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December 16 2020 CTP Snowstorm Disco and Obs


pasnownut
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At 1:00pm I have measured 0.7" total over the past 3 hours...lol.  Temp 25/22.  Steady light snow with fine flakes.  Definitely not accumulating quickly.

Looking at the latest HRRR and going through it hour by hour it looks like my area reaches the 1.5" mark within the next 2 hours by 3:00.  Then the fun begins with 1.0"/hour or more rates through 9:00pm.  The heaviest hour is between 8:00 and 9:00 when 2.4" falls.  At the end of the storm at 4:00am I have between 18 and 19".  The sleet line just barely makes it up to me around 9:00pm and sticks around for an hour or so, then back to snow.  

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14 minutes ago, yard-stick said:

Hello All...just joined the site and looking forward to an exciting winter season!   I'm in the mountains just southwest of Hazleton @ 1800' on the Luzerne/Schuylkill border.  Snowing steady now and roads are already snow covered.       

Welcome. You’re in a golden spot for this storm, methinks. Especially with the elevation. 

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1 minute ago, NeffsvilleWx said:

I hate NWS radar coverage (or lack thereof) for Lancaster/York. Always impossible to tell whether precip is weakening as it approaches, or if it's just a result of radar range/beam height. And comparing to WGAL's site is difficult -- different scales.

Agreed, Horst actually responded to me on twitter about this. Just something we have to deal with. Radar beam/height isn't sufficient for reaching Lancaster well, really struggles with squalls especially. 

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32 minutes ago, CarlislePaWx said:

At 1:00pm I have measured 0.7" total over the past 3 hours...lol.  Temp 25/22.  Steady light snow with fine flakes.  Definitely not accumulating quickly.

Looking at the latest HRRR and going through it hour by hour it looks like my area reaches the 1.5" mark within the next 2 hours by 3:00.  Then the fun begins with 1.0"/hour or more rates through 9:00pm.  The heaviest hour is between 8:00 and 9:00 when 2.4" falls.  At the end of the storm at 4:00am I have between 18 and 19".  The sleet line just barely makes it up to me around 9:00pm and sticks around for an hour or so, then back to snow.  

During the March 1993 event, sleet mixed in during the "height" of the storm with strong NE winds and lightning/thunder at that point.  So as per your analysis of the model HRRR, look for sleet and thunder and gusty winds around 8-10 pm ish...the stronger and deeper this low gets, expect sleet well inland and convective properties including charge separation and high rates of precip.  It will be interesting to be sure!

 

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7 minutes ago, NeffsvilleWx said:

I hate NWS radar coverage (or lack thereof) for Lancaster/York. Always impossible to tell whether precip is weakening as it approaches, or if it's just a result of radar range/beam height. And comparing to WGAL's site is difficult -- different scales.

Use Sterling, Dover, SC and then extrapolate...as an "old fart", I think the radar products are simply amazing!

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8 minutes ago, JTrout said:

Agreed, Horst actually responded to me on twitter about this. Just something we have to deal with. Radar beam/height isn't sufficient for reaching Lancaster well, really struggles with squalls especially. 

Yep. And in the spring/summer, TOR warnings are usually too little, too late. Near impossible to see EF0/EF1 couplets at 7k' AGL

First night in my current house, had a TOR pass within 2 miles. Had no idea until I went to lowes the following morning and saw damage.

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At 2:00pm I have picked up an additional 0.4" in the past hour and have a storm total of 1.1".  During the past 15 minutes the rate has picked up noticeably but with fine flakes I would just call it a "heavy" light.  The increased rate has caused my temp to drop a degree, now down to 24.3 degrees with a dew point of 21.4.

As others have said, we're only about an hour away from the start of the heavy snow with inch per hour rates.

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Mesoscale Discussion 1854 NWS Storm Prediction Center Norman OK 1257 PM CST Wed Dec 16 2020 Areas affected...Northeast West Virginia...northern Virginia...western Maryland...and central to eastern Pennsylvania Concerning...Heavy snow Valid 161857Z - 170000Z SUMMARY...Heavy snowfall rates around 2 inches per hour are expected to increase in coverage through the mid to late afternoon hours across portions of the Mid-Atlantic. Heavy snowfall will likely continue into the overnight hours for portions of eastern/northeastern Pennsylvania. DISCUSSION...Precipitation continues to gradually increase in coverage across much of the Mid-Atlantic region within a broad swath of strong warm air advection between 850-700 mb (per recent RAP soundings and mesoanalysis). Mixed precipitation types continue to be reported within the precipitation transition zone along the Roanoke to Fredericksburg, VA line. While a wintry mix, including pockets of freezing rain, will continue in the near term, this zone should become more limited spatially through the mid/late afternoon hours. Further north, moderate, to at times heavy, snowfall rates have been observed (as evidenced by visibility reductions to one-quarter mile and observed snow rates around 2 inches per hour for some locations in northeast WV). Heading through the afternoon, the low that is currently advancing northward along the Carolina coast will continue to deepen. As this occurs, mid-level winds will strengthen and begin to tighten the 850-700 mb baroclinic zone and augment warm advection across the region. As isentropic and frontogenetical lift increase, snowfall rates will see a corresponding uptick in intensity. Lift within the dentritic growth zone and weak instability closer to the coast will help further augment snowfall rates. Widespread snowfall rates above 1 inch per hour over the region are likely, and the potential for widespread snowfall rates exceeding two inches per hour will increase through 00 UTC as the potential for organized frontogenetical/deformation-driven snow bands increases.

FB3D8EF0-B99B-40FE-BDCC-5038E1670924.jpeg

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2 minutes ago, CarlislePaWx said:

At 2:00pm I have picked up an additional 0.4" in the past hour and have a storm total of 1.1".  During the past 15 minutes the rate has picked up noticeably but with fine flakes I would just call it a "heavy" light.  The increased rate has caused my temp to drop a degree, now down to 24.3 degrees with a dew point of 21.4.

As others have said, we're only about an hour away from the start of the heavy snow with inch per hour rates.

Yep somewhere close to 3pm and thereafter. 

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