Wildfire in California, May 17 to 18, 2018

Name: Wildfire in California, May 17 to 18, 2018
Start: 2018-05-17T13:00
End: 2018-05-18T17:00
Location: California

May 17 to 18, 2018 · NWS SGX · 1 event in 1 county or zone

A wildfire ignited a few miles south of Winchester in Riverside County on May 17th. Lower relative humidity and wind speeds between 15-20 mph helped exasperate the fire.

Where it happened

Every event with a place to put it; 1 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.

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The toll

Deaths: 0
Injuries: 0
Property damage: None recorded
Crop damage: None recorded
Events: 1

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.

What happened

The episode as NWS SGX wrote it up.

A wildfire ignited a few miles south of Winchester in Riverside County on May 17th. Lower relative humidity and wind speeds between 15-20 mph helped exasperate the fire. Evacuations were put in place for six homes near the fire, and one structure was destroyed.

What forecasters said that day

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 San Diego, CA wrote its last area forecast discussion before the first event at May 17, 12:59 PM PST, 1 minute earlier.

Area forecast discussion, May 17, 12:59 PM PST, 1 minute before

Area Forecast Discussion
National Weather Service San Diego CA
159 PM PDT Thu May 17 2018

.SYNOPSIS...
An upper level trough will persist across the West Coast through
the weekend and then deepen early next week. This will bring
onshore flow with daily windy conditions in the deserts and
passes as well as a deep marine layer that mixes out each day for
clearing. Temperatures will be near normal to slightly below. The
low clouds will be more widespread Friday and Saturday morning
due to an eddy in the California bight. A slight warming trend for
the weekend with weaker onshore flow and lighter wind in the
deserts. Early next week there is a slight chance for showers in
the mountains and High Deserts as a deeper closed upper low moves
over Southern California. This will lead to a cooler Monday and
Tuesday for inland areas, then followed by warming again mid-week.

&&

.DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE...
SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO
COUNTIES...

.SHORT TERM (Tonight through Sunday)...
Skies cleared to the beach but well defined eddy that formed
earlier is drifting towards the coast causing additional lifting
to the residual marine layer and a sharp arcing line of low
clouds. This should bring an early onset of clouds to the San
Diego County and southern Orange County coast which the high
resolution guidance depicts. There is a good onshore flow set up
and windy conditions should once again develop in the mountain
passes and into the desert floors this evening. Both the deep but
rather thin marine layer and the desert wind will be enhanced by
a short wave trough passage this evening. Low clouds should become
more widespread as result and up to 3500 feet and possibly enough
thickening for patchy drizzle by Friday morning. 850 mb northwest
winds over the California bight increase to 15 knots tonight
allowing for continued eddy spin up and closer to the coast.

The pattern repeats itself on Saturday with clearing to the coast
in post trough air mass. Another weaker short wave trough in the
mean cyclonic flow arrives Saturday evening. The 850 mb flow
decreases 5-10 knots Friday evening into Saturday morning but
stays northerly Saturday night. Should be enough for another eddy
development in the California bight and good push of marine clouds
inland and possible better chance for drizzle Saturday morning.
The air mass warms slightly on Saturday and Sunday which will
bring mid 90s to the deserts and most notable warming to the
inland valleys and mountains. Unsure how much the marine layer
will settle given the pattern supportive of coastal eddies but
warming aloft. Does look like clearing to the beach. Sunday
evening should bring an early push to expanding marine clouds on
the coast.

&&

.LONG TERM (Monday through Thursday)...

A deeper upper low is progged to closed off as it descends down
the cyclonic flow still in place on the West Coast. This backs the
low to mid level flow to southwest during Sunday night. The
center is progged by guidance to move over the High Deserts during
Monday afternoon and into early Tuesday, then wrap around flow.
Looks unstable and dynamic enough for at least slight chance of
showers. Depending on the low center track it supports an isolated
thunderstorm. This system will bring notable cooling across the
deserts and mountains for Monday and Tuesday and moderate onshore
flow. This system lifts out for warming trend Wednesday and
Thursday. The upper low is strong enough to fulling mix out the
marine layer clouds and then settle back into eddy formations.
Longer range still has troughiness on West Coast.

&&

.AVIATION...
172030Z...Coast/Valleys...BKN020-030 Tops 040 at KSAN and over the
coastal waters spreading inland across KCRQ and KSNA through 04Z.
Low clouds spreading farther inland across KONT and KSBD through 15Z
with vis 3-5 miles in haze. Clouds clearing back to the coast
through 20Z Friday.

Mountains/Deserts...Mostly clear with unrestricted vis through
Friday. West winds 15-25 knots with gusts 30-40 knots through
Friday, strongest in the afternoons and evenings along the desert
mountain slopes and through the San Gorgonio Pass.

&&

.MARINE...
Gusty northwest winds to 20 kt over the outer waters through this
evening, then decreasing overnight. No hazardous marine conditions
are anticipated Friday through Monday.

&&

.CLIMATE...Coastal sites running near normal temperatures in May
and slightly above inland. Deserts running a couple degrees above
due to the early May heat wave.

&&

.SGX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...NONE.
&&

PUBLIC...Tardy
AVIATION/MARINE...Moede

The radar

The national radar mosaic for the moment the first event began.

Open the radar archive at this moment

Event by event

1 wildfire. Local standard time, as filed.

Wildfire, San Bernardino and Riverside County Valleys - the Inland Empire

When: May 17, 1:00 PM PST to May 18, 5:00 PM PST
Where: San Bernardino and Riverside County Valleys - the Inland Empire forecast zone
Reported by: Fire Department/Rescue
Coordinates: 34.293, -116.086 (the zone’s center; the record gives no point)

The Patterson Fire ignited around 1 pm PST on May 17th. Six homes were evacuated around 1500 PST on Hidden Falls Road and Vista Road, and one unoccupied structure was destroyed in the fire. The fire rapidly grew to approximately 1,200 acres by 1830 PST on the 17th. Evacuations were lifted around 2100 PST on the 17th. The fire was contained around 1800 PST on May 18th.

What these are

Wildfire: A fire burning in wildland vegetation, with its acreage and damage where known.

After NWS Directive 10-1605, the rules offices file Storm Data by.

The same day elsewhere

Every storm in California in 2018 Every state in 2018 This day in weather history Warnings in California, May 2018

Sources

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: 758142.