Possible problem with WXSimate estimating cloud from WD

The past couple of mornings when I imported my data from WD it set the esimated clouds to over 80% both mornings. This is despite my solar sensor saying it was sunny and when I looked out at the whole sky to check I estimated yesterday to be about 10% cloud cover and today probably less than 1%. I manually adjusted this in WXSim after import of local data, however I’m sure that WXSimate is getting it wrong.

Stuart

I had similar issues here Stuart and Tom advised waiting until later in the day to do my forecast.

WxSimate will not grab data from the current hour so I try to run it right after the top of the hour.

That could be a problem as I need to do my forecast early in the day. Its also a bit of a problem if you run it at say 07:58 if it wont read data from the logs after 07:00. I dont know how far back it goes but it should be able to read the most up to date info in the log files.

Stuart

Hi Stuart and Dan,

The erroneous cloud cover estimate is almost surely from it being so early in the morning. It has to watch for at least 20 minutes to let passing clouds show themselves by sporadically blocking sunlight. There’s no way an instantaneous reading could supply a cloud cover estimate (i.e. it could be 95% cloudy, with the sun shining through a break, or 5% cloudy, with the sun right behind it).

WXSIMATE looks back 30 days for some items, and only a few minutes for others. The reason it (deliberately) defaults to just before the last hour is for coordination with METAR data. Running it at, say, 7:45 and then using regional advection could cause problems becaus the METAR data would be almost an hour old, and from before the sun was up. I’m trying to recall if I’ve provided an override of that - I need to check, though it is at least an idea. I think I left it where you can time the time (in decimal form, like 7.8 for 7:48) directly into the box and then import.

Actually, I recommend looking out the window to get your cloud cover, even in the middle of the day. The same goes for the haze estimate.

Hope that helps! :slight_smile:

Tom

That would explain why the cloud estimate was so far out because when I look at 06:00-07:00 it was indeed much cloudier. Interestingly manually adjusting the cloud cover from the weather station did not make much difference to any forecast temps today.

Stuart

Hi Stuart,

Probably the main reason correcting the clouds made little difference is because the READY clouds quickly take over as soon as the forecast starts. Current cloud cover is mainly for the calibration run, and has a smaller effect.

Tom