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Showers and isolated thunderstorms are expected to move north across locations mainly along and east of Interstate 35 today. Otherwise, it will be mostly cloudy today with highs in the 70s and winds of 5-15 mph with slightly higher gusts.
There will be chances of showers and thunderstorms on Saturday. A few scattered storms Saturday afternoon may become strong to marginally severe. The better threat for organized severe weather will be Saturday night through early Sunday morning ahead of a strong cold front. Some of the storms may be severe producing damaging downburst winds and large hail. A brief tornado or two cannot be ruled out with storms that develop ahead of the front. Cloud to ground lightning will accompany any of the storms and locally heavy rain could result in some flooding.
Rich Gulf moisture will continue pouring into North and Central Texas into the weekend. Saturday will begin with cloudy skies, but the sun will emerge as the day progresses, particularly west of the I-35 corridor. A capping inversion may prevent thunderstorm development, but with considerable instability, any storm that develops may quickly become severe. More widespread storms are expected Saturday night as a cold front moves through the region. Damaging winds will be the primary hazard with the line of storms that accompanies the front, but large hail and tornadoes will be possible with any discrete cells. A brief tornado could also occur within the line, but since these nocturnal spin-ups are often obscured by rain, they would be difficult for spotters to observe. The severe weather threat will diminish early Sunday morning as the storms move into Central and East Texas. Skies will clear on Sunday, and temperatures will reach the 70s Sunday afternoon with lower humidity. However, the gusty north winds behind the front will make it feel cooler.
Pleasant autumn weather will prevail next week with clear skies and low humidity. Another cold front will arrive Monday night, but high temperatures will generally be in the 70s Tuesday and Wednesday.

 
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The Tornadoes of May 27, 1997

 

Event Summary:

A deadly severe weather episode unfolded across portions of Central Texas during the afternoon and evening hours on Tuesday, May 27th, 1997.  This event was made infamous by one of the most powerful tornadoes on record: an F5 which tore through a subdivision of Jarrell called Double Creek Estates in extreme northern Williamson County during the mid-afternoon. Some of the most extreme damage on record occurred with this tornado, and one account states that “the earth was scoured bare, pavement was ripped from roadways, [and] homes and other buildings were completely pulverized” (Lon Curtis, Weather Bulletin).  Two F3-rated tornadoes touched down (one each in Bell and McLennan Counties), along with 8 additional tornadoes, one of which (the Prairie Dell Tornado) would eventually grow into the ¾ mile-wide F5 Jarrell tornado.  


Tornadoes of May 27th, 1997

Visible Satellite Animation
 
(Left): Map of tornadoes on the afternoon of May 27th, 1997.  The Jarrell tornado track actually consists of 3 distinct tornadoes. More information on these tornadoes can be found on NWS Austin/San Antonio's webpage. While the Jarrell tornado produced the most extreme damage just south of our area of responsibility, the initial tornado developed near the small town of Prairie Dell in extreme southern Bell County.  (Right): Visible satellite animation valid from 11 AM - 6:45 PM.
 

This event was additionally unusual because of the notable lack of upper-level forcing for ascent (lift), and generally light winds through the troposphere--where our weather occurs.  In a sense, this day was distinctly lacking two of the four crucial ingredients we typically look for on big severe weather events (strong lift and wind shear, especially near the surface).  Yet, over the course of roughly six hours, 20 tornadoes touched down across the Dallas/Fort Worth and Austin/San Antonio forecast areas of responsibility.  As we’ll examine in detail on this webpage, the Jarrell tornado was spawned from a lone, southwestward-propagating supercell which initially developed along a cold front near Waco during the early afternoon.  

 


 

Morning Atmospheric Overview:

The large scale, (or synoptic scale), weather pattern in place on this date was characterized by a northward-lifting upper-level low pressure system across Nebraska and South Dakota. As a result, the mid-level flow across Texas was actually quite weak--only on the order of 30 knots or so--with most large scale forcing (or lift) displaced well to the north across the Central and Northern Great Plains.  This weather pattern was far from a classic severe weather set-up for the region, and certainly one that did not portend the eventual occurrence of 20 tornadoes, one of which would grow into a three-quarter mile wide F5 as it plowed through the town of Jarrell during the mid-afternoon.


Morning upper-air plot

Evening upper-air plot
 

(Left): 500 mb (~20,000 feet) analysis, valid at 7 am CDT on May 27th, 1997. An upper-level area of low pressure can be seen lifting across Nebraska and South Dakota. A weak surface low across eastern Arkansas is also associated with a weak cold front which extends southwestward into Central Texas. (Right): same as on the left, except valid at 8 PM that evening. 

At the surface, observations during the morning of the 27th (roughly 10 AM CDT) revealed a cold front arcing to the southwest from a surface low near Fayetteville, Arkansas, through the DFW Metroplex, and into the Permian Basin.  This would later become an important feature, as thunderstorm updrafts continually regenerated southwestward along the front into the Texas Hill Country during the afternoon.  At the same time, visible satellite imagery showed the location of two remnant outflow boundaries laid down by an overnight area of convection across the Piney Woods of East Texas and into southern Arkansas.  The southern outflow boundary would later become a focus for thunderstorm initiation east of DFW.  An additional, very subtle feature elucidated by visible satellite imagery, was a southwestward-propagating gravity wave, also spawned by the now-decayed overnight convective system, denoted by dashed yellow lines.  The gravity wave and cold front all met up just north of Waco near a meso-low, which would eventually become the initiation point for the Jarrell supercell.

 
Surface observations and analysis by the Hydrometeorological Prediction Center (HPC, now Weather Prediction Center) valid at 15Z, or 10 AM CDT (a), and visible satellite imagery valid at 11 AM CDT (b) showing the location of remnant outflow boundaries, and a southwestward-moving gravity wave near Waco.
 
 
Morning upper-air sounding launched from Fort Worth Texas.  This sounding was released just around the time a cold front moved through, but reveals several important clues about this day’s atmospheric environment.

The morning upper-air sounding was launched from our office in Fort Worth just as the aforementioned cold front was passing overhead.  As a result, while it is not entirely representative of the afternoon environment across Central Texas, there are several keys we are able to glean from this atmospheric sounding:   

  • ‚ÄčMid-level lapse rates (between about 10,000 feet and 20,000 feet), or the change in temperature with height, were impressively steep, decreasing at a rate of 7.5 degrees C for every kilometer.  This is a sign that thunderstorm updrafts would be able to acquire substantial acceleration in the free atmosphere.
  • Moisture, while not overly deep, was very high near the surface, with the sounding measuring a surface dewpoint temperature of 73 degrees F.  Moisture content, as we’ll see in just a bit, was even more impressive across Central Texas.
  • Wind shear, or the turning of winds and/or change of speed with height was fairly minimal on this day.  However, deep layer bulk shear (the vector difference between the winds at about 20,000 feet and near the surface) was near 40 knots, which, combined with the very high instability, was more than sufficient for supercell thunderstorms.  Very weak winds in the lower-levels, however, did not appear to be very conducive for tornadic thunderstorms.
 

Surface observations and analysis valid at 18Z, or 1 PM CDT (a), and visible satellite imagery valid at 1215 PM CDT (b).

A few hours later, around noon on the 27th, the surface cold front had sagged southeastward, and was sitting directly overhead at Waco along with the previously analyzed meso-low (Figure 5a) and gravity wave feature, which conceivably was adding to the lift in this region .  Thunderstorm initiation was only minutes away at this point, and towering cumulus (just under the cold front line; Figure 5b) was evident on visible satellite near Waco.  Farther to the north and east, thunderstorms were also beginning to blossom along the outflow boundary across East Texas.  


While we have no NWS proximity soundings sampling the air that would ultimately feed this storm, a sounding was released near Calvert, Texas (just east of Temple) as part of the Texas A&M Convection and Lightning Experiment.  The sounding, shown below, was taken just before 3 PM (Wilhelmson and Houston, 2007).

 
Sounding released near Calvert, Texas at 1945 UTC (2:45 PM) as part of the Texas A&M Convection and Lightning Experiment (left).  The modified sounding utilizing surface temperature and dewpoint at 2100 UTC (4 PM) is shown on the right. Image from Houston and Wilhelmson, 2007.   

 

The left panel shows the original sounding, which reveals Convective Available Potential Energy (CAPE) of nearly 5000 J/kg, with just a hint of lingering Convective Inhibition.  If this weren’t impressive enough, the same sounding, but modified based on surface conditions a few hours later showed CAPE had increased further to over 6,500 J/kg with no lingering inhibition for surface-based parcels.  These are among the more impressive soundings--from a thermodynamic standpoint--you’ll come across.  While a bit less representative, modifying the morning sounding from Fort Worth also yields a similarly extreme thermodynamic parameter space:

 
Upper-air sounding from Fort Worth, Texas, modified to reflect noon-hour conditions at Waco.
 
The combination of incredible moisture content (a dewpoint of 79 degrees), and the previously mentioned very steep mid-level lapse rates resulted in surface-based Convective Available Potential Energy (CAPE) in excess of 5000 J/kg on this day!  In order to put this in perspective, values of 3000-4000 J/kg are typically categorized as high, so it’s fair to say that extreme levels of instability were present south and east of the cold front on the afternoon of the 27th.  An additional important value to point out is the 3CAPE reading in the bottom left of the figure.  Like SBCAPE, this is a measure of potential energy available to thunderstorms, but this parameter limits the focus area to the lowest 3 kilometers (roughly up to 700 mb).  As a result, we can think of this as a “low-level CAPE” parameter.  Research has shown this to be an important parameter in tornadic thunderstorms as higher values can support more substantial stretching of low-level vorticity (this is analogous to a figure skater’s increasing rotation as the arms are brought in towards the body).  The value of 249 J/kg is extraordinarily high (typical high-end springtime values range from 75-150 J/kg), and it’s possible these high values allowed for exceptionally strong stretching of low-level vorticity (spin) near the cold front, which ultimately aided in the production and development of the Jarrell tornado.
 

 


 

Event Timeline:

12:00 PM - 2:30 PM

Thunderstorm initiation occurred near Waco just before 12 PM on May 27th, right at the intersection of the cold front and meso-low.  If you look closely at the radar loop, you’ll notice a speckled area of reflectivity extending to the southwest along I-35.  This “fine line” is the radar sampling the density gradient (temperature contrast) along the cold front.  Between 12 and 1 PM, this initial thunderstorm drifted southwestward along the cold front at perhaps 5 mph.  Right around this time, the Storm Prediction Center issued Tornado Watch number 338 for the region due to the extreme amounts of instability present:  

SEL8
MKC WW 271754
TXZ000-LAZ000-280000-

BULLETIN - IMMEDIATE BROADCAST REQUESTED
TORNADO WATCH NUMBER 338
STORM PREDICTION CENTER NORMAN OK
1254 PM CDT TUE MAY 27 1997

THE STORM PREDICTION CENTER HAS ISSUED A
TORNADO WATCH FOR PORTIONS OF

   EAST TEXAS
   WESTERN LOUISIANA

EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 115 PM UNTIL 700
PM CDT.

TORNADOES...HAIL TO 3 1/2 INCHES IN DIAMETER...THUNDERSTORM WIND
GUSTS TO 80 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
AREAS.

THE TORNADO WATCH AREA IS ALONG AND 125 STATUTE MILES EAST AND WEST
OF A LINE FROM 25 MILES EAST OF COLLEGE STATION TEXAS TO 40 MILES
NORTH NORTHWEST OF SHREVEPORT LOUISIANA.

REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
TORNADOES AND 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.

OTHER WATCH INFORMATION...  CONTINUE...WW 336...WW 337...

DISCUSSION...VERY LARGE HAIL/LOCALLY DAMAGING WINDS AND ISOLATED
TORNADOES POSSIBLE THIS AFTERNOON IN VERY UNSTABLE AIR MASS /CAPE
TO 5000 J/KG/ OVER REGION.  ANY TORNADOES WILL LIKELY BE CONFINED
TO BOUNDARY INTERSECTIONS GIVEN COMPARATIVELY WEAK VERTICAL SHEAR.

AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
SURFACE AND ALOFT TO 3 1/2 INCHES.  EXTREME TURBULENCE AND SURFACE
WIND GUSTS TO 70 KNOTS.  A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
550.  MEAN STORM MOTION VECTOR 27020.

 

This initial storm proceeded to rapidly intensify in the extremely unstable airmass.  At 12:50 PM, the first Severe Thunderstorm Warning was issued for this storm for McLennan County (remember, the NWS issued “County Based Warnings” until October of 2007).  As the storm approached the small town of Lorena, the radars in Fort Worth and Granger (not shown), indicated low-level rotation was increasingly rapidly, which warranted an upgrade to a Tornado Warning at 1:21 PM.  Shortly thereafter, this storm produced its first tornado 5 miles southwest of Hewitt, or just outside of Lorena.

This storm then dropped another, albeit brief, tornado as it crossed into Falls County near the town of Bruceville-Eddy.  The first significant tornado of the day occurred in extreme southwestern McLennan County on the south  side of FM 107, 1.6 miles east-southeast of Moody.  This F3 tornado tossed a car and pickup truck several hundred feet and destroyed a residence and farm building during its 20 minute life cycle.  This sudden westward jog (from Bruceville-Eddy) was a sign that propagation effects were beginning to more strongly dictate the storm’s motion, and new updrafts would sequentially re-develop, paralleling I-35 over the hours to come.

 
Radar loop from Austin/San Antonio’s WSR-88D (KEWX) from 2:30 PM - 4:00 PM.  Base Reflectivity on the left, and Storm-Relative Velocity on the right.
 
The next tornado was another brief one, and actually formed ahead of the parent supercell just northwest of Belton in northern Bell County.  Towards the end of the animated loop, you’ll notice a small blob of higher (yellow and red) reflectivities “pop up” west of Temple.  This is a brand new updraft developing along the main supercell’s “flanking line”, and as vorticity near the cold front was stretched in the updraft, a brief tornado developed around 2:15 PM, as reported by Lon Curtis, who was following the storm with one of the forecasters from the Fort Worth office, Al Moller.  The next, substantial tornado of the day, was only minutes away from developing.

 

2:30 PM - 4:00 PM

Around 2:30 PM, the next tornado touched down to the north of the previous weak tornado near Morgan’s Point Resort, on the north side of Belton Lake.  As this tornado crossed a bend in the lake, it came ashore near Woodland, where “destruction to trees was nearly total” (NWS Service Assessment) and it “destroyed and damaged ten homes along Rocky Lane” (Lon Curtis).  This tornado lifted about 20 minutes later after moving only 1.4 miles.    

 
Radar loop from Austin/San Antonio’s WSR-88D (KEWX) from 2:30 PM - 4:00 PM.  Base Reflectivity on the left, and Storm-Relative Velocity on the right.
 

Another brief, F0 tornado occurred near the Stillhouse Dam near the split in I-35 and route 190.  As this monstrous storm roared into Salado, you’ll notice rotation increase substantially, and the last tornado in the Fort Worth County Warning Area developed near Prairie Dell, which sits right off of I-35 at the Bell/Williamson County line shortly after 3:00 PM.  Said Lon Curtis of this latest tornado:

“[It] looked like it was virtually stationary, although the portion of the vortex which was in ground contact was ‘wandering’ in a pasture about 3/10 of a mile from me.  Between 3:10 and 3:20 PM, the cloud base portion of the vortex began thickening.” - Lon Curtis (Weather Bulletin)

This was the beginning of one of, if not the most, powerful tornadoes in Texas history.  From most accounts, this initial pencil tornado grew into a ¾ mile-wide wedge over the course of a few minutes between Prairie Dell and the outskirts of Jarrell between 3:20 and 3:30 PM.  You’ll be able to find more information on the destructive “Jarrell Tornado” on the Austin/San Antonio National Weather Service website.

 


 

Photos of the May 27th Tornadoes and Damage 

 


Small, snake-like tornado just outside of Lorena, Texas in southern McLennan County. Photo taken around 1:30 PM by Lon Curtis.

The beginning stages of what would become the Jarrell Tornado as it crossed into Williamson County. Photo by Lon Curtis

Damage to a marina at Belton Lake from the Belton Tornado in northwestern Bell County. Photograph by L. Phan, NIST (from NWS Service Assessment)

Damage from the Moody Tornado as it crossed from McLennan County and into northern Bell County. Photograph by L. Phan, NIST (from NWS Service Assessment)

Large, wedge tornado near Jarrell, TX. Photograph by Al Moller.

Damage to a Marina near Morgan's Point Resort, TX.
 

 

References: 

Curtis, Lon. “Deadly Texas Fury!” Weather Bulletin: The Official Publication of TESSA. Summer 1997: 1. Print.

Houstoun, A. L., and R. B. Wilhelmson, 2007: Observational analysis of the 27 May 1997 Central Texas tornadic event. Part I: Prestorm environment and storm maintenance/propagation. Mon. Wea. Rev., 135, 701-726.

National Oceanic and Atmospheric Administration, NWS Service Assessment. The Central Texas Tornadoes of May 27, 1997.