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NATIONAL TECHNICAL INFORMATION MESSAGE 95-01
NATIONAL WEATHER SERVICE HEADQUARTERS
2 PM EST THU JAN 05 1995
TO: USERS OF PROBABILITY OF PRECIPITATION GUIDANCE BASED ON
THE MRF AND AVN RUNS OF THE GLOBAL SPECTRAL MODEL
FROM: FREDERICK S. ZBAR
ACTING CHIEF, SERVICES DEVELOPMENT BRANCH
SUBJECT: IMPLEMENTATION OF NEW EQUATIONS TO PREDICT THE PROBABILITY
OF PRECIPITATION (POP) FOR BOTH THE 12- AND 24-H PERIODS FROM
THE MRF RUN AND FOR THE 12-H PERIODS FROM THE AVN RUN OF THE
GLOBAL SPECTRAL MODEL.
(THE FOLLOWING INFORMATION WAS PROVIDED BY PAUL DALLAVALLE, CHIEF OF THE
SYNOPTIC-SCALE TECHNIQUES BRANCH OF THE TECHNIQUES DEVELOPMENT
LABORATORY)
Beginning on or about January 11, 1995, during the 0000 UTC cycle, new equation
> s
to predict the probability of precipitation (PoP) for both the 12- and 24-h
periods from the MRF run and for the 12-h periods from the AVN run of the Globa
> l
Spectral Model will be implemented. These equations will be used to produce th
> e
PoP forecasts that appear in the MRF-/AVN-based statistical forecast messages.
These messages are distributed on AFOS under the FMR/FAN categories and are
disseminated to external users as the FOXCxx/FEXCxx, FOXExx/FEXExx,
FOXSxx/FEXSxx, FOXWxx/FEXWxx, and FOUS20/FEAK20 messages, where xx is a two
digit number identifying each message. The PoP forecasts for 12- and 24-h
periods appear in the lines labelled "POP12" and "POP24", respectively.
The new forecasts are based on a calibrated MOS approach, in contrast to the
calibrated perfect prog approach, used to derive the original equations. With
the older equations, the PoP forecasts were not as sharp as expected,
particularly at the short-range projections when a major cyclone was forecast
over a particular location by the AVN or MRF and the PoP should have been
correspondingly high. By redeveloping the PoP equations, this time applying th
> e
MOS approach, the optimal model predictors at each projection were selected to
forecast the PoP. Comparisons of the perfect prog and MOS PoP forecasts on
independent data show that the MOS forecasts improve upon the perfect prog
forecasts at each projection. However, the difference between the overall
accuracy of the old and new equations is quite small after about 96 hours.
Technical Procedures Bulletins (TPB) Nos. 411 and 415 describe the MRF- and
AVN-based statistical guidance messages and the lines containing the PoP
guidance. If you do not have a copy of these bulletins and would like one,
please contact Debbie Greeley of the Office of Meteorology at (301)-713-0462.
If you need further information about the MRF/AVN PoP guidance or about either
statistical forecast message, please call Jack Settelmaier or Mary Erickson of
the Techniques Development Laboratory at (301)-763-8151.
END
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