Mesoscale Discussion #91

MESOSCALE DISCUSSION 0091
   NWS STORM PREDICTION CENTER NORMAN OK
   0344 PM CST THU FEB 02 2012

   AREAS AFFECTED...NRN PORTIONS OF WRN TX THROUGH TX PANHANDLE AND WRN
   OK

   CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE 

   VALID 022144Z - 022345Z

   THUNDERSTORMS ARE EXPECTED TO DEVELOP FARTHER SWD OVER PORTIONS OF
   THE TX PANHANDLE BY 00-01Z AND EVENTUALLY INTO WRN OK THIS EVENING.
   INITIAL PRIMARY THREAT WILL BE SUPERCELLS WITH ISOLATED LARGE HAIL.
   HOWEVER...A WINDOW WILL EXIST DURING THE EARLY EVENING FOR ISOLATED
   TORNADOES FROM THE SRN TX PANHANDLE INTO NWRN TX AND SWRN OK. AREA
   WILL CONTINUE TO BE MONITORED FOR A POSSIBLE WW BY 23-00Z. 

   WV AND OBJECTIVE ANALYSIS DATA SHOW AN UPPER JET STREAK FROM SRN AZ
   THROUGH SRN AND ERN NM WITHIN BASE OF TROUGH SITUATED OVER THE CNTRL
   AND SRN ROCKIES. MID-UPPER ASCENT WITHIN THE EXIT REGION OF THIS
   FEATURE AND WITHIN STEEP LAPSE RATE ENVIRONMENT IS PROMOTING
   DEVELOPMENT OF ELEVATED CONVECTION FROM NERN MN INTO THE TX AND OK
   PANHANDLES. THIS AREA REMAINS WELL NORTH OF GREATER MOISTURE AND
   INSTABILITY ACROSS W-CNTRL AND WRN TX...AND AS A RESULT IS EXPECTED
   TO REMAIN BELOW SEVERE LEVELS NEXT COUPLE HOURS. 

   LLJ IS STRENGTHENING OVER WRN TX WITHIN UPPER JET EXIT REGION AND IS
   CONTRIBUTING TO MOISTURE ADVECTION AND NWD DESTABILIZATION. STORMS
   SHOULD INCREASE IN COVERAGE AND INTENSIFY THIS EVENING FROM PORTIONS
   OF THE TX PANHANDLE...NWRN TX AND WRN OK AS THE ATMOSPHERE
   DESTABILIZES NWD WITH TIME. STRONG VERTICAL SHEAR PROFILES WITH
   LARGE 0-2 KM HODOGRAPHS WILL SUPPORT A FEW SUPERCELLS...BUT SOME OF
   THE ACTIVITY MAY EVOLVE INTO LINE/BOWING SEGMENTS. A WINDOW MAY
   EXIST FOR ISOLATED TORNADOES AS STORMS DEVELOP ON NRN FRINGE OF
   GREATER MOISTURE RETURN AND BEFORE ONSET OF NOCTURNAL COOLING.
   OTHERWISE...ISOLATED LARGE HAIL AND DAMAGING WIND WILL BE THE MAIN
   THREATS.

   ..DIAL.. 02/02/2012

   ATTN...WFO...OUN...SJT...LUB...AMA...MAF...

Storm Prediction Center - Day 2 Convective Outlook

Lets start out with the latest Storm Prediction Center outlook for Thursday. With their latest convective outlook issued earlier Wednesday Afternoon, they have a standard slight risk in effect for portions of West Texas and Southwest Oklahoma. While this outlook will likely change based on mesoscale features, at the time of this post, the risk extended from San Angelo, northwest to Childress, eastward to Ringgold and Eastland County.

0Z NAM: 850 millibar winds at 6 PM Thursday

We like to start off by analyzing the mid to upper levels of the atmosphere to get a general diagnosis of the amount of wind shear/vorticity that will come into play during an event. At 6 PM tomorrow, we have a positive tilt shortwave in place across the four corners region with the right-entrance region of the jet beginning to influence West Texas. In terms of wind shear, we like to see winds at or above 35 knots to support organized convection in the mid to upper levels of the atmosphere. By 6 PM tomorrow, it looks like we’ll have 50 to 70 knots of wind overspreading West Texas at 6 PM.

0Z NAM: 850 millibar winds at 9 PM Thursday

Taking a look at the low levels, specifically at 850 millibars, the 0Z NAM already has a sustained low level jet in place by 6 PM on Thursday. When determining the potential for specific severe weather hazards, we like to check the direction of the wind at 850 millibars. If the wind is coming from the southeast with 500 millibar winds from the southwest, that creates turning with height. If the winds at 850 millibars and 500 millibars are out of the southwest, that creates a linear type setup, which favors squall lines verses discrete supercells. It looks like we’ll have southeasterly 850 millibar winds tomorrow evening. At 6 PM, the NAM has the low level jet at 30 knots.

Fast forward three hours and you still have southeasterly winds at 850 millibars, but notice that instead of the 25 to 30 knots we were seeing earlier that we’re cranking up to 40 to 50 knots! That’s actually normal for a low level jet. After sunset and once the initial daytime heating subsides, the low level jet will increase. The process on why that occurs will make an excellent education post one day So, wind shear looks favorable for severe weather on Thursday across West Texas, but that’s only one of three necessary ingredients for severe weather. Lets take a look at instability…

The first thing to note from this graphic is that these instability values are for 9 PM on Thursday, nearly three hours after sunset. Even with the loss of daytime heating, instability remain high (for a cool season event) along the dryline and warm front. The warm front can be identified by the sudden drop off in instability across Oklahoma, while the dryline is your north-south feature located roughly along Interstate 27. During cool season events, I like to see instability values in excess of 1,000 joules per kilogram (J/kg). That doesn’t look like its going to be a problem tomorrow afternoon and evening. In fact, instability values appear to be in access of 1,500 joules per kilogram which is pretty impressive for early February. Now we have confirmed that wind shear and instability won’t be an issue.

0Z NAM: Surface dewpoints at 9 PM Thursday

Now for our final ingredient… Moisture! While wind shear and instability look supportive of severe weather, I’m a little concerned about instability. No doubt it will be sufficient for severe weather as any value above 50 degrees should be enough for severe thunderstorms, I’m looking in terms of the hazard of more significant severe weather, like tornadoes. For surface based thunderstorms capable of producing tornadoes, I generally like to see dewpoint values in excess of 60 degrees. During the spring time, that number increases to 65 degrees. Yet, there are a few factors that may help thunderstorms tomorrow develop low level rotation even with the lower dewpoint values. The first factor is the terrain and elevation. If thunderstorms form on the caprock, the higher elevation may allow thunderstorms to produce organized low level rotation with dewpoint values in excess of 55° verses the 60° dewpoint values I look for. The second factor is that surface temperatures won’t get too warm, likely upper 60s to lower 70s. That means we won’t have a large temperature/dewpoint spread which will keep cloud bases lower. The third factor is that storms may remain surface based well into the evening, when they will be able to use the abundant wind shear in place. We’ll find that out tomorrow…

Either way, it does appear we will see a complex of thunderstorms form across the eastern Texas Panhandle and Northwest Texas between 5 and 9 PM Thursday, before moving northeast into Oklahoma. The primary hazards with a squall line would be damaging winds and the possibility of large hail. In discrete thunderstorms, large hail and the possibility of a tornado would be possible. If we end up with higher moisture values then currently anticipated, the tornado threat would increase substantially. See the video for complete details…

Storm Prediction Center - Day 3 Convective Outlook

0Z NAM: Instability at 3 PM Friday

The severe weather threat will spread east to the Interstate 35 corridor on Friday as the upper level storm system begins to push northeastward. Compared to Thursday, instability values appear to be much lower. In fact, the NAM doesn’t have any instability values over 500 J/Kg across North Texas on Friday. While instability levels will be higher across South Texas, the upper level storm system will be too far north to cause any issues that far south. There may be a few severe wind reports as the squall line passes across North Texas on Friday, but at this point the severe weather threat looks fairly marginal. We’ll keep an eye on it though and provide an update with our February 2nd Daily Weather Video.

I am planning to chase in West Texas on Thursday. My laptop is still down for repairs so I’ll have to put my desktop in the car as the backup computer. I’m not sure if it has the processor power to stream live video, but if it does I’ll certainly have that available on Thursday! Stay tuned for the latest updates on our Facebook and Twitter pages. I hope to have our next weather video posted by 9:30 AM on Thursday.

Severe Thunderstorm Watch #200

 URGENT - IMMEDIATE BROADCAST REQUESTED
   SEVERE THUNDERSTORM WATCH NUMBER 20
   NWS STORM PREDICTION CENTER NORMAN OK
   1235 PM CST WED FEB 1 2012

   THE NWS STORM PREDICTION CENTER HAS ISSUED A
   SEVERE THUNDERSTORM WATCH FOR PORTIONS OF 

          CENTRAL AND SOUTHERN ARKANSAS
          NORTHERN LOUISIANA
          EXTREME SOUTHEAST OKLAHOMA
          NORTHEAST TEXAS

   EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 1235 PM UNTIL
   800 PM CST.

   HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
   MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

   THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 95
   STATUTE MILES NORTH AND SOUTH OF A LINE FROM 60 MILES SOUTHWEST
   OF DE QUEEN ARKANSAS TO 50 MILES EAST NORTHEAST OF PINE BLUFF
   ARKANSAS.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
   ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).

   REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
   FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
   AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
   THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
   AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
   DO PRODUCE TORNADOES.

   DISCUSSION...A CLUSTER OF THUNDERSTORMS OVER SOUTHEAST OK WILL
   SPREAD EASTWARD INTO AR...WHILE NEW STORMS POTENTIALLY DEVELOPING
   SOUTHWARD INTO NORTHEAST TX.  STEEP MID LEVEL LAPSE RATES AND
   MODERATE CAPE VALUES WILL PROMOTE THE RISK OF A FEW INTENSE CELLS
   CAPABLE OF LARGE HAIL AND GUSTY WINDS.

   AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
   TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
   KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 400. MEAN STORM
   MOTION VECTOR 27035.

   ...HART

Before we can use hodographs for our forecasting and analysis, we first must have at least a basic understanding of vectors. A vector is a quantity that, unlike a scalar which has just a magnitude, consists of both a magnitude and a direction. Let’s relate these terms to meteorology! When you check your local forecast, the first thing you may see that your forecast high is 52°F. This quantity is a scalar, because it has only a magnitude. What do you look for next, most likely, the chance of rain! A 70% chance of rain has no direction, just a magnitude, so this value too is a scalar. But what are you likely to look for next? The wind, of course. For the sake of this example, let’s say that the wind today will be 20 miles per hour out of the north-northwest. This value, unlike the other two examples, is a vector. With a magnitude of 20 mph and a direction of south-southeast, or 158°. Important: When people refer to a “north wind,” they usually are talking about wind that is blowing from north to south. When talking direction, north is 0°/360°, east is 90°, south is 180°, and west is 270°. The NNW wind in this is example is blowing to the SSE, and because the direction of a vector is given as the direction it points, we assigned it a direction of 158°. However, to stay consistent with the way things are done in meteorology, from here on out all winds will refer to the direction they are coming from, so a NNW wind will be about 338°.

What does this have to do with hodographs? We’ll get to that! First, let’s show you a blank hodograph just to get that image in your head.

The above image is the most common of several ways a hodograph may be presented. It is the same concept as a polar coordinate chart. The lines directed outward from the center indicate direction, and the different sized rings encircling the center represent wind speed. This is the fundamental part of hodographs that must be understood. Two things: speed, direction. Does that sound familiar? Speed and direction? It should! Remember that wind is a vector, so it has both a magnitude (speed) and a direction.

Let’s start by plotting the wind speed at the surface on this hodograph. Let’s say the wind outside is blowing at 20 knots out of the east, toward the west.

The red dot on the hodograph indicates where the surface wind in this situation would be plotted! This represents the wind vector. In case this is difficult to visualize, here’s what the hodograph would look like with the vector drawn in as an arrow.

Technically, this first image we posted could be used as a real hodograph! It has the chart, with the wind at at least one level plotted. But we will almost never encounter a hodograph with only one level plotted, as it defeats the purpose of such a useful graphical display. Let’s plot the wind speeds in a hypothetical atmosphere all the way up to six kilometers above the ground! We will use the same easterly surface wind, and add in a few more points to show other levels of the atmosphere at the same time.

We can now see the wind direction at five different heights above one location on a single plot! The wind at the surface is blowing at 20 knots from the east. One kilometer above the ground, the wind is blowing 30 knots from the ESE. At 3 km, the wind is 35 knots from the SE. At 4.5 kilometers above the ground, the wind is blowing at 40 knots from the SSW, and at 6 km the wind is blowing 60 knots from the WSW! As before, to help us visualize all of these directions, let’s take a look at the same diagram, but with the vectors plotted.

Like before, the longer the arrow and the farther the plotted point from the center, the higher the wind speed! Without knowing what the atmosphere looks like before hand, we would have no idea which point was which, so points on a hodograph will usually be labeled with either a height or a pressure for reference.

Now that we’ve plotted several points from 0-6 kilometers, there is one more step before we are done. While digitally generated hodographs will usually have more than five data points, this illustrate the same point just as effectively. When a hodograph is created, it is helpful to “connect the dots” of all of the plotted points. This helps visualize how the atmospheric wind profile actually looks more effectively than to just look at several dots. To do this, we will draw a line from the lowest point (the surface), to the second-lowest point (1 km), and continue this all the way to the highest point (6 km). Let’s take a look!

There we have it! This is what a hodograph would look like in the environment we used. The line used to connect the dots shows perfectly that the wind speed increases with height, and the wind direction veers with height. A veering wind profile is one that rotates clockwise with height, like this one. When the wind turns counter-clockwise with height, it is said to be backing. A wind profile that veers and increases with height like this one is extremely favorable for supercells and tornadoes! Here are a couple more examples of hodographs that can be useful for forecasting.

Straight-line hodograph:

This is often called a straight-line hodograph. These do not have to be, and almost never will be, perfectly straight, but hodographs that generally exhibit a straight line fit into this category. Even though significant speed shear can be present, the lack of directional wind shear tends to favor splitting supercells that are more likely to produce large hail than tornadoes.

Weak wind shear environments

In environments like this, winds are weak and sporadic throughout all levels. Coming from several different directions, this hodograph has no winds that exceed 10 knots. Environments with weak wind shear can still have severe weather if instability is high, but it will likely be in the form of multicellular storms with hail and wind as the main threads. Supercells and tornadoes are rare in these environments, but they can happen, especially with extreme instability and local boundaries. For example, the environment near Jarrell, TX, on 5/27/97 looked much like this, but the presence of incredible instability along with a gravity wave moving through the region helped a southward-moving supercell produce a violent F5 tornado.

Values that can be drawn from hodographs

In addition to the assumptions that can be made simply by glancing at a hodograph, a slightly more in-depth look at an environment’s hodograph can reveal a bit extra at times. Here we’ll discuss a couple of these!

Bulk shear and bulk wind difference

Bulk wind difference is the difference between the wind vectors at two levels of the atmosphere. We usually see 0-6 km bulk wind difference, which means the difference between the winds at 6 km and at the surface. We can see this easily on a hodograph by drawing a vector from the surface wind to the 6 kilometer wind! Once we’ve drawn this vector, we can redraw an identical vector that originates at the center of the hodograph.

From the vector we’ve added at the origin of the plot, we can see that this hodograph has an 80 knot 0-6 km bulk wind difference in the ENE direction. When taken into consideration with other factors, this is very favorable for severe thunderstorms! Bulk shear is very similar to bulk wind difference, except that “shear” is normalized over the depth over which it is taken. A wind difference of 100 m/s over 6 km, or 6000 meters, results in a bulk shear value of .0167 s^-1. ((100 m/s)/(6000 m) = .0167 s^-1)

Storm Motion and Storm Relative Helicity

When forecasting for severe weather and possibly supercells, storm motion and storm relative helicity (SRH) are two very important factors that must be considered. The two are related, and both can be estimated using hodographs, although exact values are difficult to ascertain with out help from a computer! Storm motion tends to be near the “mean wind” of the environment, so without going into too much detail, we can estimate that the storm motion in this environment will be somewhere near this area:

The actual mean wind in an environment like this would likely be a bit more northerly and possibly a bit faster, but because tornadic supercells often move right of the mean wind, we have placed our estimated storm motion a bit farther to the east. Once we’ve plotted our storm motion, we can begin finding our storm relative helicity. SRH is typically measured either from 0-1 km or from 0-3 km, and represents the amount of “spin” in the atmosphere between those levels. For supercells in general, many meteorologists use 0-3 km SRH, while 0-1 km SRH can be very helpful when forecasting tornado potential. To calculate 0-3 SRH using this hodograph, we will draw two lines from the storm motion data point to the 0 km (surface) and 3 km data points. The area between these lines and the plotted hodograph represents the SRH in meters-squared per second-squared (m²/s²). It would be difficult to calculate an exact SRH by hand for a hodograph like this, but this would be an environment with a significantly high value! Over time, after observing many hodographs, it becomes easier to estimate SRH by looking at the hodograph. 0-3 km SRH values over 250 m²/s² and 0-1 km SRH values over 100 m²/s² are considered by many to be guidelines for the minimum needed for tornado formation with supercells, but there is no exact threshold. It all depends on the environment!

We hope this has been educational and you have learned something about hodographs. We plan to add more educational postings here with time. If you have any questions or special requests, let us know through Facebook, Twitter, or our contact page. Thanks!

Austin, Texas Tornado

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
251 PM CST WED JAN 25 2012

...PRELIMINARY STORM DAMAGE SURVEY FOR NORTHEAST AUSTIN TX...

A NATIONAL WEATHER SERVICE STORM DAMAGE SURVEY WAS CONDUCTED THIS
MORNING IN THE AREA ALONG SPRINGDALE ROAD IN NORTHEAST AUSTIN.  THE
FOLLOWING HAVE BEEN DETERMINED...

EVENT DATE: JANUARY 25 2012
EVENT RATING: AWAITING FINAL DATA
ESTIMATED PEAK WINDS (MPH): AWAITING FINAL RATING
INJURIES/FATALITIES: 0
EVENT START TIME/LOCATION COORDINATES: 30.3221/-97.6536 AT 258 AM
EVENT END TIME/LOCATION COORDINATES:   30.3381/-97.6551 AT 305 AM
DAMAGE PATH LENGTH (IN MILES): 1.14
DAMAGE PATH WIDTH (IN YARDS): 50

THE TORNADO PATH BEGAN AT THE INTERSECTION OF COMMERCIAL PARK DRIVE
AND OLD MANOR ROAD...WITH RADAR INDICATING A TOUCHDOWN TIME NEAR
2:58 AM. DAMAGE CONTINUED NORTH THROUGH AN INDUSTRIAL PARK...THEN
ACROSS U.S. 290...BEFORE ENTERING THE WALNUT PLACE SUBDIVISION.
FURTHER DAMAGE OCCURRED TO HOMES ON THE WEST SIDE OF HAPPY TRAIL...
WITH TREES ON THE EAST SIDE OF HAPPY TRAIL LAYING DOWN TOWARD THE
WEST AND CONVERGING WITH THE DAMAGE TO THE HOMES.  DEBRIS WAS NOTED
ALONG FERGUSON LANE...WITH THE TORNADO PATH ENDING JUST WEST OF THE
INTERSECTION OF FERGUSON LANE AND SANSOM ROAD.;

Courtesy of City of Austin Homeland Security and Emergency Management – Tornado Track Map

San Antonio, Texas Tornado

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE AUSTIN/SAN ANTONIO TX
331 PM CST WED JAN 25 2012

...PRELIMINARY STORM DAMAGE SURVEY FOR SOUTHWEST SAN ANTONIO TX...

A NATIONAL WEATHER SERVICE STORM DAMAGE SURVEY WAS CONDUCTED THIS
AFTERNOON IN THE AREA ALONG DEER PARK (STREET) IN SOUTHWEST SAN
ANTONIO.  THE FOLLOWING HAVE BEEN DETERMINED...

EVENT DATE: JANUARY 25 2012
EVENT RATING: AWAITING FINAL DATA
ESTIMATED PEAK WINDS (MPH): AWAITING FINAL RATING
INJURIES/FATALITIES: 0
EVENT START TIME/LOCATION COORDINATES: 29.4556/-98.6645 AT 415 AM
EVENT END TIME/LOCATION COORDINATES:   29.4545/-98.6603
DAMAGE PATH LENGTH (IN MILES): 0.27
DAMAGE PATH WIDTH (IN YARDS): 30

THE TORNADO PATH BEGAN AT THE INTERSECTION OF DEER PARK AND RICHLAND
HILLS DRIVE...AND CONTINUED ALONG DEER PARK TO THE INTERSECTION OF
DEER PARK AND LEANDER.  THE PRIMARY DAMAGE WAS A CARPORT BEING
THROWN INTO A HOME AND CAUSING SUBSTANTIAL DAMAGE.

Estimated Tornado Track (This was created using the damage survey. This meant to only be an estimation of the exact track of the tornado.)

Pearland, Texas Tornado

Pearland, TX Damaging Wind and Tornado Track (From NWS Houston)

THE SURVEY TEAM FOUND A SWATH OF STRAIGHT LINE WIND DAMAGE
BEGINNING AROUND HATFIELD ROAD AND EXTENDED EAST NORTHEAST AROUND
2 MILES WHICH CONSISTED OF FENCES BLOWN DOWN AND SPORADIC TREE
DAMAGE. THE DAMAGE SWATH WAS BETWEEN 1/10 AND 1/4 MILE WIDE.
WITHIN THAT SWATH IT WAS DETERMINED THAT A SHORT LIVED TORNADO
ALSO TOUCHED DOWN AT HIGHWAY 35 AND PLUM STREET. A CHEVRON
STATION HAD ITS ITS GAS PUMP AWNING DESTROYED AND THE BUSINESS TO
THE SOUTH OF PLUM STREET HAD ITS ROOF PEELED BACK. TORNADO PATH
WAS APPROXIMATELY 200 YARDS LONG AND WAS 75 YARDS WIDE. IT WAS
RATED AN EF-0 WITH 65 TO 85 MPH WINDS.

Brenham, Texas Tornado

STRAIGHT LINE WIND DAMAGE WAS OBSERVED WITHIN THE TOWN OF BRENHAM
EXTENDING TO AREAS ALONG AND EAST OF FM 50 TO NEAR INDEPENDENCE.
THIS EVENT WAS FROM APPROXIMATELY 700 AM TO 725 AM. WINDS WERE
ESTIMATED BETWEEN 60 AND 75 MPH WHICH DOWNED POWERLINES AND
NUMEROUS TREES. THE DAMAGE WAS SPORADIC AND NOT CONTINUOUS. THE
ASSOCIATED LINE OF STORMS ALSO DROPPED A TORNADO DOWN WEST OF
COUNTY ROAD 50 JUST TO THE NORTH OF BRENHAM MUNICIPAL AIRPORT AND
TRAVELED EASTWARD TO THE INTERSECTION OF FM262 AND COUNTY ROAD 65.
THIS TORNADO DESTROYED SEVERAL METAL OUTBUILDINGS AND REMOVED THE
ROOF FROM A BARN. IT ALSO PRODUCED MINOR ROOF DAMAGE TO A HOUSE
AND SNAPPED NUMEROUS LARGE TREES. THIS TORNADO WAS RATED AN EF-0
WITH ESTIMATED 85 MPH WINDS. DAMAGE PATH WAS 2.5 MILES LONG AND 50
YARDS WIDE.

Caldwell, Texas Tornado

EVENT TIME…6:43 AM
EVENT TYPE…EF1 TORNADO
ESTIMATED PEAK WINDS (MPH)…90 to 100
INJURIES/FATALITIES…0

AN EF1 TORNADO CUT A DAMAGE SWATH THAT EXTENDED FROM JUST NORTHEAST OF DEANVILLE TO JUST SOUTHEAST OF CALDWELL. DAMAGE APPEARED TORNADIC ALONG THE SOUTHERN PORTION OF THAT AREA WITH NUMEROUS TREES SNAPPED OR UPROOTED. ONE HOUSE WAS PUSHED OFF A CINDER BLOCK BASE THEN DRAGGED ALONG A CURVED PATH FOR ABOUT 100 FEET. A FEED TRAILER WAS LIFTED OVER A FENCE THEN ROLLED ABOUT 150 FEET. SEVERAL SHEDS AND BARNS WERE DESTROYED. STRAIGHT LINE WIND DAMAGE ALSO FOUND IN THE AREA.

Madison County, Texas Tornado

EVENT TIME…8:00 AM
EVENT TYPE…EF0 TORNADO
ESTIMATED PEAK WINDS (MPH)…65 to 85
INJURIES/FATALITIES…0
DAMAGE PATH LENGTH… 1/3 MILE
DAMAGE WIDTH… 50 YARDS

TREES SNAPPED OR UPROOTED ALONG A NARROW PATH. BARN DESTROYED WITH TIN FROM ROOF FANNED OUT IN DIFFERENT DIRECTIONS AND THROWN IN SOME CASES ABOUT 200 YARDS. MINOR ROOF DAMAGE TO HOME. STRAIGHT LINE WIND DAMAGE ALSO FOUND IN THE AREA.

Huntsville, Texas Tornadoes

EVENT TIME…9:06 AM
EVENT TYPE…EF0 TORNADO
ESTIMATED PEAK WINDS (MPH)…65 to 85
INJURIES/FATALITIES…0
DAMAGE PATH LENGTH… 0.36 MILES
DAMAGE WIDTH… 50 YARDS

TORNADO TOUCHED DOWN AT CAR DEALERSHIP, LIFTED METAL AWNING AND MOVED IT 100 YARDS AWAY ON TOP OF TWO CARS. THERE WAS MINOR DAMAGE TO THE TWO CARS.

EVENT TIME…9:10 AM
EVENT TYPE…EF0 TORNADO
ESTIMATED PEAK WINDS (MPH)…65 to 85
INJURIES/FATALITIES…0
DAMAGE PATH LENGTH… 50 YARDS
DAMAGE WIDTH… 25 YARDS

TORNADO BRIEFLY TOUCHED DOWN IN A RESIDENTIAL SECTION OF HUNTSVILLE CAUSING SIGINIFICANT TREE DAMAGE. ONE OF THE TREES DID FALL ON A NEARBY HOUSE CAUSING SOME ROOF DAMAGE. TREES IN THE AREA WERE BLOWN DOWN IN DIFFERENT DIRECTIONS GIVING INDICATION OF A STRONG CIRCULATION IN THE AREA.

ADDITIONAL WIDESPREAD STRAIGHT LINE WIND DAMAGE WAS FOUND IN THE HUNSTVILLE AREA WITH NUMEROUS TREES DOWN THROUGHOUT THE CITY. THERE WAS ONE INJURY AT SAM HOUSTON STATE UNIVERSITY FROM A FALLING TREE LIMB.

Houston NWS: Huntsville, TX Tornado Track

Rainfall totals through 11 AM

This graphic came from the National Oceanic Atmospheric Administration and shows radar estimated rainfall totals through 11 AM this morning. Please realize that the actual rain totals could vary from location to location, but this is the overall average. While the new drought outlook wont be released until next week, I think its safe to say some locations in North Texas are officially out of drought conditions. Just looking at a few lake levels across Dallas, it looks like Joe Pool Lake and Mountain Creek Lake are actually one to two feet above their normal values. It will take several days for run-off to make it to area lakes and some rivers will remain in flood through the weekend.

Like I said over on our Facebook and Twitter pages, we really didn’t expect the amount of severe weather we ended up with. Short term data, even at 9 PM last night, suggested we would face some severe weather threat, but not the widespread nature we saw this morning. That goes to show you how difficult it can be to forecast severe weather during the cool season when you have several factors that cannot be determined until the event begins. We will have more on this morning’s severe weather in a discussion later tonight. We’re looking at data from this morning to find out what ingredients were stronger then expected. In addition, we’ll also post damage surveys as they are released by the National Weather Service.

Chance of Severe Wind (58+ MPH)

Here’s the risk of experiencing a tornado within 25 miles. The standard risk is 5% which can be seen inside the orange outline. There is a low probability, a 2% chance, within the yellow dotted line. The main timeframe is still expected to be 9 AM to 6 AM. Here’s the complete discussion.

DAY 1 CONVECTIVE OUTLOOK   
NWS STORM PREDICTION CENTER NORMAN OK  
0657 PM CST TUE JAN 24 2012  
  
VALID 250100Z - 251200Z  
   
..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF WCNTRL TX  
THE  
TX HILL COUNTRY AND MIDDLE TX COAST...  
   
..TX HILL COUNTRY/MIDDLE TX COAST  
  
WATER VAPOR IMAGERY CURRENTLY SHOWS AN UPPER-LEVEL LOW ENTERING WEST  
TX WITH THE LEADING EDGE OF LARGE-SCALE ASCENT MOVING ACROSS THE  
PECOS RIVER VALLEY. AS THIS BAND OF ASCENT MOVES INTO WCNTRL TX OVER  
THE NEXT 2 TO 4 HOURS...THUNDERSTORMS SHOULD INITIATE ALONG THE WRN  
EDGE OF THE MOIST AXIS FROM EAST OF ABILENE SSWWD TO AROUND EAGLE  
PASS. ALTHOUGH THE EXACT TIMING OF INITIATION REMAINS  
UNCERTAIN...THE LATEST HRRR MODEL DEVELOPS SFC-BASED THUNDERSTORMS  
ALONG THIS CORRIDOR BEGINNING AROUND 04Z. IF THIS SCENARIO PANS  
OUT...STORM COVERAGE SHOULD STEADILY INCREASE LATE THIS EVENING AS A  
LINEAR MCS GRADUALLY ORGANIZES AND MOVES ESEWD ACROSS THE TX HILL  
COUNTRY AND ONTO THE TX COASTAL PLAIN LATE TONIGHT.  
  
THE BEST ENVIRONMENT FOR SEVERE STORMS THIS EVENING APPEARS TO BE  
FROM AROUND EAGLE PASS EXTENDING NNEWD INTO THE WRN TX HILL COUNTRY.  
FORECAST SOUNDINGS ALONG THIS CORRIDOR FROM 03Z TO 06Z SHOW MODERATE  
INSTABILITY /MLCAPE 1000 TO 1500 J/KG/...0-6 KM SHEAR OF 50 TO 60 KT  
WITH 700 TO 500 MB LAPSE RATES OF 7.5 TO 8.0 C/KM. THIS ENVIRONMENT  
SHOULD BE FAVORABLE FOR SUPERCELLS WITH LARGE HAIL. IN  
ADDITION...LOW-LEVEL SHEAR APPEARS ADEQUATE FOR A TORNADO OR TWO.  
THE HAIL AND TORNADO THREAT SHOULD BE MAXIMIZED WITH CELLS THAT HAVE  
ACCESS TO THE STRONGEST INSTABILITY AND REMAIN DISCRETE. ALTHOUGH  
SOMEWHAT CONDITIONAL...HAVE RETAINED THE HATCHED SIGNIFICANT HAIL  
THREAT AREA FOR HAILSTONES GREATER THAN 2 INCHES IN DIAMETER...BUT  
HAVE MOVED THE THREAT AREA TO JUST WEST OF THE SAN ANTONIO AND  
AUSTIN AREAS WHERE THE MOST INTENSE STORMS ARE EXPECTED.  
HOWEVER...THE WIND DAMAGE THREAT MAY BECOME THE MORE DOMINANT THREAT  
ESPECIALLY AFTER MIDNIGHT AS CELLS MERGE INTO A NEARLY CONTINUOUS  
LINE. LOW-LEVEL SHEAR WILL INCREASE OVERNIGHT ASSOCIATED WITH A 40  
TO 50 KT LOW-LEVEL JET SO THIS SHOULD KEEP THE TORNADO THREAT GOING  
WITH CELLS EMBEDDED IN THE LINE OR WITH DISCRETE STORMS THAT DEVELOP  
OUT AHEAD. THE WIND DAMAGE THREAT SHOULD ALSO CONTINUE AS THE LINEAR  
MCS REMAINS WELL ORGANIZED LATE IN THE PERIOD.  
  
..BROYLES.. 01/25/2012  
 

MESOSCALE DISCUSSION 0064  
NWS STORM PREDICTION CENTER NORMAN OK  
0713 PM CST TUE JAN 24 2012  
  
AREAS AFFECTED...EDWARDS PLATEAU...HILL COUNTRY  
  
CONCERNING...SEVERE POTENTIAL...WATCH LIKELY  
  
VALID 250113Z - 250245Z  
  
THREAT FOR LARGE HAIL...ISOLATED DAMAGING WINDS...AND PERHAPS A  
TORNADO WILL INCREASE AS TSTM COVERAGE GROWS LATER THIS EVENING.  
ALTHOUGH UNCERTAINTY EXISTS OVER THE TYPE OF WW...THE PROBABILITY OF  
ISSUANCE BY 03Z IS 60 PERCENT.  
  
01Z SURFACE ANALYSIS PLACED A SERIES OF WEAK CYCLONES ACROSS THE  
PERMIAN BASIN/BIG BEND...AND ALONG THE RIO GRANDE BETWEEN DRT AND  
LRD. PRIMARY SURFACE WARM FRONT HAS BECOME QUASI-STATIONARY S OF THE  
HILL COUNTRY WITH A RELATIVELY RICH WARM/MOIST AIR MASS ACROSS MUCH  
OF S-CNTRL TX. FARTHER NW...MORE MARGINAL SURFACE-BASED INSTABILITY  
EXISTS WITH A STRONG CAPPING INVERSION CENTERED NEAR 800 MB IN THE  
00Z DRT RAOB. THIS CAPPING INVERSION WILL BE GRADUALLY REMOVED AS  
BAND OF FORCED ASCENT /NOW CROSSING THE BIG BEND/ OVERSPREADS THE  
MODIFIED WARM SECTOR OVER THE EDWARDS PLATEAU. STEEP MID-LEVEL LAPSE  
RATES AND EFFECTIVE SHEAR OF 40-50 KT WILL PROVE FAVORABLE FOR LARGE  
HAIL. WHILE A WEAKNESS IN THE LOW-LEVEL HODOGRAPH MAY PERSIST  
BETWEEN 800-700 MB...VEERING MAY BE SUFFICIENT FOR A MARGINAL  
TORNADO THREAT. HOWEVER...STRONGER LOW-LEVEL SLYS SHOULD REMAIN  
CONFINED E OF THE I-35 CORRIDOR. IN ADDITION...CONVECTION-ALLOWING  
MODELS LARGELY SUGGEST TSTMS WOULD QUICKLY TRANSITION INTO A CLUSTER  
MODE WITH PROPAGATION TOWARDS THE NE INTO A LESS UNSTABLE AIR MASS.  
  
..GRAMS.. 01/25/2012