Feb. 18-20, 2012 Disco/Analysis

[BIG FROSTY]

The whole "it's been warm" is bull****. If it's below freezing, the snow will accumulate just fine.

I agree if it comes down hard enough temps in the low thirty's it will stick even on roads. I've seen it accumulate many times with temperatures in the middle thirty's. the snow will cool off the ground. Temps the middle thirty's it will accumulate on grass.

[WilkesboroDude]

I agree if it comes down hard enough temps in the low thirty's it will stick even on roads. I've seen it accumulate many times with temperatures in the middle thirty's. the snow will cool off the ground. Temps the middle thirty's it will accumulate on grass.

May end up being a slush, freezing drizzle, or flash freeze threat.

NWS Raleigh has freezing drizzle for Greensboro. Given all the water we get, I could see some slush buildup or a flash freeze for NC late Sunday.

NWS Blacksburg has our temps going down into the mid 20s. I am thinking they add something frozen in the forecast for the foothills too by Saturday at the latest.

[GreensboroWx]

I agree if it comes down hard enough temps in the low thirty's it will stick even on roads. I've seen it accumulate many times with temperatures in the middle thirty's. the snow will cool off the ground. Temps the middle thirty's it will accumulate on grass.

I always think the "ground is warm" or the past few days "have been warm" is WAY overrated. The true key is how much/fast snow actually comes down. I've seen it in the 60s the day before huge snowfalls here in the Triad....it does happen. With this said, I do think the this system will be lacking for heavy snowfall over NW NC, at least that's the way the modeling is playing out.

[SnowNiner]

The track alone is not the only problem. Even if it took a perfect track there still isn't much in the way of cold air to work with. It would be better if the high was a bit stronger as a 1020/1024 just isn't going to do it. You can always count on dynamics to cool the atmosphere, but unless you have heavy precipitation rates you will still end up with rain. Once the rates lighten up you will end up with nothing more than light rain or drizzle.

And even if the dynamic cooling cools you to freezing that doesn't mean the ground is below freezing yet. Still lots of meltage. When I see a storm coming in and we're supposed to get a hit, that's always my first question, what's the surface tempature going to be? If it's above freezing or right at 32, accumulation is going to be greatly reduced. Dynamic cooling will get us down close to freezing and actually MAKE it snow but I've yet to see it get the piedmont below freezing by itself and help it stick. So essentially I NEVER like to rely on cooling for accumlation. Just doesn't work other than an inch or two of slush.

[SN_Lover]

I agree if it comes down hard enough temps in the low thirty's it will stick even on roads. I've seen it accumulate many times with temperatures in the middle thirty's. the snow will cool off the ground. Temps the middle thirty's it will accumulate on grass.

Here are the current soil temperatures.

While the soil temp around NC is 39.2F degrees Fahrenheit, one has to acknowledge that the ground has a high heat capacity. This would make it very hard to get soil temps hard to get below freezing. This would greatly decrease snow ratios, even if it is coming down hard, which no models are forecasting.

[GreensboroWx]

May end up being a slush, freezing drizzle, or flash freeze threat.

NWS Raleigh has freezing drizzle for Greensboro. Given all the water we get, I could see some slush buildup or a flash freeze for NC late Sunday.

NWS Blacksburg has our temps going down into the mid 20s. I am thinking they add something frozen in the forecast for the foothills too by Saturday at the latest.

No matter what happens, Monday morning could be VERY slick on the roads. Cold air WILL move in behind the departing system and whatever moisture is lying around will freeze.

[SnowNiner]

I agree if it comes down hard enough temps in the low thirty's it will stick even on roads. I've seen it accumulate many times with temperatures in the middle thirty's. the snow will cool off the ground. Temps the middle thirty's it will accumulate on grass.

Gotta disagree with that. 09 and 10 in Charlotte were classic examples. Snow would come down as hard as could be at 32-33 degrees and it did nothing but put slush on the roads. Grass is another story but the roads do not truly accumulate unless surface temps are BELOW freezining IMO. From everything I'm hearing it seems even northern sections of NC can only hope for grassy surface snow or a bit of slush at best.

[WidreMann]

Good luck getting the accumulations the maps show after a inch of rain and days of 55-60+ degree weather. It will have to come down hard and hope for at least half of whatever falls stays.

NWS Raleigh

Any wintry precipitation should be of limited duration and impact given the preceding warm ground temperatures...

They say that, but folks on the wxside have pointed out that this is more myth than fact.

As far as how long the snow pack remains, ground temps probably matter more.

[WeatherNC]

The one positive thing I am seeing with the 12z runs, and Matt & others mentioned this earlier, is the guidance starting to key in on more energy coming in late over TN into NC. The 12z GFS compared to 0z is noticeable in the difference, even if you account for some timing issues between the two.

0

12

This would likely only have a meaningful effect for areas north of 40 and east of 77 if we continue to see it trend stronger, and in the meaningful sense I mean brief period of enhanced sn-fall potential. The trend has support from the 12z UKMET also, comparing that to the 0z run it has a parcel with abs vort values around 30 s^-1 vs the 0z which was around 22, also shifted slightly to the sw over TN and a sharper backside axis.

This may be rather important for NE NC / SE VA depending on how it evolves, as the models are now starting to paint a second bullet of QPF into SE VA, even coming down into the northern coastal plain of NC just before the upper level energy moves through.

[Local Yokel Wx]

Every marginal situation over the past few yrs has stimualted this arguement; "is the ground too warm or not for snow accumulations?"

We should make an entire thread dedicted to this arguement bc sometimes it can derail a thread, lol. Now in this instance, I understand there isnt much to talk about at the moment as we await new model runs, so let it continue, but man its funny to watch both sides of the isle so to speak go at it.

Thanks to everyone for the PBP and I look forward to this afternoon's analysis.

[Tullioz]

Here are the current soil temperatures.

While the soil temp around NC is 39.2F degrees Fahrenheit, one has to acknowledge that the ground has a high heat capacity. This would make it very hard to get soil temps hard to get below freezing. This would greatly decrease snow ratios, even if it is coming down hard, which no models are forecasting.

This is also the problem in Virginia as well. This along with the air temperatures leading up to the change over to snow will inhibit accumulations. Another factor will be the speed at which the storm will be moving. There will only be about a 6 to 12 hour window for snow to fall over any given area. With half of that melting at the surface it doesn't leave much to work with as far as accumulating snow is concerned. I would be shocked to find any Virginia locations getting more than 6" outside of the higher elevations. I see DT is throwing out all kinds of crazy numbers on his Facebook page. I just don't see it.

[tonysc]

And even if the dynamic cooling cools you to freezing that doesn't mean the ground is below freezing yet. Still lots of meltage. When I see a storm coming in and we're supposed to get a hit, that's always my first question, what's the surface tempature going to be? If it's above freezing or right at 32, accumulation is going to be greatly reduced. Dynamic cooling will get us down close to freezing and actually MAKE it snow but I've yet to see it get the piedmont below freezing by itself and help it stick. So essentially I NEVER like to rely on cooling for accumlation. Just doesn't work other than an inch or two of slush.

I never worry about surface temperatures. If it snows long and hard enough, you will get accumulation. Yes I do agree that surface temps being warmer, or after it having rained, will reduce the accumulations, but we can definitely get a good accumulating sanow still. The one in 2000 that gave us a foot, didn't start accumulating till it had been snowing hard for three hours of so, and we still got a foot, although if it had all stuck, we would probably have gotten over fifteen inches.

[Suncat]

RAH NWS calling for a 30% chance of 0.1" of rain on Sunday night with a low of 30F for the Triangle area. It doesnt sound as if they are all on board for anything of consequence for Sunday Night into Monday. It will be interesting to see if this changes in the next 24 hours or not.

[mercurydime]

GSP seems not to think too much of (more widespread) wintry weather at this point:

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...

AS OF 245 AM FRIDAY...THE MODEL GUIDANCE IS COMING INTO BETTER FOCUS

FOR THE WEEKEND. BEGINNING SATURDAY MORNING...THE CONFLUENCE OF THE

SPLIT FLOW PATTERN WILL BE OVER THE MID ATLANTIC WHILE THE SRN

STREAM SHORT WAVE WILL STILL BE OVER TX. THE 21Z SREF AND THE 00Z

OPERATIONAL MODEL RUNS ARE IN GOOD AGREEMENT THAT DEEPER MOISTURE

WILL NOT ARRIVE UNTIL LATE IN THE DAY AND FORCING WILL NOT INCREASE

UNTIL AFTERNOON. THINK ANY PRECIP CHANCE IS PREMATURE ON SATURDAY

MORNING AND HAVE ELIMINATED THE LOW END POP UNTIL AFTERNOON. BEYOND

18Z...PRECIP CHANCES RAMP UP STEADILY FROM THE SW AS MOISTURE SURGES

NWD FROM THE GULF OF MEXICO AND STRONG DEEP FORCING ARRIVES AHEAD OF

A DEEPENING SURFACE LOW APPROACHING FROM THE MS DELTA REGION. ALL

SIGNS POINT TO A WIDESPREAD RAIN EVENT SATURDAY NIGHT...SO THE

PRECIP CHANCES EVENTUALLY REACH CATEGORICAL EVERYWHERE BY MIDNIGHT.

THE MAIN CONCERN AT THIS POINT IS HEAVY RAIN...BUT FOR THE TIME

BEING THE QPF IS NOT HIGH ENOUGH TO ENTERTAIN ANY ACTIONS. ALL THE

MODELS HAVE THE SURFACE LOW SOMEWHERE OVER NW GA/NE AL AT SUNRISE

SUNDAY. THE APPARENT CONSENSUS DELAY WITH THIS SYSTEM MEANS THAT THE

CATEGORICAL POP WILL HAVE TO BE EXTENDED INTO THE SUNDAY MORNING

TIME FRAME. DRY AIR WILL WRAP IN FROM THE SW DURING THE DAY TO TAPER

OFF PRECIP OVER NE GEORGIA BY AFTERNOON. THE HIGH PRECIP CHANCES

WILL BE KEPT OVER THE NC PIEDMONT LATE INTO THE DAY OWING TO THE

POTENTIAL FOR WRAP AROUND...AND OVER THE MTNS AS A BAND OF MID LEVEL

FRONTOGENESIS MOVES OVERHEAD. AFTER A MIDDAY HIGH...TEMPS SHOULD

DROP STEADILY IN THE AFTERNOON AS COLDER AIR FILTERS IN. THE

GUIDANCE IS A BIT WARMER WITH THIS CYCLE...SO ANY MIXED PRECIP TYPES

WILL NOT DEVELOP UNTIL AROUND 12Z SUNDAY AND BE LIMITED TO A

FREEZING RAIN OR SNOW POTENTIAL AT ELEVATIONS ABOVE 5000 FEET. SNOW

LEVELS SHOULD FALL QUICKLY AFTER 21Z SO A CHANGEOVER TO SNOW IS

EXPECTED AS THE FORCING CHANGES TO NW FLOW UPSLOPE WITH THE

DEPARTURE OF THE SURFACE LOW. DRY AIR ALSO MOVES IN ALOFT

OVERNIGHT...SO THE NW FLOW SHOULD END AS A SHORT PERIOD OF FREEZING

RAIN OR DRIZZLE BEFORE ENDING IN THE PRE-DAWN HOURS.

[tonysc]

Gotta disagree with that. 09 and 10 in Charlotte were classic examples. Snow would come down as hard as could be at 32-33 degrees and it did nothing but put slush on the roads. Grass is another story but the roads do not truly accumulate unless surface temps are BELOW freezining IMO. From everything I'm hearing it seems even northern sections of NC can only hope for grassy surface snow or a bit of slush at best.

Yeah I know what you're saying there and a lot of times it never accumulates on the roads, and I honestly didn't believe it was going to in the storm of 2000. but on my way to work that evening, it was rough traveling on even the main roads, and it never dropped below 35 degrees during that storm. So I know first hand that it definitely can happen.

[WilkesboroDude]

Much needed system regardless of winter precip for some...

[eyewall]

This will be dubbed the "Carolina Heartbreaker" for many as it is tough riding the line. We will see what happens with upper level support on the back end.

[dwagner88]

Honestly given how warm air tends to fill the valley in situations like this, I'll be surprised if anyone in east TN south of Knoxville even sees a flake. Accumulations seem out of the question outside of NE TN without a substantial change in the low track.

[burgertime]

Gotta disagree with that. 09 and 10 in Charlotte were classic examples. Snow would come down as hard as could be at 32-33 degrees and it did nothing but put slush on the roads. Grass is another story but the roads do not truly accumulate unless surface temps are BELOW freezining IMO. From everything I'm hearing it seems even northern sections of NC can only hope for grassy surface snow or a bit of slush at best.

Strongly disagree with the underlined part. This was one of those events in the video posted below. The problem wasn't so much the rate, it was the inconsistency at which it was falling. This was about the heaviest it fell all day and I would hardly call it hard as could be or even heavy snow it would only last in bursts of about ten minutes. Had it been heavier for an hour or two you would have seen accumulation on the roads.

[Solak]

Realtime soil temps for NC

[jburns]

Gotta disagree with that. 09 and 10 in Charlotte were classic examples. Snow would come down as hard as could be at 32-33 degrees and it did nothing but put slush on the roads. Grass is another story but the roads do not truly accumulate unless surface temps are BELOW freezining IMO. From everything I'm hearing it seems even northern sections of NC can only hope for grassy surface snow or a bit of slush at best.

Snowfall rate trumps everything as far as accumulations are concerned. I have seen roads cover many times with temps several degrees above freezing. If it comes down hard enough it will cover. The problem is, and the reason you feel roads won';t cover, is the snow rate has to remain heavy for a period of time without any lulls. That's pretty rare in these parts.

[strongwxnc]

Only a heart breaker for those that have weak hearts.. I have assumed that my area (southern foothills nc ) has been out of the race since we began tracking, give or take a few model runs. However, I hope to see that some members here cash in and enjoy what might be the only action this season.

Wonderful disco through out this entire event folks!!!

This will be dubbed the "Carolina Heartbreaker" for many as it is tough riding the line. We will see what happens with upper level support on the back end.

[Marion_NC_WX]

Other than a few token flakes, snow will be no issue for us here along the escarpment...but as Robert just updated on his site, black ice could be widespread come Monday morning even east of the mountains.

[SnowNiner]

Strongly disagree with the underlined part. This was one of those events in the video posted below. The problem wasn't so much the rate, it was the inconsistency at which it was falling. This was about the heaviest it fell all day and I would hardly call it hard as could be or even heavy snow it would only last in bursts of about ten minutes. Had it been heavier for an hour or two you would have seen accumulation on the roads.

No, most of the events I'm referring to were at night/evening and it was snowing a LOT harder than that. Christmas storm was another good example. Alot of it would depend on where exactly you were in the events, but just from my experience and location under bands of heavy snow...if it's just above freezing or right at it simply didn't do much accumulating.

[BrierCreekWx]

Snowfall rate trumps everything as far as accumulations are concerned. I have seen roads cover many times with temps several degrees above freezing. If it comes down hard enough it will cover. The problem is, and the reason you feel roads won';t cover, is the snow rate has to remain heavy for a period of time without any lulls. That's pretty rare in these parts.

Local research at NWS-RAH has shown when soil temps are warmer than 40F it does significantly affect accumulation.

[DaculaWeather]

The one positive thing I am seeing with the 12z runs, and Matt & others mentioned this earlier, is the guidance starting to key in on more energy coming in late over TN into NC. The 12z GFS compared to 0z is noticeable in the difference, even if you account for some timing issues between the two.

Just doesn't seem to be any moisture to go with the cold at 72

[sctvman]

http://twitpic.com/8l5l8p RPM Model from Brad Panovich.

[SN_Lover]

Strongly disagree with the underlined part. This was one of those events in the video posted below. The problem wasn't so much the rate, it was the inconsistency at which it was falling. This was about the heaviest it fell all day and I would hardly call it hard as could be or even heavy snow it would only last in bursts of about ten minutes. Had it been heavier for an hour or two you would have seen accumulation on the roads.

The average temperatures in 2010 was cooler than this year. there was also snow before that video, so one could think that ground temperatures was lower to support snow.

Below is data from KCLT

[RaleighWx]

My snow forecast

http://www.examiner.com/weather-in-raleigh/some-snow-likely-to-fall-north-carolina-sunday-sunday-evening

[jburns]

Local research at NWS-RAH has shown when soil temps are warmer than 40F it does significantly affect accumulation.

Didn't need to research that. Common sense would tell you the same thing. Never-the-less it will cover and will accumulate if the snow rate is heavy enough. The bottom inch or so will be slush and snow will accumulate on top of it.