Alert archive / Alabama / Flash Flood Warnings in 2021

Flash Flood Warning 47, NWS Birmingham, AL

September 18, 2021Jefferson County, Shelby County, Alabama

NWS Birmingham, AL issued this flash flood warning at Sep 18, 2021, 9:40 AM CDT for Jefferson County, Shelby County, Alabama. It was in force for 3 hr. 3 reports came from inside the area while it was in force.

The area

The outline as issued, with what was reported inside it.

The facts

Issued: Sep 18, 2021, 9:40 AM CDT (14:40 UTC)
Expired: Sep 18, 2021, 12:45 PM CDT
In force: 3 hr
Issued by: NWS Birmingham, AL
Area: Storm-based polygon
Flood severity: None

Counties Jefferson County, AL, Shelby County, AL

The radar

The Birmingham radar (KBMX), 34 km from the middle of the area, began a volume at 14:43 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

What was reported inside it

Time	Report	Where	Remark
Sep 18, 9:45 AM CDT	FLASH FLOOD	Hoover, AL	FLASH FLOODING REPORTED ALONG PATTON CREEK NEAR HOOVER COUNTRY CLUB AND STAR LAKE. FLOWING WATER OBSERVED ACROSS PRIVATE RESIDENCES. FLOOD WATERS LINGERED IN THE AREA FOR SEVERAL HOURS.
Sep 18, 10:15 AM CDT	FLASH FLOOD	1 Sw Vestavia Hills, AL	UP TO 6 INCHES OF WATER FLOWING OVER US HWY 31.
Sep 18, 11:17 AM CDT	FLASH FLOOD	Oak Mountain Amphitheat, AL	6-12 INCHES OF WATER COVERING THE ROADWAY ON SOUTHGATE DR.

Local storm reports filed while the alert was in force, from inside its polygon or its counties.

The nearest sounding before it

Birmingham, AL (KBMX), launched 12:00Z, 2.7 hours before the alert went out and 34 km from the middle of its area. This is the routine balloon launch nearest before it, the air the forecaster had in hand, not a measurement taken for the alert.

Skew-T log-p

Temperature in red, dew point in green, the mixed-layer parcel dashed.

Hodograph

The wind turning with height, colored by layer: ground to 1 km, 1 to 3 km, 3 to 6 km, 6 to 10 km.

Mixed-layer CAPE: 1167 J/kg
Mixed-layer CIN: -4 J/kg
Mixed-layer LCL: 453 m above ground
0-6 km bulk shear: 17 kt
0-1 km storm-relative helicity: 21 m²/s²
0-3 km storm-relative helicity: 2 m²/s²
Significant tornado parameter: 0.0
Supercell composite: 0.0

Open this sounding in Storm Lab

The text

As transmitted.

783 
WGUS54 KBMX 181440
FFWBMX
ALC073-117-181745-
/O.NEW.KBMX.FF.W.0047.210918T1440Z-210918T1745Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Birmingham AL
940 AM CDT Sat Sep 18 2021

The National Weather Service in Birmingham has issued a

* Flash Flood Warning for...
  Jefferson County in central Alabama...
  Central Shelby County in central Alabama...

* Until 1245 PM CDT.

* At 940 AM CDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 3.5 and 5 inches of 
  rain have fallen. Flash flooding is ongoing or expected to begin 
  shortly.

  HAZARD...Flash flooding caused by thunderstorms.

  SOURCE...Radar.

  IMPACT...Flash flooding of small creeks and streams, urban
           areas, highways, streets and underpasses as well as
           other poor drainage and low-lying areas.

* Some locations that will experience flash flooding include...
  Birmingham, Hoover, Vestavia Hills, Alabaster, Bessemer, Homewood, 
  Pelham, Mountain Brook, Trussville, Helena, Hueytown, Gardendale, 
  Irondale, Leeds, Moody, Fairfield, Chelsea, Fultondale, Columbiana 
  and Wilsonville.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Turn around, don't drown when encountering flooded roads. Most flood 
deaths occur in vehicles.

&&

LAT...LON 3335 8696 3371 8702 3379 8700 3379 8697
      3384 8689 3384 8676 3377 8665 3377 8655
      3366 8653 3362 8655 3356 8655 3355 8651
      3324 8646 3320 8646 3320 8649 3318 8650
      3312 8646 3309 8651 3307 8668 3319 8674

FLASH FLOOD...RADAR INDICATED

$$

The office that day

Everything else NWS Birmingham, AL issued on the same UTC day.

Issued	Product	Office	Counties	Lasted
Sep 17, 11:00 PM CDT	Areal Flood Advisory	BMX	Tallapoosa	2 hr
Sep 18, 8:46 AM CDT	Areal Flood Advisory	BMX	Jefferson, Shelby	3 hr
Sep 18, 12:29 PM CDT	Areal Flood Advisory	BMX	Tallapoosa	5 hr
Sep 18, 12:44 PM CDT	Areal Flood Advisory	BMX	Tuscaloosa	11 min
Sep 18, 12:55 PM CDT	Flash Flood Warning	BMX	Tuscaloosa	110 min
Sep 18, 1:10 PM CDT	Flash Flood Watch	BMX	Autauga, Barbour, Bibb, Blount, Bullock, Calhoun and 33 more	54 hr
Sep 18, 1:33 PM CDT	Areal Flood Advisory	BMX	Etowah	3 hr
Sep 18, 1:52 PM CDT	Areal Flood Advisory	BMX	Bibb, Dallas, Hale, Marengo, Perry	3 hr
Sep 18, 2:53 PM CDT	Flash Flood Warning	BMX	Tuscaloosa	112 min
Sep 18, 3:11 PM CDT	Areal Flood Advisory	BMX	Elmore, Montgomery	4 hr
Sep 18, 3:25 PM CDT	Areal Flood Advisory	BMX	Chambers, Lee	3 hr
Sep 18, 4:21 PM CDT	Areal Flood Advisory	BMX	Bullock, Montgomery, Pike	3 hr
Sep 18, 5:29 PM CDT	Areal Flood Advisory	BMX	Russell	108 min

Nearby

Flash Flood Warnings in Alabama, 2021 Every flash flood warning in 2021

Sources

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.