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Feb 24-25, 2022 Ice/Sleet/Rain/Snow (yeah sure) Storm Thread


WinterWxLuvr
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2 minutes ago, high risk said:

Surface temps around the metro area tomorrow evening, and the precip totals won't be huge, but there is a pretty clear signal for a period of sleet or freezing rain for a lot of us.    Even if sfc temps warm up above freezing, there is a still a cold layer immediately above in pretty much all guidance for at least a few hours.

I’m basically watching this just to see if I can squeeze out 0.1” of sleet in the first batch of precipitation tomorrow.

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5 minutes ago, Chris78 said:

If you believe the Nam northern MD gets a pretty good period of moderate sleet tomorrow late evening into the overnight hours.

Throw down some grass seed…I hear sleet is good for that.  Pushes it down 

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NBM at 18z continues to target the northern tier with some ice accretion beginning Thursday night into early Friday before exiting out between 10-12z. A solid advisory type event possible with the current numbers with some sleet also in the mix. Still intriguing to see the totals being spit out by the blend. Even if 75%, it would certainly be a headache for any commute on Friday AM. I would plan ahead if I lived north of I-70, especially away from the Baltimore Metro. 

439227955_NBMFRAM022318z.thumb.png.3f56bdbc3de2a4b35647f7e630d1e7b3.png

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2 minutes ago, MillvilleWx said:

NBM at 18z continues to target the northern tier with some ice accretion beginning Thursday night into early Friday before exiting out between 10-12z. A solid advisory type event possible with the current numbers with some sleet also in the mix. Still intriguing to see the totals being spit out by the blend. Even if 75%, it would certainly be a headache for any commute on Friday AM. I would plan ahead if I lived north of I-70, especially away from the Baltimore Metro. 

439227955_NBMFRAM022318z.thumb.png.3f56bdbc3de2a4b35647f7e630d1e7b3.png

What models does it blend? Cause there none that are that low that I’ve seen for PA boarder areas. 

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Just now, TSSN+ said:

What models does it blend? Cause there none that are that low that I’ve seen for PA boarder areas. 

It's actually a blend of of over 30 pieces of guidance both raw and bias corrected. There's a huge mix of guidance, some of which public doesn't have access to, and some that you do. Off the top of my head, I can name 15 or so, but there's a ton of others. Sorry I can't give the full details on the matter. 

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5 minutes ago, MillvilleWx said:

It's actually a blend of of over 30 pieces of guidance both raw and bias corrected. There's a huge mix of guidance, some of which public doesn't have access to, and some that you do. Off the top of my head, I can name 15 or so, but there's a ton of others. Sorry I can't give the full details on the matter. 

Ah ok thanks for the info. Sounds like some top secret stuff haha 

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8 minutes ago, Weather Will said:

Current temp in Frederick is 72. 18Z NAM forecast was 59….. 12Z GFS 52, EURO 61.  So colder air is behind schedule so far.

Might be more of a case where we just overperformed high temperatures. Id have to look myself but the story might be told better if we compare temps to where the front has already passed..

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2 minutes ago, Baltimorewx said:

Might be more of a case where we just overperformed high temperatures. Id have to look myself but the story might be told better if we compare temps to where the front has already passed..

Agreed, because temps behind the front (up in C&W PA) look cooler post-frontal passage than the NAM had for 21z.

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40 minutes ago, Weather Will said:

Current temp in Frederick is 72. 18Z NAM forecast was 59….. 12Z GFS 52, EURO 61.  So colder air is behind schedule so far.

I'm sitting at 54 right now in Smithsburg.  Definitely a chill in the air compared to earlier this afternoon. 

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1 hour ago, TSSN+ said:

What models does it blend? Cause there none that are that low that I’ve seen for PA boarder areas. 

 

1 hour ago, MillvilleWx said:

It's actually a blend of of over 30 pieces of guidance both raw and bias corrected. There's a huge mix of guidance, some of which public doesn't have access to, and some that you do. Off the top of my head, I can name 15 or so, but there's a ton of others. Sorry I can't give the full details on the matter. 

Having worked on aspects of the Blend, this is correct.  There are indeed some 30-plus pieces of guidance involved which include various global models, their corresponding ensembles, short-range meso models, etc.  Actually a lot more when you consider all the ensemble members, though different weather elements use different things.  It's quite complicated, actually.  The Blend takes in the newest updated cycles as they become available.  Note that the Blend cycle time does not actually include models from that cycle (as they wouldn't be available yet), e.g., the 00Z Blend would include models prior to 00Z.  So for example, the 00Z blend might include, say, the 12Z Euro, the 18Z GFS, 12Z Canadian, those respective ensemble members, the 22Z HRRR and RAP, the 18Z NAM, etc.  You get the idea.

The model fields are bias corrected in many cases and MAE (mean absolute error) weighted...though several weather elements use set, specific weights and some are not always bias corrected for things that cannot be.  The URMA (unrestricted real-time mesoscale analysis) is used as the background field for bias correcting.  It's quite the mental gymnastics exercise to figure out what cycle of what model comes in when, and matching the correct model forecast hour projections to the Blend cycle time and its forecast hours!

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1 minute ago, Always in Zugzwang said:

 

Having worked on aspects of the Blend, this is correct.  There are indeed some 30-plus pieces of guidance involved which include various global models, their corresponding ensembles, short-range meso models, etc.  Actually a lot more when you consider all the ensemble members, though different weather elements use different things.  It's quite complicated, actually.  The Blend takes in the newest updated cycles as they become available.  Note that the Blend cycle time does not actually include models from that cycle (as they wouldn't be available yet), e.g., the 00Z Blend would include models prior to 00Z.  So for example, the 00Z blend might include, say, the 12Z Euro, the 18Z GFS, 12Z Canadian, those respective ensemble members, the 22Z HRRR and RAP, the 18Z NAM, etc.  You get the idea.

The model fields are bias corrected in many cases and MAE (mean absolute error) weighted...though several weather elements use set, specific weights and some are not always bias corrected for things that cannot be.  The URMA (unrestricted real-time mesoscale analysis) is used as the background field for bias correcting.  It's quite the mental gymnastics exercise to figure out what cycle of what model comes in when, and matching the correct model forecast hour projections to the Blend cycle time and its forecast hours!

What you said! Haha

NBM is very intuitive and has so many parts, but it is a great tool to use on certain setups, and ice is actually not bad for a general storm sense since it drowns out the noise from the extreme members that could skew means considerably. I will saw it is not the best when it comes to extreme temp variations compared to climo and larger impact events that have a mesoscale foot print like a major snow/ice event or severe out break. They can give an idea of what could occur in a smoothed sense, but knowing your biases can help formulate a better forecast. 

That is awesome that you have worked with the Blend. I would love to hear more of the nitty gritty with NBM as I've used it for forecast purposes now for almost 4 years. 

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