WxUSAF

Gfs has a stronger WAA onset than before with good dendritic growth. I’m right in the R/S line during the evening as depicted with an isothermal profile right at freezing below like 900mb. The snow side of that line cashes in.

I’ll apologize Wednesday evening as needed and not before

For those who forecast by ensemble snow maps...just saw the 12z Eps probability of 6”+. I think MBY has been in the 50% contour on almost every run, maybe occasionally bumping up or down one contour. And today’s run? In the 60% contour. Biggest difference is the gradient has tightened which is what almost always happens as you get closer to start time. Howard county has just under 50% to over 90% across it.

NWS forecast looks a lot like 12z euro. More N-S gradient in MD due to how much snow falls after the flip back to snow. I like the NWS map although it’s maybe a little bullish on the 12-18” area size.

Yup confirmed.

Thanks for that tidbit, that’s excellent news. Solid advisory criteria even before the flip, even for the beltway.

Spoke to @Bob Chill via email. He and his family are healthy and well. He’s been busy with work and it’s covid impacts and changes. He doesn’t expect to post anymore but may in the future. He still lurks a bit.

Nice! Still rain here. Your new house paying off!

Ha same thought. 3” of snow, 1” of sleet, and 2-3” of snow on top? All in.

I would need hourly output to see how long the mix period is. But seems like we’d probably get a few inches on the front? Then lots of sleet, then a couple inches at the end. Sign me up.

Track is west but it’s also colder. If you’re forecasting by 10:1 snow maps you’ll like the euro. 925 stays below freezing west of 95. 850 freezing gets up toward the M-D line so sleet for much of us for a time. I’d take the euro in a hot second.

Same at 54. A bit colder than 0z

CC line has wobbled back north. Probably losing some of the best lift as the storm pulls away?

CC line has jumped south so that fits.

It can be hard to interpret. Definitely helps to orient yourself with direct surface obs for reference. The CC product will be very useful Wednesday.

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.