Probably some of the best sundogs I have ever seen.

...Long Island & into southern New England. Even if totals in lesser amounts come to fruition, strong winds producing whiteout conditions will still cause widespread disruptions. A tough forecast for many. Greatest uncertainty? West of I-95 from northern VA to south-central PA.

...with at least 600ft in elevation to work with. DC/Baltimore metro areas & closer to the coast will rely heavily on rates during the day & where bands of the developing coastal low occur. That is what is most unclear in these areas. Jackpot likely to be southern/coastal NJ...

...Northeast MD on north & east. Toughest areas are northern VA, northern MD, & southern PA where they are caught in between the transitioning coastal, & maybe half of the available QPF falls during the day Sunday. That favors elevated areas in these locations. ridge lines...

AM thoughts before 12Z guidance comes in- it is possible we never see guidance come into agreement on a uniform solution. Frankly, it is rare that happens anyway. The meteorology says a rapidly deepening mid-upper low off the coast favors areas along & east of I-95 especially...

Rare late day update to the Key Messages as new guidance continues to trickle in. Confidence is increasing in a highly impactful winter storm Sunday into Monday along the Northeast coast with disruptive snowfall as far inland as the western suburbs of I-95.

WPC has initiated Key Messages for this impending Nor'easter. While confidence in a storm system have increased, exact details on amounts & resulting impacts remain highly subjected to storm track. Continue to follow WPC's and your local WFO's forecast for the latest.

I expect some measurable snow in the Mid-Atlantic with areas east of I-95 favored for the heaviest snowfall, as well as N&W of the 500mb low (eastern PA). Think the WSSI-P Minor probabilities (24hr probs 12Z Sun - 12Z Mon, noting that for southern New Englanders) show that well.

...there is agreement on a 500mb negatively-tilted axis. There's a reason these storms don't happen every winter. Negative tilted storms are hard to come by. Inverted troughs can overperform, but I'd rather be under the deformation axis for heavier snow, & that is still in ?.

Summary-- I am not sold on how much snow falls. We are not at the final solution & it may be another 24 hours until we have a really good clue. However, given the evolution on these systems, I would anticipate a snow-hole somewhere between the Apps & east of I-95 unless...

The past 5 EC-AIFS ensemble runs have been coming in stronger, but lingering spread in how these vorticity maxima behave remains. There are still quite a few members with snow only via the inverted trough, & some with little at all. It speaks to the lingering volatility.

Speaking for the DC/Baltimore area- I would rather have that closed 500mb contour either closer to the NC/VA border, or in the GFS case if it is not fully closed, to be negatively titled. In this case, it is still working towards both by 00Z Mon when the storm is already offshore

Spread in the past 5 EC-AIFS ENS runs has steadily decreased. But where there is lingering spread, it largely comes down to phasing & 500mb trough position & tilt. There is also lingering spread south of Nova Scotia, hinting at ongoing differences in wave separation & confluence.

An exceptional winter storm that has the Carolinas, eastern TN, and northeast GA in its sights will produce a swath of heavy snow, including potential blizzard conditions along the NC coast this weekend.

A major winter storm is set to produce heavy snow, whiteout conditions, and potentially blizzard conditions in parts of the southern Mid-Atlantic this weekend. Impacts stretch as far south as Atlanta & even Savannah. You can read the WPC discussion here: www.wpc.ncep.noaa.gov/discussions/...

The latest Key Messages continue to identify the Carolinas & Southesst VA as facing the worst impacts. Unlike the last winter storm, high winds & blowing snow are a bigger concern, especially along the coasts.

Good morning! Key Messages have begun for the eastern U.S. winter storm.

I left last week to the start of one winter storm, to coming back from my weekend off to another. I try to dive into some of the scenarios & why this weekend forecast is far from a lock: www.wpc.ncep.noaa.gov/discussions/...

This is why there remains such exceptional spread in position & intensity of the storm location. Over the last 24 hours, the only thing that increased in confidence is there is likely to be a strong coastal low. Beaches are likely to take a pounding. Otherwise, a lot of ?s remain

Regarding the East Coast winter storm threat-- 06Z EC-AIFS ensembles still show high spread in a few areas: 1. The shortwave trough placement/amplitude/tilt as it track off the East Coast, 2. suppression feature south of Nova Scotia, 3. trailing shortwave in Central Plains.

That TPV is a huge deal. I am also wondering if the anomalously warm Gulf and Southeast Atlantic warm waters play any sort of role in terms of higher heights than what is currently being modeled. Lots of questions, not many answers at the moment.

Latest WPC post: "Here is the latest information regarding a potentially significant coastal storm this weekend. Chances have increased for impactful snow and/or wind along the immediate East Coast, but uncertainty remains rather high with respect to details. Be sure to keep checking for updates!"

The depth of that low-level cold air is why sleet sticks around for a while. Farther east, along and east of I-95 is where as the day progresses, the warm nose grows larger and the low-level frigid temps warm. That is when we become more concerned for freezing rain.

Also, the dendritic growth zone is saturated but smaller around 500mb and falling into that warm nose. Explains the smaller flakes so many so saw this morning.

12Z Dulles, VA sounding eqrlier this morning. Got family nearby that under 1 hour later were reporting sleet. The warm nose in the 700-750mb layer is the culprit.

"What does a classic freezing rain sounding look like?"

Exhibit A--

Probably one of the busiest weeks of my career. A big thank you to everyone who collaborated with us this week. A thank you to all those who will be in their NWS offices working this event over the weekend. Lastly, thanks to our team at WPC for their hard work this week. Be safe everyone!

Here are the latest Key Messages from WPC which now sport total snow and ice accumulations forecasts.

My "Heavy Snow and Ice Discussion" for the impending winter storm just got posted: www.wpc.ncep.noaa.gov/discussions/...

Here's the updated Key Messages from this afternoon, now highlighting the potential for locally catastrophic ice accumulations. The snow and ice is going nowhere any time soon in the east. In fact, some guidance shows much of the Northeast may struggle to get above freezing before the end of January