Alert archive / California / Red Flag Warnings in 2021
Red Flag Warning 6, NWS San Francisco Bay Area, CA
NWS San Francisco Bay Area, CA issued this red flag warning at Sep 19, 2021, 9:46 AM PDT for Alameda County, Contra Costa County, California. It took effect at Sep 19, 2021, 11:00 PM PDT. It was in force for 21 hr. No storm report in the archive falls inside the area while it was in force.
The area
The counties it named.
The facts
- Issued
- Sep 19, 2021, 9:46 AM PDT (16:46 UTC)
- In effect from
- Sep 19, 2021, 11:00 PM PDT
- Expired
- Sep 20, 2021, 8:00 PM PDT
- In force
- 21 hr
- Issued by
- NWS San Francisco Bay Area, CA
Counties Alameda County, CA, Contra Costa County, CA
The radar
The San Francisco radar (KMUX), 70 km from the middle of the area, began a volume at 16:51 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
Oakland, CA (KOAK), launched 12:00Z, 4.8 hours before the alert went out and 24 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
- 684 m above ground
- 0-6 km bulk shear
- 48 kt
- 0-1 km storm-relative helicity
- -3 m²/s²
- 0-3 km storm-relative helicity
- 150 m²/s²
- Significant tornado parameter
- 0.0
- Supercell composite
- 0.0
The text
As transmitted.
572 WWUS86 KMTR 191646 RFWMTR URGENT - FIRE WEATHER MESSAGE National Weather Service San Francisco CA 946 AM PDT Sun Sep 19 2021 ...Red Flag Warning 11 pm Sunday through 8 pm Monday for the North and East Bay hills as well as the East Bay interior valleys... .Dry northerly offshore winds will push into the Napa hills around 11 pm Sunday night and then gradually spread over the North and East Bay hills. The initial burst of winds will occur while humidity values remain fairly moist. However the dry offshore winds will begin a rapid drying of the atmosphere with humidity values dropping quickly by Monday morning. Continued moderate offshore winds on Monday as humidity values drop into the teens. Offshore winds will ease by sunset Monday night. Little or no humidity recovery Monday night into Tuesday morning but with only light offshore winds. CAZ507-511-200515- /O.UPG.KMTR.FW.A.0005.210920T0600Z-210921T1800Z/ /O.NEW.KMTR.FW.W.0006.210920T0600Z-210921T0300Z/ North Bay Mountains-East Bay Hills and the Diablo Range- 946 AM PDT Sun Sep 19 2021 ...RED FLAG WARNING IN EFFECT FROM 11 PM THIS EVENING TO 8 PM PDT MONDAY FOR DRY OFFSHORE WINDS FOR THE NORTH AND EAST BAY HILLS... The National Weather Service in San Francisco has issued a Red Flag Warning for dry offshore winds, which is in effect from 11 PM this evening to 8 PM PDT Monday. The Fire Weather Watch is no longer in effect. * AFFECTED AREA...Fire Weather Zone 507 North Bay Mountains and Fire Weather Zone 511 East Bay Hills and the Diablo Range. The Napa hills and East Bay hills that received less than a tenth of an inch of rain will be the areas of biggest concern. * TIMING...11 PM Sunday night to 8 PM Monday evening. Initial burst of gusty offshore winds overnight to mid morning Monday. Drier conditions but lighter winds Monday daytime. Offshore winds ease Monday night with continued poor humidity recovery. * WINDS...Northeast 10 to 20 mph with gusts up to 40 mph. Local gusts up to 50 mph over the highest peaks. * RELATIVE HUMIDITY...Initially 30-45% tonight drying to 15-30% on Monday with little or no recovery Monday night. * IMPACTS...Any fire starts would likely see rapid spread due to dry fuels, low humidity and gusty winds in areas that did not receive wetting rains over the last 24 hours. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Red Flag Warning means that critical fire weather conditions are either occurring now...or will shortly. A combination of strong winds...low relative humidity...and warm temperatures can contribute to extreme fire behavior. && $$ CAZ510-200515- /O.NEW.KMTR.FW.W.0006.210920T0600Z-210921T0300Z/ East Bay Interior Valleys- 946 AM PDT Sun Sep 19 2021 ...RED FLAG WARNING IN EFFECT FROM 11 PM THIS EVENING TO 8 PM PDT MONDAY FOR DRY NORTHEAST WINDS FOR EAST BAY INTERIOR VALLEYS... The National Weather Service in San Francisco has issued a Red Flag Warning for gusty offshore winds, which is in effect from 11 PM this evening to 8 PM PDT Monday. * AFFECTED AREA...Fire Weather Zone 510 East Bay Interior Valleys. * TIMING...11 pm Sunday night through 8 pm Monday evening. * WINDS...Northeast winds 10 to 20 mph gusts to 35 mph, strongest through 10 am Monday morning. * RELATIVE HUMIDITY...35-50% overnight then drying into the teens Monday afternoon with little or no recovery Monday night. * IMPACTS...Any new ignitions will spread rapidly due to gusty offshore winds, lowering humidity and dry fuels. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Red Flag Warning means that critical fire weather conditions are either occurring now...or will shortly. A combination of strong winds...low relative humidity...and warm temperatures can contribute to extreme fire behavior. && $$
4 follow-up statements
892 WWUS86 KMTR 200456 RFWMTR URGENT - FIRE WEATHER MESSAGE National Weather Service San Francisco CA 956 PM PDT Sun Sep 19 2021 ...Red Flag Warning 11 pm Sunday through 8 pm Monday for the North and East Bay hills as well as the East Bay interior valleys... .Dry northerly offshore winds will push into the Napa hills late tonight and then gradually spread over the North and East Bay hills. The initial burst of winds will occur while humidity values remain fairly moist. However the dry offshore winds will begin a rapid drying of the atmosphere with humidity values dropping quickly by Monday morning. Continued moderate offshore winds on Monday as humidity values drop into the teens. Offshore winds will ease by sunset Monday night. Little or no humidity recovery Monday night into Tuesday morning but with only light offshore winds. CAZ507-510-511-201300- /O.CON.KMTR.FW.W.0006.210920T0600Z-210921T0300Z/ North Bay Mountains-East Bay Interior Valleys- East Bay Hills and the Diablo Range- 956 PM PDT Sun Sep 19 2021 ...RED FLAG WARNING REMAINS IN EFFECT UNTIL 8 PM PDT MONDAY FOR DRY OFFSHORE WINDS FOR THE NORTH BAY MOUNTAINS AND EAST BAY HILLS AND INTERIOR VALLEYS... * AFFECTED AREA...Fire Weather Zone 507 North Bay Mountains, Fire Weather Zone 510 East Bay Interior Valleys and Fire Weather Zone 511 East Bay Hills and the Diablo Range. * TIMING...11 PM Sunday night to 8 PM Monday evening. Initial burst of gusty offshore winds overnight to mid morning Monday. Drier conditions but lighter winds Monday daytime. Offshore winds ease Monday night with continued poor humidity recovery. * WINDS...Northeast 10 to 20 mph with gusts up to 40 mph. Local gusts up to 50 mph over the highest peaks. * RELATIVE HUMIDITY...Initially 30-45% tonight drying to 15-30% on Monday with little or no recovery Monday night. * IMPACTS...Any fire starts would likely see rapid spread due to dry fuels, low humidity and gusty winds in areas that did not receive wetting rains over the last 24 hours. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Red Flag Warning means that critical fire weather conditions are either occurring now...or will shortly. A combination of strong winds...low relative humidity...and warm temperatures can contribute to extreme fire behavior. && $$
598 WWUS86 KMTR 201301 RFWMTR URGENT - FIRE WEATHER MESSAGE National Weather Service San Francisco CA 601 AM PDT Mon Sep 20 2021 ...Red Flag Warning 11 pm Sunday through 8 pm Monday for the North and East Bay hills as well as the East Bay interior valleys... .Dry northerly offshore winds over the North and East Bay hills. These winds will begin a rapid drying of the atmosphere with humidity values dropping quickly by Monday morning. Continued moderate offshore winds on Monday as humidity values drop into the teens. Offshore winds will ease by sunset Monday night. Little or no humidity recovery Monday night into Tuesday morning but with only light offshore winds. CAZ507-510-511-202115- /O.CON.KMTR.FW.W.0006.000000T0000Z-210921T0300Z/ North Bay Mountains-East Bay Interior Valleys- East Bay Hills and the Diablo Range- 601 AM PDT Mon Sep 20 2021 ...RED FLAG WARNING REMAINS IN EFFECT UNTIL 8 PM PDT THIS EVENING FOR DRY OFFSHORE WINDS FOR THE NORTH BAY MOUNTAINS AND EAST BAY HILLS AND INTERIOR VALLEYS... * AFFECTED AREA...Fire Weather Zone 507 North Bay Mountains, Fire Weather Zone 510 East Bay Interior Valleys and Fire Weather Zone 511 East Bay Hills and the Diablo Range. * TIMING...11 PM Sunday night to 8 PM Monday evening. Initial burst of gusty offshore winds overnight to mid morning Monday. Drier conditions but lighter winds Monday daytime. Offshore winds ease Monday night with continued poor humidity recovery. * WINDS...North 10 to 20 mph with gusts up to 40 mph. * RELATIVE HUMIDITY...As low as 14 percent. * IMPACTS...Any fire starts would likely see rapid spread due to dry fuels, low humidity and gusty winds in areas that did not receive wetting rains over the last 24 hours. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Red Flag Warning means that critical fire weather conditions are either occurring now...or will shortly. A combination of strong winds...low relative humidity...and warm temperatures can contribute to extreme fire behavior. && $$
002 WWUS86 KMTR 201958 RFWMTR URGENT - FIRE WEATHER MESSAGE National Weather Service San Francisco CA 1258 PM PDT Mon Sep 20 2021 ...Red Flag Warning until 8 pm Monday for the North and East Bay hills as well as the East Bay interior valleys... .Dry northerly offshore winds this afternoon and evening as humidity values drop into the teens. Little or no humidity recovery Monday night into Tuesday morning but with only light offshore winds. CAZ507-510-511-210245- /O.CON.KMTR.FW.W.0006.000000T0000Z-210921T0300Z/ North Bay Mountains-East Bay Interior Valleys- East Bay Hills and the Diablo Range- 1258 PM PDT Mon Sep 20 2021 ...RED FLAG WARNING REMAINS IN EFFECT UNTIL 8 PM PDT THIS EVENING FOR DRY OFFSHORE WINDS FOR THE NORTH AND EAST BAY HILLS AND INTERIOR EAST BAY VALLEYS... * AFFECTED AREA...Fire Weather Zone 507 North Bay Mountains, Fire Weather Zone 510 East Bay Interior Valleys and Fire Weather Zone 511 East Bay Hills and the Diablo Range. * TIMING...Until 8 PM Monday evening. Offshore winds ease Monday night with continued poor humidity recovery into Tuesday. * WINDS...Northeast 10 to 20 mph with local gusts up to 30 mph. * RELATIVE HUMIDITY...15 to 25 percent with little or no humidity recovery and continued dry into Tuesday. * IMPACTS...Any fire starts will likely see rapid spread due to dry fuels, low humidity and gusty winds. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Red Flag Warning means that critical fire weather conditions are either occurring now...or will shortly. A combination of strong winds...low relative humidity...and warm temperatures can contribute to extreme fire behavior. && $$
659 WWUS86 KMTR 210254 RFWMTR URGENT - FIRE WEATHER MESSAGE National Weather Service San Francisco CA 754 PM PDT Mon Sep 20 2021 CAZ507-510-511-210400- /O.EXP.KMTR.FW.W.0006.000000T0000Z-210921T0300Z/ North Bay Mountains-East Bay Interior Valleys- East Bay Hills and the Diablo Range- 754 PM PDT Mon Sep 20 2021 ...RED FLAG WARNING WILL EXPIRE AT 8 PM PDT THIS EVENING... Conditions no longer meet Red Flag Warning criteria and are expected to remain below criteria. Low humidities and dry fuels will continue, therefore caution is still advised. $$
Nearby
Red Flag Warnings in California, 2021Every red flag 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.