The great Alaska warm-up of January 2009
The purpose of this study is to identify useful tools to aid in forecasting future high impact events. Temperature verification statistics for Southcentral Alaska were obtained using the BOIVerify program within the Graphical Forecast Editor (GFE) used by National Weather Service Forecast Offices. BOIVerify also provides bias-corrected guidance for temperature and dew point temperature based upon a 30-day regression fit analysis. The official forecasts of Maximum and Minimum temperature issued by the Anchorage office for the period January 13th-15th, 2009 were found to have a significant cold bias. This performance was closely mirrored by most of the bias-corrected guidance. The clear top performers for this event were the 2-meter temperatures from the GFS and NAM Models. This suggests that forecasters may have relied heavily on bias corrected guidance when producing the temperature forecasts.
Forecasts from the NCEP Global Ensemble Forecast System (GEFS) for the period of the warm-up showed a consistent depiction of a strong upper level ridge centered over Southeast Alaska with a surge of warm moist air up the west side of the ridge and over Mainland Alaska. A relatively small ensemble spread indicated high confidence in this solution. A review of standardized anomalies (Precipitable Water, 850hPa Temperature, and 850hPa v-wind) was performed to identify variables that may have given an indication to the significance of the event. In addition, Area Forecast Discussions issued by the Anchorage Forecast Office leading up to this event showed there was recognition of a major shift in the upper level pattern with potential for a freezing rain event.
The use of ensemble data, standardized anomalies and indentifying the strengths and weaknesses of bias-corrected guidance will be explored. It is hoped that the use of these parameters will lead to improvements in the forecasts of future high impact events.