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Forecast from Davis Vantage Vue rarely changes

Discussion specific to Davis weather stations
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martinu
Posts: 56
Joined: Wed 01 Jan 2014 7:54 pm
Weather Station: Davis Vantage Vue
Operating System: Raspberry Pi: Raspbian Stretch
Location: Rudston, North Yorkshire

Forecast from Davis Vantage Vue rarely changes

Post by martinu »

The forecast that Cumulus displays but which is generated by my Davis Vantage Vue (as opposed to the forecast generated by Cumulus) seems to be wrong most of the time and often shows "Increasing clouds with little temperature change. Precipitation possible within 24 to 48 hours" even during a long hot spell with almost no cloud, as we've been having here for the past few days.

Has anyone else noticed this? As far as I know, I've got all the calibrations on the Davis console correct: lat/long/elevation; date/time. Pressure and temperature readings vary from day to day (ie they are not stuck) and seem to be mostly in agreement with an Oregon Scientific non-logging weather station that I have which seems to give much more sensible forecasts in terms of the sun/cloud/rain icons that it displays.

The only readings that are probably inaccurate are wind speed/direction because even with the weather sensor on a long pole about 15 feet above the ground, I think the nearby houses (a 3-house terrace about 50 feet away) shield a lot of the wind: even in very gusty weather I've not seen anything higher than 30 mph. Does the Davis forecast use wind speed in its calculations?

Any suggestions?

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steve
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Re: Forecast from Davis Vantage Vue rarely changes

Post by steve »

According to the Vantage Vue manual, the forecast uses barometric reading & trend, wind speed & direction, rainfall, temperature, humidity, latitude & longitude, time of year.
Steve

martinu
Posts: 56
Joined: Wed 01 Jan 2014 7:54 pm
Weather Station: Davis Vantage Vue
Operating System: Raspberry Pi: Raspbian Stretch
Location: Rudston, North Yorkshire

Re: Forecast from Davis Vantage Vue rarely changes

Post by martinu »

steve wrote:According to the Vantage Vue manual, the forecast uses barometric reading & trend, wind speed & direction, rainfall, temperature, humidity, latitude & longitude, time of year.
From a meterological point of view, would a wind speed that was artificially low and with some directions not listed, because of shielding from a high building, tend to cause a forecast of worse weather, if all other readings (temp, humidity, pressure, lat/long/elevation, rainfall) were correct? I'm not sure how wind speed/direction contributes to the forecast algorithm.

prodata
Posts: 225
Joined: Sat 05 Feb 2011 7:13 pm
Weather Station: VP2
Operating System: Windows - all flavours
Location: Littleport, East Cambs, UK

Re: Forecast from Davis Vantage Vue rarely changes

Post by prodata »

martinu wrote:I'm not sure how wind speed/direction contributes to the forecast algorithm.
I'd be surprised if it was given much weight.

I think the cause of similar forecasts day to day is (i) that the UK does not experience much extreme or rapidly changing weather (not saying it never happens, but it's less common); and (ii) probably more to the point, UK weather tends to get set into spells often lasting eg 2-3 weeks when the weather really isn't very different day to day. At present, In S England at least, we're in a spell of broadly high pressure when there's not a lot of change day to day. When we revert to a spell of Atlantic weather, especially in autumn or spring, when there may be a succession of deep lows queuing to the West then you might expect to see more frequent changes in the forecast text. And of course there's always WXSIM as a program to provide more detailed forecasts if you're interested enough to get to grips with it and are willing to pay.
John Dann
Prodata Weather Systems
Littleport, East Cambs, UK
http://www.weatherstations.co.uk

martinu
Posts: 56
Joined: Wed 01 Jan 2014 7:54 pm
Weather Station: Davis Vantage Vue
Operating System: Raspberry Pi: Raspbian Stretch
Location: Rudston, North Yorkshire

Re: Forecast from Davis Vantage Vue rarely changes

Post by martinu »

prodata wrote:
martinu wrote:I'm not sure how wind speed/direction contributes to the forecast algorithm.
I'd be surprised if it was given much weight.

I think the cause of similar forecasts day to day is (i) that the UK does not experience much extreme or rapidly changing weather (not saying it never happens, but it's less common); and (ii) probably more to the point, UK weather tends to get set into spells often lasting eg 2-3 weeks when the weather really isn't very different day to day. At present, In S England at least, we're in a spell of broadly high pressure when there's not a lot of change day to day. When we revert to a spell of Atlantic weather, especially in autumn or spring, when there may be a succession of deep lows queuing to the West then you might expect to see more frequent changes in the forecast text. And of course there's always WXSIM as a program to provide more detailed forecasts if you're interested enough to get to grips with it and are willing to pay.
I'm not greatly bothered by the inaccurate forecasts, though I wondered whether anyone else in the UK with a Vantage Vue had similar symptoms.

The past few days have been hot and sunny with almost no rain, although a small band of rain was forecast for early this morning (eg on The Weather Outlook and on Met Office sites) which did actually appear. For all this time, the Davis forecast has been "Increasing clouds with little temperature change. Precipitation possible within 24 to 48 hours" or "Increasing clouds with little temperature change", even when the weather has changed from cold, overcast and rainy to hot, sunny and dry. My recollection over the past few months with a variety of real weather is that the Davis forecasts generally have been very pessimistic, implying clouds or rain for most of the time. I get the impression that words like "sun", "warm" and "dry" don't appear in the Davis's vocabulary :lol:. The corresponding Cumulus forecast tends to correspond better to the weather that actually materialises. The fact that the Davis forecast is so badly wrong so much of the time makes me wonder whether there is a setting that I've set wrongly.

prodata
Posts: 225
Joined: Sat 05 Feb 2011 7:13 pm
Weather Station: VP2
Operating System: Windows - all flavours
Location: Littleport, East Cambs, UK

Re: Forecast from Davis Vantage Vue rarely changes

Post by prodata »

You do need your lat/long correctly set in the console, otherwise the forecast rules will relate to a different part of the world. But assuming that lat/long is correctly set then no, nothing else will make much difference.

But what this shows more than anything is that the prime purpose for individual weather stations is for weather reporting, not weather forecasting. There is a real limit to how much monitoring parameter trends, even the pressure trend, which is the key one, from one isolated site can tell you about weather developments probably being driven from hundreds of miles away. That is the appeal of WXSIM in that it can combine broad trends in weather patterns as predicted by the large-scale models and available on the Internet and the particular circumstances of your local environment as reported by your own weather station.
John Dann
Prodata Weather Systems
Littleport, East Cambs, UK
http://www.weatherstations.co.uk

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mcrossley
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Re: Forecast from Davis Vantage Vue rarely changes

Post by mcrossley »

Fwiw I have the same forecast on my VP2 for the last few days. And actually the cloud has increased and we had some rain last night too, so not wildly inaccurate.

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dazza1223
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Weather Station: Davis Vantage Vue
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Re: Forecast from Davis Vantage Vue rarely changes

Post by dazza1223 »

Yh I got a davis vantage vue and the weather forecast all way says it sun and cloudy and it do seem to change when we all have that storm in January it just said sun and cloud is that somthink I'm missing
Have fun and keep learning

dazza :D

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