Chagrin Falls Posted December 26, 2010 Share Posted December 26, 2010 Attached is a map of ensemble mean sea-level pressure low positions from the 00Z runs starting December 19th and ending December 25th, verification on Dec 27th at 00Z. Each point represents the forecast from either the mean NAEFS or the mean ECMWF ensemble. For verification purposes, the actual position of the of the low is plotted with the red icon at 00Z on the 27th. Points I think are reasonable from looking at the map: NAEFS: 1. The NAEFS did relatively poorly, forecasting a low too far offshore. The only 00Z ensemble that verified better than the ECMWF ENS was at 120 hours, which was a run where the ECMWF flip-flopped. It was not until the 48 hour forecast (00Z 25th ensemble output) where the NAEFS placement and low intensity verified well. ECMWF: 1. It did considerably better than the NAEFS, however hours 168 & 192 (19th and 20th 00Z output) were considerably too far offshore and too progressive. However, by hour 144 (21st at 00Z) the low placement verified well. At hour 120 (22nd at 00Z) the model flip flopped and this was the only 00Z run where the NAEFS showed skill vs. the ECMWF ENS. Starting on the 22nd at 00Z and continuing to the 25th the placement of the low seemed quite reasonable. The position of the low at hr 48 (25th/00Z) and hr 144 (21st/00Z) were about the same. Even with all the operational runs flip flopping, I think the ECMWF ENS performed adequately aside from the 120 hr flip-flop. The ensembles in general showed much more consistency than the operational runs. Comments? It would be interesting to hear post-storm thoughts on last week's forecasts, especially considering stuff like this: HPC Dec 24th INITIALIZATION ERRORS IN NUMEROUS DIAGNOSTIC QUANTITIES...INCLUDING HEIGHT/VORTICITY FIELDS/RH...ARE EVIDENT IN BOTH THE 12Z NAM/GFS WITH SMALL BUT LIKELY SIGNIFICANT SHORTWAVE TROUGHS OVER SOUTH DAKOTA/NEBRASKA ALONG WITH SASKATCHEWAN/MANITOBA...WITH THESE AREAS ALSO NOT PARTICULARLY RESOLVED OR PREDICTED WELL BY THE 00Z ECMWF. THUS...THE SPECIFIC PREDICTIONS BY ALL DETERMINISTIC GUIDANCE ARE IN QUESTION...WITH THE RECOMMENDATION TO FOLLOW CONTINUITY...WITH THE FINAL OUTCOME MOST BELIEVED TO LIE BETWEEN THE 06Z GFS AND 00Z ECMWF...WITH ALL ENSEMBLE GUIDANCE INCLUDING THE SREF MEAN/GEFS MEAN (EXCEPT NOT THE 12Z VERSION)/ECMWF ENSEMBLE MEAN ALSO CONSIDERED USEFUL TO ADDRESS THE CONTINUED UNCERTAINTY. THIS APPROACH DISREGARDS THE SUBSTANTIALLY DEEPER AND WESTWARD SHIFT OF THE 12Z GFS REGARDING THE POWERFUL LOW TRACKING UP THE EASTERN SEABOARD...AND TO A LESSER EXTENT THE 12Z NAM WHICH LIES NEAR THE FAST EDGE OF THE GUIDANCE WITH THE DEVELOPING LOW. Link to comment Share on other sites More sharing options...
winterymix Posted December 26, 2010 Share Posted December 26, 2010 I like your analysis very much but could you consider doing this: through out all the data points beyond 120 hours and let us reconsider. Point being that beyond 120 hours, luck intrudes along with the potential that a model could be luckily correct for the wrong reasons. Link to comment Share on other sites More sharing options...
wxnut Posted December 26, 2010 Share Posted December 26, 2010 Excellent analysis.. Could the eastern bias of the NAEFS have been overly influenced by the GGEM which continually showed a more eastern track? Link to comment Share on other sites More sharing options...
Chagrin Falls Posted December 26, 2010 Author Share Posted December 26, 2010 Excellent analysis.. Could the eastern bias of the NAEFS have been overly influenced by the GGEM which continually showed a more eastern track? Yes. I would have included GENS data as well but unfortunately I couldn't find the retrospective maps online. If anyone wants to do that using the above map feel free! As far as models getting lucky, I find the initialization and parametrization process so complex I can't determine if a model verified, but for the wrong reasons. Personally, I question when someone determines a model didn't initialize correctly. Obviously the models guesstimate atmospheric processes more often than not, however models can still provide useful information even though they aren't properly initialized. I'm open to comments from more educated meteorologists than I, but I certainly can't determine why a model verifies or doesn't. For example, I'd guess the NAM has the problems it does because of the mesoscale parametrization processes and perhaps spin-up gone rogue, but that is just an uneducated guess. Link to comment Share on other sites More sharing options...
bsperlin Posted December 27, 2010 Share Posted December 27, 2010 It seems to my unscientific eyes and ears that this was the most poorly forecasted major storm in the last few years. Even as late as last night the forecast for MBY, 10 mi S of DC, was about 6" with 4" much further west in this county. As of the end of the storm, now, we've had a thick dusting, maybe 1/4" (haven't measured). Can anyone identify the reason for the frequent flip-flops and major errors, even less that 12 hours before the onset of the snow? . At hour 120 (22nd at 00Z) the model flip flopped and this was the only 00Z run where the NAEFS showed skill vs. the ECMWF ENS. Even with all the operational runs flip flopping, I think the ECMWF ENS performed adequately aside from the 120 hr flip-flop. The ensembles in general showed much more consistency than the operational runs. HPC Dec 24th INITIALIZATION ERRORS IN NUMEROUS DIAGNOSTIC QUANTITIES...INCLUDING HEIGHT/VORTICITY FIELDS/RH...ARE EVIDENT IN BOTH THE 12Z NAM/GFS WITH SMALL BUT LIKELY SIGNIFICANT SHORTWAVE TROUGHS OVER SOUTH DAKOTA/NEBRASKA ALONG WITH SASKATCHEWAN/MANITOBA...WITH THESE AREAS ALSO NOT PARTICULARLY RESOLVED OR PREDICTED WELL BY THE 00Z ECMWF. THUS...THE SPECIFIC PREDICTIONS BY ALL DETERMINISTIC GUIDANCE ARE IN QUESTION...WITH THE RECOMMENDATION TO FOLLOW CONTINUITY Link to comment Share on other sites More sharing options...
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