Change to AVN MOS Guidance - Effective 1200 UTC February 13,2001
Enhancements have been made to the AVN MOS visibility, obstruction to vision, and conditional probabilities of severe thunderstorm guidance. These changes will be effective starting with the 1200 UTC model cycle on February 13, 2001.
The visibility and obstruction to vision forecast equations for the 6-, 9- and 12-h projections have been redeveloped. The observed visibility predictor used in the development of these forecast equations was retooled to correspond one-to-one with the predictands. In other words, additional cutoffs were applied to compute more binary predictors of observed visibility.
The conditional probability of severe thunderstorm forecasts have been modified for all projections. The conditional relative frequencies of severe thunderstorms have been smoothed. We suspect that the strong dependence on conditional relative frequencies in the severe thunderstorm equations led to the spikes we have been seeing in the forecasts. An example of an instance of these spikes is shown below.
KOZW AVN MOS GUIDANCE 1/16/2001 1200 UTC DT /JAN 16/JAN 17 /JAN 18 /JAN 19 HR 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 06 12 N/X 25 32 22 33 24 TMP 32 31 29 29 29 27 25 27 30 31 27 26 24 24 24 27 31 31 28 26 26 DPT 30 27 25 25 24 23 21 22 21 21 20 20 20 20 19 21 23 23 22 23 22 CLD OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV OV WDR 27 27 26 26 26 27 27 29 28 24 18 19 19 19 18 18 18 18 00 00 01 WSP 08 06 04 03 04 04 02 01 02 02 01 02 04 03 03 03 04 03 00 00 03 P06 8 3 5 6 6 0 1 9 8 14 12 P12 34 18 7 13 14 T06 0/ 0 0/86 0/ 0 0/ 0 1/ 0 0/79 0/ 0 0/ 0 0/ 0 1/ 0 T12 0/86 0/ 0 1/79 0/ 0 2/82 POZ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 POS 100100100100100100100100100100100100100100100100100100100 94 86 TYP S S S S S S S S S S S S S S S S S S S S S CIG 4 4 4 4 4 4 4 4 4 5 5 5 4 4 4 5 4 4 4 4 2 VIS 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 7 5 7 5 OBV N N N N N N N N N N N N N N N N N N HZ N BRReturn to MOS Changes page