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Idaho frost dates

Across 127 NOAA climate stations in Idaho, the median last spring frost (32°F) ranges from Apr 2 at Brownlee Dam to Jun 22 at Mccall; the typical station sees its last frost around May 16 and its first fall frost around Sep 29.

“Median” dates have a 50% chance of a later spring frost or an earlier fall frost. “10% risk” dates are the safer choice for tender plants: only 1 year in 10 has frost beyond them. Source: NOAA NCEI 1991–2020 Climate Normals. Elevation matters: within a state, frost dates can differ by a month or more between valleys and hills.

StationElevationLast frost (median)Last frost (10% risk)First frost (median)First frost (10% risk)Growing season
Aberdeen Exp Stn4,405 ftMay 21Jun 13Sep 20Sep 2118 days
American Falls4,510 ftMay 4May 21Oct 8Sep 22155 days
American Falls 6 Ne4,415 ftMay 14Jun 4Oct 2Sep 16138 days
Arco5,325 ftMay 22Jun 9Sep 22Sep 4119 days
Arco 17 Sw5,920 ftMay 24Jun 15Oct 1Sep 16130 days
Arrowrock Dam3,235 ftApr 28May 16Oct 14Oct 1169 days
Ashton 1N5,212 ftMay 21Jun 13Sep 21Sep 4121 days
Bayview Model Basin2,087 ftMay 22Jun 6Sep 22Sep 3122 days
Bellevue5,192 ftMay 13Jun 3Oct 2Sep 15139 days
Bern5,964 ftJun 17Jul 4Sep 3Aug 1877 days
Blackfoot Fire Dept4,499 ftMay 5May 22Oct 3Sep 16149 days
Boise 7 N3,885 ftMay 17Jun 10Oct 12Sep 27147 days
Boise Air Terminal2,814 ftApr 24May 9Oct 21Oct 5179 days
Boise Lucky Peak Dam2,840 ftApr 30May 18Oct 22Sep 30173 days
Bonners Ferry2,075 ftApr 30May 16Oct 4Sep 18154 days
Brownlee Dam1,844 ftApr 2Apr 20Nov 5Oct 24216 days
Bruneau2,530 ftApr 17May 7Oct 17Oct 1181 days
Buhl #23,800 ftApr 25May 10Oct 15Sep 29172 days
Burley Muni AP4,142 ftMay 7May 23Oct 4Sep 21150 days
Cabinet Gorge2,173 ftMay 9May 25Oct 8Sep 25153 days
Cambridge2,650 ftMay 15Jun 4Sep 27Sep 12134 days
Cascade 1 Nw4,896 ftMay 30Jun 21Sep 19Sep 3110 days
Castleford 2 N3,825 ftMay 17Jun 5Sep 29Sep 11132 days
Challis AP5,033 ftMay 14Jun 2Sep 25Sep 10131 days
Chilly Barton Flat6,260 ftJun 14Jun 30Sep 8Aug 2686 days
Coeur D'Alene2,133 ftApr 22May 6Oct 18Oct 4179 days
Cottonwood 2 Wsw3,945 ftMay 6May 26Oct 13Sep 28156 days
Council2,943 ftMay 10Jun 1Oct 2Sep 16145 days
Craters Of The Moon5,914 ftJun 19Jul 2Sep 9Aug 2581 days
Deer Flat Dam2,510 ftApr 23May 9Oct 18Oct 2178 days
Downey4,865 ftMay 31Jun 16Sep 18Sep 3110 days
Driggs6,120 ftJun 13Jun 28Sep 9Aug 2686 days
Dubois Exp Stn5,450 ftMay 18Jun 9Sep 30Sep 14132 days
Dworshak Fish Hatchery995 ftApr 20May 5Oct 20Sep 30182 days
Elk Rvr2,866 ftMay 16Jun 1Sep 23Sep 6128 days
Emmett 2 E2,390 ftApr 30May 17Oct 17Oct 2168 days
Fairfield Rs5,065 ftJun 8Jun 28Sep 14Aug 2997 days
Fenn Rs1,560 ftApr 26May 9Oct 20Oct 1176 days
Ft Hall 1 Nne4,465 ftMay 20Jun 12Sep 20Sep 1119 days
Garden Valley3,100 ftJun 1Jun 20Sep 10Aug 28102 days
Gibbonsville #24,480 ftJun 1Jun 19Sep 17Sep 2107 days
Glenns Ferry2,466 ftMay 1May 16Oct 3Sep 16154 days
Grace5,550 ftMay 29Jun 16Sep 17Sep 1111 days
Grand View 4 Nw2,400 ftApr 28May 13Oct 6Sep 24162 days
Grangeville3,300 ftMay 9May 27Oct 3Sep 14146 days
Hagerman 2 Sw2,897 ftMay 3May 17Oct 1Sep 16151 days
Hamer 4 Nw4,790 ftJun 3Jun 21Sep 11Aug 3098 days
Hazelton4,060 ftMay 7May 26Oct 5Sep 19149 days
Hill City 1 W5,100 ftJun 16Jul 3Sep 6Aug 2080 days
Homedale 1 Se2,230 ftApr 24May 5Oct 9Sep 26169 days
Howe4,820 ftMay 24Jun 14Sep 14Sep 1113 days
Idaho City3,965 ftJun 17Jul 4Sep 5Aug 2380 days
Idaho Falls - Kifi4,742 ftMay 9Jun 2Oct 1Sep 17142 days
Idaho Falls 16 Se5,828 ftJun 9Jun 26Sep 11Aug 2793 days
Idaho Falls 46 W4,938 ftJun 11Jul 1Sep 6Aug 2489 days
Idaho Falls Fanning Fld4,729 ftMay 23Jun 13Sep 20Sep 1114 days
Jerome3,740 ftMay 2May 30Oct 14Sep 30166 days
Jerome Co AP4,048 ftMay 1May 16Oct 14Sep 29165 days
Kamiah1,210 ftApr 29May 12Oct 5Sep 22163 days
Kellogg2,377 ftMay 14Jun 3Sep 26Sep 9131 days
Kooskia 5 Sse2,330 ftApr 30May 13Oct 11Sep 19162 days
Lava Hot Springs4,595 ftMay 21Jun 11Sep 21Sep 3118 days
Lewiston Nez Perce Co AP1,436 ftApr 6Apr 26Oct 26Oct 10200 days
Lifton Pumping Stn5,935 ftMay 19Jun 5Sep 21Sep 5123 days
Lowell Three Rivers1,480 ftApr 16May 4Oct 25Oct 5191 days
Lowman3,920 ftJun 6Jul 1Sep 4Aug 1987 days
Mackay Lost Rvr Rs5,897 ftJun 1Jun 21Sep 20Sep 4109 days
Malad City4,470 ftMay 22Jun 16Sep 20Sep 4116 days
Malta4,521 ftJun 5Jun 23Sep 13Aug 2896 days
Malta 4 Ese4,590 ftJun 1Jun 19Sep 19Sep 2111 days
Massacre Rocks Sp4,195 ftMay 20Jun 9Sep 26Sep 8125 days
May 2SSE5,050 ftJun 12Jun 29Sep 6Aug 2385 days
Mccall5,025 ftJun 22Jul 10Sep 2Aug 1472 days
Mccall AP5,013 ftJun 10Jun 28Sep 10Aug 2993 days
Mccammon4,770 ftMay 23Jun 10Sep 24Sep 7121 days
Middle Fork Lodge4,480 ftMay 21Jun 13Sep 18Sep 3115 days
Minidoka Dam4,164 ftMay 16Jun 5Oct 1Sep 13136 days
Monteview4,815 ftJun 12Jun 30Sep 7Aug 2587 days
Mtn Home3,140 ftMay 2May 23Oct 8Sep 25157 days
Mullan3,201 ftMay 12Jun 19Sep 30Sep 12138 days
Mullan Pass Vor/Dme6,028 ftJun 10Jun 25Sep 23Sep 4104 days
Murphy 10 W3,950 ftMay 17Jun 6Sep 30Sep 14134 days
Nampa Sugar Factory2,470 ftApr 29May 18Oct 13Sep 29164 days
Nezperce3,248 ftMay 24Jun 19Sep 20Sep 1116 days
Oakley4,559 ftMay 15Jun 6Oct 2Sep 16137 days
Ola3,075 ftMay 31Jun 19Sep 16Sep 2108 days
Parma Exp Stn2,290 ftApr 27May 9Oct 9Sep 26165 days
Paul 1ENE4,150 ftMay 6May 22Oct 6Sep 22151 days
Payette2,150 ftApr 19May 5Oct 20Oct 6183 days
Picabo4,839 ftJun 16Jun 30Sep 9Aug 2585 days
Pierce3,080 ftJun 3Jun 29Sep 7Aug 2293 days
Plummer 3 Wsw2,905 ftMay 11Jun 4Oct 5Sep 15143 days
Pocatello 2 Ne4,832 ftMay 16Jun 6Oct 2Sep 14137 days
Pocatello City4,460 ftMay 2May 18Oct 11Sep 26161 days
Pocatello Rgnl AP4,478 ftMay 23Jun 13Sep 18Sep 3117 days
Porthill 1 Sw1,799 ftMay 4May 28Sep 30Sep 10145 days
Potlatch 3 Nne2,760 ftMay 15Jun 2Sep 21Aug 31126 days
Powell3,530 ftMay 31Jun 26Sep 12Aug 28102 days
Preston4,719 ftMay 16Jun 4Sep 28Sep 14133 days
Prichard 3 Ese2,547 ftMay 31Jun 23Sep 5Aug 2095 days
Priest Rvr Exp Stn2,371 ftMay 20Jun 4Sep 13Sep 1114 days
Rexburg Byu Idaho5,005 ftMay 12Jun 2Sep 24Sep 6132 days
Rexburg Madison Co AP4,858 ftMay 15Jun 3Sep 23Sep 8129 days
Reynolds3,930 ftMay 21Jun 12Sep 28Sep 13126 days
Richfield4,309 ftMay 24Jun 14Sep 26Sep 10123 days
Rigby4,856 ftMay 9May 25Oct 5Sep 21148 days
Riggins2,056 ftMay 6May 26Oct 9Sep 24155 days
Saint Anthony4,910 ftMay 17Jun 10Sep 22Sep 5126 days
Saint Maries2,151 ftMay 3May 18Oct 4Sep 18152 days
Salmon-Ksra3,953 ftMay 17Jun 9Sep 24Sep 9127 days
Sandpoint Exp Stn2,126 ftMay 8May 25Sep 28Sep 11141 days
Shoshone 1 Wnw3,950 ftApr 24May 12Oct 16Oct 2173 days
Shoup3,400 ftMay 3May 21Oct 8Sep 24157 days
Silver City 5 W6,160 ftMay 31Jun 17Oct 6Sep 10128 days
Small 6N5,740 ftJun 5Jun 21Sep 20Sep 3106 days
Sugar City4,925 ftMay 29Jun 18Sep 13Aug 30106 days
Swan Falls Ph2,325 ftApr 12May 6Oct 26Oct 9193 days
Taylor Rch3,835 ftMay 11Jun 1Sep 30Sep 15140 days
Tetonia Exp Stn6,170 ftJun 15Jun 29Sep 7Aug 2485 days
Twin Falls 6 E3,960 ftMay 6May 26Oct 3Sep 16150 days
Twin Falls Sun Vly Rgnl AP4,151 ftMay 9May 28Oct 4Sep 20147 days
Twin Falls-Kmvt3,670 ftApr 30May 14Oct 9Sep 24161 days
Wallace2,710 ftMay 5May 21Oct 2Sep 17149 days
Weiser2,120 ftApr 23May 10Oct 13Oct 1174 days
Winchester3,972 ftMay 23Jun 19Sep 25Sep 7121 days
Yellowpine5,050 ftJun 12Jul 5Sep 11Aug 2688 days
Yellowpine Bar2,480 ftMay 2May 14Oct 10Sep 26159 days
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