A New Year, A New Airmass

Tranquil, bright, mild, beautiful....any synonym you use that constitutes a stable pattern can describe our weather. Following a foggy morning, the sun warmed up the air enough to fade out areas of low visibility. Other then that, the weather has been very quiet this week. Even heading into the weekend, the weather continues to be smooth with a gradual warming trend. However, by the weekend, a cold front will be the lead headline and deliver in a new airmass.

Here is the current upper level set up at Jet Stream Level:

The jet is well north of us and it is flowing from west to east without any large troughs or ridges. This type of pattern is called "zonal" and is a very progressive pattern where weather systems an glide across the US fairly easily and quickly. Additionally, since the jet i so far north, there will be no active weather here, plus the coldest air is locked up in Canada.

By the weekend, and into next week, the jet stream will have a much different look to it:

Note how the jet is not as flat anymore. By next week, there will be a large dip, or through, to the east of the Brazos Valley, while a large ridge builds to our west. A jet stream orientation like this is called "meridional". Due to this structure, we will cool down quite a bit, but the core of the coldest air will be to our east. This is good news for the suffering ski resorts of the Northeast, where snow and cold air have been lacking.

Overall, expect New Years Day to be much cooler and windier in comparison to the end of this week. Additionally, the cooler air will stick around early next week with a moderation during the middle of the first week of 2012.

Warm End to 2011, Cold Start To 2012

Sunshine is all over the place following a weekend of clouds, showers and chill. At the moment, we are in a quiet pattern with air that continues to moderate thoughout the week. We could possibly see temperatures into the low to mid 70s for the final day of 2011.

High pressure is parked to the east of us and returning a south flow on the back side, aiding warmer air to come back to the Brazos Valley. Plus, the jet stream retreated back to the northern Plains, which means that no big weather systems will impact us for a while. However, computer models are indicating that a huge cold front will form to our northwest and swing through the lower 48 by the weekend.

The following image illustrates the position of the front late Friday:

Cold air will begin to gather and make a move towards the central Plains and the east coast. If you take a look at the cold front, there are triangles at the leading edge of the cold air. These triangles are also called, "pips" and show the direction of the colder air. Note that the directions is towards the southeast, yup that means us and the rest of the lower 48.

During New Years Day, the front will swing though the Lone Star State and move east as well:

At the moment, we will see a change from highs in the 70s to highs in the 50s next week. Additionally, the upper level wind field shows that the core of the cold air will shift to the Great Lakes, Mid-Atlantic, as well as the Northeast. We should miss the coldest of the air, but we will still feel a difference. Yesterday, models were indicating that we could feel a much colder punch of cold air, with highs only in the 40s next week. Now with the latest runs, we should miss the coldest of the air.

This will be a definite shift in air-masses and as the newest computer models come in, I will adjust the temperatures accordingly. Stay tuned for the latest.

Warm Ending To Our 2011 Story

Not the greatest weather outdoors this holiday weekend, but with Rudolph's bright red nose, Santa was able to see though the clouds and rain in Texas. Messy weather was being created by a very slow moving upper level low that sat over the panhandle. It was cold enough behind this low that locations from Lubbock to the Concho Valley received a white Christmas.

Now we are seeing the final stages of this system with clouds in north Texas before pulling away. High pressure and a change in the orientation of the Jet Stream will help us bring out the sunshine and raise temperatures big time compared to this weekend.

Take a look at the Jet Stream set up this past weekend:

Notice how the Jet Stream takes a large dip into the Plains and The Lone Star State. Because of this, the doors were opened up to cooler air spilling in and keeping temperatures below average. Additionally, when the Jet Stream dips like this, weather systems tend to move slowly. However, if the jet was flat and moving from west to east, this storm would have move along pretty quick. Due to this orientation of the jet, our storm decided to take an extended stay.

At the moment, the jet is beginning to flatten out and move northward. Due to this "flattening" our latest storm is moving to the east fairly quick, plus drier air is moving in.

Here is how the jet will look over the next few days and into the weekend:

A warmer flow of air will enter Texas, plus with high pressure around, the sun will be out for a while. Yes, it it very possible that we could see some 70s around here by the time the week is out. More importantly, with the jet so far north, this will keep the Brazos Valley in a fairly quiet pattern. Typically, the Jet Stream is a highway for storms and even weak weather systems to move though. And with this kind of orientation to the jet, there will be no large, organized storms in our near future. Enjoy the warmth as we conclude 2011.

Our Christmas Gift....More Rain

As we settle into the home stretch of the Holiday season and begin a new year, the atmosphere will not cooperate with travel plans. However, rain is something we desperately need here across the entire Lone Star State.

Clouds hang overhead for now, but an area of disturbed weather that is parked over New Mexico and west Texas will slowly move here and deliver in messy weather. This system has already had a history of dumping heavy snow in the mountains of New Mexico and even delivering a white X-mas for parts of El Paso and Midland.

Energy associated with the storm is aloft, and this upper level feature will eventually churn up a surface low that will glide across the Texas coast. Because the low will be to our southeast, expect a north wind to continue, and the thermometer to remain int he 40s the entire holiday weekend.

Rain will begin after the noon hour in the Brazos Valley and continue until noon Christmas Day. Overall rain accumulations will be around 1". That's the good news, but the bad news is that travel will not be ideal. If you are going to be traveling, make sure to slow down on the roads and keep the low beams on.

Following this messy period, the remainder of 2011 will be filled with sun, and temperatures above average. Actually, the same goes for the beginning of 2012 as well. We could possibly hit 70 degrees by the end of next week.

The following images display the forecast across Texas for Christmas Eve if you are traveling tomorrow.

Have a safe and Merry Christmas.

Winter Solstice Explained

Bells are ringing, the air is turning much cooler, the malls are flooded with consumers, and students at A&M are taking a break from the stress of classes. It only means one thing, winter is right around the corner. The corner is so close that you have to be careful when you make the turn so you don't mess up your tires.

As of 11:30pm tonight, the Winter Solstice will occur. At this time, winter will officially arrive for us here in the northern hemisphere. This whole solstice thing is a very simple concept. All this really means is that the suns rays will be directed over the Tropic of Capricorn, which is located at 23.5°S latitude. If you are not familiar with this location, check out the following image.

What is interesting about the earth, is that it is not a perfect sphere, and it does not sit upright. The Earth is a shape called a spheroid. Around the equator, the Earth actually bulges out, kind of like when you eat too much at Thanksgiving dinner.

Furthermore, the Earth is tilted at a 23.5° angle. Due to this tilt, and rotation around the sun, this is what gives us seasons. During the winter solstice, the sun rays are directed at 23.5° south due to the tilt. This means that the northern hemisphere will not have as much energy from the sun. Due to this lack in energy, the temperature tends to go down. This is why it is colder in the winter because of less sun energy.

Finally, this is the shortest day of the year in terms of amount of daylight. From the winter solstice to the summer solstice that occurs in June, daylight will begin to grow over this period.

Overall, due to the Earth's tilt and relation to the sun, seasons change and amount of daylight changes too during the year. The last image will give you a good indication of the yearly cycle of the seasons.

High Pressure Is Here, But Where Is the Sun?

The obvious answer to that question is, above the clouds. This weekend, high pressure will settle over Central Texas at the surface. That means the sun should be shinning right? Well, yes for most of North Texas, this will be a bright and sunny weekend, but from the Brazos Valley to the south, its going to be cloudy.

Lets show you the set up. The following image displays the wind direction at the surface, or the ground:

Albeit light, but the wind is flowing from the north at the surface. Therefore, the air close to the ground will be cold. In the last blog, we indicated that colder air is denser and heavier than its counterpart, warm air. Due to this difference in density, any warm air that tries to come in will not have the ability to push away the denser cold air. The only way around the cold air is to flow above it.

In the mid-levels of the atmosphere, (850-700mb level, for the weather savvy), the wind its actually coming from a different direction.

The wind about 5,000ft above the surface is coming from the southwest. One, the air coming from this direction is warmer. Plus, the origin is from the Pacific Ocean. Therefore, the air is warmer and has more moisture than the colder, drier air at the surface.

During a set up like this, the warm, moist air will rise above the colder air. When air lifts, it tends to get cooler and the water vapor will condense into liquid droplets. In other words, clouds will form. This process is called overrunning.

Since the air is not being lifted at a rapid rate, there will not be any rainfall in our scenario. However, there are overrunning events that occur quite frequently ahead of a warm front. In the winter, overrunning can cause major ice storms and even significant snowfall.

Advections, It Tells Us Whats Going and Whats Coming

With a cold front playing games with us across the Brazos Valley today, most of us were feeling the tropical air, but areas just to the north and west of Bryan expereinced a much cooler air mass in place. Once the front passed, much cooler air filtered in and Cold Air Advection took place.

Advection is a meteorological term used to describe the movement of an air mass. Such terms that are used with advection are cold air advection and warm air advection. For example, if cold air advection occurs at a certain location, then that specific area will experience colder air. This is  because colder air is moving/advancing into that area, which in turn would drop the temperature.

When talking about a mature mid-latitude cyclone (or area of low pressure), there are usually 2 or more different air masses that the cyclone divides. Usually north or west of a cyclone, there is a continental polar (dry, cold air) or a maritime polar (moist, cold) air mass, while to the south and east of the cyclone is a continental tropical (dry, warm), or maritime tropical (moist, dry) air mass. All of these possible air masses have different densities or weight in a given volume), where a moist and warm has a low density, while a dry and cold air mass is more dense.

In other words, its like water and oil. Since oil has a lower density then water, the oil will float on top while the water stays on the bottom. Or you can think of it like a rubber duck floating in a bath tub on top of the water. Since the duck is hollow and made of rubber, its density is low, so it will float.

When talking about advection, moisture is important, but not as important as temperature. Colder air is more dense then warmer air. Therefore, when cold air advection occurs, the cold air will slip under the warm air and replace the warm air. In the meantime, depending on how much cold air there is, the older warm air mass, would "float" above the newer colder air mass.

From all of this information, when talking about a cold front, it is a surface which divides air masses. Behind a cold front is typically a more dense air mass, whether it is maritime polar or continental polar. Additionally, since the air mass behind a cold front is very dense, it tends to hug close to the surface. When this colder/denser air mass advances, cold air advection is taking place.

Note: Cold air is the most dense and cold air acts like a bully. When cold air advances, its not because warm air is retreating, its because the cold air wants to move in that particular direction. The same goes for a retreating cold air mass, warm air is not advancing, it is only replacing a cold air mass that has moved away. Remember, the air mass which has the most mass will have the most control.

LaNina Pattern Shows Itself

LaNina is a simple phenomenon, but it can change up the weather worldwide. Basically, during a LaNina, the waters in the Pacific Ocean along the equator are cooler than climatological average. Sounds simple, but it can have huge effects on the weather all across the United States. For us here in Texas, we typically experience a milder period. Also, storm tracks are to our north generally. However, right now, the storm track has shifted south.

Here is the current set up:

We have a flow in the upper levels coming right off the Pacific Ocean, which is typical in a LaNina pattern. Therefore, moisture is being injected into the upper atmosphere, keeping it cloudy overhead. Plus, with the flow coming off the ocean, the air is temperate. If the flow was coming from the north, then we would feel the chill of the arctic. Due to the direction of the flow, this solves the question about the reprieve from Jack Frost.

Additionally, storms coming from the Gulf of Alaska move south and get caught up in this Pacific Flow. Therefore, you get an area of low pressure that slows its progress, meandering around Baha and Southern California.

These are the type of systems that are very slow moving and pack a punch with moisture. Additionally, its because of these sluggish features that keep the weather repetitive around here. Yes, it will remain cloudy, mild, breezy, and showery from time to time.

Eventually this storm will move farther inland and increase our rain chances for the Brazos Valley Wednesday and Thursday. Following this damp period, another Low will come back into the picture, sit around Southern California and we will repeat the same process into the weekend and next week.

All I can tell you is to expect plenty of cloud cover, not too much rain, and mild air.

Not Feeling Like Christmas, More Like Easter...

Following a cold week, we are beginning to see the mercury in the thermometer rise again. Additionally, the amount of moisture in the atmosphere is going up. This combo spells out our pattern for the week, warmer, and showery. It will not rain the entire week, but quick hitting light showers will pop up from time to time.

Here is the overall pattern:

There are two major features here, a large high pressure cell dominating the eastern US and a broad body of low pressure in the southwest. Note that air around high pressure flows clockwise, while the opposite is true for low pressure. Smack in the middle of these two large scale systems (or "synoptic" in meteorology terms) is the Lone Star State.

Here is a zoomed in perspective of Texas and the Brazos Valley:

From the direction of the wind at the surface, its simple to define our pattern. Not only are we adding moisture from the Gulf of Mexico, but there is a flow coming from the Pacific Ocean as well. Therefore, we have two sources of moisture keeping the clouds around and the isolated showers. In addition, with a southerly component to the wind, the air will warm. However, the big question is, how efficiently will the air warm?

Since there will be a fair amount of clouds over head, the temperature will not be able to jump as high as it could. At the moment, our forecast is calling for temperatures in the low 70s Tuesday, and mid to upper 70s Wednesday. However, if the clouds break up for a time either of these two days, the air molecules will have extra energy and temperatures will rise.

It is not out of the realm of possibilities that we could make a run at 80 degrees on Wednesday, but we would need the sun.

As far as the rain scenario, expect an isolated shower or two, but the best chance of rain comes late Wednesday night and into Thursday. The low over California will make a move north of us and drag a weak cold front behind it and heightening our ran chances.

We will keep you updated with the latest on Facebook: www.facebook.com/kagsweather and Twitter: @KAGSweather.

Upper Level Lows Can Create Suprises

Upper level lows are beasts that can keep the weather fairly cloudy and damp for days on end, especially when they cut off from the main branch of the jet stream. Basically an upper level low (ULL) is an body of positive vorticity that can be caused from a jet streak or upper level trough. Over time, if the ULL matures, some of its energy can be translated down to the surface and on some weather maps, two lows (or a double barreled low) will show up on a surface map.

ULLs can form in a few different ways:

1: From a developed surface low associated with a mid latitude cyclone.

2: From air flowing over mountains.

3: From a shortwave.

4: In association with a jet streak.

From these different scenarios always watch for the development of an upper level low because they can hold alot of weight in your forecast. During the analysis process during forecasting, upper level lows usually show up to the west or northwest of a surface low in association with a mid latitude cyclone. Additionally, during the forecasting process, models tend to forecast a surface low much better then a low above the ground, so be careful in the event that an upper level low is near your forecast area.

Additionally, since the ULL is usually to the west or northwest of the surface low, wintry precipitation is a concern. Below the ULL the air is cold (relatively speaking), therefore, when the ULL forms precip behind a surface low, in wintertime, there will be more wintry precipitation even behind a cold front.

Finally to check is a ULL is maturing, take a look at a satellite image. If the clouds are showing up brighter (thicker) during a loop, then the ULL is maturing.

Keep these things in mind during your forecast and hopefully you will pick up on some anomalies.

Split Upper Level Flow Keeping Us Away From Bitter Chill

The past couple of nights have been blow freezing, but tonight will break the streak. Additionally, in the near term, the hard cold will fade out and a gradual warm up gets underway. One of the largest contributors to the slight increase in temperatures comes from the wind flow in the upper levels of the atmosphere. What occurs in the upper levels translate down to the surface, where we live.

Approximately 35,000 feet above the ground, there are two jet streams that are crossing the United States at this time. The following image denotes where each jet stream is flowing:

Note in the image above the Sub-Tropical jet stream and the Polar jet stream. At the moment, the Sub-Tropical jet stream is moving above the Lone Star State. Furthermore, this stream is coming off of the Pacific Ocean. Due to this flow off the Pacific, the air is able to moderate and soak in additional moisture. Therefore, we are experiencing a "cool" flow. 

On the flip side, the Polar jet stream originates from northern Canada. As the word Polar denotes, much colder air can spill in from this upper level feature. Typically in the winter, the Polar jet stream delivers very dry air, with a bitter bite. Due to the location of this jet stream at the moment, the coldest air across North America will stay well north of Texas. In addition, latest computer guidance suggest that this feature will stay well north for the next couple of weeks. In other words, the frigid air will stay away from us for now.

A Tilting Trough Tells All....

We talk about troughs and ridges occasionally when we do the weather. Typically, troughs are synonymous with cool environments, and ridges are synonymous with warmer environments. But, one of the most important aspects of forecasting troughs is how they are shaped. Their orientation can dictate whether a storm will strengthen, weaken, or unchanged.

There are three types of tilts, a positive, negative and neutral tilt.

Just like on a graph, a line with a positive slope is one that is oriented from the lower left of the point of origin to the upper right. Therefore, a positively tilted trough is one that is oriented from the southwest to the northeast. A neutral trough is oriented from north to south, and a negatively tilted trough is pointing from the northwest to the south east.

A negatively tilted trough is one which is the most recognized and has the most importance. The way this is positioned will allow a storm to grow and strengthen. Colder air will have the ability to lay on top of the warmer, more humid air that the storm is feeding from at the surface. With cold air aloft and warmer air closer to the ground, instability is created, allowing for convection and a strengthening of a storm system. Click here to see what a negatively tilted trough looks like.

The opposite is true for a positively tiled trough. Since colder air is not directly on top of the warmer air, there will be very little if any instability. Click here to see what a positively tilted though looks like. However, a positively tiled trough can swing around and become negative with enough momentum from winds in the upper levels.

There are many other factors that go into the genesis as well as dissolution of storms, but just the simple shape of a trough can pan out the future of a large scaled event.

Coldest Night Since February 12th...

Bleak, gray, windy, cold. Any of those words plus more can describe how today felt outside. This was one of the coldest days we have seen since last winter, and tonight will be the coldest since February 12th. In fact, the high of 38 degrees reported from Easterwood Airport was a record. For this date, 38 degrees is now the new record low, maximum temperature. The old record was 40 degrees, back in 1972.

A powerful cold front came through this past weekend and shuttled in the extreme cold for this time of the year. However, its not just The Lone Star State experiencing this winter chill. Most everyone across the country need to use their heaters to warm up. The only exception are the folks along the east coast. Plus, this deep pocket of cold air will stick around for quite a while, including tonight.

One of the reasons for the frigid afternoon was due to the lack of sunshine. However, the clouds will begin to break as an upper level low move out and surface high pressure moves in. This will do a few things for us. One, brighten up the sky and rebound afternoon highs into the 50s. Also, allow any "heat" from this afternoon to escape into the atmosphere overnight. Therefore, temperatures will fall though the 30s and down into the 20s.

The following image is my forecast for low temperatures for tonight and into Wednesday morning:

If these temperatures are met, this will be the coldest start we have had to a day since February 12th, where the thermometer dropped to 28 degrees. Since we have already hit 32 degrees multiple times this season, the National Weather Service will not issue any Freeze Warnings for us.

Make sure to take care of some of the essentials tonight. Keep the pets inside as well as tender vegetation, and begin to wrap up the pipes. Not only will it be quite cold tonight, expect temperatures to fall below freezing again Wednesday night.

Frost....with and Interesting Twist

Just like normal dew, frost forms the same general way, but the only difference is the air temperature. Frost is a phenomenon that occurs when the air temperature is lower then 32 degrees. There are two ways that frost can form. Depositional frost is when the temperature and dew point are equal, and below freezing. This type of frost will leave a white crystal like coating on any surface the meets the criteria. It is similar to tree branches. Depositional frost is also known as white frost or hoar frost. Yes I said hoar frost.

The other way that frost can be formed is due to cold air advection (CAA) and radiational cooling.

When CAA is the focus, dew can form normally when the temperature and dew point reach each other, above freezing levels, then a cold front can swing by overnight decreasing the temperature to below freezing. The frost will not look white, like the depositional frost, it will have a more transparent look because liquid drops are being frozen. Same goes for radiational cooling. Dew can form as a liquid and when radiational cooling occurs, the liquid drops will freeze.

Prolonged Chill

The weekend produced a big change in the weather across the entire Brazos Valley. A cold front came though and that opened up the gates to Canadian Chill. We went from the 70s Saturday, to highs in the mid 40s today. Additionally, clouds showers, and gusty winds have created a bleak scene outside. Good news is that this pattern will break....eventually.

Take a look at the following image....

This is a radar and satellite composition with a jet stream. The reason for showing the jet stream on this graphics is to illustrate how the winds in the upper levels are acting. Upper level winds are a vital part of forecasting because this shows us the path for storms. Note how the jet stream has a large dip that falls down to Texas and Northern Mexico. Because of this, weather systems will not be able to move quickly as opposed to a jet steam that is flat, or flow directly west to east.

Due to this orientation, the clouds, drizzle and cold air will stay around for another 24 to 36 hours. Therefore we will see a gray sky all the way until Wednesday morning. Eventually, high pressure will have its way and break this force field to rip up the clouds allowing the sun to shine Wednesday afternoon.

Despite the sun around, temperatures will remain in the low 50s due to a wind flow from the north around high pressure.

KAGS Weather Insider

I want to welcome all of you to KAGS Weather Insider. This will be a blog that will talk about the weather going on in the Brazos Valley. We will also touch on topics of interest across the nation. Not only will this blog go in depth with the weather forecast, but the mission is to teach you more about how weather works.

Thank you again for checking us out and we will begin to post information very soon.