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2/20 -2/22 Storm Threat Discussion


Zelocita Weather

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51-54 hours a decent hit up to Philly--very sharp cutoff

DC and ACY take a big hit at 54 hours, very impressive, and just when people down there were giving up on this winter. It's possible some areas of Central NJ could jackpot by hitting both events if the trends continue with the first wave being colder and more suppressed, and the second wave gradually shifting northwards. Looking at the 6z NAM at 48 hours, it looks as if the precipitation shield in SW PA/WV wants to expand northeast and normally would, but the progressive flow at 500mb isn't allowing much amplification. It doesn't appear as if there's too much of a southerly wind direction in the upper levels, so it won't be as juicy as a regular SW flow event, both due to lack of WAA and the first storm depleting some of the energy.

Im suspicious too, but its good that most of the guidance is trending south-- so hopefully this isnt just a blip lol.

SW flow events often bump northward at the last minute, with the sleet line advancing further than people expected...I remember this well in the V-Day 2007 storm when sleet made it all the way up to near Middlebury, VT despite few forecasts indicating that there would be mixing at that latitude. NYC also lost quite a few inches of snow in 08-09 with SW flow events that jumped north at the last second, allowing the 0C 850 line to crawl just a bit north of the city...lots of close calls that winter including 12/19, 12/21, and 1/28. We might see a hybrid 07-08/08-09 pattern in the next couple of weeks with the -PNA being dominant but having lots of cold air to our north due to the Alaska block (-EPO) and associated confluence hanging tough over Quebec/Ontario.

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DC and ACY take a big hit at 54 hours, very impressive, and just when people down there were giving up on this winter. It's possible some areas of Central NJ could jackpot by hitting both events if the trends continue with the first wave being colder and more suppressed, and the second wave gradually shifting northwards. Looking at the 6z NAM at 48 hours, it looks as if the precipitation shield in SW PA/WV wants to expand northeast and normally would, but the progressive flow at 500mb isn't allowing much amplification. It doesn't appear as if there's too much of a southerly wind direction in the upper levels, so it won't be as juicy as a regular SW flow event, both due to lack of WAA and the first storm depleting some of the energy.

SW flow events often bump northward at the last minute, with the sleet line advancing further than people expected...I remember this well in the V-Day 2007 storm when sleet made it all the way up to near Middlebury, VT despite few forecasts indicating that there would be mixing at that latitude. NYC also lost quite a few inches of snow in 08-09 with SW flow events that jumped north at the last second, allowing the 0C 850 line to crawl just a bit north of the city...lots of close calls that winter including 12/19, 12/21, and 1/28. We might see a hybrid 07-08/08-09 pattern in the next couple of weeks with the -PNA being dominant but having lots of cold air to our north due to the Alaska block (-EPO) and associated confluence hanging tough over Quebec/Ontario.

That would suck this late in the season if we didnt get a -NAO building in and if we had that kind of pattern, Id put NYC chances of breaking the snowfall record at less than 5%. We all know how paltry the snowfall totals were in those winters and the only reason 08-09 was decent was the rogue coastal in March. There's still hope this trends more like 55-56, as that had a positive AO that trended strongly negative after the first week of March, and this would save us from an 07-08/08-09 type of pattern.

Im hoping for a 2/22/08 type event, which stayed mostly snow, otherwise SWFE are mostly boring in our area, unless you include Feb 1994, but that event had a much colder airmass to work with.

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There is a good reason the 1st wave is trending south and the 2nd wave north on the 6z NAM/GFS/RGEM. They move the polar vortex faster to the east, similar to what the UKMET has been showing for a while (and what the 0z Euro showed).

The polar vortex is just N of VT/ME by the time first wave moves across the Mid Atlantic, so it gets suppressed south over southern NJ. However, by the time the 2nd wave moves across the Mid Atlantic, the polar vortex is already over Nova Scotia, which allows more room for the 2nd wave to amplify and track further north.

Weird that "Option D" looks to be happening here-- opposite trends on both waves, both favorable for us, like Feb 1994. Maybe Miketroll was onto something -- or more like on something lol.

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There is a good reason the 1st wave is trending south and the 2nd wave north on the 6z NAM/GFS/RGEM. They move the polar vortex faster to the east, similar to what the UKMET has been showing for a while (and what the 0z Euro showed).

The polar vortex is just N of VT/ME by the time first wave moves across the Mid Atlantic, so it gets suppressed south over southern NJ. However, by the time the 2nd wave moves across the Mid Atlantic, the polar vortex is already over Nova Scotia, which allows more room for the 2nd wave to amplify and track further north.

Its about the most classic example of threading the needle imaginable...basically how the 2/6/10 storm came up the coast at the worst possible moment these two systems tracks across the area at exactly the right time, the first as the PV suppresses it and then the 2nd after the PV is already too far east.

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I love Upton...but once in a while they don't get it..."rain for Monday in Stamford CT"...I will be stunned if that comes to pass....

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I would go at least 5F colder for Mon's high temp than Upton is. Their forecast is 41 at LGA, 39 at ISP, 37 at White Plains.

Hmmm they have LGA warmer than Islip and youd think LGA should be cooler, being on the north shore. But with this storm trending colder, looks like we might all have highs in the low 30s.

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I was surprised they did not give themselves any leeway by going to a watch first...if the 12Z runs or 00Z ones come in juicier they may need to upgrade some counties to warnings...especially Orange county where I say an advisory level only snow event is a rarity. I agree on not going to a watch yet in NYC since its been a snowy winter already and a small shift takes the area out of any major snows.

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The cold air source is positioned to the NE in this storm, while the warm air is advancing from the SW. So it makes sense that ISP would be colder than LGA.

Hmmm they have LGA warmer than Islip and youd think LGA should be cooler, being on the north shore. But with this storm trending colder, looks like we might all have highs in the low 30s.

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One of those storms with a major discontinuity brewing between Upton and Mt. Holly. 2-3" on the snow maps for Union County and SI a few miles to my north and east, yet <0.5" on the snow map for Middlesex County. Pulling for Upton's forecast, lol.

Mount Holly's text forecast also doesn't match the modeling -- ie. they have Sussex County NJ as 1" to 3" of snow, then slop with less than an inch additional. I suspect much will hinge on the 12z runs (as per normal course when updating the evening forecast packages). However, you would think they'd already be forecasting possible amounts in excess of 4", perhaps up to 6"+ for some spots, especially higher elevations and far north. If the 12z runs come in drier and/or warmer, they'll hold course. Otherwise, I'd be very surprised if they don't increase snowfall amounts, even if things are status quo on the modeling. Sometimes you wonder what they're thinking, especially given that it's a holiday on Monday and a heavier travel day for some (ie. college students driving to/from home for a long weekend). A 6" snowfall is quite a bit more disruptive than a 1" to 3" event and there seems to be enough data already to suggest those higher numbers are valid in some areas.

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One of those storms with a major discontinuity brewing between Upton and Mt. Holly. 2-3" on the snow maps for Union County and SI a few miles to my north and east, yet <0.5" on the snow map for Middlesex County. Pulling for Upton's forecast, lol.

Northern Middlesex County north of the raritan river should be in upton's territory and included in the eastern union county forecast - because if you look at a map of the county in certain situations you could have 6 inches north of the raitan river and the southern part of the county gets 1 inch because the snow rain line many times sits on a line from Perth Amboy through Trenton and the raritan river before the coastal plain is a natural geographical boundary - notice how the models have the snow rain line right there through much of tonights event.....

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Anytime you have these back to back systems within less then 24 hours of one another the modeling is going to adjusted upstream after the 1st one passes so don't be surprised that the 6Z and 12Z models shift in either direction tomorrow and I would say considering how the north trend has begun the 2nd system shifts more north and most of NYC area gets a last minute warning event ................

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So would this be viable? 2-5 inches from event 1 (wet snow) and 6-10 inches (powder) from the second event. 5 boros and Nassau county locations. If we get a March 2011 HECS such as a greater than 20 inch blizzard, we should be able to break the century mark for seasonal totals across the entire area. I think it is quite doable. Do you think we get banding from one of these events yielding 1" per hour snowfall.

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So would this be viable? 2-5 inches from event 1 (wet snow) and 6-10 inches (powder) from the second event. 5 boros and Nassau county locations.

I was thinking 2 -3 tonight and 4 - 7 tuesday with better ratio's .......on the modeling it wouldn't take much - 50 - 75 mile north trend to get NYC in the heavier precip and the trend is north so far but of course that could change when you are dealing with less then 75 miles either way at 48 hours out on the second event - what is the error range in miles for these models ?

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FWIW JB just tweeted he is going with the UKMET which is further north

http://twitter.com/BigJoeBastardi

http://raleighwx.ame...bTSLPp06060.gif

JB will go with anything -- JMA, Korean model, any model -- that shows the most snow for the most population. It's called looking for any model that fits. Not the way to forecast accurately but a good way to get web hits.

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