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Front End Thump Event 12-17 / 12-18

ChescoWx

By ChescoWx,
in Philadelphia Region

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Ralph Wiggum

Ralph Wiggum

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18Z NAM halts the rapid warming upper levels trend. Even a tad slower at warming upper levels this run and just a hair snowier across SE PA vs 12z. 3-4" locally this run. This is what we needed to see, ie, stopping the upper level warming trend. Still going to rain but maybe we can still salvage a general 1-3" before the flip with some isolated 4" lollipops.

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hazwoper

hazwoper

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2 hours ago, Ralph Wiggum said:


Good talk ;-)

I was being facetious, but I do believe we are on the outside looking in when earlier in the week I had some hopes for a general 3-5" in our area.  I'll certainly still track it and probably try and stay up for the beginning of the event, but this one isn't for us.  Once we lose a storm like this north, it tends to stay north.

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hazwoper

hazwoper

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24 minutes ago, Ralph Wiggum said:

18Z NAM halts the rapid warming upper levels trend. Even a tad slower at warming upper levels this run and just a hair snowier across SE PA vs 12z. 3-4" locally this run. This is what we needed to see, ie, stopping the upper level warming trend. Still going to rain but maybe we can still salvage a general 1-3" before the flip with some isolated 4" lollipops.

Not sure what you are seeing.  Sounding data by me has 800 at 0.7C at 42 (start of precip is between 39 and 42) and it only cranks upward from that point.  This is a quick dusting over to slop and rain on 18Z NAM

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Ralph Wiggum

Ralph Wiggum

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Not sure what you are seeing.  Sounding data by me has 800 at 0.7C at 42 (start of precip is between 39 and 42) and it only cranks upward from that point.  This is a quick dusting over to slop and rain on 18Z NAM

Rgem also 2-4" generally across extreme SE PA before fzra/sleet->rain. Probably going to hold tight with my 1-3" range unless something disastrous happens at 0z.

Eta: Rgem has the non-frozen precip line just starting to encroach on extreme SE PA around 18z Saturday.

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hazwoper

hazwoper

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2 minutes ago, Ralph Wiggum said:

For what area?

Eta: Wait, you're the guy that told me the January snowstorm last year didn't warrant it's own thread when I started it aren't you? Makes sense now ;-)

Did you look at my location?  Wrightstown (a colder area compared to Warminster).  You need to look at the soundings on the NAM, Ralph.  They do NOT support your numbers.  I am just responding to your post that the NAM supports 3-4" locally.  It does not.

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Ralph Wiggum

Ralph Wiggum

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Did you look at my location?  Wrightstown (a colder area compared to Warminster).  You need to look at the soundings on the NAM, Ralph.  They do NOT support your numbers.  I am just responding to your post that the NAM supports 3-4" locally.  It does not.

In not using the NAM 32k I am using the much higher resolution NAM 12k which handles thermal profiles much better. That is where our discrepancy is. It's all good man. This was never our storm or a large scale event anyway.

Eta: You are correct the 'regular' NAM is a coating to an inch at best before slop. Big differences the when u start looking at the higher res stuff like the 12k NAM and the Rgem which are just a bit snowier.

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hazwoper

hazwoper

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2 minutes ago, Ralph Wiggum said:

In not using the NAM 32k I am using the much higher NAM 12k which handles thermal profiles much better.

OK.  Do you have access to the soundings?  I'd like to see them if they support 3-4".  I just know the sounding for the NAM show in our area temps at 800-850 above freezing shortly after precip starts.  Does it mean its right?  No.

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Ralph Wiggum

Ralph Wiggum

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OK.  Do you have access to the soundings?  I'd like to see them if they support 3-4".  I just know the sounding for the NAM show in our area temps at 800-850 above freezing shortly after precip starts.  Does it mean its right?  No.


Cannot post here as they are not free data, but I assure you the warm tongue 725-800 mb is slower getting here on the 12k. Rgem, another higher res model, hinting at same thing. Will it make a major difference? Probably not....maybe the difference between an inch or 2-3".
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hazwoper

hazwoper

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3 minutes ago, Ralph Wiggum said:


Cannot post here as they are not free data, but I assure you the warm tongue 725-800 mb is slower getting here on the 12k. Rgem, another higher res model, hinting at same thing. Will it make a major difference? Probably not....maybe the difference between an inch or 2-3".

OK, well here is to hoping the trend to slowing the warm up aloft continues.

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shemATC

shemATC

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1 hour ago, Nate8833 said:

Thanks!  I'll keep an eye on this thread (great forum BTW!) to see if anything changes.  

Yeah, I might have been a little late on that time.  Harrisburg might be seeing snow by midnight.  If you are arriving at 2am it might be a little dicier.

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zenmsav6810

zenmsav6810

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I think the most sounding modeling isn't quite in range yet. I have a feeling this might flip back to more rain. Although NAM 12k is encouraging. I think it did well with the Eagles snow game and its right where we want it for this range. We shall see. I don't believe elevation helped much with the Eagles snow game. 

 

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ChescoWx

ChescoWx

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Latest Wxsim with 6z data ticked up with frozen precip. Now has light snow starting at 230am temp at 19.2. Moderate snow by 4am temp at 18.9. Heavy Snow at 7am with 2.5" on the ground and a temp of 20.5. Snow will transition to Heavy IP by 8am with 3.2" of snow on the ground. IP then accumulates another 0.4"  before changing to ZR by 1130am. Total snow/sleet accumulation 3.6".

The Wxsim keeps temps below freezing all day (not that I agree) despite indicating 850 temps soaring through the 50's topping out at 58 degrees at 5am Sunday. It has a total of 0.98" of precipitation falling before temps rise above freezing at 4am on Sunday. Surface temps top out at 41.5 on Sunday PM with heavy rain during the day 0.90" falling as liquid. Rain will cut off before 850's drop back below 0c at 5pm Sunday. A little bit of something for everyone!

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Ralph Wiggum

Ralph Wiggum

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12Z NAM 12km slight increase in frozen precip again for SE PA....warm nose 725mb-825mb slightly slower getting here again this run with precip starting a hair earlier as well....better trend than headed towards less frozen anyway I suppose if you like this sort of stuff. 1-3" extreme SE PA with 4" lollipops far NW burbs with up to 6" lollis in Northern LV and Poconos. Inevitable transition to sleet/fzra then plain rain for most.

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hazwoper

hazwoper

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3 hours ago, Ralph Wiggum said:

12Z NAM 12km slight increase in frozen precip again for SE PA....warm nose 725mb-825mb slightly slower getting here again this run with precip starting a hair earlier as well....better trend than headed towards less frozen anyway I suppose if you like this sort of stuff. 1-3" extreme SE PA with 4" lollipops far NW burbs with up to 6" lollis in Northern LV and Poconos. Inevitable transition to sleet/fzra then plain rain for most.

Took a look at the soundings and it is definitely colder at those levels for sure.  Borderline for changeover by 7am Sat on the 12z whereas on the 6z there was no doubt changeover had taken place well before 7am.  Still, not much qpf during the timeframe where frozen would be depicted.  Thinking up to 1-2" in extreme SEPA before fairly quick changeover (this based on NAM).  GFS is a bit colder and more qpf and is part of the reason why I am even suggesting 2" is possible

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Ralph Wiggum

Ralph Wiggum

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Took a look at the soundings and it is definitely colder at those levels for sure.  Borderline for changeover by 7am Sat on the 12z whereas on the 6z there was no doubt changeover had taken place well before 7am.  Still, not much qpf during the timeframe where frozen would be depicted.  Thinking up to 1-2" in extreme SEPA before fairly quick changeover (this based on NAM).  GFS is a bit colder and more qpf and is part of the reason why I am even suggesting 2" is possible


Rgem slight tick colder again at 12z with 2-4" SE PA changeover after 9am. If u gander at the 4km NAM even colder than the 12km version with 2-4" SE PA also and decent icing potential. Changeover after mid morning. GFS nudged totals in SE PA as well based on prior runs and is REALLY hitting the ice potential in my area with .25" ice accretion and still 31F at 10am tomorrow but turnover rather close. Higher res models are hinting that LV and even as far S as my area in Bucks remain majority frozen with a dry slot impeding on the region at the time of turnover with just drizzle to follow. Rather touch-and-go situation coming up tomorrow for the burbs. Feeling great attm with my 1-3" call right outside PHL in the N and W burbs. Icing potential looking like a potentially bigger concern now out in the burbs.
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hazwoper

hazwoper

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Just now, RUMG11 said:

Whats the chances my flight out of Philly Saturday morning at around 7:45 am is gounded/delayed/canceled? Concerned about the ice, although its not looking like Philly should see too much... would likely need long extended periods of freezing rain, correct?

Youll be fine.  Perhaps a slight delay for de-icing, but it wont be canceled

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ChescoWx

ChescoWx

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Wxsim with 12z data GFS/NAM blend

Flurries starting around 1230am with light snow by 230am (temp 17.9) / Moderate Snow at 4am (temp 17.9) with 0.8" of snow so far / 7am S+ temp 18.4 with 1.6" / 930am Heavy Sleet Temp 21.1 with 3.5" of snow/sleet on the ground / 130pm ZR temp 28.0 / Freezing drizzle continues the rest of the day with the temp reaching 29.5 at midnight with 0.92" of liquid falling by then / Temps finally rise above freezing at about 430am on Sunday morning with still 3.3" of snow on the ground. Heavy rain moves back in during Sunday PM with 0.75" falling.  High on Sunday 42.0 degrees. Wxsim still shows 0.7" of snow on the ground at 7am Monday morning.

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