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NYC/PHL Jan 18-19 Potential Threat Thread


am19psu

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Disagree. By what Earthlight/Tombo said last night, the cold air was no where near any of us. The Canadian is very close to be a nice even for us. Cold air is close, but no cigar this run.

It looks as if the GGEM would start as snow here and then change to rain, north of NYC in the suburbs. The 540m thickness line is right over NYC so it's a very close call. This event could produce a lot of headaches especially with the current snowpack and cold temperatures.

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You're talking about the snowpack as if it's all fresh snow. Underneath the snow that just fell, there is a layer of rock hard snow. That's not going anywhere fast.

Here is my opinion:

1. The snow pack along the major cities such as Newark, New York and maybe Philly if it rains, there will be urban flooding from the standing water from the melting of this snow pack and the fact that storm inlets are still blocked with snow.

2. Basements will flood because the ground is frozen and there is no place for the rain and snow melt runoff to go except in the lowest spot-- a basement. That will be one of the major problems we will hear throughout this storm event

3. The rivers will not flood. Why? Because as one poster has already said, there is no snow in the Poconos, Catskills (where the Delaware River Watershed is located) . The Raritan River may reach flood stage but that is a big maybe at this point unless we get 2 inches of rain

4. Everyrone has forgotten that many of the major stream and rivers are currently frozen. Ice jams could be a major problem resulting in flooding if it gets to warm.

5. Freezing rain is a good bet with this type of storm. Power outages are a possibility. But the worst ice storms occur when the rain falls on the backend of the storm and the cold front moves in too quickly. This is a warm frontal freezing rain event. Even though it will freezing rain, it may warm up enough to melt before it causes major problems. I guess we will see how this plays out

6 A good thump of snow for LV and north on the front end of the storm is a good bet. This is typical of these type of storms

7. This storm is a now cast storm based on the type of precip expected to fall

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the GGEM looks like a quick snow to mix event, even in the immediate suburbs of the big cities. While we go slightly above 0C at H85, the low takes a good track and there is a high in a good position on the GGEM, albeit somewhat weak. I would think in a setup like the GGEM shows, there would be a prolonged period of IP/ZR not far away from the coast due to the low level cold air that would stay in place.

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The Current Wxsim module forecast for the NW Philadelphia burbs for Monday

Snow arriving by noon with 2" (0.19") of snow accumulating by midnight when the snow will change to an IP/ZR (0.25" qpf) mix that will fall till around 9am on Tuesday morning. Heavy rain (1.23") before ending Tuesday night.

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If you look at the 12z GFS and most guidance what I believe will play a large roll will be this weekends clipper disturbance. What is evident on the 12z GFS is that this weekends shortwave creates some resemblance of "blockiness" which prevents the area of HP from slipping out as quickly. This allows colder air to remain dominant for a longer duration and delivers a fresh source of cooler air. Some runs of the EURO and GGEM also had some resemblance of blocking, which resulted in a more coastal type track. If you will notice the 12z GFS keeps the primary low that cuts into the OV the main center of attention, but its solution looks a bit wacky considering it continues hour after hour to try and advance the LP into the area of confluence to no avail. This looks suspicious to me as one would expect either secondary development or futher placement S and E. Regardless the 12z GFS still shows a good amount of a 'front end' dump before temps warm at the surface. But like I said the most evident thing on 12z GFS is at 500mb as it now shows some blocking.

What I consider the biggest factor is how much confluence will remain north before sliding out to sea, and whether this weekends shortwave can create some resemblance of blockiness or clutter upstream to prevent a quicker transition. This is what everyone should be looking at and focussing on in future models runs. How stubborn will the cold air be, will any blocking be present, and does the high pressure remain over us for an extended period of time (possibly as a result of the aforementioned factors)? Like many meteorologists in this thread have discussed, I believe there is potential present for front end snows at the least, will see what future model runs bring. We are still a while away from this event and much will change. This winter season seems to be very kind and seasons like this typically tend to be favorable, so at the least I would not be shocked to see a more favorable solution transpire. A lot of factors and influences to keep on eye on which will all have an impact on the eventual outcome.

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through hr 84, the clipper that becomes a pseudo 50/50 is a good bit stronger...trofing over the northeast is stronger...the /s in the south is a little faster..

This is exactly the feature I referenced in my post above. The GFS seemed to develop the clipper into the pseudo 50/50, it is nice to see that the EURO is also doing the same. Considering this was already a borderline event, any resemblance of blocking would be huge. The longer the confluence remains present the better our likelihood of seeing more white then wet.

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