Wednesday, June 30, 2010

Tropical Weather Resources

Here are a few of my favorite sources for tracking tropical weather:

"Official" Information & Advisories:
The National Hurricane Center, of course...

Satellite Imagery:
Cooperative Institute for Meteorological Satellite Studies

When the storm is impacting Texas, here is a good visible satellite image source, courtesy of the Texas Center for Environmental Quality.

Model Data:
Kind of a "one stop shop" for tropical weather data, including model forecasts, the Weather Underground's Tropical Weather Invest Page.

Radar Data:
GRLevel2 and/or 3 are, of course, excellent.  If you don't already have the program(s), download the full trial version here.

Once you're using GRLevel2 and/or 3, I highly recommend subscribing to the additional resources of Allisonhouse, which include hurricane model data, forecast track data, model data and hurricane hunter aircraft data that can be overlain right on the radar imagery!  Here is a sample image of what I'm talking about:

Center of Alex Nearing Mexican Coast

Above is the WSR-88D (NEXRAD) radar image from the Brownsville, TX (KBRO) site taken a few moments ago.  You can clearly see the eye of Hurricane Alex about 30 miles East of the Mexican Coastline.  This same position is about 96 miles South/Southeast of Brownsville, TX.  

As of the 6pm Central Time National Hurricane Center Advisory, hurricane force winds extended out about 70 miles from the center of the storm.  This means that hurricane force winds would impact land up to about 20 miles South of the Texas/Mexico border, on the present track.  Tropical Storm force winds extend out from the center by just over 200 miles, and tropical storm force wind gusts have indeed been occurring across far South Texas during the last couple of hours.

So far for deep south Texas, very heavy rains have been the main story, along with some isolated wind damage reports:

The image below is the Brownsville radar estimate of storm total precipitaition thus far, through 6pm local time.  The dark purple areas show rainfall estimates of 9-10 inches, while the lighter purple areas show rainfall estimates of 7-9 inches:
Widespread, sometimes heavy, rains will continue across far South Texas through much of the night and into Thursday.  This will undoubtedly lead to flash flooding in many of the same areas.

Further North across central and the remainder of south Texas, rains have been tempered a bit today by the concentration of activity further South near the center of Alex.  As the system moves inland tonight and tomorrow, additional moisture and energy is likely to flow Northeast into the remainder of the region, which will result in increasing rain chances there as well.

Tuesday, June 29, 2010

Alex Nearing Hurricane Strength

Despite the normal computer model guidance flip-flopping of the last few days, the general trend of expecting the center of Alex to move across Northern Mexico (as reflected in my original post a few days ago) appears to be coming more certain.  The ridge of high pressure that was expected to build over the central & southern U.S. is indeed doing so, which will turn Alex more toward the West/Northwest rather than North/Northwest track over the next 24-36 hours.  

The latest National Hurricane Center forecast track reflects the above thinking, with the center of the storm expected to strike land in Northern Mexico sometime before 1am on Thursday morning, central time:

It would be an error to focus solely on where the center of the storm will make landfall, as its reach will extend far from the center.  Certainly the strongest, (likely hurricane force by that time), winds will take place near and immediately surrounding the center, however tropical storm force winds currently extend outward over 170 miles from the center.  On the current forecast track, this means that widespread tropical storm force winds can be expected well into the Rio Grande  Valley of far South Texas.

Alex is currently still classified as a tropical storm.  I suspect he will be upgraded to a hurricane by the next advisory this evening.  Another Air Force Reconnaissance flight will pass through the storm around 7pm Central Time.  The data obtained by that flight will likely determine an intensification to hurricane strength, based on what we're seeing on satellite imagery (like the one at the top of this post). 

Alex will also spread heavy rainfall well into central and south Texas throughout the end of the week.  Summer rains from tropical systems can be both beneficial and hazardous, depending on how much flooding takes place as a result.  It is literally a mixed blessing.

Saturday, June 26, 2010

Tropical Storm Alex

Above is a recent satellite image of Tropical Storm Alex, with the 1pm CDT National Hurricane Center (NHC) statistics superimposed in the upper-left hand corner of the image.

Now that Alex has formed, the $64,000 question is, of course, where will he go?  Well, the Yucatan Peninsula is obviously directly in Alex's path at the movement, with the system likely to traverse that land mass from about 8pm this evening through 8pm Sunday evening.  The land mass will quickly result in Alex weakening back down to depression stage after making landfall, but with plenty of warm, Gulf water on the other side, he will likely reintensify upon emerging back out into the Gulf on Monday.  In fact, most of the models have the system reaching hurricane force out over the Southwest Gulf early next week.

Below is the forecast track of Alex as indicated by the latest computer model runs (at total of 7 different computer model forecasts are included, indicated by the color coded legend at the top of the map).
As you can see, the "mean" (or average) track is toward the West/Northwest.  Not one model is currently forecasting a "direct hit" on Texas (the GFDL model does brush the center of Alex on the far southern tip of the state late Wednesday night or early Thursday morning).

The main feature that will determine the track of Alex at the moment appears to be the ridge of high pressure that has dominated the central & southern U.S. weather pattern over much of the last week to 10 days.  The ridge is currently undergoing some weakening/transitioning, but is forecast to regain a foothold on the region again by Tuesday.  If this expectation occurs, then the above forecast tracks of Alex having more of an impact on Mexico rather than the U.S. are likely to come to pass.  

Needless to say, if you live in South Texas or Mexico, you'll want to keep a close eye on the progress of Alex over the coming days.

Tuesday, June 22, 2010

Tornadic Supercell in Nebraska Panhandle

The above image was taken by the Cheyenne, WY (KCYS) NEXRAD a moment ago.  It's in reflectivity mode, which shows all precipitation echoes being sent to the radar (rain, hail, etc.).

This storm is also rotating, as shown by the strong "mesocyclone" on the Storm Relative Velocity (wind motion) image taken at the same time, below:
Note the strong motion toward and away from the radar associated with the storm (just Southeast of Harrisburg).  This is what is referred to as a mesocyclone.  Remember that green/blue colors are motion toward the radar while red/orange colors are motion away from the radar.  The radar is located just off of the lower left corner of the screen.  

Monday, June 21, 2010

Oh Yeah...I Almost Forgot...

Today is the first "official" day of summer.  Forgive me if I don't seem too excited, but it's been 95+ degrees with a heat index of 100+ degrees for what seems like the last month here in southcentral Texas, so I guess my senses already thought we've been there and done that...

None-the-less, the Summer Solstice took place at around 6:30 local time this morning.  Folks near the Arctic Circle up in Alaska won't see the sun set for the next 4 days...hence the nickname "land of the midnight sun".  I haven't seen that in person, but sure would love to some day...

Tornadic Storm in NW Kansas

Above is the Storm Relative Velocity (wind motion toward & away from the radar taking the storm's movement into account) image taken from the Goodland (KGLD) NEXRAD radar a few moments ago in Northwest Kansas.  Can you locate the mesocyclone about 13 miles South of Atwood, KS?

See below for a hint:

Remember, green is indicating wind blowing toward the radar, while red is indicating wind blowing away from the radar.  The radar is located just off the bottom left corner of the screen in these images:

Look even more closely within the mesocyclone and you can see Tornadic Vortex Signature, or where a tornado is most likely taking place on the ground:

So far there have not been any ground truth reports of tornadoes South of Atwood, but with the above signature I am confident that something is going on.  This is mainly in a rural area, so whether or not actual reports will be received remains to be seen.

Tornado In Billings Yesterday

Incredible image of a very picturesque tornado near Billings, Montana yesterday afternoon.  The image was shown on this website, which does not give credit to any particular photographer.  (If you are the photographer and would like for me to give you credit or remove the picture, please e-mail me at my profile address).

As beautiful as that picture is (particularly since the tornado appears to be causing no harm over open rangeland), it did cause damage earlier when crossing through parts of the city of Billings.  Fortunately only 1 injury has been reported thus far, and no deaths.

Here is a link to some videos taken in Billings as the tornado hit parts of town.

What Will Become of 93L?

The above visible satellite image was taken at 5:15 pm Central Time, and shows the broad tropical wave that has been identified thus far as "93L", in the eastern Carribean Sea.  This wave is currently moving slowly Westward, and present indications are that the wind & instability profile throughout the atmosphere will become more and more conducive for this system to develop and become better organized over the next several days.

Below is an image depicting 2 computer forecast model solutions on the track of "93L" over the next 144 hours.  Both models develop the system into at least a Tropical Storm during that period of time, with a general track toward the mouth of the Gulf of Mexico by this coming weekend.

If this system does indeed become a Tropical Storm or Hurricane, it will be named "Alex".

Saturday, June 19, 2010

20 Years - Seems Like Yesterday

On this date and at about this time 20 years ago, a massive windstorm was gathering over south-central Kansas.  Later called the "inland hurricane", the system caused widespread damage from near Pratt, Kansas through the greater Wichita area, into the southeast part of the state.  Winds were measured at near 120 mph near Kingman, which spread East into the Wichita area.

It wasn't really a hurricane, obviously, but a strong bow echo/derecho type system that traversed southern Kansas on that very hot, unstable day.  Damage was widespread, over $70 million in total.  Some folks were without power for over a week after the event.

Damaging, straight-line windstorms such as that one don't get the "glory" that tornado events do.  For some reason it's much more glamorous to be hit by a tornado than a straight-line wind event, I guess.  I'll never forget that day, personally.  I remember opening the roof hatch on the 2nd floor of KAKE-TV (where I worked at the time), sticking my head out to discover a massive wall of dust advancing toward the city from the West.  It was truly unbelievable.  I had no idea at the time the amount of damage that was about to be done to the city.  You see, even though the "top of the line" new radar technology at the time was the WSR-88D (NEXRAD), it wasn't until 2 full years after the "inland hurricane" that the technology was installed in Wichita (October 13, 1992, to be exact).  We could only rely upon ground-based reports from storm spotters to give us a "heads-up" on the wind speeds exhibited by the storm at that time.

Funny enough, some widespread wind damage has occurred during the last 24-48 hours, some 20 years later, almost to the day.  This type of activity is fueled by the extreme heat and instability present on a summer afternoon, so this should be little surprise.  Below is a map of the wind damage reports from yesterday:

This system was responsible for some widespread, significant wind damage in the Chicago Metro area yesterday afternoon as well:

While the event 20 years ago in Wichita did not cause any deaths (but over 30 injuries), there is no doubt that today's advanced radar and warning technology gave residents of Chicago a greater "heads-up" than we were able to give residents of Wichita in 1990.

For more information on bow echoes/derechos and other straight-line wind phenomena, go here for an excellent overview by Bob Johns, a true pioneer on the subject.  The image that will appear at the top of the screen when you go to that link looks much like what I saw on the roof of KAKE-TV that fateful day in 1990 (I wish we had digital cameras back then).

Thursday, June 17, 2010

'Popcorn' Showers Give a Small Break from Summer Heat

Isolated showers (like the top of one that you can see in the above picture taken near Kyle) developed across south-central Texas today, giving some folks a brief but much needed break from the hot, humid weather.  Of course, once the shower moved on, it was even more humid, but hey, in the middle of June we're not going to complain about any rain we can get, right?

Wednesday, June 16, 2010

Vortex 2 Comes to An End for 2010

The Vortex2 project has officially come to an end for the 2010 season.  Yesterday was the last "official" operations day.  

I obviously wasn't on the team, but from what I've seen since operations began back in May, this year was far more productive than last as far as "operational" severe weather was concerned.  The team deployed on numerous severe and several tornadic storms, and invaluable data sets were undoubtedly obtained.

Now the scientists go "back to the lab", study the data and hopefully make meaningful advances in our understanding of the development, organization and intensification of severe/tornadic thunderstorms.

Here is a site were you can look at the day-by-day chronicles of the experiment over the past month and a half.

Tropical Disturbance Remains Disorganized

On Sunday I blogged about the above disturbance that was moving West off of the coast of Africa.  At the time it looked like there was ample opportunity for this system to organize and become the first tropical depression of the season in the Atlantic.  Well, as the saying goes, "time changes everything" and tropical disturbances are apparently no exception.

Winds in the middle and upper levels of the atmosphere have become less and less favorable for tropical development and/or organization over the past few days.  The Tropical Prediction Center (TPC) now forecasts only a 10% chance of development or intensification with this system  over the next 48 hours.

Sunday, June 13, 2010

First Tropical Depression of the Season Developing?

You are looking (bottom center of the image) at satellite picture of an area of disturbed weather moving West/Northwest off the coast of Africa this morning.  This may soon become the first Tropical Depression of the season in the Atlantic.

Below is a snapshot of the latest track guidance from the various computer forecast models on this system (it has been identified as "92L"):

Saturday, June 12, 2010

Monster Size Hail in the Texas Panhandle

A severe thunderstorm in the far northern Texas Panhandle has produced hailstones up to 6 inches in diameter (yes, 6 inches!!!) just south of Sunray, TX.  Below is a reflectivity image of the cell near the time the report was received:
AMA NEXRAD Reflectivity image at 3:19 PM CDT

The Storm Attributes algorithm on the radar attempted to estimate the maximum potential hailstone size as 2.75 inches, as depicted by the solid green triangle in the image below (near Sunray):

In my earlier post regarding the new Phased Array Radar (PAR) system that is being tested in Norman, OK, I pointed out that PAR samples the atmosphere about once every minute, whereas the current NEXRAD network samples the atmosphere once every 4 to 6 minutes.  In situations like this afternoon's, the PAR would have had a better chance at "catching" the rapid intensification of the hail producing thunderstorm, and perhaps could have given stronger indication that the hail diameter potential was larger than 2.75 inches estimated by the NEXRAD algorithm.  Only time (and testing) will tell for sure, but there's little doubt that we would have had more information with a once per minute sampling vs. a once every 4-6 minute sampling of this storm!

Below is an image of the AMA Vertically Integrated Liquid (VIL) scan at about the same time as the image above.  VIL estimates the amount of liquid that is located in the air column at a given point.  In this particular case, the radar indicated a VIL value near 80 (denoted by the bright white colored area immediately Southeast of Sunray).  An 80 VIL is extremely high, and is more indicative of the super-size hail potential with this storm, even more so than the hail detection algorithm that predicted 2.75 inch hail:

Below is a snapshot of the GRLevel2 vertical cross-section of this storm shortly after it moved Northeast of Sunray:

On a reflectivity image (such as the cross section above), rain, hail, etc. are sending back echoes to the radar measured in "decibels of Z" (also known as dBZ).  To put some sort of generic perspective in place, 10-20 dBZ echoes would be considered light, 20-40 would be considered moderate, 40-60 heavy and anything above 60 would be considered "intense".  I've noted on the above image where a fairly good size core of 70 dBZ (getting toward the top of the intense scale) echoes were noted about 10,000 feet above ground level.  This is undoubtedly representing the heart of the intense hail core associated with this particular storm.

UPDATE 6/13/10:  Here is an impressive video of the hail from yesterday on YouTube:

Personally, I can't wait until Phased Array Radar comes onboard across the country and we can hopefully get a better handle on this type of situation.  Again, I'm not saying we don't already do a better job than we did even 5 or 10 years ago, but a more frequently updating radar system would result in even further improvement - and likely save additional lives each year as well!

The Next Generation of 'Next Generation' Radar...

In my last post I remarked that NEXRAD (NWS abbreviation for Next Generation Radar), was not perfect at estimating rainfall.  The original NEXRAD systems were launched in 1988, some 22 years ago.  Don't get me wrong, the system is far superior to its predecessors (the WSR-57 and WSR-74 radars - which offered no computer-based interpretation of data such as rainfall estimates, hail and wind shear algorithms, etc.) and has had several hardware and software upgrades since the original launch date.  My point was that you can't read a NEXRAD precipitation estimate of 3.0 inches for a given location and be 100% sure that 3.0 inches of rain fell at that location.  There will be some variance based on distance of the radar site from the area being estimated, the overall intensity and coverage of precipitation (particularly near the radar site), etc.  

The next generation of "Next Generation" radars, called a Phased Array, is currently under research and development at none other than the weather capital of the universe:  Norman, OK (home of the University of Oklahoma School of Meteorology, the National Severe Storms Laboratory (NSSL), the National Weather Center, and the Atmospheric Radar Research Center (ARRC), among other weather superstars).  
Phased Array Radar at the National Radar Testbed in Norman, OK

The Phased Array was originally developed and used by the Navy and other military outlets to detect ships, air traffic and missiles, among other things (and is still used for ths purpose today).  The Navy quickly found that the weather sometimes "interferes" with the radar's original mission of missile and aircraft hunting.  As the saying goes, one man's loss is another man's gain!

One of the downsides of NEXRAD is that it takes anywhere from 4 to 6 minutes for the radar to take a sampling of the entire environment (referred to as a volume scan) of a severe storm.  The Phased Array, on the other hand, takes less than 1 minute for a complete "volume scan".  Needless to say, the environment in and around a severe storm (particularly one that is producing or about to produce a tornado) can change quite significantly in a 6 minute period.  As a result, the much faster scanning rate of the Phased Array should result in greater lead time and warning updates on active severe weather.  In fact, it is likely that Phased Array will lead to faster, more accurate prediction of all types of weather phenomena, including severe storms, tornadoes and even rainfall and hail forecasts.  

Image taken from a PAR case study.  Note that the PAR took 29 images during the same time period that NEXRAD was only able to take 4 images of the same storm!

The Phased Array system (called PAR for short) is currently being tested actively at the NSSL's National Radar Testbed in Norman.  You can get more information, including a few case studies, related papers, and a look at the radar in action here.  The next time there is some active weather across central Oklahoma, I'll try to archive and post some images comparing the PAR data to the current NEXRAD data.

Other Links:
OU School of Meteorology
National Weather Center

Thursday, June 10, 2010

Rain, Rain and More Rain...

Most of my posts this week have revolved around the heavy rain producing systems that have been traversing Texas the past few days, and one way that you can anticipate rainfall potential for a given area (by taking a look at precipitable water values).

Once an event is unfolding, there are also several tools that I like to use to monitor actual rainfall.  One is the 1-hour, 3-hour and Storm Total precipitation products generated by local NEXRAD sites.  The Storm Total Precipitation image shown below is via GRLevel3:
While NEXRAD isn't perfect at estimating rainfall, it does give you a very good idea as to where more concentrated areas of heavy precipitation are taking place.  

Another tool is to use satellite imagery as a source of precipitation estimates during an ongoing convective (thunderstorm) event.  The NOAA Satellite and Information Service (also known as the SSD - Satellite Service Division) is an excellent source of satellite based precipitation products during an ongoing event.

The SSD will issue several text and graphics-based products during an active convective/precipitation event.  Such products usually consist of a text bulletin, accompanied by a corresponding, computer/human-generated graphic.

You can also become part of the action when it comes to reporting ground-truth rainfall totals.  One such group that I'm a member of, CoCoRaHS, allows you to observe and report rain, hail and snow information on their website to share with others (including the National Weather Service) for reporting and verification.  The official CoCoRaHS rain gauge is one of the most accurate that I've ever owned.  You can purchase one here.

Wednesday, June 9, 2010

One Last Post (Maybe) on Precipitable Water

I've been blogging the past few days about weather balloons/soundings, and specifically how "precipitable water" is one of the pieces of information that can be gleaned from the resulting data.  
The above image was captured a few moments ago from the New Braunfels, TX (KEWX) NEXRAD.  The image depicts "storm total precipitation", or at least the radar's estimate of the total precipitation, across the area since 6-7-10 (at 9am to be exact).

In my blog posts of the past couple of days, I've noted how there was around 2 inches of "precipitable water" in the skies over south & central Texas.  So if that's the case, how is it that over 3 inches of rain (depicted by the darker orange, red and purple colors on the above image) has fallen across a large part of the region during the last 24-36 hours?  

It's not necessarily a "that's all she wrote" situation with respect to precipitable water.  While it's true that the weather balloon and/or computer forecast model sounding indicate (or estimate/forecast in the case of the computer forecast model) how much precipitable water is present in the atmosphere at that given moment, you have to remember that as long as the wind is blowing from the right direction, additional moisture is being transported back into the same areas, often times as fast as the moisture is being "rained out" of the atmosphere.

While one thunderstorm (or thunderstorm complex) may have "rained out" the 1.9 inches of precipitable water that was indicated at 7 o'clock in the morning on the weather balloon sounding, Southeast winds continued to transport "replacement" moisture back into the same areas, resulting in additional heavy rains as more storms developed over the same areas.  As a result, and as in the above image, several inches of rain may ultimately end up falling over one or more areas.  

Nobody ever said that forecasting the weather was easy.  The bottom line is that we knew the atmosphere was very moist across the area, based in part on the high precipitable water values that we had observed over the previous 48 or so hours.  A forecast of widespread, sometimes heavy, rain was made, and indeed verified.  Some areas (noted by the pink/purple colors on the above image) received over 6 inches of rain before all was said and done!

Tuesday, June 8, 2010

Point-Specific Soundings

In a post last night, I wrote about upper-air weather "balloon" soundings and their utility in, among other things, determining rainfall potential in a given area.  At one point in the post I mentioned that the nearest weather balloon launch locations to the Austin-San Antonio corridor are Del Rio (DRT) and Corpus Christi (CRP).  I've had several e-mails from folks today asking why a major city like San Antonio and/or Austin is not a balloon launch site.
The above map shows the upper-air "weather balloon" network across the nation.  (I obtained this map from the RAP/UCAR website, which is an excellent source of raw weather data, by the way).

The primary goal of the upper-air network is to provide the "initial" weather data that feeds the computer forecast models.  The computer forecast models then produce their versions of weather forecasts for not only the nation, but much of North America as well.  Rather than focusing on the size of a city in determining whether a launch site is located there, the main focus is on the grid spacing between stations that feed the data to the various computer models.

With that said, I've often thought that there was an unusually large "spacing" between stations in Central and East Texas (i.e., Del Rio to Midland to Ft. Worth to Shreveport to Corpus Christi to Del Rio).  That leaves a pretty big "donut hole" (which happens to correspond to a heavily populated area) in my opinion.  But no one asked me, so that doesn't really matter...

Getting over my balloon frustration and moving on, I will say that several positive developments have taken place in the past several years (thanks mainly to computer technology) that allows us to access a "point specific" sounding "analysis" or forecast for any location we wish, regardless of whether an actual balloon was released in that location or not.  These point-specific soundings are produced by many of the same computer programs that produce the larger-scale forecast models.

So, where do you go to get that information?  There are several sources, actually, but one of my favorite "free" sources is direct from NOAA website located here.  Once you reach the main page, you are given several options for the type of model that you want to use to generate the point sounding.  When just taking a quick glance at things I typically use the default settings (which are already selected for you in the first 3 sections), then select the station location that I wish to view.  For example, if you wish to view a point sounding for San Antonio, you'd enter "KSAT" in the box in the 4th section.  For a list of some of the more popular surface observation stations (from which you may wish to select a point sounding), you can go here.  You can also enter a latitude/longitude combination if you wish.

Once the above are selected/entered and you click on the "Simple JAVA Plots" button (just my preference, you can use any of the 3 choices), wala, a point specific sounding is produced like this one (for Austin, TX today):

Now, how about all of that nifty "derived" information like Precipitable Water values and other things I mentioned in last night's post?  Well, "PW" is certainly calculated for you (note on the above image "PW=49") but the trick is this model calculates the field in kilograms per meter squared.  If you're like me and don't "do metrics", you need to then go somewhere and translate that value into "English" (i.e., inches).

There are many sites that can accomplish this task for you, my favorite (for the moment) is WolframAlpha.  Once there, you can enter the field into the box and hit the "=" (compute) button at the end of the box.  For example, in the above case, I entered "49 kg/m2", then hit the orange "equal" sign, which resulted in this output.  Scroll about halfway down the resulting page (under the "corresponding quantities" section) and you'll finally be able to tell that 49 kg/m2 = 1.9 inches of rain.

If you're lazy (like me) and don't mind paying for your point-sounding data, there are several programs out there that will calculate the fields for you in any "language" that you desire.  I won't list any here because I know Google is your best friend anyway...

Whew.  Glad that's over with.  I hope this helps some of you that inquired...

Monday, June 7, 2010

Humid Is As Humid Does....

If you live in Central or South Texas and walked outside undoubtedly noticed one thing:  it was freaking humid!
As you can see by examining the above surface map (taken at 9pm this evening, central time), dew point temperatures (show in green text) are in the mid to upper 70s across most of the area, with values near 80 degrees in far South Texas (that is downright tropical, folks)!

So why let all of this moisture go to waste?  An upper level weather disturbance is forecast to move slowly across the state during the period Tuesday through Thursday.  When this disturbance interacts with the copious amounts of moisture already present in the atmosphere, locally heavy rains are sure to take place.  Take a look at the HPC (Hydrometeorological Prediction Center - fancy name for National Weather Service Headquarters) rainfall forecast for the period 7pm Monday through 7pm Wednesday:

So how exactly do we determine how much rain may fall in a given area?  Weather balloons are released twice daily at certain locations across the country, in an effort to help us better understand (1). what is going on right now in the atmosphere and (2). what will be going on in later hours and days (the data is fed into computer models that derive forecasts, among other things).  The stations nearest the Austin-San Antonio corridor that release balloons are Del Rio (DRT) and Corpus Christi (CRP).  As the balloon rises up through the atmosphere, it transmits data back to the surface via a radio transmitter/receiver, which plots data such as temperature, dew point, humidity, wind speed and direction, etc., on a vertical map called a "sounding".

Below is an image of the sounding taken near Del Rio at 7am this morning:

Among all of the wiggly, wavy lines (which I'll go into in greater depth in a later post), there are some derived fields as well.  If you look closely at the chart toward the bottom left section of the image, you'll see "PW=1.87 in."  That stands for "Precipitable Water = 1.87 inches".  Simply put, precipitable water is the amount of water in a given column of the atmosphere (in this case, the column was over Del Rio).  

What this means is that if all of the water accumulating in the air column above Del Rio were to be precipitated (or rained) out, it would equal approximately 1.87 inches.

Anytime precipitable water is above 1 inch, that means the potential exists for locally heavy downpours that can accumulate rather quickly (i.e., an inch or more in an hour).  As all Texans know, that can be good news in the middle of a hot, otherwise dry summer.  So bring it on, we're ready for it!

Sunday, June 6, 2010

Widespread Severe Weather Reports Yesterday

You naturally always hear about the "major" severe weather outbreaks where "significant" tornadoes, large hail, etc. strike heavily populated areas.  I have to admit I wasn't watching TV or anything like that yesterday evening, but just scanning news headlines, etc. this morning there is relatively little being said about what a big severe weather day Saturday actually was.

Reports of severe weather were received from 24 states yesterday:

There were really 3 specific areas of activity.  1st being the Northern Plains into the Midwest and Ohio Valley:

2nd (and rather unusual) being in New England:

And a 3rd area, mainly consisting of wind damage reports, in the Southeast:

The area of most "intense" activity seemed to be across the Midwest (although the New England reports sure were interesting because of the relative lack of severe weather in that part of the country most of the time).  I'm going to try to find some video of one particular storm and post it later today.

Back to the Midwest, there were several tornadoes reported late yesterday evening from a couple of supercells that moved across northern Illinois, later crossing the Indiana border:

In a post yesterday evening, I loaded this impressive image of the Storm Relative Velocity (wind motion) display from the Chicago area (KLOT) doppler radar.  The rotation was occurring in a storm near Aroma Park, IL shortly after 10pm central time.  Your eyes will immediately be drawn to the center of the image, where a strong "couplet" of wind moving both toward (indicated by the blues and greens) and away (indicated by the reds and oranges) from the radar  was taking place.
The radar estimated winds moving both toward and away from the radar at about 135 mph at the center of the couplet (where the brightest yellow and blue colors touch in that very small geographic location).  The radar is located just off the upper-center of the image, and at that distance the 135 mph winds were being measured at about 2500 feet above ground level.  A ground report of a tornado "1 mile wide" was received from this area shortly after the image was taken.

Another Wild Day Instore for New England

After unusual severe weather events in parts of New England yesterday, a more widespread outbreak is forecast today.  In fact, a "moderate risk" of severe weather, including tornadoes, is forecast for a large part of New England today.  A rare (for that region) Public Severe Weather Outlook has also been issued.  This risk includes the New York City and Boston metro areas.

Things are getting started early today as well, with a tornado watch already in effect to the immediate West of the moderate risk area.  Here is a shot of the Binghamton, NY (KBGM) NEXRAD taken a moment ago.  A tornado warning is in effect on the cell west of Binghamton.

Severe weather will spread East with time today, and persons particularly in the moderate risk area should remain alert and prepare to seek shelter if threatening weather approaches their area.

Saturday, June 5, 2010

Intense Rotation Continues In Northeast Illinois

The above storm relative velocity (wind motion) image was taken within the last 5 minutes by the Chicago area (KLOT) doppler radar.  It shows very strong wind motion toward and away from the radar (where the red/orange and blue/green colors meet in a couplet near the center of the image) just East of Aroma Park, Illinois.

At the center of the couplet, the radar estimates the wind is blowing toward and away from the radar (i.e., in a circular pattern like a tornado)  at 118 knots, which is about 135 mph.  The radar is located about 34 miles North/Northwest of the center of the couplet, which means the 135 mph winds are being measured at about 2700 feet above ground level.  This location is about 1.5 miles East of Aroma Park.  A tornado is likely on the ground in this area.  This is a very dangerous tornado situation moving through a populated area.

As I was typing this, a storm report came in with spotters indicating a "mile wide" tornado on the ground near the radar indicated rotation couplet.  As I stated above, this is a very dangerous situation.  This storm will be entering Northwest parts of Indiana over the next 30-60 minutes.

Tornadoes Ripping Across Northern Illinois

A reportedly "large" and long track tornado continues to move across portions of northern Illinois this evening.  Note the reflectivity (precipitation) and storm relative velocity (wind motion) images from the Chicago area (KLOT) doppler radar taken within the past 10 minutes:

On the above storm relative velocity image, the green/blue colors are motion toward the radar (which is located off the image on the upper-center portion of the screen), while the red/orange colors are motion away from the radar.  Note the "couplet" (where wind movement toward and away from the radar meet in a small, compact geographic area) showing strong rotation just North of Herscher.  This is the radar signature known as a "TVS" or Tornadic Vortex Signature.  This is most likely where the tornado is taking place on the ground.  This is a very dangerous situation taking place in a populated area.

Below is another view of the same rotation/TVS taken from the same radar, but on GRLevel2, which shows data in a higher resolution.  This image was taken about 10 minutes after those above.  The strong rotation is now just North/Northwest of Irwin:

As I was typing the above another updated GRLevel2 image came in; the rotation is now even better defined to the East/Northeast of Irwin: