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1/17-1/18 Southern Special


phlwx

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it all comes down to how strong and how far north that vort gets. Also, how far south that pv is.

Thanks.  I can get models not performing in harmony on dynamic cooling or synoptic banding.   It is baffling to me that the 2 major features can be that divergent in modeling at this range.   Anything you picked up on initialization of current features that would lend more credibility in verification from one model to another at this point?

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CIPS analogs really arguing for this to be some sort of event for this area but they are skewed by some bad storms that don't match well like 2/16/96...however there is 1 storm that stands out and its the 2nd closest analog...12/12/82 and its the 2nd closest match...looking at the charts you wouldn't figure much snow fell but Philly got 7 inches and JFK 4 inches...not sure what fell at the coast.

 

http://www.meteo.psu.edu/~fxg1/NARR/1982/us1212.php

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I'm not confident about Philly getting a trace on this ;)

 

This has been one annoying winter for forecasting, unlike 09-10 and 10-11 when you knew everything would be pretty much snow for everyone these events of rain/snow line and if the storm will be close enough have been a pain, I've had to sweat out every forecast and badly blew the event on the 29th for NYC sticking with 3 inches til the very last minute even with the high res models all saying no that NNE surface wind made me a believer.

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I can't because I still haven't figured out how to read those darn things after all these years.I made this sounding primer last year to cover the basics:

Just to add to that, where the "rain/snow" line "0 temp" is located from 850mbs to the SUrface, made this real quick:

post-810-135837642066.jpg

if that red line stays on the left side of the 0 line all the way up, its snow..... if it crosses it anywhere between the surface and 850 generally 3 things can happen,

rain, sleet, or zr...depending on the sounding. Just keeping it plain here for ya. I had snow, sleet, rain and zr soundings on my laptop before it crapped out. hopes this helps.

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Looking at the 6-12hr progs vs the 500mb soundings, I would not expect a more robust solution with the southern vort with the upcoming 00z run. (Now watch it go to town).  Its been kind of a mish-mosh modeling verification at 00z, pbly best if one could put 1 part gfs, 1 part 12z nam and 2 parts euro in a blender and use that as a best fit.

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For the population centers in this sub-forum, I think it's a final nail.  However, it's an improvement over the 18Z run IMHO in terms of just misses/grazes the coastal areas.  Very juicy and much closer to a hit than 18Z.  Just a slight tick back NW (ala a NAM/SREF/GFS/Euro compromise) and the coast gets a nice hit.  If the NAM and the last run of the Euro verify verbatim, however, then everyone in here loses.

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For the population centers in this sub-forum, I think it's a final nail.  However, it's an improvement over the 18Z run IMHO in terms of just misses/grazes the coastal areas.  Very juicy and much closer to a hit than 18Z.  Just a slight tick back NW (ala a NAM/SREF/GFS/Euro compromise) and the coast gets a nice hit.  If the NAM and the last run of the Euro verify verbatim, however, then everyone in here loses.

I noticed that too with the NAM. Even the 18Z GFS is juicier for my area .25 than at 12Z, .15. Rgem was about the same.

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I made this sounding primer last year to cover the basics:

sounding_primer.png

 

Ellinwood - this is a great explanation.  It's been about 30 years since I learned about psychometric charts and things like this, so I'm rusty, but your explanation makes perfect sense.  Let me see if I then have the path of precipitation correct (I'm using my chemical eng'g knowledge, which might not translate perfectly into meteorological language, so bear with me).  I'm guessing that these charts are for conditions throughout the column at some sort of steady state equilibrium, given the statement that the dewpoint must always be less than the air temperature and that this is the baseline situation into which unsteady state changes are introduced producing snow/rain.  That is, that vertical transport of relatively warm, saturated air from near the surface to the much colder snow growth region (or raindrop formation region) occurs and then those parcels of warm, saturated air quickly become supersaturated as they cool below the dewpoint, providing the driving force for formation of snowflakes, via supersaturation-driven primary nucleation to form the inital tiny ice crystals, followed by supersaturation-driven vapor deposition onto the initial tiny ice crystals, driving crystal growth to form snowflakes (or in the case of rain, the supersaturation drives formation of water droplets which then grow, via vapor deposition into larger raindrops; all depends on the temp at that altitude).  Is that correct or at least mostly correct?  And, if so, how does one determine how much snow is generated and falls?  I'm guessing that's a rate (kinetics) question, in which the rate of transport of moist air into the precipitating layer must be estimated from vertical velocities - that sounds like what goes on in the meteorological models and that the soundings are just a representation the state of the atmosphere into which the unsteady state perturbations are added.  Thanks, in advance, for any feedback you can provide. 

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