Investigation of high and low predictability periods in medium range forecasts.

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Author
Curtis, John E.
Date
1985Advisor
Wash, C.H.
Boyle, J.S.
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Show full item recordAbstract
Medium-range five-day forecasts from the U.S. Navy
Operational Global Atmospheric Prediction System (NOGAPS)
are investigated to study high and low predictability
periods from two winter seasons. Northern hemisphere 500 mb
height fields are scored using the anomaly correlation coefficient-
An objective method is used to choose high and low
scoring periods which are analyzed using height tendencies
and wavenumber structure. Results show that it is possible
to objectively determine why some high and low periods
occurred. Flow characteristics leading to high scoring
five-day forecasts include: long wave amplitude decay, transition
from meridional to zonal flow, and more meridionally
extensive flow patterns. This study revealed that persistence
is not a good indicator of model performance, and no
appreciable skill difference exists between good and poor
five-day forecasts at the 48 hour point- However, no single
measure of the flow patterns is found to be a unique indicator
of high or low scoring forecasts.
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