The Winter Weather Events
of January 3-5, 2005
Answer to Question 2
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2. Scan through the forecast discussions that accompanied each of these forecasts. Zone/County forecasts are usually quite "narrow", even if the forecaster is wrestling with a wide range of issues.

  • Are the forecasters from each office wrestling with similar concerns, even if their "official" forecasts were different at times?
  • What are the weather threats to consider for Tuesday into Wednesday?
  • What are the causes of uncertainty in the forecast? Why are these important in a winter weather scenario?
  • What level of confidence would you assign to each "official" forecast?
  • What details are available in the discussions that aren't available in the "official" forecasts?




Answer.

  • Both forecast discussions mention flooding, heavy rains and winter weather as threats.
  • Both forecast offices are agonizing over the position of the surface boundary, largely because forecast models do not handle shallow layers very well. In fact, most of the forecast uncertainty revolves around placement of the surface front, and the poor handling of shallow aurface layers by the forecast models:
    • "CHALLENGING FORECAST FOR THE NEXT COUPLE OF DAYS. FRONT HAS PUSHED FURTHER SOUTH THAN MODELS INDICATED"
    • "BOUNDARY WILL UNDOUBTEDLY CAUSE HEADACHES TEMPWISE FOR TNGT AND TUES"
    • "HOW FAR NORTH BNDRY WILL MOVE IS DIFFICULT"
    • "SFC STNRY FRONT WILL PLAY HAVOC WITH TEMPS TUE"
    • "HOW FAR SOUTH FROZEN PRECIP WILL OCCUR IS STILL DIFFICULT TO DISCERN"
    • "MODELS CONT TO BE WARMER IN LOW LVLS COMPARED TO CURRENT CONDITIONS"
    • "POOR HANDLING OF THE CURRENT SHALLOW AIRMASS BY THE MODELS"
    • "VERY TOUGH CALL ON WHERE FRONT WILL END UP BEING LATE TUE AFTN"
    • "SHIFTS WILL CONT TO MONITOR AS DETAILS DEVELOP"
    • "CONSIDERED EXPANDING SWD DUE TO PSBLTY THAT ETA SOLUTION VERIFIES AND COLD AIR GETS TO SRN TX PNHDL QUICKER. INSTEAD ... WILL DEFER THAT TO LATER SHIFTS TO PONDER OVER"
    • "ETA WHICH CONTINUES TO BE CLUELESS WITH THE BOUNDARY LAYER TEMPS AND FRONTAL POSITION "
    • "VERY COMPLEX WEATHER SCENARIO DEVELOPING TODAY"
  • The high number of scenarios presented in the discussions and the repeated statements of uncertanty should cast some doubt on the certainty of the official forecast.
  • Extremely valuable details available in the forecast discussions that are not available in the official forecasts include:
    • the expected position of features
    • various axes of threats
    • statements of uncertainty
    • if-then scenarios
    • an autopsy of the last forecast
    • an appraisal of current model performance

The Bottom Line:

  • Models usually have a decent grasp on big masses of air - it's the minor details that need to be cleaned up. In a winter weather scenario, those "minor" details include surface temps around 32F, which play a huge role in outcomes.
  • Forecast discussions provide much more detail about the range of possibilities that can threaten your jurisdiction, the level of confidence in the current forecast, and the placement and timing of certain features related to hazardous weather.
 
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