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WeatherOrNot

Making Sense of Forecasts

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So, following the whole Hermine situation, I'm not in any of the "bad" zones by any stretch, at least not according to Tom's FB narrative....I should be in the "may not even rain much" category, being West or S/W of the city.   I followed Accuweather and WTC and their bizzarre forecasts they always have when there's tropical activity "TROPICAL STORM TO AFFECT THE AREA: Winds 0MPH, Rain 0.18"!!!

So I went to the trusty WPC - and that's where my question for you guys, namely the Mt. Holly guys comes in when I see the following forecast:

This Afternoon
Sunny, with a high near 79. North wind around 7 mph.
Tonight
Partly cloudy, with a low around 61. Northeast wind around 6 mph.
Saturday
A slight chance of rain after 1pm. Partly sunny, with a high near 78. Northeast wind 9 to 14 mph. Chance of precipitation is 20%.
Saturday Night
A slight chance of rain. Cloudy, with a low around 58. Northeast wind around 11 mph. Chance of precipitation is 20%.
Sunday
A slight chance of rain. Cloudy, with a high near 77. North wind 10 to 16 mph. Chance of precipitation is 20%.
Sunday Night
Tropical storm conditions possible. A chance of rain. Cloudy, with a low around 62. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.
Labor Day
Tropical storm conditions possible. Mostly cloudy, with a high near 78.
Monday Night
Tropical storm conditions possible. Mostly cloudy, with a low around 63.
Tuesday
Tropical storm conditions possible. Mostly sunny, with a high near 85.
Tuesday Night
Tropical storm conditions possible. Partly cloudy, with a low around 64.
Wednesday
Mostly sunny, with a high near 89.
Wednesday Night
Partly cloudy, with a low around 68.
Thursday
Mostly sunny, with a high near 91.

 

 

And suddenly the forecast makes little sense.   Based on Tom's excellent description of the models, there's pretty much a 0% chance of "Tropical storm conditions" inland, especially West of the city.  But ok, I get it, there's uncertainty in everything.  But how do you get "Tropical storm conditions possible, a chance of rain, cloudy, 30% chance of precip."  And "Tropical storm conditions possible, mostly sunny?"  

The weather nerd in me wants to go with "they mean there could be tropical storm conditions, but if there's not it'll be sunny depending on track."  The non-weather nerd in me says "Forecast for tomorrow 2-3ft snow, high 87, cloudy with bright sunshine" is an odd forecast. Though to be fair I imagine only weather nerds are reading the WPC.....

 

I also realize they're just putting all possibilities on the board, no matter how remote, but "Tropical storm conditions possible" listed for Sunday, Monday, and Tuesday for an area that from the WphillyWX forecast, even the "worst case" track wouldn't really be doing that in this location...I'm curious about how a forecast like this actually comes to be (and how non-geeks in the public would actually be expected to interperet that?)

 

No rush to answer in the height of storm tracking (Except for Tony...you have nothing better to do these days ;) )

 

BTW, OT: Haven't been here in a while, beautiful work on the forum software, Tombo, the new editor is truly beautiful!

 

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There are threshold triggers that have to do with chances of tropical storm winds occurring that automatically include that wording.

 

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Thanks Tony for your great answer to weatherornot's question. I too had been wondering the same thing regarding the tropical storm conditions possible wording in the forecast for my area (north of Philly) in NW Jersey. Yeah, I had noted the wind probability map from the NHC but had not connected the dots. B)

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This was a major drawback with Hermine. The frequent mentions of tropical storm conditions possible made no sense in a lot of cases, the wording is triggered at 15%. Feedback was passed on from our office that this percentage was way to low to trigger that wording. 

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On 9/2/2016 at 3:17 PM, Rainshadow said:

There are threshold triggers that have to do with chances of tropical storm winds occurring that automatically include that wording.

 

A belated thanks, Tony, as always!  I meant to reply when you wrote this, then got caught up in other things and ended up forgetting to come back to it entirely!

 

 

6 hours ago, Mitchg said:

This was a major drawback with Hermine. The frequent mentions of tropical storm conditions possible made no sense in a lot of cases, the wording is triggered at 15%. Feedback was passed on from our office that this percentage was way to low to trigger that wording. 

And thanks for chiming in with more detail so long after even I forgot my original post!  And glad to see that your office already noticed it was a bit off in this instance.

 

The trigger threshold itself is probably troublesome, and especially when applied to such a chaotic storm system, though I think maybe presentation counts for a lot of why it looked so wrong.  The disjoint between "WARNING WARNING SUPER BIG DANGER and kinda cloudy and stuff with a minor chance of sprinkles."  Something tells me there's an industry standard in there somewhere, what with the vendor type systems (points finger at accuweather) that also has a severe disjoint between their tropical (and non-tropical major storm, including winter storm) forecasts where they have "NAMED STORM ASMODEUS WILL AFFECT THE AREA" Winds 3-7mph, chance precip 12% 0.18" for days leading out to whatever storm storm.  So I'm guessing it's not just NWS or just Vendors but some intentional standard at play with how the forecast descriptions work.  And I'm guessing it actually makes sense to the people who produce the forecasts.  I just doesn't make sense to the folks they're produced FOR :P

Although, do the warning/watch/statements fall into the same trap of "numeric threshold includes the text", or are they all written out by hand?  Some of those confuse me for various (not just tropical) storms as well. 

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On 9/26/2016 at 9:49 AM, WeatherOrNot said:

A belated thanks, Tony, as always!  I meant to reply when you wrote this, then got caught up in other things and ended up forgetting to come back to it entirely!

 

 

And thanks for chiming in with more detail so long after even I forgot my original post!  And glad to see that your office already noticed it was a bit off in this instance.

 

The trigger threshold itself is probably troublesome, and especially when applied to such a chaotic storm system, though I think maybe presentation counts for a lot of why it looked so wrong.  The disjoint between "WARNING WARNING SUPER BIG DANGER and kinda cloudy and stuff with a minor chance of sprinkles."  Something tells me there's an industry standard in there somewhere, what with the vendor type systems (points finger at accuweather) that also has a severe disjoint between their tropical (and non-tropical major storm, including winter storm) forecasts where they have "NAMED STORM ASMODEUS WILL AFFECT THE AREA" Winds 3-7mph, chance precip 12% 0.18" for days leading out to whatever storm storm.  So I'm guessing it's not just NWS or just Vendors but some intentional standard at play with how the forecast descriptions work.  And I'm guessing it actually makes sense to the people who produce the forecasts.  I just doesn't make sense to the folks they're produced FOR :P

Although, do the warning/watch/statements fall into the same trap of "numeric threshold includes the text", or are they all written out by hand?  Some of those confuse me for various (not just tropical) storms as well. 

Last question. Its a combination. Tropical related products have more predetermined information based on forecaster parameters of the storm.

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31 minutes ago, Laddm said:

What is the reason there are no QPF/precip or 2m thermos made available for the Euro models? 

$$$$$$$$$$$$$$$; private consortium, they are not going to give away the goods completely for free.

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I figured as much...makes sense y there is so much euro model hugging. Good to know its out there somewhere. Guess we just have to learn to read between the lines ;)

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