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Central PA - Fall 2021


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Beyond that, is something bad running through the GFS algorithm when it’s putting out these numbers for the Central US for D5? That’s some 10-20 degrees higher than other models. Maybe our hot stretch is error carried forward from this:
512B9C6D-7923-434B-B06C-CB976E5E6553.thumb.jpeg.6bd0ad5be23c5326756beac39461c57c.jpeg

That may shatter a few records


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4 minutes ago, TimB84 said:

I feel like I used to be able to get it from Wunderground back in the day but that was a long time ago. I don’t use that site near as much ever since TWC took it over and it went to crap. As for the programming language stuff, you might as well be speaking Russian to me.

I am not even sure it would be helpful to gather info on the highest DP of a given day.  Rain causes the RH to go up obviously but raining into relatively dry air at the surface will cause the temp to fall and DP to rise a bit.  So we could have a day with DP's in the 50's, we get a shower, and the DP rises to the 60's for a bit and then back down when the shower is over...but that day is then recorded as a 60's DP day. 

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5 minutes ago, TimB84 said:

Beyond that, is something bad running through the GFS algorithm when it’s putting out these numbers for the Central US for D5? That’s some 10-20 degrees higher than other models. Maybe our hot stretch is error carried forward from this:

 

The 850 positive anomalies are outrageous in conjunction with those temps.   I checked out zone forecasts for Ok and Kanas, this Saturday, and they are 10-20 degrees lower. 

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3 minutes ago, Jns2183 said:


That may shatter a few records


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It’s highly unlikely to happen, as there’s no support for it, but this is the GFS showing something only 105 hours out that is way out of sync with other models (and 20+ degrees above the official NWS forecast for those areas). As for the magnitude of what it’s depicting, verbatim those temps are 6-7 degrees higher at Omaha and Lincoln, NE than any September day on record.

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1 minute ago, Bubbler86 said:

The 850 positive anomalies are outrageous in conjunction with those temps.   I checked out zone forecasts for Ok and Kanas, this Saturday, and they are 10-20 degrees lower. 

So here’s a topic for discussion: if the average high for a particular date is 82 and the GFS models a high of 113 at 4.5 days out, then the actual high is 88, how egregious of a modeling error is that? I mean the GFS is modeling above normal temps, and above normal temps may verify.

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Just now, Bubbler86 said:

This site takes the Sept DP's and is comparable to May/Early June

 

image.thumb.png.277339f4176cb4f04ff5a1e115728a73.png

 

https://weatherspark.com/y/21982/Average-Weather-in-Harrisburg-Pennsylvania-United-States-Year-Round

 

 

So that would indicate that even in mid-September, one can expect that over 1/3 of the days would have at least slightly uncomfortable dewpoints of 60+, and that 9 out of 15 wouldn’t be that extreme.

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1 minute ago, TimB84 said:

So here’s a topic for discussion: if the average high for a particular date is 82 and the GFS models a high of 113 at 4.5 days out, then the actual high is 88, how egregious of a modeling error is that? I mean the GFS is modeling above normal temps, and above normal temps may verify.

Personally I would judge on departure from forecast so its a very egregiously bad forecast in your example. 

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2 minutes ago, Bubbler86 said:

Personally I would judge on departure from forecast so its a very egregiously bad forecast in your example. 

So your view on the matter is, a +5 departure on a day when a model showed a +30 departure is just as bad as a +5 departure on a day when a model showed a -20 departure. As a math/stat person, I very much agree. Just didn’t know if I was missing something.

And of course, I would say such an error on D5 should be weighted a lot more heavily than such an error on D15.

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2 minutes ago, TimB84 said:

So that would indicate that even in mid-September, one can expect that over 1/3 of the days would have at least slightly uncomfortable dewpoints of 60+, and that 9 out of 15 wouldn’t be that extreme.

I agree with your assertion using that data as a basis.  Its really hard to pinpoint the 9 out of 15 piece but fairly easy to be confident in taking that data and saying its normal for a lot of Sept days to have DP's into the 60's or higher.  Believe the chart suggests that close to half of Sept 7's are above 60 DP. 

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8 minutes ago, TimB84 said:

So your view on the matter is, a +5 departure on a day when a model showed a +30 departure is just as bad as a +5 departure on a day when a model showed a -20 departure. As a math/stat person, I very much agree. Just didn’t know if I was missing something.

And of course, I would say such an error on D5 should be weighted a lot more heavily than such an error on D15.

Yes, its all about getting the temp right not playing a 50/50 game of above or below normal.  I believe the agencies that rank model scores (though I think they do it more on fronts vs. temps) have different scales to accommodate length of time out into the 15 days and weighing errors appropriately.   The only time I would not agree with your first sentence is if winter precip is involved.    A winter day where a model suggests 25 and snow but it is 50 and rain is worse (at least to the public view) than a prediction of 40 and rain that turned into 65 and rain. 

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7 minutes ago, Bubbler86 said:

Yes, its all about getting the temp right not playing a 50/50 game of above or below normal.  I believe the agencies that rank model scores (though I think they do it more on fronts vs. temps) have different scales to accommodate length of time out into the 15 days and weighing errors appropriately.   The only time I would not agree with your first sentence is if winter precip is involved.    A winter day where a model suggests 25 and snow but it is 50 and rain is worse (at least to the public view) than a prediction of 40 and rain that turned into 65 and rain. 

...and that’s the bottom line. The general public isn’t looking at the GFS, the general public is looking at a forecast on an iPhone app that is a blend of models, and the vast majority of them have no idea where any of the data comes from. Beyond that, if you took 10 random people, even people who have lived in Harrisburg their whole lives, off the street and asked them “what’s the average high in Harrisburg on September 15th,” I’d say a majority of them wouldn’t be able to produce a number within 5 degrees of the actual value.

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Just now, TimB84 said:

...and that’s the bottom line. The general public isn’t looking at the GFS, the general public is looking at a forecast on an iPhone app that is a blend of models, and the vast majority of them have no idea where any of the data comes from. Beyond that, if you took 10 random people, even people who have lived in Harrisburg their whole lives, off the street and asked them “what’s the average high in Harrisburg on September 15th,” I’d say a majority of them wouldn’t be able to produce a number within 5 degrees of the actual value.

If more than 2 of them gave an accurate number I would be surprised though there are a LOT of hidden weather weenies in the world.  But even weather weenies do not keep track of average temps by heart.  I suspect at least one of them would say that there is no Dew Point when below freezing...its called the frost point then.  :-). 

image.thumb.png.cb76c4f8050724faef1107f56c23842f.png

 

 

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So here’s a topic for discussion: if the average high for a particular date is 82 and the GFS models a high of 113 at 4.5 days out, then the actual high is 88, how egregious of a modeling error is that? I mean the GFS is modeling above normal temps, and above normal temps may verify.

I have looked into how they determine model errors vs actual forecasts vs observed and god help you if you don’t have a strong background in statistics. I sorta understand it, and maybe could explain it when I have time to review my notes, but it is not intuitive. I suspect it’s more correct doing it how they do it, but I was hoping to find more localized analysis and that seems not possible unless you posses a login for noaa to access certain information


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36 minutes ago, TimB84 said:

...and that’s the bottom line. The general public isn’t looking at the GFS, the general public is looking at a forecast on an iPhone app that is a blend of models, and the vast majority of them have no idea where any of the data comes from. Beyond that, if you took 10 random people, even people who have lived in Harrisburg their whole lives, off the street and asked them “what’s the average high in Harrisburg on September 15th,” I’d say a majority of them wouldn’t be able to produce a number within 5 degrees of the actual value.

Euro still insisting on extremes next week. 

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Looks like someone "talked" WPC into issuing a FFW for Eastern PA. Throw the science out the window.  It's gut feeling time.   
Just like on these boards, peoples true thoughts come out in seemingly agnostic postings. The AFD writing Met for Phl thinks tomorrow is a big risk day
while CTP's met is reaching for the sun screen and thinking its a nothing burger. 

SPC/WPC continue to place MRGL outlooks for Excessive Rain and
SVR over the eastern 1/3 to 1/2 of the CWA for Wed afternoon and
evening, INVOF a nearly north-south lee trough. Marginally
stronger llvl winds and vorticity will occur across our mid and
upper Susq Mainstem counties where the close proximity of the
aforementioned warm front will create a very low prob of a few
transient supercells and perhaps an isolated, weak tornado
(indicated by PCs inclusion of the 2% risk area over CTP`s
eastern zones in their Dye outlook). Heavy rainfall risk is
highest well east of my CWA, and WPC was talked into a
Day 2 SLGT risk over far eastern PA for Wednesday afternoon/eve.
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