Alert archive / Idaho / Flash Flood Warnings in 2021

Flash Flood Warning 2, NWS Boise, ID

July 31, 2021Owyhee County, Twin Falls County, Idaho

NWS Boise, ID issued this flash flood warning at Jul 31, 2021, 7:06 PM MDT for Owyhee County, Twin Falls County, Idaho. 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
Jul 31, 2021, 7:06 PM MDT (01:06 UTC)
Expired
Jul 31, 2021, 10:02 PM MDT
In force
3 hr
Issued by
NWS Boise, ID
Area
Storm-based polygon
Flood severity
None

Counties Owyhee County, ID, Twin Falls County, ID

The radar

The Boise radar (KCBX), 183 km from the middle of the area, began a volume at 01:04 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

Elko, NV (KLKN), launched 00:00Z, 1.1 hours before the alert went out and 154 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-pSkew-T log-p diagram, Elko, NV at 00:00Z on 2021-08-01Temperature and dew point through the depth of the atmosphere, with the mixed-layer parcel. CAPE 84 joules per kilogram.LCLLFCEL10008507005003002001001 km2 km3 km6 km9 km12 km15 km-30°-20°-10°0°10°20°30°40°
Temperature in red, dew point in green, the mixed-layer parcel dashed.
HodographHodograph, Elko, NV at 00:00Z on 2021-08-01The wind through the lowest 10 kilometers. Zero to 1 km storm-relative helicity -45 square meters per square second.1939Sfc1 km3 km6 km9 kmRMLM
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
84 J/kg
Mixed-layer CIN
-93 J/kg
Mixed-layer LCL
1100 m above ground
0-6 km bulk shear
7 kt
0-1 km storm-relative helicity
-45 m²/s²
0-3 km storm-relative helicity
47 m²/s²
Significant tornado parameter
0.0
Supercell composite
0.0

Open this sounding in Storm Lab

The text

As transmitted.

849 
WGUS55 KBOI 010106
FFWBOI
IDC073-083-010415-
/O.NEW.KBOI.FF.W.0002.210801T0106Z-210801T0415Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/

BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service Boise ID
706 PM MDT Sat Jul 31 2021

The National Weather Service in Boise has issued a

* Flash Flood Warning for...
  Southwestern Twin Falls County in south central Idaho...
  Southeastern Owyhee County in southwestern Idaho...

* Until 1015 PM MDT.

* At 706 PM MDT, Doppler radar indicated thunderstorms producing 
  heavy rain across the warned area. Between 1 and 1.5 inches of 
  rain have fallen. Additional rainfall amounts up to 1 inch are 
  possible in the warned area. 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, county
           roads, poor drainage and low-lying areas.

* Some locations that will experience flash flooding include...
  Cedar Creek Reservoir, Black Butte, Roseworth, Three Creek.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Be aware of your surroundings and do not drive on flooded roads.

In hilly terrain there are many low water crossings which are 
potentially dangerous in heavy rain. Do not attempt to cross flooded 
roads. Find an alternate route.

Please report observed flooding to local emergency services or law 
enforcement and request they pass this information to the National 
Weather Service when you can do so safely.

&&

LAT...LON 4200 11513 4200 11522 4220 11521 4242 11515
      4251 11495 4247 11492 4241 11482 4231 11473
      4217 11475 4207 11477 4200 11477 4200 11479
      4200 11481 4200 11483 4200 11484 4201 11503
      4200 11503

FLASH FLOOD...RADAR INDICATED

$$

BOI
2 follow-up statements
064 
WGUS75 KBOI 010301
FFSBOI

Flash Flood Statement
National Weather Service Boise ID
901 PM MDT Sat Jul 31 2021

IDC073-083-010415-
/O.CON.KBOI.FF.W.0002.000000T0000Z-210801T0415Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Owyhee ID-Twin Falls ID-
901 PM MDT Sat Jul 31 2021

...FLASH FLOOD WARNING REMAINS IN EFFECT UNTIL 1015 PM MDT THIS 
EVENING FOR WEST CENTRAL TWIN FALLS AND EASTERN OWYHEE COUNTIES...

At 901 PM MDT, Doppler radar indicated that the heavy rain had moved 
out of the area but light to moderate rain continues. Between 1 and 
1.5 inches of rain have fallen. Flash flooding is likely in some 
areas.

HAZARD...Flash flooding caused by thunderstorms.

SOURCE...Radar.

IMPACT...Flash flooding of small creeks and streams, county
         roads, as well as poor drainage and low-lying areas.

Some locations that will experience flash flooding include...
  Roseworth, Cedar Creek Reservoir.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

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

Please report observed flooding to local emergency services or law 
enforcement and request they pass this information to the National 
Weather Service when you can do so safely.

&&

LAT...LON 4220 11510 4226 11512 4233 11512 4244 11510
      4251 11495 4247 11492 4241 11482 4234 11476
      4224 11477 4223 11478 4222 11479 4221 11482
      4220 11486 4219 11491 4219 11495 4217 11499
      4216 11506

FLASH FLOOD...RADAR INDICATED

$$

BOI
593 
WGUS75 KBOI 010402
FFSBOI

Flash Flood Statement
National Weather Service Boise ID
1002 PM MDT Sat Jul 31 2021

IDC073-083-010412-
/O.CAN.KBOI.FF.W.0002.000000T0000Z-210801T0415Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
Owyhee ID-Twin Falls ID-
1002 PM MDT Sat Jul 31 2021

...FLASH FLOOD WARNING IS CANCELLED FOR WEST CENTRAL TWIN FALLS AND 
EASTERN OWYHEE COUNTIES...

Flooding is no longer expected to pose a threat. 

A Flash Flood Watch remains in effect until 600 PM MDT Monday for 
portions of Idaho and Oregon.

LAT...LON 4220 11510 4226 11512 4233 11512 4244 11510
      4251 11495 4247 11492 4241 11482 4234 11476
      4224 11477 4223 11478 4222 11479 4221 11482
      4220 11486 4219 11491 4219 11495 4217 11499
      4216 11506

$$

BOI

The office that day

Everything else NWS Boise, ID issued on the same UTC day.

IssuedProductOfficeCountiesLasted
Jul 31, 6:40 PM MDTSpecial Weather StatementBOITwin Falls35 min
Jul 31, 7:39 PM MDTFlash Flood WarningBOITwin Falls3 hr
Jul 31, 9:32 PM MDTSpecial Weather StatementBOIAda28 min
Jul 31, 9:33 PM MDTAreal Flood AdvisoryBOIElmore, Owyhee117 min
Jul 31, 10:12 PM MDTFlash Flood WarningBOIAda, Boise3 hr
Jul 31, 11:58 PM MDTFlash Flood WarningBOICanyon, Gem, Owyhee, Payette2 hr
Aug 1, 12:43 AM MDTAreal Flood AdvisoryBOIPayette, Washington2 hr
Aug 1, 1:47 AM MDTAreal Flood AdvisoryBOICamas103 min
Aug 1, 1:11 PM MDTSpecial Weather StatementBOITwin Falls49 min
Aug 1, 1:25 PM MDTAreal Flood AdvisoryBOITwin Falls3 hr
Aug 1, 2:15 PM MDTSpecial Weather StatementBOIJerome60 min
Aug 1, 2:39 PM MDTFlash Flood WarningBOIElmore5 hr
Aug 1, 3:21 PM MDTAreal Flood AdvisoryBOIJerome, Twin Falls3 hr
Aug 1, 3:39 PM MDTFlash Flood WarningBOICamas, Elmore3 hr
Aug 1, 4:01 PM MDTFlash Flood WarningBOIOwyhee3 hr
Aug 1, 4:49 PM MDTAreal Flood AdvisoryBOIElmore3 hr
Aug 1, 5:32 PM MDTFlash Flood WarningBOIElmore3 hr
Aug 1, 5:39 PM MDTAreal Flood AdvisoryBOIOwyhee2 hr

Nearby

Flash Flood Warnings in Idaho, 2021Every 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; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.