A cold upper level trough moved through California on April 16 bringing light precipitation to Central California by early morning. A cold and very unstable airmass pushed into the area by the early afternoon hours.
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The episode as NWS HNX wrote it up.
A cold upper level trough moved through California on April 16 bringing light precipitation to Central California by early morning. A cold and very unstable airmass pushed into the area by the early afternoon hours. As a result, showers and thunderstorms developed over the San Joaquin Valley and Southern Sierra Foothills. Due to the showery nature of the precipitation, rainfall amounts varied; but generally ranged from a tenth of an inch to half an inch of rain in these areas. There were several reports of small hail and brief heavy rainfall. Higher elevations in the Southern Sierra Nevada picked up between 4 and 8 inches of new snowfall although portions of Yosemite National Park did pick up a bit more with Tuolumne Meadows measuring 14 inches of snow snowfall. Up to an inch of snow fell over the Kern County Mountains above 5000 feet while a few indicator sites measured brief wind gusts above 60 mph. The trough moved east of the area by the morning of April 17 with drier air building in behind it.
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 16, 3:23 AM PST, 7 hours 58 minutes earlier.
Area Forecast Discussion National Weather Service San Joaquin Valley - Hanford CA 423 AM PDT Mon Apr 16 2018 .SYNOPSIS...A storm system will bring showers and higher elevation snow to the region today into tonight along with much colder temperatures. The desert will remain dry with strong and gusty winds through this evening. Tuesday through Wednesday will be dry and slightly cooler than normal. Showers and higher elevation snow could return to the region by Thursday, especially over the Sierra. && .DISCUSSION...Winter weather will make a return to the central California interior today. A cold front will herald its arrival as it moves southward through the CWA early this morning. As of this writing, the frontal boundary shows up as a broken line of showers that extends from Mariposa county southwestward into San Luis Obispo county. The upper level trough that follows behind it will produce more numerous showers as it moves inland this afternoon. In fact, precipitation will likely blossom over the mountains this midday and afternoon as the core of the 300 mb jet settles over the CWA and generates healthy orographic lift. Additionally, the cold core aloft (-30 C at 500 mb) will destablize the lower layers of the atmosphere and lead to the development of isolated thunderstorms with small hail, briefly heavy rain and gusty winds this afternoon into early this evening. A few thunderstorms may approach severe levels in Merced county-the part of our CWA where the air aloft will be coldest and most unstable. Otherwise, the advection of cold air southward will bring snow levels down to about 4000 feet in the Sierra later today and eventually that low in Kern County tonight. Due to the convective nature of precipitation, rain and snow totals will be highly varied over the central California interior from this storm system. In general, we're not expecting much more than a quarter of an inch in the San Joaquin Valley from it. The foothills and higher elevations of the Sierra will fare the best with precip totals of a half inch to a little more than an inch by daybreak Tuesday. Snow accumulations will vary from a dusting to as much as 7 or 8 inches in heavier showers over the highest elevations. Whatever the case, motorists should be prepared for slick, snow covered roads in the mountains through Tuesday morning. I-5 through the Grapevine as well as other roads at and above pass level in Kern county could end up icy and snow covered by late tonight with potentially long travel delays. Winter Weather Advisories remain in effect for all mountain zones. Meanwhile, strong westerly winds will buffet the Kern county mountains and desert today. The strongest winds will occur right below the passes. This includes Highway 58 near Mojave and along U.S. 395 in the Indian Wells Valley where gusts could exceed 70 mph this afternoon. A High Wind Warning remains in effect for this region through early tonight. This wintry storm will exit eastward into the Great Basin this evening. By that time, shower activity will be diminishing in the San Joaquin Valley and adjacent foothills. Precip will linger a bit longer over the higher elevations as well as the north facing slopes of the Tehachapi mountains, but even in these areas, precip should come to an end by or shortly after daybreak. Dry weather will rule in the wake of this storm system Tuesday as a weak ridge of high pressure aloft moves over central California. On Wednesday, high clouds will invade the northern half of our CWA as yet another cold storm approaches from the northwest. The models forecast this storm to track southeastward through central California Wednesday night into Thursday with generally light precipitation, the bulk of which will likely fall over the Sierra. Like its predecessor, this late week storm will also be accompanied by gusty winds, especially through and below the mountain passes. At this time it does not look as though this particular storm will be as wet or as cold as the current one, so any accumulating snow should remain above pass level in Kern county. Nonetheless, the higher elevations of the Sierra stand to receive another fresh blanket of snow from this storm. It looks like our current stormy pattern might transition to a more tranquil one by Friday. This could be the start of a long stretch of dry weather for us as an upper level ridge of high pressure builds over the Golden State. During this period, we can expect a pronounced warming trend. Thermometer readings could top the 90 degree mark in the San Joaquin Valley, lower foothills and the desert by Sunday. From today through at least Thursday, however, it will feel more like Winter than Spring as temperatures average much cooler than normal. && .AVIATION... Over the Southern Sierra Nevada and adjacent foothills, mainly MVFR conditions in low clouds and precipitation with areas of mountain obscuring IFR. In the Tehachapi Mountains, becoming mainly MVFR in low clouds between 15Z Mon and 18Z Mon with areas of mountain obscuring IFR. In the San Joaquin Valley, local MVFR in low clouds and showers. Isolated thunderstorms possible between 18Z Mon and 03Z Tue. In the Kern County Deserts, areas of MVFR in blowing dust between 18Z Mon and 06Z Tue otherwise VFR. Wind gusts above 50KT possible in the Tehachapi Mountains and Kern County Deserts between 18Z Mon and 10Z Tue. && .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 medium. Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.php for additional information an/or to provide feedback. && .HNX Watches/Warnings/Advisories... Winter Weather Advisory until 2 AM PDT Tuesday CAZ097. Winter Weather Advisory until 11 PM PDT this evening CAZ096. High Wind Warning from 11 AM this morning to 10 PM PDT this evening CAZ095. Winter Weather Advisory from 10 PM this evening to 8 AM PDT Tuesday CAZ095. High Wind Warning from 11 AM this morning to 3 AM PDT Tuesday CAZ098-099. && public...Durfee avn/fw...DS synopsis...Durfee weather.gov/hanford
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE HANFORD CA
804 AM PDT MON APR 16 2018
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0800 AM SNOW TUOLUMNE MEADOWS 37.87N 119.36W
04/16/2018 M7.0 INCH TUOLUMNE CA CO-OP OBSERVER
ELEVATION 8,694 FEET.
&&
BSOThe national radar mosaic for the moment the first event began.
3 high wind, 1 heavy rain. Local standard time, as filed.
Spotter report of 0.65 inches of rainfall in a five hour period. Most of the rain was from an afternoon thunderstorm.
The Bear Peak RAWS reported a peak wind gust of 66 mph.
The Blue Max RAWS reported a peak wind gust of 66 mph.
The Bird Springs Pass RAWS reported a peak wind gust of 61 mph.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in California in 2018Every state in 2018This day in weather historyWarnings in California, April 2018
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: 740940, 740941, 740942, 740943.