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NYC/PHL Jan 18-19 Potential Threat Thread


am19psu

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12z GFS ensemble mean is west of the op run. It is a coastal hugger.

Is there a potential for a major ice storm in my area?? It seems as if some mets are starting to pick up on it. Ice is nasty in many regards especially considering power outages and downed trees. It would be even more worrisome as it's going to get really cold behind the storm meaning the ice wouldn't be able to thaw enough before it froze.

What are the chances(remember I do not like on the coast and I live about 125 miles to the NW of I-95) that it's snow instead of ice?

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I am pretty much in agreement with you. If the 500mb ends up as depicted by current modeling, it would defy laws for this primary to cut. The difference maker in my opinion is however that the primary could still achieve enough northward advancement to allow enough WAA and rising hghts ahead of it that it becomes to warm for the secondary. If you look at the GFS it has this large strung out primary that has moisture stretching a great distance from S to N, simply because it doesn't know where to send the energy. It will more likely be one consolidated LP, and if it is able to slide S and E under the confluence then it brings in colder air as it hooks up with the LP in the SE US. Problem right now is they remain two seperate distinct LPs.

yep... agreed.

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Is there a potential for a major ice storm in my area?? It seems as if some mets are starting to pick up on it. Ice is nasty in many regards especially considering power outages and downed trees. It would be even more worrisome as it's going to get really cold behind the storm meaning the ice wouldn't be able to thaw enough before it froze.

What are the chances(remember I do not like on the coast and I live about 125 miles to the NW of I-95) that it's snow instead of ice?

In my opinion.. the chances of a widespread freezing rain issue decreases as the chances for a consolidated coastal increases. With freezing rain, you basically want a large scale southwesterly flow over-riding a very shallow cold layer right near the surface, however, with a coastal in the area, it is going to have a tendency to draw in more of a northerly wind component as a low pressure between the surface and 850 mb develops.. so, if anything, I think the chances of sleet would be higher as the warm layer in the atmosphere decreases enough to where the precip can refreeze before getting to the surface. If we are talking about more of a warm frontal passage just to your south trying to progress northward, I would definitely say that freezing rain is more likely.

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Well there's def going to be a lot of low level cold air around so this isn't just a plain cold rain event. If the low level cold air gets even stronger, than a widespread sleet or freezing rain event is likely. If more emphasis is placed on the coastal and the low out west is much weaker, than maybe we'll get snow out of it. Still, the coastal has to be offshore, it can't hug the coast or we're still screwed.

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In my opinion.. the chances of a widespread freezing rain issue decreases as the chances for a consolidated coastal increases. With freezing rain, you basically want a large scale southwesterly flow over-riding a very shallow cold layer right near the surface, however, with a coastal in the area, it is going to have a tendency to draw in more of a northerly wind component as a low pressure between the surface and 850 mb develops.. so, if anything, I think the chances of sleet would be higher as the warm layer in the atmosphere decreases enough to where the precip can refreeze before getting to the surface. If we are talking about more of a warm frontal passage just to your south trying to progress northward, I would definitely say that freezing rain is more likely.

But how serious is this ice storm threat? .25 to .50 is not to bad anything over .75 is serious. I agree nothing is worse than 1 inch of ice and a cold front blowing through with no power.. Everyone has forgotten about the sleet storm of 2007 in the same general area that is being discussed - a storm that was not forecasted to be sleet . Somebody better wake up and the smell the roses. Instead of discussing the chances of coastals and snow, lets discuss the chances of a serious ice storm from ABE to Hazelton. Frankly, I am tired of hearing about the chances of lows developing along the coast and snow chances in NYC when the real threat is an ice storm in the LV to Scranton. Thanks

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But how serious is this ice storm threat? .25 to .50 is not to bad anything over .75 is serious. I agree nothing is worse than 1 inch of ice and a cold front blowing through with no power.. Everyone has forgotten about the sleet storm of 2007 in the same general area that is being discussed - a storm that was not forecasted to be sleet . Somebody better wake up and the smell the roses. Instead of discussing the chances of coastals and snow, lets discuss the chances of a serious ice storm from ABE to Hazelton. Frankly, I am tired of hearing about the chances of lows developing along the coast and snow chances in NYC when the real threat is an ice storm in the LV to Scranton. Thanks

I'd say the chance for .25 - .50 of sleet is fairly decent... but not a blockbuster ice storm. I'd be concerned if I saw a 1040 mb high sitting just north of us and all of this precip headed our way on the heels of a slow warm frontal passage, with light due, northerly winds at the surface and a screaming south wind from 925 mb and up..

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I am just worried that a 'tunnel' forms between the HP over C/NW Canada and the HP sliding east OTS off the coast, and the primary tracks through this area of "weakness". Problem with that is if a secondary does indeed develop this would favor a warmer/closer to the coast solution. I am really just hoping we avoid appreciable precipitation and wait till the cold comes back and legitimate snow chances arise.

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NWS NYC forecast:

Monday Night: A chance of snow, mainly after midnight. Cloudy, with a low around 24. Chance of precipitation is 50%.

Tuesday: Snow likely before 9am, then snow and freezing rain likely between 9am and noon, then rain likely after noon. Cloudy, with a high near 40. Chance of precipitation is 70%.

Tuesday Night: A chance of rain. Cloudy, with a low around 33. Chance of precipitation is 50%.

Wednesday: A chance of showers. Partly sunny, with a high near 40. Chance of precipitation is 30%.

NWS EWR forecast:

Monday Night: A chance of snow, mainly after midnight. Cloudy, with a low around 24. Chance of precipitation is 50%.

Tuesday: Snow likely before 9am, then snow and freezing rain likely between 9am and noon, then rain likely after noon. Cloudy, with a high near 40. Chance of precipitation is 70%.

Tuesday Night: A chance of rain and snow. Cloudy, with a low around 32. Chance of precipitation is 50%.

Wednesday: A chance of rain and snow showers. Partly sunny, with a high near 40. Chance of precipitation is 30%.

Talk about cutting it close.

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CTP Tamaqua forecast.

County text version:

MARTIN LUTHER KING JR DAY...PARTLY SUNNY. HIGHS IN THE LOWER 20S.

NORTHEAST WINDS AROUND 5 MPH...BECOMING SOUTHEAST.

.MONDAY NIGHT...A WINTRY MIX LIKELY. LITTLE OR NO SNOW

ACCUMULATION. NOT AS COOL. NEAR STEADY TEMPERATURE IN THE LOWER

20S. CHANCE OF PRECIPITATION 70 PERCENT.

.TUESDAY...RAIN OR FREEZING RAIN LIKELY. NOT AS COOL WITH HIGHS IN

THE MID 30S. CHANCE OF PRECIPITATION 70 PERCENT.

.TUESDAY NIGHT...CLOUDY WITH A CHANCE OF SNOW OR RAIN SHOWERS. LOWS

IN THE MID 20S. CHANCE OF PRECIPITATION 30 PERCENT.

Point & click version:

M.L.King Day: A slight chance of snow after noon. Partly sunny,

with a high near 21. Calm wind becoming southeast around 5 mph. Chance

of precipitation is 20%.

Monday Night: Rain and snow

likely. Cloudy, with a low around 19. Chance of precipitation is 70%.

New precipitation amounts between a tenth and quarter of an inch

possible.

Tuesday: Rain likely. Cloudy, with a high near 37. Chance of precipitation is 70%.

Tuesday Night: A chance of rain and snow showers. Cloudy, with a low around 24. Chance of precipitation is 30%.

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Current Wxsim forecast timing breakdown for the upcoming wintery event for the NW Philadelphia suburbs

Light Snow arriving by midnight with a temp at 22.8

IP/SN mix continuing at 6am temp 25.4

IP/ZR mix at 9am temp 28.0 (0.29" qpf thru this point)

ZR continues for most of the rest of the storm with one hour between 3 and 4 tuesday where temps get to 32.5...they then begin to slip back with ZR continuing (0.66") of ZR falls

Total precip (most frozen is 0.96") here in Chester County PA

NWS point forecast

Monday Night: Snow, mainly after 9pm. Low around 22. Chance of precipitation is 90%.

Tuesday: Snow before noon, then rain. High near 38. Chance of precipitation is 80%.

Tuesday Night: A chance of rain. Mostly cloudy, with a low around 29. Chance of precipitation is 50%

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The 12z GFS depiction portrays two areas of LP, which will have a large impact on the forecast for our area. What has become more and more apparent with time is that models continue to show some resemblance of blocking upstream, which allows for confluence to remain over the area for longer. This area of HP prevents the primary low in the OV from cutting like originally anticipated and instead stalls its northward progress, and as the GFS shows almost pushes it E under the HP. The current depiction stills allows enough northward progress so that hghts ahead of the primary rise on the east coast associated with WAA. That is the reason why even with the GFS having a good coastal track it remains a bit warm, as some have asked. The primary steals the show essentially. What we need to see progressing forward for this solution to become more favorable is increased confluence remaining over the region in association with the psuedo 50/50 which prevents the primary progression N. I see a few possible outcomes. The primary is squashed and phases into the secondary allowing the cold air to flow into the region with secondary cycologenisis. Another outcome would be the LP in the SE US simply moves OTS and the LP over the OV moves into the area in a clippper like fashion with a fresh blast of cooler air, but no connection between the two systems occurs. Or third, models are overestimating the blocking and confluence and the primary cuts allowing for significant WAA and a nice soaking.

I disagree with the idea that there is a resemblance of blocking upstream. In fact, the upper air pattern throughout Greenland and Baffin Island as well as Northeast Canada is very poor--heights are very low with low height anomalies even on the GEFS means. The confluent flow is there initially but is allowed to escape due to the lack of blocking all together.

There is the potential for some initial surface cold air to hang on, especially inland, and provide the possibility for some ice/snow and wintry mix initially. But the below depicted height pattern is not one which allows for any type of significant wintry precipitation given the degree of warm air advection occurring at all levels of the atmosphere.

post-6-0-67186600-1295115037.png

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