On Thursday, January 3, 2019 at 1:56:52 PM UTC-5, nineback wrote:
>
> I have set up up the forecast add-in and have it set up to produce NWS and
> Weather Underground forecast which it is doing. It is also producing a
> Zambretti Forecast but it ais showing "The forecast is Fine weather" for
> the past couple of days I have had forecast running. The weather has not
> been fine. It has been raining for the past couple of days. Pressure had
> been up and down between 30.23 to 30.06 inHG. This is the latest
> output from the zambretti.html file:
>
> The forecast is Fine weather
> Issued at 03-Jan-2019 10:55
>
> Any ideas why I am not getting an accurate forecast?
>
the zambretti forecast is REALLY crude. here are the comments from the
code:
# Zambretti Forecaster
#
# The zambretti forecast is based upon recent weather conditions.
Supposedly
# it is about 90% to 94% accurate. It is simply a table of values based
upon
# the current barometric pressure, pressure trend, winter/summer, and wind
# direction. Apparently it is most accurate when used at 09:00 to provide
# the forecast for the day.
#
# The forecast is generated using data from a period of time prior to
09:00.
# The forecast will be the same no matter what time of day it is requested,
as
# long as there are data for the period prior to 09:00. A request for
forecast
# before 09:00 will return the previous day forecast. If the forecast has
# already been generated, it will not be re-generated.
#
# The periods for calculating wind direction and pressure trend can be
# specified via configuration file.
and here are links to some history and detailed description:
http://www.whitbyweather.com/index.php?p=1_56_Zambretti-Forecaster
http://www.meteormetrics.com/zambretti.htm
i am not sure where the 90% to 94% accurate comes from, nor is it clear
exactly what that 'accuracy' is measuring. i happen to like rain, so
'fine' for a rainy day sounds good to me :)
look at the function 'ZambrettiCode' in forecast.py to see exactly how the
forecast is calculated. it is just a lookup table. using the data from
your weewx database you could run the calculations manually to verify that
the zambretti is calculated properly.
m
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