Heavy Snow in Idaho, May 22 to 23, 2010

Name: Heavy Snow in Idaho, May 22 to 23, 2010
Start: 2010-05-22T18:00
End: 2010-05-23T10:00
Location: Idaho

May 22 to 23, 2010 · NWS MSO · 1 event in 1 county or zone

A broad and cold upper level trough of low pressure moved over the northern Rockies, providing moisture to most locations across western Montana and north central Idaho. Snow levels lowered enough to impact mountain passes with accumulating snow.

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.

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.

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 22, 5:47 PM MST, 13 minutes earlier.

Area forecast discussion, May 22, 5:47 PM MST, 13 minutes before

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE MISSOULA MT
647 PM MDT SAT MAY 22 2010

.UPDATE...LOWERED THE CHANCE OF PRECIPITATION IN NORTHWEST MONTANA
FOR TONIGHT.

&&

.DISCUSSION...RADAR HAS SHOWN MOSTLY CONVECTIVE DRIVEN SHOWERS
ACROSS NORTHWEST MONTANA THIS EVENING WHICH SHOULD DISSIPATE
SHORTLY AFTER SUNSET. BEFORE THEY DISSIPATE GUSTY WINDS CAN BE
EXPECTED NEAR THESE SHOWERS. A NARROW BAND OF SHOWERS MOVING
THROUGH EASTERN WASHINGTON MAY HOLD TOGETHER LONG ENOUGH TO AFFECT
CENTRAL IDAHO SO LEFT THE POTENTIAL FOR SHOWERS IN THIS AREA FOR
TONIGHT. A BAND OF RAIN AND SNOW STRETCHING FROM SOUTHERN IDAHO TO
BUTTE WILL LIKELY PERSIST FOR MUCH OF THE NIGHT SO SNOW
ACCUMULATIONS ARE STILL LIKELY ACROSS LEMHI COUNTY...SILVER BOW
AND DEER LODGE COUNTIES.

&&

.AVIATION...THE ATMOSPHERE REMAINS QUITE MOIST AND UNSTABLE UNDER
A BROAD UPPER LEVEL TROUGH OF LOW PRESSURE. CLOUDS AND SHOWERS
WILL PERIODICALLY OBSCURE THE MOUNTAINS AND PASSES THROUGH THE NEXT
24 HOURS. A FEW THUNDERSTORMS ARE EXPECTED OVER NORTH-CENTRAL
IDAHO AND PORTIONS OF WESTERN MONTANA THROUGH THIS EVENING. THESE
THUNDERSTORM AND EVEN SOME OF THE HEAVIER SHOWERS MAY PRODUCE
SMALL HAIL AND GUSTY WINDS. VISIBILITY AND CEILINGS WILL BE
REDUCED AT TIMES OVER TERMINALS KMSN AND KBTM AS SHOWERS PASS
OVER THESE AREAS TONIGHT.

&&

.PREV DISCUSSION... /ISSUED 250 PM MDT SAT MAY 22 2010/

DISCUSSION...
TONIGHT THROUGH SUNDAY NIGHT...

RADAR AND SATELLITE IMAGERY SHOWING AN INCREASING TREND IN
CONVECTIVE SHOWER DEVELOPMENT THIS AFTERNOON. THE COOL MOIST
UNSTABLE ATMOSPHERE WILL RESIDE OVER THE NORTHERN ROCKIES REGION
THROUGH THIS PERIOD. THERE ARE TWO DISTINCT AREAS WHERE THE BEST
DYNAMICS AND INSTABILITY EXIST THIS AFTERNOON/EVENING FOR
THUNDERSTORM DEVELOPMENT: 1) CENTERED OVER THE CLEARWATER
MOUNTAINS OF NORTH CENTRAL IDAHO AND THE NORTHWEST CORNER OF
MONTANA...AND 2) ACROSS EASTERN LEMHI COUNTY IN NORTH CENTRAL
IDAHO. BRIEF GUSTY WINDS AND SMALL HAIL (PEA-SIZED OR SMALLER) MAY
ACCOMPANY ANY STORM THAT DEVELOPS. SNOW LEVELS WILL REMAIN LOW
ENOUGH TO IMPACT MANY MOUNTAIN PASSES WITH THE GREATEST POTENTIAL
FOR SIGNIFICANT SNOW OVER THE MOUNTAIN PASSES BETWEEN EASTERN
LEMHI AND BEAVERHEAD COUNTIES...AND THE GEORGETOWN LAKE AREA
TONIGHT. ANOTHER COOL SHOWERY DAY IS EXPECTED FOR SUNDAY.

MONDAY...THE NEXT WEATHER FEATURE OF INTEREST WILL BE SPREADING
CONSIDERABLE MOISTURE INTO LEMHI COUNTY AND THE BETTER PORTION
OF WESTERN MONTANA. THIS FEATURE MAY TAP INTO SOME ADDITIONAL SUB-
TROPICAL MOISTURE AS IT APPROACHES FROM THE SOUTH...RESULTING IN
MODERATE PRECIPITATION OVER THE MOUNTAINS ALONG THE CONTINENTAL
DIVIDE.

MONDAY NIGHT THROUGH TUESDAY...THE LATEST MODEL RUNS SHOW THIS
FEATURE TRACKING INTO WYOMING MONDAY NIGHT RATHER THAN THROUGH
SOUTHEASTERN IDAHO...AND UP INTO SASKATCHEWAN CANADA ON TUESDAY.
AT THIS TIME...THE HEAVIEST PRECIPITATION IS STILL EXPECTED TO
OCCUR MAINLY OVER SOUTHWEST MONTANA AND ALONG THE CONTINENTAL DIVIDE
MONDAY NIGHT AND QUICKLY MOVE NORTHWARD ALONG THE DIVIDE AND OUT
OF THE REGION TUESDAY. THE POTENTIAL STILL EXISTS FOR THIS SYSTEM
TO TAP INTO GULF OF MEXICO MOISTURE WHICH COULD FURTHER ENHANCE
PRECIPITATION IN FAVORED UPSLOPE AREAS ALONG THE DIVIDE...
PARTICULARLY IN THE GLACIER PARK REGION. FORECAST MODELS ARE
KEEPING SNOW LEVELS FAIRLY HIGH WITH THIS SYSTEM WHICH COULD
RESULT IN TRAVEL IMPACTS OVER MOUNTAIN PASSES AND HIGHER
ELEVATIONS DUE TO LIGHT SNOW ACCUMULATIONS. ELSEWHERE IN THE
NORTHERN ROCKIES...MOST LOCATIONS SHOULD RECEIVE MEASURABLE
RAINFALL MONDAY NIGHT AS THE REGION REMAINS UNDER AN UNSTABLE
NORTHWEST FLOW ALOFT. OVERALL THERE REMAINS A LEVEL OF UNCERTAINTY
REGARDING TIMING AND PLACEMENT OF THIS SYSTEM SINCE FORECAST
MODELS ARE TRENDING TOWARD THE BULK OF MOISTURE AND ENERGY
POTENTIALLY STAYING FURTHER EAST OF THE DIVIDE DURING THIS
TIMEFRAME. WILL CONTINUE TO MONITOR THIS SYSTEM FOR MORE
DEFINITIVE DETAILS.

TUESDAY NIGHT THROUGH FRIDAY...A BRIEF BREAK IN PRECIPITATION IS
POSSIBLE TUESDAY NIGHT AS YET ANOTHER CLOSED LOW PRESSURE SYSTEM
BEGINS TO IMPACT THE INTERMOUNTAIN WEST WEDNESDAY THROUGH FRIDAY.
INCREASED SOUTHERLY FLOW ON WEDNESDAY SHOULD ADVECT WARMER AIR INTO
THE REGION...POTENTIALLY MAKING WEDNESDAY THE WARMEST DAY OF THE
WEEK. WITH DIFFLUENT FLOW ALOFT...THE POTENTIAL FOR AFTERNOON
THUNDERSTORM DEVELOPMENT EXISTS...HOWEVER MODEL INCONSISTENCIES
WITH THE MONDAY SYSTEM ARE ADVERSELY IMPACTING THE TIMING OF THE
WEDNESDAY SYSTEM AND HAVE OPTED TO KEEP THUNDERSTORM MENTION OUT
OF THE FORECAST FOR THE TIME BEING. THE REMAINDER OF THE WORK WEEK
WILL FALL UNDER THE INFLUENCE OF THIS LOW...WHICH WILL RESULT IN
CONTINUED WET CONDITIONS AND DAYTIME TEMPERATURES COOLER THAN
NORMAL.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...WINTER WEATHER ADVISORY UNTIL 6 AM MDT SUNDAY ABOVE 6000 FEET
     FOR THE BUTTE/BLACKFOOT REGION.

ID...WINTER WEATHER ADVISORY UNTIL 6 AM MDT SUNDAY ABOVE 6000 FEET
     FOR THE EASTERN LEMHI COUNTY.

&&

UPDATE/AVIATION...LOEFFELBEIN
PREVIOUS DISCUSSION....MSJ/KITSMILLER

The radar

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

Open the radar archive at this moment

Event by event

1 heavy snow. Local standard time, as filed.

Heavy Snow, Eastern Lemhi County

When: May 22, 6:00 PM MST to May 23, 10:00 AM MST
Where: Eastern Lemhi County forecast zone
Reported by: COOP Observer
Coordinates: 44.943, -113.933 (the zone’s center; the record gives no point)

Four inches of snow was observed by the Co-Op observer in May. Four inches of snow was also reported 9 miles southeast of Salmon by a trained spotter. Power was out from Barker to Tendoy for twelve hours with broken branches and downed trees reported due to the heavy, wet snow.

What these are

Heavy Snow: Snowfall reaching the local warning threshold without the other hazards of a winter storm.

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

The same day elsewhere

Every storm in Idaho in 2010 Every state in 2010 This day in weather history Warnings in Idaho, May 2010

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: 230855.