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It's the Same Old Song

By: Lee Grenci , 3:35 PM GMT on March 16, 2017

Just a short blog about a few of my takeaways from the winter storm in the Northeast this week...I had no doubt that precipitation type would be an issue in some of the major cities, and I thought forecasters were aware of the difficulties with regard to predicting snowfall.

However, all the forecasts I saw were deterministic rather than probabilistic. And many forecasts were framed in the context of the European and GFS models (essentially, choosing the model of the day). I'm certain many forecasters looked at the ensembles, but I didn't see anybody frame the forecast in probabilities (probability of snowfall exceeding six or twelve inches, for example, or even probabilities of precipitation type). Instead, it was the same old song...although some forecasters talked about uncertainty, they refused to issue probabilistic forecasts and universally defaulted to deterministic maps of snowfall.

It was pretty clear early on that some major metropolitan areas might not receive all snow. And probabilities, especially early on, conveyed this uncertainty. Check out the forecast for probabilities of snowfall greater than 12 inches from WPC's super ensemble issued 00 UTC on Monday (Sunday evening) and ending 00 UTC Wednesday (Tuesday evening). And yet, the some media still ran with huge snowfalls in Philadelphia and New York City. In fairness, probabilities increased toward the onset of the storm, but there was still enough uncertainty for some forecasters to be a bit more cautious. That's what happens when media starts publishing hyperbolic numbers two to three days in advance of the storm. Yes, a swing for the fences, hoping that the pitcher throws a fast ball right down the middle of home plate. When are we going to learn that the atmosphere is a knuckle-ball pitcher?


A loop of successive SREF forecasts (36-, 30-, 24-, 18-, 12-, and 6-hour forecasts) for the probabilities of snow, all valid at 21 UTC on March 14, 2017. Courtesy of SPC.

Yes, I know. The public wants deterministic forecasts. Why do we, as a profession, always acquiesce to this demand? Like I always say...maybe this isn't too difficult to understand in light of this country never adopting the metric system.

Nothing ever seems to change these days, including some of the bad science used to convey the meteorology of the storm. For example, I saw water-vapor imagery being used to generally quantify the moisture feeding into the storm's circulation. For the millionth time, water vapor imagery cannot routinely detect moisture in the lower troposphere (below 700 mb), where most water vapor resides. If that's the message you want to convey, you should not use water vapor imagery; you should use charts of precipitable water (PWAT).


The loop of GFS model analyses of 500-mb heights (in meters) and 500-mb absolute vorticity (color-filled) from 00 UTC on March 14 to 12 UTC on March 15. Only vorticity values greater than or equal to 16 x 10-5 sec-1 are shown in order to emphasize vorticity maxima. Courtesy of Penn State..

After the storm, I read media blogs / discussions that claimed that the prominent northern and southern 500-mb short-wave troughs actually phased during the storm. In my opinion, such phasing did not occur, Check out (above) the loop of GFS model analyses of 500-mb heights and 500-mb absolute vorticity from 00 UTC on March 14 to 12 UTC on March 15. Note that I only present contours of absolute vorticity (color-filled) of 16 x 10-5 sec-1 or greater in order to emphasize the vorticity maxima.

I don't see any phasing...just a Fujiwhara near the end of the loop. Why am I raising such a fuss? Well, the lack of phasing probably resulted in the storm jogging a bit more westward, allowing warmer air to gain more ground inland and to knock snow totals down in places. Yes, you gotta know your science.

All in all, however, I believe forecasters had a pretty good handle on this storm. Their deterministic tenor of their message, however, likely gave some people the wrong impression about the lingering uncertainty of the storm.

As for some of the media's explanations after the storm (phasing, use of water-vapor imagery, etc.), I can only shake my head.

It's the same old song.

Many thanks to Jon Nese and Steve Seman of Penn State's Department of Meteorology for their helpful input.

Lee


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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20. WunderAlertBot (Admin)
6:34 PM GMT on March 21, 2017
24hourprof has created a new entry.
19. georgevandenberghe
3:20 PM GMT on March 20, 2017
Quoting 12. Astrometeor:



Forecast discussions are great resources from the NWS, but the vast majority of the public cannot decipher or understand what those discussions mean, nor can they locate them. As such, the public relies on their local media and broadcast meteorologists or people like Capital Weather Gang or The Weather Channel to give them forecasts and snow predictions.


Forecast discussions are on weather.gov. Click on your location and it's one of the large buttons underneath the regional map. OR click on the map and it will be under the blown up local area map that pops up to the right of the forecast test. I am surprised that anyone halfway interested in what is going on wouldn't find one of these two locations on the web page.

Member Since: December 31, 1969 Posts: Comments:
18. georgevandenberghe
3:15 PM GMT on March 20, 2017
Quoting 16. BaltimoreBrian:

My little bit of original weather wisdom. Not very scientific but often valid: When winter wanes rain reigns!


Mine (from the 70s)

Spring in Winter is followed by Winter in Spring

Also (my original)

"If you get sunburned planting your tomatoes that will be the last sun you see for a month"
and I came up with this one at Penn State in 1979. (nope, didn't work at FSU)
Member Since: December 31, 1969 Posts: Comments:
Quoting 16. BaltimoreBrian:

My little bit of original weather wisdom. Not very scientific but often valid: When winter wanes rain reigns!

:-)
Member Since: December 31, 1969 Posts: Comments:
16. BaltimoreBrian
12:13 AM GMT on March 20, 2017
My little bit of original weather wisdom. Not very scientific but often valid: When winter wanes rain reigns!
Member Since: December 31, 1969 Posts: Comments:
Quoting 12. Astrometeor:



Forecast discussions are great resources from the NWS, but the vast majority of the public cannot decipher or understand what those discussions mean, nor can they locate them. As such, the public relies on their local media and broadcast meteorologists or people like Capital Weather Gang or The Weather Channel to give them forecasts and snow predictions.

Exactly, Nathan!
Member Since: December 31, 1969 Posts: Comments:
Quoting 11. WU_216252:

Well, maybe this doesn't count, but I certainly remember that in the forecast discussions, there was quite a bit of talk of the ensembles and probabilities. For example, Sunday night or Monday morning, my local Buffalo office forecast discussion noted the fact that there was an unusually large spread in uncertainty in the snow accumulation. I believe they said that, while the middle of the road was 8-16", the 10 percentile range had the area getting only an inch or so and the 90 percentile range had something like 40". [Unfortunately, I don't seem to be able to go back far enough in time on the NWS website to retrieve that discussion.] In our case, the issue was not precipitation type but just how much QPF there would be...including how much lake enhancement might come into play.

And certainly, there was a lot of discussion about precipitation type being an issue in the Washington DC forecast discussion, which I was also reading (as I drove down to visit family there on Monday).

But I guess the forecast discussions don't really qualify as public pronouncements from the forecasters, even though they are now publicly-available to those who are motivated enough to seek them out.


My point is that, even though these discussions take place, it's not what the public sees. For example, TWC issued a deterministic snowfall map on Saturday...on Saturday!!!! 48-60 hours before the event. Philly was 12-18". NYC was 18-24". Boston was 12-18".
Member Since: December 31, 1969 Posts: Comments:
13. WU_356252
1:41 PM GMT on March 19, 2017
Thank you for the information and for pointing out the shortcomings of media forecasting. I think that you are right: they go for the "home run", so they can add that as a credit if it happens as they say. And, they trust that people will not remember mis-predictions because they will be drowned out with all of the excitement that comes with media hype. An analogy i think of is that gossip is much more popular with the general public than is factual information.

If you have the time or inclination, maybe you could touch on a more local weather issue. I live in western New York state and we have had a predominance of cloudiness, with only small amounts of precipitation (until now !), most of the winter. (I am excluding the lake-effect snow region close to Lake Erie.) Many people have remarked about how little sunshine we have had...far from typical. Do you have an explanation for this? Is it due to more than just the jet stream pattern?

Peter Mohr,
Bath, NY
Member Since: December 31, 1969 Posts: Comments:
12. Astrometeor
2:29 AM GMT on March 19, 2017
Quoting 11. WU_216252:

Well, maybe this doesn't count, but I certainly remember that in the forecast discussions, there was quite a bit of talk of the ensembles and probabilities. For example, Sunday night or Monday morning, my local Buffalo office forecast discussion noted the fact that there was an unusually large spread in uncertainty in the snow accumulation. I believe they said that, while the middle of the road was 8-16", the 10 percentile range had the area getting only an inch or so and the 90 percentile range had something like 40". [Unfortunately, I don't seem to be able to go back far enough in time on the NWS website to retrieve that discussion.] In our case, the issue was not precipitation type but just how much QPF there would be...including how much lake enhancement might come into play.

And certainly, there was a lot of discussion about precipitation type being an issue in the Washington DC forecast discussion, which I was also reading (as I drove down to visit family there on Monday).

But I guess the forecast discussions don't really qualify as public pronouncements from the forecasters, even though they are now publicly-available to those who are motivated enough to seek them out.


Forecast discussions are great resources from the NWS, but the vast majority of the public cannot decipher or understand what those discussions mean, nor can they locate them. As such, the public relies on their local media and broadcast meteorologists or people like Capital Weather Gang or The Weather Channel to give them forecasts and snow predictions.
Member Since: December 31, 1969 Posts: Comments:
11. WU_216252
2:09 AM GMT on March 19, 2017
Well, maybe this doesn't count, but I certainly remember that in the forecast discussions, there was quite a bit of talk of the ensembles and probabilities. For example, Sunday night or Monday morning, my local Buffalo office forecast discussion noted the fact that there was an unusually large spread in uncertainty in the snow accumulation. I believe they said that, while the middle of the road was 8-16", the 10 percentile range had the area getting only an inch or so and the 90 percentile range had something like 40". [Unfortunately, I don't seem to be able to go back far enough in time on the NWS website to retrieve that discussion.] In our case, the issue was not precipitation type but just how much QPF there would be...including how much lake enhancement might come into play.

And certainly, there was a lot of discussion about precipitation type being an issue in the Washington DC forecast discussion, which I was also reading (as I drove down to visit family there on Monday).

But I guess the forecast discussions don't really qualify as public pronouncements from the forecasters, even though they are now publicly-available to those who are motivated enough to seek them out.
Member Since: December 31, 1969 Posts: Comments:
Quoting 8. RBM49:

What a great column and spot-on analysis. The term that the author was too polite to use was "stupidity". There are some great scientists out there, but some of the television coverage was truly cringe-worthy.

Well done, Dr. Grenci, and thank you!


Wow! You folks are so nice to me. Thanks so much!
Member Since: December 31, 1969 Posts: Comments:
Quoting 7. PedleyCA:

Thanks for the explanation, always learn something here.


Thanks so much!
Member Since: December 31, 1969 Posts: Comments:
8. RBM49
5:56 PM GMT on March 17, 2017
What a great column and spot-on analysis. The term that the author was too polite to use was "stupidity". There are some great scientists out there, but some of the television coverage was truly cringe-worthy.

Well done, Dr. Grenci, and thank you!
Member Since: December 31, 1969 Posts: Comments:
7. PedleyCA
2:37 PM GMT on March 17, 2017
Thanks for the explanation, always learn something here.
Member Since: December 31, 1969 Posts: Comments:
Quoting 5. georgevandenberghe:

This storm was a frustration for me in that there was a lot going on that we could learn from and I just did not have the time to really dig in because of professional and family responsibilities. That is again (a distinction I often make in complex situations) a separate issue from the forecast community's failure to communicate the true situation.


Understood, George. I always enjoy reading your insights.

Take care. Lee
Member Since: December 31, 1969 Posts: Comments:
5. georgevandenberghe
2:06 PM GMT on March 17, 2017
This storm was a frustration for me in that there was a lot going on that we could learn from and I just did not have the time to really dig in because of professional and family responsibilities. That is again (a distinction I often make in complex situations) a separate issue from the forecast community's failure to communicate the true situation.
Member Since: December 31, 1969 Posts: Comments:
Quoting 2. dawnbyrd:

Thanks, Lee.

I think it all needed to be said :)


Thanks!!!!
Member Since: December 31, 1969 Posts: Comments:
Quoting 1. rpointwx:

Would a complete phasing have brought the southern vort max even further west with the northern vort max displaced to the northwest? That's how it looks to me but I could be mistaken. As always Lee very enjoyable read. Keep ranting so we keep learning. All the best.


The trailing vort max created a sort of Fujiwhara (as I point out in my blog), which helped to pull the main low a tad westward, closer to the coast. Therefore, logic dictates that, if the two shortwaves had phased, the phasing would have cased the low to track farther east than it did...in which case, more snow might have fallen in places closer to the coast.
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2. dawnbyrd
11:24 AM GMT on March 17, 2017
Thanks, Lee.

I think it all needed to be said :)
Member Since: December 31, 1969 Posts: Comments:
1. rpointwx
9:32 PM GMT on March 16, 2017
Would a complete phasing have brought the southern vort max even further west with the northern vort max displaced to the northwest? That's how it looks to me but I could be mistaken. As always Lee very enjoyable read. Keep ranting so we keep learning. All the best.
Member Since: December 31, 1969 Posts: Comments:

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About 24hourprof

Retired senior lecturer in the Department of Meteorology at Penn State, where he was lead faculty for PSU's online certificate in forecasting.