Archive for January, 2007

Beware of Black Ice on the Roads
January 31, 2007

On my way to meteorology lab this afternoon, I saw many people driving way too fast on the roads. I saw several close calls with many cars slipping and sliding around the OU Campus. The roads may not look bad visually, but they are very slick with a thin layer of ice due to freezing drizzle we’ve seen. I also had to make use of an ice scraper and defroster as I had ice all over my windows. Stay safe as the drizzle continues across the metro.

Vivek
Weather Intern

My 6-12 hour rule proved itself today
January 31, 2007

There was a weather tidbit I picked up from the National Weather Service in Tulsa back in ’99 and 2000 which stated a rule of thumb. Snow in these situations typically starts as much as 6 to 12 hours faster than what computer models say. In our case, yesterday, they said around noon today. In reality, it started snowing around midnight out west and started coming to ground by 3am in western Oklahoma where Elk City picked up an inch of snow by daybreak. The snow quickly moved east and laid a coating of the white stuff around Ponca City and El Reno by 6:30am.

Looking at the models yesterday they were up to their old tricks. One model said the atmosphere would be cold enough to produce snow and snow only from today through Saturday morning. However, another one said expect rain, sleet, and snow today through Thursday.

When I came in early this morning and analyzed the latest, this is what I found: The model predicting snow only held it’s ground. The model predicting a mix of precip, backed off showing all snow today with a 6-10 hour mix tonight of freezing rain, sleet, and snow before switching back over to all snow by tomorrow morning. I’m leery to believe the all snow model, so my forecast this morning went with the other calling for a mix tonight then back to all snow tomorrow as colder air deepens and erodes any layers of warm air that may sneak in tonight.

More light snow is forming out west as I type this, so we’re not finished yet. Off and on through Saturday morning is the method to the madness. I talked earlier about the temperatures in the extended. Really from Friday on into early next week we are going to get two shots of polar air. Temperatures in these source regions are as much as 40 degrees below zero. The airmasses will move so fast in this weather pattern that they don’t have a lot of time to modify or erode. What does that mean for us? It means that those highs in the 20s and lows in the 10s are conservative estimates and could easily differ by as much as 10 degrees or more meaning highs in the teens and lows in the single digits. Computer models offer no help for us in these situations, so we use our best guess work. When and if they do latch on giving forecasters more confidence, you will see temperatures trending downward in this direction. As they say…stay tuned!

AT

Snow and the Dry Layer
January 31, 2007

Since the snow is here (and falling in Norman as I type!), a question some may ask is why it sometimes takes a while after the first radar echoes appear for snow to reach the ground. First some background information! At least twice a day weather balloons (radiosondes) are launched across parts of the world. These balloons contain instruments that send temperature, dew point, pressure and other variables back down to be analyzed by meteorologists. This data can be plotted on diagrams called SKEW-T diagrams.

On the SKEW-T diagram to the left, temperature increases as you move to the right and height increases as you move up. The red line is the temperature of the atmosphere starting at the surface all the way up to beyond 50,000 feet. The green line is the dew point temperature. This data allows meteorologists to see a profile of what the state of the atmosphere was at the time of the balloon launch. The purple line I marked is the freezing line.

This SKEW-T diagram is from the 6 AM balloon launch in Norman this morning. Notice the yellow shaded area I have colored in. That area is a dry layer in the atmosphere since the temperature and dew point are far apart. Saturation (100% relative humidity) is when the dew point equals the temperature. So as the snow falls, it sublimates (in a sense evaporates) in the dry layer. That’s what can cause snow to basically disappear before reaching the ground! The sublimation helps the snow to eventually reach the ground by cooling the atmosphere. It is like getting out of a swimming pool in the summer and feeling cold because all that water is evaporating off your skin. It is also why we sweat–to keep our bodies cooler.

So we often see radar echoes before the snow reaches the ground because there can be a column of relatively dry air that has to saturate first!

Vivek
Weather Intern

The Snow Has Arrived!
January 31, 2007

OK, the snow is here. A little faster than I had envisioned, but it’s here. So far it has been pretty light, but there’s a thin, white coating on the ground. The latest radar information shows that this first round will end by mid morning, but more light snow will likely develop for the afternoon. A couple of more rounds will be likely tonight into tomorrow with about 1-3 inches total accumulation in the metro, perhaps a bit more in the north.

Koco.com is in winter storm mode meaning that Aaron and I will keep the “Bulletin” on the front page updated at least once an hour, more if needed.

I’m off to take the kids to school, then I’ll dive deeper into the latest computer models.

Rick

Tuesday Evening Update
January 31, 2007

I’ve gotten a look at the latest computer guidance and I have no major changes to make to my latest forecast. The NAM shows the system currently over the Southwest U.S. moving east with time and producing a wintry mix of precipitation starting tomorrow.

Our atmosphere is quite dry so it will take some time for it to moisten up, therefore I don’t look for any precip in the metro are before 8 am. After that, we’ll likely see some snow. That will change over to a mix of rain, snow and sleet through the day, then back to light snow tomorrow night into Thursday.

The precip will probably come in waves, so there will some some dry hours mixed in over the course of the next couple of days.

Accumulations by late Thursday look to be in the 1-3 inch range with a few spots around 5 inches, especially in the north.

Another shot at light snow comes late Friday into early Saturday, but accumulations look light.

In addition to the precip, the cold weather will intensify with highs only in the 20s Friday through the weekend.

Make sure you check out Aaron at 5 am on Wednesday. He’ll have the very latest.

Rick

What an Intern Does in the Weather Center
January 31, 2007

Hey everyone,
I am currently a weather intern at KOCO and a sophomore meteorology student at the University of Oklahoma. I had previously interned at the Fox affiliate in Tulsa. I hope to bring you my thoughts on weather related items throughout the semester!

You might be wondering what an intern does in the weather center. The interns’ job is to assist Rick with making weather graphics such as the 7-Day forecast or the state temperature forecast maps. Rick makes the forecast and writes it down on a clipboard and then hands it off to an intern. Rick can use all the help he can get since he has many other things to do such as radio, newspapers, promotional shots, etc. During severe weather events interns may help with controlling the radar or doing other tasks such as ripping warnings off the printer.

Weather wise, it still looks like our next storm system will impact the state tomorrow. A big factor on snow accumulations will be where the rain/mix/snow line sets up. The earlier it comes down (and stays) as snow, the higher the accumulations. After this system moves out, it looks to stay cold for a while. One huge surge of cold air should move in by Friday, which will keep us cold through the weekend. The European model (one of the many we look at) shows another decent surge could be possible early to mid week next week!

By the way, when looking at average highs and lows, the coldest time of the year in OKC is from Jan. 6-13th–our average high reaches 50 tomorrow! It looks like we’ll be a far cry from that for sometime to come.

Vivek
Weather Intern

Tuesday Morning Update
January 30, 2007

A cold and challenging forecast is what lies ahead of us. The general theme remains cold with periods of wintry precipitation. The details are what will be hard.

TODAY: The sunshine is deceiving this morning as temperatures are only in the teens and 20s most areas. Temperatures will run about 10-12 colder than yesterday with afternoon highs in the 30s to low 40s. Clouds will gradually increase this afternoon.

TONIGHT: Dry and cold as temperatures fall into the teens and 20s. Winds will gradually become southerly, which will help to warm us slowly tomorrow.

TOMORROW: This is where it gets tricky. A warm advection pattern sets up over the state as surface pressures drop to our west in response to an approaching upper low. While the day will start off cold, temperatures will warm above freezing by afternoon. At the same time, precipitation breaks out across the west and moves east. At that point it will likely still be cold enough for snow. But as temperatures climb, the snow will change over to rain in the central and south, but stay as snow in the far north. All of the precip will be on the light side.

TOMORROW NIGHT: The light precip will continue as the upper low approaches the southern Plains, mainly as snow in the north, a mix of rain and snow central, and mainly rain south. Temperatures will only slowly fall as warm to neutral advection continues.

THURSDAY: Some cold air advection finally kicks in, changing any rain or freezing rain over to snow across central and southern Oklahoma. As the upper low weakens and moves east, the precip gradually ends from west to east. Accumulations will likely be heaviest where it snows the longest in the north. There will likely be enough snow to cause some travel problems.

FRIDAY: The next wave of cold air moves across the state. This will be the most impressive shot of cold air so far with temperatures on Friday staying in the 20s and wind chills in the single digits. There will also be some light snow or flurries, especially in the upslope areas in the west.

THE WEEKEND: More of the same…..very cold with a few bouts of light snow or flurries. Highs only in the 20s and lows in the teens and single digits.

WHAT TO WATCH: The models always have serious issues with cold air. They struggle to get a handle on just how cold it is, how fast it will move, and how long it will stick around. We’ve been saying that once it arrives, the cold air will be here for a couple of weeks. Watch how the models will try to bring an end to the cold by mid-next week. It won’t happen. The cold is here to stay through at least mid February.

Rick

New Model Update
January 30, 2007

The new European and NAM models are in. A quick scan shows no surprises tomorrow. As expected, it will be colder but dry.

An upper low currently spinning just off the California coast is projected to move east into the southern Rockies on Wednesday. Warm advection will start as surface pressures decrease to our west and we’ll have a south wind. That will help warm us above freezing on Wednesday afternoon.

The NAM breaks out precip by midday Wednesday with thicknesses such that the precip could start as snow, then change over to rain south and central by early afternoon, with light snow farther north. Snow would become the predominate precip type Wednesday night and Thursday as cold air advects in from the north, and as the remains of the upper low move east into the southern Plains.

The QPF from the NAM suggests accumulating snow in the state. We’ll watch with great interest.

Gotta go do the news now…

Rick

The Front Is Through
January 30, 2007

The leading edge of cooler air is now moving through the state. The only change noted so far is a witch in the wind direction from south to north. The more noticeable cold air is still to our north. We’ll notice the colder weather tomorrow with highs mostly in the 30s.

Despite tomorrow being colder, it will be dry and rather tranquil. The weather turns more interesting Wednesday when some rain and snow will break out.

Temperatures will likely warm above freezing on Wednesday allowing some of the precipitation to be in the form of rain, most likely in the south. The north could remain cold enough for light snow. The rain/snow line will likely move south during Wednesday night and Thursday as colder air once again moves into Oklahoma.

Right now this does not look like a big storm, but it will be worth watching as the week goes on. Several other cold shots will keep temperatures below normal deep into next week.

Rick

Downhill From Here
January 29, 2007

You know it’s not going to be a pleasant week of weather when today’s weather is going to be the best. We’ll see plenty of clouds today and temperatures will climb into the mid to upper 40s, then it’s all downhill.

A cold front will move across Oklahoma today. The wind will switch around to the north this afternoon and colder air will filter in tonight. Tomorrow’s temperatures won’t make it out of the 30s.

Other waves of cold air will move into the southern Plains over the course of the next week to 10 days. Some will be accompanied by light wintry precipitation, and all of them will have cold enough air for our temperatures to remain well below normal for an extended period of time. In fact, for most people, this will be the longest stretch of cold weather that they’ve had to endure for many of years. I don’t know if we will break any temperature records, but it will stay cold for a long time.

Rick