Tornadoes in northern Oklahoma, May 19, 2010
It was a busy day for the Storm Prediction Center and NWS Forecast offices in Texas and Oklahoma on May 19. There were 25 tornado reports, 8 reports of damaging winds, and 23 hail reports (The largest reported was 3.25 inches). Preliminary news reports suggest there was one injury associated with the severe weather when a tractor-trailer rig was blown over by winds. Of the NWS offices responsible for Oklahoma, Norman issued 24 tornado warnings, Amarillo 16, and Tulsa 12.
Two well-defined supercells were responsible for most of the tornado reports in Oklahoma. Here's how they looked on radar:
Reflectivity image from KTLX at 2301Z May 19 2010.
The reflectivity image shows two classic supercells with hook echoes in northern Oklahoma. Both storms have strong velocity shear couplets in the Doppler velocity radar image, indicating they both have mesocyclones.
Storm-relative velocity image from KTLX at 2301Z May 19 2010.
Video of three of the May 19 tornadoes is available on YouTube, and I've embedded it here.
Hennessey, OK Tornado
This is a very nice cone tornado. It reminds me of the Sitka, KS 1999 tornado which I saw while participating in SubVortex. The clear area behind and to the left of the tornado/wall cloud is the rear-flank downdraft.
Mulhall, OK Tornado
Stillwater, OK Tornado
On May 10, a tornado threatened the southern edge of OU's campus. On May 19, it was Oklahoma State's turn. This is pretty good for cell phone video.
Possible Severe Weather Outbreak for Oklahoma, Again
UPDATE SPC has upgraded a portion of the Moderate Risk region over central Oklahoma to High Risk. They've also just issued a Tornado Watch with the "Particularly Dangerous Situation" description.
In the watch's discussion, SPC makes the following points:
"tstms expected to form in the next hour or so invof slowly retreating W/E outflow boundary in W cntrl OK. Other storms also may form a bit later near intersection of outflow boundary with confluence line in cntrl OK... and in more strongly heated environment near warm front in se OK /ref mcd 623/. Given strength of wind field... expectation of continued low lvl destabilization... and eventual onset of mid lvl cooling/ascent with upr impulse now in the wrn TX Panhandle... setup appears favorable for the development of strong supercells. One or two of these may become long-lived... and yield a couple strong tornadoes... as they
interact with backed low lvl flow near outflow boundary and/or warm front."
Essentially, everything has come together to produce an environment favorable for tornadoes. It's now a matter of waiting.
A situation similar to that of May 10, 2010 is forming in Oklahoma. A strengthening surface low in the Oklahoma Panhandle in conjunction with an upper-level low over Colorado/Wyoming is bringing the ingredients of wind shear and moist instability necessary for severe storms. The dryline and numerous outflow boundaries from yesterday's storms will provide many different locations for storms to form. SPC thinks that individual storms will form over Oklahoma by 4PM CDT along the dryline and other boundaries in western Oklahoma. Based on my experience, I would estimate that these storm will produce their first mesocyclones after an hour. Just like May 10, the storms will move to the east-northeast parallel to I-44 after forming.
However, today is not quite a carbon copy of May 10. The instability is slightly weaker and the wind shear is weaker. This is notable because the forecast storm motion is much slower, 25 knots (29 mph) instead of the forecast/observed storm motion of 50 knots (60mph). This will make storm intercept operations easier for Vortex 2.
This is a triple-threat day, and SPC has issued a Moderate Risk for Central/Eastern Oklahoma. Strong tornadoes, very large hail, and damaging straight-line winds are expected over Oklahoma today. The tornado and hail threat is associated with the supercell phase of today's storms. Later, as these storms merge and form a linear system, swaths of damaging straight line winds are expected in eastern Oklahoma and the Arklatex region.
12 Day 1 Convective Outlook issued by the Storm Prediction Center.
Probability of 1 inch or larger hail within 25 miles of a location.
I've included the second figure because I can't remember seeing a 60% hail contour before. Today's going to be a bad day to be caught outside when the storms come, so keep an eye on the skies today.
Updated: 7:58 PM GMT on May 19, 2010
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Trough Swinging Out, Tornado Threat Picks Up
As an upper-air trough swings out over the southern Plains, the severe weather threat will increase for Texas/New Mexico/Colorado. SPC has a Slight Risk region along the 100'th Meridian from the Big Bend north into Colorado. All of the ingredients are coming together to produce supercells with large hail in this region. The area facing the most risk from tornadoes is the Texas Panhandle south to Midland/Odessa and San Angelo. Later in the day, the supercells are expected to transition into squall lines/mesoscale convective systems.
12Z Day 1 Convective Outlook from the Storm Prediction Center.
However, Wednesday is looking like the best day to see a tornado this week. SPC has already issued a Moderate Risk for western Oklahoma for Tuesday. To quote from the discussion, "A POTENTIAL FOR STRONG TORNADOES MAY DEVELOP
DURING THE LATE AFTERNOON AND EARLY EVENING". There's also the risk of a large damaging wind event in Oklahoma in the evening as the storm transition from individual supercells into mesoscale convective systems.
06Z Day 2 Convective Outlook from the Storm Prediction Center.
Here's a cool video of a hail storm over a pool in Oklahoma City from a few days ago. It reminds me of my storm chasing days.
Action shifts to the Midwest
There was some scattered severe storms in western Oklahoma on May 12. The public made 6 tornado reports, 64 reports of damaging winds, and 74 reports of hail. A spotter reported that a tornado crossed I-40 near Clinton. Figures 1 and 2 show the storm before it crossed I-40. There is a well-defined hook echo in the reflectivity image, and the Doppler velocity scan shows a strong velocity shear couplet.
Fig. 1 Base reflectivity from KFDR 753PM May 12, 2010
Fig. 1 Doppler velocity scan from KFDR 753PM May 12, 2010
Looking at today's prospects for severe weather, SPC has a Slight Risk region covering the Midwest. The primary threat is damaging winds and isolated tornadoes. SPC also thinks that the thunderstorms will organize into a squall line/mesoscale convective system later in the evening. The "SEE TEXT" over Texas means that SPC thinks there is a small possibility of severe weather there, but that things are too uncertain to warrant a Slight Risk. It's quite possible that the forecast will change later today.
12Z Day 1 Convective Outlook from the Storm Prediction Center
It's May, Something Might Happen
The title is a paraphrase of a forecast discussion for SubVortex '99, and that's the case for today. The primary threat is hail and wind, but there is a small risk of isolated tornados from the Kansas/Missouri border running down the I-35 corridor.
The Norman, OK NWS Forecast Office has setup a page for the May 10, 2010 tornado outbreak. No damage survey results yet, but the pages do have preliminary storm reports and a timeline of warnings issued. Check it out...
The May 10, 2010 Tornado Outbreak in Oklahoma
This was a significant severe weather day for Oklahoma and Kansas. Local reports say there are at least 5 fatalities in Oklahoma due to the severe weather. By the numbers, there were 37 tornado reports, 39 reports of damaging winds and 69 reports of hail. There were multiple reports of 4+ inch diameter hail (softballs) with a peak size of 4.75 inches. The NWS issued 70 tornado warnings (31 from Norman, OK) and 88 severe thunderstorm warnings. As you can see in the below figure, many storms formed just off the dryline as SPC predicted.
Fig. 1 Base reflectivity scan from KTLX at 622CDT. The NWS office in Norman, OK estimates at least 10 tornadoes touched down in Oklahoma based on radar data. Damage surveys will be necessary to determine how many tornadoes touched down and they are starting today.
Fig. 2 Extremely preliminary estimate of OK tornado paths on May 10, 2010 from the Norman, OK NWS Forecast Office
There were many interesting tornado reports. Moore, OK got hit, again (That would be at least the fourth time since 1998). A funnel cloud reached out from the sky directly overhead the National Weather Center (The location of OU's School of Meteorology, the Storm Prediction Center, and the Norman, OK NWS Forecast Office) and touched down just east of the NWC. For once, OU students didn't have to drive far to see a tornado.
However, the main storm of this event has to be the storm that produced a large tornado 1 mi north of Seminole, OK. The damage report came in from Vortex 2 teams, and it's easy to see why they were there. You could use Figure 3 in a textbook to demonstrate what a tornadic supercell looks like on radar. The ball at the end of the hook echo is reminiscent of the May 3, 1999 Bridge Creek-Moore storm.
Fig. 3Base reflectivity from KTLX at 622PM CDT.
The Doppler velocity data show that this storm had a powerful mesocyclone with winds speeds greater than 110 knots (125 mph, EF-2 winds, or Category 3 on the Saffir-Simpson Scale)
Fig. 4Base Doppler velocity from KTLX at 622PM CDT.
Here are a few YouTube videos from Norman:
Students from the University of Michigan's Department of Atmospheric, Oceanic, and Space Sciences are participating in Vortex 2, working with Texas Tech. They're somehow finding the time to write a blog for us here. So please check it out.
Looking at today's forecast, SPC has a Slight Risk out over central Oklahoma and Kansas. The main threat of this forecast is hail and the possibility of isolated tornadoes.
12Z Day 1 Convective Outlook issued by the Storm Prediction Center
And here are a few WunderPhotos of a tornado that touched down west of Oklahoma City from our users.
Updated: 9:42 AM GMT on May 11, 2010
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Risk of a Tornado Outbreak in NE Oklahoma and SE Kansas
All of the ingredients are coming together for a tornado outbreak in Oklahoma and Kansas. An upper level trough is moving eastwards, creating strong wind shear favorable for tornadoes. Copious amounts of moisture at the surface and cool air aloft will provide the instability necessary for strong storms. Finally, a dryline is expected to form in western Oklahoma that will provide the initiation mechanism for storms to form. This threat is why SPC has issued a High Risk covering NE Oklahoma and SE Kansas.
Figure 112Z Day 1 Convective Outlook issued by Storm Prediction Center
SPC thinks that storms will form in a region along I-35 from Oklahoma City north towards Wichita, KS. Based on the forecast wind profiles, these storms will move ENE along I-44 towards Tulsa and SE Kansas at an estimated speed of 50 knots (58 mph). Somewhere along the way, "strong to violent" tornadoes will form.
Given the situation, it's likely that some of the tornado watches issued by SPC today will have the enhanced wording "THIS IS A PARTICULARLY DANGEROUS SITUATION", these are colloquially known as PDS watches. To quote from SPC's FAQ: "The 'particularly dangerous situation' wording is used in rare situations when long-lived, strong and violent tornadoes are possible"
In terms of geographical extent, today's situation reminds me of the 1991 Andover, KS tornado outbreak. There were 55 tornadoes that day including 7 F3's, 4 F4's, and 1 F5. There were two tornadoes of note that day, the Andover tornado (F5) which lasted for an hour and was filmed by many different individuals, and the Red Rock tornado (F4). The Red Rock tornado was observed by many chasers, including a group lead by Prof. Howard Bluestein. Bluestein's group had a portable Doppler radar and they measured near F5 wind speeds in this tornado, which was the record until the DOW's measurements of the Bridge Creek-Moore tornado on May 3, 1999.
And speaking of chasers, radars, and DOW's, it's a certainty that Vortex 2 will be going on the road today. Where they'll be, it's tricky to say. The fast storm motions will make intercept a difficult matter (The phrase most likely to be heard on V2 communications today, "Expedite"). Also, the topography and land cover east of I-35 isn't as favorable (trees and hills) for storm intercept as it is west of I-35. In any event, I know they'll do their best to gather as much data as possible.
Updated: 8:55 PM GMT on May 10, 2010
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More Rain in Tennessee
The flooding in Tennessee was the main weather story for May 2. Nashville International Airport received 7.25 inches of rain, once more setting a new record. Unfortunately this was not an isolated event.
Figure 1Radar-estimated precipitation
Looking ahead to Monday, there is a risk of hail and damaging winds for Illinois and from the Carolinas to the Florida Panhandle.
1200Z Day 1 Convective Outlook issued by SPC
And to look further into the misty, distant future, conditions look somewhat favorable for severe weather over the southern Plains on Thursday, and it looks like conditions will be more favorable for severe weather over Ohio on Friday.
Flooding on May 1 and a look ahead
The main story from May Day is the record amounts of rain in western Tennessee, with 5 deaths reported due to flooding. At Nashville International, the weather station reported 6.32 inches, shattering the old record of 2.96 set just last year. However, in the regional context, 6 inches is not that extreme.
Figure 124-hour Estimated precipitation for the Ohio/Mississippi River valley ending 0300 PDT.
West of Nashville, the NWS estimates that storms produced over 10 inches of rain. This is a consequence of several storms systems moving through the area on Saturday. Data like this is obtained from the Nexrad radar systems. They estimate the amount of precipitation reaching the ground so forecasters can issue flood watches and warnings. The product is known as the Storm Total Precipitation and we have it on the site. Here's a look at Nashville's STP
Figure 2Storm Total Precipitation Estimate for Nashville on May 1-2, 2010.
In the Slight Risk region, Tennessee/Alabama/Mississippi have more risk for tornadoes and damaging winds. To the north, the threat is more from squall lines.
You can find photos of the flooding at WunderPhotos.
In non-flooding news, there were 15 tornado reports, 23 damaging winds reports, and 15 reports of hail. Most of the tornado reports were centered on the Arkansas/Tennessee border. Unfortunately, that area is still under a Slight Risk for Sunday, May 2.
12Z Day 1 Convective Outlook from SPC
As for Monday, might be some hail in the Great Lakes region, including Weather Underground Global Headquarters in Ann Arbor, MI, and a risk of tornadoes in the Carolinas south towards the Florida Panhandle.
Updated: 2:37 PM GMT on May 02, 2010
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Moderate Risk for Mississippi/Ohio River Valley
SPC is forecasting widespread severe weather over the Mississippi River Valley from eastern Arkansas to southern Illinois. The primary threat is strong (EF-2 or greater) tornadoes, but damaging straight-line winds and hail are also likely today. The combination of a stalled cold front for initiating storms with a fast jet stream and good surface moisture is capable of producing supercells and tornadoes.
0100Z Convective Outlook issued by SPC
For those interested in the ponies, Louisville is not in the Moderate Risk region, which is where the greatest threat of tornadoes is. However, it is still in a Slight Risk region, where there is a threat of damaging straight-line winds and hail along with a small risk of tornadoes. If you do go to the races, keep an eye on the sky (and keep a hand on your hat).
Looking back, the High Risk for Arkansas on April 30 was a good forecast. As of 0300PDT, there are 20 tornado reports, 50 damaging wind reports, and 44 reports of hail (A three inch hailstone in Missouri was the champ today). News reports indicate at least 1 fatality and 25 injuries due to this event. The fatality was from Van Buren County, which is northwest of Little Rock.
Figure 1 Reflectivity image of the storm responsible for the Van Buren county tornado.
Figure 2 Doppler velocity image of the storm responsible for the Van Buren County tornado.
This was a significant severe event. South of Little Rock, there were two separate lines of supercells moving northeast ahead of the front. Here's a reflectivity image of a storm southeast of Little Rock that caught my eye.
Figure 3 Reflectivity images from KLZK at 0237Z.
The notch in the storm west of Sheridan, near the county line is known as a "inflow notch". These are features of classic supercells, and are caused by strong winds headed for the storm's updraft (that would be the inflow).
Looking ahead, there's a large Slight Risk region from the Mississippi River valley along the Appalachians to New York. Tornadoes and damaging wind gusts are the threats associated with this forecast. There's also the chance of some hail storms in northeastern OK.
Today's a big day for severe weather research. It's the opening day of Vortex 2's final field season. They'll be operating in the central US from now until June 15 gathering data on tornadoes and the storms that produce them. May they have plenty of storms going through unpopulated farmlands and no sunburn days.
Updated: 4:06 PM GMT on May 01, 2010
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Tornado Threat for Arkansas
SPC is forecasting dangerous, long-track tornadoes for Arkansas.
Figure 10100Z Convective Outlook issued by SPC
To quote from the outlook:
DISCRETE SUPERCELL STORMS HAVE DEVELOPED OFF THE PRE-FRONTAL
BOUNDARY INTO THIS ENVIRONMENT. ADDITIONAL STORMS ARE EXPECTED TO DEVELOP UPSTREAM OVER THE ARKLATEX AND WITHIN THE FREE WARM SECTOR ACROSS NRN LA/SRN AR AND MOVE ENE OVERNIGHT ACROSS THE HIGH/MDT RISK AREAS. IN ADDITION TO THE ENHANCED TORNADO THREAT...VERY LARGE HAIL AND DMGG WIND GUSTS CAN BE EXPECTED.
And to quote from Tornado Watch 118:
DANGEROUS TORNADO SITUATION IS EXPECTED TO PERSIST
OVERNIGHT AS MULTIPLE DISCRETE SUPERCELLS TRACK THROUGH A
MOIST...MODERATELY UNSTABLE...AND STRONGLY SHEARED ENVIRONMENT.
To sum it up, all of the ingredients necessary for long-track tornadoes have come together: moisture, an unstable atmosphere, strong wind shear (winds changing with height), and convection. Be careful out there.