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Chubbs

Feb 8th-9th RUSH HOUR CRUSHER

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3 minutes ago, simple295 said:

Sorry to clutter the thread up, but what does this show exactly? I don't know what any of that means, frontogenesis is familiar but that's it haha. 

Frontogenesis is basically a thermal front,those thermal differences cause big time lift in the atmosphere. The lift creates very heavy bands of precip along the front.  Then again if you're outside of that, you can get subsidence, which is sinking air and decrease in precip. 

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1 hour ago, tombo82685 said:

This would be my guess. Feel confident on the 6-10 zone. Not confident on the 4-6. 2-4, and <2 pretty confident 

 

sorry for the cruddy map, I was at the gym while doing this. I wanted to also say, in that 6-10 zone I could see higher amounts of a foot or so.

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19 minutes ago, tombo82685 said:

Frontogenesis is basically a thermal front,those thermal differences cause big time lift in the atmosphere. The lift creates very heavy bands of precip along the front.  Then again if you're outside of that, you can get subsidence, which is sinking air and decrease in precip. 

So essentially this map is showing strong lift? Strong lift means heavy precip?

 

The poster said this was the strongest they've seen. I didn't understand why that was remarkable. 

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1 minute ago, simple295 said:

So essentially this map is showing strong lift? Strong lift means heavy precip?

 

The poster said this was the strongest they've seen. I didn't understand why that was remarkable. 

Yup exactly. That map shows insane lift, meaning very heavy precip in that band

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Must be a big storm. All the local TV stations are using two meteorologists to tell everyone about the storm.  :crazy:

 

I'd rather just tune in here.

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I like 6-10" in my backyard. 6" if I miss the best rates/changeover late. 10" if all goes well. Either way, really fun event to track with you guys, and best of luck to all of your backyards!

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1 hour ago, irishbri74 said:

nOT gonna lie, I'm a bit shaky if we tick north again @0z runs. May miss out on best dynamics around the 95 region. Something to watch.

I didn't see anything really tick north. The nam and gfs were almost in the same position at 18z as 12z, right off the delaware beaches. The nam was closer than the gfs.  It was warmer IMO because the models were both to cold to begin with on modeled highs at 12z, so it had to adjust for that. As well as the dynamics weren't as solid as 12z and will continue to shift around. As long as you keep your expectations in check, which they seem to be with your 4-6 then you should be fine. 

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1 hour ago, tombo82685 said:

Frontogenesis is basically a thermal front,those thermal differences cause big time lift in the atmosphere. The lift creates very heavy bands of precip along the front.  Then again if you're outside of that, you can get subsidence, which is sinking air and decrease in precip. 

If we're being picky, it's the time rate of change of the intensity of the potential temperature gradient.  The lift results from the thermally-direct ageostrophic circulation that forms in response to the strong frontogenesis destroying thermal wind balance.  As the warm air rises, it cools (moist) adiabatically, reducing the theta gradient.  The stronger the fgen, the stronger lift required to produce enough cooling to restore thermal wind balance.  tl;dr stronger fgen, stronger lift, stronger precip

 

41 minutes ago, simple295 said:

So essentially this map is showing strong lift? Strong lift means heavy precip?

 

The poster said this was the strongest they've seen. I didn't understand why that was remarkable. 

See above.  Not actually lift, but an indication thereof.  The stability of the layer in which there's fgen matters too.

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13 minutes ago, Coltsfan1217 said:

I like 6-10" in my backyard. 6" if I miss the best rates/changeover late. 10" if all goes well. Either way, really fun event to track with you guys, and best of luck to all of your backyards!

Seems reasonable. I always worry about delayed changeovers in a set up like this at our lower elevation. Like a surprise extra hour or two of sleet as we transition. For that reason my conservative self am thinking 4-8" here. Looks like we get 2-3 hours of light rain and sleet, then 6-7 hours of accumulating snow. If we average an inch an hour (a few higher, a few lower) over those 6-7 hours we'd fall safely in there. My IMBY goal is a solid 6". 

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3 minutes ago, Parsley said:

Seems reasonable. I always worry about delayed changeovers in a set up like this at our lower elevation. Like a surprise extra hour or two of sleet as we transition. For that reason my conservative self am thinking 4-8" here. Looks like we get 2-3 hours of light rain and sleet, then 6-7 hours of accumulating snow. If we average an inch an hour (a few higher, a few lower) over those 6-7 hours we'd fall safely in there. My IMBY goal is a solid 6". 

If I had to guess for you 8-10

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Tom what are your thoughts for here in the higher spots in NW Chesco?

I am sure we will wet bulb down quickly and do relatively well.....not really buying sleet as anything more than a relatively quick transition. If I were forecasting for here I would bet 7"  to 9" but I have much less knowledge than most folks here....so we shall see. The wildcard is where will that Fgen forcing set up....basically impossible to forecast at this point.

thoughts...for NW Chesco above 650 ft from the experts?

Paul

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2 minutes ago, tombo82685 said:

If I had to guess for you 8-10

Hopefully. 

Good thing is we'll be sleeping during the changeover period so no stressing out during the transition.

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2 minutes ago, chescopawxman said:

Tom what are your thoughts for here in the higher spots in NW Chesco?

I am sure we will wet bulb down quickly and do relatively well.....not really buying sleet as anything more than a relatively quick transition. If I were forecasting for here I would bet 7"  to 9" but I have much less knowledge than most folks here....so we shall see. The wildcard is where will that Fgen forcing set up....basically impossible to forecast at this point.

thoughts...for NW Chesco above 650 ft from the experts?

Paul

Paul, Id be shocked if you fell short of 6" I think you're same as parsley and me in that 8-10 range. If banding sets up good over us, maybe a foot?

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Just now, tombo82685 said:

Paul, Id be shocked if you fell short of 6" I think you're same as parsley and me in that 8-10 range. If banding sets up good over us, maybe a foot?

it should be interesting...won't take much to make this the biggest storm of season...heck it might happen for you, parsley or me in 1 hour in the 6 to 9am hour tomorrow....

 

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8 minutes ago, chescopawxman said:

it should be interesting...won't take much to make this the biggest storm of season...heck it might happen for you, parsley or me in 1 hour in the 6 to 9am hour tomorrow....

 

Yea it's been a bad winter for us out here so far for sure. 

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10 minutes ago, tombo82685 said:

Paul, Id be shocked if you fell short of 6" I think you're same as parsley and me in that 8-10 range. If banding sets up good over us, maybe a foot?

Yeah, those higher elevations in NW Chesco. (I know we have a poster in West Caln Twp. who always does well) whether it's better ratios or a quicker start so probably they need a higher range/ceiling. Like 6-12". 

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1 minute ago, tombo82685 said:

Yea it's been a bad winter for us out here so far for sure. 

We've begged for QPF, we get it tomorrow. Hopefully the thermals can cooperate. I'm not asking for the moon.

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5 minutes ago, Parsley said:

We've begged for QPF, we get it tomorrow. Hopefully the thermals can cooperate. I'm not asking for the moon.

i just my total for the season to surpass 10" already

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35 minutes ago, tombo82685 said:

Paul, Id be shocked if you fell short of 6" I think you're same as parsley and me in that 8-10 range. If banding sets up good over us, maybe a foot?

I could see someone up there getting a foot. The main reason to be cautious is the speed of the system. Rates will be good.

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I thought it is odd that Philadelphia Public Schools have decided to wait until tomorrow am to make closing decision..they are usually one of the first to close..

 

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2 minutes ago, tropicalwx said:

I thought it is odd that Philadelphia Public Schools have decided to wait until tomorrow am to make closing decision..they are usually one of the first to close..

 

 

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Absolutely classic cross section through the developing noreaster at 12z tomorrow. Strong frontogensis sloped toward the cold air, -EPVg, which with no CAPE (theta-e* lines are in lime green) means strong, deep-layer CSI.  Of course, the result is intense upward motion. Lot of riming though, with the forcing dropping off in intensity quite significantly before reaching the DGZ.

xsec_2017020818_GFS_F18_EPVg.gif

xsec_loc.png

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That does change as you head north+east, though.  Notice two hours later, at this next xsec location, how the fgen and lift are much deeper and the DGZ is a bit lower.

xsec_2017020818_GFS_F20_EPVg_2.gif

xsec_loc_2.png

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