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Central PA - March 2018


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What a roller coaster ride the last several days, this has easily been the worst storm of the winter to get a handle on. Model's are finally starting to converge on a more consolidated solution for this potentially long duration storm and have shifted heavier snows back north into the region. 

One thing that's different about this storm is the track of the parent low approaching from the south central US. With the blocking and suppressed storm track, this will keep the low south of PA vs trying to transfer a parent Great Lakes low to a coastal storm. The transfer spot is in a very good spot for our region with regards to maximizing the potential for a miller B. Models are showing a very broad and significantly anomalous (-3 to -4 and greater) easterly fetch developing which is always a hallmark of a major snowstorm in the Northeast/Mid Atlantic. It seems clear that models have made a noted shift on getting northern extent up to at least I-80 or so after spending several runs struggling to even get precip to the turnpike. However, key will be organization of precip shield..especially during daylight hours. Some models (esp GFS) still show a weakness with the precip shield and separate maxes... initially thrusting into OH and western PA and then southeastern PA with the coastal leaving a weakness in accums in the middle.  A weakness this time of the year equates to rates that don't get fully realized on the ground. 

I had been pretty pessimistic on this storm the past couple days but with things looking more organized, I do think the potential of excessive totals is there. At the same time though, bust potential is absolutely there as well. I think we'll see both, and it's going to ultimately come down to where the best and most consistent precip rates and banding set up. Northern extent is going to be tight. It may or may not surpass I-80 but there looks to be a pretty good gradient. I think @Voyager's best bet is running I-80 as much as he can in PA. CTP will likely need to be throwing up headlines very soon and I would bet watches on the bottom two tiers of counties to open things up.  

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Watches up

 

Here is mine

Tuesday Night
A chance of snow. Cloudy, with a low around 29. Northeast wind around 7 mph. Chance of precipitation is 50%. New snow accumulation of less than a half inch possible.
Wednesday
A chance of snow before 11am, then a chance of rain and snow. Cloudy, with a high near 40. North wind around 8 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.
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URGENT - WINTER WEATHER MESSAGE
National Weather Service State College PA
332 PM EDT Mon Mar 19 2018

...Early spring storm to bring potential for long duration
wet snow and mixed precipitation to portions of south central
Pennsylvania Tuesday through Wednesday...

PAZ033>036-064>066-201015-
/O.NEW.KCTP.WS.A.0006.180320T1000Z-180322T0000Z/
Somerset-Bedford-Fulton-Franklin-Adams-York-Lancaster-
Including the cities of Somerset, Bedford, McConnellsburg,
Chambersburg, Gettysburg, York, and Lancaster
332 PM EDT Mon Mar 19 2018

...WINTER STORM WATCH IN EFFECT FROM TUESDAY MORNING THROUGH
WEDNESDAY EVENING...

* WHAT....Total snow accumulations of 6 inches or more are
  possible, especially in the higher elevations. Snow will mix
  with rain, freezing rain and sleet at times with ice
  accumulations of a light glaze possible.

* WHERE...Portions of south central Pennsylvania.
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And the wording for the other area of the LSV:

...WINTER STORM WATCH IN EFFECT FROM TUESDAY EVENING THROUGH
WEDNESDAY EVENING...

* WHAT...Heavy snow possible. Total snow accumulations of 2 to 4
  inches, with localized amounts up to 6 inches possible.

* WHERE...Perry, Dauphin, Schuylkill, Lebanon and Cumberland
  Counties.
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1 minute ago, canderson said:

And the wording for the other area of the LSV:


...WINTER STORM WATCH IN EFFECT FROM TUESDAY EVENING THROUGH
WEDNESDAY EVENING...

* WHAT...Heavy snow possible. Total snow accumulations of 2 to 4
  inches, with localized amounts up to 6 inches possible.

* WHERE...Perry, Dauphin, Schuylkill, Lebanon and Cumberland
  Counties.

I think this is a very good call for CTP get the public on notice with a watch and be conservative with amounts for now. Knowing how complicated this storm is. 

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14 minutes ago, MAG5035 said:

What a roller coaster ride the last several days, this has easily been the worst storm of the winter to get a handle on. Model's are finally starting to converge on a more consolidated solution for this potentially long duration storm and have shifted heavier snows back north into the region. 

One thing that's different about this storm is the track of the parent low approaching from the south central US. With the blocking and suppressed storm track, this will keep the low south of PA vs trying to transfer a parent Great Lakes low to a coastal storm. The transfer spot is in a very good spot for our region with regards to maximizing the potential for a miller B. Models are showing a very broad and significantly anomalous (-3 to -4 and greater) easterly fetch developing which is always a hallmark of a major snowstorm in the Northeast/Mid Atlantic. It seems clear that models have made a noted shift on getting northern extent up to at least I-80 or so after spending several runs struggling to even get precip to the turnpike. However, key will be organization of precip shield..especially during daylight hours. Some models (esp GFS) still show a weakness with the precip shield and separate maxes... initially thrusting into OH and western PA and then southeastern PA with the coastal leaving a weakness in accums in the middle.  A weakness this time of the year equates to rates that don't get fully realized on the ground. 

I had been pretty pessimistic on this storm the past couple days but with things looking more organized, I do think the potential of excessive totals is there. At the same time though, bust potential is absolutely there as well. I think we'll see both, and it's going to ultimately come down to where the best and most consistent precip rates and banding set up. Northern extent is going to be tight. It may or may not surpass I-80 but there looks to be a pretty good gradient. I think @Voyager's best bet is running I-80 as much as he can in PA. CTP will likely need to be throwing up headlines very soon and I would bet watches on the bottom two tiers of counties to open things up.  

I always think of this document when I see those kind of anomalies https://journals.ametsoc.org/doi/pdf/10.1175/WAF964.1

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54 minutes ago, sauss06 said:

Watches up

 

Here is mine

Tuesday Night
A chance of snow. Cloudy, with a low around 29. Northeast wind around 7 mph. Chance of precipitation is 50%. New snow accumulation of less than a half inch possible.
Wednesday
A chance of snow before 11am, then a chance of rain and snow. Cloudy, with a high near 40. North wind around 8 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

lol

just lol

 

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3 minutes ago, canderson said:

I always - always - root for you on this events because it seems you are forever fringed. I really hope you get the goods.

Yeah it seems we cant get the big totals up this way...Its all nickle and dime type stuff all winter with an occasional 3-6" storm once in a while.

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15z SREF's are through the roof at KAOO, which looks like the station that was the winner this afternoon. A nearly 15" snowfall mean and a notable majority of members weighted ABOVE that mean. LSV stations were generally 10" or so. Without getting too wrapped up in how ridiculous those numbers are, it is definitely strongly supportive of a warning type snowfall for a bigger portion of the region than the initial watches encompass. That also illustrates that elevation is probably going to dictate where these excessive totals pop up if they do. KAOO is about 1500' asl. That whole central ridge and valley region as well as the southern Laurel's would really be favored for the biggest snowfall potential given strong easterly fetch (upsloping) and better thermals (elevation). 

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5 minutes ago, AllWeather said:

South of Turnpike, a lot of that is sleet verbatim. Check out Ferrier Method snow accumulation on the 3k. DRASTICALLY different. 

Definitely so, especially south of the mason-dixon line. That's a huge difference down there. That's also another worry this time of the year with the strong anomalous low level flow off the ocean... mixing potential especially in the southern fringes of the LSV. On the other hand, some of these bands that might set up under some of the better 700 lift could produce snow growth a tad above 10:1 that might get realized on the ground if it's intense or potentially at night.. as a lot of this storm is supposed to take place in the evening/overnight now. Like I mentioned in my last post, I think the best potential for excessive totals may end up being further west in the south central (ridge and valley and Laurel's) where there is more elevation while the LSV is still under the gun for warning snows. There are still some higher elevations in that region too. Nothing like things going crazy at the last minute. 

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Here's Pivotal's representation of the 3K using Kuchera.  As best I can tell most of Cumberland county gets 12-15" except the southwest mountainous region which gets 20".  I manually searched around the county with my cursor and it suddenly blew up from 14" to 21" around South Mountain region.

snku_acc.us_ne.png

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