DIFFERENCES BETWEEN THE GFS (American) AND ECMWF (European) MODELS - Northern HemisphereMAXIMUM SKILL RANGE (WHEN MODELS ARE BETTER THAN CLIMATE NORMALS)
GFS: Days 1 to 8 (Summer and Fall) and Days 1 to 9 (Winter and Spring).
ECMWF: One more day than GFS.
Implication: GFS’s accuracy is similar to that of yesterday’s ECMWF model run.
Reason: ECMWF is run at higher resolution, with better observational data and statistical post-processing.
PATTERN SHIFTS
GFS does a good job of predicting pattern shifts 37% of the time.
ECMWF does a good job of predicting pattern shifts 61% of the time.
(“Good job” means anomaly correlation coefficient of 0.9 or better, skillful at synoptic changes.)
After 5 days, the GFS will tend to only detect large scale pattern shifts.
After 6 days, the GFS will tend to only detect the very largest scale global pattern shifts.
ECMWF is half a day ahead at catching synoptic pattern shifts and is more accurate.
WINTER WEATHER SKILL
1 Day Ahead: GFS is better
2 Days Ahead: Average of GFS and ECMWF is best
Days 3 and Beyond: ECMWF has higher skill
YEAR ROUND SKILL (IN GENERAL)
Days 1 to 5: GFS and ECMWF are comparable
Days 6 and on: ECMWF significantly higher skill (gap between the 2 models increases substantially)
SEASONALITY
Greatest model errors for GFS and ECMWF are in Winter, which are double the errors in Summer.
ECMWF is ~10% more accurate than GFS in Summer months and ~20% more accurate in Winter months.
MODEL QUIRKS* *GFSOnce a month, GFS has “dropouts”, where the forecast is a major fail, a major outlier, and very divergent from the ECMWF, which does not have dropouts. GFS scientists are trying to fix dropouts through better initializations. One proposal is to use ECMWF initializations (better quality satellite observations), which would lower dropouts by 90%, but solutions are taking time.Can run a cold bias in the Eastern U.S. *(but OK in the West).Ensembles can be over-confident (low ensemble spreads can still have low forecast accuracy).Tends to have a warm bias in the upper troposphere.Tends to have a cold bias for afternoon temperatures during warm months.* *ECMWFTends to underestimate heavy precipitation events, but GFS has no such bias.Tends to have greater model bias; GFS tends to have greater model absolute error.Tends to have a cold bias in the stratosphere.Tends to have a warm bias for morning temperatures.DIFFERENCE BETWEEN GFS (OPERATIONAL) and GFS (ENSEMBLE)
GFS Operational is run at a higher resolution (more precision) than the GFS Ensemble. The GFS Ensemble uses as its “control” or “base run” a low resolution (watered-down) version of the GFS Operational run (to save on computing resources), then perturbs or varies this control “base run” slightly to produce the various members of the ensemble. As a result, sometimes the GFS Operational is different from the GFS Ensemble…and can even be more accurate at times. In general, use the ECMWF as an indicator as to whether to lean more heavily to the GFS Operational or the GFS Ensemble.
رد: ::: مناقشة الأحوال الجوية السائدة والمتوقعة في شهر كانون ثاني / يناير 2016::
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