#!/usr/bin/env python
# pywws - Python software for USB Wireless Weather Stations
# http://github.com/jim-easterbrook/pywws
# Copyright (C) 2008-13 Jim Easterbrook jim@jim-easterbrook.me.uk
# Inspired by beteljuice.com Java algorithm, as converted to Python by
# honeysucklecottage.me.uk, and further information from
# http://www.meteormetrics.com/zambretti.htm
# This program is free software; you can redistribute it and/or
# modify it under the terms of the GNU General Public License
# as published by the Free Software Foundation; either version 2
# of the License, or (at your option) any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
def _(msg) : return msg
forecast_text = {
'A' : _("Settled fine"),
'B' : _("Fine weather"),
'C' : _("Becoming fine"),
'D' : _("Fine, becoming less settled"),
'E' : _("Fine, possible showers"),
'F' : _("Fairly fine, improving"),
'G' : _("Fairly fine, possible showers early"),
'H' : _("Fairly fine, showery later"),
'I' : _("Showery early, improving"),
'J' : _("Changeable, mending"),
'K' : _("Fairly fine, showers likely"),
'L' : _("Rather unsettled clearing later"),
'M' : _("Unsettled, probably improving"),
'N' : _("Showery, bright intervals"),
'O' : _("Showery, becoming less settled"),
'P' : _("Changeable, some rain"),
'Q' : _("Unsettled, short fine intervals"),
'R' : _("Unsettled, rain later"),
'S' : _("Unsettled, some rain"),
'T' : _("Mostly very unsettled"),
'U' : _("Occasional rain, worsening"),
'V' : _("Rain at times, very unsettled"),
'W' : _("Rain at frequent intervals"),
'X' : _("Rain, very unsettled"),
'Y' : _("Stormy, may improve"),
'Z' : _("Stormy, much rain")
}
del _
[docs]def ZambrettiCode(pressure, month, wind, trend,
north=True, baro_top=1050.0, baro_bottom=950.0):
"""Simple implementation of Zambretti forecaster algorithm.
Inspired by beteljuice.com Java algorithm, as converted to Python by
honeysucklecottage.me.uk, and further information
from http://www.meteormetrics.com/zambretti.htm"""
# normalise pressure
pressure = 950.0 + ((1050.0 - 950.0) *
(pressure - baro_bottom) / (baro_top - baro_bottom))
# adjust pressure for wind direction
if wind != None:
if not north:
# southern hemisphere, so add 180 degrees
wind = (wind + 8) % 16
pressure += ( 5.2, 4.2, 3.2, 1.05, -1.1, -3.15, -5.2, -8.35,
-11.5, -9.4, -7.3, -5.25, -3.2, -1.15, 0.9, 3.05)[wind]
# compute base forecast from pressure and trend (hPa / hour)
if trend >= 0.1:
# rising pressure
if north == (month >= 4 and month <= 9):
pressure += 3.2
F = 0.1740 * (1031.40 - pressure)
LUT = ('A', 'B', 'B', 'C', 'F', 'G', 'I', 'J', 'L', 'M', 'M', 'Q', 'T',
'Y')
elif trend <= -0.1:
# falling pressure
if north == (month >= 4 and month <= 9):
pressure -= 3.2
F = 0.1553 * (1029.95 - pressure)
LUT = ('B', 'D', 'H', 'O', 'R', 'U', 'V', 'X', 'X', 'Z')
else:
# steady
F = 0.2314 * (1030.81 - pressure)
LUT = ('A', 'B', 'B', 'B', 'E', 'K', 'N', 'N', 'P', 'P', 'S', 'W', 'W',
'X', 'X', 'X', 'Z')
# clip to range of lookup table
F = min(max(int(F + 0.5), 0), len(LUT) - 1)
# convert to letter code
return LUT[F]
[docs]def ZambrettiText(letter):
return forecast_text[letter]
[docs]def main(argv=None):
from pywws import conversions
for pressure in range(1030, 960, -10):
for trend_txt in ('S', 'R-S', 'R-W', 'F-W', 'F-S'):
trend, month = {
'R-W' : ( 0.2, 1),
'F-W' : (-0.2, 1),
'R-S' : ( 0.2, 7),
'F-S' : (-0.2, 7),
'S' : ( 0.0, 7),
}[trend_txt]
for wind in (0, 2, 14, None, 4, 12, 6, 10, 8):
if wind is None:
wind_txt = 'calm'
else:
wind_txt = conversions.winddir_text(wind)
print '%4d %4s %4s %3s' % (
pressure, trend_txt, wind_txt,
ZambrettiCode(pressure, month, wind, trend))
print ''
if __name__ == "__main__":
main()