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Freezing Rain, Sleet, Snow, Rain...Kitchen Sink (12/15-16)

Myfrotho704_ said:
Is this even surprising ?! View attachment 57389
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Lol nope, and many wonder why I've been so gung-ho, seen this happen more times than I can count during CAD/Miller B events.

Keep in mind that we still have another 3 days to go for this to keep trending colder/drier prior to onset (which often happens).
 
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I don’t understand how the EPS is going away from a look yet the GEPS/GEFS are trending favorable for winter weather DE1D4935-1920-4BA8-9DD7-E8C876F0D9A4.gif122FD23E-D9F8-45F0-A2DD-3718EC571710.gif
 
Really cool study from Sanders & Barjenbruch (2016) wrt ice liquid ratios that's worth reading imo.

https://journals.ametsoc.org/view/journals/wefo/31/4/waf-d-15-0118_1.xml?tab_body=fulltext-display


For ice radial accumulations, which are the standard for measuring freezing rain accumulation, they found that for every inch of radial ice accrual about 3-4" of liquid equivalent is measured (via ASOS).

1607849076612.png




Thus, when you see maps like this, especially when there's a ton of QPF, it's usually a good idea to take ~25-33% of these 1:1 QPF-ice accumulations.

1607849422590.png


Pivotalweather also now has an option for those w/ a subscription where you can select for the Freezing Rain Accumulation Model (FRAM) accumulations described in the aforementioned study & these are considerably more reliable than 1:1 QPF-ice accum model output. The FRAM model uses regression on modeled precipitation rate, wet bulb temperature, and wind speed to estimate ice accrual. It's certainly better than using straight 1:1 QPF-ice output, but I would still urge caution in using a product like this.

1607849529918.png
 
06z NAM looking more like the Euro? Warmer less QPF! I think? I certainly could be wrong.


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449be786f14c5b1edbf17d2083da31e7.png
 
Myfrotho704_ said:
More confluence, and definitely a way less amped trend, which is toward the GFS rather than the euro, it’ll be interesting to see what they do later View attachment 57450
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I like the meso high it has over the NY/PA border should help to reinforce the cold push
87F4568E-5CC3-44A3-9978-8EAAE9C60106.jpeg
 
Myfrotho704_ said:
Just a tad bit, more so in SC however, but it does switch it over to rain
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I bet we see the cold models begin a warming trend today, so they can fall inline with the KING! Not a good sign, IF you want a winter storm. If it was just 12-48 hours out I would not put as much emphasis on the Euro, short range models will do better then (But that’s what they’re job is)! But I’m just a babbling Snowman what do I know? Lol I know a lot of people don’t want an ice storm, but me personally I would like to see a decent Ice storm haven’t had one in a long time.


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Webberweather53 said:
Really cool study from Sanders & Barjenbruch (2016) wrt ice liquid ratios that's worth reading imo.

https://journals.ametsoc.org/view/journals/wefo/31/4/waf-d-15-0118_1.xml?tab_body=fulltext-display


For ice radial accumulations, which are the standard for measuring freezing rain accumulation, they found that for every inch of radial ice accrual about 3-4" of liquid equivalent is measured (via ASOS).

View attachment 57443




Thus, when you see maps like this, especially when there's a ton of QPF, it's usually a good idea to take ~25-33% of these 1:1 QPF-ice accumulations.

View attachment 57444


Pivotalweather also now has an option for those w/ a subscription where you can select for the Freezing Rain Accumulation Model (FRAM) accumulations described in the aforementioned study & these are considerably more reliable than 1:1 QPF-ice accum model output. The FRAM model uses regression on modeled precipitation rate, wet bulb temperature, and wind speed to estimate ice accrual. It's certainly better than using straight 1:1 QPF-ice output, but I would still urge caution in using a product like this.

View attachment 57445
Click to expand...

I knew it was a lot less than 1:1, but thought it was on average roughly about 1" of radial ice to 2" of QPF. So. it is more like 1" of ice to 3-4" of qpf on average?

One thing I noticed with ATKL ice storms was that the ice tends to accrue more when both the winds were lighter (maybe because higher winds blow more of the dripping rain off the branches before it can freeze?) and the rainfall rate was lighter (maybe because heavier rain has an easier time to drip off the branches because it takes longer to freeze?). Also, I assume the colder the temp, the more it will accrue. So, there are a lot of variables including these 3 meaning it wouldn't surprise me if you really could have 1:2 accrural rate if, say, the rainfall rate is low, the winds are light, and the temps are 30 or lower instead of 31-32.
 
First Call. Up to 6 hour event of wintery weather for most then up to 8 to 10 hours Mount Airy NC northward. Starts as sleet (even snow for the northern foothills out to Winston Salem). Most see light glaze but 0.1 to 0.25 ice along and west of i77 and mostly north of i40. Snow up to an inch or more over the mtns and maybe half inch over parts of the foothills mixed with sleet. Little accumulations of sleet may sneak east out to Greensboro and Statesville line. Mostly cold rain Charlotte to Raleigh. A few counties of South Carolina and Georgia (extreme) will start as sleet or flake then go to a light glaze of ice.
 
GaWx said:
I knew it was a lot less than 1:1, but thought it was on average roughly about 1" of radial ice to 2" of QPF. So. it is more like 1" of ice to 3-4" of qpf on average?

One thing I noticed with ATKL ice storms was that the ice tends to accrue more when both the winds were lighter (maybe because higher winds blow more of the dripping rain off the branches before it can freeze?) and the rainfall rate was lighter (maybe because heavier rain has an easier time to drip off the branches because it takes longer to freeze?). Also, I assume the colder the temp, the more it will accrue. So, there are a lot of variables including these 3 meaning it wouldn't surprise me if you really could have 1:2 accrural rate if, say, the rainfall rate is low, the winds are light, and the temps are 30 or lower instead of 31-32.
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Yes, it's more like 1" Radial ZR:3-4" QPF according to this study. Stronger winds actually enhance ice accrual efficiency because it increases the rate of evaporative cooling, the rate of sensible heat transfer from cooler surrounding air to slightly warmer adjacent air near a freezing object that's undergoing latent heating & stronger winds increase a horizontal cross section's mass flux (of ice), all serving to increase ice accumulation efficiency at higher wind speeds. The effect is pretty small until wind speeds begin to approach exceed 10-15 knots.

"It is inferred that the increasing wind speed replaces air near the ice surface warmed by latent heat release, alters the droplet collision efficiency, increases the horizontal mass flux, and promotes evaporational cooling. Although, the data show that these processes are not as noticeable in the ILRs until wind speed reaches >15 kt, and may rely on the thermodynamic environment as well. Wind gusts had a similar influence on ILR with an increasing trend in ILR as wind gusts increased."

1607859861078.png


As for surface temperatures, your intuition is correct in that there's a strong temperature dependency, with wet bulb temperatures above -1C (~30F) experiencing significantly lower ice liquid ratios (ILRs) than those with temperatures between -4 to -1C. The relationship reverses and lower ILRs are observed for temps lower than about -4C (~25F), as the low-mid levels usually become more supportive of sleet instead of freezing rain, in environments where the surface temperatures are this cold or colder.

1607860417565.png



They also found rather unsurprisingly, that ice accumulation efficiency is dependent on precipitation rate with the largest changes in ILRs between rain equivalent rates of a few hundredths to a tenth or so per hour, with it asymptoting towards ILRs of about 1:7.5 or so in heavy precipitation.

1607860524833.png
 
GSP AFD


LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

AS OF 330 AM SUNDAY...AN UPPER TROUGH WILL QUICKLY TRACK
EAST FROM THE MIDWEST TO THE CENTRAL APPALACHIANS TUESDAY
NIGHT-WEDNESDAY, PROVIDING STRONG UPPER SUPPORT FOR A MILLER-B
TYPE LOW DEVELOPMENT. MEANWHILE, AN ~1035 MB SFC HIGH WILL BE
OVER SOUTHERN QUEBEC, MAKING FOR A CLASSICAL CAD WEDGE TO SET UP
OVER THE AREA BY TUESDAY NIGHT. THE MODELS ARE IN GOOD AGREEMENT
ON THIS SYSTEM CONSIDERING IT'S STILL DAY 4, SHOWING CYCLOGENESIS
JUST OFF THE CAROLINA COAST. THE PARENT MIDWEST LOW WILL TAP INTO
ENOUGH MOISTURE TO SPREAD LIGHT PRECIP ATOP THE WEDGE LATE TUESDAY
NIGHT. THIS SHOULD HELP LOCK IN SOME SUB-FREEZING TEMPS ACROSS THE
NC MOUNTAINS AND OUT ACROSS THE NC FOOTHILLS AND NW PIEDMONT BY
DAYBREAK WEDNESDAY. AREAS TO THE SOUTH ARE MORE MARGINAL, AND LOOK
TO REMAIN JUST ABOVE FREEZING. MODELS ARE ALSO IN GOOD AGREEMENT
ON THE LOW-LEVEL THICKNESSES AND PROFILES SHOWING A WARM NOSE
QUICKLY PUNCHING TOWARD THE N/NW TO THE NORTHERN MOUNTAINS BY 12Z
WED THANKS TO STRONG WAA. SO CONFIDENCE IS INCREASING ON A MIXED
BAG OF -S/PL/FRZA FOR MUCH OF THE HIGH TERRAIN AND OUT ACROSS THE
I-40 CORRIDOR EAST OF THE MOUNTAINS. HOW QUICKLY THINGS TRANSITION
TO ALL RAIN WITH POCKETS OF FRZA WEDNESDAY MORNING IS STILL UP
IN THE AIR. THE MODELS ARE LIKELY A BIT TOO FAST WARMING THE SFC
TEMPS ALONG THE ESCARPMENT DUE TO THE STRONG CAD. BUT AS THE LOW
RAPIDLY DEEPENS ALONG THE MID-ATLANTIC COAST, LOW-LEVEL FLOW WILL
TURN OUT OF THE WEST THEN NORTHWEST, AND THE CAD SHOULD ERODE. ALL
THIS TO SAY, THAT IT WILL BE A MESS P-TYPE-WISE. ONE CONCERN IS THAT
MODELS CONTINUE TO TREND UP WITH QPF, AND WE COULD SEE ENOUGH FOR
POCKETS OF 0.25" LIQUID EQUIVALENT OF WINTRY ACCUMS, WHICH COULD
RESULT IN IMPACTS APPROACHING WINTER STORM WARNING CRITERIA. STILL,
THE MOST LIKELY SCENARIO LOOKS TO BE ADVISORY-LEVEL ICE/SLEET/SNOW
ACCUMS, WITH SOME HAZARDOUS ROAD CONDITIONS WEDNESDAY MORNING,
HOPEFULLY IMPROVING BY THE AFTN. THE I-85 CORRIDOR WILL LIKELY
SEE ALL RAIN. WILL CONTINUE TO HIGHLIGHT THIS EVENT IN THE HWO.

BROAD HIGH PRES BUILDS IN QUICKLY WED NIGHT AND DOMINATES OUR
WEATHER THRU THE END OF THE WORK WEEK. TEMPS WILL BE HELD A FEW DEG
BELOW NORMAL. THE NEXT CHANCE FOR PRECIP LOOKS TO BE NEXT WEEKEND,
BUT THE MEDIUM RANGE GUIDANCE HAS BEEN TRENDING SLOWER. TOO MUCH
UNCERTAINTY ON WHETHER ANY OF THAT WILL BE WINTRY IN NATURE.
 
If you sleep in past 8am you may miss any glaze from Charlotte to Raleigh. This is largely gonna be a cold rain in bigger cities..with all the action in the north and west (Hickory, Yadkinville, Greensboro).
 
Webberweather53 said:
Yes, it's more like 1" Radial ZR:3-4" QPF according to this study. Stronger winds actually enhance ice accrual efficiency because it increases the rate of evaporative cooling, the rate of sensible heat transfer from cooler surrounding air to slightly warmer adjacent air near a freezing object that's undergoing latent heating & stronger winds increase a horizontal cross section's mass flux (of ice), all serving to increase ice accumulation efficiency at higher wind speeds. The effect is pretty small until wind speeds begin to approach exceed 10-15 knots.

"It is inferred that the increasing wind speed replaces air near the ice surface warmed by latent heat release, alters the droplet collision efficiency, increases the horizontal mass flux, and promotes evaporational cooling. Although, the data show that these processes are not as noticeable in the ILRs until wind speed reaches >15 kt, and may rely on the thermodynamic environment as well. Wind gusts had a similar influence on ILR with an increasing trend in ILR as wind gusts increased."

View attachment 57455


As for surface temperatures, your intuition is correct in that there's a strong temperature dependency, with wet bulb temperatures above -1C (~30F) experiencing significantly lower ice liquid ratios (ILRs) than those with temperatures between -4 to -1C. The relationship reverses and lower ILRs are observed for temps lower than about -4C (~25F), as the low-mid levels usually become more supportive of sleet instead of freezing rain, in environments where the surface temperatures are this cold or colder.

View attachment 57460



They also found rather unsurprisingly, that ice accumulation efficiency is dependent on precipitation rate with the largest changes in ILRs between rain equivalent rates of a few hundredths to a tenth or so per hour, with it asymptoting towards ILRs of about 1:7.5 or so in heavy precipitation.

View attachment 57461
Click to expand...

So what you are saying is that the wet bulb has to be below -1C in the mid-levels or it will experience lower ILRs.

Anything colder then that the ILRs are more in the realm of IP?


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RainlessSnowless & Grumpy said:
It always has been a cold rain here. Nothing has changed.
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Plenty of models have ice well into the upstate? And models have trended colder. Only model that is warm is the euro with its over amp idea and trying to drive the LP directly into the CAD and that isn’t going to happen. Even if you had the over amp wave like the euro, it would deviate around the CAD and you’d deal with a stronger warm nose which means nothing here as we were going to be ICE regardless.
 
Comparison. Most strong cad warm noses fail to make it to Wilkes. This event easily should bring it north into Danville Virginia if not further N. Meaning...cold rain more likely in the south at times from Mooresville to Charlotte etc with freezing rain barely hanging on north of there near Elkin NC. Light to moderate event. Not a severe ice storm by any means that I see. I honestly wouldn’t prepare or stock for this event but I would avoid early morning travel if possible from Elkin NC north and elsewhere in the piedmont I would just slow down over bridges before dawn. That’s all.
 
Webberweather53 said:
For a really big ice storm, you usually want to see dews in the 10s or even single digits, low-mid 20s as shown verbatim on the 3km aren't ideal but potentially just enough to get the job done for a low-moderate end icing event.

View attachment 57463
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Most of the models have me at 33 and rain for a good portion of the event :(. But even if that was to drop a degree of two, that still wouldn't give me (or others in similar setup) a big event. As you said, we need the lower dew point to web bulb down into the upper 20s. Ice cycles are pretty but it means your losing a lot to run off.
 
One thing to note is those DP have been dropping more and more every run. South and western VA are in the teens from the onset with low 20’s even in the upstate. You keep those dropping another 4-8 degrees and this really will be a problem quickly.
 
What we already know....

Hazardous Weather Outlook
Hazardous Weather Outlook
National Weather Service Raleigh NC
411 AM EST Sun Dec 13 2020

NCZ007>010-021>026-038>041-073>076-141000-
Person-Granville-Vance-Warren-Forsyth-Guilford-Alamance-Orange-
Durham-Franklin-Davidson-Randolph-Chatham-Wake-Stanly-Montgomery-
Moore-Lee-
411 AM EST Sun Dec 13 2020

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Today and tonight.

Hazardous weather is not expected at this time.

.DAYS TWO THROUGH SEVEN...Monday through Saturday.

A soaking rain is expected late tonight through Monday as low
pressure crosses the region. Rainfall amounts up to 2 inches are
expected, and minor flooding is possible.

A second storm system Tuesday night and Wednesday will bring a threat
of wintry weather, particularly over the northern and western
Piedmont of North Carolina.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

$$


And RAH's long range discussion:

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 345 AM Sunday...

The chance for wintry weather across the N and W Piedmont Tue night
into Wed is increasing. Chilly temps will persist through Sat.

Tue through Wed night: In contrast to tonight`s/Monday`s Miller A
storm, the midweek system will be a Miller B, centered around a
potent mid level shortwave trough moving from the S Plains through
the Ohio Valley to the Northeast Tue to Wed night, along with a
frigid Canadian high centered over S Quebec nosing southward into
NC. Despite the expected slight weakening of the mid level trough,
it will still approach Tue evening/night with a surge of strong
forcing for ascent, including vertically-aligned 850 mb moisture
convergence, 500 mb DPVA and height falls, and vigorous upper
divergence in the RRQ of a 135+ kts jet streak. The inverted trough
over SW NC/E TN/N GA will weaken/fill as intense cyclogenesis takes
place just off the GA/SC coast, with this low deepening (and
possibly bombing) as it tracks NNE along coastal NC to the Mid
Atlantic/Northeast. This type of cyclogenesis pattern, with a chilly
high centered in a favorable location and a surging warm nose aloft
atop the surface-based cold layer, supports a good chance of icing,
especially across the N and W Piedmont (roughly N/W of a line from
Lake Gaston to the Triangle to Albemarle), although we`re likely to
see light rain mixed with light sleet at the onset. Will trend pops
up to good chance then likely after midnight Tue night through Wed
morning, with mostly freezing rain and a little sleet over the N/W
Piedmont and mostly just rain elsewhere. Will depict a gradual
warming to near and above freezing by early Wed afternoon with the
influence of the growing warm nose aloft and the limitation process
of latent heat release, although any ice accrual could last through
the day. Expect pops to trend down and out SW to NE late Wed
afternoon into early evening as the deep lift and coastal surface
low both exit. Highs 43-52 Tue, lows 28-39 Tue night, highs 36 to 60
(NW to SE) Wed, and lows 26-35 Wed night. Any lingering ice esp in
the Piedmont could produce travel problems into Thu morning. It`s
worth noting that a lot can change over the next few days, so stay
tuned for forecast adjustments as this time frame draws closer.
 
iGRXY said:
Plenty of models have ice well into the upstate? And models have trended colder. Only model that is warm is the euro with its over amp idea and trying to drive the LP directly into the CAD and that isn’t going to happen. Even if you had the over amp wave like the euro, it would deviate around the CAD and you’d deal with a stronger warm nose which means nothing here as we were going to be ICE regardless.
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We'll see. And I'll gladly come on here and eat crow if I have to. I'm just not feeling this one at all. We'll see where it goes in the next 24 hrs. For some reason even with a strong high in decent position the cold air push isn't what it should be. Even the NAM is very borderline which is telling to me. Anywhere south of 74 in NC is on the outside looking in if you ask me.
 
I did not like 6Z NAM 00Z Euro. If that is the beginning of a trend to warmer drier, this will not be much of a storm. We had a bad run 18z Friday I think from several models and that reversed. But closer to go time now so reversals seem less likely.
 
RainlessSnowless & Grumpy said:
We'll see. And I'll gladly come on here and eat crow if I have to. I'm just not feeling this one at all. We'll see where it goes in the next 24 hrs. For some reason even with a strong high in decent position the cold air push isn't what it should be. Even the NAM is very borderline which is telling to me. Anywhere south of 74 in NC is on the outside looking in if you ask me.
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The NAM isn’t even in its wheelhouse yet. We are still dealing with the Hr69 to Hr84 nam. Still have at least 24 hours minimum before we even get into the NAMs range.
 
These elevated dews we've been having the last few years is gonna make this another cold rain for RDU.


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Sorry if this doesn't belong here but something I don't get is how TWC and other met forecasts have highs in the lower 40s for the CLT metro area when even the warm Euro has us at the upper 30s at the warmest and the GFS keeps the area in the mid 30s.

Are they anticipating a weaker CAD?
 
SimeonNC said:
Sorry if this doesn't belong here but something I don't get is how TWC and other met forecasts have highs in the lower 40s for the CLT metro area when even the warm Euro has us at the upper 30s at the warmest and the GFS keeps the area in the mid 30s.
Are they anticipating a weaker CAD?
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Probably anticipating the lull in precip (as seen in a lot of guidance) could easily send temps up a few degrees. Doesn’t help that overall qpf is going down either.
 
BHS1975 said:
These elevated dews we've been having the last few years is gonna make this another cold rain for RDU.


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Right now I would have to agree with you. Still time for the models to trend a little better. Still a few wild cards out there; like snow cover up over the western sections of the MA. Maybe this could help. RAH currently has slightly colder temps forecasted over the Triangle area. They're usually conservative (but very good) so they may be thinking a slightly colder solutions will win out. But I would say a win for us would be a few hours of ice in the trees on Wednesday morning. Here's my grid forecast:
Tuesday Night
A chance of freezing rain and sleet between 1am and 3am, then a chance of rain or freezing rain after 3am. Mostly cloudy, with a low around 31. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.
Wednesday
Rain or freezing rain, becoming all rain after 8am. High near 43. Chance of precipitation is 80%.
 
If there’s any weenies out there that want to see onset sleet I bet it occurs very far south (North half of Georgia, upstate South Carolina, Charlotte, NC) before the warm nose takes over to liquid. But may have to stay up overnight. I’m not sure about Raleigh as it’s so Far East and less favorable timing.
 
BirdManDoomW said:
If there’s any weenies out there that want to see onset sleet I bet it occurs very far south (North half of Georgia, upstate South Carolina, Charlotte, NC) before the warm nose takes over to liquid. But may have to stay up overnight. I’m not sure about Raleigh as it’s so Far East and less favorable timing.
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What does the bird man think about Zebulon?
 
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