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dryslot

New Year Storm Thread 12/29-01/01

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2 minutes ago, ORH_wxman said:

ORH is an interesting forecast. They have a pretty high max temp in the warm layer...which usually tells me to go ZR...but the cold layer below it is deep and gets to around -6. That's clear sleet there. 

So which method do we give more weight to? Typically when the warm layer gets higher than 3C, you're gonna go ZR...but when the cold layer goes to -6C or colder, it's sleet. But in this case a lot of guidance has both occurring around the ORH area. 

I was thinking they may flirt with IP and ZR until the aftn when it gets torchy aloft. It’s cold below 850 and that even cools a tad late morning so would think that would bolster IP chances. But the whole trend has been to warm things up aloft a bit. Obviously that increases ZR chances. 

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Both nams ripping the IP pretty far north, eventually up to the whites. 

I think even the mesos are still too high with sfc Ts over the interior, but the nam can be good at sniffing out those pesky warm layers. 

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1 minute ago, OSUmetstud said:

Isn't it really difficult to refreeze pure liquid drops with minus 6? If you're really warm aloft I'd lean towards a zr solution regardless of how cold it is below. 

Yeah...once you lose any remnant of an ice nuclei it gets tough. It’s hard enough to get deposition at -6C even with salt nuclei.

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NWS is missing a critical conceptual component to this thing when reading their AFD's from overnight.  This excerpt exposes that,

"..

air located around 3-4kft at about -6C! Shallow cold air likely gets
replenished later Mon into Mon night as frontal wave emerges off the
NJ coast.  This will increase low level northerly ageostrophic flow
across southern New England. The net effect will be for the high

..."

What they are suggesting of the storm moving off the NJ coast enhancing the "draw" of colder air down from the N is true at a baser fundamental level, but that is not ageostrophic!  No, that process is a standard PGF (pressure gradient force) mechanical response.   The ageostrophic forcing comes from a mass discontinuity that is set up because of a planetary/atmospheric topographical interface circumstance that is unique to this geographical region.  Namely...the ~ N-S cordillera with the sloped to sea-level coastal plain elevation to the east ...and when cold air "folds" around the northern end of this topographic circumstance up over eastern Ontario and N. Maine, particularly when it's back-built by confluence/DVM supplying more mass, that dense weightier colder air starts filling in the described region, and will do so disproportionately at positive anomaly, relative to the existing pressure contour suggestion that is on the synoptic charts during the invasion process. It's the Earth-atmosphere interface doing that, not the PGF.  

That is the ageostrophic forcer... The low coming off the NJ coast enhances the motion of air but that's not causal...The ageostrophy is coming because that wedge of air is doing the work... wedging under whatever existing pressure gradient- balanced geostrophic wind there is in place.

That is critically missing in their content ... If this were included, they might have modulated for a colder profile N of CT/RI borders in that region there... They speak of the initial condition of -6C at 4-6K feet as an impressive core of cold, offering to elevation sleet and ZR bomb in the Berks with more IP the Worcester Hills and ...and that's really clad work.  But then they later only mention cold as reenforced later Monday afternoon ...almost as an afterthought in the cadence and style of delivery in that AFD and that's under-evaluating what is likely to be a pretty impressive flag touting invasion of steeply colder air with that, and it will probably surge farther south than even the finer-meshed guidance are assessing. 

That said, these are not intended to be dramatic terms or turns of phrase, either. Just a bit of a clarification.  Their current headlines and Warn/Adv layout is ..prrooobably sufficient either way, because the general public doesn't delve this deeply ..much less have a clue what the difference is between ageo and PGF balanced mass fields even mean. May as well be talking about the far side of the moon.  Even in a deeper more impressive cold surge mid or 2/3rds of the way through ( which to be fair, I was thinking that would happen earlier in time so I may be error..but given to their lack of aggresivity with that factor, they could be late, too), much of the QPF for southern/SW zones will be light, thus...this won't matter.  Although, things my be error-dicey up there in NE Mass/interior SE NH where they've gone Adv ..but again, phew...the public doesn't really pay that close attention.

Just a quarterbacking from the office chair moment

( Caveat:  ...this could all pan out true by behavior, and still we end up annoyingly too warm by a degree ...)

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15 minutes ago, HoarfrostHubb said:

I don’t think the two or three on here who want damaging ice are going to get any.  

Unfortunately it looks like my favorite places to ski in the Berkshires are going to get hit:(

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5 minutes ago, OSUmetstud said:

Isn't it really difficult to refreeze pure liquid drops with minus 6? If you're really warm aloft I'd lean towards a zr solution regardless of how cold it is below. 

Yeah it's hard to refreeze pure water but if the cold layer is deep then it's possible...and -6 can produce ice nuclei...esp around here on a NE flow.

Not sure I've ever seen like a +5 warm layer right on top of a -6 cold layer though. One of them is probably overdone. Wouldn't surprise me it ends up more like +3 aloft if it's going -6 at 875-900mb or if it hits +5 aloft, it's verified more like -3 or -4 below it. 

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Just now, OSUmetstud said:

Isn't it really difficult to refreeze pure liquid drops with minus 6? If you're really warm aloft I'd lean towards a zr solution regardless of how cold it is below. 

Yea that’s my thinking as well; at least in terms of the physical processes—latent heat of fusion. I think dewpoints just above the surface would matter a lot here. Unless they are well below freezing I’d lean Freezing Rain. I’m also seeing guidance trend towards greater warming aloft, while the surface cold remains more or less constant. Trend is towards more freezing rain, less sleet...

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I am surprised how pesky the NAM is with not getting much cold past ORH or even to ORH. I still take the under a bit as we’ve all said.....but I do wonder if that stubbornness is trying to tell us something. Regardless, it’s a lock for ORH to be under 32 by a few degrees at least. 

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It's an interesting mico-physical question/problem...  Almost quantum mechanical/thermal.  

Stepping back, I learned when very young that the 'liquid' water in rain below 32 F (0 C) that is freezing on contact, is in a super-cooled state,  ...similar to why water in a fast flowing stream still flows despite the water temperature being sufficient to phase change to solid.  The kinetic motion of the stream water ...or in this case, the falling hydrometeors  (always loved the Met term!), is not being allowed to change phases from liquid to solid because in order to change phases, there is a "puff" of smoke ..ha, a small quanta of thermal energy has to burst from the molecules as they assume the lattice of the crystalline form.  The kinetic energy of the moving super -cooled stream water, or the falling super -cooled rain drop, is adding energy at the same rate, thus...keeping the liquid liquid. 

The reason why the liquid in these circumstance does eventually freezes is because the temperature falls below the kinetic energy balance, and it goes ahead and changes phase - it's just a matter of the freezing point being "reset" a bit down the scale as a thermal subtraction/addition problem. 

What then makes this even that much more complicated is that in the case of falling rain, we have to deal with the veritical height of the falling column - and as others have indicated, the melt level inputs energy into the hydrometeoroids at greater quantities, in situations when the sounding is exceptionally sloped positively.  Like...say, this time!  Anyway, if the height of the < 32 F (0 C) that exists under the melting layer, is very tall, even a very warm layer won't ( likely ) add so much energy to fail accretion when the droplets of water make contact and shed their kinetic energy.  However, that concomitantly means that if the warm layer is very warm, and the cold is shallow, there's going to be less proficiency in accretion - but, ...that's concept. A calculation may demonstrate that the add/subtract therms aspect isn't appreciably large.   So, with a +5 C 800 mb warm tongue flicking over top a -6 C 925 mb ageostrophic lower DP barrier jet, with that melt layer precipitating liquid into that region beneath, that may be tall enough and cold enough to send a goodly amount of mass through phase transition and scalp fest the surface.  It's just deep and tall and a long time to feed lower DP air at an ~ constant, which helps cool the rain drops faster.

Which brings us to another aspect... that final puff of released thermal energy when the molecules formulate into crystals, that adds heat to the column.  An initially cold ZR will eventually torpedo it's own ability to ZR because of this process.  I've actually witnessed dead calm ZR at 19 F end up 33.5 drizzle inside of 6 hours because there was 0 input of lower DP air to keep that thermal imbalance in play.

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16 minutes ago, CoastalWx said:

I am surprised how pesky the NAM is with not getting much cold past ORH or even to ORH. I still take the under a bit as we’ve all said.....but I do wonder if that stubbornness is trying to tell us something. Regardless, it’s a lock for ORH to be under 32 by a few degrees at least. 

I’m feeling the same way about BDL to HFD in terms of taking the under, but I’m still not all the way there. Much more confidence in a sig event in the NW hills this morning, but the central valley over to eastern CT is still up in the air for me.

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1 hour ago, PowderBeard said:

I have zero knowledge on ice storms but found this very easy to comprehend. Interesting conclusions on the lower dew points, and falling at night increasing accretion. 

 

https://www.weather.gov/media/box/science/December_2008_Ice_Storm.pdf

Thanks, it is a nice writeup.  As an eyewitness I disagree with their comments about the east slope and the berks.  It was catastrophic there, for sure the equal to pics from N ORH county, albeit with the worst accretion slightly higher up in elevation. (Esp over ~1200')   Single most impactful weather event I've ever observed for sure in parts of Ashfield/Goshen/etc..  Crushed.

Even at Umass there was a significant electrical disturbance and dirty power.  The MA1 radar held up valiantly for a while and we observed strong echoes out on the east slope, pouring, but the UPS batteries only last an hour or two.

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8 minutes ago, radarman said:

Thanks, it is a nice writeup.  As an eyewitness I disagree with their comments about the east slope and the berks.  It was catastrophic there, for sure the equal to pics from N ORH county, albeit with the worst accretion slightly higher up in elevation. (Esp over ~1200')   Single most impactful weather event I've ever observed for sure in parts of Ashfield/Goshen/etc..  Crushed.

Even at Umass there was a significant electrical disturbance and dirty power.  The MA1 radar held up valiantly for a while and we observed strong echoes out on the east slope, pouring, but the UPS batteries only last an hour or two.

Yeah I remember seeing big damage from Berkshires. But as you said, much higher in elevation. I think even MPM at 1000 feet didn't get much ice but at 300 feet in Leominster off to the east side of the ORH hills had catastrophic damage. You had to go much higher off to the west to see the equivalent damage. 

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1 hour ago, mahk_webstah said:

Even if a lot of sleet at least we start the true pack building

It's not building if it's melted within the week following.  :)

1 hour ago, ORH_wxman said:

ORH is an interesting forecast. They have a pretty high max temp in the warm layer...which usually tells me to go ZR...but the cold layer below it is deep and gets to around -6. That's clear sleet there. 

So which method do we give more weight to? Typically when the warm layer gets higher than 3C, you're gonna go ZR...but when the cold layer goes to -6C or colder, it's sleet. But in this case a lot of guidance has both occurring around the ORH area. 

Split the diffference.  A lot of meh.

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1 minute ago, ORH_wxman said:

Yeah I remember seeing big damage from Berkshires. But as you said, much higher in elevation. I think even MPM at 1000 feet didn't get much ice but at 300 feet in Leominster off to the east side of the ORH hills had catastrophic damage. You had to go much higher off to the west to see the equivalent damage. 

The difference between my place at 1000' and a mile away at 1200' was staggering.

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3 minutes ago, moneypitmike said:

 

Split the diffference.  A lot of meh.

I could see ORH getting IP/ZR in enough of a split to minimize the impact. Like they end up with quarter inch or less of accretion with an inch of sleet...and maybe even some cold rain for a while early on. 

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4 minutes ago, ORH_wxman said:

I could see ORH getting IP/ZR in enough of a split to minimize the impact. Like they end up with quarter inch or less of accretion with an inch of sleet...and maybe even some cold rain for a while early on. 

The wind speed component is a factor.  As Ryan as pointed out wind increases accretion rates. Complex formulas involved but Utilities especially need all parameters to prepare. 

Once the occurrence of freezing rain was determined by one of the above methods, estimates of ice accretion thickness on surface objects were calculated at each model grid point using the simple ice accretion model (Jones 1998). The uniform radial ice thickness on a cylinder, accumulated over the duration of a storm, is calculated by

Fig thumbnail _i10

where Req is the uniform radial ice thickness (mm), N is the number of hours of freezing precipitation, ρi is the density of ice (=0.9 g cm−3), ρ0 is the density of water (=1.0 g cm−3), P is the precipitation rate (mm h−1), V is the wind speed (m s−1), and W is the liquid water content (Wj = 0.067P0.846j

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4 minutes ago, ORH_wxman said:

I could see ORH getting IP/ZR in enough of a split to minimize the impact. Like they end up with quarter inch or less of accretion with an inch of sleet...and maybe even some cold rain for a while early on. 

The RGEM surface temps would argue for a fair amount of plain rain unless there's a colder layer above it.  This is going to go down as 40-page event discussion that will be pedestrian outside of 4 posters in SNE.  :lol:

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Just now, Ginx snewx said:

The wind speed component is a factor.  As Ryan as pointed out wind increases accretion rates. Complex formulas involved but Utilities especially need all parameters to prepare. 

Once the occurrence of freezing rain was determined by one of the above methods, estimates of ice accretion thickness on surface objects were calculated at each model grid point using the simple ice accretion model (Jones 1998). The uniform radial ice thickness on a cylinder, accumulated over the duration of a storm, is calculated by

Fig thumbnail _i10

where Req is the uniform radial ice thickness (mm), N is the number of hours of freezing precipitation, ρi is the density of ice (=0.9 g cm−3), ρ0 is the density of water (=1.0 g cm−3), P is the precipitation rate (mm h−1), V is the wind speed (m s−1), and W is the liquid water content (Wj = 0.067P0.846j

Yea, just give me an ice-clown map...thanks lol

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6 minutes ago, Ginx snewx said:

The wind speed component is a factor.  As Ryan as pointed out wind increases accretion rates. Complex formulas involved but Utilities especially need all parameters to prepare. 

Once the occurrence of freezing rain was determined by one of the above methods, estimates of ice accretion thickness on surface objects were calculated at each model grid point using the simple ice accretion model (Jones 1998). The uniform radial ice thickness on a cylinder, accumulated over the duration of a storm, is calculated by

Fig thumbnail _i10

where Req is the uniform radial ice thickness (mm), N is the number of hours of freezing precipitation, ρi is the density of ice (=0.9 g cm−3), ρ0 is the density of water (=1.0 g cm−3), P is the precipitation rate (mm h−1), V is the wind speed (m s−1), and W is the liquid water content (Wj = 0.067P0.846j

image.png.eed82861f9574e3d35630aa3e305da4b.png  * 0 = MeH

image.png

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The high res nammy sends a cold front through the Berks around 5pm tomorrow.  By then it's probably pinging more than accreting, but the wind shift could bring down a few.

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Just now, PaulyFromPlattsburgh said:

I am highly concerned that many local weather stations are undermining icing threat. mesoscales really starting to point to a confined but solid area of significant icing

Given how confined it is, a simple mention of that fact that could a case in a small area should be enough.  This will not be a wide-spread area of significant (damaging/disrupting) icing.

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