Friday Night/Saturday Morning Freezing Rain Threat

[Jon]

NAM showing snow to ice.

 

Haven't loaded it in bufkit but I imagine a lot of that snow won't reatch the ground and is extremely light precip. I remember this issue last year, tropical tidbits is good but 4dbz is nothing. Would be cool if precip trended stronger while 850's are cold enough for a flurry surprise.

[drfranklin]

is that a DP of 4 for Greenville, SC Fri afternoon? wow

(I enjoy these CAD events - it's one of the few times where Greenville is colder than Asheville)

[No snow for you]

2 minutes ago, drfranklin said:

is that a DP of 4 for Greenville, SC Fri afternoon? wow

(I enjoy these CAD events - it's one of the few times where Greenville is colder than Asheville)

Yep. I doubt much of any rain will make it to the ground with the air that dry. Or course the wet bulbs will be insane as well. 

[DopplerWx]

yea don't be sucked into the nam sim radar.  gets people every year.

[Jon]

Didn't feel like reposting here, but this is what I mean and how the sim radar can fool you

[mackerel_sky]

14 minutes ago, DopplerWx said:

yea don't be sucked into the nam sim radar.  gets people every year.

It's all we've got to look at, most likely until January! Let us enjoy the NAM! 50s and 30s after next Tuesday's " event" ain't gonna bring a lot of snow or ice

[burrel2]

27 minutes ago, drfranklin said:

is that a DP of 4 for Greenville, SC Fri afternoon? wow

(I enjoy these CAD events - it's one of the few times where Greenville is colder than Asheville)

It's actually showing a dew point of -4 for Greenville.

[NEGa]

those are some mega-low dewpoints.  with that magnitude of dry air its going to be hard to get anything to reach the ground

[drfranklin]

Burrel, thanks, my eyesight is diminishing in my old(er) age LOL

NEGa, yes agree, I don't see anything reaching the ground for hours

Mack, agree, the WB readings will be insane

[msuwx]

58 minutes ago, Jon said:

 

 

Didn't feel like reposting here, but this is what I mean and how the sim radar can fool you

 

 You are correct.

However, here is my yearly reminder to the board that simulated reflectivity and QPF are different animals. Model QPF outputs account for evaporation.  Now could be overdoing the amount of precipitation? Certainly. 

[AshevilleCityWx]

If a model were to have a bias of over doing precip, you will really see its errors trifold in a CAD setup because fake precip makes for fake cooling and the blue snow you are seeing on the images is likely not supportive due to having the wrong thermal profile throughout.

[drfranklin]

20 minutes ago, AshevilleCityWx said:

If a model were to have a bias of over doing precip, you will really see its errors trifold in a CAD setup because fake precip makes for fake cooling and the blue snow you are seeing on the images is likely not supportive due to having the wrong thermal profile throughout.

thank you for the sound analysis - live by the models/die by the models - the local mets are being very conservative with this "event"

[mackerel_sky]

8 minutes ago, drfranklin said:

thank you for the sound analysis - live by the models/die by the models - the local mets are being very conservative with this "event"

The fox Carolina morning weather, seemed the most interested of all the local weather I saw. Saying could be more than a nuisance if everything lined up!! I don't even know why I look at Dale Gilbert

[rowjimmy73]

1 hour ago, Jon said:

 

 

Didn't feel like reposting here, but this is what I mean and how the sim radar can fool you

 

absolutely, having lived in nj most of my life im aware of how it all works out normally. just excited that my 4 and 2 yr old have even a remote chance of anything frozen occuring. it would be even nicer to have it happen before 12/28 as i am having a hip replacement on 12/29 and will spend the rest of the winter being unable to partake of winter fun. cant help but let my inner weenie rage a bit lol

 

[drfranklin]

8 minutes ago, mackerel_sky said:

The fox Carolina morning weather, seemed the most interested of all the local weather I saw. Saying could be more than a nuisance if everything lined up!! I don't even know why I look at Dale Gilbert

Dale Gilbert LOL - he must be pushing 70yo - I fall asleep every time he's on television - (as for WYFF) Dale is the antithesis of Christ Justus - I like Chris but he LOVES wintry weather (he's from the Asheville area) - at times he seems to wishcast

[Jon]

 You are correct.

However, here is my yearly reminder to the board that simulated reflectivity and QPF are different animals. Model QPF outputs account for evaporation.  Now could be overdoing the amount of precipitation? Certainly. 

Agree 100%. Good to see you posting Matt!

[Jonathan]

3 hours ago, rowjimmy73 said:

cant help but let my inner weenie rage a bit lol

 

Gotta be careful with those raging weenies.

We've been burned many a time by simulated radars and whatnot. Best not to even look at those unless it's the HRRR; it usually does pretty well.

Gonna take a miracle to make this a decent event. Extremely dry air and heavier precip looks scarce. Then again, you don't want too heavy of precip because of latent heat release. Could be a virga storm or a rain storm with the slightest of changes.

[FallsLake]

I understand that this NAM-12km is showing a lot of virga, and the NAM-32km does show a lot less coverage. But I did find the high pressure showing up over western NC interesting:

 

[mackerel_sky]

6 minutes ago, FallsLake said:

I understand that this NAM-12km is showing a lot of virga, and the NAM-32km does show a lot less coverage. But I did find the high pressure showing up over western NC interesting:

 

In - situ strong enough to form its own high pressure?? I think I've seen that happen before!

[FallsLake]

3 minutes ago, mackerel_sky said:

In - situ strong enough to form its own high pressure?? I think I've seen that happen before!

I've seen that as well. This is an unusual setup with very low dew points. If (if if if) we can get more preic in early we might have something.

[jshetley]

3 hours ago, drfranklin said:

Dale Gilbert LOL - he must be pushing 70yo - I fall asleep every time he's on television - (as for WYFF) Dale is the antithesis of Christ Justus - I like Chris but he LOVES wintry weather (he's from the Asheville area) - at times he seems to wishcast

Agree.

[GaStorm]

Would there have to be a good amount of precip to create a new high on the map for in-situ?

[griteater]

I feel kind of slimy commenting on this one given how light the precip should be, but here goes...

Looking at the 850mb warm advection maps on the College of Dupage site for the NAM & GFS, it looks like the strongest low level upglide forcing for precip generation will occur during the time when the temperatures will be most supportive of freezing rain & drizzle which will be Fri night and overnight Friday.  Looking at forecast soundings, although we have low level upglide, saturation only exists in the low levels.  There is not enough moisture or lift in the mid and upper levels to support the precip generation process.  So, that leads to scattered light showers and drizzle due to the low level upglide alone.  Here's what GSP says on the subject, "Mid and upper levels in profiles have very little opportunity to moisten up during the coldest part of the early weekend period given the westerly flow aloft over the southeast and with our area being so far removed from the better height falls. However, low level moiture and upglide should become rather robust over the region as a 40 to 50 kt low level jet sets up overhead by the early morning hours Saturday."

Map below is 1AM Saturday on the NAM showing sfc wet bulb temps below freezing well down into SC and GA.  The NAM and CMC are the coldest, with the Euro and GFS warmer, but still supportive of frz rain overnight Friday into the upstate.  It's normally best to go with the colder modeling in damming setups / or when cold, dry arctic air is banked up against the mtns.   

Bottom line: I would go with scattered light frz rain and drizzle to break out after sunset Friday, and continuing overnight, with the best opportunity for a light to very light glaze to occur from Burlington to Monroe, through the upstate, into NE GA, and west / northwest to the Blue Ridge.  Should expect that there will be some areas in there that miss out on the precip given the modest setup.

[burrel2]

I've seen this scenario play out too many times... here's my call right now for the upstate of SC.

Light drizzle to at times light rain will start falling around 8 or 9pm Friday evening with temps averaging around 34/10. As soon as precip gets heavy enough to wet the ground good we will drop below freezing and wind up wetbulbing down to around 27 or 28 degree's when the heaviest precip comes through in pre-dawn hours.  The temp will ever slowly climb from that point, reaching 32 by 9 or 10am, at which point most of the significant precip will have departed anyways. I don't think there will be much in the way of moderate rates at any time during the night, but we should have a constant drizzle falling for most of the night with the heaviest rates around 2 or 3am.  

These temps will be cold enough to cause very slick spots on roads and I expect wrecks will be numerous saturday morning. We are very near the lowest sun angle of the year and Friday will be very cold, which will aid in making the bridges/roadways susceptible to ice patches.  Total ice accretion will only amount to around 1/10th for the upstate so no issues with power loss. The ice accretion maxima will be found along the escarpment where it appears they might pick up 1/4 inch or more of liquid before dawn on Saturday, (one caveat being that these places with elevation will go above freezing sooner, maybe around 6 or 7am).

In summary, I expect freezing rain advisory level accumulations for the upstate, but with a very severe impact on roadways that catches people by surprise.

There only two caveats to this forecast. One would be if this airmass turns out to be not nearly as dry/cold as the models are depicting. But right now even the global models are plenty dry/cold on Friday for me to feel comfortable with this forecast. You really just have to throw away the GFS temperature forecast beyond that point, it's garbage. Two would be if we wind up not getting any measurable precip from this event. I think we would need to see at least five hundredth's liquid in the gauge to cause problems with freezing rain and I think we're going to get that much or more. We'll see...

 

[burrel2]

I think back to the "event" we had last year where the upstate was literally forecast to only get around 1/100th of liquid during the day in the form of freezing rain. The event was February 15th, 2016.

The Greenville/Spartanburg area wound up catching a patch drizzle that morning and there was something like 200+ wrecks  when there are normally like 5.

[Lookout]

9 hours ago, burrel2 said:

ARPEGE has the 32 line extending all the way to Atlanta,Augusta,Columbia at 7am Saturday morning. Even keeps a sliver of the upstate below 32 at 1pm on Saturday.

FWIW, I believe this model did slightly better with CAD events last winter at this lead time when compared to others.

I was going to post about this earlier until you beat me to it but yeah it seems to be the only model with a clue as to what is going on and the new 12z continues to do so. Although the 18z nam is a little better, showing temps only in the mid 30s as late saturday evening in the heart of the wedge which is exactly what I would expect. By sat afternoon, the nam and gfs are 20 degrees apart in some places, in particular north carolina. 

right before precip reaches the ground the 4km nam has dewpoints of -2 to 7 across ne ga/upstate with surface temps of 31 to 35 with wetbulbs roughly in the 25 to 27 range. by 06z everyone is subfreezing....in the 29 to 31 range with dewpoints low enough that there could another degree or two worth of cooling. remains to be seen if there will be enough to actually reach wetbulb temps in the 25 to 27 range  but one thing is for sure...the gfs is on crack with it's warming surface temps even before 12z saturday and the canadian looks like it's been smoking a few joints itself with it's lack of evap response and rapid warming saturday. temps are not likely to get out of the 30s across the heart of the wedge/i-85 corridor/nc foothills saturday unless there are some breaks in the clouds. If there isn't and it remains solidely overcast, no chance. 

6 hours ago, NEGa said:

those are some mega-low dewpoints.  with that magnitude of dry air its going to be hard to get anything to reach the ground

true and to be sure this isn't likely to be a big deal for most areas..although it could be quite slippery for a while saturday morning given the cold airmass tomorrow and friday as even light freezing rain and drizzle could cause some slick roads. Best chance of significant icing looks to be from extreme ne ga, far northwest upstate and southern nc foothills as this is where the models show the most overall precip falling through 18z sat. I think there is a shot that temps stay subfreezing into mid afternoon saturday over extreme ne ga and upstate if precip remains steady enough before waa and eventually latent heat release brings temps to/above freezing...although any actual accretion probably stops before then since temps aloft will be so warm. 

To me though, This event isn't terribly interesting in terms of how much freezing rain there is but rather  just how poorly the models are likely handling the temps....including temps after they go above freezing...as it looks like the gfs is going to make an attempt at duplicating it's 10 to 20 degree bust with the last ice event we had. It's hard to believe that the model is actually worse today than it was a few years ago with handling CAD and wedges breaking down. 

1 hour ago, mackerel_sky said:

In - situ strong enough to form its own high pressure?? I think I've seen that happen before!

yep.. such meso highs have been responsible for some of our more impressive model busts and cold air hanging on longer than anticipated.  Interestingly the gfs actually hinted at this a few days ago before getting worse as we got closer. 

 

 

[Lookout]

25 minutes ago, burrel2 said:

I've seen this scenario play out too many times... here's my call right now for the upstate of SC.

Light drizzle to at times light rain will start falling around 8 or 9pm Friday evening with temps averaging around 34/10. As soon as precip gets heavy enough to wet the ground good we will drop below freezing and wind up wetbulbing down to around 27 or 28 degree's when the heaviest precip comes through in pre-dawn hours.  The temp will ever slowly climb from that point, reaching 32 by 9 or 10am, at which point most of the significant precip will have departed anyways. I don't think there will be much in the way of moderate rates at any time during the night, but we should have a constant drizzle falling for most of the night with the heaviest rates around 2 or 3am.  

These temps will be cold enough to cause very slick spots on roads and I expect wrecks will be numerous saturday morning. We are very near the lowest sun angle of the year and Friday will be very cold, which will aid in making the bridges/roadways susceptible to ice patches.  Total ice accretion will only amount to around 1/10th for the upstate so no issues with power loss. The ice accretion maxima will be found along the escarpment where it appears they might pick up 1/4 inch or more of liquid before dawn on Saturday, (one caveat being that these places with elevation will go above freezing sooner, maybe around 6 or 7am).

In summary, I expect freezing rain advisory level accumulations for the upstate, but with a very severe impact on roadways that catches people by surprise.

There only two caveats to this forecast. One would be if this airmass turns out to be not nearly as dry/cold as the models are depicting. But right now even the global models are plenty dry/cold on Friday for me to feel comfortable with this forecast. You really just have to throw away the GFS temperature forecast beyond that point, it's garbage. Two would be if we wind up not getting any measurable precip from this event. I think we would need to see at least five hundredth's liquid in the gauge to cause problems with freezing rain and I think we're going to get that much or more. We'll see...

 

Good post and nice summary of what to expect.  

Good thing this is happening on the weekend.....I hope there aren't too many people caught off guard early saturday by the road conditions because as you nicely said, it doesn't take a huge ice storm to cause a lot of traffic problems with  cold/subfreezing surfaces ..which should be the case friday night/sat am. Indeed..the lightness of the event could  cause more problems. Slower rates/less amounts means less runoff before freezing and due to how light the amounts are, there won't be much hype around it which results in less unawareness by drivers which in turn  could lead to more accidents. 

[oconeexman]

Excellent posts Burrell and Lookout! I expect a nice glaze here in Mid upper Oconee over towards Central. Probably very slick in Mtn Rest to upper NE Ga. Same for Sunset to Travelers Rest.

Appreciate the explanations guys.

[mackerel_sky]

When's the next NAM run?

[chapelhillwx]

1 minute ago, mackerel_sky said:

When's the next NAM run?

9ish, then GFS around 11, then Euro around 1:30.