MRF MOS TEMPERATURE AND DEW POINT DEVELOPMENT

February 3, 2000

Predictand Definition

The predictands for the MRF-based MOS max/min guidance were values corresponding to a local daytime maximum and nighttime minimum temperature. The daytime is defined as 7 AM to 7 PM Local Standard Time (LST); nighttime from 7 PM to 8 AM LST. An algorithm is used to calculate max/min from METAR observations. The predictands for the 6-h temperature and dew point guidance were observations reported at specific times each day. Predictands are valid at projections 18 to 192 hours from after model run time (00 UTC).

Predictors

• •MRF model predictors: temperatures, thicknesses, dew points, mean relative humidity, model precipitation, u- and v- wind components, wind speeds and vertical velocities on isobaric surfaces; pressure, K-index, and lapse rates. The predictors were offered as values at the specific time of the forecast and as 12-h time-averaged fields.
• •Geoclimatic predictors: sine and cosine of the day of the year and twice the day of the year.

• •Observed predictors: 06 UTC temperature and dew point at projections valid 18 to 36 hours after 00 UTC.

• •Frequently chosen predictors: 1000-mb temperature, 2-m temperature, low level thicknesses, 1000-mb dew point and the 1000-500-mb mean relative humidity. The 2-m temperature was the favored predictor for the daytime max and the 18 UTC and 00 UTC temperature and dew point. However, the temperature at a particular layer (usually 1000-mb) was most common for the nighttime min and the 06 UTC and 12 UTC temperature and dew point. At the extended projections, the climatological terms were more frequently used.

Developmental Sample

• •Cool season (October through March): 1992-97 MRF re-analysis forecast data (every 5^th day), 1997-98 and 1998-99 MRF cool season data.
• •Warm season (April through September): 1992-96 MRF re-analysis forecast data (every 5^th day), 1997, 1998 (except June 16 through July 21) and 1999 MRF warm season data.
• •For seasonal transition, a two week overlap at the beginning and end of each season was added.

Test Sample

• •Last 15 days of each month in the 1998-99 cool season and the 1999 warm season.

Verification

• •Test forecasts were evaluated in terms of mean algebraic and mean absolute error.
• •Daytime max and nighttime min were more accurate than the old MRF MOS out to 108 hours and comparable in skill thereafter (out to 192 hours).
• •Temperature and Dew point guidance improved significantly over direct model output and climatology at all projections.

Additional results can be found on our web site at http://www.nws.noaa.gov/tdl/synop .