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January 3-4 Storm Thread part II

rduwx

By rduwx,
in Southeastern States

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PackWxMan

PackWxMan

Posted
Posted

Confidence is continuing to increase that a moderate-high impact winter storm will affect east-central North Carolina as soon as late tomorrow and Thursday. A broad area of low pressure is anticipated to form in relatively short order near or just east of north-central Florida and rapidly intensify as it moves north-northeast and gets awfully close to Cape Hatteras and the rest of the Outer Banks some time on Thursday. Meanwhile, a weak trough of low pressure diving out of Saskatchewan/Alberta and into the Northern Rockies will impinge on the incipient low pressure off the Carolina and Georgia coast, ultimately impacting the large-scale steering flow and track of the rapidly intensifying low which may undergo instant occlusion as the upper level trough eventually overruns it. It needs to be stressed that this setup is exceptionally fickle and most of the standard, coarse grid numerical weather prediction computer models most local meteorologists are looking to for guidance in a situation like are likely going to miss very key, subtle features in the overall pattern that will ultimately have a massive impact forecast and be the difference between extremely heavy snow and next to nothing at all. This includes the placement and intensity of clusters of showers and thunderstorms over the Northeastern Gulf Coast that will develop later tomorrow. The reason the convection (i.e. thunderstorms) over the Gulf coast matters a lot for us in determining whether we get a lot of snow or not is because within these large-scale convective clusters, condensation and deposition (process where water vapor turns into snowflakes) is occurring on a mind boggling scale. These processes release heat into the surrounding atmosphere. As many of you are well aware, the heat released allows the surrounding air to expand, which causes the pressure and the density directly within that mass of air to drop. In the most basic sense, this drop pressure within the clusters of storms actually reflects onto the synoptic-scale low pressure system. This may then allow the low pressure center to deepen or change its track in the direction of where the pressures are falling the most within the convection! Furthermore, the winds spiraling around this center of low pressure that's formed in part from the clusters of storms can help advect (or move/push) Atlantic moisture inland into Carolinas over top of the cold, arctic airmass that's been in place recently. This set of ingredients then leads to potentially large amounts of snow and ice. Therefore, it's important for weather models and local meteorologists to properly analyze, forecast, and correct their forecast mistakes for these groups of thunderstorms hundreds of miles away on the Gulf Coast because they're capable of growing upscale and affecting our weather in a short period of time. Essentially, if these thunderstorms aren't properly forecast then what would be a forecast for little-no snow at all in NC could turn into several inches of heavy, wet snow. Thus, as we roll deeper into tomorrow the growing convective cluster along the NE Gulf coast will begin to spread moisture over the Carolinas. The airmass in place will be pretty dry to start so some of the initial precipitation that moves in from the southwest may have trouble reaching the ground. However, as the low pressure center off our coast continues to intensify and slugs copious amounts of Atlantic moisture inland across east-central North Carolina, areas along/east of US Highway-1 (including Fayetteville & Raleigh-Durham) may not have much trouble receiving a significant dose of moderate-heavy precipitation, which will likely be in the form of snow. Some of this snow may be particularly heavy at times, with graupel and even thundersnow possible over the hardest hit areas. However, if the low pressure center moves closer to the Carolina coast as some models are insisting some of the moderate-heavy snow could mix with or change over to sleet especially the further southeast you go in the state. Given how cold the temperatures have been over the past few days, any snow or sleet that falls will immediately stick to the ground and the roads. Therefore, residents in east-central NC should make preparations in case travel is heavily limited by this storm for a few-several days afterwards. I'm currently expecting at least several inches of snow and/or snow/sleet to fall over NC tomorrow night and into Thursday, especially for areas along/east of US Highway 1, with the potential for 4 to 8 inches of snow to fall generally in and around the US highway 1 and I-95 corridors, with locally higher amounts probable-likely. These numbers are highly variable and expect potentially large future changes as we approach this event. The closest analog I can find to this current storm is the January 2000 event which crippled the Triangle Area and the US-1 corridor. Attached below I provide the mid-level voriticity (essentially spin) and radar forecasts for tomorrow's event and compare those w/ the analyses provided by the NWS RAH and ECMWF's 20th Century Reanalysis (ERA-20C), you should note how uncanny the similarities are While it is not safe at all or very wise to currently expect this storm to pan out EXACTLY like January 2000, the similarities between this winter storm and that event are impressive say the least and those who have lived here long enough are well aware of how bad the forecasts were even the night before the storm struck. Thus, take this forecast with a massive grain of salt as it could change a lot between now and tomorrow afternoon/evening. - ERIC WEBB

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Cold Rain

Cold Rain

Posted
Posted
9 minutes ago, Poimen said:

Is this based on pre-storm/upstream radar presentations looking better than modeled? ;)

Partly.  This system is going to be so dynamic, I’m not sure it’s being correctly modeled with respect to precip placement and intensity.  I will be surprised if precipitation is not more widespread, farther west, and higher in totality than we are being lead to believe.  This could very easily overperform.  Of course, by the same token, the 0z Nam might shut us out. :)

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SEwakenosnowforu

SEwakenosnowforu

Posted
Posted
2 minutes ago, Cold Rain said:

Partly.  This system is going to be so dynamic, I’m not sure it’s being correctly modeled with respect to precip placement and intensity.  I will be surprised if precipitation is not more widespread, farther west, and higher in totality than we are being lead to believe.  This could very easily overperform.  Of course, by the same token, the 0z Nam might shut us out. :)

Just wish this thing was not zipping along! Imagine if eastern nc was looking at a 36 hour event...like 1989

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cbmclean

cbmclean

Posted
Posted

To keep myself grounded in reality I went back and re-read Cold Rain's "what we learned" post after last January's wonderfest.  I reproduce here

Well, it appears that yet another winter storm has baffled meteorologists, forecasters, models, and snow enthusiasts everywhere.  Personally, I'd put this in the Top Five Busts of All Time category, probably in the top three, behind only the Carolina Crusher and the epic December Debacle in 2000.

I personally want to thank all of the mets and forecasters that do their best to interpret the data and give us useable information so that we can prepare for the conditions ahead.  They shouldn't be the target of anger or hateful rhetoric, as they often are on social media after events like this.

I also want to thank all of you who show up here, post maps, provide analysis, give historical context, and post obs.  This is the very first place I go for weather info.

So, with that said, what have we learned here?  I can think of a few things.  Feel free to add your own:

The NW "trend" is real and almost always occurs.

Model snowfall maps are useless at any lead or range.

Pink areas on a p-type map indicate slightly colder rain than the green areas.

Models usually vastly underestimate both the degree and duration of warm layers.  If the model is even hinting at a warm layer, cut your snowfall forecast by at least 50%.

Models usually overestimate QPF.

Cold air moving in concurrently with the storm will be much slower to do so than indicated by forecast models.

A high pressure located in a near ideal spot is needed for a widespread snowstorm.

Modeled backside snow usually vastly underperforms.

The duration of wintry weather will usually be much shorter than you think.

A Miller A taking a near ideal track in the heart of winter with apparent sufficient supply of cold air can still produce a lot of rain.

The change-over from rain to sleet or sleet to snow usually takes much longer than anticipated.

Even with ideal conditions, forecasted snowfall totals should be trimmed by at least 25%.

Snow and sleet can easily accumulate and remain on a ground that was above freezing ahead of the storm.

Snow and sleet can easily accumulate on a wet ground.

Optimism and hope do not make it snow in the south.

Congrats to all of you to the north and west that saw lots of snow.  Enjoy it, have lots of fun, and take lots of pics.  Everybody else, enjoy your wintry mix and the upcoming mild period before winter hopefully returns later this month or next.

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nchighcountrywx

nchighcountrywx

Posted
Posted
11 minutes ago, frazdaddy said:

It seems Mr. Webber has thrown down the proverbial gauntlet. 

 

Let’s Roll !

At least for everyone down east.  

Hope everyone gets smothered in flakeage!

I am very appreciative of Webber’s insight and analysis.  A master at his craft.  Plan your future well brother as you are blessed.

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Cold Rain

Cold Rain

Posted
Posted
8 minutes ago, cbmclean said:

To keep myself grounded in reality I went back and re-read Cold Rain's "what we learned" post after last January's wonderfest.  I reproduce here

Well, it appears that yet another winter storm has baffled meteorologists, forecasters, models, and snow enthusiasts everywhere.  Personally, I'd put this in the Top Five Busts of All Time category, probably in the top three, behind only the Carolina Crusher and the epic December Debacle in 2000.

I personally want to thank all of the mets and forecasters that do their best to interpret the data and give us useable information so that we can prepare for the conditions ahead.  They shouldn't be the target of anger or hateful rhetoric, as they often are on social media after events like this.

I also want to thank all of you who show up here, post maps, provide analysis, give historical context, and post obs.  This is the very first place I go for weather info.

So, with that said, what have we learned here?  I can think of a few things.  Feel free to add your own:

The NW "trend" is real and almost always occurs.

Model snowfall maps are useless at any lead or range.

Pink areas on a p-type map indicate slightly colder rain than the green areas.

Models usually vastly underestimate both the degree and duration of warm layers.  If the model is even hinting at a warm layer, cut your snowfall forecast by at least 50%.

Models usually overestimate QPF.

Cold air moving in concurrently with the storm will be much slower to do so than indicated by forecast models.

A high pressure located in a near ideal spot is needed for a widespread snowstorm.

Modeled backside snow usually vastly underperforms.

The duration of wintry weather will usually be much shorter than you think.

A Miller A taking a near ideal track in the heart of winter with apparent sufficient supply of cold air can still produce a lot of rain.

The change-over from rain to sleet or sleet to snow usually takes much longer than anticipated.

Even with ideal conditions, forecasted snowfall totals should be trimmed by at least 25%.

Snow and sleet can easily accumulate and remain on a ground that was above freezing ahead of the storm.

Snow and sleet can easily accumulate on a wet ground.

Optimism and hope do not make it snow in the south.

Congrats to all of you to the north and west that saw lots of snow.  Enjoy it, have lots of fun, and take lots of pics.  Everybody else, enjoy your wintry mix and the upcoming mild period before winter hopefully returns later this month or next.

Given this excellent analysis, can I phone a friend and perhaps trim my forecast a bit?! :)

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mrdaddyman

mrdaddyman

Posted
Posted
25 minutes ago, PackWxMan said:

Confidence is continuing to increase that a moderate-high impact winter storm will affect east-central North Carolina as soon as late tomorrow and Thursday. A broad area of low pressure is anticipated to form in relatively short order near or just east of north-central Florida and rapidly intensify as it moves north-northeast and gets awfully close to Cape Hatteras and the rest of the Outer Banks some time on Thursday. Meanwhile, a weak trough of low pressure diving out of Saskatchewan/Alberta and into the Northern Rockies will impinge on the incipient low pressure off the Carolina and Georgia coast, ultimately impacting the large-scale steering flow and track of the rapidly intensifying low which may undergo instant occlusion as the upper level trough eventually overruns it. It needs to be stressed that this setup is exceptionally fickle and most of the standard, coarse grid numerical weather prediction computer models most local meteorologists are looking to for guidance in a situation like are likely going to miss very key, subtle features in the overall pattern that will ultimately have a massive impact forecast and be the difference between extremely heavy snow and next to nothing at all. This includes the placement and intensity of clusters of showers and thunderstorms over the Northeastern Gulf Coast that will develop later tomorrow. The reason the convection (i.e. thunderstorms) over the Gulf coast matters a lot for us in determining whether we get a lot of snow or not is because within these large-scale convective clusters, condensation and deposition (process where water vapor turns into snowflakes) is occurring on a mind boggling scale. These processes release heat into the surrounding atmosphere. As many of you are well aware, the heat released allows the surrounding air to expand, which causes the pressure and the density directly within that mass of air to drop. In the most basic sense, this drop pressure within the clusters of storms actually reflects onto the synoptic-scale low pressure system. This may then allow the low pressure center to deepen or change its track in the direction of where the pressures are falling the most within the convection! Furthermore, the winds spiraling around this center of low pressure that's formed in part from the clusters of storms can help advect (or move/push) Atlantic moisture inland into Carolinas over top of the cold, arctic airmass that's been in place recently. This set of ingredients then leads to potentially large amounts of snow and ice. Therefore, it's important for weather models and local meteorologists to properly analyze, forecast, and correct their forecast mistakes for these groups of thunderstorms hundreds of miles away on the Gulf Coast because they're capable of growing upscale and affecting our weather in a short period of time. Essentially, if these thunderstorms aren't properly forecast then what would be a forecast for little-no snow at all in NC could turn into several inches of heavy, wet snow. Thus, as we roll deeper into tomorrow the growing convective cluster along the NE Gulf coast will begin to spread moisture over the Carolinas. The airmass in place will be pretty dry to start so some of the initial precipitation that moves in from the southwest may have trouble reaching the ground. However, as the low pressure center off our coast continues to intensify and slugs copious amounts of Atlantic moisture inland across east-central North Carolina, areas along/east of US Highway-1 (including Fayetteville & Raleigh-Durham) may not have much trouble receiving a significant dose of moderate-heavy precipitation, which will likely be in the form of snow. Some of this snow may be particularly heavy at times, with graupel and even thundersnow possible over the hardest hit areas. However, if the low pressure center moves closer to the Carolina coast as some models are insisting some of the moderate-heavy snow could mix with or change over to sleet especially the further southeast you go in the state. Given how cold the temperatures have been over the past few days, any snow or sleet that falls will immediately stick to the ground and the roads. Therefore, residents in east-central NC should make preparations in case travel is heavily limited by this storm for a few-several days afterwards. I'm currently expecting at least several inches of snow and/or snow/sleet to fall over NC tomorrow night and into Thursday, especially for areas along/east of US Highway 1, with the potential for 4 to 8 inches of snow to fall generally in and around the US highway 1 and I-95 corridors, with locally higher amounts probable-likely. These numbers are highly variable and expect potentially large future changes as we approach this event. The closest analog I can find to this current storm is the January 2000 event which crippled the Triangle Area and the US-1 corridor. Attached below I provide the mid-level voriticity (essentially spin) and radar forecasts for tomorrow's event and compare those w/ the analyses provided by the NWS RAH and ECMWF's 20th Century Reanalysis (ERA-20C), you should note how uncanny the similarities are While it is not safe at all or very wise to currently expect this storm to pan out EXACTLY like January 2000, the similarities between this winter storm and that event are impressive say the least and those who have lived here long enough are well aware of how bad the forecasts were even the night before the storm struck. Thus, take this forecast with a massive grain of salt as it could change a lot between now and tomorrow afternoon/evening. - ERIC WEBB

Where did you get this?

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