Terpeast

IAD is close to flipping at 48 (18z) on HRRR. This is probably the time it flips.

Love the HRRR run. Probably out of its range, but see its trying to start a coastal.

Yes thats snow, but probably with some riming. Think this would give us an hour before fully flipping to sleet

That warm layer on your sounding is 5-10kft. Far above 3,000 but plenty of room to refreeze into sleet

If I had to guess where the true northern extent of the 800-750 warm nose, it would be along the darkest blue line instead of that 0 line on this 700 map. Maybe not even that far.

I think the gfs and euro are meeting in the middle, with the cmc joining them. Starting tomorrow the synoptics should be in place, and we’ll start taking the thermals seriously. Hopefully the NAM is wrong today and shifts colder tomorrow. All we need is a 20-30 mile shift to the cooler side at 700-850, and double digits is in play along and west of the fall line.

I don't know how reliable 3k is with thermal profiles at 51 hours out, but that warm nose really punches through at 750-800 mb. One hour prior to this, it was still left of the 0C line.

Low end map from LWX

Fwiw 3k has the sleet line a tick south at hr 34.

I usually don’t report sleet on top of snow. This time I will, but I’ll take separate measurements to get the snow accum right when it flips, and then get the sleet accum just to differentiate the two when reporting the total. Also given that sleet is counted, the bullish nws forecasts make a little more sense.

RGEM mixes us at the same time/hour as the Euro does. Gives us 10" areawide before mixing. I'll take it!

Here's my first call on what I think is going to happen in our forum. More confidence in a 30 mile corridor along DC/Balt and NW. Less confidence in the SW quadrant of this map (so please don't hammer me if you live somewhere like Roanoke or Cville.

Busy times ahead!

Yep. This is the kind of storm I've often seen when I was a kid. PA gets the most snow while we mix. I was jealous of State College then. But they've had a terrible, terrible run at snowfall in recent years. Like, worse than us.

Sorry, meant 25%. iow, use 75% of gfs values

Just catching up. So the gfs didn’t fully cave, but pretty much all guidance met in the middle. I’d cut gfs accums by 75% though to account for ip/zr. That gets us to 6-10 for dc/balt metros, with a foot being in play for NW suburbs (1-2 counties off from I-95 and north of 50)

Thanks for pointing that out. The 12k and 3k might as well be two different models. May sound like a weenie, but I’d lean more on the 3k within 48 hours of onset.

From the POV of NWS, their mission is to protect life and property. Given a difficult call between forecasting a few inches of plowable snow/sleet and a devastating ice storm, where it could really go either way or have both in the same region, I think they would rather warn people of the worst case scenario. Because if they don’t, and the ice storm happened, that would be a mission failure on their part, and it may cost people lives and property. Yes, there is also risk of a busted ice storm forecast in the eyes of the public, but that would be preferable over the former scenario.

So that’s 4z-12z or 8 hours of snowfall before the flip.

When JB posted that, he just guaranteed the bullish gfs scenario isn’t gonna happen. Thanks a lot JB!

That would be welcome news for S VA if its mostly sleet instead of zr.

Looks realistic tbh, can’t say I have anything to pick at against

Minimum 12 hours of snow for DCA before flip, with progressively increasing intensity.

I was hoping to see some more consensus with either gfs caving to other guidance, or both sides meeting in the middle. But they could not be further apart. We may have to wait until 0z tonight to see where this is heading.

They may be going with a blend of the Euro and GFS. Which isn't entirely unreasonable, just not something we would run with ourselves.