Unseasonally warm air ahead of a strong cold front provided the ingredients for severe thunderstorm development over parts of South Central Idaho on the 30th.
Every event with a place to put it. 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.
Unseasonally warm air ahead of a strong cold front provided the ingredients for severe thunderstorm development over parts of South Central Idaho on the 30th.
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 Dec 30, 2:34 PM MST, 5 hours 16 minutes earlier.
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOISE ID
234 PM MST FRI DEC 30 2011
.SHORT TERM...APPROACHING COLD FRONT HAS A FLAT WAVE ON IT IN
CENTRAL OREGON WHICH WILL SLIGHTLY SLOW FORWARD SPEED OF THE
FRONT...NOW DUE IN SWRN IDAHO 00Z-03Z THIS EVENING AND SCENTRAL
IDAHO 03Z-06Z. LIFTED INDEX GOES SLIGHTLY NEGATIVE IN BOTH GFS
AND NAM THIS EVENING IN WRN AND SWRN IDAHO FOR A SLIGHT CHANCE OF
THUNDERSTORMS...BEST CHANCE RIGHT ALONG THE FRONT. TIGHT EAST-WEST
SURFACE PRESSURE GRADIENT UNDER STRONG W-NW FLOW ALOFT REMAINS
FAVORABLE FOR A WIND EVENT TONIGHT IN THE SNAKE BASIN AND WIND
ADVISORY CONTINUES IN ZONES LISTED BELOW. TEMPS AND SNOW LEVEL
WILL FALL SHARPLY TONIGHT BEHIND FROPA AND RAIN SHOWERS WILL CHANGE
TO SNOW SHOWERS...ALTHOUGH MOST OF THE SHOWERS WILL BE AHEAD OF THE
FRONT IN THE WARMER AIR. SURFACE HIGH PRESSURE WILL BUILD RAPIDLY
IN FROM THE WEST OVERNIGHT AND WINDS WILL DIE DOWN SATURDAY...BUT
MODERATE NWLY WINDS WILL CONTINUE AT HIGHER ELEVATIONS. CLEARING
SATURDAY NIGHT WITH LIGHT WINDS WILL ALLOW GOOD RADIATIONAL COOLING
AND COLDER MIN TEMPS NEW YEARS MORNING. WE DON/T SEE A FOG EVENT
JUST YET AS THE AIR MASS WILL BE RAPIDLY DRYING SATURDAY AND
SATURDAY NIGHT. DRY WITH NORMAL MAX TEMPS NEW YEARS DAY UNDER
BUILDING UPPER RIDGE.
.LONG TERM...SUNDAY NIGHT THROUGH FRIDAY...THE UPPER LEVEL RIDGE
REMAINS IN PLACE OVER THE INTERMOUNTAIN REGION THROUGH WEDNESDAY...
ALONG WITH THE VALLEY TEMPERATURE INVERSION. ON MONDAY A SHALLOW
SHORTWAVE TROUGH WEAKENS CONSIDERABLY AS IT CROSSES NORTHERN IDAHO
WITH LITTLE EFFECT OTHER THAN TEMPORARILY WEAKENING THE INVERSION.
THIS WILL ALLOW HIGH TEMPERATURES ON MONDAY TO BE SLIGHTLY WARMER
THAN SUNDAY. THE RIDGE BREAKS DOWN THURSDAY ALLOWING AN UPPER LEVEL
TROUGH TO DEEPEN OVER THE REGION ON FRIDAY. MODELS HAVE BEEN
CONSISTENTLY SHOWING THIS PATTERN SHIFT AND ECMWF/GFS ENSEMBLE MEANS
ARE IN CLOSE AGREEMENT. ON THURSDAY THIS CHANGE WILL BRING A CHANCE
OF SNOW SHOWERS...ALONG WITH WARMING DUE TO MIXING OUT OF THE
INVERSION. ON FRIDAY COOLER AIR ALOFT WILL LOWER TEMPERATURES A FEW
DEGREES AND LOWER SNOW LEVELS TO THE LOWER VALLEYS.
&&
.AVIATION...WIDESPREAD PRECIPITATION WILL CONTINUE THIS EVENING AS A
COLD FRONT CROSSES THE AREA. VALLEYS WILL CONTINUE VFR WITH AREAS OF
LOW VFR CEILINGS. MOUNTAINS WILL SEE WIDESPREAD MVFR CEILINGS/LOCAL
IFR CONDITIONS. SNOW LEVELS...3K FEET MSL IN THE NORTH TO 5K FEET
MSL IN THE SOUTH LOWERING TO THE VALLEY FLOORS AFTER 06Z. SURFACE
WINDS...WEST TO NORTHWEST 20-35 KTS GUSTING TO 45 KTS 03Z-10Z
DECREASING TO 10-20 KTS AFTER 10Z. WINDS ALOFT...WEST UP TO 50 KTS
AT 12K FEET MSL.
SATURDAY AND SUNDAY...VFR EXCEPT LOCALLY LOWER CONDITIONS IN SNOW
SHOWERS OVER THE CENTRAL IDAHO MOUNTAINS SATURDAY MORNING.
&&
.BOI WATCHES/WARNINGS/ADVISORIES...
ID...WIND ADVISORY FROM 8 PM THIS EVENING TO 3 AM MST SATURDAY
IDZ014>016-030.
OR...NONE.
&&
WEATHER.GOV/BOISE
SHORT TERM...LC
LONG TERM....JT/BB
AVIATION.....JTHAZARDOUS WEATHER OUTLOOK NATIONAL WEATHER SERVICE BOISE ID 551 AM MST FRI DEC 30 2011 IDZ015-016-030-311300- SOUTHWEST HIGHLANDS-WESTERN MAGIC VALLEY- SOUTHERN TWIN FALLS COUNTY- 551 AM MST FRI DEC 30 2011 THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL IDAHO AND SOUTHWEST IDAHO. .DAY ONE...TODAY AND TONIGHT A WIND ADVISORY IS IN EFFECT FROM 11 PM MST TONIGHT THROUGH 5 AM MST SATURDAY MORNING. A STRONG COLD FRONT WILL MOVE THROUGH THE AREA DURING THIS TIME...CAUSING SUSTAINED WINDS OF 30 TO 40 MPH WITH GUSTS AS HIGH AS 55 MPH ALONG AND BEHIND THE FRONT. STRONG WINDS WILL ALSO BE ACCOMPANIED BY REDUCED VISIBILITIES IN RAIN OR SNOW. REFER TO THE WIND ADVISORY PRODUCT...BOINPWBOI...FOR MORE INFORMATION. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER VIA ESTABLISHED PROCEDURES. IDZ011>014-028-029-033-ORZ061>064-311300- WEST CENTRAL MOUNTAINS-LOWER TREASURE VALLEY ID-BOISE MOUNTAINS- UPPER TREASURE VALLEY-CAMAS PRAIRIE-OWYHEE MOUNTAINS- UPPER WEISER RIVER-HARNEY COUNTY-BAKER COUNTY-MALHEUR COUNTY- LOWER TREASURE VALLEY OR- 551 AM MST FRI DEC 30 2011 /451 AM PST FRI DEC 30 2011/ THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST IDAHO...WEST CENTRAL IDAHO...NORTHEAST OREGON AND SOUTHEAST OREGON. .DAY ONE...TODAY AND TONIGHT A STRONG COLD FRONT WILL SPREAD ADDITIONAL PRECIPITATION ACROSS THE FORECAST AREA THROUGH TONIGHT. EXPECT GUSTY WINDS...RAIN AND SNOW...AND RAPIDLY FALLING TEMPERATURES AS THE FRONT MOVES EAST ACROSS THE AREA BEGINNING THIS AFTERNOON. .DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY NO HAZARDOUS WEATHER IS EXPECTED AT THIS TIME. .SPOTTER INFORMATION STATEMENT... SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER VIA ESTABLISHED PROCEDURES.
PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BOISE ID
717 PM MST FRI DEC 30 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0455 PM TSTM WND GST 3 SE CALDWELL 43.63N 116.63W
12/30/2011 M55.00 MPH CANYON ID OFFICIAL NWS OBS
0618 PM TSTM WND GST N MOUNTAIN HOME AIR FOR 43.05N 115.87W
12/30/2011 M52.00 MPH ELMORE ID OFFICIAL NWS OBS
&&
TWBPRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE BOISE ID
743 PM MST FRI DEC 30 2011
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0742 PM TSTM WND GST 5 WSW TWIN FALLS 42.53N 114.55W
12/30/2011 M54.00 MPH TWIN FALLS ID TRAINED SPOTTER
SUSTAINED WINDS OF 40 WITH GUSTS TO 54
&&
TWBThe Pocatello radar (KSFX), 165 km away, was scanning. The volume nearest the first event began at 02:50 UTC.
1 thunderstorm wind. Local standard time, as filed.
The Twin Falls ASOS at Kimberly reported a wind gust of 68 MPH and the Idaho Department of Transportation automated observation system on the Hansen Bridge reported a gust of 67 MPH as a line of thunderstorms passed through the Twin Falls area.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Idaho in 2011Every state in 2011This day in weather historyWarnings in Idaho, December 2011
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: 354943.