Name: Heavy Snow in Idaho, May 21 to 22, 2002
Start: 2002-05-21T20:00
End: 2002-05-22T11:00
Location: Idaho

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 PIH wrote it up.

A late spring snowstorm brought heavy snow to the Upper Snake Highlands. The heaviest snow fell overnight on the 21st and some measured totals were: 8 to 10 inches in Island Park, 6 inches in Macks Inn, 8 inches at the Sheep Mountain SNOTEL site. The snow level with this storm was around 5500 feet. Very cold air accompanied the storm throughout all of southeastern Idaho with the city of Pocatello recording a record low high temperature on the 21st of 47 degrees.

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 Pocatello, ID wrote its last area forecast discussion before the first event at May 21, 1:10 PM MST, 6 hours 50 minutes earlier.

Area forecast discussion, May 21, 1:10 PM MST, 6 hours 50 minutes before

SOUTHEAST IDAHO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE POCATELLO/IDAHO FALLS ID
210 PM MDT TUE MAY 21 2002

UPPER LOW IS TRACKING TO THE NORTHEAST OVER SE ID.  SFC ANALYSIS SHOWS
STRONG THETA-E BOUNDARY ALONG THE ID/WY BORDER.  HEAVIEST PRECIP
ACTIVITY IS LOCATED IN CONJUNCTION WITH THE THETA-E BOUNDARY AND
TRAVELING NORTH TO NORTHWESTWARD ALONG IT.  THIS AREA WILL BE THE MAIN
FOCUS FOR PRECIP FOR THE REMAINDER OF TODAY AND TONIGHT AS THE UPPER
LOW AND CYCLOGENESIS ALONG THE MT/WY BORDER ENHANCE ATMOSPHERIC LIFT.
COLD AIR ADVECTING INTO THE CWFA FROM THE SOUTHWEST...WITH THE SNOW
LEVELS DROPPING BETWEEN 5500 AND 6000 OVER THE SOUTHERN CWA SLOPING UP
TO 6500 OVER ZONE 19.  QPF AMOUNTS FROM KBYI KPIH AND KIDA...WHILE
HEAVIEST PRECIP BAND PASSED OVER EACH SITE...AVERAGED ABOUT 0.10
IN/HR.  ADDITIONALLY THE OBS SITE IN DRIGGS...ZONE 19...REPORTED 0.48
INCHES SINCE 16Z WITH A TEMP FALLING TO 34F.  THE ADDITION OF
OROGRAPHIC LIFT OVER ZONE 19 WILL ENHANCE SNOWFALL RATE AT OR JUST
ABOVE 1 INCH PER HOUR THIS EVENING AND TONIGHT.  WILL UPGRADE THE
WATCH TO A WARNING FOR ZONE 19 ABOVE 6000 FEET WITH TOTAL
ACCUMULATIONS OF 4 TO 8 INCHES BY WEDNESDAY MORNING.

SECOND AREA OF FOCUS IS THE MAIN UPPER LOW CIRCULATION IN NORTHERN
UTAH.  THIS FEATURE IS TRACKING NNE AND SHOULD MOVE INTO SRN ID THIS
EVENING.  INSTABILITY IS GREATER UNDER THIS CIRCULATION WITH NUMEROUS
SHOWERS AND THUNDERSTORMS CONTINUING TO DEVELOP THIS AFTERNOON.  LOW
WET BULB ZEROS WILL SUPPORT SMALL HAIL FROM THE STRONGER UPDRAFTS.

UPSTREAM AND IN THE LEE OF THE MT/WY ROCKIES...CYCLOGENESIS WILL
RESULT IN A STRONG SFC PRESSURE GRADIENT FOR WINDY CONDITIONS.  WITH
UPPER LOW TRACKING OVER US TONIGHT DONT THINK SNAKE PLAIN WINDS WILL
REACH ADVISORY CRITERIA.

UPPER LOW REMAINS CLOSE ENOUGH TO SE ID TO SUPPORT WINDY CONDITIONS
AND SLIGHT CHANCE POPS ALONG THE WY BORDER ON WEDNESDAY AS S/W ENERGY
ROTATES BY ON THE BACK SIDE OF THE UPPER LOW.  ANOTHER PIECE OF S/W
ENERGY MOVES IN FROM THE NORTHWEST ON THURSDAY BEFORE A RIDGE BUILDS
OVER IDAHO ON FRIDAY ALLOWING TEMPERATURES TO RETURN TO CLIMO NORMALS
ON SATURDAY.

MEMORIAL DAY WEEKEND...AVN/MRF ALONG WITH ECMWF SHOWS A TROF
APPROACHING THE COAST SUNDAY WITH A WARM SOUTHWEST FLOW AHEAD OF IT.
WILL KEEP THE CURRENT EXTENDED GOING.

BRONG

.KSFX...OPERATIONAL...VCP 21.

BYI 39/57/38/61 5311

.PIH...WINTER STORM WARNING FOR IDZ019 ABOVE 6000 FEET TONIGHT AND
       WEDNESDAY MORNING.

PIH NB 038/056 034/060 034 15632

Event by event

1 heavy snow. Local standard time, as filed.

Heavy Snow, Upper Snake Highlands

When: May 21, 8:00 PM MST to May 22, 11:00 AM MST
Where: Upper Snake Highlands forecast zone
Reported by: UNKNOWN

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

More

Every storm in Idaho in 2002 Every state in 2002 This day in weather history Warnings in Idaho, May 2002

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: 5299846.