Author Topic: Confused by forecasts  (Read 1029 times)

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Offline groston

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Confused by forecasts
« on: June 28, 2023, 06:03:24 PM »
Not sure if this is the proper topic area, but…

I am confused by weather forecasting. Yes, I know that there are different models and that they will produce results that are somewhat different from each other. However, I am seeing three forecasts for my local region which, to me, are quite different from each other:
  • weather.com: partly cloudy and high 83 F
  • 1weather (Android app): sunny and 80 F
  • api.openweathermap.org: rainy and 78F

Yesterday, these forecasts were even more divergent from each other. So, two questions: 1) Why are they so different from each other? 2) Is there one source which has been shown to be more reliable than the others?

Thank you.

Offline ocala

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Re: Confused by forecasts
« Reply #1 on: June 28, 2023, 06:36:56 PM »
Weather forecasting is not an exact science, and it never will be. Just too many variables. I have seen my forecast change drastically from morning to the afternoon.
Your best bet for an accurate forecast is to use the NWS point forecast. It's made by mets who live in the general area and understand the weather patterns for the general area. Local knowledge is a great asset when making a forecast.
As for why those are so different I don't know. One met could have put more weight on a particular model, or the forecast was made by a computer which takes into account all models. Bottom line is mets don't always know what's happening 30K feet in the air and sometimes they make their best guess. Most of the time they get it right and sometimes they don't.
The blues had a baby and they named it Rock & Roll

Online PaulMy

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Re: Confused by forecasts
« Reply #2 on: June 28, 2023, 09:57:48 PM »

Hi,
I've often wondered how close the forecasts are to actual, especially a forecast of a few days out.
I have a script that gets the 5-day forecast from Weather Underground and publish that on my website:
Code: [Select]
The 5-day Forecast for London/Middlesex, Ontario, Canada
Wednesday - Mainly sunny. Highs 23 to 25C and lows 8 to 10C.
Thursday - Partly cloudy. Highs 26 to 28C and lows 17 to 19C.
Friday - Morning showers and thunderstorms. Highs 28 to 30C and lows 17 to 19C.
Saturday - Thunderstorms. Highs 25 to 27C and lows 16 to 18C.
Sunday - Showers possible. Highs 25 to 27C and lows 15 to 17C.
Monday - Scattered thunderstorms possible. Highs 26 to 28C and lows 16 to 18C.



I then lists those daily forecast so I have the past 6 days of forecasts for the current day, and then add the actual conditions (manually taken from my weather station). 
Code: [Select]
The 5-day Forecast for London/Middlesex, Ontario, Canada:
Made on Thursday for: Tuesday - Chance of showers. Highs 19 to 21C and lows 12 to 14C.
Made on Friday for: Tuesday - Showers. Highs 19 to 21C and lows 12 to 14C.
Made on Saturday for: Tuesday - Showers, maybe a rumble of thunder. Highs 20 to 22C and lows 13 to 15C.
Made on Sunday for: Tuesday - Periods of light rain. Highs 20 to 22C and lows 13 to 15C.
Made on Monday for: Tuesday - Chance of showers. Highs 19 to 21C and lows 12 to 14C.
Made on Tuesday for: Tuesday - Cloudy. Highs 20 to 22C and lows 11 to 13C.
Actual...         Tuesday - Smoke cover from mid-morning, 919 W/m2, No rain.  High 20.3°C and Low 15.5°C.  Wind gust 42.8 km/h, and 142.9 km wind run.


Made on Friday for: Wednesday - Showers. Highs 18 to 20C and lows 11 to 13C.
Made on Saturday for: Wednesday - Showers. Highs 16 to 18C and lows 12 to 14C.
Made on Sunday for: Wednesday - Cloudy. Highs 18 to 20C and lows 11 to 13C.
Made on Monday for: Wednesday - Mix of sun and clouds. Highs 22 to 24C and lows 9 to 11C.
Made on Tuesday for: Wednesday - Sunshine. Highs 23 to 25C and lows 8 to 10C.
Made on Wednesday for: Wednesday - Mainly sunny. Highs 23 to 25C and lows 8 to 10C.


Made on Saturday for: Thursday - Mix of sun and clouds. Highs 23 to 25C and lows 12 to 14C.
Made on Sunday for: Thursday - A few clouds. Highs 24 to 26C and lows 13 to 15C.
Made on Monday for: Thursday - Mix of sun and clouds. Highs 26 to 28C and lows 14 to 16C.
Made on Tuesday for: Thursday - Mix of sun and clouds. Highs 26 to 28C and lows 15 to 17C.
Made on Wednesday for: Thursday - Partly cloudy. Highs 26 to 28C and lows 17 to 19C.


Made on Sunday for: Friday - Occasional showers possible. Highs 25 to 27C and lows 15 to 17C.
Made on Monday for: Friday - Scattered thunderstorms. Highs 26 to 28C and lows 15 to 17C.
Made on Tuesday for: Friday - A few thunderstorms possible. Highs 27 to 29C and lows 16 to 18C.
Made on Wednesday for: Friday - Morning showers and thunderstorms. Highs 28 to 30C and lows 17 to 19C.


Made on Monday for: Saturday - Scattered thunderstorms. Highs 24 to 26C and lows 14 to 16C.
Made on Tuesday for: Saturday - A few thunderstorms possible. Highs 26 to 28C and lows 15 to 17C.
Made on Wednesday for: Saturday - Thunderstorms. Highs 25 to 27C and lows 16 to 18C.


Made on Tuesday for: Sunday - Scattered thunderstorms possible. Highs 24 to 26C and lows 14 to 16C.
Made on Wednesday for: Sunday - Showers possible. Highs 25 to 27C and lows 15 to 17C.


Made on Wednesday for: Monday - Scattered thunderstorms possible. Highs 26 to 28C and lows 16 to 18C.

While there can be significant change from previous forecasts to the actual day, generally they are quite good - I am amazed!
Granted this is from one-and-the same forecasting service, not from different sources like groston quoted.


Enjoy,
Paul

Offline Bunty

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Re: Confused by forecasts
« Reply #3 on: June 29, 2023, 02:34:23 AM »
For Wednesday, June 28, the NWS surprisingly predicted the high in Stillwater would be 109 and 108 in Oklahoma City.  What a way to have 100s for the first time this summer.  I guess NWS saw the record breaking heat way arriving to central Oklahoma big time.  But the high for both places only got to 98.  Apparently, dewpoints didn’t turn out as expected so temperatures didn’t get as high as expected. However, much of western Oklahoma managed to get to over 100.

Also the 2nd home page using modified AltDashboard 6.95 at http://stillwaterweather.com/2ndhome.php

Offline SteveFitz1

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Re: Confused by forecasts
« Reply #4 on: June 29, 2023, 09:39:01 AM »
I wrote an api script for my site that pulls 5-day temp and precip forecasts from the NWS, AccuWeather, Weather Channel, Aeris, ECMWF, GFS, and my own WxSim forecast.
https://www.tylertexasweather.com/allforecasts8.htm

The forecasts are always quite variable.

Steve

 

anything