Meteorologic Necessities
The 540-decameter line/ Temperature: This is a measure of atmospheric thickness. Atmospheric thickness is essentially a function of average temperature within that atmospheric layer. Generally speaking for the southeastern United States, the 540-line depicts the thickness of the surface to mid-troposphere, and typically the average air temperature is cold enough for the production of wintry precipitation.
- In the case of this storm on Sunday morning, the models are calculating the 540-line to be north and west of Raleigh
- The other situation concerning this is the temperature profile of the lower atmosphere. The average temperature can be way below freezing, but the lowest 500-750 feet is above freezing; in this case rain would be the falling precipitation.
Moisture, Frozen Particles: It's very hard to have precipitation without moisture, naturally. Moisture is required for the production of precipitation, and even more so supercooled water (liquid droplets colder than -20 C) and ice particles are almost necessary for frozen precipitation. Supercooled water droplets need something to adhere to. If there are cold dust particles, ice fragments, or other particles in the atmosphere, supercooled water droplets adhere to them on contact.
- Lack of moisture does not seem to be the problem now as models are in agreement that a storm is materializing, however the lower atmosphere are projected to be above freezing, and the layer even to the middle troposphere will just not be cold enough.
- In the case of the warmer atmosphere, there will not be as much supercooled water and there will be significantly less ice crystals, and therefore a significantly smaller chance of mixed precipitation.
Processes:
Tonight the temperature is going to begin cooling off. The Canadian High pressure system is building down into the central and northeastern United States. Actually, the NWS has issued wind chill warnings and advisories for much of ND, SD, NE, IA, WI, IN.
The winds we experience as the temperature is cooling off however will shift to a more northerly wind. The cyclone which will affect us is moving through the southeast along the Gulf coast now. When the cyclone moves along the Carolina coast, moisture from both the Gulf and the Atlantic will move quickly over land. Cloud cover increasing overnight tonight will aid in temperatures remaining warm.
Precipitation will fall from morning until after lunch but should end in the early afternoon, varying in time from location to location with eastern NC receiving precipitation later into the day than further west.
Forecast: Precipitation Location and P-type
My precipitation forecast is a bit complicated, so I will split it into 3 parts representing Mountainous NC, the Foothills into the Piedmont, and the Eastern Piedmont to the coast.
Mountains:
The mountains will solely receive precipitation in the form of snow. The temperatures will be cold enough already even if there was no elevation, although the mountains will help lift moisture into colder air.
Based on what the models are putting out for precipitation amounts, I could see the mountains receiving between 0.25 and 0.5 inches of liquid precipitation. Typically in a dry snow event, the ratio of liquid to frozen is about 1:10, meaning 1 inch of rain equates to about 1 foot of snow. In this case though, the precipitation will likely be pretty wet, meaning 0.5 inches of snow could be between 4-5 inches of snow. I would say the mountains could receive about 2-5 inches of snow depending on elevation.
Western Piedmont:
The 540-line, as discussed above, is projected to be located from Roanoke Rapids over to Greensboro and down through Charlotte. In these areas and west into South Hill, VA over toward Mount Airy and down through Hendersonville, NC, will likely see a mix of primarily snow and sleet transitioning to rain in the late morning around lunch.
The Western Piedmont will not see as much precipitation accumulation, and only part of that will be a wintry mix. I would be surprised to see more than a 0.25" - 0.5" of snow while the rest may only be rain.
Eastern Piedmont to the Coast: Due to the warmth which will be found in central NC and east, I have a hard time believing that much of the area east and southeast of the aforementioned area will see anything other than rain. It is possible that in over to VA Beach, Elizabeth City, Raleigh, and down through Sanford may see some mix in the early morning but it is unlikely.
The southeast will likely receive between 0.5" and 1" of liquid precipitation. In the case of this storm, I have a hard time believing that any wintry accumulation will come of that.
I hope everyone has a great weekend!!
- Lack of moisture does not seem to be the problem now as models are in agreement that a storm is materializing, however the lower atmosphere are projected to be above freezing, and the layer even to the middle troposphere will just not be cold enough.
- In the case of the warmer atmosphere, there will not be as much supercooled water and there will be significantly less ice crystals, and therefore a significantly smaller chance of mixed precipitation.
Processes:
Tonight the temperature is going to begin cooling off. The Canadian High pressure system is building down into the central and northeastern United States. Actually, the NWS has issued wind chill warnings and advisories for much of ND, SD, NE, IA, WI, IN.
The winds we experience as the temperature is cooling off however will shift to a more northerly wind. The cyclone which will affect us is moving through the southeast along the Gulf coast now. When the cyclone moves along the Carolina coast, moisture from both the Gulf and the Atlantic will move quickly over land. Cloud cover increasing overnight tonight will aid in temperatures remaining warm.
Precipitation will fall from morning until after lunch but should end in the early afternoon, varying in time from location to location with eastern NC receiving precipitation later into the day than further west.
Forecast: Precipitation Location and P-type
My precipitation forecast is a bit complicated, so I will split it into 3 parts representing Mountainous NC, the Foothills into the Piedmont, and the Eastern Piedmont to the coast.
Mountains:
The mountains will solely receive precipitation in the form of snow. The temperatures will be cold enough already even if there was no elevation, although the mountains will help lift moisture into colder air.
Based on what the models are putting out for precipitation amounts, I could see the mountains receiving between 0.25 and 0.5 inches of liquid precipitation. Typically in a dry snow event, the ratio of liquid to frozen is about 1:10, meaning 1 inch of rain equates to about 1 foot of snow. In this case though, the precipitation will likely be pretty wet, meaning 0.5 inches of snow could be between 4-5 inches of snow. I would say the mountains could receive about 2-5 inches of snow depending on elevation.
Western Piedmont:
The 540-line, as discussed above, is projected to be located from Roanoke Rapids over to Greensboro and down through Charlotte. In these areas and west into South Hill, VA over toward Mount Airy and down through Hendersonville, NC, will likely see a mix of primarily snow and sleet transitioning to rain in the late morning around lunch.
The Western Piedmont will not see as much precipitation accumulation, and only part of that will be a wintry mix. I would be surprised to see more than a 0.25" - 0.5" of snow while the rest may only be rain.
Eastern Piedmont to the Coast: Due to the warmth which will be found in central NC and east, I have a hard time believing that much of the area east and southeast of the aforementioned area will see anything other than rain. It is possible that in over to VA Beach, Elizabeth City, Raleigh, and down through Sanford may see some mix in the early morning but it is unlikely.
The southeast will likely receive between 0.5" and 1" of liquid precipitation. In the case of this storm, I have a hard time believing that any wintry accumulation will come of that.
I hope everyone has a great weekend!!
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