452 Precipitation

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452 Precipitation
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Northwest Weather Terrain Ocean Influence
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Annual Precipitation
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SW Olympic Slopes-Hoh Rain Forest 150-170
inches yr-1
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Sequim roughly 15 inches per year. .
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Puget Sound Convergence Zone
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Bias scores for the (a) 1.33- and (b) 4-km model
simulations for 1400 UTC 13 Dec 2001 through 0800
UTC 14 Dec 2001.
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Human Versus Objective Skill for Precipitation
Forecasts NWS Offices Around the US
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Prob. Of Precip. Cool Season(0000/1200 UTC
Cycles Combined)
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Brier Scores for Precipitation for all stations
for the entire study period.
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Brier Score for all stations, 1 August 2003 1
August 2004. 3-day smoothing is performed on the
data.
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Precipitation
Brier Score for all stations, 1 August 2003 1
August 2004, sorted by geographic region.
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Reliability diagrams for period 1 (a), period 2
(b), period 3 (c) and period 4 (d).
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Rain Psychology
More than a day out.Human Forecasters Tend to
Overpredict 10-30 --exaggerating the threat of
rain when it is not likely. Its probably not
going to rainbut I will throw in 10-30 anyway
to cover myself And underpredict rain when it
is fairly definite. Well it looks like it will
rainbut I am unsureso I will knock down the
probabilities to 60-80 to cover myself
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Humans Help with Heavier Precipitation
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Convective Precipitation

• Need at least 2-4 km resolution to get most
  convection even half right.
• If grid spacing is more coarse must have cumulus
  parameterization--Kain-Fritsch is used for MM5.
• Convection is least skillful precipitation in
  virtually all models.
• High resolution models can potentially give a
  heads on type of precipitation a day ahead
  (squall line, supercell, etc.)

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Real-time WRF 4 km BAMEX Forecast
Valid 6/10/03 12Z
Composite NEXRAD Radar
4 km BAMEX forecast 36 h Reflectivity
4 km BAMEX forecast 12 h Reflectivity
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Real-time 12 h WRF Reflectivity Forecast
Valid 6/10/03 12Z
Composite NEXRAD Radar
4 km BAMEX forecast
10 km BAMEX forecast
22 km CONUS forecast
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Hurricane Isabel Reflectivity at Landfall
18 Sep 2003 1700 Z
41 h forecast from 4 km WRF
Radar Composite
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The End