Quantitative Precipitation Forecast

The quantitative precipitation forecast, or QPF, is an estimate of the amount of precipitation which usually occurs under the given forecast conditions. I personally don't use it for my forecasts, so I don't know how accurate it tends to be.

The QPF is given as two numbers separated by a slash. The number to the left of the slash is the category of precipitation forecasted for the preceding six-hour period, and the number to the right of the slash (if present) is the category of precipitation forecasted for the preceding twelve-hour period

The categories are defined as follows:

• 0: no measurable precipitation
• 1: 0.01 inches to 0.09 inches
• 2: 0.10 inches to 0.24 inches
• 3: 0.25 inches to 0.49 inches
• 4: 0.50 inches to 0.99 inches
• 5: 1.00 inches or more

For the 12-hour QPF, there's an additional category:

• 6: 2.00 inches or more

So for example, suppose our forecast period runs from 0600 UTC October 17 to 0600 UTC October 18. The forecasted category from 0600 UTC to 1200 UTC (six-hour QPF) is 0, from 1200 UTC to 0000 UTC (twelve-hour QPF) is 0, and from 0000 UTC to 0600 UTC (six-hour QPF) is 2. Thus, MOS would suggest a forecast of between 0.10 inches and 0.24 inches for the period.

DTW EC NGM MOS GUIDANCE 10/16/96 1200 UTC DAY /OCT 16 /OCT 17 /OCT 18 / HOUR 18 21 00 03 06 09 12 15 18 21 00 03 06 09 12 15 18 21 00 MN/MX 57 72 54 60 TEMP 70 70 66 62 61 59 59 65 69 69 64 61 59 57 55 56 57 55 51 DEWPT 56 56 57 57 56 55 55 56 56 55 55 54 52 51 50 49 46 44 42 CLDS SC SC SC SC BK OV OV OV OV OV OV OV OV OV OV OV OV OV OV WDIR 23 23 17 18 19 18 17 17 18 17 15 15 16 19 20 21 23 23 23 WSPD 11 10 05 06 06 07 08 12 16 14 11 14 15 15 16 19 23 25 18 POP06 8 36 27 20 22 55 66 62 50 POP12 45 39 80 75 QPF 0/ 1/ 0/1 0/ 0/0 2/ 3/3 2/ 1/2 TSV06 9/ 5 23/ 3 11/ 5 7/ 4 12/10 24/ 6 20/ 7 13/ 3 12/16 TSV12 27/ 7 15/ 8 30/13 26/ 9 PTYPE R R R R R R R R R R R R R R R POZP 0 1 0 1 0 0 0 0 0 0 0 0 0 0 0 POSN 0 0 0 0 0 0 0 0 0 0 0 2 6 10 21 SNOW 0/ 0/ 0/0 0/ 0/0 0/ 0/0 0/ 0/0 CIG 7 7 7 7 6 6 6 6 6 7 7 6 4 VIS 5 5 5 5 4 4 4 4 5 5 5 5 4 OBVIS H H H H F F H H N N N N F

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