For this case the 18 UTC, 25 January MDSS run was used which would have provided a
9 hour forecast for the start of the event. Comparisons between the observed and forecast
air temperature (Fig. 10.15) show that they matched quite well during the snow event.
Unfortunately, there was a 10-hour gap in all RWIS observations toward the end of the
event. These data were unrecoverable. With the close match of the RWIS observations to
the METAR observations for this parameter during the prior portion of the time series it
is fair to assume that the forecast also matched the RWIS observations well.
Air Temperature Comparison for Jan 26, 2004
0
AMW OB
-5
-10
-15
AMW METAR OB
-20
AMW METAR wFSL
AMW METAR woFSL
AMW RWIS OB
AMW RWIS wFSL
AMW RWIS woFSL
-25
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)
Jan 26, 2004
Jan 27, 2004
Fig. 10.15. 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.
Prior to the start of the snowfall the air temperature forecasts were low by a few degrees
Celsius, but they were very closely matched during much of the snowfall event. Towards
the end of the event, the forecast air temperatures again started to diverge and eventually
became too warm by as much as 5C. One possible reason for this warm forecast may be
that the forecast dew point temperatures (Fig. 10.16) only fell to -17C while the actual
air temperature dropped to -20C. This implies that forecasted air temperature could not
possibly go lower then -17C even if the air was saturated, which was not the case. The
dew point temperature time series shows fairly good agreement during most of the event,
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