Winter Storm Jonas

*This storm is likely going to do some crippling in NC and on up into the northeast.*

Below I have laid out the weather, hazards, and class/game cancellation forecast in that order.

P-Type, Timing, and Accumulation

Precipitation will start Friday morning after midnight. Initial precipitation type will likely be a snow/sleet mix with possible accumulation of between 1-2 inches before a true transition to sleet and freezing rain after sunrise on Friday. 

Throughout the day Friday we can expect a mix of sleet and freezing rain with accumulations around 0.3-0.5" of ice in the Piedmont with possible 0.60" or more down toward Charlotte.
*Updated from last night based on latest model runs and temperature/precipitation forecasts.

Late Friday night, a "warm nose", or area of warmer air above cooler air in the lower atmosphere , will arise from warm air advection ahead of the low pressure system (likely due to a coastal warm front in this case). This warmth will likely allow for the production of liquid rain which will last a few hours before transitioning back to sleet/freezing rain until early morning Saturday (before sunrise).

*This rain is potentially devastating for two reasons. First, it will allow for melting in some areas while refreezing to create black ice. Secondly, it will potentially reach the surface as freezing rain depending on specific temperatures creating an even heavier glaze. 

Saturday around sunrise precipitation will make a transition back to snow and will remain a combination of snow/sleet for the duration of the event. This will last until late afternoon and even on into the evening depending on how quickly the storm propagates and will allow for another 0.5-1" of accumulation on top of the glaze from overnight. 

Hazards

1. Traffic/Travel: Obviously, the first and most important hazard is traffic. Traffic will be horrendous if anyone is on the road and with the roads being as slick as they will be with this event, it would be wise to stay home after going to get bread and milk on Thursday night (if there is any left). Once the event starts, it will not finish for a couple days.

2. Power Outages: If you are home tomorrow or preparing for this storm and you have a generator, tomorrow would be the day to make sure it is working properly. With how much ice this storm is capable of producing and forecasted to produce, it is likely that there will be some power outages at the very least localized in heavier areas of ice accumulation if not more widespread from tree limbs and trees falling under the weight of the ice. 

*Power outage possible in areas where heavier ice accumulation expected in the Piedmont. 

3. Gas: I'm not sure how many of you have gas stoves or furnaces, but tomorrow would be a good day to not only prepare those and make sure propane tanks are filled, but also to fill up your cars in case you get caught out somewhere this weekend, just to make sure you won't run out of fuel. 

4. Lighting: No, not light'n'ing, but lighting. Make sure extra candles and lighters are accessible and flashlights have fresh batteries in case of a power outage.

Class Cancellation Forecast

And now, the moment the students have all been waiting for! Drum Roll, Please!

Okay so cutting to the chase. We will not have classes on Friday. It may take the university until late Thursday night or even Friday morning before cancelling classes as: 

1. The university staff needs to sleep as well and 

2. The university staff wants to make sure precipitation has fallen and is making for hazardous road conditions before cancelling classes. 

This forecast is two-fold as well. The second question is whether the Duke game on Saturday will still happen. Last year Duke did not travel to UNC in a couple inches of snow for the safety of the players and coaches, and this year the trip for the team will be slightly longer than last year with more menacing road hazards. I, at this point before any precipitation has fallen and seeing how the state and universities handle clearing the roads and highway safety, will say that the game will need to be postponed. However, there have been "snow" games in the past at PNC Arena, and I think it would be pretty awesome to have one again!

Monday is a toss-up for right now. We will likely have classes on Monday, however there is a slight chance at this point that there will be a two hour delay. That delay is based on how long clouds stick around from this system and how warm the temperature gets on Sunday, because Sunday night anything left on the ground will re-freeze creating another travel nightmare for Monday morning. 

Snow, or No Go? Cleaning up the Confusion

What's up Wolfpack! I want to see snow as much as all of you, but this storm just doesn't look like it is going to be the one to produce the heavy accumulation we are hoping for. Allow me to discuss the now 12-15 hours leading up to the event. For the summary and my forecast for Sunday, scroll to the bottom. If you want to read the science behind it, awesome!

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.