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

Planting zone for 15633 — Forbes Road, PA

ZIP code 15633 (Forbes Road, Westmoreland County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is May 2 and the first fall frost October 14.

Where ZIP 15633 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.

Zone6b−5 to 0 °F
Coldest night−20.6 to −17.8 °C
Last frostMay 2
First frostOct 14
2012 zone6a

Was 6a 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 6b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Forbes Road, PA…

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 Forbes Road, PA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 2median — 50% chance of a later frost
Safe for tender plantsMay 18only 10% chance of frost after
First fall frostOctober 14median — 10% chance by Oct 2
Growing season163 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 22 and returns around October 25.

From the NOAA station Loyalhanna Lake, PA — 7 miles away, elevation 991 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 15633

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 21 – Apr 4
SpinachSow outdoors · Mar 21 – Apr 11
Broccoli, cabbageStart indoors · Feb 21 – Mar 7
Broccoli, cabbageTransplant · Apr 11 – Apr 25
Onion setsPlant outdoors · Apr 4 – Apr 18
PotatoesPlant outdoors · Apr 11 – Apr 25
LettuceSow outdoors · Apr 4 – Apr 18
Carrots, beetsSow outdoors · Apr 11 – Apr 25
TomatoesStart indoors · Mar 7 – Mar 21
TomatoesTransplant · May 9 – May 23
Peppers, eggplantStart indoors · Feb 21 – Mar 7
Peppers, eggplantTransplant · May 16 – May 30
BeansSow outdoors · May 9 – May 23
Sweet cornSow outdoors · May 9 – May 23
Cucumbers, squashSow outdoors · May 9 – May 23
Fall lettuce, spinachSow outdoors · Aug 19 – Sep 2
GarlicPlant cloves · Sep 30 – Nov 4
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 2) and first fall frost (Oct 14) 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 15633 came on Mar 10 — 19 days earlier than the 1991–2020 average (Mar 29).

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).

Soil in Forbes Road, PA

The soil mapped at the center of ZIP 15633 is Dormont — silt loam, moderately well drained.

TextureSilt loama good balance for most vegetables
pH6.2slightly acidic; most vegetables like 6.0–7.0
DrainageModerately well drainednatural drainage class
Organic matter2.6%moderate
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Dormont silt loam, 15 to 25 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 15633; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Forbes Road, PA

Summer high83 °Faverage high, July
Winter low19 °Faverage low, January
Hot days14days a year at 90 °F or more
Freezing nights130nights a year at 32 °F or less
Growing degree days2,771base 50 °F — the season’s usable heat
Longest day15 h 03 mindaylight on June 21
Shortest day9 h 17 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation43.4 inper year, rain and melted snow

Average high and low, by month

10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 37 °F, low 19 °F 37°19° JanFebruary: average high 40 °F, low 20 °F 40°20° FebMarch: average high 49 °F, low 27 °F 49°27° MarApril: average high 62 °F, low 36 °F 62°36° AprMay: average high 72 °F, low 46 °F 72°46° MayJune: average high 80 °F, low 55 °F 80°55° JunJuly: average high 83 °F, low 59 °F 83°59° JulAugust: average high 82 °F, low 58 °F 82°58° AugSeptember: average high 76 °F, low 51 °F 76°51° SepOctober: average high 64 °F, low 40 °F 64°40° OctNovember: average high 52 °F, low 30 °F 52°30° NovDecember: average high 41 °F, low 24 °F 41°24° Dec

Precipitation by month inches

0″1″2″3″4″5″January: 3.07 in precipitation 3.1 JanFebruary: 2.51 in precipitation 2.5 FebMarch: 3.25 in precipitation 3.3 MarApril: 3.76 in precipitation 3.8 AprMay: 4.00 in precipitation 4.0 MayJune: 4.13 in precipitation 4.1 JunJuly: 4.33 in precipitation 4.3 JulAugust: 4.60 in precipitation 4.6 AugSeptember: 4.00 in precipitation 4.0 SepOctober: 2.88 in precipitation 2.9 OctNovember: 3.34 in precipitation 3.3 NovDecember: 3.57 in precipitation 3.6 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Loyalhanna Lake, PA (7 mi away); precipitation: Loyalhanna Lake, PA (7 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6b.

156356b
Hannastown, PA · 1 mi
156626b
Luxor, PA · 2 mi
156246b
Crabtree, PA · 2 mi
156196b
Bovard, PA · 3 mi
156016b
Greensburg, PA · 3 mi
156056b
Greensburg, PA · 4 mi
156066b
Greensburg, PA · 4 mi
156266b
Delmont, PA · 5 mi

Pennsylvania planting zones →

Questions about 15633

What planting zone is ZIP code 15633?

ZIP code 15633 (Forbes Road, PA) is in USDA hardiness zone 6b on the 2023 map: the coldest night of an average winter reaches −5 to 0 °F (−20.6 to −17.8 °C).

When is the last frost in Forbes Road, PA?

The median last spring frost (32 °F) near 15633 is May 2; after May 18 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Loyalhanna Lake station.

When is the first frost in Forbes Road, PA?

The median first fall frost near 15633 is October 14, giving a median frost-free growing season of 163 days.

When should I plant tomatoes in 15633?

Start tomato seeds indoors around Mar 7 – Mar 21 and set transplants outside around May 9 – May 23, one to three weeks after the median last frost.

How much rain and snow does 15633 get?

About 43.4 inches of precipitation a year (NOAA 1991–2020 normals, Loyalhanna Lake station).

How hot do summers get in Forbes Road, PA?

The average high peaks at 83 °F in July, with about 14 days a year at 90 °F or more.

What kind of soil does 15633 have?

The USDA soil survey maps Dormont at the center of ZIP 15633: silt loam, moderately well drained, pH about 6.2 (slightly acidic).

Did spring come early in Forbes Road, PA in 2026?

Spring leaf-out near 15633 came on Mar 10 in 2026, 19 days earlier than the 1991–2020 average (Mar 29), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Forbes Road, PA?

Long-day onions: the longest day near 15633 is 15 h 03 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 15633 change?

Yes. The 2012 USDA map put 15633 in zone 6a; the 2023 map puts it in zone 6b. The newer map uses 1991–2020 data and more weather stations.