February; Snow Wait, Not Winter This Time! Increasing Chances for Severe Wx!

This time, instead of posting about a snow or ice storm and class cancellations from slick roads, my post has a much more uncanny message to it for this time of year. This time we are talking about the very real and increasing potential for Supercell thunderstorms, hail greater than 1" in diameter, straight-line wind gusts of over 70 mph, heavy rains, and the possibility for an isolated tornado, or maybe a few. In this post I have broken down the setup in the Synoptic Scale, Mesoscale, and Microscale systems in order to help everyone better understand different atmospheric interactions that produce such awesomely powerful storms.

*At the bottom I have described expected types of weather which we could experience here and* *potential hazards to be aware of, and the timing of storms.*

Terminology

1. CAPE - Convective Available Potential Energy: A measure of instability in the atmosphere. This value represents the "ability" for an unstable air parcel to rise and condense, ultimately forming cumulus towers an creating a pressure anomaly in the atmosphere
2. LFC - Level of Free Convection: This term refers to the point at which an atmospheric parcel is completely buoyant and will rise freely until it reaches the atmospheric temperature again
3. EL - Equilibrium Level: This level in the atmosphere is that point which the parcel temperature again reaches atmospheric temperature and is no longer positively buoyant.
4. Wind Shear: Wind shear refers to the change in wind speed and direction. Wind shear can be calculated both horizontally and vertically and is used in a variety of ways including being able to visualize the rotation in the atmosphere.
5. Helicity: This parameter is used in severe weather forecasting. One of the variables which goes into calculating helicity is wind shear. It allows forecasters to compute atmospheric rotation.

Synoptic (Large) Scale: 100km - 1000km

A cold front has made its way down into the southeastern United States, meaning colder air temperatures. The area of interest with this particular front lies in the "warm sector" of the front, or the area ahead of the front associated with warmer temperatures. When a front passes, there is a shift in the wind and a change in the air mass. Cold fronts, because of the nature of cold air to forcefully shove warm air out of its way, are typically associated with severe weather as the temperatures warm up and moisture with that warmth helps to increase instability along the front. Instability is measured in a meteorological parameter called CAPE, or Convective Available Potential Energy. The value of CAPE is calculated by taking the area on a skew-t chart under the moist adiabat from the LFC (Level of Free Convection) to the EL (Equilibrium Level).

This frontal system has a strong cold wind behind it from a Canadian air mass, and a strong warm wind ahead of it, yet in almost the opposite direction, from the seasonally warming Gulf of Mexico. In addition, the sub-tropical jet stream, or the jet stream typically associated with changing weather here in the southeast, is racing eastward. This jet lies atop a southward-blowing wind behind the front, and a northward-blowing wind ahead of the front. This change in wind speed and direction both horizontally and vertically is referred to as "wind shear".

The severity of these storms depends on where the boundary is for the warm sector. That boundary between the colder air mass and the warm sector is where the most instability is to be found, and if sufficient moisture is present then it is possible for cumulus towers to form rapidly.

Mesoscale (Medium Scale): 1km - 100km

The wind shear I mentioned above really comes to play in the mesoscale. A supercell thunderstorm is basically a thunderstorm rotating around a centralized rotating updraft. Typically a supercell is associated with the production of hail, heavy rains, and tornadoes. There are exceptions to every rule, but for all intents and purposes a supercell is a severe, rotating thunderstorm.

The wind shear is essentially what spins up the thunderstorm in order to produce a "mesolow" or "mesocyclone", or an area at the base of the supercell which descends slightly from the base of the thunderstorm and typically results stronger counter-clockwise rotation. In addition, the presence of the jet stream aloft, cooling air from precipitation will not hinder the main updraft caused by instability. This off-set cooling actually increases the temperature gradient in the smaller scale and thus increases the storms ability to move air rapidly upward. As a result, these storms could last for hours.

In the main updraft of a supercell, near the mesocyclone but in-between the precipitation underneath the anvil and the precipitation-free mesocyclone is where the hail-core can be found in storms that produce hail. Why?  Well, updrafts are strong enough to carry a droplet up into the cloud where there are ice crystals and supercooled water droplets. Supercooled water then freezes to the ice crystals and the droplets grow. They fall into the updraft where they are carried back up and the process continues until it falls out of the updraft or becomes too heavy for the updraft to lift again.

Microscale (Small Scale): 1m - 1km

The microscale/mesoscale boundary is where a lot of the forecast difficulties take place. Within the microscale we look at the 0-1km helicity, or rotation in the atmosphere. Basically, if the helicity is strong enough, that means the surface rotation is strong enough that tornado production is possible.

Other importance in the microscale involves the Rear Inflow Jet, surface interactions between the ground moisture and the base of the mesocyclone, and circulation around the mesocyclone, but going into detail in these areas is not necessary for this post.

Thresholds:

In severe weather forecasting, we have various parameters and thresholds for those parameters which tip us off as to whether there is a significant threat or not.

1. CAPE - Varies, but anything more than 1000 Joules/kg is sufficient for strong instability, especially this time of year.
2. SCP (Supercell Composite Parameter) - If greater than 1 there is a good chance for supercell formation
3. STP (Significant Tornado Parameter) - If greater than 1 there is a good chance of tornado formation
4. 0-1 km Helicity - If greater than 200 m^2/s^2 there is a good possibility of strong rotation at the surface
5. 0-6 km Wind Shear - If greater than 40 m/s there is sufficient change in the wind direction in the atmosphere to produce a tall rotating column (main updraft in a supercell)

What we are looking at for tomorrow:

1. CAPE: 1300 J/kg
2. SCP: 7
3. STP: 6
4. 0-1 km Helicity: ~250
5. 0-6 km Wind Shear: ~80 m/s

Basically, all roads lead to Rome, and all parameters for tomorrow lead to a severe weather outbreak in Central-Eastern North Carolina.

Hazards:

There are many hazards to be aware of for this event:
1. Wind - Straight-line winds from heavy falling precipitation as well as rear inflow jets from pressure differences could allow for wind gusts tomorrow over 60 mph.
2. Flooding - Heavy rains associated with supercell thunderstorms or a squall line could cause flash flooding.
3. Lightning - With this type of system being made of mix-phased clouds, charge differences develop and lightning can be a dangerous aspect of the storms.
4. Hail - Because the updrafts are so strong, hail formation is definitely possible. How large that hail gets depends on each specific storm, but the National Weather Service has mentioned the possibility of hail up to 1" in diameter with the strongest storms.
5. Tornadoes - With these types of storms and the parameters we are looking at for tomorrow, isolated tornadoes are a real threat.

As a result of these hazards, power outages are also a threat. Quick, heavy rains can cause saturation in the surface dirt and heavy winds can blow over trees. In addition to recommending staying off the roads during these storms, I would recommend parking your cars under a cover for falling debris associated with strong winds.

Timing

For Raleigh it looks as though the most opportune time for storms to make their appearance would be between 1:00 p.m. and 4:00 p.m. tomorrow afternoon. Before that time frame the instability will likely not be high enough for supercell production, and after that the moisture in the atmosphere will have been precipitated out. Areas to the west could see activity earlier than lunch, and the further east you go the later the chance gets. Rain is likely throughout the morning, afternoon, and evening, however the big storms have their main shot from early afternoon to early evening.

Please stay tuned in to your local weather stations for the most updated information! Be safe! As always, go Wolfpack!

The Main Event - Oh what a mess it will be

Well, this time I'll cut to the chase since the weather is already causing some issues.

Snow has already begun falling from the Tennessee and Virginia borders all the way down to the Triangle. Raleigh has not received any snow yet because the snow is evaporating before it reaches the ground again.

What to Expect: P-Type

So, unfortunately with this setup is that the cold air is present but warmer air is coming. If the air were going to stay cold all the way up, this could be a pretty good snow event. However, the atmosphere between 1-2 kilometers is going to be warm again due to some southerly wind components.

Initially, tonight (Sunday, 2/14) overnight precipitation will be all snow in Raleigh. Not much accumulation is expected and here in Raleigh we could see up to 0.25" of snow. If the temperature stays cold in the mid-troposphere then we could easily see more than that, but model data suggests that the warming is very likely to take place.

Early tomorrow morning (Monday, 2/15) a couple hours before sunrise the precipitation will switch over to more of a sleet/snow mix due to the warming aloft. This will likely last for a couple hours.

Around sunrise tomorrow morning, the surface layer will be below freezing however the warm advection aloft will have been sufficient for melting frozen precipitation before falling to the surface layer. At this time the mix will be more of a freezing rain/sleet mix for a couple hours before switching to a primarily freezing rain event into the early afternoon.

Throughout the afternoon the precipitation will switch to liquid rain. Freezing rain at the surface late in the morning will warm the temperature to the freezing point, then warm advection will warm the surface to above freezing. By that point though the damage will already be done and roads will be a mess.

Accumulations

For Raleigh, we could get up to about 0.25" of snow before sleet begins. Sleet added in will give us between 0.3-0.5" probably. Freezing rain after that is really a toss-up. Some models have us receiving more than 0.05" of freezing rain, and a couple others have us receiving almost 0.25". P-type is crucial for accumulation, and p-type is difficult to determine for this system.

Hazards

As is the case again with winter weather, road conditions will be pretty bad. They will likely clear up a bit tomorrow night as the rain will work to melt what precipitation sticks. In this case too, because temperatures will warm up, I do not expect power outages to be much of a problem either even though there will likely be some short-lived ice accumulations.

One hazard which may be unanticipated by the general public with this type of system is flooding. Icing could block paths to city waterways, and rain falling on top of that will have difficult at first for the rain to melt through the layer. Flowing water on top of ice is a horrific combination for travel, so please stay off the roads tomorrow if you can avoid it!

Class Cancellation

Well, I said it by word of mouth earlier and it doesn't mean as much now that the University has wisely made a decision about morning classes tomorrow.

Classes before noon cancelled, and dozens of counties closed school.

Going further: Tomorrow morning the University will cancel the rest of classes tomorrow.

Class will likely remain as-scheduled on Tuesday

I hope everyone has an awesome day off tomorrow! Go Pack!

Another Taste of Winter

Hello All! It's time again for another dusting here in the triangle! Fortunately for us, it will be mostly if not all snow for wave one to start the weekend, then snow transitioning to rain early next week. On the tail end of this pocket of precipitation though there is a chance for a wintry glaze to form from a combination of sleet and freezing rain.

Tomorrow the low will be tracking south of NC and will bring moisture with it. The air will be cold enough throughout the atmosphere for the production of crystal dendrites high up in the atmosphere which will form crystal agregates as they fall. It will take a couple hours for the process of sublimation, or ice crystals evaporating into the atmosphere, to saturate the lower atmosphere enough for the snow to fall to the ground.

Snow will begin falling late morning but will likely take a couple hours into the early afternoon for the dusting to be seen on the ground.

Accumulation

WRAL Accumulation Forecast: found at http://www.wral.com/

Not much snow will accumulate on the ground here in the Triangle. This is not because of the temperature, but rather because there will not be as much moisture this far inland with this storm system. We could see around 0.25" or maybe even 0.5" in some places, but I would not count on more than a nice dusting, or a trace, with a glaze on top.

If you want more snow, you can travel to northeast North Carolina. The further north and east of Raleigh you go, the closer to the epicenter of this storm up toward Elizabeth City, North Carolina. There it is possible that 2" or even a bit more could fall.

Concerns / Hazards

As is the case with all winter weather, road conditions will be a toss-up. I do not anticipate that road conditions will be very bad here in the Triangle as the NCDOT has already done a fantastic job spreading the brine solution on main roads. Back roads could get a bit messy in areas of heavier accumulation, but the roads will not be like they were a couple weeks ago.

That being said, IT WOULD STILL BE WISE TO STAY OFF THE ROADS IF YOU DO NOT NEED TO BE OUT. Better to be safe than sorry, and in the case of slick roads anything can happen and even a glaze can strip traction from the best vehicles.

Counties north and east of Raleigh have cancelled school for tomorrow including Bertie, Edgecombe, Halifax, Hertford, Wayne, and Wilson County Schools as well as Nash-Rocky Mount and Roanoke Rapids Schools.

Thus far Wake, Franklin, Nash, Johnston, Harnett, Lee, and Chatham County Schools will still run on normal schedule.

Class Cancellation Forecast

As of right now, classes are still as scheduled on campus However, I presume that once precipitation begins sticking in the early afternoon the University will make a decision on evening classes and activities.

I would imagine that if we start reaching 0.1"-0.2" of accumulation then the University will cancel class. The notification for cancellations will likely come earlier in the day as the storm materializes further and begins making it's mark. I would say that classes in the mid afternoon and evening will be cancelled. Those classes beginning at 3:00 and later will probably cancelled, however that is all dependent on the amount of precipitation that falls and sticks (obviously).

For the private and public schools north and east of Raleigh, I would imagine that there will be an early dismissal tomorrow.

Stay tuned to your local news stations for the most up-to-date information for your areas!!

I hope everyone has a great day! The Wolfpack Women had a hard-fought win against Boston College tonight, and the men have a big game to stay positive on the season this Saturday. Also, Valentine's Day and the Kay Yow Hoops for Hope game are Sunday. It is going to be a busy weekend!

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.

Day of the Demon Deacon's Demise

It's game day again in Wolfpack country! This will be the first game this season we have the full band at where it doesn't rain. Currently I am en route to Winston Salem with the NCSU Power Sound of the South Marching Band in preparation for our third conference game of the season.

We have some history, though bad, in Winston Salem. We have not won away at Wake Forest since 2001, 14 years ago. Philip Rivers, Russel Wilson, and Mike Glennon all tried and failed to pull out a W in Winston Salem.

Gameday Stats

Let's look at some offensive stats from this year. In the 4 games with rain, NC State  has put 132 points up on the board. In the two games without rain, NC State has amounted 101 points. In games with rain, NC State put up a total of 1,371 yards of offense and in games without, NC State moved the ball for 1,021 yards. I understand that the comparison for points and yards above does not take into account the difference in difficulty in the conference games against VT and Louisville, however I am just looking at the numbers. NC State is an 8.5 point favorite today with an over/under line of 45 points, and I sure hope it's over that.

Gameday Weather

The weather is going to be gorgeous in Winston Salem today! There is nothing really to speak of. The sun is going to be shining through partly cloudy to mostly sunny skies, and the air closer to the surface will still be relatively dry though moisture may increase slightly with a slight easterly breeze in the afternoon. Those making the drive can expect a temperature of around 60 or 61 at the time of kickoff with a high peaking in the late afternoon after the game reaching about 66-67.

Gameday Items

I only recommend a couple things today: chap stick and sunglasses. The band in the past has been on the east side of the stadium looking west, and the sun has always been directly in our eyes. In addition, the dry air mass we have been experiencing along with the sunshine and a light breeze today can chap lips pretty quickly by evaporating the moisture on your lips. Protect your lips and eyes!

We need your support, Wolfpack Nation! There is plenty of time to still have an awesome season, and it's going to be a larger mental battle than physical battle today! Let's get ourselves a conference win and break a 2-game losing streak in the season and a 6-game losing streak in Winston Salem! Let's go Wolfpack!

Wolfpack Going Turkey Hunting

It's game day again Wolfpack! Today though we are back out of state, hunting the Hokies in Blacksburg, VA. Unfortunately, it is likely going to be another rain game...

An approaching cold front will help to produce precipitation in Virginia this evening, overnight, and throughout the day tomorrow. The game is at 8:00 tonight and our 100-piece pep band are bringing our ponchos because of the chances for rain tonight. I'm not sure whether Lane Stadium allows umbrellas or not, so it would be a good idea to bring a rain coat with you to have. 

Blacksburg

The temperature today is likely going to reach the upper 70's, however tonight ahead of that cold front the temperature is going to drop down into the low 50's. There is a northeasterly breeze which will be persistent but not strong throughout the game helping the temperature to cool off a bit. Tomorrow the cold front will make it's way through Blacksburg and Raleigh, The high tomorrow in Blacksburg will likely not rise out of the 50's, and tomorrow night after the heavier rain and thicker clouds clear out the temperature will drop into the low 40's. 

Raleigh

The temperature today in Raleigh has already risen into the low 80's and may rise a few more degrees before increasing cloudiness slows the solar heating to a stop. Increading cloud cover tonight will turn into precipitation tonight ahead of the approaching cold front, and the low tonight will drop into the low 60's. Tomorrow, the high will settle around the mid 60's due to overcast skies and precipitation, and tomorrow night after the front passes the temperature will drop to near 50, so be sure to take a jacket out with you tomorrow night if you go out. 

Put on your game faces everyone and help get our team the conference win we need! This would be an awesome win for our team, and a great momentum builder into the next couple weeks. It's Game Day! Let's go Wolfpack!