A very cold and moist low pressure system dropped south out of the Gulf of Alaska on April 4 and moved slowly southward off the California coast on April 5 and 6. This system brought moderate to heavy precipitation to the area between the afternoon of April 5 to the afternoon of April 6.
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Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS HNX wrote it up.
A very cold and moist low pressure system dropped south out of the Gulf of Alaska on April 4 and moved slowly southward off the California coast on April 5 and 6. This system brought moderate to heavy precipitation to the area between the afternoon of April 5 to the afternoon of April 6. Several stations in the Sierra Nevada and adjacent foothills picked up between 1.5 and 3 inches of liquid precipitation while much of the eastern San Joaquin Valley picked up between 0.75 and 1.5 inches of rainfall. The west side of the San Joaquin Valley along with the Kern County Mountains and Deserts generally picked up between half and inch and an inch of rain. Several STOTEL stations in the Sierra Nevada above 5500 feet picked up an estimated 18 to 36 of new snowfall with a few stations above 8000 feet picking up higher amounts. There were reports of localized nuisance flooding, as a few thunderstorms popped up during the afternoon of April 6. One of the thunderstorms produced a funnel cloud near Laton which was observed by several spotters and reported by several media outlets.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Hanford, CA wrote its last area forecast discussion before the first event at Apr 5, 12:17 PM PST, 1 hour 49 minutes earlier.
Area Forecast Discussion National Weather Service Hanford CA 117 PM PDT Sun Apr 5 2020 .SYNOPSIS... A strong late season storm system will bring heavy rain and snowfall to the region through Monday afternoon. Additional precipitation is possible into the southern half of the district late Tuesday into Wednesday. Conditions will dry out and warm up by the end of the week. && .DISCUSSION... After a nice stretch of days, we are tracking a major storm system that is dropping south from the Gulf of Alaska. It is a very cold storm system that is remaining over the oceans and is tapping some decent moisture with it. Regional radar and satellite loops are indicating two main bands of moderate to heavy rainfall. The first band is making its way through Merced and Fresno with only light amounts. The main cold front is still north of Merced and will be making its way south this afternoon and evening. We are already seeing gusty winds along the west side of the SJV and into the coastal hills. We issued a wind advisory this morning and as the main cold front gets closer, wind will increase across the SJV and over the Sierra ridges. Rainfall rates up to one half of an inch per hour are possible over the Briceburg/Ferguson burn scar and flooding is possible. Rainfall amounts are fairly impressive across the SJV as well. We are a bit concerned that they might be a bit overdone, but when the front pushes through overnight tonight is when we expect the heaviest rain. the orientation of the front is also important as the low center slides down the coast the front will become more of a north and south orientation and we could see training storms and heavy rain going over the same area. This could lead to some minor flooding over poor drainage areas in the SJV. The current snow level as of noon was around 5500 feet and is expected to stay there most of the event. It will drop to around 4000 feet in the Sierra behind the front tomorrow morning. Snow fall rates will be as high as two to three inches per hour with the frontal band over night in the Sierra. Couldn't rule out some rumbles of thunder in the heaviest snow bands. The NAM and hires NMM are trying to shadow the SJV as the front pushes through. However we are still expecting decent rainfall over the region. this is a different soln from the EC and GFS deterministic runs from 12z which are both wetter for the SJV. This could be a resolution issue. Snow levels are expected to be around 6000 feet for the Kern county mountain areas and they could see significant snow in the Cuddy Valley area and around Pine Mountain Club. The upper level low center will be veryslow to move south on Monday as it will remain nearly stationary off the CENCAL coast. Continued impulses will keep the chances of rain and high elevation snow across the CENCAL interior. A continued possibility of thunderstorms on Monday mainly along the west side of the SJV. Periods of moderate to heavy rain is still expected on Monday afternoon and evening. The low center is forecast to slide south towards Pt. Conception by Tuesday with the focus turning to kern county and the possible impacts there. Strong southerly flow will potentially create downsloping wind issues through the Grapevine pass as well as moderate rain and high elevation snow Tuesday night as wrap around moisture becomes more intense. As the low center continues to move south and east on Wednesday, we are expecting drying conditions from the north and spreading south Wednesday night. EPAC ridge of high pressure will build on behind the exiting low center. Warming trend with dry conditions are expected late Thursday and continue through next weekend. && .AVIATION... For the southern San Joaquin valley and Sierra foothills: MVFR conditions with local IFR ceilings and visibilities likely. Additionally, moderate to locally heavy rain showers and isolated thunderstorms will intensify throughout the day, eventually ending by Monday afternoon. Over the Sierra Nevada and Kern County mountains: expect IFR due to precipitation and mountain obscurations through at least Monday evening. && .AIR QUALITY ISSUES... None. && .CERTAINTY... The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is high. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information an/or to provide feedback. && .HNX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 5 PM PDT Monday for CAZ192>194. Wind Advisory until 8 PM PDT this evening for CAZ179-180-182. Winter Storm Warning from 5 PM this afternoon to 11 PM PDT Monday for CAZ195>197. && public......JDB aviation....JDB pio/idss....AB weather.gov/hanford
The San Francisco radar (KMUX), 97 km away, was scanning. The volume nearest the first event began at 22:04 UTC.
14 heavy snow, 1 flood, 1 funnel cloud. Local standard time, as filed.
California Highway Patrol reported roadway flooding at the intersection of SR 165 and August Ave. in Hilmar.
The Tenaya Lake SNOTEL (8150 feet) picked up an estimated 44.0 inches of new snow.
The Devils Postpile SNOTEL (7569 feet) picked up an estimated 33.9 inches of new snow.
The Chilkoot Meadow SNOTEL (7150 feet) picked up an estimated 26.3 inches of new snow.
The Lower Kibbie Ridge SNOTEL (6700 feet) picked up an estimated 25.0 inches of new snow.
The Agnew Pass SNOTEL (9450 feet) picked up an estimated 25.4 inches of new snow.
The Ostrander Lake SNOTEL (8200 feet) picked up an estimated 25.0 inches of new snow.
The Gin Flat SNOTEL (7050 feet) picked up an estimated 22.5 inches of new snow.
The Kaiser Point SNOTEL (9200 feet) picked up an estimated 37.0 inches of new snow.
The Upper Providence SNOTEL (5611 feet) picked up an estimated 30.8 inches of new snow.
The West Woodchuck Meadow SNOTEL (9100 feet) picked up an estimated 29.8 inches of new snow.
The Blackcap Basin SNOTEL (10300 feet) picked up an estimated 29.4 inches of new snow.
The Upper Bull SNOTEL (8073 feet) picked up an estimated 25.8 inches of new snow.
The Volcanic Knob SNOTEL (10050 feet) picked up an estimated 20.0 inches of new snow.
The State Lakes SNOTEL (10300 feet) picked up an estimated 18.9 inches of new snow.
Several public reports and videos were received of a funnel cloud near Laton.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2020Every state in 2020This day in weather historyWarnings in California, April 2020
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 876220, 876200, 876201, 876202, 876203, 876205, 876206, 876207, 876208, 876210, 876211, 876213, 876214, 876215, 876217, 876222.