Feb 16th/17th/18th Winter Wx

[NCSNOW]

Thanks for everyone contributions and mods. Great job.

Dps are gonna be single digits and thick clouds by sunrise. Even if we can make upper 20s from mid teen lows without solar insulation, the wetbulb are sending alot on NC into the teens when moisture gets started.

[GaWx]

Here's something interesting . Although the GFS 2 M #'s shown at MeteoStar have typically been cold biased, they have done a rare switch to being too warm in the ATL-AHN corridor as well as nearby areas to the NE as of 18Z vs the 12Z GFS progs. Actually, this isn't really that surprising since it tends to underdo Arctic air at the surface. Regardless, I wonder it this has any implications as we head to handling the wedge of cold tomorrow. Opinions?

Examples:

ATL prog 38; actual 36

AHN prog 44; actual 42

GVL prog 41; actual 36

GSP prog 38; actual 34

PDK prog 38; actual 34

MGE prog 36; actual 33

So, all of these are 2-5 below the 1PM progs. Any significance to this?

[PackGrad05]

Here's something interesting . Although the GFS 2 M #'s shown at MeteoStar have typically been cold biased, they have done a rare switch to being too warm in the ATL-AHN corridor as well as nearby areas to the NE as of 18Z vs the 12Z GFS progs. Actually, this isn't really that surprising since it tends to underdo Arctic air at the surface. Regardless, I wonder it this has any implications as we head to handling the wedge of cold tomorrow. Opinions?

Examples:

ATL prog 38; actual 36

AHN prog 44; actual 42

GVL prog 41; actual 36

GSP prog 38; actual 34

PDK prog 38; actual 34

MGE prog 36; actual 33

So, all of these are 2-5 below the 1PM progs. Any significance to this?

That's why I'm taking the precip forecasts and trending them south a little bit..  i don't think the cold air is being handled properly

[Cold Rain]

Thanks for everyone contributions and mods. Great job.

Dps are gonna be single digits and thick clouds by sunrise. Even if we can make upper 20s from mid teen lows without solar insulation, the wetbulb are sending alot on NC into the teens when moisture gets started.

I can't see most being in the teens at that time. Maybe the NW Piedmont. That just seems like too extreme of a scenario to me. I don't recall an ice event where temps were like that.

[packfan98]

Honestly, it's probably time to be looking more at the NAM/RGEM and then to the RAP tonight to see how everything is unfolding. 

You are probably right.  I also thought it might be a decent idea to recap all of the models given that we are just under 24 hours out.  It might be easier to see what ends up verifying the best in the aftermath.  Thank you for all of the pbp!

[Vorticity]

Here's something interesting . Although the GFS 2 M #'s shown at MeteoStar have typically been cold biased, they have done a rare switch to being too warm in the ATL-AHN corridor as well as nearby areas to the NE as of 18Z vs the 12Z GFS progs. Actually, this isn't really that surprising since it tends to underdo Arctic air at the surface. Regardless, I wonder it this has any implications as we head to handling the wedge of cold tomorrow. Opinions?

Examples:

ATL prog 38; actual 36

AHN prog 44; actual 42

GVL prog 41; actual 36

GSP prog 38; actual 34

PDK prog 38; actual 34

MGE prog 36; actual 33

So, all of these are 2-5 below the 1PM progs. Any significance to this?

Always a concern with the wedge and wet bulb effect, on the other hand in recent progged cold outbreaks this season projections of lows in the single digits have ended up like this morning in the teens to mid 20s, and if precip does not come in until after lunch hour to ATL for example, well then...

[GaWx]

That's why I'm taking the precip forecasts and trending them south a little bit.. i don't think the cold air is being handled properly

If the cold air is not handled properly, would that mean a likely further south low track? Opinions? As it is, the track into the wedge doesn't make a whole lot of sense and I couldn't even find a similar track for ANY of the widespread major NC winter storms since at least 1950 fwiw.

[Dunkman]

I can't see most being in the teens at that time. Maybe the NW Piedmont. That just seems like too extreme of a scenario to me. I don't recall an ice event where temps were like that.

We have had multiple zr events here in the last 15 years with temps in the teens. I'm not saying its likely but it is definitely possible. I think it would require an active flow of cold air though.

[deltadog03]

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[HurricaneTracker]

If the cold air is not handled properly, would that mean a likely further south low track? Opinions?

Euro was a hair further south compared to 00Z. Need to watch SREF and RGEM to see what changes once the shortwaves are fully sampled.

Heck, even 18Z NAM could be a wild swing south.

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[packbacker]

Euro tracks the SLP right over CAE and then over the NC/VA border. Dryslot just SE of that track. It has RDU topping out at 29F while FAY is at 50.

[griteater]

Based on the latest Euro, GFS, and NAM, the bigger amounts might need to shift further north again, well into Virginia. South of I-40 in NC is a dusting to an inch. North of I-40, 1-3". The best snows will be across KY, VA, and WV.

Bigger story that's unfolding is a damaging ice storm for most of NC.

 

That's a good summary of where we are at HT.  I agree.  Looks like a great snow storm for KY into southern West Virginia.  For Charlotte, I would say a dusting of snow/sleet, then 0.25-0.40 of frz rain accretion  There is strong 850mb warming from 00z to 06z Tues on the Euro across central and eastern NC (still below 0 in NW corner).  Total storm QPF for CLT is only 0.6

[HurricaneTracker]

That's a good summary of where we are at HT. I agree. Looks like a great snow storm for KY into southern West Virginia. For Charlotte, I would say a dusting of snow/sleet, then 0.25-0.40 of frz rain accretion There is strong 850mb warming from 00z to 06z Tues on the Euro across central and eastern NC (still below 0 in NW corner).

Yep. Even at Asheville, 850mb warms to a balmy +4° at midnight Tuesday. Incredible! This warmth expands east to include CLT and FAY.

Putting it simply, either the existing CAD is exceptionally poorly handled, or it is not anchored well enough to influence the track. That means it's quicker to erode which is what the Euro is showing. I mean, it's suggesting rain for even the southwest mountains, where just 72 hours ago, they were to get 12" of snow!

Enough of the global models. Time to take a closer look at RAP, RGEM, and 4km NAM. But everyone in NC should be ready for decent freezing rain accums. Definitely winter storm warning criteria...except that it's ice and not snow that triggers the warning.

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[Cold Rain]

We have had multiple zr events here in the last 15 years with temps in the teens. I'm not saying its likely but it is definitely possible. I think it would require an active flow of cold air though.

That's what I'm thinking too. If we don't have a strong cold feed, dews should bounce back some by game time.

[franklin NCwx]

Yep. Even at Asheville, 850mb warms to a balmy +4° at midnight Tuesday. Incredible! This warmth expands east to include CLT and FAY.

Putting it simply, either the existing CAD is exceptionally poorly handled, or it is not anchored well enough to influence the track. That means it's quicker to erode which is what the Euro is showing. I mean, it's suggesting rain for even the southwest mountains, where just 72 hours ago, they were to get 12" of snow!

Enough of the global models. Time to take a closer look at RAP, RGEM, and 4km NAM. But everyone in NC should be ready for decent freezing rain accums. Definitely winter storm warning criteria...except that it's ice and not snow that triggers the warning.

Sent from my iPad

lol that was only 24 hours ago including the ensembles. King my....

[Wow]

lol that was only 24 hours ago including the ensembles. King my....

 

Ask NYC and NJ what they think of the Euro.   

 

Inside of 2 days I don't even bother looking at it.  It's SR model time.

[WxJordan]

My first accumulations map for this system....

 

 

This system has been a nightmare to track, and will probably have more surprises in store for us. I am worried about busting on the low ends in terms of snow and more ice in the foothills of NC. Other than that, I feel like my forecast is pretty good.

 

Here is a portion from the blog I wrote describing the system....

"Snow and sleet will develop in North Carolina, South Carolina, and Virginia before changing to a cold rain in the far eastern part of the Carolinas and the piedmont of South Carolina. An icy mess of sleet and freezing rain will set up in the eastern piedmont of North Carolina, including Raleigh, Fayetteville, and Charlotte. Major ice accumulations are likely in this area. West and north of I-85, expect snow changing to a mix of snow, sleet, and freezing rain. Hickory and Winston-Salem will see up to a half a foot of snow and sleet mix with moderate ice accumulations. In the mountains, up to 10 inches of snow will be possible with a little sleet mixing in. In northern South Carolina, 1-4 inches of snow is possible with a quarter of an inch of ice possible. Far western NC, around Franklin, will see a mix of snow, sleet, freezing rain, and rain with up to an inch of snow and light ice accumulations."

 

You can read the blog post here: http://wxjordan.com/weather-forecast/forecast/172-winter-storm-brings-mixed-bag-of-snow-sleet-and-freezing-rain-to-nc-and-va

[Lookout]

I honestly am still at a loss for words for how much this has changed in last 24 hours.  I really am.  There might not be much snow south of I-40 on this at all.  Matter of fact, any warmer, the I-40 corridor is going to have to deal with some rain issues.  NC looks SAFE, for now, from just a rain storm, but looks very very icy with ZR and a poop load of Sleet.  GA/SC/AL....lets just hurry this crap up so we can kiss winter *or a lack there of* goodbye.  I really feel bad for the people who have to deal will all the negativity this will bring because of the changes.  

I wasn't around last night to see the models but looking at them this morning, i have to agree this is pretty extraordinary and frustrating.

 

Even though it's bleak, I still have some concerns that areas that appear out of the woods in terms of freezing rain over northeast ga and sc are actually not. The last 2 runs of the gfs in fact suggest temps still get to freezing from around gainesville to my location...as low as 28 or 29 around gainesville northeast.  In fact tomorrow it even has the northern burbs of atlanta getting to freezing before warming up. So for areas along and east/northeast of a line from gainesville to athens/elberton I still believe there is a chance for a period of icing..though confidence is real low at the moment. .   I think areas north of 85 and at/east of gainesville get major icing still...especially up around toccoa, cornelia, etc

 

 

 

You think the models can't handle dynamic processes and evaporative cooling?

When there are huge dewpoint depressions/high potential for evap cooling..they normally do not cool the temps as much as  From my experience in cad situations,  the nam and gfs are typically 1 to 3 degrees too warm after saturation. That's a pretty big deal when they model progs are 32/33 degrees such as in this . There have been many a ice events here where the models insisted on it being 33 or 34 degrees after saturation. With this system, i've seen the  gfs and nam hiking dewpoints  20 to 25 degrees after precip starts without much of a temp response. For example, across portions of north ga the nam/gfs have insisted on temps being roughly 35 degrees with dp's in the single digits to around 10 before precip starts  and only dropping the temp to 33 or 34 when the wetbulb is actually 28 or 29.

 

That said, it's possible that can happen if ONLY the near surface is that cold and dry. In other words, if it's cold and dry from 950 to 925mb down to the surface, temps are more likely to fall close to the wetbulbs if there is appreciable precip to do so. if there is strong waa and the near surface cold layer is only a couple of hundred feet deep the temp will not respond nearly as much. In this case, at least initially, temps at 925mb to the near surface are below freezing so i expect quite a temp drop in those areas where the cold extends up to 950mb at least...which is over a good portion of north ga/sc midlands.

 

For those on the edge, watch for how much surface warming there is tomorrow and how low the dewpoints are when precip is likely to start. If temps end up warming too much before precip arrives and based on wetbulbs/dewpoints that is generally 40 degrees, or dewpoints start rising before precip arrives, it should remain rain. (except starting out as sleet or mix).

[calculus1]

I know how some of you feel about analogs, but here's the CIPs analog for this storm based on 15 previous storms with similar setups.  Courtesy of Brad P:

 

[BullCityWx]

I think what we need to watch for tomorrow is an earlier onset of precip. The earlier we can get going, the better.

[Jon]

My first accumulations map for this system....

 

This system has been a nightmare to track, and will probably have more surprises in store for us. I am worried about busting on the low ends in terms of snow and more ice in the foothills of NC. Other than that, I feel like my forecast is pretty good.

 

Here is a portion from the blog I wrote describing the system....

"Snow and sleet will develop in North Carolina, South Carolina, and Virginia before changing to a cold rain in the far eastern part of the Carolinas and the piedmont of South Carolina. An icy mess of sleet and freezing rain will set up in the eastern piedmont of North Carolina, including Raleigh, Fayetteville, and Charlotte. Major ice accumulations are likely in this area. West and north of I-85, expect snow changing to a mix of snow, sleet, and freezing rain. Hickory and Winston-Salem will see up to a half a foot of snow and sleet mix with moderate ice accumulations. In the mountains, up to 10 inches of snow will be possible with a little sleet mixing in. In northern South Carolina, 1-4 inches of snow is possible with a quarter of an inch of ice possible. Far western NC, around Franklin, will see a mix of snow, sleet, freezing rain, and rain with up to an inch of snow and light ice accumulations."

 

You can read the blog post here: http://wxjordan.com/weather-forecast/forecast/172-winter-storm-brings-mixed-bag-of-snow-sleet-and-freezing-rain-to-nc-and-va

Nice Jordan. I agree, the freezing rain threat south is concerning...some wild amounts on the GFS for KFAY likely overdone but still...0.9" accumulating ZR...that's nothing to mess with, can be a huge impact down there.

[NC_WX10]

My first accumulations map for this system....

 

Great information. Love the map. Hope it is right!

[superjames1992]

Damn, those CIPS analogs look nice.

 

I'll be rooting for your map to verify, Jordan!

[Jon]

I think what we need to watch for tomorrow is an earlier onset of precip. The earlier we can get going, the better.

The WRF-ARW gets it going pretty early.

 

[Buddy1987]

Fellas has the start time changed at all for onset of precip?

[superjames1992]

Fellas has the start time changed at all for onset of precip?

 

I wouldn't be surprised if the start time is earlier than any of the modeling indicates.  It seems that often happens with overrunning.  No guarantees, of course.

[kvegas-wx]

The WRF-ARW gets it going pretty early.

Well thats 3pm but clearly that has to be a virga storm for the first few hours given DPs. But by early evening, game on if that is accurate.

[strongwxnc]

The WRF-ARW gets it going pretty early.

img]

10am ?

I see now 3pm.

Sent from my iPhone

[WxBlue]

10am ?

Sent from my iPhone

 

3pm

[Jon]

Well thats 3pm but clearly that has to be a virga storm for the first few hours given DPs. But by early evening, game on if that is accurate.

Well at 4pm dews shoot up in central NC so I wouldn't read into them too much, that's an hour. If it's virga it's only virga for short time before the column is saturated, per this model of course. It's also one of the wettest, 1.1" in RDU...