An upper level low pressure system moved slowly inland across central California on May 4. The low brought enough moisture and instability to the area for scattered showers and thunderstorms to develop across the area.
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The episode as NWS HNX wrote it up.
An upper level low pressure system moved slowly inland across central California on May 4. The low brought enough moisture and instability to the area for scattered showers and thunderstorms to develop across the area. While precipitation amounts were generally a quarter of an inch or less, some stations in Merced and Mariposa Counties measured between a quarter and three quarters of an inch of rainfall. In addition, some of the thunderstorms produced funnel clouds as the environment was highly sheared.
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 May 4, 1:05 AM PST, 8 hours 33 minutes earlier.
Area Forecast Discussion National Weather Service Hanford CA 205 AM PDT Thu May 4 2023 .SYNOPSIS...An upper level low will move slowly inland across central California, keeping a chance of precipitation over the region through the end of the week. Temperatures will remain well below normal through Saturday with a warming trend taking place on Sunday and Monday. && .DISCUSSION...An upper level low pressure system centered off the central CA coast is moving slowly eastward and is progged to move inland over our area today. KHNX is showing some showers moving northward ahead of the low over the San Joaquin Valley and West Side Hills. As the low moves inland across central CA today, it will provide for enough instability for showers across much of our area through this afternoon with snow levels between 5000 and 6000 feet. Precipitation is expected to be generally light with most of area picking up between one to three tenths of an inch of precipitation. The low is progged to shift into the Great Basin tonight and Friday which keep unsettled conditions over our area with temperatures remaining unseasonably cool and a slight chance of showers over the Sierra Nevada. The operational WRF is indicating another upper low moving into NORCAL on Saturday, but ensemble members are showing widespread disagreement with regards to the timing and placement of this system. The NBM is indicating that the deeper moisture and stronger dynamics with this system will remain to the north of our area. Temperatures are progged to remain well below seasonal averages through Saturday then a slow warming trend will take place on Sunday and Monday. Ensemble means are showing a pattern change taking place later on next week with an upper ridge strengthening over the western CONUS next Wednesday and Thursday suggesting temperatures rising to more seasonable levels. && .AVIATION...In the Sierra Nevada, widespread MVFR with areas of mountain obscuring IFR in low clouds and showers. Elsewhere, VFR conditions will prevail across the Central CA interior for the next 24 hours. && .AIR QUALITY ISSUES...None. && .CERTAINTY... The level of certainty for days 1 and 2 is medium. The level of certainty for days 3 through 7 is low. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information and/or to provide feedback. && .HNX WATCHES/WARNINGS/ADVISORIES...None. && public/aviation/fire wx...DAS pio/idss...JEB weather.gov/hanford
The San Joaquin Valley radar (KHNX), 68 km away, was scanning. The volume nearest the first event began at 17:38 UTC.
3 funnel cloud. Local standard time, as filed.
KFTV Channel 30 filmed a funnel cloud west of Trimmer. The video was posted on Twitter.
KMPH Channel 26 filmed a funnel cloud over Atwater.
A cooperative observer observed a funnel cloud over Dos Palos.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2023Every state in 2023This day in weather historyWarnings in California, May 2023
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: 1086602, 1085036, 1085037.