psuhoffman

It also happened up here in March 2018 with the front running WAA snow....models had that flipping to sleet up here after only a couple inches and it stayed heavy snow through the whole WAA thump and we got about 8" before the dry slot when we got snizzle until the ULL associated stuff that got the whole area with 4-8" the next day.

There is a closed mid level low over Missouri and the winds are screaming out of the SW at h85 and h7 so.... For us to stay snow south of the MD/PA line we really need less phasing and a less amplified wave to our west. The 50/50 is sliding out not locked in, the block is centered over northern Greenland, its not suppressive enough to offset a phase system that far to our west like that. For the amplitude the NAM has we would need a more suppressive look over top. But...even with this we can get a really nice thump snow before any mix, and the NAM could be overdoing the warming during the heavy precip some...that does happen sometimes the dynamic cooling can overcome the WAA and mix out the warm layer longer than expected...we've seen this so many times. Dec 2013, Feb 2014, Feb 2015. It hasn't happened as much recently because we've either been warm or cold and dry the last 9 years lol. It is also still possible to get a less amplified wave like the GFS and some of the EPS members show. And frankly most of the globals are slightly less amplified also. This primary cutting to our west was my worst case scenario 48 hours ago but I said even in that case we would still be looking at 6"+ of snow to ice...and it looks like that's holding as the worst case we've seen across guidance...which isn't a bad floor to have.

It’s been several years so I’m not sure if this is still true but I know at one point t the UK ensembles were counting ice as snow which inflated their output. That kinda looks like it still does.

Only thing I don’t get is everyone loves the 18z NAM and 0z is colder/flatter and more seem to be upset with it.

0z Nam at 78 is colder/flatter than 18z NAM. I don’t think the exact position of the Baja low matters that much assuming it does eventually eject most of the energy. The confluence matters but the ridging does also. One can offset the other. I think the ridging matters more. There is plenty of cold. Less southerly flow matters more. I think perhaps the most important and hardest to predict factor is the interaction with the two NS shortwaves, one over the top and the other coming in behind. The icon had one of those features gone and phased fully with the other and that’s why it went off the rails. Looking across guidance the handling of those features seems to be the most significant determinate.

Yea I see several offsetting thing. Less amped phases STJ wave more a stronger NS vort. Slightly less confluence to our north but less ridging to our south and a slightly flatter flow heading in. There is more than one variable. Can’t make definitive conclusions based on what one variable does.

EPS didn’t really move from my early look

Isn’t that the case usually? When we see these shifts inside 100 hours it seems to usually be related to NS features which are harder to resolve anyways and are diving down from sparsely sampled regions.

Ok this is not me being a weenie, yes it sucks BUT as we get closer it does eventually have to find the right solution and now it looks like the AIFS which is the best model lol. And the icon sucks even more. Ok pep talk over

I’ll feel better about everything if we clear 0z tomorrow night without major changes.

12z was really south though. 850s never get north of the northern neck

I don’t expect it. Just that’s the only way I can see this going completely devastatingly wrong.

the do sometimes but there is still a tendency to amp more the final 36-48 hours so we need this to stop stat and get maybe a bit of a south trend to give us room for what is likely to be a bit of bleeding north at the end.

Nothing shows this right now so this is purely me thinking “what could go wrong” and the only way I see Maryland not getting at least a warning level event from this would be if the wave splits and there is a front runner WAA wave that targets VA south of us then the main wave amplifies and cuts and we end up in between.

Looks similar to 12z ggem

so far 18z (NAM/ICON) coming in with slightly better confluence in front of the system and a flatter flow over the top. Not major changes but we don't need major changes. These changes are showing up at 48 hours which is a pretty believable range...if we see this continue across 18z guidance it would be a significant step in the right direction of avoiding the over amplified solutions.

one is simulated radar and the other is the previous time period precip, different things tend to show...different things

The 18z NAM is better than the 12z and was about to obliterate us...and that is the end of my analysis of the NAM at 84 hours.

it's super light... DC starts to lose thermals at 1pm and only gets like .15 QPF after that. 95% of the precip falls before the thermals get problematic then hours and hours of very light freezing rain

Once it's in range...I would trust the NAM over other guidance with the thermals and precip type zones associated with that. Not at 84 hours...but once were close. Especially the 3k. It's the only thing I do trust the NAM with over other guidance.

Chuck was comparing the 18z NAM to the 12z GFS, which is apples to oranges IMO but he isn't looking at what the rest of us are looking at...which explains the "what is he seeing" stuff. The 18z NAM is less phased and has more confluence in front than the 12z NAM through 60 hours.

FYI, when you do analysis of a model run, everyone assumes you are comparing it to its previous run. If you are comparing it to a different model you have to say that or no one will know what you're talking about...even more than normal.

heavy precip is over there...they go to mix during the light precip that lingers after the WAA thump...the dryslot stuff. DC doesn't actually lose much QPF to mix on this EC run...it was close...but they held the thermals through the crazy heavy precip then warmed immediately after...which is common.

Yea we won't see those 18-1 crazy ratios...BUT...QPF tends to overperform in those crazy WAA driven thumps so it actually tends to be a wash (in terms of snowfall performance compared to modeled QPF. In one case we overperform due to rations in the other because of QPF.

Thanks... heavy precip holds off the warming...which is normal in these type setups...so we don't actually lose that much qpf to the mix...the thump is mostly snow even in DC according to that