snowstormcanuck Posted January 27, 2013 Share Posted January 27, 2013 Whats the QPF to accretion factor for ZR? In non-marginal cases (time of year with strong sun angle, temps right at 32) I've always assumed 1:1. Link to comment Share on other sites More sharing options...
Chicago Storm Posted January 27, 2013 Share Posted January 27, 2013 In non-marginal cases (time of year with strong sun angle, temps right at 32) I've always assumed 1:1. Using a recent event as an example.. With the Jan. 12th ice event here I picked up 0.10" of ice accural off of 0.11" of precip. Link to comment Share on other sites More sharing options...
Hoosier Posted January 27, 2013 Share Posted January 27, 2013 Whats the QPF to accretion factor for ZR? Depends on a lot of things which include ground/object temps, precip rate, raindrop temperature just to name a few. I usually don't assume that the entire amount on those accumulated zr graphics is going to accrete, but sometimes it seems like it's pretty close. Of course that assumes that the modeled precip amount that falls as freezing rain is close to accurate. Link to comment Share on other sites More sharing options...
snowstormcanuck Posted January 27, 2013 Share Posted January 27, 2013 Using a recent event as an example.. With the Jan. 12th ice event here I picked up 0.10" of ice accural off of 0.11" of precip. But the 0.10" of ice was an estimate right? Link to comment Share on other sites More sharing options...
hm8 Posted January 27, 2013 Share Posted January 27, 2013 In non-marginal cases (time of year with strong sun angle, temps right at 32) I've always assumed 1:1. Using a recent event as an example.. With the Jan. 12th ice event here I picked up 0.10" of ice accural off of 0.11" of precip. Depends on a lot of things which include ground/object temps, precip rate, raindrop temperature just to name a few. I usually don't assume that the entire amount on those accumulated zr graphics is going to accrete, but sometimes it seems like it's pretty close. Of course that assumes that the modeled precip amount that falls as freezing rain is close to accurate. fair enough. Guess it makes sense...outside of the amount water expands when it freezes, I guess there'd be no reason for anything but a 1:1 ratio, assuming everything that made it to the ground froze. Link to comment Share on other sites More sharing options...
Stebo Posted January 27, 2013 Share Posted January 27, 2013 fair enough. Guess it makes sense...outside of the amount water expands when it freezes, I guess there'd be no reason for anything but a 1:1 ratio, assuming everything that made it to the ground froze. Late to the party, but I have always gone with 1:1 in non-marginal events like SSC. I would suspect given time of day and forecast temperatures that this won't be marginal until close to sunrise when the temperatures approach 32. Link to comment Share on other sites More sharing options...
Chicago Storm Posted January 27, 2013 Share Posted January 27, 2013 But the 0.10" of ice was an estimate right? Measured. Didn't think we had that much, but it was right on the dot. Link to comment Share on other sites More sharing options...
Thunder Road Posted January 27, 2013 Share Posted January 27, 2013 GFS shows VPZ getting 0.43" before 2 m temps rise above 32 F. http://wxweb.meteostar.com/sample/sample.shtml?text=KVPZ Edit: 0.51" at LOT, 0.48" at ORD. Should mention that 1) I think that is overdone, and 2) if precip rates did end up being on the higher side, that would push actual accrual rates down to less than 1:1, so it kind of ends up being somewhat of a negative feedback loop. Still though, impressive numbers. Link to comment Share on other sites More sharing options...
Thunder Road Posted January 27, 2013 Share Posted January 27, 2013 Contrast the GFS with the NAM (BUFKIT for GYY), which shows only 0.09" of definite accrual (although with another 0.11" falling between 0z and 01z during which time surface temps rise from 0.0 C to 0.2 C, so in reality it's probably suggesting closer to 0.15") Link to comment Share on other sites More sharing options...
Thunder Road Posted January 27, 2013 Share Posted January 27, 2013 What do the pro mets (and other qualified members) think about the claim that even if 2 m temps are slightly above 32 F, the "surface" can still be accruing ice? Link to comment Share on other sites More sharing options...
Hoosier Posted January 27, 2013 Share Posted January 27, 2013 What do the pro mets (and other qualified members) think about the claim that even if 2 m temps are slightly above 32 F, the "surface" can still be accruing ice?We had an event in LAF several years ago where it seemed like we were accreting with 2m temps around 33-34. I know it was late December but can't remember the year. It had been very cold prior to the storm.Edit: I think it was 12/23/08. High temps were in the teens and low temps were near 0 in the 1-2 days prior to the storm Link to comment Share on other sites More sharing options...
Stebo Posted January 27, 2013 Share Posted January 27, 2013 What do the pro mets (and other qualified members) think about the claim that even if 2 m temps are slightly above 32 F, the "surface" can still be accruing ice? It is possible especially after a strong arctic outbreak, though I wouldn't bank on that adding much more to the accretion. Link to comment Share on other sites More sharing options...
Harry Perry Posted January 27, 2013 Share Posted January 27, 2013 00z model guidance is looking frightening to the I-94 corridor from about I-80 north to a GRR to Flint line south… Model spread is now 0.15″ to 0.46″ ice accumulation. If this continues, there will be a sizeable ice storm. Latest guidance also shows temperatures staying below freezing longer until around midday Monday. GFS is giving Battle Creek .39" QPF below freezing. Link to comment Share on other sites More sharing options...
Geos Posted January 27, 2013 Share Posted January 27, 2013 I remember a freezing rain event during late January 1999. After all the arctic air had moved out, there was a system that produced freezing rain, and I remember that it was 33-34° with ice on ground surfaces. Not in the trees, but because of all the snow and cold ground there was ice on untreated surfaces. Link to comment Share on other sites More sharing options...
Thundersnow12 Posted January 27, 2013 Share Posted January 27, 2013 Link to comment Share on other sites More sharing options...
Harry Perry Posted January 27, 2013 Share Posted January 27, 2013 Imagine if there was high pressure over Ontario! lol Oh well then... Didn't see that there. Well just imagine if it was closer ushering a cold East wind in here. Link to comment Share on other sites More sharing options...
turtlehurricane Posted January 27, 2013 Share Posted January 27, 2013 Temperature has stopped rising, now at 23 F with increasing southerly winds. I've never seen a good freezing rain event so I'm hoping this one comes through, it should melt pretty quick anyways. Link to comment Share on other sites More sharing options...
Nelson Posted January 27, 2013 Share Posted January 27, 2013 Actually down a bit out here in Mt. Horeb - were at 22F now down to 19.9F Don't mind a little bit of ice on Sunday as long as it doesn't stick around til Monday (which it looks like it won't) Link to comment Share on other sites More sharing options...
Harry Perry Posted January 27, 2013 Share Posted January 27, 2013 Surprised how quickly the temperatures decided to drop around here in the last 2 hours. Should begin to do the same across the lake. Link to comment Share on other sites More sharing options...
IWXwx Posted January 27, 2013 Share Posted January 27, 2013 I remember a freezing rain event during late January 1999. After all the arctic air had moved out, there was a system that produced freezing rain, and I remember that it was 33-34° with ice on ground surfaces. Not in the trees, but because of all the snow and cold ground there was ice on untreated surfaces. Good point. I discussed that with our EMA group yesterday. I'm thinking that with the temp profiles that are forecast, ice accretion should not be too much of an issue on trees/powerlines in this area. However road conditions could be . Link to comment Share on other sites More sharing options...
DAFF Posted January 27, 2013 Share Posted January 27, 2013 Good point. I discussed that with our EMA group yesterday. I'm thinking that with the temp profiles that are forecast, ice accretion should not be too much of an issue on trees/powerlines in this area. However road conditions could be . I give it the frozen turkey theory.... Even with surrounding air temps above or well above freezing it can take some time to remove the frost from the ground. There are many factors to consider for the dethawing of surfaces. The intensity and temperature of the rain will make all the differences with the thaw. Air to frozen ground will take time to pull the cold out, but add some warm water to the sink where the turkey is sitting.... During a flash freeze surfaces will freeze at different rates. One of the fastest ones is wood. When I see the wood deck starting to ice over then its time to head out. This usually give me a 1hr window to get the salt in place. Here is my list of freeze ups from fast to slow.... Wood, grass, bridges, concrete, gravel and lastly asphalt. I would expect the opposite for tonight.... Watch out for the northern side of buildings. These will tent to take more time to thaw simpilly for the lack of radiant heating. Link to comment Share on other sites More sharing options...
Stevo6899 Posted January 27, 2013 Share Posted January 27, 2013 I don't know why it bothers me but why is dtx always the last area to post advisories. It seems for every event, PA, OH, and areas to the east always have advisories before we even do. What's the point of issuing an advisory if the event is less than 24 hours away. Link to comment Share on other sites More sharing options...
csnavywx Posted January 27, 2013 Share Posted January 27, 2013 30F and everything glazed over Link to comment Share on other sites More sharing options...
Natester Posted January 27, 2013 Share Posted January 27, 2013 Woke up to heavy sleet. It is only a matter of time before the sleet changes to ZR. EDIT: Spoke too soon. Just switched over to ZR. Let the ice storm begin. Link to comment Share on other sites More sharing options...
daddylonglegs Posted January 27, 2013 Share Posted January 27, 2013 Blob is moving this way.... 28F here. Link to comment Share on other sites More sharing options...
gosaints Posted January 27, 2013 Share Posted January 27, 2013 Blob is moving this way.... 28F here. Gonna be interesting to see what falls. Dry slot going to hit us too. Link to comment Share on other sites More sharing options...
A-L-E-K Posted January 27, 2013 Share Posted January 27, 2013 dry air really hanging on over Chicagoland...should help limit ice accums Link to comment Share on other sites More sharing options...
metalicwx366 Posted January 27, 2013 Share Posted January 27, 2013 dry air really hanging on over Chicagoland...should help limit ice accums It's looking kinda lame for Chicago. It seems whenever there is an ice event for Chicago, it melts away just as quickly as it arrived. Then near record breaking temps 2 days later. Link to comment Share on other sites More sharing options...
Chitown Storm Posted January 27, 2013 Share Posted January 27, 2013 dry air really hanging on over Chicagoland...should help limit ice accums the current radar image is a true microcosm of how this winter has gone......chicago sitting in a hole. Link to comment Share on other sites More sharing options...
daddylonglegs Posted January 27, 2013 Share Posted January 27, 2013 I'm guessing snow or sleet to start.... Link to comment Share on other sites More sharing options...
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