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lilj4425

Feb 15-16 Possible Mixed Event.

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Looks to spread across the northern piedmont (Triad over to Triangle) from 9 to midnight. over .25 falls by dawn.

TW

 

A lot of that will be virga.

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Hope to get some of that Atlantic moisture off the SC coast to come in up our way, like Shawn was talking about earlier

 

With dewpoints so low, a lot of it is going to get eaten up by the dry air before it can get up that way.  Literally, total precipitation on the new NAM 4KM is printing 0.1 even this far South in Columbia.  In other words, basically nothing.

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The 24-hr QPF at hr the 42/48 panels between the 00z and 18z runs shows how the initial overrunning precip shifted south:

51a9ad.gif

The WB map shows right about 0.5" QPF for GSO and RDU.

That blue is sinking down into NC now.

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There is formal criteria. 

 

Winter Storm Watch - Conditions are favorable for either heavy snow, heavy sleet, damaging ice accumulations, or a combination of these factors, to develop within the next 48 hours. For the GSP CWFA, heavy snow is defined as 3 inches accumulating across the foothills and piedmont and 4 inches across the NC mountains in a 12-hour period, or 4 inches across the foothills and piedmont and 5 inches across the NC mountains in a 24-hour period. Damaging ice accumulations typically result from freezing rain accumulating 1/4 inch or more on exposed surface. It has been locally determined that 1/2 inch of sleet is considered "heavy" for Watch and Warning purposes.

 

http://www.weather.gov/media/gsp/winter/Product%20Description.pdf

 

You can also verify storm criteria with impacts. What defines an impact or how much does it take to reach "storm" criteria?  Good question. A wet 3" snow at 33F on a Sunday clearly has less impact than 1/2" snow at 26F which melts and refreezes on a weekday midday in Atlanta, yet by purely meteorological definitions, the 3" would verify while the 1/2" would not. Thus the addition of "impacts" as a criteria to issue a winter storm watch/warning. -SNELSON :)

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A lot of that will be virga.

 

The models take into account virga with the QPF output, though.  The first QPF makes it into our area between 00z and 03z on Monday morning, which is Sunday evening.  Looks like the first radar returns make it through between 21z and 00z on Sunday night (so, Sunday afternoon), but we start off with a few hours of virga, as expected.

 

Precip makes it to RDU about 3 hours later.  GSO starts out with temperatures around 22F while RDU is 24F.

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You can also verify storm criteria with impacts. What defines an impact or how much does it take to reach "storm" criteria?  Good question. A wet 3" snow at 33F on a Sunday clearly has less impact than 1/2" snow at 26F which melts and refreezes on a weekday midday in Atlanta, yet by purely meteorological definitions, the 3" would verify while the 1/2" would not. Thus the addition of "impacts" as a criteria to issue a winter storm watch/warning. -SNELSON :)

 

Source: NWSI 10-513. See page 6. http://www.nws.noaa.gov/directives/sym/pd01005013curr.pdf

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The models take into account virga with the QPF output, though.  The first QPF makes it into our area between 00z and 03z on Monday morning, which is Sunday evening.  Looks like the first radar returns make it through between 21z and 00z on Sunday night (so, Sunday afternoon), but we start off with a few hours of virga, as expected.

 

Precip makes it to RDU about 3 hours later.

 

I know they do. I also know that they sometimes underestimate the amount of precip that will lost to evaporation.  I've seen it over and over for years.

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I know they do. I also know that they sometimes underestimate the amount of precip that will lost to evaporation.  I've seen it over and over for years.

 

Oh, yeah, they definitely might.  I just know sometimes people on these forums think that you have to subtract QPF to account for virga, but they account for it (whether they account for too much of it or not enough just depends on the situation... more drier air than the model is predicting will result in less precip, of course).

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The stronger CAD signature continues at 39. At that point .25 to .50 qpf has fallen in central and western NC. After that precip lightens up until hour 48 where some precip develops near the SC coast and moves up into eastern NC (low pressure?). 

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No it's not compare the total accum maps and the radar precip map... The total accum map shows when it starts hitting the ground it filters out virga

See my follow up post.

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The 00z NAM keeps the Triad smack-dab at 32 degrees as the main heavy precip comes blasting through late Monday night/early Tuesday.  Makes you wonder...

 

This run really beefed up the QPF with the main band.  GSO - 2.2", RDU/HKY - 1.6"...  Typical NAM, eh?

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The 00z NAM keeps the Triad smack-dab at 32 degrees as the main heavy precip comes blasting through late Monday night/early Tuesday.  Makes you wonder...

 

This run really beefed up the QPF with the main band.  GSO - 2.2", RDU/HKY - 1.6"...  Typical NAM, eh?

If any area is going to fight to the last minute to stay at freezing it's your area.

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The 00z NAM keeps the Triad smack-dab at 32 degrees as the main heavy precip comes blasting through late Monday night/early Tuesday.  Makes you wonder...

 

This run really beefed up the QPF with the main band.  GSO - 2.2", RDU/HKY - 1.6"...  Typical NAM, eh?

What was the temp for HKY with the main band?

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The 00z NAM keeps the Triad smack-dab at 32 degrees as the main heavy precip comes blasting through late Monday night/early Tuesday.  Makes you wonder...

 

This run really beefed up the QPF with the main band.  GSO - 2.2", RDU/HKY - 1.6"...  Typical NAM, eh?  .

 

With all the waa with the second batch, I don't see it having a lot of impact at that point.  Heavy rates and marginal temps usually don't amount to a lot of impactful zr in the Triad.  Now, if temps are 30 or less, it will be a different story.  Hope we see 4-6" tomorrow night.

TW

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0z nam the coldest yet. Now has temps at or slightly below 32 through most of the event in the heart of the damming region from ne ga onward. . Also for the first time dewpoints remain below 32 through all the precip. Bottom line is the nam is ever so slightly catching on.

 

Interesting to note it actually has precip reaching the ground here as early as around 03z.

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0z nam the coldest yet. Now has temps at or slightly below 32 through most of the event in the heart of the damming region from ne ga onward. . Also for the first time dewpoints remain below 32 through all the precip. Bottom line is the nam is ever so slightly catching on.

Interesting to note it actually has precip reaching the ground here as early as around 03z.

now seems I gotta to keep an eye on this because I don't want any glaze on the roads when I have to head to class, should be above freezing by then I think

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If any area is going to fight to the last minute to stay at freezing it's your area.

 

Yeah, in in-situ CAD situations, this is usually one of the last areas to changeover (of course, areas further to our north changeover later, but we often stay below freezing longer than areas closer to the foothills for some reason).

 

What was the temp for HKY with the main band?

 

About the same.  Maybe a hair warmer (32-33).

 

With all the waa with the second batch, I don't see it having a lot of impact at that point.  Heavy rates and marginal temps usually don't amount to a lot of impactful zr in the Triad.  Now, if temps are 30 or less, it will be a different story.  Hope we see 4-6" tomorrow night.

TW

 

I think it depends on how much snow/sleet we get on the ground, too.  There will be a lot of latent heat release with the main band (if we get freezing rain or sleet), but at the same time snowcover on the ground will help to combat this to some degree.  I don't really see the main band being frozen at this point, but you never know and it'll have to be watched.  Of course, the Euro has us in the 50s at the same time, so no chance there, haha. :lol:

 

The 4 km NAM is the same with temps.  32 here at the warmest.  Even RDU and CLT are showing 33.

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0z NAM illustrates how impossible this is for forecasters. Shelby (EHO) receives 30 mm of precip (@ 1.2 inches) from Monday evening through early Tuesday. Temp is .1C to .6C during that span. And the temp trend is dropping with each run. Absolutely impossible. 

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0z nam the coldest yet. Now has temps at or slightly below 32 through most of the event in the heart of the damming region from ne ga onward. . Also for the first time dewpoints remain below 32 through all the precip. Bottom line is the nam is ever so slightly catching on.

Interesting to note it actually has precip reaching the ground here as early as around 03z.

If we stay a few degrees colder somehow, as the main band comes through later Monday, 1" plus QPF and we are around 29 or so, which is totally possible, it would be a lights out ZR event!

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I see the 4km NAM once again trended colder... It now keeps me at 32 or below for the whole event. Also, it is really starting to expand the wedge southward into southern Georgia. Macon, GA may not reach 40 degree's on Monday. One more trend like this one and we're looking at a major ice storm for all of the upstate and northeast georgia.

 

It even drops the Gainesville area back down to 31 degree's when the final band pivots through.  

 

Also, It holds the columbia area at 33 degree's all day monday and through monday night.

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Have not seen any posts about analogs for this. Is that because there are none?  I can't remember anything that looked like this in may days of model watching and even the early days of TWC.  It is a strange setup and maybe that is why there is still so much model disagreement?  Anyway, I'll be test firing my generator tomorrow and already have wood staged for both stoves that are already being pushed hard tonight.  Hoping for mostly frozen here and very good to see the colder trends.

 

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