AVN MOS TEMPERATURE AND DEW POINT GUIDANCE

February 3, 2000

PREDICTANDS:

• 2-m temperature and dew point valid every 3 hours from 6 to 72 hours after initial model time of 0000 and 1200 UTC.
• Daytime maximum temperature (defined as 0700 LST - 1900 LST) valid approximately 24, 48, and 72 hours after 0000 UTC and 36 and 60 hours after 1200 UTC.
• Nighttime minimum temperature (defined as 1900 LST - 0800 LST) valid approximately 36 and 60 hours after 0000 UTC and 24, 48, and 72 hours after 1200 UTC.

All predictands were taken from TDL's archive of the hourly METAR data. The daytime max and nighttime min temperatures are not explicitly observed and reported, but are inferred from hourly temperatures and max/min observations valid for 6-h periods.

PREDICTORS:

• AVN forecasts of temperature and dew point at isobaric levels in the lower troposphere; low-level thicknesses; sea level pressure tendency; relative humidity and thermal stability over layers in the lower troposphere; mean relative humidity from the surface to approximately 500 mb; precipitation amount; u- and v-wind components, wind speed, and vertical velocity at isobaric levels in the lower troposphere.
• 2-m temperature and dew point observed at initial model time + 3 hours; observations are potential predictors for the 6- through 39-h forecast projections. Note: the use of observed predictors in an operational environment necessitates development of both primary and secondary equations for forecast projections in which the observations may be used; the secondary equations are used when observations are missing.
• Sine and cosine of day of year and twice day of year

FINAL DEVELOPMENTAL SAMPLE:

• warm season (April-September): April 1, 1997 - October 15, 1997; March 16, 1998 - October 15, 1998; March 16, 1999 - October 15, 1999
• cool season (October-March): September 16, 1997 - April 15, 1998; September 16, 1998 - April 15, 1999. Note that extra developmental data were added at either end of the seasons to increase sample size and provide a smoother transition between seasons. The exact sample dates reflect the time at which the final equation development was done.

TEST SAMPLES: The warm and cool season samples were divided into two parts to assess the quality of the new guidance, namely, a dependent sample used to develop test forecast equations, and an independent sample on which to evaluate the forecasts made by the test equations.

• warm season independent sample: April 1, 1999 - September 30, 1999.
• cool season independent sample: the last 15 days of October, November, and December 1998 as well as the last 15 days of January, February, and March 1999.

VERIFICATION RESULTS:

• The AVN MOS max/min temperature and 2-m temperature guidance were comparable in skill through 48 hours to the NGM MOS guidance. Significant regional variations within the CONUS were seen. Beyond 48 hours, the AVN MOS forecasts were generally more accurate than the NGM MOS.
• The AVN MOS dew point guidance was generally more accurate than the NGM MOS.

Detailed results may be seen on the TDL home page at: http://www.nws.noaa.gov/tdl/synop/results.htm