My temperature forecasts for the next 15 days

Jump to the forecasts or to the verification

Brief outline of the method

  1. The starting point for the forecasts are NCEP ensemble forecasts (available at a resolution of 1x1 (latitude-longitude) degrees); I use the control run and 2 ensemble members - 3 forecasts in all.
  2. The forecasts cover the period 6-384 hours after the analysis time - providing 15 days of daily forecasts.
  3. For a given location (at which daily maximum and minimum temperatures must also be available), the average maximum and minimum forecast temperatures at each forecast time are determined from the model output.
  4. Analysis of previous forecasts for each of the 15 forecast lengths (1 day, 2 days, etc) against the subsequent verifying observations for a period of up to 30 days before the start time of the current forecasts, produces a bias correction which is applied to the model-derived forecast to generate my station forecast (the 'issued' forecast). This allows the bias to vary with time of year, etc.
  5. The issued forecasts relate to the period 0000-2400C for maximum and minimum temperatures.
  • Once the observations become available, they are compared against the issued forecasts in order to analyse the error in the issued forecast, both as a function of forecast length (0-day, 1-day, 2-day, etc.) and calendar date (by combining all forecasts made for that date).
  • More details of these validation results will be posted once sufficient forecasts have been created.

Guide to the forecasts

The forecasts contain:

  • Recent observations of minimum, maximum and mean (i.e. the average of minimum and maximum) temperature for up to 10 days. Observations from sites are extracted automatically from SYNOP reports and for a given day cover the period 0000-2400UTC.
  • Forecasts for 15 days ahead of
    • minimum (0000-2400UTC) temperature,
    • maximum (0000-2400UTC) temperature and
    • mean temperature.
  • An indication of the forecast confidence based on the standard deviation of the value of the error (equal to the issued forecast minus the observation) of the past 30 forecasts - for each of the forecast lengths (0 days, 1 day, 2 days, etc.). In general the confidence will get less as the forecast length increases.
    • 'Hi' denotes a standard deviation in the error of under 1.5C (a 'high' accuracy forecast)
    • '-' denotes a standard deviation in the error of 1.5-3.0C (mid-range accuracy), while
    • 'Lo' denotes a standard deviation in the error of over 3.0C.
  • Note that no account has been yet taken of the forecast uncertainty implied by the spread of the individual ensemble forecast values, as it is considered that interpolation from the gridded data to the observation location probably creates a larger uncertainty.

Time zones

An approximate guide to time zones and the times of extremes temperatures is as follows:

Location Winter local time zone UTC time of minimum temperature (assumed 6am local time) UTC time of maximum temperature (assumed 3pm local time) Summer local time zone UTC time of minimum temperature (assumed 6am local time) UTC time of maximum temperature (assumed 3pm local time)
Maine EST 1100UTC 2000UTC EDT 1000UTC 1900UTC
Chicago CST 1200UTC 2100UTC CDT 1100UTC 2000UTC
Phoenix MST 1300UTC 2200UTC MDT 1200UTC 2100UTC
Los Angeles PST 1400UTC 2300UTC PDT 1300UTC 2200UTC
Alaska (mainland) AKST 1500UTC 2400UTC AKDT 1400UTC 2300UTC
Hawaii HST 1600UTC 0100UTC HST 1600UTC 0100UTC

The latest observations

The latest forecasts

  • Canada
    Edmonton Winnipeg St Johns
    Halifax Toronto Quebec
    Whitehorse Victoria Fredericton
    Resolute Charlottetown Regina
  • United States - listed by state
    AL Montgomery AR Fort Smith AZ Phoenix
    CA Los Angeles CO Alamosa CT Hartford
    DC Washington Dulles FL Miami GA Atlanta
    IA Des Moines ID Boise IL Chicago
    IN Indianapolis KS Topeka KY Lexington
    LA Lake Charles MA Boston ME Caribou
    MI Detroit MN International Falls MO Kansas City
    MS Meridian MT Helena NC Raleigh
    ND Bismarck NE Grand Island NH Concord
    NJ Newark NM Albuquerque NV Reno
    NY New York JFK OH Columbus OK Oklahoma
    OR Portland PA Philadelphia RI Providence
    SC Columbia SD RapidCity TN Memphis
    TX Houston UT Salt Lake City VA Richmond
    VT Burlington WA Olympia WA Spokane
    WI Milwaukee WV Charleston WY Cheyenne

    Verification

    To see how good (or bad) recent forecasts actually were, see these comparisons of observations for yesterday against previous forecasts valid for yesterday:

    24-hour forecasts,
    48-hour forecasts,
    72-hour forecasts.

    The images above show the standard deviation (SD) and the absolute value (AB) of the forecast error (where the error is the difference between the forecast and the subsequent observation), averaged across all sites for the 30-day periods indicated.

    • In general the forecast quality reduces with increasing forecast length with maximum temperature forecasts prone to a larger error than those for minimum temperatures.

    • Forecasts for these locations are currently (1 September 2008) larger than those for the European and British Isles locations as the latter forecasts have been in operation for a longfer period. The algorithm used means that it takes about two months for the forecasts to settle down - in the absence of any other influences.

    Comments?

    Your comments are welcome, and can be posted to me.

    Disclaimer

    The forecasts listed above use model data that are kindly provided by NCEP and a computer algorithm of my own devising. Neither my employers nor myself are professional weather forecasters and, while these forecasts may give an indication of conditions to come, we cannot accept any responsibility for the accuracy of this forecast.

    The weather over Europe is part of an ever-changing system. The data on these pages should be used as a guide only and there are times when any forecast beyond about 2-3 days is likely to prove unreliable. In addition, it it unwise to make inferences about other weather elements, e.g. rainfall, from temperature forecasts alone.

    Always check the latest forecast from Environment Canada or the US National Weather Service before undertaking any weather-dependant activity.




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