A line of strong to severe thunderstorms tracked from Alabama into southern middle Tennessee during the late afternoon and early evening hours. A severe bow echo with a history of wind damage in north central Alabama produced wind damage in Franklin County.
Every event with a place to put it. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS HUN wrote it up.
A line of strong to severe thunderstorms tracked from Alabama into southern middle Tennessee during the late afternoon and early evening hours. A severe bow echo with a history of wind damage in north central Alabama produced wind damage in Franklin County.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Huntsville, AL wrote its last area forecast discussion before the first event at May 20, 5:23 PM CST, 12 minutes earlier.
Area Forecast Discussion National Weather Service Huntsville AL 623 PM CDT Sat May 20 2017 .UPDATE... For 00Z TAFS. && .NEAR TERM...(Tonight) Issued at 254 PM CDT Sat May 20 2017 Local area radars show a fairly extensive area of showers and thunderstorms covering much of Mississippi and western/southern Alabama. This activity developed along an existing outflow boundary from convection this morning, and was aided by a weak convergence axis. Given ample instability, with temperatures in the mid to upper 80s and dewpoints in the mid to upper 60s, thunderstorms have been able to maintain themselves, though organization has been hard to come by due to relatively weak bulk shear. The main upper level trough that is driving this activity will shift from the Central Plains and into the Great Lakes region overnight. The TN Valley will remain within the warm sector of this system, with southerly flow continuing to stream an abundance of moisture through the area. Latest hires guidance did not initialize well and has therefore not handled the current activity very well. However, given the unstable airmass in place and the potential for outflow boundaries to continue convective initiation, thunderstorms will continue a slow eastward progression through the remainder of the afternoon and into the evening hours. The coverage may dwindle as the convection pushes east of the I-65, but given the uncertainty, have maintained a high pop in through 06Z. As stated above, although instability is fairly high, relatively weak bulk shear is led to a fairly disorganized area of thunderstorms. CAPE values within the hail growth zone do support the hail potential, however high wet bulb zero heights will likely lead to only small hail actually reaching the ground. There may also be enough downdraft CAPE for strong wind gusts to occur, but these gusts are expected to remain below severe limits. One concern remains the potential for localized flash flooding. We have seen some storms tend to train over the same area, with radar estimated rainfall rates nearing 2 inches. Latest trends do show the activity weakening slightly and moving slightly quicker, but it does bear watching through the remainder of the afternoon/evening. The area will likely see a break in the more widespread precip, as the initial activity pushes east of the area around midnight and convection begins to develop to our west along the cold front. However, given the very moist environment, scattered showers may continue within this lull. The cold front will push east of the Mississippi River just before daybreak on Sunday, with showers and thunderstorms expected to develop just to our west. There is some uncertainty regarding the speed of this "second" round of showers and storms so the pops were adjusted to account for this uncertainty. .SHORT TERM...(Sunday through Monday) Issued at 254 PM CDT Sat May 20 2017 Showers and thunderstorms will be ongoing to our west just before sunrise and then push eastward through the morning hours. This activity will be ahead of the main cold front which will move through the TN Valley during the day. Surface based instability may be a bit more limited with this activity, given the timing. However, elevated instability will remain across the area, thus kept thunderstorms in the forecast. Not anticipating much in the way of strong to severe thunderstorms, given the main upper dynamics will be well to the north of the forecast area and the lack of surface based instability. However, PW values will remain high once again on Sunday and heavy rain will be a possibility, which will keep the threat for isolated flash flooding across the TN Valley. However, this will be highly dependent on the amount of rain a given location receives today and again, should be fairly localized due to the extended period of dry conditions the area experienced prior. The cold front will push east and through the TN Valley late Sunday evening, bringing an end to the more widespread precip. There may be some lingering showers across our far eastern areas early on Monday, however the coverage should be fairly low. Northerly flow will usher in drier air and dewpoints will fall into the low to mid 50s. Temperatures will feel rather pleasant compared to the last couple of days, with highs on Monday in the mid to upper 70s. .LONG TERM...(Monday night through Friday) Issued at 254 PM CDT Sat May 20 2017 An unsettled weather pattern will continue into the middle of the week with cooler temps lingering through the extended forecast. A series of disturbances will round the base of an amplifying trough swinging SE across the Midwest and develop some showers Monday night and thunderstorms on Tuesday. On Tuesday, in combination with a sfc low, Gulf Coastal convection will develop and could affect convective development in the TN Valley. There is not a lot of time for moisture recovery in advance of the system with dewpoints reaching ~60 degrees, the coastal convection will cut us off from anything further, and lower our instability. There is still model disagreement on the evolution of the coastal convection and its timing, so will have to see how additional runs handle it. A cold front will move into the TN Valley late Tuesday/early Wednesday bringing additional showers and thunderstorms across the area. At this time there is decent 0-6 km shear but not a lot of CAPE, with PWATs reaching ~1 inch. However based on the coastal convection, these values could change. Wednesday will be the coolest day of the week with highs around 70s and overnight lows around 50! A few showers are possible on Thursday as the upper level trough passes overhead, otherwise sfc high pressure will build in bringing dry conditions and warmer temps by Friday! High temps on Friday will be near 80 degrees with overnight lows around 60 degrees. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 623 PM CDT Sat May 20 2017 Widespread thunderstorms have pushed east of the KMSL and KHSV terminals, with lingering light to moderate rain extending westward towards the MS/AL border. There may be isolated embedded thunderstorms within the lingering rainfall, however the coverage is too low to keep mention of thunderstorms and have removed the VCTS through the evening. There will be a break in the -SHRA between 05Z and 10Z, and then the activity will redevelop and move into the terminals. Along with the additional rainfall, MVFR cigs will move into the terminals between 08Z and 10Z and persist through 19Z and 20Z. Thunderstorms will also be possible after 15Z at each terminal, though the confidence is fairly low on timing and have only included VCTS at this point. The precip will come to an end and conditions will improve to VFR at KMSL ~19Z and ~20Z at KHSV. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && NEAR TERM...73 SHORT TERM...73 LONG TERM...JMS AVIATION...73 For more information please visit our website at weather.gov/huntsville.
Hazardous Weather Outlook National Weather Service Huntsville AL 244 PM CDT Sat May 20 2017 ALZ001>010-016-TNZ076-096-097-211100- Lauderdale-Colbert-Franklin AL-Lawrence-Limestone-Madison-Morgan- Marshall-Jackson-De Kalb-Cullman-Moore-Lincoln-Franklin TN- 244 PM CDT Sat May 20 2017 This Hazardous Weather Outlook is for north Alabama and portions of southern middle Tennessee. .DAY ONE...Through Tonight... Thunderstorms will continue to develop across the area through this evening, with gusty winds up to 40 MPH and very heavy rainfall possible. Isolated instances of flash flooding are possible during this time. .DAYS TWO THROUGH SEVEN...Sunday through Friday... Showers and thunderstorms are possible again Sunday with a strong storm possibly producing gusty winds and small hail. Heavy rain and isolated Flash Flooding will once again be the greatest threat. Thunderstorms will taper off Sunday night from west to east as a cold front moves through. Scattered showers and thunderstorms are then possible Tuesday and Tuesday night as another cold front approaches from the west. Brief heavy rainfall and gusty winds are possible with a few of the stronger storms. .SPOTTER CALL TO ACTION STATEMENT... Activation of storm spotters and emergency management personnel is not anticipated at this time. 12
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HUNTSVILLE AL
610 PM CDT SAT MAY 20 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0549 PM TSTM WND DMG 5 SSE MOORES MILL 34.78N 86.50W
05/20/2017 MADISON AL NWS EMPLOYEE
A 16-18IN TREE WAS BLOWN DOWN NEAR THE
INTERSECTION OF JORDAN RD AND NAUGHER RD.
&&PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HUNTSVILLE AL
612 PM CDT SAT MAY 20 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0550 PM TSTM WND DMG 4 SSE MOORES MILL 34.80N 86.49W
05/20/2017 MADISON AL PUBLIC
LARGE LIMBS KNOCKED DOWN ALONG HOMER NANCE
ROAD.
&&
STUMPFSpecial Weather Statement
National Weather Service Huntsville AL
613 PM CDT SAT MAY 20 2017
TNZ076-096-202345-
Moore TN-Lincoln TN-
613 PM CDT SAT MAY 20 2017
...SIGNIFICANT WEATHER ADVISORY FOR MOORE AND CENTRAL LINCOLN
COUNTIES UNTIL 645 PM CDT...
At 613 PM CDT, Doppler radar was tracking a strong thunderstorm 7
miles west of Lynchburg, moving northeast at 20 mph.
Winds in excess of 40 mph will be possible with this storm.
Locations impacted include...
Lynchburg, Tims Ford Lake, Mulberry, Chestnut Ridge, Howell,
Belleville, Lois, Mimosa, Booneville and Smithland.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike several miles away from a thunderstorm. Seek a
safe shelter inside a building or vehicle.
&&
LAT...LON 3541 8625 3539 8628 3538 8625 3537 8627
3535 8624 3534 8627 3533 8626 3509 8639
3524 8668 3537 8656 3535 8654 3536 8649
3533 8646 3532 8642 3535 8641 3536 8633
3541 8629
TIME...MOT...LOC 2313Z 213DEG 16KT 3525 8649
15PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HUNTSVILLE AL
619 PM CDT SAT MAY 20 2017
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0540 PM TSTM WND DMG 2 ENE HUNTSVILLE 34.71N 86.59W
05/20/2017 MADISON AL EMERGENCY MNGR
BROKEN POWER POLE AND TRANSFORMER DOWN NEAR
THE LEEMAN FERRY ROAD AND MEMORIAL PARKWAY.
&&
STUMPFSpecial Weather Statement
National Weather Service Huntsville AL
623 PM CDT SAT MAY 20 2017
ALZ009-010-TNZ076-096-097-210000-
De Kalb AL-Jackson AL-Franklin TN-Moore TN-Lincoln TN-
623 PM CDT SAT MAY 20 2017
...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN JACKSON...
NORTHEASTERN DEKALB...MOORE...SOUTHEASTERN LINCOLN AND FRANKLIN
COUNTIES UNTIL 700 PM CDT...
At 623 PM CDT, Doppler radar was tracking strong thunderstorms along
a line extending from near Fayetteville to near Ider. Movement was
northeast at 40 mph.
Winds in excess of 40 mph will be possible with these storms.
Locations impacted include...
Winchester, Fayetteville, Bridgeport, Lynchburg, Decherd, Estill
Springs, Stevenson, Cowan, Monteagle and Huntland.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike several away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
&&
LAT...LON 3461 8556 3514 8658 3539 8626 3537 8627
3533 8620 3536 8616 3531 8595 3522 8586
3499 8586 3498 8561 3462 8554
TIME...MOT...LOC 2323Z 234DEG 35KT 3513 8646 3468 8558
15Special Weather Statement
National Weather Service Huntsville AL
631 PM CDT SAT MAY 20 2017
ALZ010-210000-
De Kalb AL-
631 PM CDT SAT MAY 20 2017
...SIGNIFICANT WEATHER ADVISORY FOR DEKALB COUNTY UNTIL 700 PM CDT...
At 631 PM CDT, Doppler radar was tracking a strong thunderstorm near
Collinsville, or 10 miles south of Rainsville, moving northeast at 35
mph.
Winds in excess of 40 mph will be possible with this storm.
Locations impacted include...
Fort Payne, Rainsville, Little River Canyon National Preserve,
Henagar, Collinsville, Sylvania, Fyffe, Powell, Geraldine and Ider.
LAT...LON 3450 8555 3450 8556 3449 8556 3448 8558
3444 8558 3441 8561 3437 8563 3436 8566
3433 8569 3422 8589 3436 8603 3469 8573
3463 8553 3455 8552
TIME...MOT...LOC 2331Z 230DEG 32KT 3434 8590
15The Northeast Alabama radar (KHTX), 31 km away, was scanning. The volume nearest the first event began at 23:32 UTC.
1 thunderstorm wind. Local standard time, as filed.
Numerous trees and power lines were knocked down. Power outages were reported in Decherd.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Tennessee in 2017Every state in 2017This day in weather historyWarnings in Tennessee, May 2017
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 688650.