The wxnow.txt file is created by Cumulus once a minute by default, in the Cumulus program folder, unless you have disabled it by setting

CreateWxnowTxt=0

in the [Station] section of Cumulus.ini. Below is the file format, simply for information.

Sample File

This is a simply text file containing two lines of data.

Feb 01 2009 12:34
272/010g006t069r010p030P020h61b10150

Format of the file

The first line is the time the file was created in local PC time.

The second line is the wx report, in the format used in APRS "complete weather reports". The format is:

272 - wind direction - 272 degrees
010 - wind speed - 10 mph
g006 - wind gust - 6 mph
t069 - temperature - 69 degrees F
r010 - rain in last hour in hundredths of an inch - 0.1 inches
p030 - rain in last 24 hours in hundredths of an inch - 0.3 inches (Cumulus does not supply this value)
P020 - rain since midnight in hundredths of an inch - 0.2 inches
h61 - humidity 61% (00 = 100%)
b10150 - barometric pressure in tenths of a millibar - 1015.0 millibars

From Build 1097 of version 1.9.4:

Selecting APRS/CWOP option to send solar radiation now also adds it to wxnow.txt
Pressure in wxnow.txt is now 'altimeter' rather than MSLP