Update, 7 PM: 100,000 are now without power, according to Fox 29. Snow continues at a moderate clip across South Jersey, with light to moderate snow continuing in Philadelphia and points north and west. We should see things wind down after 9 PM in Philadelphia, towards midnight in South Jersey. It may snow lightly past 9 in Philadelphia and the burbs but precipitation should begin to slowly wind down across the immediate city.
Here's a really
good satellite loop of the storm over the past few hours, taking its sweet time working east slowly (like a turtle almost).
Update, 6 PM: Wind and snow continues through the region, with about
30,000 without power according to PECO at this time. Wind gusts over 35 mph are occurring in Delaware and South Jersey and will continue for the next several hours. Snow may begin to diminish slowly over the next 2-3 hours across the region but the winds will continue to remain gusty through the night. We're up to 17" here in Royersford and I'll assume Philadelphia will be around 14-16" at 7 PM when the snowfall update is provided. You can continue to get updated (when the NWS can) snowfall totals
at this link.
Update, 5 PM: Heavy snow is continuing to work southeast into and through the Philadelphia area. Heavy snow is also breaking out across Central and South Jersey as well. We'll see this continue over the next couple of hours and then slowly begin to wind down from west to east across the region. Snow in the heaviest bands will fall at almost a two inch per hour rate -- I'm at 14.2" as of 4 PM with snow still falling out there.
Winds are picking up at the Airport, along the river into South Jersey, and across Delaware with gusts to over 35 mph. We'll see winds continue to pick up over the next few hours across the city and northern burbs as the storm pulls way and this weak trough responsible for the heavy snow pulls out.

Update, 4 PM: Radar is going to town across the north and western suburbs as a heavy band of snow has fired up and rotated around from Central Jersey. This band will work down through Pottstown and into Chester County over the next couple of hours and then slowly wind its way back into South Jersey.
Across South Jersey, a dryslot is hindering snowfall across your area but the bands to the north will gradually wind back around and through South Jersey. They may not be as heavy as they are now across Bucks and Upper Montgomery Counties but you will see the snow pick up again around or just after 5 PM. Snowfall in these areas is accumulating at an inch or two inches per hour, with some isolated areas getting more than that.
Update, 2:30 PM: Snow is continuing and it is heavy at times in spots. The winds are also gusting and in spots are gusting to over 30 mph. In the last hour, wind gusts are to 32 in Millville and at Philadelphia International, higher than that to the south of Philadelphia. The stronger wind energy with the storm system is working to the south of Philadelphia across Delaware and South Jersey. Around the northern and western burbs, winds will be gusty at times but the blizzard criteria wind speeds may not be reached for a while. We'll see things crank up further as the afternoon progresses -- it is taking a bit longer for winds to pick up around here but as the storm continues to intensify and the remainder of its energy coalesces offshore we'll see the wind energy crank into the region.

1 PM Update: So, yeah, this thundesnow thing is moving through due to a convergence zone that has developed (wind shift line, boundary line) across the city and Main Line. This boundary si slowly working eastward and is allowing for reports of thundersnow across Philadelphia and now into Lower Montgomery County. As it works east, I would not be surprised to see it work into Lower Bucks, Northeast Philly, and then towards Trenton in the next 1-2 hours.
Philadelphia is still getting blitzed with snow but this convergence zone is helping to reduce some of the snow thumping that was taking place across Chester County. When I say some it's not as heavy -- still coming down at a good clip in places.
Philadelphia's snowfall total is now 8.8" for the storm.

Update, Noon: Snow is really starting to work its way back into the region and picking up in intensity. Philadelphia is reporting heavy snow at Noon and the sleety/sloppy mess across the Northeast and across Bucks is now gradually transitioning over to snow as well. Snowfall is coming down at an inch per hour in spots, with some two inch per hour totals occurring in the heaviest bands.
While blizzard like conditions aren't occurring now in Philadelphia, winds will gradually worsen through the afternoon in the city. Winds along the Jersey Shore are gusting to over 35 mph and winds down near Washington have been gusting to over 40 mph. We will see winds continue to pick up through the afternoon, with significant worsening of road conditions and in the weather over the next several hours as snow picks back up in the second phase of the storm. Again, in some spots some locations will see 1-2" per hour rates. If you have not, I would suggest you get out and shovel now while temperatures are around freezing as the snow that has fallen earlier was wet and almost concrete like. As temperatures slowly drop, the heavier and wet snow layer will freeze up and become much harder to shovel and clear up.
Update, 10:30 AM: Snow has really picked up in the past hour or so across the western burbs, as has the wind,. We're getting occasional but not frequent gusts over 20 mph with moderate snow falling. Philly, you will get your snow and it's slowly working its way towards you. A band of more steadier precipitation is lifting northwest along the AC Expressway and that should work its way into Philadelphia around 11:30 or Noon...we should see the sleet/slop finding turn back over to snow and things will pick up from there.
Look at the temperatures down around DC -- currently in the lower and middle 20's with biting wind chills. The storm is bombing out and strengthening rapidly but it takes a little bit of time for the colder air to work in everywhere...it also does not help the dryslotting issues raised their ugly head this morning from Philadelphia on east. However, snow will increase in intensity as we work into the afternoon.
Update, 9:30 AM: Winds are really cranking up down the Shore and to our south. We'll see winds increase as we work into the midday hours. Around Philly, if you're getting sleet and light precipitation, it's due to mild air that's still aloft in the atmosphere. As heavier bands of precipitation work over you, they will mainly fall in the form of snow as the precipitation drags colder air down from aloft to the surface. You may see light sleet/snizzle (lull) and then moderate snow and then light sleet/snizzle (lull) for a time for the remainder of the morning as these waves of heavier precipitation lift northwestward from the developing coastal storm. Pressures with the developing coastal are continuing to drop...generally down into the low 29's (29.15" at Millville at 9 AM, equivalent of a low end Category 1 hurricane). We won't see hurricane force winds on land but as the storm continues to intensify we will see winds increase significantly in the next few hours.
Update, 8:30 AM: Banding of snow is starting to increase to the south of Philadelphia, working northward into the city and western suburbs. This is the first signs of the heavier banding of snow that should break out over the next few hours across the city. As of 8:15 the radar is showing that heavier banding along the NJ Turnpike and near Route 40 in Salem County and other patchy heavier areas of snow in Delco and near Flourtown. You can see a bit of a dryslot working up the coast in Central Jersey and another one down near Cape May. The snow bands should organize more as they work northward into the city and western burbs and I would not be surprised to see the dryslot down south work north up the coast a bit later on this morning.
Update, 7 AM: In my backyard, we're at 4.8" of snow and things have transitioned back to snow from a couple of hours of wintry slop. We'll see that transition continue over the next couple of hours from west to east. I'm also watching lighter areas of rain try to sneak up the Delaware coastline towards South Jersey. I don't expect that to work into Philadelphia but it may sneak up the Jersey coast a ways over the next few hours before the afternoon kicks in and snow picks up at the Shore.

Update, 6:30 AM: I have to admit defeat and when to throw in the towel on lower snowfall totals. I've bumped my totals and think we're going to see 14-22" from Philly on north/west through the suburbs back through Lancaster and east through Central New Jersey once the storm ends.
This is not new snow but is total snow including the 3-7 that has fallen across much of the region last night and this morning. In other words, the region should pick up around a foot, maybe a notch more, of snow later today from the incoming snowfall across the region later on this morning. Last night's snow burst was greater than expected and pretty much drove myself into bustogenesis territory. Best to admit defeat, throw in the towel, and fall in line with the rest than go it alone and go down with the ship when you know the ship is sinking.
Anyways, note that snow is breaking out in Maryland (see my earlier update) and that precipitation is slowly transitioning back from a wintry slop across Maryland's Eastern Shore and across the DC area to snow...we'll see that transition continue to work east slowly over the next few hours, reaching the Philly and our part of the I-95 corridor around 9 or 10 AM.
Update, 5:30 AM: Radar depicts a some "lull" going on across the Delaware Valley as warmer air aloft and at the surface has worked on in. We're going to see a wintry slop at times during the morning hours during the lull, with that wintry slop having covered more of the region than anyone had expected. That's ok...the slop won't eat much into your snowfall totals but it will compact your snowcover down a bit.
Between now and around 9 or 10 AM we should see this slop continue in Philadelphia, with the slop continuing towards Noon at the Shore. After those mentioned timeframes the transition to snow will begin to take place, with conditions worsening after midday into the afternoon.
Yes, we are under a blizzard warning but that doesn't mean we'll see blizzard conditions right out of the gate this morning. Blizzard conditions are more likely from midday on through the duration of Wednesday from Philadelphia on north and west and then from the early afternoon on east of the Delaware River. Blizzard conditions are defined as low visibility due to blowing snow and very strong winds in excess of 35 mph sustained or frequent gusts.
Round two of the storm may ultimately bring more damaging impact to the region in the form of power outages and general impact to travel and livelihood as the storm's winds, snow, and slowly falling temperatures will help slicken things back up. The "good" thing from the current slop that is falling is that it is compacting the current snowpack in place and will make that less prone to whip around when winds pick up. Unfortunately, the snow in round two will compensate for that as it will be a fluffier snow and more powdery than what fell last night. With the higher winds around we should see that snow whip around a fair bit.
Watch the areas down by Washington back to Hagerstown over the next few hours on radar and see the snow fill in down there...assuming that takes place, that will be the afternoon main course. That should work through and drop another significant round of snow this afternoon.
Update, 5 AM: Got
some sleep and am waking up to see that a blizzard warning is in place for much of the region for the day today. We're in the "lull" part of the storm this morning as milder air as crept into parts of the region, leading to freezing drizzle, sleet, freezing rain, or even rain from Philadelphia on south and east, with some sleet mixing in across the suburbs. Last night's snow burst dropped a general 3-7" across the region and was more impressive than I expected...at this point I admit it's likely my snow totals across the region are going to be too low and really thought the first round was going to be more of a dud than it was. I'm in the process of reviewing the rest of last night's computer modeling and current surface trends to confirm that this will be a bust for me or if there is anything I can hang my hat on lol
I'll be back with an update regarding the rest of this morning and the blizzard warnings we are under in a little bit...
Update, 9 PM: Watching precipitation continue to blossom over Virginia and Maryland with the developing coastal. Snow is falling just about everyone with the exception of the coastal Delmarva, where some sleet and freezing rain are mixing in at Ocean City and Salisbury. I would expect some of the warmer air aloft to work northward but at this point modeling from the NAM is shying away from Philadelphia getting in on the mix...it does approach the NJ Turnpike though but it seems to be trending away. Sleet/mix is still an issue at times later tonight in South Jersey (Millville-Atlantic City down). Philadelphia at 9 PM is reporting heavy snow. The 2-4 for north/west /1-3 for the city discussion for earlier is probably to be more like 2-4 for most...if not more.
Update, 8 PM: Precipitation over the past hour or two has broken out in additional coverage across Virginia and Maryland and is lifting northeast. Snow is being reported throughout parts of the Delaware Valley and we should see light to at times moderate snow continue through the evening and tonight from Philadelphia on north/west. Precipitation will pick up but milder air should work up the coast (at least aloft if not at the surface in some locations), resulting in a sleet mix or rain at the immediate coast. Washington has picked up a couple of inches so far and here in Royersford a dusting of snow has accumulated. We'll see this first batch continue on through overnight before a lull sets in towards morning...with the main course tomorrow.
Update, 7 PM:

I've updated snowfall totals slightly after some significant thought and hemming/hawing over the dryslot/mix issue. I still think it's significant but I have increased totals to 9-15" in Philadelphia and points just south and east of Philadelphia. One thing I did was increase the snowfall totals slightly to reflect higher ratios with the backside of the storm as the heavy band of snow develops (assuming it's as expected). Snow should be powdery with relatively higher ratios (12 to 1 compared to the standard 10 to 1), which is why I've nudged the totals up a notch.

The first part of a one-two pop is starting to work on into the western portions of the region. Tonight's first nudge of precipitation will be minor in nature and will not bring huge accumulations at first as energy between the incoming storm and the southern energy are just beginning to interact.
There are two mitigating factors for snow accumulation tonight to the south and east of Philadelphia. One, this is not bringing a ton of precipitation to begin with and the relatively weak amount of precipitation should allow for milder air to sneak on in aloft from the Delaware River on south and east. To the north and west, snow should be light to moderate overnight.
Precipitation will start over the next couple of hours here in Philadelphia. Accumulations tonight across the region will range from 2-4" north/west, 1-3" in Philadelphia, and an inch or so south and east. Milder air will result in that changeover from snow to sleet, with rain possible along the coast. In Philadelphia, that sleet area may work in in lighter lulls in precipitation. It won't substantially cut down on your snowfall totals but may knock an inch or so off compared to folks to the northwest.
You may wake up in the morning and wonder what's going on -- well, the main part of the storm will just be firing up. The coastal will be firing up, precipitation will be enhancing and increasing, and the storm will crank up big time after about 7 or 8 AM in the region. North and west of Philadelphia will see snow, heavy at times, with that snow band working into Philadelphia and then working across New Jersey during the afternoon hours. There may be a longer lull EAST of Philadelphia than west due to the potential development of a dryslot along the coast or just inland. If that doesn't happen, snowfall accumulations will be higher than what I'm advertising. This will ultimately be a nowcast setup and will be monitored, especially early tomorrow.
Arguably, the worst of the storm will be between 10 AM and 4 PM on Wednesday, when snowfall rates in Philadelphia and north/west will be an inch per hour or more. Combined with increasing winds from the north at 20-30 mph, blizzard like conditions will result.