmer air just prior to the cold front moving through the area.

This is a difficult thing to forecast and the RWFS temperature forecast never recovered

through the rest of the time series. The forecast was as much as 6C off at times, with an

average error of about 3C. Another possible reason for the poor air temperature

forecasts is a poor cloud cover forecast (Fig. 10.29). The forecast and observed air

temperatures really start to diverge during the hours just after sunset, when the RWFS

under-predicted the cloud cover. This should have resulted in an over-prediction of

surface cooling. Forecasts for the next day had overpredictions of cloud cover during

daylight hours, so the air temperature was held down further because of a thicker cloud

cover compared to reality.

Air Temperature Comparison for Feb 9, 2004

AMW

-2

-4

-6

-8

-10

-12

AMW METAR OB

AMW METAR wFSL

-14

AMW METAR woFSL

AMW RWIS OB

AMW RWIS wFSL

AMW RWIS woFSL

-16

18 20 22 0 2 4 6 8 10 12 14 16 18 20 22 0 2 4 6 8 10 12 14 16 18

Time (UTC)

Feb 10, 2004

Feb 11, 2004

Fig. 10.28. Air Temperature (C) time-series plot comparing the Ames

METAR and Ames RWIS observations to the RWFS forecasts (both with

and without the FSL supplemental models) for the METAR and RWIS site.

The vertical lines represent the time period that the Ames METAR was

reporting falling precipitation.