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Friday, January 6, 2023 Light snow event


weatherwiz
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Potent shortwave amplifying and passing near Rhode Island combined with enhanced upper-level divergence, and sufficient moisture will help aid in the blossoming of a precipitation shield across the region. Thermal profiles, particularly away form the coastal Plains support snow, especially under heavier rates. 12z NAM bufkit sounding for ORH shows a perfect crosshair signature (maximum lift within the DGZ) indicating at least a period of moderate-to-heavy snow is possible. 

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1 minute ago, UnitedWx said:

This hasn't really been forecast in the general media except for maybe some snow in the air. It feels like one of those events where there's early afternoon traffic nightmare somewhere nearby if it verifies

Yeah, that does have me a little worried. Interested to see what the euro does.

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BOX AFD relative to this event:

Quite the interesting setup on Friday with a potent fast moving upper level disturbance crossing the region. The difficult part of this forecast revolves around marginal boundary layer temperatures coupled with a relatively narrow/brief swath of precipitation. We will discuss this more below. The 00z model guidance has really caught onto a potent shortwave and its associated cold pool aloft with 500T around -30C! As this strong shortwave/cold pool aloft approaches the forcing for ascent will rapidly increase. Precipitation will overspread the region from west to east Friday morning. While the boundary layer is marginal...model soundings coupled with strong forcing and dynamic cooling should allow Ptype to be mainly wet snow northwest of I-95. In fact...while short-lived an impressive band of 20+ units of omega in the DGZ is depicted. The cold pool aloft also generates steep mid level lapse rates and a -EPV signature, which would support a few hours of moderate to heavy snow convective type snow in a relatively narrow band. The question is where that band sets up, as the global guidance appears have this axis a bit further northwest than the high resolution models. Based on evaluating the data...feel the best chance for a few inches of snow will be northwest of I-95 into central and northeast MA. Even the low risk for localized 4-5" amounts depending on how this unfolds. Southeast of I-95, model soundings indicate boundary layer may be just warm enough to support rain or rain mixed with snow. However, intense omega could briefly overcome the warm boundary layer and flip ptype to wet snow as the heaviest precipitation crosses the region. There could also be a few inches of snow in the higher terrain of the Berks and maybe a coating to slushy inch or two in the Ct River Valley...but that will depend on the boundary layer temps. Later shifts may have to consider a Winter Weather Advisory depending on how the 12z guidance trends. Greatest risk for that right now appears to be northwest of I-95 with a focus on central and northeast MA, but that area may shift.

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3 minutes ago, HoarfrostHubb said:

BOX AFD relative to this event:

Quite the interesting setup on Friday with a potent fast moving upper level disturbance crossing the region. The difficult part of this forecast revolves around marginal boundary layer temperatures coupled with a relatively narrow/brief swath of precipitation. We will discuss this more below. The 00z model guidance has really caught onto a potent shortwave and its associated cold pool aloft with 500T around -30C! As this strong shortwave/cold pool aloft approaches the forcing for ascent will rapidly increase. Precipitation will overspread the region from west to east Friday morning. While the boundary layer is marginal...model soundings coupled with strong forcing and dynamic cooling should allow Ptype to be mainly wet snow northwest of I-95. In fact...while short-lived an impressive band of 20+ units of omega in the DGZ is depicted. The cold pool aloft also generates steep mid level lapse rates and a -EPV signature, which would support a few hours of moderate to heavy snow convective type snow in a relatively narrow band. The question is where that band sets up, as the global guidance appears have this axis a bit further northwest than the high resolution models. Based on evaluating the data...feel the best chance for a few inches of snow will be northwest of I-95 into central and northeast MA. Even the low risk for localized 4-5" amounts depending on how this unfolds. Southeast of I-95, model soundings indicate boundary layer may be just warm enough to support rain or rain mixed with snow. However, intense omega could briefly overcome the warm boundary layer and flip ptype to wet snow as the heaviest precipitation crosses the region. There could also be a few inches of snow in the higher terrain of the Berks and maybe a coating to slushy inch or two in the Ct River Valley...but that will depend on the boundary layer temps. Later shifts may have to consider a Winter Weather Advisory depending on how the 12z guidance trends. Greatest risk for that right now appears to be northwest of I-95 with a focus on central and northeast MA, but that area may shift.

Fluid situation.

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That's a pretty good BOX AFD that covers the specifics.

The potential for a heavier burst is where the biggest bust potential lies. IF we get 4 or 5 hours of heavier snow, then it's going to be a positive bust with some 4-6" lollis....but if it stays mostly light, then it will be a general C-2" type deal with maybe a 3"+ lolli or two in the highest terrain.

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12 minutes ago, Damage In Tolland said:

10:1 ratio . Will be more like 4:1

If its just light rates, ratios will be crappy. But given the soundings on these more aggressive runs they wouldn't be terrible, provided the lift materializes. Some pretty good lift through the DGZ. 

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RAP is interesting. It has two areas. Basically a fronto area extending into SNH from central MA, and then the meso low convergence. Reminds me a bit of those "injection lows" that we have said in the past. An injection of higher theta-e air from low levels up and over the colder air. That looks to blitz here verbatim, but lower levels a little more challenging. It's close though, but I could see those two areas of lift to watch. 

 

In any case, it's not surprising that guidance is a little all over with QPF from these. 

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3 minutes ago, CoastalWx said:

RAP is interesting. It has two areas. Basically a fronto area extending into SNH from central MA, and then the meso low convergence. Reminds me a bit of those "injection lows" that we have said in the past. An injection of higher theta-e air from low levels up and over the colder air. That looks to blitz here verbatim, but lower levels a little more challenging. It's close though, but I could see those two areas of lift to watch. 

 

In any case, it's not surprising that guidance is a little all over with QPF from these. 

Take a ride with Bryce to Blue Hill when he gets off school if you rain 

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I’m hoping my little bit of weenie elevation being out near 495 will do the trick. 
 

And yes, I think for ORH county and other elevated areas, it will prob be close to 10 to 1 ratios because it’s going to be good snow growth I think. A little trickier lower down but if you dynamically cool to 32F, then ratios will be closer to 10 to 1 when that happens or maybe even a little higher….but during the 34F SN- periods it will be 5 to 1 slop. 

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1 minute ago, ORH_wxman said:

I’m hoping my little bit of weenie elevation being out near 495 will do the trick. 
 

And yes, I think for ORH county and other elevated areas, it will prob be close to 10 to 1 ratios because it’s going to be good snow growth I think. A little trickier lower down but if you dynamically cool to 32F, then ratios will be closer to 10 to 1 when that happens or maybe even a little higher….but during the 34F SN- periods it will be 5 to 1 slop. 

cobb techniques actually go nuts with ratios during the window of maximized lift. That's what to really watch out for. Wouldn't be surprised to see some 1-2'/HR type stuff (of course though this will all be moving quick) and that's where you'll see totals get in the 3-4'' range. 

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3 minutes ago, ORH_wxman said:

I’m hoping my little bit of weenie elevation being out near 495 will do the trick. 
 

And yes, I think for ORH county and other elevated areas, it will prob be close to 10 to 1 ratios because it’s going to be good snow growth I think. A little trickier lower down but if you dynamically cool to 32F, then ratios will be closer to 10 to 1 when that happens or maybe even a little higher….but during the 34F SN- periods it will be 5 to 1 slop. 

Let’s grab 3-6” and call it a day . 

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Just now, weatherwiz said:

cobb techniques actually go nuts with ratios during the window of maximized lift. That's what to really watch out for. Wouldn't be surprised to see some 1-2'/HR type stuff (of course though this will all be moving quick) and that's where you'll see totals get in the 3-4'' range. 

My biggest "worry" from a forecasting perspective on bust potential is the IVT/norlun look prolongs the heavier snow over central/eastern areas for 3-4 hours tomorrow evening. That could turn a 2-3" event into a 6er.

The lower end bust potential will be if the BL has trouble cooling (esp lower elevations...don't think this will apply for higher terrain)....but if we're ripping 20-30 microbars in the DGZ, I have a hard time believing even the coastal plain doesn't flip to moderate/heavy snow for a time.

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