Fig. 10.43. Same as Fig. 10.38 except for probability of precipitation (%) and quantitative precipitation forecast (mm/hr)

Fig. 10.42. Same as Fig. 10.38, except for visibility (mi)

Fig. 10.44. Same as Fig. 10.43 except the 06 UTC 20 February run

MDSS_Tech_Perf_Report_2912
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64

As mentioned above, this case was a very complex system to forecast. The timing and

type of precipitation expected were difficult to capture with much certainty until just

prior to the start of the event. The run time compared here is for a 6 hour lead time

forecast before the start of the event. Forecasts of POP and QPF (Fig.10.43) without the

FSL models result in a prediction of very light precipitation to start about 3 hours too

early at the METAR site. When the FSL models were added in the start time was over-

corrected and ended up being about 2 hours too late. That same, later start time was also

indicated for the RWIS site both with and without FSL. The POP and QPF forecasts

remained quite high well after the actual end of the event, and the stop times were

predicted to be 7-10 hours later than observed. In this case, the event ended at hour 13,

which is at the tail end of the period where FSL models are used. Looking at a later

RWFS run from 06 UTC on 20 February, the same problem is exhibited with the end

time prediction (Fig. 10.44). With the end time of the precipitation within 7 hours of the

run time, the cessation of the event is still predicted to be 5 hours too late. This latter run

was better than the 00 UTC run, however, even with the FSL models in the mix the end

of this event was not well predicted.

POP and QPF for Feb 20, 2004

1.4

AMW OB

AMW METAR POP wFSL

AMW METAR POP woFSL

AMW RWIS POP wFSL

AMW RWIS POP woFSL

1.2

AMW METAR QPF wFSL

AMW METAR QPF woFSL

AMW RWIS QPF wFSL

AMW RWIS QPF woFSL

0.8

0.6

POP Threshold

0.4

QPF Threshold

0.2

METAR w/wo FSL End

METAR woFSL

Start

METAR wFSL/RWIS w/woFSLStart RWIS w/woFSL End

10 12 14 16 18 20 22

Feb 20, 2004

Feb 21, 2004

Fig. 10.43. Same as Fig. 10.38 except for probability of precipitation (%)

and quantitative precipitation forecast (mm/hr). The blue arrows indicate

the forecasted start (without FSL) and stop (with and without FSL) times

at the METAR site, the orange arrow indicates the start time (with FSL) at

the METAR site and (with and without FSL) at the RWIS site, and the

green arrow indicate the stop (with and without FSL) times at the RWIS.

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