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CAD storms thread.


dsaur

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Don't be so quick to write this one off as a non-event. Models are only a guide as to what could happen. This is far from being written in stone and I don't believe we have seen the final solution yet.

 

I don't dismiss any hype for this ice storm on the east coast. We have posters in VA who will emphasize the cold trends and rightfully should. However, we have widespread model support of the CAD getting destroyed in NC. This is nearly a classic example as GSP pointed out. Cold trends won't mean much if the trend consistently screams transit south of the VA border. Maybe all the models will be wrong on the erosion and it can last a bit longer into Sunday...but even then look at the rates in NC compared to VA going into Sunday afternoon. There may not even be precip in spots could be drizzle.

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If tonight's euro follows suit in a colder outcome, then we have a trend.

 

Euro has always been colder than the GFS.. GFS catching up on the cold.  Also, we are getting into the timeframe where GFS does a pretty good job when you get inside 84 hours.  I am a huge Euro fan for long range.. I guess we will see but right now all models seem to be trending colder.. GGEM just came in really cold.

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The GGEM sticks to its guns, more or less...

 

 

That would be warning criteria in NC if it lasted that long...or even half that long. I think its out to lunch starting around Sunday afternoon unless it beats all the other models.

 

It's been showing pretty much the same solution for days now.  It may be out to lunch, but it's been consistently so.  One could hypothesize that its higher resolution is helping it pick up on the CAD more, but I don't really know for sure.

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That would be warning criteria in NC if it lasted that long...or even half that long. I think its out to lunch starting around Sunday afternoon unless it beats all the other models.

 

There's actually a several hour lull in between as it looks like it pops a low off the coast then ramps back up again. A few hours of light precip before the lull, then gets heavier after that.

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There's actually a several hour lull in between as it looks like it pops a low off the coast then ramps back up again. A few hours of light precip before the lull, then gets heavier after that.

 

I think that might be why this model is so overboard. The other models have this lull or very light/spotty rains in NC and respond by warming us up a degree or 2 into Sunday afternoon. This model acts like nothing happens. Based on past CAD events...we do warm up slightly because of a lull the further south you are.

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I think that might be why this model is so overboard. The other models have this lull or very light/spotty rains in NC and respond by warming us up a degree or 2 into Sunday afternoon. This model acts like nothing happens. Based on past CAD events...we do warm up slightly because of a lull the further south you are.

 

Well its a bit more complicated than that... whether or not the models are properly handling surface WAA is one thing, but freezing precipitation actually releases heat. You can see that when you look at an upper air sounding in NW NC. Note how the coldest temperatures are actually around 925-950 hPa rather than at the surface (which is markedly warmer). As precipitation reaches the subfreezing surface and starts to freeze on contact, water undergoes an exothermic reaction to transition from liquid to ice. This results in warming the surrounding air in response. Thus, unlike wet snowfall, where melting snowflakes actually are an endothermic reaction that cools the surrounding atmosphere, the surface freezing rain actually helps to warm the surface.

 

Thus freezing rain almost by necessity needs a continuing source of cold relatively dry air from a parent cold high pressure to replenish the cold air that eventually is eroded away at the surface by the chemistry of water phase change. Its why classical CAD almost always results in serious ice storms while hybrid CAD (in which the Parent high erodes away or moves offshore) often only results in minor ice accumulation before a transition to rain. Using this same logic if there is a lull is precipitation in the middle of this event, that would actually favor colder surface temperatures to persist for longer with less ice accretion during that period (which means the GGEM isn't necessarily off its rocker). 

 

NAM_218_2013120500_F84_36.5000N_80.5000W

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Thanks, Phil.  And the source just has to keep it steady.  That's why I got well over 3 inches of ice at 32 for a whole event, and it nearly all froze.  For whatever heat was released there was an immediate cooling that took it away because there was a steady supply of dry 32 degree air.  Or air that stayed at 32 after dissipating all that heat. Over 2 1/2 inches liquid in about 12 hours. Oh, sure, there was some water on the ground, but not much missed freezing.  If things line up right you can have a frog choker all freeze....just have to mitigate the heat released.  And a frog choker brings a lot of heat, so you need the perfect steady feed to make it work.  And I'm sure that's why it doesn't happen much. Thankfully!

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Very interesting Phil and complex! 

 

Guess it does make meteorological sense but it actually happening is another thing I suppose. 

 

 

Here is what I currently think with no weight on that model.

 

Freezing Rain Advisory Chances:

High Risk: Northern NC mountain counties, Northern NC foothills counties

Moderate Risk: Central NC Foothills/Mountains, Piedmont Triad

Low Risk: Southern NC Piedmont

 

Ice Storm Warning Chances:
Moderate Risk: Northern NC mountain counties
Low Risk: Northern NC foothill counties

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If the Canadian where to be correct, Ashe, Alleghaney, Avery, Watauga,Wilkes Surry, Stokes Rockingham entire counties would receive 20 straight hours of freezing rain, with only about a 2-3 hour lull in the middle. Counties that border those counties would have issues as well but a transition to just good old cold rain would set up shop.Interesting to see all this unfold and check the model verifcations. This is the 3rd event I've tracked this season so far and the models collectively have done a good job of sniffing all 3 out well in advance. I was watching this one last weekend. Of course the 8-12 inches the GFS was given Charlotte on one run isn't going to happen, but you could see the potential was there and it's looking like it will take place only a 100 miles futher north than we would prefer.

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If the Canadian where to be correct, Ashe, Alleghaney, Avery, Watauga,Wilkes Surry, Stokes Rockingham entire counties would receive 20 straight hours of freezing rain, with only about a 2-3 hour lull in the middle. Counties that border those counties would have issues as well but a transition to just good old cold rain would set up shop.Interesting to see all this unfold and check the model verifcations. This is the 3rd event I've tracked this season so far and the models collectively have done a good job of sniffing all 3 out well in advance. I was watching this one last weekend. Of course the 8-12 inches the GFS was given Charlotte on one run isn't going to happen, but you could see the potential was there and it's looking like it will take place only a 100 miles futher north than we would prefer.

 

The euro gives several hours of ice too in far north-west NC if you check it...look around Boone to Sparta.

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I'm not sure if we have even 1 poster in most these counties like Ashe, Alleghany, Wilkes, and maybe about 2 in Surry. Have at least 1 in Watauga. This is where the best icing will occur...0.1 to 0.25.

I will actually be in Boone this afternoon through Sunday morning (unless there's ice, in which case I'll leave early to get back home).

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I will actually be in Boone this afternoon through Sunday morning (unless there's ice, in which case I'll leave early to get back home).

What are you doing in my neck of the woods? You should have more reason to stay if there is ice!! You can go with me to fly my quad copter to get some nice aerials of the ice. www.nelsonaerials.com

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Matthew East just updated his blog. Looks like we have a battle with the NAM and Canadian vs. the GFS and Euro. Which one will be right? I think this could turn out to be a little surprise. Here is what East said about it.

 

The NAM and Canadian models are the coldest model solutions and push temps below freezing all of the way down to I-40 for an extended period of time Sunday. The GFS and Euro keep the freezing line up near the VA border. The Canadian model is often quite good around here in CAD situations, and I am easing my forecast in the direction of the colder modeling. You also have to keep in mind that the models often under-estimate the cold air a bit in CAD situations too.

 

 

Here's the link to his video today.

 

http://mattheweast.blogspot.com/2013/12/warm-today-and-tomorrowthen-big-changes.html

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Exactly.  If you go back and look through this thread, none of the mets are completely writing off this CAD threat.  The NAM and Canadian should not be completely thrown out.  It's also getting close to the time where other hi-res models will be beneficial.  Lets see what they have to say.  1-2 degrees will make a big difference in sensible weather and it seems there is still a little wiggle room for this to trend that much colder (or warmer).

 

Matthew East just updated his blog. Looks like we have a battle with the NAM and Canadian vs. the GFS and Euro. Which one will be right? I think this could turn out to be a little surprise. Here is what East said about it.

 

 

 

Here's the link to his video today.

 

http://mattheweast.blogspot.com/2013/12/warm-today-and-tomorrowthen-big-changes.html

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What are you doing in my neck of the woods? You should have more reason to stay if there is ice!! You can go with me to fly my quad copter to get some nice aerials of the ice. www.nelsonaerials.com

That would be totally awesome! I wish I could. The wife and I are sort of celebrating our anniversary a bit late. We only have a couple of family members that can keep our son, so we get away once or twice a year. We love the High Country and plan to move up there one day. We'll have to get back if it looks like the roads will be bad, as my mom won't be able to stay past Sunday. Otherwise, we'd tough it out. :)

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Exactly.  If you go back and look through this thread, none of the mets are completely writing off this CAD threat.  The NAM and Canadian should not be completely thrown out.  It's also getting close to the time where other hi-res models will be beneficial.  Lets see what they have to say.  1-2 degrees will make a big difference in sensible weather and it seems there is still a little wiggle room for this to trend that much colder (or warmer).

 

Yes, it looks like it could be a really thin line between who gets rain and who gets ice. Like you said, 1 or 2 degrees will make all the difference in the world.

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