Thanks for the link.
Looks as though the forecast for tomorrow there has already shifted: "day":12, "month":10, "year":2014, "yday":284, "hour":19, "min":"00", "sec":0, "isdst":"1", "monthname":"October", "monthname_short":"Oct", "weekday_short":"Sun", "weekday":"Sunday", "ampm":"PM", "tz_short":"CDT", "tz_long":"America/Chicago" }, "period":2, "high": { "fahrenheit":"64", "celsius":"18" }, "low": { "fahrenheit":"55", "celsius":"13" }, "conditions":"Overcast", "icon":"cloudy", "icon_url":"http://icons.wxug.com/i/c/k/cloudy.gif", "skyicon":"", "pop":10, "qpf_allday": { "in": 0.61, "mm": 15 }, "qpf_day": { "in": 0.00, "mm": 0 }, "qpf_night": { "in": 0.61, "mm": 15 }
Anyone please do jump in to correct me, but I'm guessing the interpretation of the revised forecast might be: There's a 10% chance of rainfall >= 0.01" tomorrow. If it does rain, then the expected amount of precipitation is 0.61", all at night and none during the day.
Come to think of it, maybe the earlier pop of zero that you reported wasn't really zero in the sense of 0.0000. Maybe it was a float that was greater than zero but less than 0.5, and it got rounded to the nearest integer (zero) for reporting purposes.
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I agree. Error on the side of water conservation.
And, yes, the stuff I pasted came from here:
http://api.wunderground.com/api/---your_key_here ---/forecast/q/KS/SHAWNEE_MISSION.json
You don't need a key to get it, but, without the key, the URL format is a little different. But the keys are free and give you 500 hits a day.
That is the place Python goes to to get the forecast. And I've looked at it several times in the past and the 0% probability and then significant amount of precip happens often. I am sure it makes sense to people who understand what it actually means.
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Originally posted by frankc View PostBut, I am not using the qpf figure. I need to fix that. Maybe reduce the amount of irrigation by that qpf figure?Last edited by NeverDie; October 11, 2014, 11:03 PM.
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Originally posted by frankc View PostHere is what I don't understand about pop and qpf:
This is for tomorrow:
"pop":0,
"qpf_allday": {
"in": 0.51,
"mm": 13
so there is a 0% chance of precip. But prediction is half an inch of rain.
pop = probability of precipitation
qpf = quantified precipitation forecast
Just a wild guess, but I suppose it might come about as an infrequent glitch if WU used one model/methodology to compute pop and a completely different model/methodology to compute qpf. Maybe then, because the two models don't completely agree with each other, you could get anomalies like this. However, I don't see how it could happen if pop and qpf were derived from the same forecast model.
I haven't myself run across an anomaly like the one you posted, but I had been looking at accuweather, not WU, because until today I didn't notice WU having a qpf.Last edited by NeverDie; October 11, 2014, 10:10 PM.
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Here is what I don't understand about pop and qpf:
This is for tomorrow:
"pop":0,
"qpf_allday": {
"in": 0.51,
"mm": 13
so there is a 0% chance of precip. But prediction is half an inch of rain.
For the next day:
"pop":90,
"qpf_allday": {
"in": 1.57,
"mm": 40
That makes more sense to me: 90% chance and 1.57" predicted.
??
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