Hurricane Hilary moved up the Baja peninsula and dissipated in our region as an extratropical cyclone, bringing heavy rain and periods of gusty winds.
Every event with a place to put it; 3 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
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 BOI wrote it up.
Hurricane Hilary moved up the Baja peninsula and dissipated in our region as an extratropical cyclone, bringing heavy rain and periods of gusty winds.
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 Boise, ID wrote its last area forecast discussion before the first event at Aug 20, 7:22 PM MST, 4 hours 38 minutes earlier.
Area Forecast Discussion
National Weather Service Boise ID
822 PM MDT Sun Aug 20 2023
.DISCUSSION...The westward shift noted earlier today continues
in the latest guidance. The flood watch has been shifted to end
earlier in the Western Magic Valley and Southern Twin Falls
zones. Concerning the High Wind Warning - latest guidance
supports what we have in place so this will be maintained. So
far this evening, showers have been mainly confined to areas
south and east of a line from Rome, Oregon to McCall, and some
significant rainfall totals have occurred. These include over an
inch so far today near Featherville and Pine. Additional heavy
rain is expected overnight and again Monday. There is a trend
for lower totals in the Upper Treasure and this is being
monitored to determine if they also need to be taken out of the
flood watch. No changes will be made at this time.
&&
.AVIATION...VFR, becoming MVFR/IFR with local LIFR after Mon/06z as
widespread rain and isolated thunderstorms from the remnants of
Hurricane Hilary continue to move NNE through Monday. Showers will
be heavy at times, with mountain obscuration and low ceilings
expected. Widespread MVFR ceilings around Mon/18z. Very strong low-
level wind shear of 40-60 kt will develop over southwest Idaho after
Mon/10z until Tue/00z as the tropical depression moves overhead.
Surface winds: E-SE 5-15 kt becoming E-SE 15-25 kt by Mon/14z. Gusts
up to 35-45 kt from KONO to KJER/KTWF, and along the ID/NV border.
Winds aloft at 10kft MSL: S-SE 10-20 kt, increasing to SW-SE 30-60
kt after Mon/12z, strongest over ID.
&&
.HYDROLOGY...Tropical moisture from the remnants of Hurricane
Hilary are forecast to move north into the area late tonight and
Monday, but slightly west of previous forecasts. Record amounts
of rainfall along with flash flooding are possible through
Monday evening. The highest precipitation should occur Monday
morning across Harney, Malheur and Baker Counties in Oregon, and
Payette, Washington, Adams, Gem, and Canyon Counties in Idaho.
For more details, check http://www.nhc.noaa.gov.
&&
.PREV DISCUSSION...
SHORT TERM...Tonight through Tuesday night...The forecast
track of Hilary has slowed slightly and also shifted slightly
westward, now aimed through Harney County midday Monday, then
western Baker County late Monday. The threat for flooding rain
is therefore decreasing Monday in south-central Idaho, and
increasing in Harney and Baker Counties in Oregon. Western-most
Idaho and Malheur County are still expected to get heavy rain
from early Monday morning through the day Monday, but possibly
clearing Monday afternoon in south-central Idaho. Forecast
wind speeds have also been lowered slightly in south- central
Idaho. The High Wind Warning for gusts up to 60 mph is still in
effect for the southwest Idaho Highlands and southern Twin Falls
County, but the Wind Advisory has been cancelled in the Western
Magic Valley, Camas Prairie, Boise Mountains, and Upper
Treasure Valley. The Wind Advisory will continue, however, in
the Owyhee Mountains, but only until 6 PM MDT Monday rather than
9 PM as issued earlier.
After Hilary exits north of our CWA Monday night, there will still
still be showers and thunderstorms Tuesday as an upper trough off
California moves through Oregon into northern Idaho. Temperatures
will be several degrees warmer Tuesday.
LONG TERM...Wednesday through Sunday...Wednesday and Thursday
should be warmer and drier under southerly flow aloft between
an Upper high in the southern Plains and another upper trough
off the California coast. Friday will bring a chance of showers
and thunderstorms to eastern Oregon and west-central Idaho as a
weak impulse moves out of the California trough. Saturday should
be dry with normal temperatures for late August.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...Flood Watch through Monday evening IDZ011>015-028-029-033.
High Wind Warning from 9 AM to 6 PM MDT Monday IDZ015-030.
Flood Watch until 6 AM MDT Monday IDZ016.
Wind Advisory from 9 AM to 6 PM MDT Monday IDZ029.
OR...Flood Watch through Monday evening ORZ061>064.
&&
www.weather.gov/Boise
www.facebook.com/NWSBoise
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DISCUSSION...SP
AVIATION.....AL
HYDROLOGY....LC/SP
PREV SHORT TERM...LC
PREV LONG TERM....LCThe Boise radar (KCBX), 97 km away, was scanning. The volume nearest the first event began at 07:00 UTC.
4 heavy rain, 3 high wind, 1 thunderstorm wind. Local standard time, as filed.
The mesonet station DEHI1, Deer Haven, measured 0.91 inches of rain.
The mesonet station FLEI1 on Fleck Summit measured 1.41 inches of rain.
Spotter reported 2.15 inches of rain total near Featherville.
The ASOS station at Twin Falls airport measured a strong wind gust.
The mesonet station UP065 6.2 miles West of Weiser recorded a high wind gust.
The mesonet station DEAI1 at Catfish recorded a high wind gust.
The ASOS at the Boise airport measured 0.73 inches of rain. The mesonet station GW0891 one mile south of Boise measured 0.81 inches of rain.
Spotter reported thunderstorm wind gusts resulting in 3 large pine trees knocked down, small branches breaking, and one large branch breaking.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2023Every state in 2023This day in weather historyWarnings in Idaho, August 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: 1124920, 1124921, 1124922, 1124928, 1124916, 1124918, 1124919, 1124914.