Cumulus (Zambretti) forecast never changes

[ahagadorn]

I have the forecast setting for my Vantage Pro2 station set on Cumulus (Zambretti). It never changes, always says "Exceptional Weather, Stormy, much precipitation". Its been like this for months. I have a second instance of Cumulus running for my Weatherflow Tempest station, set the same way, and it shows a pretty accurate variable forecast. The barometer readings between the two stations are pretty consistent.

Any ideas on why this is happening? Can it be reset somehow?

Thanks

[freddie]

What are your max and min allowable pressures set to? Is your altitude setting correct? How about latitude and longitude? If you have a public website that this instance of MX feeds then a link to that would be useful too.

[ahagadorn]

What are your max and min allowable pressures set to? Is your altitude setting correct? How about latitude and longitude? If you have a public website that this instance of MX feeds then a link to that would be useful too.

Min/max pressure is 950/1050 for both instances. Altitude is set the same for both instances, the Tempest setup and the Davis console. Same with lat/long all settings the same for both Cumulus instances and both station setups.

[freddie]

Okay thank you. The Zambretti algorithm relies on the sea level pressure value supplied, a realistic range of sea level pressures, and also the pressure tendency. If you are happy with the values you are seeing against those parameters then you can rule them out. There is also a dependence on wind direction but I believe this is a smaller contribution than the other parameters.

The algorithm as used by MX is common to all instances of MX so I think that can be ruled out as we are not seeing widespread similar issues.

Therefore I am stumped. If you are positive that all aspects of your configuration that affect the algorithm are okay then I'm unsure what to suggest next.

[ahagadorn]

Okay thank you. The Zambretti algorithm relies on the sea level pressure value supplied, a realistic range of sea level pressures, and also the pressure tendency. If you are happy with the values you are seeing against those parameters then you can rule them out. There is also a dependence on wind direction but I believe this is a smaller contribution than the other parameters.

The algorithm as used by MX is common to all instances of MX so I think that can be ruled out as we are not seeing widespread similar issues.

Therefore I am stumped. If you are positive that all aspects of your configuration that affect the algorithm are okay then I'm unsure what to suggest next.

Thanks, I agree with your analysis, so I'm stumped too. I have to be missing something. Only thing I can think of is that some initial value stored somewhere is throwing it off. I even checked the calibration settings - they are also identical.

[mcrossley]

Odd, the Cumulus forecast just uses the pressure, pressure trend, and wind direction as input, and the code to create and use it is common to all station types.

[ahagadorn]

Well, I fixed it by comparing the Cumulus.ini files between the two instances:

Code: Select all

FCpressinMB=1
FClowpress=950
FChighpress=1050

For the Davis instance, FCpressinMB was set to zero. I changed it to 1 and it worked. How it ever got set to zero, I have no idea.