psuhoffman

Actually it's warmer than the GGEM, pushes the 850 about 20 miles further NW than the GGEM.

AIFS is not a disaster...but over the last 24 hours it went from being one of the best solutions to now maybe the worst at 12z. Its 8-9" for DC and Baltimore...about 10" up here. Jack zone shifted quite a bit to our NW. Looks similar to GGEM with track and thermals

12z AIFS is significantly NW and warmer...

Just one damn time...

This... I mentioned this after Mitch posted the 6z UK ensembles...the UKMET 10-1 snow maps counts sleet as snow so they are inflated on the southern end. Can't compare them to other models that don't do that...it gives the false impression the UK is further south than it is...if you just look at those maps...which you shouldn't anyways

I've been using that storm as a guide here but displaced 75 miles south or so...very similar but the thermal boundary is a little further south this time.

The GFS doesn't see mid level thermals as well as the Euro or NAM...that is a known thing

It definitely won't see the mid level warm layers as well as the euro/nam when we get closer... but could it be correct about a less amplified system? Sure. Would I stake anything I care about on it...no.

mod to heavier precip would be I would think...light stuff mix but who cares. We know the drill

GFS is noise level changes...as close to a "hold" run as you will ever see at this range

I was somewhat giving you a hard time...but Frederick is in a shadow zone between the Catoctins and Parrs Ridge and doesn't do as much better than places closer to 95 as you would think. Places closer to DC and Baltimore like Damascus and Mt Airy actually do better.

If you moved to Frederick for snow purposes...umm...we need to have a talk

Oh that RGEM was a significant improvement and was 90% snow for us on that run...we ride the mix line for 12 hours BUT its rate dependent, during dry slots its sleet and the snow line sinks south during heavier periods...and even during lighter periods the mix line never gets more than a few miles NW of us...1 degree colder and it's 100%...a huge improvement from 12 hours ago! BUT...that stuff you see to our SW won't make it here...we are about to dry slot at the end of the run and its over. The stuff in WV and OH won't make it across the mountains because with the primary going to our NW the flow ill be out of the west and downsloping and the mid level dynamics are going to our NW so there won't be anything to cause additional precip.

It's the high res version of the GFS so....

the mid level low is tracking pretty far NW to hope for any meaningful snow on the back end. Typically we need that to be tracking over us or to our south for that to work out...its tracking well to our NW. Unless we see that change I would not really put any stock in any significant snow on the back end.

That post was specific for northern MD and southern PA. Closer to 95 the warm layer is a bit more significant the last 6 hours.

@TSSN+ @mitchnick @HighStakes The warm layer at the end of the NAM is really thin and only around +1 around h7 for our area, it shows as sleet but heavy enough precip would be able to mix that out...it would probably still be a mix of snow/sleet depending on intensity through the end of the run up here...the dryslot was coming soon after anyways.

I never even looked at its 6z run lol

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