corresponding sites show a similar divergence. The inclusion of the FSL models did not
appear to have a significant impact on the forecasts of air temperature and dew point
temperature for this event.
Dew Point Temperature
Comparison for Mar 15, 2004
0
AMW OB
AMW OB
-1
-2
-3
-4
-5
AMW METAR OB
AMW METAR wFSL
-6
AMW METAR woFSL
AMW RWIS OB
AMW RWIS wFSL
AMW RWIS woFSL
-7
6 8 10 12 14 16 18 20 22 0 2 4 6 8 10 12 14 16 18 20 22 0 2 4 6
Mar 15, 2004
Mar 16, 2004
Mar 17, 2004
Fig. 10.54. Same as Fig. 10.53, except for dew point temperature (C).
Visibility forecasts for this event (Fig. 10.55) are not very good during most of the
snowfall period. The forecasts are too slow to decrease during the early portion of the
snowfall and too fast to increase near the end of the main event. The visibility forecast
never decreased for the secondary, minor snowfall towards the end of the time series
even though the snowfall, itself, was well forecast by the system. Wind speeds during
this event were never more then 8 m/s and the forecasts of wind speed (Fig. 10.56) and
direction (not shown) were of good quality, with an average difference of less than 1 ms-1
(2 kt) throughout the time series. Intermittent, low-level (1 out of 3) blowing snow alerts
were indicated in the Ames area, starting at 15Z on 15 March, about 2 hours after snow
began falling. Initially, winds were too light for blowing snow, but they increased by
15Z (Fig. 10.56). Blowing snow alerts were somewhat intermittent through 21Z because
of forecasts of mixed rain and warm temperatures, implying wet snow that was less likely
to be lofted. More consistent, low-level blowing snow alerts were given from 22Z on 15
March until they ended at 2Z on 16 March, when forecast winds again became too light
for blowing snow to be a concern.
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