MRF-based MOS QPF guidance

February 3, 2000

Predictand

• •12- and 24-h Probabilistic Quantitative Precipitation Forecast (PQPF) guidance has been produced for several cutoffs, including the accumulation of 0.01, 0.10, 0.25, 0.50, 1.00, and 2.00 inches of precipitation (a cutoff of 3.00 inches is also available for 24-h PQPF's). A PQPF value can be defined as the probability that (liquid-equivalent) precipitation accumulation will equal or exceed its corresponding cutoff value.
• •Forecasts containing both 12- and 24-h PQPFs are available every 12 hours for projections valid 24 to 156 hours after 0000 UTC (the PoP, or the probability of 0.01 inches or more of liquid-equivalent precipitation, is available out to 192 hours).
• •Categorical forecasts will also be available (similar to the QPF system in the current operational NGM MOS text message).
• •Our precipitation data came from hourly observations, which gave us 6-h precipitation reports at synoptic times.

Predictors

• •Several MRF forecasts were offered to the regression analysis including relative humidities at specific levels and in tropospheric layers, precipitation amount, u- and v- wind components at multiple levels in the troposphere, moisture convergence, temperature advection, relative vorticity advection, specific humidity advection, vertical velocities, k index, and relative vorticity.
• •Climatic relative frequencies of 0.01, 0.1, 0.25, and 0.5 inches (valid for the 1992-99 period) were also offered, as was the sine of 2x the day of the year.

Developmental sample

• •The developmental sample contained various dates from 1992-99. For the years of 1992-96, and partially 97, MRF data were obtained from NCEP's reanalysis project. This data set provided us with a model run every 5^th day from January 1992 through March 1997.
• •From April 1997 to October 1999, all MRF runs available were used.
• •The months of April-September were used for warm season, and October-March for cool season.
• •To aid in seasonal transition, a two week overlap at the beginning and end of each season was added.

Test sample (independent data set)

• •During the test development, the last 15 days of each month in the 98 (warm) season, and 98-99 (cool) season were held out and used as independent data.

Verification/results

• •Verifications were done in terms of Brier score.

• •All of the verification scores show PQPFs percent improvement over the Brier score of climate and are available on the TDL home page at http://www.nws.noaa.gov/tdl/synop Also, when available, the newly developed MRF PoP is compared to the current operational PoP.
• •New 12- and 24-h PoP forecasts improve over the operational MRF PoP for nearly all projections.
• •New 12- and 24-h PQPF forecasts show improvement over climate for nearly all projections and cutoffs.