Title: Improving ExtendedRange Forecasts through Analog Ensemble Calibration Edward OLenic and Scott Handel
1Improving Extended-Range Forecasts through
Analog Ensemble CalibrationEdward OLenic and
Scott Handel NOAA-NWS-Climate Prediction
Center
2- Purpose to improve the skill of probabilistic
6-10-day and 8-14-day forecasts of 2m T. - 10 best analogs in the historical record
(Re-analysis) to the operational GFS 500-hPa
height forecast for each of the 23 members of the
forecast system in a 35-day window centered on
the forecast date. - The corresponding 230 2m T maps are used to
formulate probabilistic 3-class forecasts. - Compare the reliability of these forecasts with
that for 3-class probability forecasts of two
meter temperature composed from un-calibrated raw
GFS ensemble 2m temperature forecasts. - The analog ensemble forecasts are much better
calibrated than those from the raw surface
temperature forecasts. - Graphs of spread-skill indicate that the analog
ensembles - Have rmse about twice that of the GFS.
- Show a wider range of spread than the GFS, but
only in the warm season. - Categorical skill of analog ensemble 6-10 day
surface temperature is comparable to that from
the CDC re-forecast.
3Official 6-10-day 2m Temperature
4Average of the ten best analogs to the pattern.
The top 5 analog dates are listed in the lower
right-hand corner. The correlation of this
10-analog mean map with the original forecast map
over the PNA region is listed in the upper left.
Forecast made Oct 12, 2004.
Correlate the GFS forecast 500-hPa height
pattern, over the Pacific North American Region
(20-90N, 175E-60W), with observed patterns in the
NCAR-NCEP Re-analysis from 1950-1999 in a 35-day
seasonal window centered on the forecast date.
5Probability of each of three classes of 2m
temperature. Forecast made Oct 12, 2004. Top
un-calibrated GFS 23-member ensemble. Bottom
230-member analog ensemble.
610-analogs to GFS ENS mean Z500
Uncalibrated 23-member GFS
2-meter Temperature
Reforecast
230-analogs
7500-hPa height Oct 2003-Oct 2004
8500-hPa height Oct-Mar 2003-4
500-hPa height Apr-Sep 2004
96-10-day 2m Temperature Categorical Skillvs
Analogs and ReforecastS ((C-E)/(T-E))100.
Summer 24.98 Winter 17.41 Summer 26.43 Winter
23.99
Summer 19.95 Winter 25.49 Summer 26.43 Winter
23.99
10Summary
- 230 member ensembles of the 10 best analogs to
the 500-hPa height forecast over the PNA region
to each of the 23 GFS ensemble members improves
the calibration of probabilistic 6-10-day 2m T
forecasts, compared with un-calibrated T
forecasts from the 23 members, and with official
T forecasts. - Analogs also improve the sharpness of the 2m T
forecasts over official forecasts. - Graphs of 500-hPa spread-skill indicate that the
analog ensembles - Have rmse about twice that of the GFS.
- Show a wider range of spread than the GFS, but
only in the warm season. - Categorical skill of analog 2m T forecasts is
higher than CDC reforecast in - summer and lower in winter, over the 1-year
sample.