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A brief summary of 07-10 April 2016 CA/NV cutoff low event
Nina Oakley; WRCCMarty Ralph and Brian Kawzenuk; CW3E
Reno NV April 9 2016Photo: Ben Hatchett
Summary
• 2 consecutive cutoff lows brought precipitation to CA, Great Basin, Las Vegas area
– Low #2 more widespread impact than Low #1
– 72 hr totals generally <1-3 in
• Periods of heavy precipitation as areas of high vorticity circulated around low
• Subtropical moisture entrainment into low; does not reach atmospheric river criteria
5 pm Tues Apr 5
Low #1 centerLow #1 track
“Cutoff” low has:• Area of low pressure well
removed from mean westerly flow (jet stream)
• Closed height contour(s) at 500 hPa
• cyclonic (counterclockwise) winds encircling low center
5 am Mon Apr 4 5 pm Tues Apr 5
5 am Thurs Apr 7 5 pm Thurs Apr 7
Cutoff low #2starts to form
Low #1 centerLow #1 trackLow #2 centerLow #2 track
Cutoff low #1Apr 4-7
Cutoff low #1developing
5 am Thurs Apr 7 5 pm Fri Apr 8
5 pm Sat Apr 9 5 pm Sun Apr 10
Cutoff low #2starts to form
Low #1 centerLow #1 trackLow #2 centerLow #2 track
Cutoff low #1Apr 4-7
5 am Mon Apr 4 5 pm Tues Apr 5
5 am Thurs Apr 7 5 pm Thurs Apr 7
Integrated Water Vapor (IWV)
Cutoff low #1Apr 4-7
5 am Thurs Apr 7 5 pm Fri Apr 8
5 pm Sat Apr 9 5 pm Sun Apr 10
Integrated Water Vapor (IWV)
Cutoff low #2Apr 7-10
5 am Mon Apr 4 5 pm Tues Apr 5
5 am Thurs Apr 7 5 pm Thurs Apr 7
GPS-Met IWV
Cutoff low #1Apr 4-7
GPS-Met IWV
5 am Thurs Apr 7 5 pm Fri Apr 8
5 pm Sat Apr 9 5 pm Sun Apr 10
Cutoff low #2Apr 7-10
5 am Mon Apr 4 5 pm Tues Apr 5
5 am Thurs Apr 7 5 pm Thurs Apr 7
GOES-West IR: Cutoff low #1 Apr 4-7
5 am Thurs Apr 7 5 pm Fri Apr 8
5 pm Sat Apr 9 5 pm Sun Apr 10
GOES-West IR: Cutoff low #2 Apr 7-10
5 am Mon Apr 4 5 pm Tues Apr 5
5 am Thurs Apr 7 5 pm Thurs Apr 7
Cutoff low #1Apr 4-7
NEXRAD Composite
Radar Imagery
Areas of convection rotate around cutoff low
5 pm Thurs Apr 7
Cutoff low #2Apr 7-10
5 pm Fri Apr 8
5 pm Sat Apr 9 5 pm Sun Apr 10
NEXRAD Composite
Radar Imagery
Areas of convection rotate around cutoff low
Areas of convection rotating around cutoff low
Likely orographic forcing on eastern side of Sierra
8:48 pm Fri Apr 9
1 pm Sat Apr 9
Well developed cutoff low is entraining moisture plume; moisture wrapping around low
8pm apr 9
72 hr total precipitationending 1 pm Sun Apr 10
• Bay Area coast ranges 1-2 in
• Reno area: 0.5-1 in• Central/southern Sierra
Nevada 1-3 in• Central Valley 1-2+
inches• 1-2+ in San Gabriel,
Santa Ynez, San Bernardino Mtns
• 1-2 in Las Vegas area• San Diego 0.55 in 6-
10th, 71% of Apr normal
• Fresno 0.95 in 8th-9th, 100% of Apr normal
• Reno 0.67 in Apr 9-10, 142% Apr normal
72 hour snowfall totals*
Squaw Ski Area 2 in
Mt Rose Ski Area 2 in
Heavenly Ski Area 4-5 in
Kirkwood Ski Area 12 in
Mammoth Ski Area 13 in
*As reported by each ski resort
Snow Level Radar: San Bernadino, CA
Snow level ~10,000 ft. Snow level ~9,000 ft.
Snow Level Radar: San Luis Reservoir, CA
Snow level begins >9,000 ft. drops to <7700 ft and rises to >9,000 ft by the end of the heavy precipitation
Impacts
• Minor impacts
– Delayed/impacted outdoor events
• Giants/Dodgers game in SF delayed
– Some flooding in Las Vegas area
• Generally beneficial precipitation
• May have impact on fire season in Great Basin, CA)
– Spring rains increase vegetation that dries out in summer fire months
Some of worst drought areas saw a ~0.5-3 inches in this storm– namely southern Sierra, southern Central Valley, and Santa Barbara, San Luis Obispo counties
April ‘tis the season for closed and cutoff lows in the Southwest
Based on Oakley and Redmond (2014)
Vandenberg AFBSaturday afternoon (4/9)500 J/kg CAPE,Lifted Index: -2.25Appreciably unstable for this area!
??????????Saturday afternoon (4/9)500 J/kg CAPE,Lifted Index -2.25
Reno (KREV)Saturday afternoon (4/9)Surface-based parcel 734 J/kg CAPE,Lifted Index: -3Appreciably unstable for this area!