(updated ~7am)
Well, here we go...been a while since the Triad has had to deal with wintry conditions, and the stage is set for just that early tomorrow, Thursday. A Winter Storm Watch was upgraded to a Winter Storm Warning early this morning.
In going over the new data sets I regularly use, the bull's eye for a likely travel mess will be the greater Triad region (NW Piedmont and Foothills), especially along and north/west of I-85 corridor. Yesterday I remarked how the ETA MOS had Charlotte unusually cold...this morning, the models are flipped and Charlotte's #s are a tad warmer, where Greensboro may see all of a 2-degree temperature swing all day. Yep, lookin' a bit yucky.
Now, we aren't talking inches of snow and howling winds...it will be far more subtle than that. First, winds are no issue. Second, the chance for a good snow should be dampened (pun intended) by sleet and rain mixing in. The bottom line is it takes so little icy accumulation to cause travel problems...the quantity issue is almost secondary to the issue of precipitation-type.
And so I found these graphics from USA Today that will help refresh your mind on how the various wintry forms are produced. Keep in mind the atmosphere is like a layer cake, and at different altitudes you can have varying temperatures, humidities, winds, and all kinds of 'stuff' that makes a huge difference what falls on our noggins.
It does all start as snow, even in the summer...it's just so high up you'd never know. Air temps all the way to the surface above freezing make for good ol' liquid form.
Freezing rain is often our nemesis. Good winter storms mean moisture coming up from the Gulf or in off the Atlantic, which means it's being transported in a warmer air mass aloft...that slides on top of freezing or sub-freezing air at the surface. If that cold layer is thin, the liquid does not have enough distance/time to refreeze into sleet pellets, much less recrystallize into snow. Drops hit in liquid form, and depending on the surface it hits rather quickly forms an icy glaze. Extended periods of freezing rain accumulate enough ice to break trees and powerlines. Remember that horrific ice storm we had in December 2002? I was on-duty in the Charlotte office of News 14 when it hit...and watched it POUR rain for hours with the air temperature at 27-28 degrees. May I never see that again.
It would be nice to have a thicker layer of cold air so that the rain could refreeze into some sort of sleet or ice pellet. That's still very slippery when it accumulates, but you at least have some better chance to negotiate travel, where as freezing rain/ice is the great equalizer and neutralizer for travel. As a disclaimer, I do not advocate travel in winter weather, but some of us have to get places, regardless. Give me sleet over freezing rain any day. Will our cold layer stay thick enough to prolong sleet/snow, or will it be too shallow after sunrise and give us freezing rain? That's the biggee right now...
Good ol' snow...air column all the way up is cold, cold, cold. I don't see the air nearly thick enough for that tomorrow, although I do expect a few hours of snowfall early, albeit getting mixed now and then with other forms.
CURRENT THOUGHT: for the Triad, while precipitation could fall anytime after midnight, I see the best statistical window for precipitation to be 7am - 1pm. Snow and sleet have their best shot at us early in the AM before freezing rain joins in in earnest by 8am. That will beat down any accumulations and make for a slippery mess. So far my thinking has leaned toward more limited accumulations (like 1-3") toward our NW corridor, and very little for Greensboro. When you mix in rain and such you really just focus on roads and travel issues. The NWS is forecasting 0.1- 0.3" of icing from this storm for all but the far eastern and southern edges of our region...they're most concerned about that, and not snow/sleet accumulations. Air temperatures during this period are forecast to be 31 and 32 degrees for 7-8 hours, so you can imagine why 1 degree lower or higher will have a huge impact on tomorrow morning's weather.
Too, evaporative cooling principles will be front and center after midnight...I'll try to write more about that later on...time to head in to the salt mine!
Well, here we go...been a while since the Triad has had to deal with wintry conditions, and the stage is set for just that early tomorrow, Thursday. A Winter Storm Watch was upgraded to a Winter Storm Warning early this morning.
In going over the new data sets I regularly use, the bull's eye for a likely travel mess will be the greater Triad region (NW Piedmont and Foothills), especially along and north/west of I-85 corridor. Yesterday I remarked how the ETA MOS had Charlotte unusually cold...this morning, the models are flipped and Charlotte's #s are a tad warmer, where Greensboro may see all of a 2-degree temperature swing all day. Yep, lookin' a bit yucky.
Now, we aren't talking inches of snow and howling winds...it will be far more subtle than that. First, winds are no issue. Second, the chance for a good snow should be dampened (pun intended) by sleet and rain mixing in. The bottom line is it takes so little icy accumulation to cause travel problems...the quantity issue is almost secondary to the issue of precipitation-type.
And so I found these graphics from USA Today that will help refresh your mind on how the various wintry forms are produced. Keep in mind the atmosphere is like a layer cake, and at different altitudes you can have varying temperatures, humidities, winds, and all kinds of 'stuff' that makes a huge difference what falls on our noggins.
It does all start as snow, even in the summer...it's just so high up you'd never know. Air temps all the way to the surface above freezing make for good ol' liquid form.
Freezing rain is often our nemesis. Good winter storms mean moisture coming up from the Gulf or in off the Atlantic, which means it's being transported in a warmer air mass aloft...that slides on top of freezing or sub-freezing air at the surface. If that cold layer is thin, the liquid does not have enough distance/time to refreeze into sleet pellets, much less recrystallize into snow. Drops hit in liquid form, and depending on the surface it hits rather quickly forms an icy glaze. Extended periods of freezing rain accumulate enough ice to break trees and powerlines. Remember that horrific ice storm we had in December 2002? I was on-duty in the Charlotte office of News 14 when it hit...and watched it POUR rain for hours with the air temperature at 27-28 degrees. May I never see that again.
It would be nice to have a thicker layer of cold air so that the rain could refreeze into some sort of sleet or ice pellet. That's still very slippery when it accumulates, but you at least have some better chance to negotiate travel, where as freezing rain/ice is the great equalizer and neutralizer for travel. As a disclaimer, I do not advocate travel in winter weather, but some of us have to get places, regardless. Give me sleet over freezing rain any day. Will our cold layer stay thick enough to prolong sleet/snow, or will it be too shallow after sunrise and give us freezing rain? That's the biggee right now...
Good ol' snow...air column all the way up is cold, cold, cold. I don't see the air nearly thick enough for that tomorrow, although I do expect a few hours of snowfall early, albeit getting mixed now and then with other forms.CURRENT THOUGHT: for the Triad, while precipitation could fall anytime after midnight, I see the best statistical window for precipitation to be 7am - 1pm. Snow and sleet have their best shot at us early in the AM before freezing rain joins in in earnest by 8am. That will beat down any accumulations and make for a slippery mess. So far my thinking has leaned toward more limited accumulations (like 1-3") toward our NW corridor, and very little for Greensboro. When you mix in rain and such you really just focus on roads and travel issues. The NWS is forecasting 0.1- 0.3" of icing from this storm for all but the far eastern and southern edges of our region...they're most concerned about that, and not snow/sleet accumulations. Air temperatures during this period are forecast to be 31 and 32 degrees for 7-8 hours, so you can imagine why 1 degree lower or higher will have a huge impact on tomorrow morning's weather.
Too, evaporative cooling principles will be front and center after midnight...I'll try to write more about that later on...time to head in to the salt mine!
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