Monthly Archives: January 2012

Active Weather returns by Thursday & Friday

Tuesday, 31 January 2012 05:50
David Reimer
0 Comments

Beginning February 1, 2012  we will begin to produce a daily weather video. This video will feature the same content as these blog posts, except be on a daily basis. It’s our hope that these videos will explain the weather for the upcoming days by discussing weather data you don’t normally see on TV broadcasts. That being said, we’ll also keep the discussions simple enough for the non-weather weenies to understand.

We’ve had pretty tranquel weather across Texas, and frankly most of the United States, since our severe weather event last Wedensday. A strong cold front pushed through the region which brought in very dry air. It takes several days for the Gulf of Mexico to recover after a strong cold front pushes through. We don’t normally see moisture just surge back northward. Indeed, that is the case with a dewpoint of 56° here at my house in Duncanville (just southwest of Dallas) five days after the event. That being said, a lack of moisture is usually why we don’t get potent severe weather events during the cool season. Still, we do get enough moisture from time to time and you saw last Wednesday what the results can end up being. So keep in mind that we need good moisture in place to support severe weather, and more specifically surface-based convection. For those that don’t know what surface based convection means… That would be a thunderstorm that is rooted in the boundary layer (Thunderstorms that break the cap) that can pull in the warm, moist air at the surface and possibly become quite severe with tornado potential. Convection that is not surface-based is elevated, or above the cap. That means there is no tornado potential, but there is still a risk of hail and damaging winds. What does all that have to do with this blog post? Well absolutely nothing since I’m not going to be getting that detailed with this post, but hey, now you can say you learned something about weather!

[caption id="attachment_5714" align="aligncenter" width="600" caption="0Z NAM: Surface dewpoint values and surface winds at 6 PM Thursday"][/caption]

Speaking of surface moisture, this graphic comes from the 0Z NAM (North American Model) and is 72 hours out, otherwise known as 6 PM Thursday. The bright yellow line represents the 50° isotherm for dewpoints. That’s pretty much the lowest value you can get substantial severe weather. There are exceptions to that rule, but those won’t apply to this situation. Notice the less evident line across Central Texas, which is the 60° isotherm line for dewpoints. The 0Z NAM has the higher moisture values (50°> dewpoint values) are being pulled northward ahead of a storm system developing across Colorado.  As this storm system begins to develop on Wednesday, we should see moisture begin to surge northward in response to southeasterly surface winds. As I’m going to stress several times in this discussion, we’re still over three days away from Thursday and nothing is set in stone. As you’ll see when I show you the 500 millibar graphics, weather models are still differing pretty significantly on the overall setup. The point of me showing the surface moisture chart is to show that we will have higher moisture values surging northward ahead of our next storm system.

[caption id="attachment_5715" align="aligncenter" width="600" caption="0Z NAM: Most Unstable Instability (MUCAPE) at 6 PM Thursday"][/caption]

Since the weather models are still differing quite a bit on the whole setup, there’s no point in digging down and looking at specifics like instability values and low level wind patters. However, I will show you this graphic which shows the most unstable instability values off the 0Z NAM. Anything over 1,000 joules per kilogram is pretty substantial for late February. As you can see, the NAM has a fairly large instability pool across West Texas at 6 PM on Thursday. That’s one of the reasons why I’m already talking about this setup because those are pretty good instability values for a cool season event.  I won’t dig any further into that, but keep those in mind for future discussions.

[caption id="attachment_5717" align="aligncenter" width="600" caption="0Z NAM: 500 millibar winds at 6 PM Thursday"][/caption]

Lets take a look at the mid-level setup of this upcoming storm system. This graphic is also from the 0Z NAM at 6 PM and is for 500 millibars, which translates to about 18,500 feet above sea level. The 0Z NAM has a positive tilt trough digging through Utah and Colorado with the base of the trough and right-entrance region located over New Mexico. For organized thunderstorms, I want to see values at or above 35 knots. Generally speaking, the NAM values above 50 knots across most of the Texas Panhandle and northern cap-rock. If we had a piece of energy swing through that trough and move across the panhandle at the right time, that would help initiate thunderstorms and with the overall setup shown above, we would likely see a few organized thunderstorms, maybe even supercells depending on how much forcing was present. However, lets take a look at a different weather model for the same time…

[caption id="attachment_5718" align="aligncenter" width="600" caption="0Z GFS: 500 millibar winds at 6 PM Thursday"][/caption]

This graphic comes from the 0Z GFS (Global Forecast System) and shows the same graphic as the one above and applies at 6 PM Thursday. Notice anything different? First off, the GFS has the system running slower and further south. Instead of Utah and Colorado like the NAM shows, the GFS has the base of the trough located over Arizona and New Mexico. Still, it has a good southwesterly flow in place over the Panhandle, although its a bit further south then the NAM. Keeping this model variability in mind, lets take a look at Friday.

 

[caption id="attachment_5719" align="aligncenter" width="600" caption="0Z GFS: 500 millibar winds at 6 PM Friday"][/caption]

Fast forward twenty four hours and we see the setup at 6 PM on Friday. This is using the same parameters as the 500 millibar graphic above. It looks like the GFS wants to go negative tilt with the trough and shortwave with it much stronger then it was on Thursday. Winds in the base of the trough exceed 90 knots and overall, the GFS has a strong system in place by Friday evening. It takes a lot more then a strong shortwave to create organized severe weather. It takes instability, low level wind shear, and rich moisture to create a severe weather event.  That being said, there is some indication that we could be dealing with another severe weather event on Friday across parts of East Texas out into Dixie Alley (Arkansas/Louisiana). That’s four days out and with models not behaving particularly well, we won’t make speculation at this point. However, this is something we need to keep an eye on. Stay Tuned!

Beginning February 1, 2012  we will begin to produce a daily weather video. This video will feature the same content as these blog posts, except be on a daily basis. It’s our hope that these videos will explain the weather for the upcoming days by discussing weather data you don’t normally see on TV broadcasts. That being said, we’ll also keep the discussions simple enough for the non-weather weenies to understand.

“Tornado!!! Put your shoes and helmet on!“

Saturday, 28 January 2012 19:00
Jenny Brown
0 Comments

With spring right around the corner, and severe weather season already upon us (approximately 64 tornadoes this year so far!), it’s time to start thinking about your household severe weather safety plan.

Most people already have the “where” figured out…the basement or a small interior room or closet away from windows…but have you also thought about what you should have with you when you go into your shelter?  It may sound silly, but you may want to consider stocking your safe area with not only a flashlight, but also a pair of old shoes, a jacket…perhaps a blanket…and a bicycle or motorcycle HELMET!

[caption id="attachment_5680" align="aligncenter" width="600" caption="Me (Jenny Brown) Sporting Sean Casey's helmet"][/caption]

A study conducted by the University of Alabama at Birmingham suggests a number of fatalities from the April 27, 2011 Super Outbreak were caused by trauma to the head and neck.  They suggested that motorcycle helmets, football helmets and bicycle helmets offer a practical, inexpensive solution to reducing the risk of head injuries during a tornado.  Even if it’s only minimal protection from being hit by debris tossed about at 100+ mph, a helmet is certainly better than nothing and can help prevent a more serious head injury such as a concussion or laceration.  For children, just purchase an inexpensive bike helmet dedicated to your tornado safe spot.

This advice could also benefit my fellow chasers, especially the ones who think they are fast enough to run between the hailstones a mach speed to grab the biggest one.  Put a helmet on your head and making that dash could be a lot less painful.

To view an article by the Universality of Alabama summarizing their research, click here.

For a complete list of severe weather safety tips, visit the Storm Prediction Center.

This is only the first in a many of discussions meant to help increase your knowledge about severe weather. We’ll have more on what you can do to protect your family during severe weather in subsequent discussions. 

NOAA’s 2011 Climate Summary

Saturday, 28 January 2012 10:40
Jenny Brown
0 Comments

I’m sure I can speak for just about every Texan when I say that I’m beyond glad that 2011 has passed.  What a historic year for not only us, but other parts of the United States as well.  Below is the 2011 State of the Climate summary released today from NOAA‘s National Climatic Data Center.  Here’s to hoping we never have another year like it…

 

What happened to Winter?

Friday, 27 January 2012 14:04
David Reimer
0 Comments

[caption id="attachment_5626" align="aligncenter" width="600" caption="Snow Cover (February 10, 2011)"][/caption]

[caption id="attachment_5628" align="aligncenter" width="600" caption="Snow Cover (January 27, 2012)"][/caption]

While we have experienced some brief cold spells, most folks across Texas are asking what happened to winter. It’s not just us in Texas that are wondering, but most of the United States. Take these two snow cover graphics for example, the first graphic is from February 10, 2011 (about a week after our major winter storm and coldest spell in 20 years in Texas). A majority of the United States, east of the Rockies, have snow on the ground. In fact, the snow cover extended south to the Interstate 20 corridor from Texas all the way into Alabama. Even Houston had some snow! Fast forward about 50 weeks and you have the second graphic. You’re hard pressed to find any snow across the Country. Sure, you have a few inches on the ground in  the Dakotas east to Wisconsin, but this time last year they had almost two to three feet on the ground!

So why the major difference this year? We remain in La Nina conditions, similar to last winter, so what gives? It’s actually pretty simple and can be attributed to one specific parameter. For the meteorological definition, we differ to the Climate Prediction Center. For more detailed information on the NAO, visit the CPC at http://www.cpc.ncep.noaa.gov/data/teledoc/nao.shtml

“The NAO consists of a north-south dipole of anomalies, with one center located over Greenland and the other center of opposite sign spanning the central latitudes of the North Atlantic between 35°N and 40°N. The positive phase of the NAO reflects below-normal heights and pressure across the high latitudes of the North Atlantic and above-normal heights and pressure over the central North Atlantic, the eastern United States and western Europe. The negative phase reflects an opposite pattern of height and pressure anomalies over these regions. Both phases of the NAO are associated with basin-wide changes in the intensity and location of the North Atlantic jet stream and storm track, and in large-scale modulations of the normal patterns of zonal and meridional heat and moisture transport (Hurrell 1995), which in turn results in changes in temperature and precipitation patterns often extending from eastern North America to western and central Europe (Walker and Bliss 1932, van Loon and Rogers 1978, Rogers and van Loon 1979).” (Source 1).

 

Now that we have the official, wordy definition out of the way, let me explain it in a way most of you will be able to understand. When the NAO is in a positive state; very cold air often has great difficulty making it to the Southern United States. In order for cold air of arctic origin to make it south into the United States, the jet-stream must originate from a high latitude and then dive south, known as a trough. That type of  setup is commonly associated with a negative NAO. Cold air can still make it into the United States, but not the bitterly cold, arctic air that can cause several days of freezing weather in Texas with sub-zero temperatures across northern US. During a positive NAO, we generally have a warmer pattern across the country. We definitely can get cold snaps, but not to the extremes or duration as we would get with a negative NAO. During a positive NAO, we generally have above average temperatures across the southern US.

[caption id="attachment_5627" align="aligncenter" width="558" caption="North Atlantic Oscillation from September 30, 2011 through January 27, 2012"][/caption]

Now that I’ve explained the basics with the NAO, lets take a look at what it’s been showing over the past few months. This graphic shows the North Atlantic Oscillation from September 30, 2011 to January 27th. The red lines are model guidance for the next 14 days, we’ll talk about that in a minute. Over the past few months, we have not seen any major negative trends in the NAO, which is why we have not had any major cold spells or winter storms across the Country as a whole. Now there have been localized events, especially in Iowa/Wisconsin/Illinois, but they’re at a higher latitude and have localized features (The Great Lakes) that can help enhance their events. Until we see the NAO go negative, we will not see a major cold spell. Looking in the next two weeks, there really is no sign of the NAO going negative. We’re actually pretty close to neutral right now, but the NAO will head back up into the positive territory as we get into February.

That generally means we won’t likely see any long-duration cold spells in the near future. We’ll have cold fronts come through once in a while that will cool us back down to our average temperatures across Texas, but the duration of those cool spells won’t last long.

[caption id="attachment_5625" align="aligncenter" width="600" caption="6-10 Day Temperature Anomaly Forecast"][/caption]

As would be expected with the positive NAO, much of the country will be experiencing above average temperatures for the next two weeks. This graphic comes from the Climate Prediction Center and shows that they expect much of the country has a good chance of experiencing above average temperatures over the next two weeks. While the Continental US will be warm, take a look at Alaska. With the positive NAO, the colder air is being bottled up north so they will likely experience colder then average temperatures for their neck of the woods. One thing we’ll have to watch for in February is that cold air to push south. It’s been bottled up north for a while now and we rarely make it through a winter without one cold spell. Let me remind you that many of our biggest winter storms have been in February, so just because it’s been warm so far, don’t think we’re going to get through the rest of winter without a major cold spell. We’ll keep an eye on things as we head into February, but I hope you’ve learned a bit about what we look for when forecasting cold spells across the USA.

Just to recap…
Positive NAO = Average/Above Average Temperatures Possible

Negative NAO = Below Average Temperatures Possible

Source 1: Climate Prediction Center Internet Team. "North Atlantic Oscillation (NAO)." Climate Prediction Center. National Weather Service, 10 Jan. 2012. Web. 27 Jan. 2012. <http://www.cpc.ncep.noaa.gov/data/teledoc/nao.shtml>.

Are They Nuts??? The psychology behind why people attempt driving across flooded roadways.

Wednesday, 25 January 2012 21:06
Jenny Brown
0 Comments

Every time a flash flood event happens, we’re barraged by media reports of high water rescues, pictures of stalled vehicles and news video of cars just floating down the road on a river of water.  We stand there in front of the TV proclaiming “Are they nuts?  Why would anyone drive into that?  Are they stupid?”

Our first assumption is yes…they must be stupid! But research is starting to show us that stupidity actually has very little do to with it.  Instead, sociologists call it “making a calculated decision.”

What was determined after last year’s tornado outbreaks in Dixie Alley and Joplin is that people, upon receiving a Warning of imminent danger, tend to look for confirmation that something dangerous IS about to happen to THEM before they will take action.  Research after those tragic events showed that most people are solid on the difference between a “Watch” and a “Warning”.  They understand the different meanings and realize there could be danger.  But when it comes down to actually ACTING upon a Warning is when it gets a little shaky.

It’s no different in the case of flooded roadways.  They’ll stop.  Look.  Maybe place a call to a neighbor to see if they made it.   Some will wait until another vehicle comes along, see if they make it, and decide… “If they made it, so will I!”   Even if they can clearly see the signage or barricade, not everyone perceives that the situation is currently dangerous to them without some additional source of confirmation or past experience with a similar situation.  There is also our basic homing instinct.  The phrase “Come he** or high water” comes to mind, and it applies quite nicely to this topic.

People in general know they should not drive through flooded areas.  But what needs to be considered is the possibility that the decision to do so is not always because of stupidity or irrational thinking.  Those working in emergency management need to more fully understand how humans perceive and process imminent threats in order to develop better strategies to help save lives.

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