Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated

Planting zone for 82643 — Midwest, WY

ZIP code 82643 (Midwest, Natrona County) is in USDA zone 5a: the coldest winter night averages −20 to −15 °F. The median last spring frost is May 22 and the first fall frost September 22.

Where ZIP 82643 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone5a−20 to −15 °F
Coldest night−28.9 to −26.1 °C
Last frostMay 22
First frostSep 22
2012 zone4b

Was 4b on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 5a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Midwest, WY…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Midwest, WY

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 22median — 50% chance of a later frost
Safe for tender plantsJune 6only 10% chance of frost after
First fall frostSeptember 22median — 10% chance by Sep 8
Growing season121 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 9 and returns around October 2.

From the NOAA station Midwest, WY — within 1 mile, elevation 4,859 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 82643

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Apr 10 – Apr 24
SpinachSow outdoors · Apr 10 – May 1
Broccoli, cabbageStart indoors · Mar 13 – Mar 27
Broccoli, cabbageTransplant · May 1 – May 15
Onion setsPlant outdoors · Apr 24 – May 8
PotatoesPlant outdoors · May 1 – May 15
LettuceSow outdoors · Apr 24 – May 8
Carrots, beetsSow outdoors · May 1 – May 15
TomatoesStart indoors · Mar 27 – Apr 10
TomatoesTransplant · May 29 – Jun 12
Peppers, eggplantStart indoors · Mar 13 – Mar 27
Peppers, eggplantTransplant · Jun 5 – Jun 19
BeansSow outdoors · May 29 – Jun 12
Sweet cornSow outdoors · May 29 – Jun 12
Cucumbers, squashSow outdoors · May 29 – Jun 12
Fall lettuce, spinachSow outdoors · Jul 28 – Aug 11
GarlicPlant cloves · Sep 8 – Oct 13
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 22) and first fall frost (Sep 22) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 82643 came on Mar 10 — 29 days earlier than the 1991–2020 average (Apr 8).

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Native plants for zone 5a in Wyoming

542 plants native to the lower 48 states, recorded in Wyoming, and rated by the USDA to survive −20 °F or colder — the bottom of zone 5a. Each links to its USDA PLANTS profile.

Trees 22

American elm120 ft · blooms early spring · medium shade tolerance · to −46 °Fbalsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °Fblue spruce100 ft · blooms late spring · medium shade tolerance · to −38 °Fboxelder60 ft · blooms early spring · low shade tolerance · to −46 °FDouglas-fir200 ft · blooms mid spring · medium shade tolerance · to −33 °F

Shrubs 98

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °Falderleaf mountain mahogany15 ft · blooms late spring · medium shade tolerance · to −41 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °FAmerican black currant3 ft · blooms early spring · to −46 °FAmerican plum24 ft · blooms mid spring · high shade tolerance · to −38 °Fantelope bitterbrush6 ft · blooms early spring · medium shade tolerance · to −36 °F

Wildflowers & perennials 249

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °Falpine sweetvetch2 ft · blooms early summer · high shade tolerance · to −62 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °F

Grasses 161

Alaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °Falkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °FAlpine Meadow-Foxtail0.5 ft · blooms mid spring · medium shade tolerance · to −33 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °Fanalogue sedge1.5 ft · blooms late spring · medium shade tolerance · to −38 °F

Vines 3

American bittersweet15 ft · blooms spring · low shade tolerance · to −38 °Friverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Fwestern white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °F

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Midwest, WY.

Soil in Midwest, WY

The soil mapped at the center of ZIP 82643 is Arvada — clay loam, well drained.

TextureClay loamholds water and nutrients; slow to drain and warm up
pH8.4alkaline; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter1.5%low — add compost
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Arvada-Absted-Slickspots complex, 0 to 6 percent slopes.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 82643; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Midwest, WY

Summer high88 °Faverage high, July
Winter low12 °Faverage low, January
Hot days37days a year at 90 °F or more
Freezing nights187nights a year at 32 °F or less
Growing degree days2,101base 50 °F — the season’s usable heat
Longest day15 h 25 mindaylight on June 21
Shortest day8 h 57 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation12.4 inper year, rain and melted snow
Snowfall46 inper year; 62 days with snow on the ground

Average high and low, by month

0°10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 36 °F, low 12 °F 36°12° JanFebruary: average high 38 °F, low 13 °F 38°13° FebMarch: average high 49 °F, low 21 °F 49°21° MarApril: average high 56 °F, low 28 °F 56°28° AprMay: average high 66 °F, low 38 °F 66°38° MayJune: average high 79 °F, low 46 °F 79°46° JunJuly: average high 88 °F, low 53 °F 88°53° JulAugust: average high 86 °F, low 50 °F 86°50° AugSeptember: average high 76 °F, low 41 °F 76°41° SepOctober: average high 61 °F, low 30 °F 61°30° OctNovember: average high 46 °F, low 20 °F 46°20° NovDecember: average high 35 °F, low 12 °F 35°12° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 0.32 in precipitation, 5 in snowfall 0.3❄5 JanFebruary: 0.53 in precipitation, 8.3 in snowfall 0.5❄8 FebMarch: 0.96 in precipitation, 7.7 in snowfall 1.0❄8 MarApril: 1.39 in precipitation, 5.7 in snowfall 1.4❄6 AprMay: 2.52 in precipitation, 0.7 in snowfall 2.5❄1 MayJune: 1.59 in precipitation 1.6 JunJuly: 1.07 in precipitation 1.1 JulAugust: 0.66 in precipitation 0.7 AugSeptember: 0.88 in precipitation, 0.3 in snowfall 0.9 SepOctober: 1.29 in precipitation, 4.1 in snowfall 1.3❄4 OctNovember: 0.57 in precipitation, 6.6 in snowfall 0.6❄7 NovDecember: 0.61 in precipitation, 7.5 in snowfall 0.6❄8 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Midwest, WY (within 1 mile); precipitation: Midwest, WY (within 1 mile). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 5a.

826355a
Edgerton, WY · 3 mi
826405a
Linch, WY · 12 mi
826015a
Casper, WY · 25 mi
826395a
Kaycee, WY · 30 mi
826025a
Casper, WY · 37 mi
826055a
Casper, WY · 38 mi
826485a
Powder River, WY · 39 mi
826465a
Natrona, WY · 39 mi

Wyoming planting zones →

Questions about 82643

What planting zone is ZIP code 82643?

ZIP code 82643 (Midwest, WY) is in USDA hardiness zone 5a on the 2023 map: the coldest night of an average winter reaches −20 to −15 °F (−28.9 to −26.1 °C).

When is the last frost in Midwest, WY?

The median last spring frost (32 °F) near 82643 is May 22; after June 6 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Midwest station.

When is the first frost in Midwest, WY?

The median first fall frost near 82643 is September 22, giving a median frost-free growing season of 121 days.

When should I plant tomatoes in 82643?

Start tomato seeds indoors around Mar 27 – Apr 10 and set transplants outside around May 29 – Jun 12, one to three weeks after the median last frost.

How much rain and snow does 82643 get?

About 12.4 inches of precipitation a year and 46 inches of snowfall (NOAA 1991–2020 normals, Midwest station).

How hot do summers get in Midwest, WY?

The average high peaks at 88 °F in July, with about 37 days a year at 90 °F or more.

What kind of soil does 82643 have?

The USDA soil survey maps Arvada at the center of ZIP 82643: clay loam, well drained, pH about 8.4 (alkaline).

Did spring come early in Midwest, WY in 2026?

Spring leaf-out near 82643 came on Mar 10 in 2026, 29 days earlier than the 1991–2020 average (Apr 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Midwest, WY?

Long-day onions: the longest day near 82643 is 15 h 25 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 82643 change?

Yes. The 2012 USDA map put 82643 in zone 4b; the 2023 map puts it in zone 5a. The newer map uses 1991–2020 data and more weather stations.