WxUSAF

Snow line showing up very well on correlation coefficient radar product. Looks like the line is along Harpers Ferry-Frederick-just west of mappy's house.

The 12K NAM was replaced by the 3k NAM several years ago for a reason. The 3k is probably worth looking at starting with tomorrow's 12z run.

Repeat this week in prime climo season and it's the best week since Feb 2010 for most places. Just sayin'.

NWS take looks pretty good to my eyes

Woohoo! I'm in the "assload" zone!

5 days out: everyone sets unreasonable lower bound expectations based on the best model run 2 days out: everyone jumps when they realize it’s not going to be a HECS for them 1 day out: most people accept reality and realize yes, it’s going to snow 4-8 hours out: radar hallucinations 1 day after: everyone’s happy and can’t wait to get the next storm every. Single. Time.

I'm not convinced there's any trend at all. It's wobbling back and forth for the reasons I and others have laid out. 6z Euro wobbled left, 6z RGEM wobbled right. And these moves are so small in reality, even if it did "trend" left for 4 runs, a bump right on tomorrow's 12z runs could easily happen that would put it right back where it started. This (and other reasons) is why snowfall forecasts always have ranges.

At this range the Op runs are much prioritized and you really never should use ensembles snowmaps for prime forecasting methods. I know we all look at them but it's not what ensembles are for. Op Euro, GGEM, and GFS all give us a really nice storm. It's going to wobble back and forth a little and then come down to mesoscale/microscale features in the end like it always does on final snow amounts. But the goalposts have narrowed and stayed in place pretty much for the last 48-72 hours. There's no primary to Cleveland or Miller B screw job on the way. It's not suppressed or OTS. It's a coast-running Miller A in mid-December. Thermal gradient is more onshore than it would be in January-March due to the water temp and respectable, but unremarkable, cold airmass ahead of the storm. Give me that basic information alone and I think I could give you a snow forecast that would be pretty reasonable for most of the area...

Nice place for us.

Every model, even the GFS, has this baggy area of low pressure stretching from onshore to well offshore as it approaches and pass our latitude. Where the "L" gets put on the surface map isn't always a fine science. All comes down to how convection plays in (we really won't know this until tomorrow or Wednesday) and where the surface low starts to get stacked with the upper level energy. That later detail just keeps wobbling just onshore and just offshore.

I really, really want that CCB. Seems like the front half of the storm is pretty well set for MBY. 3-5" of snow+sleet.

Seems like we've seen 0z/6z euro runs bump NW and then 12z runs move SE. All-in-all, these are ultimately small differences, even if this was 24hrs before start time, but it obviously makes a big difference to most of us in snow totals.

Good thread from @tombo82685 on Twitter. I wonder if the weaker s/w is a reflection of more complete sampling now that it's onshore?

40N/70W is the classic location from the KU book for major east coast snow storms. That's past our latitude, but when it's at the benchmark a storm is usually about to hit NYC and Boston.

After 6z Thursday it really doesn't gain much more latitude. Just moves ENE out to sea. That's very nice for us. Better chance the CCB cranks overhead and then snows itself out as the storm moves away. Some of the runs where the CCB is much farther north into the Poconos and NY state had the storm moving toward the benchmark and farther NE.

Ha, that little dot in eastern Howard County is the higher terrain near Howard High School. Gets up to 500-600' on that hill. That's like 2-3mi from my house as the crow flies.

18z EPS has the surface low in exactly the canonical spot, ~50mi off OCMD, at 6z Thursday. Don't overthink things. Use the ensembles the way they're supposed to be used for, not agonizing over 5-10mi wiggles in 10:1 snow maps. Going forward now, we can start seeing mesoscale effects like thermal profiles and banding.

Let's do this same thing again in a month with temps 5-10F colder please

If there's any time to try and hold onto snow cover, it's 5 days before the solstice...

Mt. Holly hoisted watches

You just want all of us to see how you're in the 20"+ zone

Oops, you accidentally left me off the list!

He's still around some, but lives just across the PA border now.

Present from @mitchnick. 18z GGEM liquid equivalent precip that falls as snow. @mappy jackpot, but all of central and north MD is solid. http://meteocentre.com/numerical-weather-prediction/precipitation-accumulation.php?lang=en&map=qc&run=18&mod=gemglb&hi=000&hf=120&type=SN&mode=latest&yyyy=latest&mm=latest&dd=latest&capa_verif=off

84hr CIPS analogs to the 12z GFS. Some absolute classics on here: http://www.eas.slu.edu/CIPS/ANALOG/DFHR.php?reg=EC&fhr=F084&rundt=2020121312&map=thbCOOP72