ace0927 Posted January 31, 2011 Share Posted January 31, 2011 I agree with your thoughts especially regarding the shallow cold air and the deep warm layer, but your marker is centered over Buoy 5545. the second I posted in located in Westchester Link to comment Share on other sites More sharing options...
LocoAko Posted January 31, 2011 Share Posted January 31, 2011 I agree with your thoughts especially regarding the shallow cold air and the deep warm layer, but your marker is centered over Buoy 5545. Yeah, you have to be careful with those Twister sites. The "point and click soundings" sound great, but the grid spacing on them is huge. You'd have much better luck typing in your coordinates into the Plymouth site to make your own 3-hourly soundings... Link to comment Share on other sites More sharing options...
Zir0b Posted January 31, 2011 Share Posted January 31, 2011 Mt.Holly has issued Winter Storm Warnings for NYC's western and southwest burbs. (Morris/Middlesex/Somerset) THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY HAS ISSUED A WINTER STORM WARNING FOR A WINTRY MIX OF PRECIPITATION, ESPECIALLY ICE... WHICH IS IN EFFECT FROM 11 PM THIS EVENING TO 4 PM EST WEDNESDAY. THE WINTER STORM WATCH IS NO LONGER IN EFFECT. * PRECIPITATION TYPES: SNOW TONIGHT WILL MIX WITH SOME SLEET AND OR FREEZING RAIN ON TUESDAY DAY. A WINTRY MIX OF SLEET AND FREEZING RAIN IS EXPECTED TUESDAY NIGHT AND THEN TRANSITION TO ALL FREEZING RAIN WEDNESDAY MORNING AND POSSIBLY PLAIN RAIN DURING THE DAY ON WEDNESDAY BEFORE ENDING. * ACCUMULATIONS: CONFIDENCE IS LOW AS TO ACCUMULATION AS THEY ARE PRECIPITATION TYPE DEPENDENT. BEST ESTIMATE IS FOR 2 TO 4 INCHES OF SNOW AND SLEET. OF GREATER IMPORTANCE ONE THIRD TO TWO THIRDS OF AN INCH OF ICE IS LIKELY TO ACCUMULATE ON TREES AND WIRES AS WELL AS UNTREATED ROADWAYS. * TIMING: THE PRECIPITATION SHOULD OVERSPREAD THE REGION CLOSE TO MIDNIGHT TONIGHT. THERE WILL BE A LULL IN THE PRECIPITATION INTENSITY DURING TUESDAY AFTERNOON AND EVENING BEFORE HEAVIER PRECIPITATION MOVES BACK IN OVERNIGHT TUESDAY AND WEDNESDAY MORNING. PRECIPITATION SHOULD TAPER OFF WEDNESDAY AFTERNOON. * IMPACTS: TRAVEL WILL BECOME DIFFICULT IN THE REGION FROM LATE TONIGHT THROUGH WEDNESDAY AFTERNOON DUE TO SNOW AND THEN ICE. ICE WILL ACCUMULATE ON TREE LIMBS AND UTILITY WIRES FROM TUESDAY NIGHT INTO WEDNESDAY. WIDESPREAD POWER OUTAGES ARE POSSIBLE. THE TUESDAY MORNING COMMUTE WILL BE IMPACTED BY SNOW. THE TUESDAY EVENING COMMUTE SHOULD BE EASIER BECAUSE OF THE EXPECTED LULL IN THE PRECIPITATION INTENSITY. THE WEDNESDAY MORNING COMMUTE WILL BE EXTREMELY DIFFICULT DUE TO THE ICE. THIS EVENT SHOULD BE OVER BY THE TIME OF THE WEDNESDAY EVENING COMMUTE. Link to comment Share on other sites More sharing options...
ace0927 Posted January 31, 2011 Share Posted January 31, 2011 Yeah, you have to be careful with those Twister sites. The "point and click soundings" sound great, but the grid spacing on them is huge. You'd have much better luck typing in your coordinates into the Plymouth site to make your own 3-hourly soundings... yeah- you have no idea how many times i tried to get closer! either way, if the NAM is right we are going to have serious flooding issues...unfortunately our snowpack is going to take a very large hit Link to comment Share on other sites More sharing options...
gkrangers Posted January 31, 2011 Share Posted January 31, 2011 yeah- you have no idea how many times i tried to get closer! either way, if the NAM is right we are going to have serious flooding issues...unfortunately our snowpack is going to take a very large hit Good street parking is becoming a pain. Link to comment Share on other sites More sharing options...
meteorjosh Posted January 31, 2011 Share Posted January 31, 2011 Just to clarify, 18z NAM gives no snow to NYC as 850s outrun the start of precip, sleet for a while but a quick turn to rain. Again the high to the north is the key, there's a gap in the banana, with one 1032 sliding off the east coast and the large western high's 1032 isobar not reaching much further east than western NY state's longitude. If that gap is real watches will become WWAs for much of Upton's forecast area. Don't mean to upset people but these the facts with THIS model (and a few others haha). Link to comment Share on other sites More sharing options...
earthlight Posted January 31, 2011 Share Posted January 31, 2011 Tons of atmospheric processes ongoing if you take the 18z NAM verbatim over Western Union county (using my backyard as an example). You can see that this is, by definition, a southwest flow event. Almost the entire atmosphere down to the 850-900mb level has screaming southwest winds. There's a very strong push of mid level warm air advection around 900-925mb which does make sense given the primary so far northwest and the warm air advection regime in place aloft. Still, cold air drainage is so strong given the ageostrophic flow positioning that the low level cold wedge is able to remain stout for several hours. At this hour (39hrs) there's heavy precipitation over the area and it's likely falling in the form of pounding sleet. By 42 hours the warm layer becomes so wide that it encompasses an area from 800mb to 925mb. The low level cold wedge in the boundary layer is still there with northeast winds, but that's not going to be enough. It is at this point where the depth of the warm layer becomes important. You're not going to maintain frozen precipitation with that warm layer depth..and the heavy precipitation and marginal surface temperatures suggests ice accretion won't occur easily. So this is likely a bit of snow, over to pounding sleet and then rain...which may be icy on the roads in spots. Further north and west, you have more significant problems as the cold wedge becomes more significant. <br><br><br> Link to comment Share on other sites More sharing options...
ag3 Posted January 31, 2011 Share Posted January 31, 2011 Just to clarify, 18z NAM gives no snow to NYC as 850s outrun the start of precip, sleet for a while but a quick turn to rain. Again the high to the north is the key, there's a gap in the banana, with one 1032 sliding off the east coast and the large western high's 1032 isobar not reaching much further east than western NY state's longitude. If that gap is real watches will become WWAs for much of Upton's forecast area. Don't mean to upset people but these the facts with THIS model (and a few others haha). How is it rain when surface temps are in the 20's thru hour 42 and barely 32 at hour 45? And .75"-1" of liquid has fallen. Link to comment Share on other sites More sharing options...
earthlight Posted January 31, 2011 Share Posted January 31, 2011 How is it rain when surface temps are in the 20's thru hour 42 and barely 32 at hour 45? And .75"-1" of liquid has fallen. Read my post in regards to the depth of the warm layer. I've seen rain fall with temperatures in the lower 20's. It has much more to do with the process ongoing aloft and the depth of the mid level warm air nose. Link to comment Share on other sites More sharing options...
Kaner587 Posted January 31, 2011 Share Posted January 31, 2011 Just to clarify, 18z NAM gives no snow to NYC as 850s outrun the start of precip, sleet for a while but a quick turn to rain. Again the high to the north is the key, there's a gap in the banana, with one 1032 sliding off the east coast and the large western high's 1032 isobar not reaching much further east than western NY state's longitude. If that gap is real watches will become WWAs for much of Upton's forecast area. Don't mean to upset people but these the facts with THIS model (and a few others haha). Until you show me text soundings that have NYC above 32 before hour 45, this post is completely bogus. Link to comment Share on other sites More sharing options...
EasternLI Posted January 31, 2011 Share Posted January 31, 2011 It seems like the NAM has a weaker/further north HP thus the warmer scenario. Once again, the HP will ultimately dictate the final result in our area. Link to comment Share on other sites More sharing options...
ag3 Posted January 31, 2011 Share Posted January 31, 2011 Read my post in regards to the depth of the warm layer. I've seen rain fall with temperatures in the lower 20's. It has much more to do with the process ongoing aloft and the depth of the mid level warm air nose. Understand that John. But NAM has at least .50" of liquid when NYC is 25 degrees. That is ICE. When surface is 25 degrees, it freezes. 30-32, yes. But when its 25-29, freezing will be widespread. Link to comment Share on other sites More sharing options...
ace0927 Posted January 31, 2011 Share Posted January 31, 2011 NYC and LGA are in the 20's thru hour 45 with .75"-1" fallen. After this period, only .25"-.50" of rain fall. That is no where near flooding concern. Text soundings will show surface temps in the 20's. I'll post them when available. ive seen them..its 34.2 in NYC at 48hrs Link to comment Share on other sites More sharing options...
uofmiami Posted January 31, 2011 Share Posted January 31, 2011 18Z NAM FOUS at LGA: LGA//463362 00822 323605 29979294 06000624066 01322 320609 31979295 12000768066 01120 310909 33979396 18004979364 03610 260814 37989800 24018978866 01103 210414 42990400 30004947547 -0106 200313 44980302 36001958266 01908 210410 43970001 42033979667 08910 140819 47990002 48063995519 01203 030415 46000502 Link to comment Share on other sites More sharing options...
meteorjosh Posted January 31, 2011 Share Posted January 31, 2011 How is it rain when surface temps are in the 20's thru hour 42 and barely 32 at hour 45? And .75"-1" of liquid has fallen. I should have written "liquid", my point is simply that the warm layer will be significant enough to melt whatever is falling, thus rain, whether it accretes or not is another question, but according to the NAM, rain it will Link to comment Share on other sites More sharing options...
Chris L Posted January 31, 2011 Share Posted January 31, 2011 A slighty off topic, but it regards to what John said, the thermal profiles aloft determine whether we have good snow ratios and bad ratios, you can't say that 25 degrees and snow equals a slightly better than 12:1 ratio; the surface temps mean nill unless ALL the thermal profiles are well below zero, for example during the 2003 President's Day snowstorm, which had temps near five degrees and warmed up to 26-27, still had sleet mixed in due to the mid level warm advection push. Same for the 1996 blizzard as well, huge mid-level advection pushed the total snowfall slightly downward, epesically near PHL. Link to comment Share on other sites More sharing options...
Kaner587 Posted January 31, 2011 Share Posted January 31, 2011 Read my post in regards to the depth of the warm layer. I've seen rain fall with temperatures in the lower 20's. It has much more to do with the process ongoing aloft and the depth of the mid level warm air nose. you obviously know a heck of a lot more than I do but last night when a couple of the mets were posting about the storm, I'm not sure who but one of them commented on one of your comments regarding rain and below freezing temps, suggesting maybe that you weren't completely correct regarding your analysis. I don't remember if you responded but you clearly haven't changed your tune. I'm wondering if you remember the post I'm talking about? Link to comment Share on other sites More sharing options...
IsentropicLift Posted January 31, 2011 Share Posted January 31, 2011 Obviously Mt. Holly has gone with warnings so they must think the 18z NAM is too warm. My WSW text reads 4-10" of snow followed by 0.25" - 0.75" of ice accumulation, and I'm only a half hour west of NYC. Link to comment Share on other sites More sharing options...
killabud Posted January 31, 2011 Share Posted January 31, 2011 what happen to the snowpack "absorbing" cold rain...its not like its going to be in the 40's..not much of a flooding risk is there? Link to comment Share on other sites More sharing options...
NorEaster27 Posted January 31, 2011 Share Posted January 31, 2011 Read my post in regards to the depth of the warm layer. I've seen rain fall with temperatures in the lower 20's. It has much more to do with the process ongoing aloft and the depth of the mid level warm air nose. yea its called freezing rain, I have seen zr at temps in the low teens. Link to comment Share on other sites More sharing options...
LocoAko Posted January 31, 2011 Share Posted January 31, 2011 Tons of atmospheric processes ongoing if you take the 18z NAM verbatim over Western Union county (using my backyard as an example). You can see that this is, by definition, a southwest flow event. Almost the entire atmosphere down to the 850-900mb level has screaming southwest winds. There's a very strong push of mid level warm air advection around 900-925mb which does make sense given the primary so far northwest and the warm air advection regime in place aloft. Still, cold air drainage is so strong given the ageostrophic flow positioning that the low level cold wedge is able to remain stout for several hours. At this hour (39hrs) there's heavy precipitation over the area and it's likely falling in the form of pounding sleet. By 42 hours the warm layer becomes so wide that it encompasses an area from 800mb to 925mb. The low level cold wedge in the boundary layer is still there with northeast winds, but that's not going to be enough. It is at this point where the depth of the warm layer becomes important. You're not going to maintain frozen precipitation with that warm layer depth..and the heavy precipitation and marginal surface temperatures suggests ice accretion won't occur easily. So this is likely a bit of snow, over to pounding sleet and then rain...which may be icy on the roads in spots. Further north and west, you have more significant problems as the cold wedge becomes more significant. <br><br><br> Good post John, but I'm just curiouis why you think this wouldn't accrete? Temperatures in the mid-to-near-upper-20s should let it freeze, especially if there is snow on surfaces to help the ZR stick to. I don't know much about it admittedly, but I assume the intensity and related latent heat release would only become an issue once you get to the 31/32F range. No? Link to comment Share on other sites More sharing options...
ace0927 Posted January 31, 2011 Share Posted January 31, 2011 And? at 48 there is nothing left. LGA soundings are 29 degrees at hour 42. http://68.226.77.253/text/meso/NAM_Klga.txt at 45 it slightly above freezing.... Link to comment Share on other sites More sharing options...
Stormlover74 Posted January 31, 2011 Share Posted January 31, 2011 Unless the heaviest part of the storm falls in the form of plain rain I dont see much flooding with temps barely squeaking above freezing. Even .75" of liquid with a temp of 34 would mostly get absorbed. Melting yes but nothing like losing 20" of snow overnight with temps in the 50s like in '96. The greater risk is down the road if we keep adding moisture to the snowpack and keep getting significant snow events. Eventually we will warm up and rain and if that happens in a short period of term with a still frozen ground thats when we have issues. what happen to the snowpack "absorbing" cold rain...its not like its going to be in the 40's..not much of a flooding risk is there? Link to comment Share on other sites More sharing options...
ag3 Posted January 31, 2011 Share Posted January 31, 2011 LGA soundings are 29 degrees at hour 42 and .50"-.75" of liquid has fallen. How is that not a lot of ice? Link to comment Share on other sites More sharing options...
ag3 Posted January 31, 2011 Share Posted January 31, 2011 at 45 it slightly above freezing.... I posted that 8 posts ago. So the .50"-.75" that falls thru hour 42 is not significant icing? I still dont understand your point. Link to comment Share on other sites More sharing options...
Dosh Posted January 31, 2011 Share Posted January 31, 2011 Good post John, but I'm just curiouis why you think this wouldn't accrete? Temperatures in the mid-to-near-upper-20s should let it freeze, especially if there is snow on surfaces to help the ZR stick to. I don't know much about it admittedly, but I assume the intensity and related latent heat release would only become an issue once you get to the 31/32F range. No? Intensity of the precipitation combined with the temperature of the rain thats falling. if the air is +5C (41F) 3-5,000 feet above the ground, it may only cool one or two degrees before it hits the surface, not giving it enough time on cooled surfaces such as trees and powerlines to freeze before it runs off. If the warm layer were thinner or cooler, we would see much more accretion, but the strength of the warm air advection is just too strong. Link to comment Share on other sites More sharing options...
winterwarlock Posted January 31, 2011 Share Posted January 31, 2011 Obviously Mt. Holly has gone with warnings so they must think the 18z NAM is too warm. My WSW text reads 4-10" of snow followed by 0.25" - 0.75" of ice accumulation, and I'm only a half hour west of NYC. I dont think they took into consideration the NAM before their disco. I think they are going bullish so people dont get caught off guard and more for the ice than anything else. I think its unlikely that Central Jersey gets the 2-4 they are forecasting. There should be some sort of special ice advisory I think that makes more sense in situations like this Link to comment Share on other sites More sharing options...
ace0927 Posted January 31, 2011 Share Posted January 31, 2011 18Z NAM FOUS at LGA: LGA//463362 00822 323605 29979294 06000624066 01322 320609 31979295 12000768066 01120 310909 33979396 18004979364 03610 260814 37989800 24018978866 01103 210414 42990400 30004947547 -0106 200313 44980302 36001958266 01908 210410 43970001 42033979667 08910 140819 47990002 48063995519 01203 030415 46000502 so its over 0C at 800 and 900mbs from 24hrs...so there is no snow and it doesnt get over 0C at the surface until sometime between 42-48....but the 99 (-1) at 42 indicates that ZR wouldnt be a huge issue Link to comment Share on other sites More sharing options...
RU848789 Posted January 31, 2011 Share Posted January 31, 2011 Mt.Holly has issued Winter Storm Warnings for NYC's western and southwest burbs. (Morris/Middlesex/Somerset) THE NATIONAL WEATHER SERVICE IN MOUNT HOLLY HAS ISSUED A WINTER STORM WARNING FOR A WINTRY MIX OF PRECIPITATION, ESPECIALLY ICE... WHICH IS IN EFFECT FROM 11 PM THIS EVENING TO 4 PM EST WEDNESDAY. THE WINTER STORM WATCH IS NO LONGER IN EFFECT. * PRECIPITATION TYPES: SNOW TONIGHT WILL MIX WITH SOME SLEET AND OR FREEZING RAIN ON TUESDAY DAY. A WINTRY MIX OF SLEET AND FREEZING RAIN IS EXPECTED TUESDAY NIGHT AND THEN TRANSITION TO ALL FREEZING RAIN WEDNESDAY MORNING AND POSSIBLY PLAIN RAIN DURING THE DAY ON WEDNESDAY BEFORE ENDING. * ACCUMULATIONS: CONFIDENCE IS LOW AS TO ACCUMULATION AS THEY ARE PRECIPITATION TYPE DEPENDENT. BEST ESTIMATE IS FOR 2 TO 4 INCHES OF SNOW AND SLEET. OF GREATER IMPORTANCE ONE THIRD TO TWO THIRDS OF AN INCH OF ICE IS LIKELY TO ACCUMULATE ON TREES AND WIRES AS WELL AS UNTREATED ROADWAYS. * TIMING: THE PRECIPITATION SHOULD OVERSPREAD THE REGION CLOSE TO MIDNIGHT TONIGHT. THERE WILL BE A LULL IN THE PRECIPITATION INTENSITY DURING TUESDAY AFTERNOON AND EVENING BEFORE HEAVIER PRECIPITATION MOVES BACK IN OVERNIGHT TUESDAY AND WEDNESDAY MORNING. PRECIPITATION SHOULD TAPER OFF WEDNESDAY AFTERNOON. * IMPACTS: TRAVEL WILL BECOME DIFFICULT IN THE REGION FROM LATE TONIGHT THROUGH WEDNESDAY AFTERNOON DUE TO SNOW AND THEN ICE. ICE WILL ACCUMULATE ON TREE LIMBS AND UTILITY WIRES FROM TUESDAY NIGHT INTO WEDNESDAY. WIDESPREAD POWER OUTAGES ARE POSSIBLE. THE TUESDAY MORNING COMMUTE WILL BE IMPACTED BY SNOW. THE TUESDAY EVENING COMMUTE SHOULD BE EASIER BECAUSE OF THE EXPECTED LULL IN THE PRECIPITATION INTENSITY. THE WEDNESDAY MORNING COMMUTE WILL BE EXTREMELY DIFFICULT DUE TO THE ICE. THIS EVENT SHOULD BE OVER BY THE TIME OF THE WEDNESDAY EVENING COMMUTE. Actually, Mt. Holly issued two WS Warnings, a more severe one for Morris/Sussex/Warren and the Lehigh Valley/Poconos, where they expect 4-10" of snow/sleet, followed by 0.25-0.50" of freezing rain and possibly no plain rain, and a less severe one for the next tier of counties (Middlesex, Somerset, Hunterdon, Mercer, Bucks, Berks, Montgomery and Chester), where they expect 2-4" of snow/sleet, followed by 0.33-0.66" of freezing rain (and then some plain rain with temps above freezing). WW Advisories are up for the next tier to the S/E of there. http://forecast.weather.gov/showsigwx.php?warnzone=NJZ007&warncounty=NJC041&firewxzone=NJZ007&local_place1=Blairstown+NJ&product1=Winter+Storm+Warning http://forecast.weather.gov/showsigwx.php?warnzone=NJZ012&warncounty=NJC023&firewxzone=NJZ012&local_place1=Edison+NJ&product1=Winter+Storm+Warning Link to comment Share on other sites More sharing options...
Zir0b Posted January 31, 2011 Share Posted January 31, 2011 freezing rain can occur even if the surface temperature is above freezing. Since we will be well below freezing prior to any change to plain rain and if you take into account the deep frozen snowpack, ice accretion WILL occur on colder and elevated surfaces including trees/powerlines/etc. I don't expect any icing on the main roads though. If the ground temperature is warmer than 0 C but the air temperature is colder than 0 C, then heat conduction may prevent freezing on the ground/streets, but freezing will occur on elevated cold surfaces, i.e., trees, power lines, and cars. If the ground is frozen, then freezing rain can occur despite air temperatures above 0 C (at least for awhile). http://www.crh.noaa.gov/lmk/soo/docu/precip_type.php Link to comment Share on other sites More sharing options...
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