Flood in Montana, May 31, 2020

Name: Flood in Montana, May 31, 2020
Start: 2020-05-31T13:00
End: 2020-05-31T23:59
Location: Montana

May 31, 2020 · NWS MSO · 1 event in 1 county or zone

Thunderstorms passed through the area early Sunday, bringing a half inch to one inch of rain, which combined with ongoing snow melt to produce a near historical high discharge and river level.

Where it happened

Every event with a place to put it. Tap one for its entry below.

Tornadoes
Tropical storms and surge
Floods
Wind
Hail
Winter weather
Heat and drought
Cold
Fire, smoke and dust
Marine and coastal
Other

Open the live radar over this ground

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 MSO wrote it up.

Thunderstorms passed through the area early Sunday, bringing a half inch to one inch of rain, which combined with ongoing snow melt to produce a near historical high discharge and river level.

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 Missoula, MT wrote its last area forecast discussion before the first event at May 31, 3:04 AM MST, 9 hours 56 minutes earlier.

Area forecast discussion, May 31, 3:04 AM MST, 9 hours 56 minutes before

Area Forecast Discussion
National Weather Service Missoula MT
404 AM MDT Sun May 31 2020

.DISCUSSION...A slow moving low pressure system is slowly making
is way into the Northern Rockies this morning. Numerous showers
and thunderstorms, some strong, extend off this low from Eastern
Washington and Oregon into Southern Idaho. Showers are rapidly
developing across central Idaho into western and southwest
Montana. These are expected to strengthen into the early morning
hours. Movement of all showers and storms will generally be from
south to north with the brunt of the stronger storms impacting
central Idaho into portions of Northwest Montana. This system
will quickly move northward this afternoon. Scattered showers and
a few thunderstorms are expected to linger across Northwest
Montana along the Canadian Border this afternoon.

The overall weather pattern will transition to a westerly flow
aloft. A few weak disturbances will trigger rain showers through
Wednesday.

A trough of low pressure will amplify across the Pacific Northwest
Thursday and Friday. This will leave the Northern Rockies in a
moist southwesterly flow. The increased moisture and instability
is expected to trigger showers and thunderstorms across Lemhi
county Idaho into Southwest Montana Thursday. Right now it looks
like shower and thunderstorm activity will extend further north
Friday impacting much of western Montana and central Idaho.

Models do show the upper low moving into the Northern Rockies
Saturday and Sunday and bringing widespread possibly significant
precipitation. However there are considerable model differences
with timing and location of most precipitation. The main message
for next weekend is wetter and cooler with exact details to come
later this week.

&&

.AVIATION...A low pressure system will continue to push band of
showers and thunderstorms through the Northern Rockies today.
Currently a band of showers extend across north central Idaho into
west central Montana and will steadily move northward into
northwest Montana. KGPI, KMSO and KBTM will experience vicinity
showers through 31/12z. A more robust line of showers and
thunderstorms will be moving into the Northern Rockies later this
morning. This line of storms will be capable of producing
dangerous erratic winds, small hail and heavy rain. The path of
the storms appears to mainly impact north central Idaho up into
northwest Montana. A storm could graze KMSO around 31/14z. While
KGPI should be heavily impacted by thunderstorms between 31/14z to
31/18z. As this band moves through the area, gusty westerly winds
will mix to the surface causing breezy conditions for the
remainder of the day. Wind gusts up to 30 mph will be possible in
valley locations and the higher terrain of northwest Montana could
experience gusts in excess of 40 mph.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...None.
ID...None.
&&

In the hours before

Local storm report, May 31, 12:27 PM MST, 33 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
127 PM MDT SUN MAY 31 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0814 AM     TSTM WND GST     2 WNW BIGFORK           48.07N 114.11W
05/31/2020  M57 MPH          FLATHEAD           MT   PUBLIC

&&

Local storm report, May 31, 12:44 PM MST, 16 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
144 PM MDT SUN MAY 31 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0815 AM     TSTM WND DMG     2 NNW KALISPELL         48.22N 114.33W
05/31/2020                   FLATHEAD           MT   PUBLIC

            LARGE PINE TREE BLOWN OVER TO THE NORTHEAST
            DIRECTION AT PARKWAY DENTAL.

&&

Local storm report, May 31, 12:45 PM MST, 15 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
145 PM MDT SUN MAY 31 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0813 AM     TSTM WND GST     KALISPELL               48.20N 114.31W
05/31/2020  M55 MPH          FLATHEAD           MT   PUBLIC

&&

Local storm report, May 31, 12:47 PM MST, 13 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
147 PM MDT SUN MAY 31 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0815 AM     TSTM WND GST     8 NNE MARION            48.21N 114.61W
05/31/2020  M52 MPH          FLATHEAD           MT   PUBLIC

&&

Local storm report, May 31, 12:56 PM MST, 4 minutes before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
156 PM MDT SUN MAY 31 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1206 AM     TSTM WND GST     8 ENE LIBBY             48.43N 115.40W
05/31/2020  M56 MPH          LINCOLN            MT   MESONET

            MESONET STATION ZONM8 ZONOLITE. ALSO
            MEASURED 0.34 OF RAIN IN THE PREVIOUS HOUR.

&&

Local storm report, May 31, 12:59 PM MST, 1 minute before

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE MISSOULA MT
159 PM MDT SUN MAY 31 2020

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0830 PM     TSTM WND GST     1 E GILMORE             44.46N 113.24W
05/30/2020  M56 MPH          LEMHI              ID   DEPT OF HIGHWAYS

            GILMORE SUMMIT ON HIGHWAY 28.

&&

The radar

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

Open the radar archive at this moment

Event by event

1 flood. Local standard time, as filed.

Flood, Flathead

When: May 31, 1:00 PM MST to 11:59 PM MST
Where: Flathead County, 13.03 mi NW of Polebridge Sonderson to 2.73 mi NNW of Polebridge Sonderson
Cause: Heavy Rain / Snow Melt
Reported by: Law Enforcement
Coordinates: 49.001, -114.503

Overbank flooding was reported along much of the North Fork of the Flathead River, from the North Fork and Camas Road intersection, north to the Canadian border. While much of the adjacent areas are rural, flooding did occur on North Fork Road and other local roads around Polebridge through June 1.

What these are

Flood: Flooding that develops more slowly than a flash flood: rivers leaving their banks, or water standing over land for an extended time.

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

The same day elsewhere

Every storm in Montana in 2020 Every state in 2020 This day in weather history Warnings in Montana, May 2020

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: 884042.