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Posts Tagged ‘Flash’
Sunday’s Chase Video Available!
September 18 was a day that featured moderate to high amounts of instability and marginal, but sufficient amounts of wind shear to support the development and organization of severe thunderstorms. The first thunderstorms developed across Cooke county along the Red River before additional thunderstorms began building further southwest. Eventually, a broken line of thunderstorms developed into South Texas. Texas Storm Chaser David Reimer intercepted several severe thunderstorms throughout the evening, experiencing several rounds of severe wind and hail. Most of this video is after 6 PM. For your convenience, a time line of the video has been created below with specific locations.
00:00 - 00:04 - Thunderheads as seen from Celina, TX looking north
00:05 - 00:31 - Nickel to Quater Size Hail falling while moving east on Highway 902 east of Howe, TX
00:32 - 00:57 - Strong winds and some hail while getting out ahead of the storm on Highway 2729.
00:58 - 01:08 - Line of storms looking north from Highway 121/Highway 160 in Collin County
01:09 - 01:42 - Severe Thunderstorm impacting Plano
01:43 - 02:45 - High Winds and Hail on I-635 in Garland
02:46 - 04:21 - Severe Winds impact Waxahatchie, TX
Severe Weather expected across North Texas Today
SPC Day 1 Convective Outlook issued at 11:30 AM Sunday
The above graphic is the Day 1 Convective Outlook from the Storm Prediction Center issued at 11:30 AM this morning. Each ‘box’ is labeled for the specific hazard in question, and the graphic can be enlarged by clicking on it. SPC increased the probabilities of severe weather across portions of North Texas with their latest outlook. In order to find your specific risk, look for your area on the graphic above. If you’re in D/FW, you have a 30% chance of seeing severe wind/hail within 25 miles of your location. Outside the 30% area, a larger area of 15% probabilities, meaning you have a 15% chance of seeing severe weather within 25 miles of your location. Severe Weather (excluding tornadoes) is defined as 1 inch or larger hail and winds at or above 58 MPH.
12Z RUC at 7 PM Sunday - 500 MB (18,500 Feet) Winds
As we look at upper level winds, we note that North Texas will be on the southern edge of the stronger 500 MB winds. Most location will be around 30 knots across North Texas. To see sustained, organized severe weather (supercells) we want to see winds at 500 MB above 35-40 knots, so we’re very borderline on that. Low level wind fields remain weak with 850 MB winds at or below 20 knots. Needless to say, this is not a major severe weather event. Today’s severe weather threat will be comprised of marginally severe hail (“coin sizes”) and damaging outflow winds between 60-65 MPH in some cases. The tornado threat is non-zero. Personally, I don’t expect any issues with tornadoes today across North Texas because of the weak wind shear, however there are a few boundaries laying around which could briefly allow storms to develop low level rotation, but that chance is very low. If by chance there was a tornado today, it would be brief and likely very weak. Like I said, I don’t see that happening today. Instability values should be between 1,500 and 2,500 joules. Those moderate instability values will support the possibility of some severe weather this afternoon into early this evening. The severe weather threat should diminish by mid-evening as instability values decrease.
12Z RUC at 7 PM Sunday - 500 MB Wind Barbs, Surface Instability Values, and 1 Hour Precipitation
In terms of timing, much of that will depend on when the atmosphere becomes unstable enough to support thunderstorms along with when an upper level disturbance begins to influence the region. We should see thunderstorms begin developing by mid-afternoon across North Texas, likely around the D/FW metroplex. The above graphic is just one of severe different model solutions. It shows a line of thunderstorms impacting North Texas roughly from Gainesville, down to Fort Worth, southwest to Glen Rose. Today’s situation is quite complex, so please don’t expect the radar to look like that come 6-7 PM tonight. Thunderstorms over the past few days have left numerous boundaries across the region, which then become focus points for possible thunderstorm development. Models are having a hard time depicting all these boundaries which then make it difficult to pin-point where thunderstorms will develop and then move. Most models are in agreement that D/FW should see a heavier batch of showers and thunderstorms later this evening with more storms impacting East Texas.
In summary, we’re not expecting a major severe weather event. Some storms this afternoon will likely be severe with marginally severe hail (coin sizes), damaging winds over 60 MPH, and excessive cloud to ground lightning, in addition to heavy rainfall. It’s a good idea to stay close to a source of weather information later this afternoon and evening so you can stay up to date with weather warnings. We’ll be posting constant updates on our Facebook and Twitter pages this afternoon. We’re also planning to venture out later this afternoon once storms begin approaching the D/FW Metroplex, and we will have our live streaming video available once again. Stay tuned and thanks for stopping by!
- David
Tropical Storm Lee Forms in the Gulf of Mexico; Major Flooding expected in Louisiana
Tropical Storm Irene - 5:45 PM CDT
Tropical Storm Lee remains disorganized in terms of a tropical cyclone, but is producing lots of convection, especially across the eastern quadrant of the storm. It’s really quite a large system in terms of total space converted by convection, with most of the western Gulf of Mexico (excluding the extreme NW portion) covered by this system. This definitely isn’t a pretty storm to look at, but it will bring rain that is needed in drought stricken Lousaiana, Mississippi, and Alabama before continuing northeast.
Watches/Warnings for the Gulf Coast
Currently, Tropical Storm Watches have been issued for all of Coastal Lousaiana and a few counties inland. The bigger and more important consideration with this system will be the extremely heavy rainfall amounts expected. Due to the tropical nature of this storm (It is a tropical storm after all) and the slow movement, significant rainfall amounts are likely. In some areas, the rainfall amounts may approach two feet or twenty four inches. This will end the drought for southeast Louisiana, Mississippi, and the northern half of Alabama. Thankfully, the region hasn’t seen much rain in the past few months and the rivers are fairly low. That will allow more rainfall to accumulate before any sort of flooding begins, but there will still be major flooding in areas.
Rainfall through Wednesday Evening
Now, the first to notice here is how high the scale goes on this graphic. The largest amount indicated on the scale is 15 inches of rain. Now notice the number imprinted over the New Orleans area. That is 23.2 inches of rain in the next five days. It doesn’t take a genius to see the problem and the significance of the expected rain amounts. Obviously rainfall amounts that high will cause major to catastrophic flooding in areas, and lets hope the pumps in New Orleans can keep a handle on the rainfall. As the system begins to eject northeastward during the next few days, it will continue dropping heavy rain. Rain amounts over five inches are forecasted well inland. Also, the system could begin to affect the Northeast US in about five to seven days. This could cause more flooding in those areas, although not likely to the scale we saw with Hurricane Irene.
Tropical Storm Lee Model Tracks (18Z Suite)
As I hinted to above, most models keep Lee stationary on the Louisiana Coast through the weekend before beginning to eject it northeastward across Mississippi into Alabama with a continued slow movement. This will likely cause major rivers all across the deep south to flood at some point, but that will depend on much rain falls. This is the kind of storm we need in Texas to end our drought in one swift punch. For those in the mid-south, they will be lucky to receive that kind of storm, but it’s going to cost them with flooding.
On a brighter note, Lee will allow for a major pattern shift over Texas and a end to the summer heat wave with a northerly flow aloft dragging in a strong cold front that will drop highs down into the 80′s across most of the state. We’ll have more on that in a separate blog post later this evening.
- David
Invest 93L – 18Z (1 PM CDT) Model Tracks
1 PM CDT Model Tracks
For a full discussion, check out our blog post made at lunch time
This is just a short update with the latest model tracks, please see our noon time discussion for the full discussion. The models didn’t change much compared to the 12Z runs earlier this morning. It still appears that Invest 93L will move slowly northwest for the next few days before possibiliy being picked up by the trough and pushed northeast. Again, its important not to focus on the exact center track because we don’t yet have a defined low level circulation plus the effects will be felt well away from the center of the storm.
Tropical Weather Outlook - 9/1/2011 2 PM EDT
The National Hurricane Center has given Invest 93L a 80% chance of becoming a Tropical Depression/Storm within the next 48 hours. This is nearly certain and a increase in probabilities since earlier this morning. We’ll have another update later this evening.
- David
Invest 93L – Thursday Lunchtime Update
Visible Satellite - 10:15 AM CDT
Every few years we seem to get one system that will spin up in the Gulf of Mexico, whether it be caused by a frontal boundary or a large convective complex. This system is actually produced from a more tropical origin. If you reference the blog post a few days ago, we were talking about a disturbance in the Caribbean that was forecasted to slowly move into the Gulf of Mexico. This is the same disturbance, now located in the central Gulf of Mexico. Taking a look at Invest 93L this morning, we see a large area of disorganized convection across the Central Gulf of Mexico, roughly along and east of 80W. So far, there is no signs of a defined low level circulation which would classify this as a Tropical Depression or Tropical Storm.
Wind Shear - 10 AM CDT
One reason why Invest 93L remains disorganized can be attributed to the wind shear present over the Gulf of Mexico. Right now, wind shear is analyzed around 30 knots across the central and eastern sections of the Gulf, with lesser amounts of wind shear across the western section. Invest 93L is located in the region of 30 knots of wind shear, which is pretty strong and will keep the development of this system ongoing at a slow pace, which is good for a few reasons which I’ll outline below.
Invest 93L - 12Z Model Tracks
Before I dive into the model guidance, I thought it would be benifitial to explain what models we’re looking at. A forecaster at the National Weather Service in Fort Worth published this explanation this morning and I figured it would help explain tropical models a bit.
THERE ARE FOUR TYPES OF MODELS USED...STATISTICAL...STATISTICAL- DYNAMICAL...DYNAMICAL...AND TRAJECTORY. ENSEMBLE AND CONSENSUS FORECAST METHODS ARE ALSO USED BUT THESE METHODS USE A COMBINATION FOUR TYPES OF MODELS LISTED ABOVE. STATISTICAL MODELS USE FACTORS SUCH AS LOCATION OF THE STORM...TIME OF YEAR...AND PAST STORM TRACK AND INTENSITY TO MAKE THEIR FORECASTS. AS SUCH...THEY PROVIDE A HISTORICAL BASELINE FOR A STORMS TRACK. THE AVERAGE TRACK ERROR FOR THE CLIPER5...THE MOST WIDELY USED STATISTICAL MODEL...WAS 200 N MI AT 96 HRS. THESE MODELS HAVE RECENTLY BEEN SURPASSED IN ACCURACY OF TRACK BY DYNAMICAL MODELS. DYNAMICAL-STATISTICAL MODELS...SUCH AS THE SHIPS AND LGEM...ARE BASED ON STATISTICAL RELATIONSHIPS BETWEEN CLIMATOLOGY...THE DYNAMICAL OUTPUT FROM THE GLOBAL MODELS...SUCH AS SEA SURFACE TEMPERATURES AND VERTICAL WIND SHEAR...AND STORM MOTION AND INTENSITY. THE SHIPS MODEL IS ONE OF THE MOST RELIABLE TROPICAL CYCLONE MODELS. DYNAMICAL MODELS...SUCH AS THE GFS...ECMWF...GEM...AND CMC...ARE THE MODELS TYPICALLY USED IN EVERYDAY FORECASTING. THERE IS A LONG LIST OF THESE TYPE OF MODELS AND THEY VARY IN DOMAIN FROM GLOBAL TO MESOSCALE. THE BEST PERFORMING MODELS IN 2010 WERE THE ECMWF...GFS..AND UKMET..IN THAT ORDER. ONE THING THAT SHOULD BE NOTED ABOUT DYNAMICAL MODELS IS THE DIFFERENCE BETWEEN EARLY-TRACK VERSUS LATE-TRACK MODEL GUIDANCE. LATE-TRACK GUIDANCE IS TYPICALLY WHAT WE THINK OF WITH COMPUTER MODELS. LATE-TRACK GUIDANCE INCLUDES THE ENTIRE FORECAST OF A PARTICULAR MODEL RUN. THE EARLY- TRACK GUIDANCE IS THE FORECAST DATA FROM THE PREVIOUS RUN OF MODEL IS INTERPOLATED SO THAT THE 6 HOUR FORECAST MATCHES THE OBSERVED DATA. EARLY-TRACK MODEL RUNS ARE NOT NEW MODEL RUNS. DYNAMICAL MODEL RUNS USUALLY TAKE THREE TO FOUR HOURS TO COMPLETE. FOR EXAMPLE...THE EARLY-TRACK 12Z IS NOT A NEW MODEL RUN. THE 12Z RUNS OF THE GLOBAL MODELS ARE USUALLY AVAILABLE AROUND 16Z WHILE THE REGIONAL AND MESOSCALE MODELS AROUND 15Z. TRAJECTORY MODELS...SUCH AS THE BAM...ARE VERY SIMPLE AND MOVE A TROPICAL CYCLONE BASED ON THE PREVAILING FLOW OUTPUT FROM DYNAMICAL MODELS. THEY INCLUDE A CORRECTION TERM FOR THE SPIN OF THE EARTH...KNOWN AS THE VARIABLE BETA...AND ARE SOMETIMES CALLED BETA-ADVECTION MODELS. IF THE FLOW IS WEAK AND THERE ARE NO MAJOR SYNOPTIC CHANCES...TROPICAL CYCLONE WILL FOLLOW THESE MODELS CLOSELY. ENSEMBLE AND CONSENSUS MODELS USUALLY PROVIDE THE BEST FORECAST. CONSENSUS MODELS FOR THE TRACK FORECAST BEGIN WITH THE LETTER T...SUCH AS THE TCON AND TVCN WHILE THE CONSENSUS MODELS FOR THE INTENSITY BEGIN WITH THE LETTER I...SUCH AS THE ICON AND IVCN. HOPEFULLY THIS INFORMATION WILL HELP SHED SOME LIGHT ON THE COMPLEX SPAGHETTI PLOTS. MOST OF THIS INFORMATION WAS FOUND IN TWO DOCUMENTS PRODUCED BY THE NHC. THESE DOCUMENTS CAN BE FOUND AT WWW.NHC.NOAA.GOV/VERIFICATION/PDFS/VERIFICATION_2010.PDF AND WWW.NHC.NOAA.GOV/PDFS/MODEL_SUMMARY_20090724.PDF
Hopefully that helps explain tropical models and our terminolgy. Now with that out of the way, lets dive into the latest tracks. Tracks for Invest 93L can be described best as a ‘bowl of spaghetti’. There isn’t much to steer or move Invest 93L along, so movement is going to be very slow to at times, stationary. This could result in a very interesting and potentially dangerous flooding event wherever this system ends up. Much of the deep south is experiencing drought conditions, and this is the type of system that can break a drought. However, remember that droughts are often ended in major rainfall and flooding events. Just because we’re in a drought, that does not make us immune to flooding. In fact, it increases that potential slightly as the ground is unable to absorb heavy rainfall quickly because it’s so dry. As we continue to track Invest 93L, keep in mind that this system has a high potential of causing flooding.
Until a defined low level circulation forms, it’s likely that the models will continue to shift around in their solutions. Last night’s 0Z models had this system sitting on top of New Orleans, dropping upwards of 20 inches of rain over the parishes in southeast Louisiana. This morning’s models have shifted a bit west, which would allow portions of Texas to get in on the rain. I’m going to be honest, it’s nearly impossible to say where this system is going to end up until we get a defined low level circulation, but the effects of this system will be fairly widespread and not confined to the center of the storm. We’ll keep continous updates on the track updates with this system.
Invest 93L - 12Z Intensity Guidance
As I said above, moderate to strong wind shear should keep Invest 93L in check from getting too out of hand, however it still appears likely that it should be able to attain Tropical Storm status. Beyond that, it will all depend on several factors such as the organization of the low level circulation, strength of the wind shear in the coming days, and how close this system ends up to the coastline. Right now, this system does not look like it will become anything more then a Tropical Storm, maybe a minimal hurricane. This should not become a major hurricane. This is exactly what we need, a tropical storm with lots of rain, but without the major damage a huge hurricane can bring.
Rainfall through Tuesday Morning
The rainfall forecast depends on where Invest 93L ends up, which as I said above is still uncertain, but this is the latest rainfall forecast from the Hydrometeorological Prediction Center. Currently, they have the heaviest rains just east of Texas with a astoundingly high 19 inches of rain falling over the southern parishes of Lousiana. If this were to play out as shown above, I would be extremely concerned about major to catastrophic flooding in that area, including New Orleans. Lets hope the levee system can support that much water. Luckily, we’re still a few days out and its quite possible that the heavy rainfall will shift west. If the 12Z models are right, then that heavy rainfall threat will extend into Texas. Based off this forecast, extreme southeast Texas would receive a few inches of rain, but 99 percent of the state would remain fairly dry.
Another consideration is the northerly flow aloft that would help bring in some milder air across Texas. Because we would be on the western side of the circulation, the northerly flow would allow milder air to flow into the state. We’ll see how that plays out, but it looks like we should be getting a cool off by next week. For the latest information on all Texas weather, follow us on Facebook and Twitter. Links are available on the right side of the sidebar and on the top of the page. We’ll have another blog post by 11 PM central tonight. Thanks for stopping by!
- David
Chase Status
This shows the probability of a storm chase within the next 5 days.
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