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PoTFrost - Request to lower sky mask and add a PoP mask

JM
Joseph Moore, modified 6 Years ago.

PoTFrost - Request to lower sky mask and add a PoP mask

Padawan Posts: 88 Join Date: 11/1/13 Recent Posts

I want to revive an old topic, but I thought I'd start a new thread since it's a new frost season and the code may have changed since the original topic.

 

I would like to request (1) the Sky threshold be changed to a lower number (currently 70% per the last conversation) and (2) add a PoP threshold. The Sky threshold just seems way too high to me, and while I don't have hard evidence, we typically see early/late season frost on cool, clear, and calm nights. If sky cover is over even 40% I can't see us getting widespread frost. So, I think the number should be lowered to at least 50% from the current 70%. Second, having both frost and precipitation in the same period sounds silly. While it's possible in a 6-hour time frame (rain ending then skies clearing out and temps crashing), in most cases where frost will be mentioned, it again needs to be a cool, clear, and calm night. While yes, precip chances are probabilities, and if we have a 15% chance of rain it means there's an 85% chance it won't rain, it still sounds silly to mention frost and precip for the same timeframe.

I've attached some screenshots all valid for the same time period that shows an example of frost being included when we have cloudy skies and precip chances.

DB
David Barjenbruch, modified 6 Years ago.

RE: PoTFrost - Request to lower sky mask and add a PoP mask

Youngling Posts: 21 Join Date: 9/2/14 Recent Posts

Hi Joseph,

 

I think most of us would agree to remove Frost from the forecast when we have a PoP sufficient to warrant any chance of weather.  We may also want to revisit the cloud cover rule as well, as anything broken or more should really limit frost development.  There's also work being done to clean up the original University of Kentucky Frost Flow Chart.  

Thanks for the input!

Dave

JM
Joseph Moore, modified 6 Years ago.

RE: PoTFrost - Request to lower sky mask and add a PoP mask

Padawan Posts: 88 Join Date: 11/1/13 Recent Posts
Thanks for the response, Dave! I wanted to try to get this feedback in before the frost season is over.

In my subjective assessment of the current tool performance, I really think just eliminating the times when it puts in 20%/Patchy ("slight chance of dew" on the Kentucky diagram) would be an improvement. Frost is one of those things we usually only include when we really think it's going to happen and by limiting the inclusion of frost wording to only when the probability of frost is high (especially in the medium/long-range timeframe) I think the output would better match what we would forecast if we didn't have this tool.

-Joe

On Sun, Sep 23, 2018 at 7:59 AM David Barjenbruch <VLab.Notifications@noaa.gov> wrote:

Hi Joseph,

 

I think most of us would agree to remove Frost from the forecast when we have a PoP sufficient to warrant any chance of weather.  We may also want to revisit the cloud cover rule as well, as anything broken or more should really limit frost development.  There's also work being done to clean up the original University of Kentucky Frost Flow Chart.  

Thanks for the input!

Dave

Virtual Lab Message Boards https://vlab.noaa.gov/web/forecastbuilder/forums/-/message_boards/view_message/4916666 VLab.Notifications@noaa.gov http://vlab.noaa.gov


--
Joseph J. Moore
Meteorologist | WFO Duluth Social Media & IDSS Program Leader | Open Source GIS Evangelist
NOAA/National Weather Service Duluth, MN
AJ
Andy Just, modified 6 Years ago.

RE: PoTFrost - Request to lower sky mask and add a PoP mask

Padawan Posts: 99 Join Date: 6/2/15 Recent Posts

Joe, 

  I am in agreement as well with lowering the sky cover threshold.  BKN or OVC is in the flowchart, and following DAS, we should have Sky >= 57% (begin of BKN threshold) to not allow dew to occur.

  The PoP sounds good too and will add that to the tool.  Hopefully in most cases, like your example, the Sky check would occur prior to the PoP check having to come into play.

AJ
Andy Just, modified 6 Years ago.

RE: PoTFrost - Request to lower sky mask and add a PoP mask

Padawan Posts: 99 Join Date: 6/2/15 Recent Posts

Joe,

  I have had second thoughts on the PoP.  I'm concerned that you may have say a 6 hour PoP grid, but the majority of that PoP is for the first hour for example. Then you have clearing skies.  As a result I want to hold off on the PoP inclusion for now. As I mentioned, the sky cover check being lowered should help catch a lot more cases, including those with PoPs.

JM
Joseph Moore, modified 6 Years ago.

RE: PoTFrost - Request to lower sky mask and add a PoP mask

Padawan Posts: 88 Join Date: 11/1/13 Recent Posts
Andy,

Thanks for the consideration on the sky cover adjustment! I do agree that the sky adjustment would probably resolve most of the PoP issues anyway. I realize that we could have precip and frost within the same six hour period (or, as is more often the case in the medium/long range, the POP mention is a low probability scenario), but it still does sound silly to say "slight chance of rain showers / patchy frost" in the forecast. I'm fine with just the sky mask adjustment, though, and will be sure to provide feedback next frost/freeze season on how it works out.

-Joe

On Mon, Sep 24, 2018 at 11:03 AM Andy Just <VLab.Notifications@noaa.gov> wrote:

Joe,

  I have had second thoughts on the PoP.  I'm concerned that you may have say a 6 hour PoP grid, but the majority of that PoP is for the first hour for example. Then you have clearing skies.  As a result I want to hold off on the PoP inclusion for now. As I mentioned, the sky cover check being lowered should help catch a lot more cases, including those with PoPs.

Virtual Lab Message Boards https://vlab.noaa.gov/web/forecastbuilder/forums/-/message_boards/view_message/4921913 VLab.Notifications@noaa.gov http://vlab.noaa.gov


--
Joseph J. Moore
Meteorologist | WFO Duluth Social Media & IDSS Program Leader | Open Source GIS Evangelist
NOAA/National Weather Service Duluth, MN