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Pittsburgh PA ❄️ Winter 2017-2018

north pgh

By north pgh,
in Upstate New York/Pennsylvania

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north pgh

north pgh

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Canadian is east too. Big jump. Still needs to come further to put us in the sweet spot. Not to complain but most of our snow falls overnight. I like to watch it snow. Going to bed and waking up to 6 inches of snow to shovel and it may be over. Tomorrow's models will be interesting. It's been a while since things have trended are way. One more day! 

Also Monday night Tuesday may be a little surprise clipper. 

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MAG5035

MAG5035

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Posted
2 hours ago, Rd9108 said:

idk if that's a dry slot or what but that's the 0z run. 

The minimum of accums is likely attributed to the Kuchera algorithm used for that snowfall map. A look at thermals during the heaviest frame of precip in the Pit region (Hr 54) shows a kink in the 850 zero line where it cuts through the middle of PA til near UNV and then cuts westward roughly to Indiana and then turns south towards Morgantown. Pretty much lines up with where the Euro has the 850mb low at the time (right over central PA) Should also note the column is quite marginal all the way up from 850 to 700, with a pretty good chunk of west central PA actually above 0 in between the 700-800mb level while 850 is below zero while cold air undercuts below 850mb. The cross section I made off the Euro illustrates this pretty nicely. I provided a VERY rough guesstimate of locations the cross section refers to as you look left to right. I also looked at the 0z NAM's cross section and it was much colder in those mid levels over western PA and it really had a significant undercutting wedge of lower level cold.. likely attributing to the bigger snow totals it threw out. 

5a5718e69e487_ScreenShot2018-01-11at2_57_02AM.png.124f3a8d5c4ca09390a686949804b884.png

Far E OHIO------WHEELING-------KPIT-------------- LBE--------------------------------JST----------------------------AOO             

At any rate, the above description is talking generally about the area where theres a "dry slot". The Kuchera method is simply an equation that plugs in the warmest temp in the column (below 500mb) and puts out a ratio and associated snow number. So it's going to put out lousy numbers where this lingering warm air aloft is near 0ºC. 

Quote

Find the maximum temperature in the lowest 500 hPa in degrees K (MaxT). 2) If MaxT is greater than 271.16K, then the liquid equivalent ratio (RAT) is 12.0 + 2.0*(271.16-MaxT). 3) If MaxT is less than 271.16K, then the liquid equivalent ratio (RAT) is 12.0 + (271.16-MaxT)

I'm not going to get too math-y with this but I will say you have to convert to K from Celsius for this (0ºC = 273.15K). So say you use a borderline temp of 0ºC or 273.16K and apply to the above equation you get a ratio of 8:1. If you look at the far left of the cross section (Far E OH/Far western PA) and apply the colder max temp of about -5ºC near the 750mb layer your going to come up with a ratio of 15:1. Kuchera method doesn't consider snow growth and lifting processes that truly dictate the real world snow ratios. Honestly I personally think it is a good method to use in colder situations where the thermal column stays pretty stable the whole event but I'd be careful using it for this type of event..especially in this region where we have a complicated but progressively cooling thermal column. It's one of those type events where the ratio can start off bad but get better as cold air establishes. I'd probably just use a straight 10:1 map to get a rough idea on accums. It's a complicated scenario anyways so I wouldn't get too hung up on exact numbers yet but just the fact the models have trended southeast enough to give the region a good shot at decent changeover snowfall with the deform precip band being in a good spot. There's still going to be the issue of mixed precip too before any snow.. potentially for a pretty sizable chunk of the rest of western and eventually central PA. 

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RitualOfTheTrout

RitualOfTheTrout

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3 hours ago, MAG5035 said:

The minimum of accums is likely attributed to the Kuchera algorithm used for that snowfall map. A look at thermals during the heaviest frame of precip in the Pit region (Hr 54) shows a kink in the 850 zero line where it cuts through the middle of PA til near UNV and then cuts westward roughly to Indiana and then turns south towards Morgantown. Pretty much lines up with where the Euro has the 850mb low at the time (right over central PA) Should also note the column is quite marginal all the way up from 850 to 700, with a pretty good chunk of west central PA actually above 0 in between the 700-800mb level while 850 is below zero while cold air undercuts below 850mb. The cross section I made off the Euro illustrates this pretty nicely. I provided a VERY rough guesstimate of locations the cross section refers to as you look left to right. I also looked at the 0z NAM's cross section and it was much colder in those mid levels over western PA and it really had a significant undercutting wedge of lower level cold.. likely attributing to the bigger snow totals it threw out. 

5a5718e69e487_ScreenShot2018-01-11at2_57_02AM.png.124f3a8d5c4ca09390a686949804b884.png

Far E OHIO------WHEELING-------KPIT-------------- LBE--------------------------------JST----------------------------AOO             

At any rate, the above description is talking generally about the area where theres a "dry slot". The Kuchera method is simply an equation that plugs in the warmest temp in the column (below 500mb) and puts out a ratio and associated snow number. So it's going to put out lousy numbers where this lingering warm air aloft is near 0ºC. 

I'm not going to get too math-y with this but I will say you have to convert to K from Celsius for this (0ºC = 273.15K). So say you use a borderline temp of 0ºC or 273.16K and apply to the above equation you get a ratio of 8:1. If you look at the far left of the cross section (Far E OH/Far western PA) and apply the colder max temp of about -5ºC near the 750mb layer your going to come up with a ratio of 15:1. Kuchera method doesn't consider snow growth and lifting processes that truly dictate the real world snow ratios. Honestly I personally think it is a good method to use in colder situations where the thermal column stays pretty stable the whole event but I'd be careful using it for this type of event..especially in this region where we have a complicated but progressively cooling thermal column. It's one of those type events where the ratio can start off bad but get better as cold air establishes. I'd probably just use a straight 10:1 map to get a rough idea on accums. It's a complicated scenario anyways so I wouldn't get too hung up on exact numbers yet but just the fact the models have trended southeast enough to give the region a good shot at decent changeover snowfall with the deform precip band being in a good spot. There's still going to be the issue of mixed precip too before any snow.. potentially for a pretty sizable chunk of the rest of western and eventually central PA. 

Thanks for the explanation! I think snow maps in general are ok when you have a colder stable column, but like you said any algorithm is going to have a tough time putting out accurate numbers in this situation, so I'd say use caution when getting excited or disappointed over anything they show.

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blackngoldrules

blackngoldrules

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Hopefully we can see just a little more SE adjustment to get Westmoreland and the Southern counties in on the Winter Storm Watch. It would be nice to have the whole region in on a storm for once rather than drastic cutoffs 30 miles away, plus as it stands on I'm on the eastern edge.26239609_1496070790490999_1803995444190600865_n.png.9d4d6478f10b074e60c86d08afd7838c.png
It's odd seeing us under a WSW and not the mountains. It's usually the opposite. I honestly can't remember the last time we were under an actual warning. We've had a few watches over the years that ended up being downgraded to advisories or nothing at all. Hopefully, we get one to finally work out for us.

Sent from my SM-G920P using Tapatalk

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KPITSnow

KPITSnow

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Posted
2 minutes ago, Burghblizz said:

You guys are forgetting a fair number of 5-10”  type storms in the 2011 to 2014 timeframe. I think we all just think of getting 50” in February 2010 and revert back there.  It’s just been brutal really the last 3 years and the near misses don’t help. Now a widespread 10+ has been the unicorn since then.

I don’t remember any 5-10 type storms in that timeframe. I’m not sure we’ve seen anything over 6-7 inches since 2010, and those were over performing clippers.

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MikeB_01

MikeB_01

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1 hour ago, SteelCity08 said:

Safe to say todays runs are the most important we've had in about 8 years. Was the storm fully sampled on the 00z runs?

Still waiting for some of the energy to come in off of the pacific. The energy for the storm itself has been sampled. The energy that comes in behind it and helps position it, comes on shore today.

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Burghblizz

Burghblizz

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19 minutes ago, KPITSnow said:

I don’t remember any 5-10 type storms in that timeframe. I’m not sure we’ve seen anything over 6-7 inches since 2010, and those were over performing clippers.

All I’m saying is you gotta remember the regular season wins, not just the super bowl. :-) Off the top of my head, there were nice storms in feb ‘11, dec ‘11, and March ‘12

i think this one has a chance to be like the feb ‘11 storm. This one had a lot of people stranded on the parkway north because the changeover happened quick and heavy

http://pittsburgh.cbslocal.com/2011/02/22/latest-snow-sets-record-in-pittsburgh/

 

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cwc

cwc

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5 hours ago, MAG5035 said:

The minimum of accums is likely attributed to the Kuchera algorithm used for that snowfall map. 

 

MAG, thanks for the science lesson!  I was just wishing that this sub had a met that could opine on all this data.  Clearly, my psych major did not qualify me for figuring out the Kuchera algorithm....

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SteelCity08

SteelCity08

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49 minutes ago, Burghblizz said:

You guys are forgetting a fair number of 5-10”  type storms in the 2011 to 2014 timeframe. I think we all just think of getting 50” in February 2010 and revert back there.  It’s just been brutal really the last 3 years and the near misses don’t help. Now a widespread 10+ has been the unicorn since then.

I got a little caught up in seeing the 10+ on the 0z nam and euro. I remember feb 11' pretty well. Got 8" in about 5 or 6 hours, probably our last real storm. I don't think I fared as well in the others. Maybe 5 or 6".  

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