The snow, sleet, and freezing rain oh my Dec 27-30 thread

[WidreMann]

Dude, just stop. It may not be a mega CAD situation, but with 1032-1034 down into NC, it's not gone and there won't be WAA at the surface. The GL low is not a strong powerful low. Even with strong lows, we still can see CAD hang out quick hardily before getting scoured as the low approaches. This is not even a scenario like that.

[jburns]

37 minutes ago, burrel2 said:

Read more post less..... Nam has surface temps around 32 with single digit dew points in the upstate. If any precip makes it there it would drop surface temps in to the low 20's or colder.

Also, your bolded statement is just wrong... look at the wind profiles.

 

36 minutes ago, FLweather said:

Maybe you should take you own advice

Maybe you both should take my advice. KNOCK IT OFF.   

[cwick20]

3 hours ago, cwick20 said:

I'm trying to understand what I'm seeing with the models and how some don't seem to be reconciling the differences they have with each other. The GFS has a 1040+ HP that comes out of Montana and progresses southeast essentially squashing the low pressure. The high pressure seems to make it as far south east as the Kansas, Nebraska, Missouri, Iowa border so the low pressure in the gulf being suppressed makes sense. However, as best I can tell the European takes this high pressure across the great lakes yet for some reason the moisture from the gulf doesn't seem to come any further north. The hi-res models have this same high pressure that meanders within 100 miles of its location for several frames but then move is several hundred miles from one frame to the next. This seems odd as well. Someone help me understand this.

I guess what I'm saying is...with these differences and oddities it seems to me that something exciting could still be on the table for us. It seems to me with some of these differences there should be a wider range of possibilities than what is being shown.

No one has any input on this?

[downeastnc]

Wow GFS much improved with the New Year threat ...significant winter storm for NC, upstate SC.... Much more amped with WSW flow....

[burrel2]

German model didn't back down at 12z.

[downeastnc]

Just a wee bit chilly with the snow pack 

 

[burrel2]

25 minutes ago, jburns said:

 

Maybe you both should take my advice. KNOCK IT OFF.   

When someone makes a model analysis post that is that far off base, it needs to be called out and/or removed. 

[WidreMann]

12 minutes ago, cwick20 said:

No one has any input on this?

The HP doesn't squash the LP. That's not how this works. Weather is happening in a 3d space and a lot of what drives precip and air movement is happening aloft. Precipitation is not generated at the ground.

[snowlover91]

6 minutes ago, burrel2 said:

German model didn't back down at 12z.

Since the NAM trended this way and the GFS has a stronger vort, it might be on to something. 

[mackerel_sky]

15 minutes ago, downeastnc said:

Wow GFS much improved with the New Year threat ...significant winter storm for NC, upstate SC.... Much more amped with WSW flow....

There's a separate thread for this storm!

[lilj4425]

3 minutes ago, snowlover91 said:

Since the NAM trended this way and the GFS has a stronger vort, it might be on to something. 

The German model did really well last system so I wouldn’t discount it. It is definitely holding its own and being consistent also. 

[snowlover91]

Just now, lilj4425 said:

It also did really well last system so I wouldn’t discount it. The German model is definitely holding its own and being consistent. 

It’s incredible to me the completely different handling of the shortwave by the models when we are less than 72 hours out. I have a feeling once this comes ashore we will finally see some agreement. 

[mackerel_sky]

1 minute ago, snowlover91 said:

It’s incredible to me the completely different handling of the shortwave by the models when we are less than 72 hours out. I have a feeling once this comes ashore we will finally see some agreement. 

That's not until tomorrow, iirc??

[CAD_Wedge_NC]

1 minute ago, lilj4425 said:

The German model did really well last system so I wouldn’t discount it. It is definitely holding its own and being consistent also. 

Well, whatever happens, the German model has been very consistent with it's handling of the pattern. Maybe the other globals are more susceptible to small fluctuations in the pattern and it flaws their solutions. I don't know at this point. Just a wild guess. With that being said, if this model is correct, we will give it much more respect through the rest of winter.

[snowlover91]

UK seems a bit stronger with our low and precip at 72...

[WidreMann]

1 minute ago, CAD_Wedge_NC said:

Well, whatever happens, the German model has been very consistent with it's handling of the pattern. Maybe the other globals are more susceptible to small fluctuations in the pattern and it flaws their solutions. I don't know at this point. Just a wild guess. With that being said, if this model is correct, we will give it much more respect through the rest of winter.

The German model uses the ECMWF as its base: https://en.wikipedia.org/wiki/Integrated_Forecast_System.

[Orangeburgwx]

German model for my area has me with ZR from 11am Thursday to 4am Friday

[FLweather]

6 minutes ago, snowlover91 said:

It’s entirely possible for folks in GA and SC to see sleet and freezing rain in this setup. Evaporation also cooling combined with the HP forcing winds from the NE at the surface will keep the cold air in place. There is little to no warm air advection either. The Great Lakes Low is irrelevant in this scenario because of the existing airmass in place. 

Freezing rain is a self limited process.  WAA always over rides CAA.  Unless  the HP is anchored  providing low level cold air at the surface WAA will over take.  Especially if you have a weak GL low cutting off the CAA by squeezing a HP to the north.If the Nam Euro GFS etc etc etc is right or wrong. It really  doesn't matter. Cause at the end of the day weather right or wrong there is no way GA SC NC gets hit with a freezing rain from a squeezed off modified CAA or CAD.  Even 12z Gfs shows this just more progressive.  Good day. 

 

[snowlover91]

7 minutes ago, FLweather said:

Freezing rain is a self limited process.  WAA always over rides CAA.  Unless  the HP is anchored  providing low level cold air at the surface WAA will over take.  Especially if you have a weak GL low cutting off the CAA by squeezing a HP to the north.If the Nam Euro GFS etc etc etc is right or wrong. It really  doesn't matter. Cause at the end of the day weather right or wrong there is no way GA SC NC gets hit with a freezing rain from a squeezed off modified CAA or CAD.  Even 12z Gfs shows this just more progressive.  Good day. 

 

Sure it’s a self-limiting process but when you have the best models like the NAM showing sleet and freezing rain, you can trust it with pretty high confidence as they are great with thermals, CAD, and they do in fact factor in WAA vs CAA and the latent heat release. Inside 48 hours no global model should be relied on as the mesoscale models like the 3km NAM and RGEM are vastly superior. 

Notice on the 12km NAM the winds are NE indicative of the HP still dominating the surface flow. If the GLL was dominant these winds would be out of the SE. Even well to our west there is no SW wind at the surface as the GLL is simply not relevant here. 

Now notice the dewpoints to the NE. Plenty of cold, dry air to advect in and sustain the ice. Again notice winds are NE.

[griteater]

3 hours ago, cwick20 said:

I'm trying to understand what I'm seeing with the models and how some don't seem to be reconciling the differences they have with each other. The GFS has a 1040+ HP that comes out of Montana and progresses southeast essentially squashing the low pressure. The high pressure seems to make it as far south east as the Kansas, Nebraska, Missouri, Iowa border so the low pressure in the gulf being suppressed makes sense. However, as best I can tell the European takes this high pressure across the great lakes yet for some reason the moisture from the gulf doesn't seem to come any further north. The hi-res models have this same high pressure that meanders within 100 miles of its location for several frames but then move is several hundred miles from one frame to the next. This seems odd as well. Someone help me understand this.

I guess what I'm saying is...with these differences and oddities it seems to me that something exciting could still be on the table for us. It seems to me with some of these differences there should be a wider range of possibilities than what is being shown.

To go along with what Widre said, processes that produce precipitation mostly occur aloft, above the surface.  The movement of surface highs and lows are also dictated by the flow configuration above the surface.  In a simple view for this 'storm', just look at the direction of the flow at 500mb over the southeast.  If you want to see precip get back into the upstate, you want to see more of a SW to NE orientation to the height lines over the southeast instead of the predominant west to east (see 2 images on the left at 500mb and 700mb) - that would lead to an increase in both the moisture transport and rising motion for precip generation.

 

[GAdawg]

7 minutes ago, FLweather said:

Freezing rain is a self limited process.  WAA always over rides CAA.  Unless  the HP is anchored  providing low level cold air at the surface WAA will over take.  Especially if you have a weak GL low cutting off the CAA by squeezing a HP to the north.If the Nam Euro GFS etc etc etc is right or wrong. It really  doesn't matter. Cause at the end of the day weather right or wrong there is no way GA SC NC gets hit with a freezing rain from a squeezed off modified CAA or CAD.  Even 12z Gfs shows this just more progressive.  Good day. 

 

I do not post but I do read...and I personally think you need to be put in time out....JBurns told you to knock it off.

[CAD_Wedge_NC]

5 minutes ago, FLweather said:

Freezing rain is a self limited process.  WAA always over rides CAA.  Unless  the HP is anchored  providing low level cold air at the surface WAA will over take.  Especially if you have a weak GL low cutting off the CAA by squeezing a HP to the north.If the Nam Euro GFS etc etc etc is right or wrong. It really  doesn't matter. Cause at the end of the day weather right or wrong there is no way GA SC NC gets hit with a freezing rain from a squeezed off modified CAA or CAD.  Even 12z Gfs shows this just more progressive.  Good day. 

 

You are correct, freezing rain is a self-limiting process if you don't have a constant feed of low level cold air. In this case, the low-level winds are feeding cold dry air from a very cold source region. I think the disconnect is that you believe this feed will be cut-off by a great lakes low and a retreating high. I understand what you are implying, but I don't think it will happen in this instance.

[griteater]

Heck I've seen freezing rain in light southeasterly winds when the precip was moving into an airmass that was cold and dry...it happened just a few years ago

[griteater]

14 minutes ago, FLweather said:

Freezing rain is a self limited process.  WAA always over rides CAA.  Unless  the HP is anchored  providing low level cold air at the surface WAA will over take.  Especially if you have a weak GL low cutting off the CAA by squeezing a HP to the north.If the Nam Euro GFS etc etc etc is right or wrong. It really  doesn't matter. Cause at the end of the day weather right or wrong there is no way GA SC NC gets hit with a freezing rain from a squeezed off modified CAA or CAD.  Even 12z Gfs shows this just more progressive.  Good day. 

Ha, it's a Larry Cosgrove flashback.  Issue with this system isn't cold, it's the wretched setup for good precip

[HKY_WX]

In situ cad has happened many times bf. There's no threat of a changeover to rain in the favored cad areas in any system from now till new years.

[FLweather]

2 minutes ago, griteater said:

Ha, it's a Larry Cosgrove flashback.  Issue with this system isn't cold, it's the wretched setup for good precip

You are correct sir.  Unless we see some major changes and an odd ball coming in from the left field aloft. It's pretty well a cold zonal flow.  Depending on which side of the shortwave trough you on. But nothing at h5 supports a ice storm around GA SC NC let a know any significant  CAD. 

[CAD_Wedge_NC]

30 minutes ago, WidreMann said:

The German model uses the ECMWF as its base: https://en.wikipedia.org/wiki/Integrated_Forecast_System.

 I know the background behind the model. However, I am a little confused as to why the German and the Euro are so vastly different. What's the benefit?

[snowlover91]

9 minutes ago, FLweather said:

You are correct sir.  Unless we see some major changes and an odd ball coming in from the left field aloft. It's pretty well a cold zonal flow.  Depending on which side of the shortwave trough you on. But nothing at h5 supports a ice storm around GA SC NC let a know any significant  CAD. 

If the precip is there as indicated by the NAM there will be ice in GA, SC and NC. It digs the vort enough to bring ice to these areas. 

[griteater]

2 hours ago, NC DataDude said:

Also, I hear a lot of mention of scores. Do these scores only represent "winter" scenarios or are they year round scores totals?

Almost always, you will see the Euro scoring best, then UKMet, then GFS or CMC, then Navgem (FNMOC).  Click on this link, then on the left side of the page, it has the various parameters.  The first dropdown has 'Height', Temp (temperatures), and 'SLP' (sea level pressure).  At the top of the page are the various levels of the atmosphere (1000mb near the sfc, 500mb, etc) and the location over the globe (NH for Northern Hemisphere, PNA for the Pacific Ocean to North America)

http://www.emc.ncep.noaa.gov/gmb/STATS_vsdb/

 

This link is for sea level pressure verification, but in addition to the operational models, it has the ensembles and the WPC forecasts for verification comparison as well

http://www.wpc.ncep.noaa.gov/pmsl_verif/index.html

 

Lastly, we've been tracking model verification for SE Winter Storms over the past 2 winters in this tread...

https://www.americanwx.com/bb/topic/49398-southeast-winter-storm-threats-model-performance/

[griteater]

2 hours ago, NC DataDude said:

Is there a time period where we lean on the short term models more so than the mid/long term?

As we get closer in, the short term models like the NAM 3km are good at showing the details of where precipitation should be located....and finer details about temperature profiles