Table of Contents
THE PERFORMANCE OF THE NCEP OPERATIONAL MODELS FROM AN HPC PERSPECTIVE
Understanding the performance of the operational model is critical to being able to forecast the sensible weather
Why models have forecast problems
The way the physics are approximated can lead to model errors, for example
ETA MODEL IS BEST
ETA IS BETTER AT FORECASTING PRECIPITATION OVER COMPLEX TERRAIN
ETA MODEL TERRAIN OVER NORTHERN CA.
MORE ON ETA PERFORMANCE
ETA AND STORM TRACKS
COMMON ETA ERROR ALONG EAST COAST
NOTE THAT THE ETA SURFACE LOW IS A LITTLE WEST OF ITS 500 MB CENTER. THE NGM HAS A MUCH BETTER FIT TO THE 500 MB PATTERN.
THE LOW VARIES A LITTLE NORTH AND EAST OF THE NGM. REMEMBER, THE NGM IS TYPICALLY TOO SLOW WITH LOWS ALONG THE COAST.
VERIFYING PRECIPITATION
MODEL BIAS AND THREAT SCORE
Eta 12-24 Hr Bias (Forecast/observed) Using A Point Verification Dec 97-Feb 98
Eta 24-36 Hr Observed Bias Dec 97-Feb. 98
Eta 12-24 Hr Bias During August (Left) And Sept (Next Slide) 97
Eta Has A High Bias Across The South During The Warm Season
Regional ETA verification using model grid (80 km)
Regional ETA verification using model grid (80 km)
ETA .50” OR MORE PERFORMANCE DURING WARM SEASON
ETA PERFORMANCE FOR .50 OR GREATER AMOUNTS APR 96-NOV 97
Regional ETA verification using model grid (80 km)
Regional ETA verification using model grid (80 km)
ETA MODEL HAS PROBLEMS PREDICTING THE STABILITY.
WHEN HIGH SOIL MOISTURE IS PRESENT, OR WHEN THE MODEL FIRST GUESS THINKS THE SOIL MOISTURE IS HIGH,
WHEN LOW SOIL MOISURE IS PRESENT DURING SUMMER OVER THE HIGH PLAINS, ESPECIALLY WEST TX, THE FORECAST CAPE IS TOO LOW
WHEN SO MOISTURE IS LOW IN SUMMER IN THE PLAINS, THE SURFACE DEWPOINT IS TOO LOW AND THE TEMPERATURE IS TOO HIGH
Forecast vs. Observed Best Cape Spring 96
A NUMBER OF AVN/MRF PERFORMANCE CHARACTERISTICS HAVE CHANGED IN THE PAST YEAR.
AVN/MRF Often Have Problems Handling Upslope Events
About 75% of the AVN Rainfall Over the OK Panhandle Was Grid-scale Precipitation (Not Convection).
Another Case: AVN Wraps Low Too Far North And West. Both Surface and 500 mb Lows Are Too Deep.
Aviation Model handling of 500 mb trough
BIAS COMPARISON OF 12-36 HR MRF AND EARLY ETA FORECASTS
The MRF and MRFX spin-up precipitation bombs and tropical systems erroneously at all time ranges.
MRF PERFORMANCE FOR 3-5 DAY FORECASTS
MRF PERFORMACE (3-5 DAY) CONTINUED.
NGM AND THE SURFACE PATTERN
THE NGM AND AVN/MRF HAVE SERIOUS PROBLEMS WITH ARCTIC AIRMASSES
THE NGM LOWERS HEIGHTS TOO MUCH IN THE NORTHERN ROCKIES AND HIGH PLAINS
Why models have problems with arctic airmasses
LOWS TO THE LEE OF THE ROCKIES
NGM 12-36 Hr Winter Threat Score For .50” Or Greater Amounts
12-36 HR .50” OR GREATER NGM WARM SEASON THREAT SCORE
NGM .50” OR GREATER WINTER BIAS
THE NGM ALMOST ALWAYS SIGNIFICANTLY UNDERPREDICTS THE MAXIMUM
NGM WARM SEASON BIAS FOR .50” OR GREATER AMOUNTS
IN CONCLUSION
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