Author Topic: AJAX VWS/Weatherflash script  (Read 3655 times)

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Offline 92merc

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AJAX VWS/Weatherflash script
« on: March 16, 2009, 09:35:40 PM »
I setup my Weatherflash demo, and have now added my AJAX scripts using PHP.  Everything is pretty much working except Heat Index and Windchill.  Those just show dashes.  I've double checked what code to use.  I think it's right.  Any ideas?

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Offline saratogaWX

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Re: AJAX VWS/Weatherflash script
« Reply #1 on: March 16, 2009, 10:50:55 PM »
The ajaxVWSwxf.js script is set to not display Heat Index or Wind Chill when those readings would be outside the range specified by the NWS.

Wind Chill is valid for temperatures <= 40F

Heat Index is valid for temperatures >= 80F

So if the temperature is >40F and <80F, both Wind Chill and Heat Index will display as '---'

Somewhat unfortunately, VWS doesn't set the basic windchill and heatindex variables to 'off' when the outside temperature is not within the range for the variable, so the basic page will always show a value (even if it's not supposed to).

Hope this helps..

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Offline sam2004gp

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Re: AJAX VWS/Weatherflash script
« Reply #2 on: March 17, 2009, 08:21:02 AM »
The ajaxVWSwxf.js script is set to not display Heat Index or Wind Chill when those readings would be outside the range specified by the NWS.

Wind Chill is valid for temperatures <= 40F

Heat Index is valid for temperatures >= 80F

So if the temperature is >40F and <80F, both Wind Chill and Heat Index will display as '---'

Somewhat unfortunately, VWS doesn't set the basic windchill and heatindex variables to 'off' when the outside temperature is not within the range for the variable, so the basic page will always show a value (even if it's not supposed to).

Hope this helps..

Best regards,
Ken
Ahhhh, that Affirms/explains what I noticed playing around in VWS the other day thinking about summer coming up.  I had saw some websites that were showing the "---" while mine (being VWS based) was showing 32F for an outdoor heat index.

Is it common practice for the Heat Index to be a degree or two cooler then the Outside Temp reading?   <<< I suppose a slight wind does the same thing as a windchill factor even if it is 85F outside.   

I am also amazed at how my local TV station will say its 90F outside right now and humidity is 80%, but it feels like a 105F or some large "shock quailifying" number.  I have never seen a Heat Index in VWS vary more than 2 or 3 degrees in either direction, for the last 16 months, even in the "doggy-ist" days of summer.
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Offline mackbig

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Re: AJAX VWS/Weatherflash script
« Reply #3 on: March 17, 2009, 08:54:34 AM »
Heat index is not usually displayed till it becomes material, so typically it would never be lower than actual.  Might be a problem with cold weather usage of the calc...

Is it common practice for the Heat Index to be a degree or two cooler then the Outside Temp reading?   <<< I suppose a slight wind does the same thing as a windchill factor even if it is 85F outside.   

90F with 80% is a pretty strong head index event.  The actual calc for that is 113F
I dont use heat index, as we have Humidex up here.  I think it is actually more realistic for the sticky factor.  in your 90 - 80% example, the humidex would actually be 118.4 (48C).   Which is fairly close, but for lower temps the range widen significantly.  So 80F with 50% rh would only register 81F for heat index.... but using same variables in Humidex it would be 80F 50%RH equals 86 humidex.   Heat index seems more geared towards danger levels, and humidex more toward how it feels .....

Andrew

I am also amazed at how my local TV station will say its 90F outside right now and humidity is 80%, but it feels like a 105F or some large "shock quailifying" number.  I have never seen a Heat Index in VWS vary more than 2 or 3 degrees in either direction, for the last 16 months, even in the "doggy-ist" days of summer.

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Offline WeatherBeacon

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Re: AJAX VWS/Weatherflash script
« Reply #4 on: March 17, 2009, 08:54:38 AM »

Is it common practice for the Heat Index to be a degree or two cooler then the Outside Temp reading?   <<< I suppose a slight wind does the same thing as a windchill factor even if it is 85F outside.

For lower humidity, yes. At lower humidity the body's perspiration evaporates more readily and therefore the body feels cooler. It's true: at high temps, "it's a dry heat" is more comfortable than a muggy heat. At high humidity, perspiration doesn't evaporate as efficiently, so it feels more uncomfortable.

I am also amazed at how my local TV station will say its 90F outside right now and humidity is 80%, but it feels like a 105F or some large "shock quailifying" number.  I have never seen a Heat Index in VWS vary more than 2 or 3 degrees in either direction, for the last 16 months, even in the "doggy-ist" days of summer.

At 80% humidity and 90oF, the Heat Index is actually 113oF. Here's a NOAA chart showing Heat Index:

      http://www.weather.gov/om/heat/index.shtml

You can find other charts on the web that give HI at even lower humidities. Heat index and wind chill are definitely an inexact science. In fact, the NWS published a revised wind chill formulation in 2001.

Canada (and perhaps some other countries) uses what is called a "Humidex":

      http://www.msc-smc.ec.gc.ca/cd/brochures/humidex_table_e.cfm

Kevin...

EDIT:  Sorry Andrew. We posted nearly simultaneously.
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Offline 92merc

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Re: AJAX VWS/Weatherflash script
« Reply #5 on: March 17, 2009, 09:14:45 AM »
Thanks Ken.  That explains it because this morning I now notice a wind chill, but no heat index.  Can that file be edited to tweak the wind chill?  Just curious.

But in ND, I would say above 40 is no longer a chill.  That's freaking shorts weather compared to what we've been having!
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Offline sam2004gp

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Re: AJAX VWS/Weatherflash script
« Reply #6 on: March 17, 2009, 09:21:17 AM »
Thanks Kevin and Andrew.  I will have to pay more particular attention to the TV forecast this summer and what type of index they are using and adjust my webpage accordingly.
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Offline mackbig

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Re: AJAX VWS/Weatherflash script
« Reply #7 on: March 17, 2009, 11:28:10 AM »
Kevin,
wow 4 seconds.... and similar long form content.  no need for sorry.   Unless its an exact short answer, I will post through the "someone has replied" message....

Andrew


EDIT:  Sorry Andrew. We posted nearly simultaneously.

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Offline mackbig

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Re: AJAX VWS/Weatherflash script
« Reply #8 on: March 17, 2009, 11:30:16 AM »
My wife was in Florida during a "cold" snap in February.  They had wind chill warnings at 36... 

Andrew

But in ND, I would say above 40 is no longer a chill.  That's freaking shorts weather compared to what we've been having!

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Offline Cienega32

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Re: AJAX VWS/Weatherflash script
« Reply #9 on: March 17, 2009, 02:14:36 PM »
For lower humidity, yes. At lower humidity the body's perspiration evaporates more readily and therefore the body feels cooler. It's true: at high temps, "it's a dry heat" is more comfortable than a muggy heat. At high humidity, perspiration doesn't evaporate as efficiently, so it feels more uncomfortable.
Not to hijack the thread but on the 'sweat notes', it reminded me of when I first moved to Las Vegas NV in '81 from Long Island NY. Summer was great - 100*+ days and the sweat was basically non-existent because it evaporated so quickly. It was cooling. 25 years and a million more people with landscaping factors later, such was not the case. You could feel that increase in humidity, as small as it may have been, in that 'sweat factor' alone.

Getting off a plane in Miami at 12 noon in mid-August a few years ago was brutal...

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