Moderately Unstable

So, first, water vapor is actually a ghg, in the sense that it blocks outgoing lw radiation. In fact, water vapor is our MOST important ghg. Look it up on Google. The reason we talk about CO2 & CH4 is because we produce those en masse and they have a long lifetime. The reason earth's avg temperature is 287 K instead of 255 isn't due to the lapse rate. The lapse rate defines how temperature changes but doesn't cause the changes. The dry adiabatic lapse rate is a conceptualized rate of temperature change in which heat is not added or released to an air parcel. Using the ideal gas law, changes to the parcel temperature depend on changes to volume and pressure. Convection, the process of warm air with higher internal energy rising, expanding, and cooling, is responsible for the dry adiabatic lapse rate. As air rises and expands, it does work (1st law of thermo), and cools as it loses internal energy U. The IGL has a different constant for dry air vs moist air which basically is to say, moist air has more interal energy and therefore requires a moist parcel do more work to cool, hence the lower moist adiabatic lr. Ok so onto the skew t. Earth's sfc T avg is 287.15 kelvins. For both of these measures it seems you are off mostly because of a calculation error. For the dry adiabat to me it looks like around -34, perhaps you followed the wrong line...the 30 degree line perhapsas that appears to intersect at -24? If you plug that in, we have a delta of 47 (14.15 sfc, ~-34 @5km). 47/5=9.6. Close enough to 9.8 that I expect the plot likely is showing a 9.8 lapse rate and I just can't see that fine grained of a resolution. Let me know if this helps.

This is an easy answer: yes, I am. Can't speak for others. The biggest thing I've learned being on amwx is that a large number of folks pile onto the extreme bandwagon whenever something is progged to happen. Tornadoes, winter storms, hurricanes. Then a couple runs look bad and everyone screams bloodly murder. Then, almost always, something between "nothing" and "the best possible scenario" happens, everyone vows to be more rational moving forwards, and then apparently get amnesia and repeat the process for the next storm. In this case, the basic facts are that the models have objectively been sh*t this winter when it comes to cold, particularly in the PBL. They have consistently, with every storm we've had, suggested a rain snow line farther S&E than what actually happened. This has happened the last several years more generally. In addition, the models clearly didn't have a great handle on this storm until recently. We all thought it was headed out to sea and needed to thread the needle. Welp, it looks like it threaded the needle...it hit the phase with the northern stream. But almost every run of every model so far has moved the sfc low further N. That trend has to stop, soon, or this WILL be an issue for a lot of folks...and I don't think the forum is appreciating that risk adequately. The RPM keeps trending farther N, last I checked it had the heaviest axis up in the LV with philly just getting a couple inches...and 0...nada near the shore. Frankly I think that's more likely than the opposite with a big blast along the corridor, due to the pattern, and the model trend. As of the 00z run, it is now also showing 0" in PHL, and an axis NE to SW near Allentown gets over a foot. Now, that's one model, and I have seen it be **spectacularly** wrong before. Sometimes it picks up on things earlier than other models though. So, carry on looking at the other models. Nevertheless, I'm nervous, that trend has to stop. Otherwise by 12z tomorrow the models will all be tucked in with it. At the end of the day, my objective sense is, this could bust entirely...we could get nothing, or, the rpm could cave and move back south. It's already too late in terms of messaging now if this busts. People expect 3-6. The weenie in me hopes for the best. The meteorologist in me has questions.

Insane omega values in that FGEN band on the 18z NAM (pull a forecast sounding in the 3+"/hr rate zone....). Also happens to maximize right in the optimal snow growth zone temperature-wise. That would be quite epic. It is notable that models are still oscillating a bit closer to the coast. Monitor that trend--too close and we have the classic "oops just the poconos" setup. W.r.t. precip types, Ralph is right I think w/95 being a dividing line. As such, I think the 6abc map, and many of the snowfall maps on the models, are a bit generous S of the city. Great dynamics only help if you've got sufficient cold air. Good positioning of the 850 mb low though. FWIW, latest 4km RPM has the dividing line smack dab across Philly and 95--almost to the mile. It does suggest that the corridor will be the locus of the fgen band for at least some period, and that some of that will be in the form of heavy snow. Towards the end of the event, heavy precip rates and less WAA as the low moves NE will likely push the snow line SE. On basis of this being a somewhat classical setup, I'm expecting 4-6 in the city and the 95 corridor, isolated areas of 8" where banding aligns with the best thermal profiles. On basis of the RPM, I think this will be a prototypical "nail biter" for city folks like me, as small deviations right now could really change this forecast and move the axis out to the N&W burbs, or even to C. NJ though I view that as less likely. That's probably the reason for the broad brush 3-6" abc call. Regardless, this doesn't look to be a 10:1 ratio snow..it'll be heavy and wet. If you look at the ratio estimates for this on the models, it's more 1:6,1:7...so even if you buy a more "snowy" solution from these models, you won't see those 10:1 ratio estimates verify.

Cool. Go design a better model then and give us your best accurate forecast for the next one.

Charming discussion. I feel I should chime in here. No forecaster--professional or amateur, would've predicted some of the totals we've seen today with this storm. Often, in complex setups that bust, we can look back and go, "ah, well really the signal was there in the form of {these models/the basic physics/some meteo concept}. None of that applied here. The models were unanimous: lots of snow. Maybe some mixing. Not tons. Not super far N. The physics backed that up--cold air mass in place. This afternoon's afd mentioned that the warm air was actually due to air coming in from the ORIGINAL low, e.g. over Ohio. Frankly none of us were paying attention to that, and neither were the models, or anyone else. But that isn't necessarily a fault. In cases where one model say snowtopia and the other says "oops all sleet!", you can castigate mets who go the weenie route. The thing with Miller B's is, we do have all these axioms...dry slot here, don't trust this, someone's getting shafted. That *isn't* actual meteo. That's how you justify to yourself why you feel cursed. Miller A and B storms are, scientifically, OBJECTIVELY, the Philly area's best chance for sig snow. The analogy of a car engine is correct: for many reasons, to get a good snow here, conditions need to align quite well. And with climate change, as we have seen, those opportunities are dropping. As I said a few days ago, I strongly believe climate change is affecting model performances for these events. If you can't correctly model incoming and outgoing radiant flux, you're going to screw up a lot of your secondary calculations. Weather models depend on, well, certain assumptions about our climate. If those assumptions are now even slightly off, we all know well enough how that translates via the butterfly effect (*cough 180 hour forecasts cough*). In 2009/2010, Miller B storms were what gave us those historic incredible snow totals. In 2016, a miller A hammered us. WE ARE NOT WRONG in expecting major Nor' Easters to produce snow for most of us, and it is NOT bad forecasting if that doesn't pan out. On average, if you assume big snow totals out of a miller B with arctic air in place, you will be right more than wrong. Forecasting is an art not just a science. Figuring out the low position down to the mile at a given hour in advance is very hard. Models do fairly well...within 10-20 miles. The problem here wasn't the coastal low's placement, it was warm air from the original low. Case and point, I, in CC phl, had to scrape 2" of sleet off my car today below the snow. That is about 6" of a 10:1 ratio snow, that we got 2" of instead. That'll do it. Now, here's another thing to realize. Snow is going away long term, for us due to climate change. Waive goodbye. So instead of feeling sad cause you didn't get 2 feet, be happy this isn't 2020 where we couldn't get an inch....heck, it's been 3 years since we had a significant storm that didn't TOTALLY bust (2018). As the planet warms, our local climate does too on average. We aren't gonna see the end of snow any time soon, but over time, average yearly snowfall around here will drop. We've already been seeing it to a degree. Shorter cold periods, 70s heatwaves in December. Less sustained cold. More mixed precip events perhaps (not sure there's a study on that but would be unsurprised if that finding held up). You tell me.... look back on your time in Philly and tell me winter today feels like it did 20, 30, 40 years ago (for those who were around here then). Yeah you can cherry pick a good year here or there, I mean on average. Is it any wonder then, that we bust so often, and miss out so often? We are in a La Nina this year as well. We were not expecting much in terms of snow. We've had 2 fairly-decent storms. We may see a couple more in Feb alone if we are lucky. We're doing quite well, relative to what a La Nina can do for us. I for one, am happy--I had an extra unplanned day off from work, I went for a walk and enjoyed the snow we DID get, and just appreciated the return of a feeling of winter and the happiness I saw on so many people's faces today (at least those that weren't driving). So instead of complaining things didn't work out exactly as planned, STOP. Sit. Breathe. Appreciate that we got some snow, that we have technology that remotely lets us predict the freaking future, and will probably still get a bit more tomorrow. You're (probably) not going to die tomorrow...there will be MORE snow events to freak out over (and be disappointed by). If you truly want to see amazing snow without having to get everything perfect...do what professional chasers do...GO to IT. Figure out where it's gonna snow crazily, book a trip, and go there. And finally, to those who DID get snow, don't be an ahole. Don't rub it in people's faces, don't say "I don't care about so and so region"...do you know how that makes people feel? Think about it a sec will ya? Angry. Sad. Upset. Stop it. Stop throwing out insensitive crap into the universe: it very, very clearly sucks enough these days as it is...so please, practice some freaking decency and kindness to others, and learn some empathy. We are all on this planet together, and most in this forum are quite close, at that. End rant.

Hope isn't TOTALLY lost. Radar shows right now that the winds still have a major easterly component. Not warm, but not cold. As the low tracks up NE, winds will assume a more classical NE flow regime...that should force the line south. Flakes starting to fall again now 3 NW of CC. Edit: now mostly snow.

Well, That's what happens when you encounter a dry slut.

If that trend keeps up they'll need to extend the warnings....

Yes. No 24k NAM. 12k and 3k are both on Pivotal.

I've been trying to come up with a way to express how excited the NAM caving makes me but I literally can't. Agghhh. Looks like it finally clears philly early Wed am. Weather channel uped philly estimate to 12-18" storm total. Muahahahahahahaha!!!!!!!!

I really like the RPM. Weather channel's parent company's in-house model. 12km res goes to 72 hrs. 4km res goes to 51hrs these days. Almost every broadcast met you know uses it. Do the NE forum members post the maps or no? As of now, it is trending more euro/rgem than nam/hrrr. I think the euro has a good handle on things overall. It does well with headline type miller B's; NAM facing retirement and is known for kooky solutions to a level that "being NAMed" is common meteo vernacular. Looks like the NAM is coming around finally. Wrt the last euro, all I want to say is, that European model looks very plowable tonight .

Sorry guys, I wrote that on my phone. I promise I know better haha. Thanks Jim for formatting.

PSA: A few folks here yesterday made statements like..."under 6-8 WILL NOT happen". Remember not to predict ultimatiums before an event occurs. Weather gods don't like hubris. Mt. Holly is not going w/NAM. If they were, they'd have to majorly cut those totals particularly around Philly. They're just not going into rgem land. They seem to be splitting the difference. Not very weenieish, does seem logical though. The models all show good qpf in Philly and surroundings. The differential in the snow amounts is mostly differences in how much warm nose pushes in and hence how much mixing occurs. My exp is that given the cold air that's been in place, and the high precip rates expected due to the rapid deepening low, you'll get the typical evap cooling effect where the heavy rates keep the column at freezing so long as precip is sufficiently robust. The lull period tnght tmrw am is where the risk is as has been stated. Heaviest rates, 1-2" hr are really only progged for a short time on any of the models, and it's right after precip ramps back up. Some models show that period being sleet for many of us; that cuts the totals. Others keep it all snow. That will be the difference for the corridor though btwn a 6-8-12-15 storm total. Remember that if we got 2" thundersnow type rates for several hours, we'd be talking plural feet in the corridor, not 10ish inches over 3 days. *Most* of this event is clearly NOT heavy snow. So, don't panic if things don't work out exactly as the models project. Expect that they won't be perfect. One thing they all show is that this system is with us for awhile and should produce some snow most of that time. By Tuesday pm, we will probably add up to what this forum expects, but, expect a lot of panic and concern from people here tonight and Monday, beyond the lull..just bc I think people are expecting a major 2"+ hr rate situation and again, outside a few hour window, this is a low and slow burn. I also think based on what I'm seeing live that the models may be underdoing the overrunning totals a bit, and that may also help us get to expected totals. We're going to be fine, folks.

The thing worth considering here, is that, unlike the *December* storm, this storm is sticking around a long time. Yeah, the event starts within 24 hours. But the actual ramp up where we expect to see the transfer and thus, the bigger totals, isn't until Monday (e.g. 36 hours ish out). I think we could safely predict right now what happens tomorrow. The overrunning precip comes through, gives a widespread several inches, semantics dependent on mesoscale details. Hence, we have 12 hours before we'll be at the point where, in December, the models started making everyone cry (they began that trend sooner though) wrt the actual Nor' Easter component to this storm. I think 10-14" is what I'm going with for the city. Someone in the LV will see north of 2". I don't necessarily buy the pie in the sky 3-4 feet. Mixing is a concern for the corridor, but the transfer should probably limit duration. I think the above comments were right vis a vis the NWS was pointing it out as something to be aware of and consider, not buying or not buying it. It's one of those things to keep an eye on. If that signal sticks around and it starts showing in other models, pay attention. If not, just a good-to-know. Wishing all in this forum good luck the next few days, if you're chasing, staying home etc. May the snow totals be forever in your favor.

Does anyone have a link to a website that shows a high temperature verification map for today? Ideally something that compares actuals to the statistical and dynamical guidance?

Not necessarily. The high res and proprietary guidance today has been a bit all over the map. Several typically good short range models are progging the axis being more along the apps with PHL at 6-10. Of course several globals clearly show more. Personally, I'd have called 8-12" for the moment in CC PHL, because it's less jarring for the public to shift up or down a peg from that range. No point in forecasting max possible amount just yet, sets up a lot of room to bust. Too many things have to go right for 12-18. We can't miss the overrunning, fgen needs to be good, transfer of low has to be good. 6-10 is nothing to sneeze at, and model variability is the reason it is useful to wait to go full tilt until I'd say the 00z runs tonight. This IS philly after all. If all the models are honking together then you raise the bar. 12-18 is your best case for phl, 5-8 is your worst case....8-12 is a safe middle. They say fortune favors the bold, perhaps that explains my misfortune. I am genuinely curious right now to see if winds and visibilities end up hitting blizzard criteria somewhere in the mt holly forecast area. Seems possible. Edit: I like the epawa map.

Mt holly has hoisted initial warnings.

1) Yes Mt Holly write up was good. 2) I'm refraining from posting right now, or getting excited, as I've learned the very hard way (as have all of you) that we've been burned SO MANY TIMES on winter setups. There's an excellent article the inquirer put out earlier basically making the point by talking about the improvements in modeling coupled with myriad high profile busts over the last dozen years. Moral of the story is, Philly weather is hard to predict wrt snow. Complex almost always. You've got an elevation change, variable coastal effects (sometimes intrastorm), etc. I'll try to make a call tomorrow night just to be part of the bandwagon bc yolo. The things I DO like about this setup are its long duration, the favorable teleconnection pattern, the existing cold air "cold air is the bully"--> meteo refrain referring to cold air being more dense, thus if you want to bet on something, bet that cold air sticks around longer bc it takes longer to dislodge. The long duration aspect means that if one element underwhelms, say, overrunning, or fgen, there's 2 other components that can make up for it. Much better than a quick hitter that is progged with 2" rates. If you miss an hour, or 2, of those 2" rates bc the low tracks differently than you expect or the column takes longer to saturate than you think, you're sol. With a storm like this, it's kinda lumbering and that makes it harder to bust. The PG is impressive--will be interesting to see what type of warning (*ahem*, if a warning) is hoisted. That all said, this is Philly, my above axiom stands vis a vis the models' ability to prognosticate a major event that doesn't happen. A lot of historical data points to this being a good setup. Air travel is still down though (# flights): weather data from aircraft are fed into the models as part of their initialization. I also tangentially think that climate change may be (possibly) hurting model performance. Your basic assumptions have to change a bit when the energy budget shifts (e.g. less energy coming through atmos can get back out to space). I'm sure modelers are factoring that in, but, cursorily, I have noticed a trend for models to be more finicky the last several years than in the past, and I do wonder if climatic effects are partially responsible. Anyway, looks promising, but I'm not gonna start letting model variability and run to run updates consume my life till tmrw night.

I'm almost certain everyone knows this, but the "precipitation depiction" pane on RadarScope also shows the R/S line as well. Similarly, hydrometeor classification is very helpful. I know everyone has their own "go to" radar services for different events so I just want to share in case anyone reading this (member or not) wanted another tool to look at.

18z nam is definitely an improvement for my area. 500 mb heights down substantially, better CCB positioning.

Well, yeah, I *do* agree that if a model is showing a 1:10 ratio for SEPA for this storm, regardless of which one, that's not credible. Sometimes, Kuchera does go ham --when the conditions aren't so marginal--and can indeed overdo things substantially. Here though, I honestly think the "main story" is, the models are, collectively, shifting the storm North. They're doing that due to the Canadian HP traveling more E than previously forecast, so the expected strong block in place that would preclude a negative NAO from shoving a low into the coast, is not progged as being as influential, so the tucked in solutions end up working more. I don't think the Kuchera ratios were wrong relative to the dynamics the models in question forecasted earlier on. They weren't 1:10. The maps I have with 1:10, and in this thread, show 18-20+" in Philly consistently. Kuchera is more in the 10-15 range. Both seem high now, but Kuchera was lower. The thing I am disputing is that "kuchera inflates the totals". At best, it isn't deflating them enough. Euro may have incorrectly parameterized the column temp, sure. Again, not an issue with the method itself though, and the theory behind it. Final point (unrelated to Kuchera): the storm isn't here yet, and won't peak until tomorrow night for this forum's area. The trends are bad, the fat lady has left her dressing room, but she is not yet at the microphone. In other words, trends are bad. They will keep oscillating, one way or another.

Mkay gotta correct the record here. Kuchera totals are used because they calculate how TEMPERATURE affects RATIOS. Sometimes, that results in greater than 1:10, but NOT always. Here, the Kuchera ratios have been *consistently* less than the 1:10 ratios. Therefore, Kuchera ratios are NOT giving falsely high amounts. If anything, the 1:10 maps do that. Let's check out how: Ratio= 12 + 2(271.16K-T_max), when Tmax is >271.16K. Note, 273.15K=0C; 1 degree increment C=1 degree increment K. Ratio = 12 + (271.16K-T_max), when Tmax is <271.16K. Cool. So, the max temp in the column here is between 1 and 1.5 degrees C. 273.15+1=274.15, 273.15+1.5=274.65. Let's plug that in. 12+2(271.16-274.15)=12 MINUS 2*3...12-6....SIX. 1:6. Kuchera ratios are not the problem. GFS Kuchera ratio for hour 42, 12z run, attached, for PHL. Please note, I am not "defending the models" here, or trying to claim the city will see more snow. I'm mainly saying, there's a lot of claims of Kuchera being pointless. It isn't. It takes 1:10, which is the forecast equivalent of using the 540 line as your rain snow line, and makes it more scientifically precise by calibrating it to the situation. Right or wrong, the Kuchera method itself is not the problem.

They were on point at the time they issued that forecast. Subsequent runs have been more dicey. Some proprietary mesoscale models still show more snow farther south. There is very strong hp. Hard to see the low make it as far inland as some of the models currently take it. Being a good met means looking at the physics, not just the models. Models have utility but they're a tool, not THE forecast. Plenty of times on this forum the models have said BIG STORM and then, poof, nothing, and everyone on here went along with it. Conversely, sometimes situations outperform the models. In closing, unless you are currently working as a paid met, please sitith thy butt down, and stop critiquing those who studied and do this professionally.

Haha, I believe we have but not certain. 2009-2013ish. Larry's friend.. I did the senior project involving northeastern storm chasing.