Alert archive / California / Flash Flood Warnings in 2021
Flash Flood Warning 15, NWS San Francisco Bay Area, CA
NWS San Francisco Bay Area, CA issued this flash flood warning at Dec 13, 2021, 10:45 AM PST for San Mateo County, Santa Cruz County, California. It was in force for 60 min. 1 report 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
- Dec 13, 2021, 10:45 AM PST (18:45 UTC)
- Expired
- Dec 13, 2021, 11:45 AM PST
- In force
- 60 min
- Issued by
- NWS San Francisco Bay Area, CA
- Area
- Storm-based polygon
- Damage threat
- Considerable
- Flood severity
- None
Counties San Mateo County, CA, Santa Cruz County, CA
The radar
The San Francisco radar (KMUX), 29 km from the middle of the area, began a volume at 18:48 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 |
|---|---|---|---|
| Dec 13, 10:54 AM PST | FLOOD | 1 W Boulder Creek, CA | MUD/DIRT/ROCKS FLOWING ONTO ROADWAY NEAR 295 RIDGE DRIVE. |
Local storm reports filed while the alert was in force, from inside its polygon or its counties.
The nearest sounding before it
Oakland, CA (KOAK), launched 12:00Z, 6.8 hours before the alert went out and 66 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.
- Mixed-layer CAPE
- 0 J/kg
- Mixed-layer CIN
- No buoyant parcel
- Mixed-layer LCL
- 449 m above ground
- 0-6 km bulk shear
- 60 kt
- 0-1 km storm-relative helicity
- 87 m²/s²
- 0-3 km storm-relative helicity
- 299 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
185
WGUS56 KMTR 131845
FFWMTR
CAC081-087-131945-
/O.NEW.KMTR.FF.W.0015.211213T1845Z-211213T1945Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
BULLETIN - EAS ACTIVATION REQUESTED
Flash Flood Warning
National Weather Service San Francisco CA
1045 AM PST Mon Dec 13 2021
The National Weather Service in San Francisco has issued a
* Flash Flood Warning for...
The CZU Lightning Complex burn area in...
Southeastern San Mateo County in northern California...
Northwestern Santa Cruz County in northern California...
* Until 1145 AM PST.
* At 1045 AM PST, Doppler radar and automated rain gauges indicated
heavy rain falling over the CZU Lightning Complex Burn Area. The
expected rainfall rate is 0.5 to 1 inch in 1 hour. Flash flooding
is ongoing or expected to begin shortly.
Excessive rainfall over the burn area will result in debris flow
moving through the CZU Lightning Complex burn area. The debris flow
can consist of rock, mud, vegetation and other loose materials.
HAZARD...Life threatening flash flooding. Heavy rain producing
flash flooding in and around the CZU Lightning Complex
Burn Area.
SOURCE...Radar and automated gauges.
IMPACT...Life threatening flash flooding of areas in and around
the CZU Lightning Complex Burn Area.
* Some locations that will experience flash flooding include...
Boulder Creek.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
This is a life-threatening situation. If you observe movement of
soils move to higher ground immediately.
Move away from recently burned areas. Life-threatening flooding of
creeks, roads and normally dry arroyos is likely. The heavy rains
will likely trigger rockslides, mudslides and debris flows in steep
terrain, especially in and around these areas.
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 3714 12234 3717 12232 3720 12235 3725 12230
3726 12232 3727 12227 3722 12218 3722 12224
3720 12216 3704 12209 3703 12213 3706 12214
3707 12212 3708 12214 3706 12217 3704 12215
3704 12222 3709 12228 3711 12227 3710 12228
FLASH FLOOD...RADAR AND GAUGE INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE
EXPECTED RAINFALL RATE...0.5-1 INCH IN 1 HOUR
$$
MM2 follow-up statements
712
WGUS76 KMTR 131921
FFSMTR
Flash Flood Statement
National Weather Service San Francisco CA
1121 AM PST Mon Dec 13 2021
CAC081-087-131945-
/O.CON.KMTR.FF.W.0015.000000T0000Z-211213T1945Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
San Mateo CA-Santa Cruz CA-
1121 AM PST Mon Dec 13 2021
...FLASH FLOOD WARNING FOR THE CZU LIGHTNING COMPLEX BURN AREA
REMAINS IN EFFECT UNTIL 1145 AM PST THIS MORNING FOR SOUTHEASTERN
SAN MATEO AND NORTHWESTERN SANTA CRUZ COUNTIES...
At 1121 AM PST, Doppler radar and automated rain gauges indicated
that heavy rain was falling over the CZU Lightning Complex Burn
Area. The expected rainfall rate is 0.5 to 1 inch in 1 hour. Flash
flooding is ongoing or expected to begin shortly.
Excessive rainfall over the burn area will result in debris flow
moving through the CZU Lightning Complex burn area. The debris flow
can consist of rock, mud, vegetation and other loose materials.
HAZARD...Life threatening flash flooding. Heavy rain producing
flash flooding in and around the CZU Lightning Complex
Burn Area.
SOURCE...Radar and automated gauges.
IMPACT...Life threatening flash flooding of areas in and around
the CZU Lightning Complex Burn Area.
Some locations that will experience flash flooding include...
Boulder Creek.
Anyone living or traveling on roads in the CZU Lightning Complex
burn area or along secondary roads like Swanton Road...Jamison Creek
Road...and Hwy 9 from Boulder Creek to Brookdale...should be alert
for possible road problems due to erosion...debris flows...rockfalls
and debris. Roadways and bridges may be washed away in places.
Some drainage basins impacted include...Butano Creek...Gazos Creek...
Waddell Creek...Scott Creek....Big Creek and Boulder Creek
PRECAUTIONARY/PREPAREDNESS ACTIONS...
This is a life-threatening situation. If you observe movement of
soils move to higher ground immediately.
Move away from recently burned areas. Life-threatening flooding of
creeks, roads and normally dry arroyos is likely. The heavy rains
will likely trigger rockslides, mudslides and debris flows in steep
terrain, especially in and around these areas.
Turn around, don't drown when encountering flooded roads. Most flood
deaths occur in vehicles.
&&
LAT...LON 3714 12234 3717 12232 3720 12235 3725 12230
3726 12232 3727 12227 3722 12218 3722 12224
3720 12216 3704 12209 3703 12213 3706 12214
3707 12212 3708 12214 3706 12217 3704 12215
3704 12222 3709 12228 3711 12227 3710 12228
FLASH FLOOD...RADAR AND GAUGE INDICATED
FLASH FLOOD DAMAGE THREAT...CONSIDERABLE
EXPECTED RAINFALL RATE...0.5-1 INCH IN 1 HOUR
$$
MM681
WGUS76 KMTR 131941
FFSMTR
Flash Flood Statement
National Weather Service San Francisco CA
1141 AM PST Mon Dec 13 2021
CAC081-087-131951-
/O.EXP.KMTR.FF.W.0015.000000T0000Z-211213T1945Z/
/00000.0.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
San Mateo CA-Santa Cruz CA-
1141 AM PST Mon Dec 13 2021
...FLASH FLOOD WARNING FOR THE CZU LIGHTNING COMPLEX BURN AREA WILL
EXPIRE AT 1145 AM PST THIS MORNING FOR SOUTHEASTERN SAN MATEO AND
NORTHWESTERN SANTA CRUZ COUNTIES...
The heavy rain has ended. Flooding is no longer expected to pose a
threat. Additional rain will continue to occur through this evening.
Please continue to heed remaining road closures and standing water
on roads.
LAT...LON 3714 12234 3717 12232 3720 12235 3725 12230
3726 12232 3727 12227 3722 12218 3722 12224
3720 12216 3704 12209 3703 12213 3706 12214
3707 12212 3708 12214 3706 12217 3704 12215
3704 12222 3709 12228 3711 12227 3710 12228
$$
MMThe office that day
Everything else NWS San Francisco Bay Area, CA issued on the same UTC day.
| Issued | Product | Office | Counties | Lasted |
|---|---|---|---|---|
| Dec 13, 4:29 AM PST | Areal Flood Advisory | MTR | San Mateo, Santa Clara, Santa Cruz | 18 hr |
| Dec 13, 5:31 AM PST | Areal Flood Advisory | MTR | Alameda, Contra Costa, San Mateo, Santa Clara | 7 hr |
| Dec 13, 9:14 AM PST | Areal Flood Advisory | MTR | City and County of San Francisco, San Mateo, Santa Clara, Santa Cruz | 3 hr |
| Dec 13, 12:00 PM PST | Flood Watch | MTR | Alameda, Contra Costa, Marin, Monterey, Napa, San Benito and 5 more | 13 hr |
| Dec 13, 1:26 PM PST | Areal Flood Advisory | MTR | San Mateo | 11 hr |
| Dec 13, 1:45 PM PST | Flash Flood Warning | MTR | Monterey | 6 hr |
| Dec 13, 2:42 PM PST | Areal Flood Warning | MTR | Santa Cruz | 4 hr |
Nearby
Flash Flood Warnings in California, 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; local storm reports from the same archive; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.