Alert archive / Alabama / Flash Flood Warnings in 2017

Flash Flood Warning 35, NWS Birmingham, AL

December 20, 2017Jefferson County, Alabama

NWS Birmingham, AL issued this flash flood warning at Dec 20, 2017, 7:54 AM CST for Jefferson County, Alabama. It was in force for 3 hr. No storm report in the archive falls inside the area while it was in force.

The area

The outline as issued.

The facts

Issued: Dec 20, 2017, 7:54 AM CST (13:54 UTC)
Expired: Dec 20, 2017, 11:00 AM CST
In force: 3 hr
Issued by: NWS Birmingham, AL
Area: Storm-based polygon
Flood severity: None

County Jefferson County, AL

The radar

The Birmingham radar (KBMX), 42 km from the middle of the area, began a volume at 13:55 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.

The nearest sounding before it

Birmingham, AL (KBMX), launched 12:00Z, 1.9 hours before the alert went out and 41 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: 290 J/kg
Mixed-layer CIN: -4 J/kg
Mixed-layer LCL: 517 m above ground
0-6 km bulk shear: 79 kt
0-1 km storm-relative helicity: 327 m²/s²
0-3 km storm-relative helicity: 312 m²/s²
Significant tornado parameter: 0.4
Supercell composite: 2.1

Open this sounding in Storm Lab

The text

As transmitted.

239 
WGUS54 KBMX 201354
FFWBMX
ALC073-201700-
/O.NEW.KBMX.FF.W.0035.171220T1354Z-171220T1700Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Birmingham AL
754 AM CST WED DEC 20 2017

The National Weather Service in Birmingham has issued a

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

* Until 1100 AM CST

* At 753 AM CST, Doppler radar indicated heavy rain across the 
  warned area. Up to two inches of rain have already fallen in a 
  few spots. Flash flooding is expected to begin shortly.

* Some locations that will experience flooding include...
  Birmingham, Hoover, Vestavia Hills, Bessemer, Homewood, Mountain
  Brook, Trussville, Hueytown, Irondale, Leeds, Moody, Fairfield,
  Fultondale, Center Point, Pleasant Grove, Tarrant, Midfield,
  Adamsville, Brighton and Lipscomb.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

&&

LAT...LON 3362 8655 3352 8655 3347 8661 3347 8667
      3343 8670 3341 8675 3348 8731 3349 8729
      3350 8728 3350 8726 3352 8726 3355 8719
      3358 8720 3363 8714

$$

16

The office that day

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

Issued	Product	Office	Counties	Lasted
Dec 19, 6:37 PM CST	Dense Fog Advisory	BMX	Autauga, Barbour, Bibb, Blount, Bullock, Calhoun and 33 more	11 hr
Dec 20, 7:21 AM CST	Areal Flood Advisory	BMX	Jefferson	3 hr
Dec 20, 8:00 AM CST	Flash Flood Warning	BMX	Etowah	3 hr
Dec 20, 8:36 AM CST	Areal Flood Advisory	BMX	Calhoun, Clay, Cleburne, Randolph, St. Clair, Shelby and 1 more	3 hr
Dec 20, 10:38 AM CST	Tornado Warning	BMX	Randolph	14 min
Dec 20, 12:09 PM CST	Special Weather Statement	BMX	Lee	36 min

Nearby

Flash Flood Warnings in Alabama, 2017 Every flash flood warning in 2017

Sources

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