Thanks so much, Les. I recognize that it's ephemeral, but your guidance helped me learn a few things about weewx that might help me do some other calcs!
Cheers - Jon On Saturday, March 13, 2021 at 4:11:21 PM UTC-7 ln77 wrote: > First, I misspoke — the change is in heatindexF(), not dewpointF() (duh!) > In the weewx software directory (/usr/share/weewx when installed as a > Debian package), there is a file weewx/wxformulas.py. Look for the line > "if T is None or R is None:” — it’s line 164 in the 4.4.0 version. Add “ > or T < 68”, so that the line becomes “if T is None or R is None or T < 68:” > You could change 68 to 80 or whatever you want the low-temperature > threshold to be. > > WARNING: this is the wrong way to maintain weewx software. The change > will get overwritten when weewx is updated. There are better ways to > implement this, but that would’ve taken me more time than I wanted to spend > so I’m OK with the hack for my installation. But use at your own risk. > > -Les > > > > On 13 Mar 2021, at 14:03, n7uv...@gmail.com <n7uv...@gmail.com> wrote: > > Hi there Les - less than two days ago I updated my weewx from an older > 4.xx version to the current one, and suddenly i was getting the same weird > plot. Finally typed in "heat index wind chill" into the forum and out > popped this thread. I want to feel better as well - where is the spot where > you tweaked DewpointF()? > Cheers - Jon > > On Friday, March 12, 2021 at 2:00:13 PM UTC-7 ln77 wrote: > >> It looks strange to see the heat index suddenly dropping a few degrees >> below the temperature when the temperature gets above 40ºF. (I just saw >> this this morning.) After looking through the thread on weewx’s new heat >> index calculation, I noticed an oddity at the National Weather Service: >> while their calculator calculates a heat index down to 40ºF, on the page >> where they describe the HI equation >> <https://www.wpc.ncep.noaa.gov/html/heatindex_equation.shtml> they say >> the “Rothfusz regression is not valid for extreme temperature and relative >> humidity conditions beyond the range of data considered by Steadman.” >> Looking at Steadman’s sultriness papers from 1979 >> <https://journals.ametsoc.org/search?f_0=author&q_0=R.+G.+Steadman> he >> never looked at temperatures below 68ºF. I couldn’t find any reference to >> indicate why they arbitrarily extended the javascript calculator down to >> 40ºF. Other authors, and the NWS tables, suggest that the heat index isn’t >> really of value below 80ºF. >> >> So I tweaked dewpointF() in my installation to return None if the >> temperature is below 68, and now I feel better. >> >> -Les >> >> >> >> On 24 Feb 2021, at 12:54, gjr80 <gjrod...@gmail.com> wrote: >> >> Pat, >> >> v4.2.0 saw a new heatindex formula implemented, refer issue 601 >> <https://github.com/weewx/weewx/issues/601>. The new formula gives some >> results in some circumstances that may appear counterintuitive. v4.3.0 >> added back the ‘old’ heatindex formula and gives the user the ability to >> choose between the two algorithms . This is covered here >> <http://www.weewx.com/docs/usersguide.htm#%5B%5BWXXTypes%5D%5D> in the >> User’s Guide under [[[heatindex]]]. >> >> By the looks of it you are seeing the ‘new’ algorithm. >> >> Gary >> >> On Thursday, 25 February 2021 at 06:36:38 UTC+10 pobri...@gmail.com >> wrote: >> >>> I thought heat index wasn't calculated unless the temperature was over >>> 80F? Today it's about 49 F and I'm seeing heat index in my charts (which is >>> reporting lower than temperature - I thought that was wind chill?). I don't >>> recall seeing it before at this temperature range. >>> >>> I just want to make sure this is expected for temperatures so low to >>> have a heat index reading? >>> >>> Top graph is Seasons skin and bottom is Belchertown skin. The values >>> match across skins >>> >> >> -- >> You received this message because you are subscribed to the Google Groups >> "weewx-user" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to weewx-user+...@googlegroups.com. >> To view this discussion on the web visit >> https://groups.google.com/d/msgid/weewx-user/f46bd022-500d-414e-b96b-c2bc382d37b9n%40googlegroups.com >> >> <https://groups.google.com/d/msgid/weewx-user/f46bd022-500d-414e-b96b-c2bc382d37b9n%40googlegroups.com?utm_medium=email&utm_source=footer> >> . >> >> >> > -- > You received this message because you are subscribed to the Google Groups > "weewx-user" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to weewx-user+...@googlegroups.com. > > To view this discussion on the web visit > https://groups.google.com/d/msgid/weewx-user/c9ac3f2e-8a1b-4dc5-8168-74fff1cc44e9n%40googlegroups.com > > <https://groups.google.com/d/msgid/weewx-user/c9ac3f2e-8a1b-4dc5-8168-74fff1cc44e9n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > > -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to weewx-user+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/18fa3da2-010d-4352-836d-c49806b4356an%40googlegroups.com.