Pennsylvania Freeze-Thaw Cycles by Town (NOAA) and How to Build

At the Pennsylvania weather stations we checked, the air drops to freezing and climbs back above it anywhere from about 50 to 131 days a year, based on NOAA’s 1991–2020 climate normals. In the West Branch valley, Lock Haven averages about 109 of these freeze-thaw days and Williamsport about 95; State College gets about 87. Every one of those days is a chance for water in concrete, under pavers or behind a wall to freeze, expand and do damage. Below are the counts by town, how they compare with the rest of the country, and the build practices that hold up.

How many freeze-thaw days does each Pennsylvania town get?

NOAA publishes, for each station, the average number of days a year with a low at or below 32°F (freezing nights) and with a high at or below 32°F (days that stay frozen). Subtract the second from the first and you get the days that freeze and then thaw. Averages for 1991–2020:

NOAA station	Freezing nights	Stays frozen all day	Freeze-thaw days
Clarence (Centre County)	175.4	44.2	131.2
Clarion 3 SW	155.2	41.4	113.8
Renovo	138.4	28.1	110.3
Lock Haven Sewage Plant	138.4	29.0	109.4
Bradford Regional Airport	160.4	60.7	99.7
Allentown International Airport	118.1	22.0	96.1
Williamsport	121.8	26.9	94.9
Wilkes-Barre International Airport	121.8	34.8	87.0
State College	121.5	34.9	86.6
Linesville 1 S	135.5	48.9	86.6
Harrisburg Capital City Airport	101.5	17.0	84.5
Pittsburgh International Airport	113.6	31.7	81.9
Erie International Airport	111.4	41.6	69.8
Philadelphia International Airport	77.3	13.1	64.2
Philadelphia Franklin Institute	62.4	12.3	50.1

Colder doesn’t always mean more freeze-thaw. Bradford has the most freezing nights in the table after Clarence, but about 61 of its days never get above freezing, so it ends up with fewer freeze-thaw days than Lock Haven. State College trails Lock Haven for the same reason: about 35 days stay frozen there, against 29 in Lock Haven and 27 in Williamsport. The places that take the most cycles are the ones with many freezing nights and winter afternoons that still climb above 32°F.

How does Pennsylvania compare with other states?

Using the same NOAA normals and the same count, Philadelphia’s airport (64) lands between New York’s Central Park (about 51) and Baltimore-Washington International (about 83). Central Pennsylvania runs higher: Lock Haven’s 109 is closer to Denver International Airport (134) and Cheyenne, Wyoming (about 138) than to Philadelphia, and Clarence in Centre County nearly matches them at 131. Los Angeles International Airport averages none.

What does freeze-thaw do to concrete?

Concrete soaked with water expands when that water freezes, and the pressure builds inside the slab. The National Ready Mixed Concrete Association’s guide to scaling (CIP 2) explains that air-entrained concrete, which has tiny air bubbles mixed in, relieves that pressure. Deicers make it worse by keeping the surface wetter and adding more freeze-thaw cycles. The usual result is scaling: the top surface flakes off, starting in small patches that can spread.

What holds up in Pennsylvania winters:

• Air-entrained concrete. PennDOT designs its concrete at 6.0% air in the plastic state, 7.0% for paving and bridge decks, held within 1.5 points during placement, using an air-entraining admixture (Pub. 408/2020, Section 704). NRMCA recommends about 6% total air for concrete with ¾- or 1-inch stone.
• Enough strength. NRMCA calls for 4,000 psi for exterior slabs that stay moist and see deicers or freezing, and 3,500 psi where they won’t.
• Don’t water it down on site. NRMCA suggests a 3- to 5-inch slump and says not to add excessive water at the jobsite.
• Proper finishing and curing. Don’t finish while bleed water is on the surface, skip the steel trowel outside, and cure with a membrane or wet burlap and plastic.
• Go easy on deicers. No deicers on new concrete the first winter, moderate amounts after. NRMCA says never to use ammonium sulfate, ammonium nitrate or magnesium-based salts. A breathable silane or siloxane sealer, applied once the slab is dry, also helps.
• Watch the calendar. PennDOT’s cold-weather rules kick in when concrete is placed below 40°F or the forecast drops to 40°F within 24 hours. NRMCA warns against pouring exterior concrete late in fall when it may freeze while still saturated.

What does freeze-thaw do to pavers and patios?

Most of the damage comes from the ground, not the paver. NRCS describes frost action as soil moisture moving into the freezing zone and forming ice lenses that push the ground up (frost heave), followed by a loss of strength when it thaws. Silty soils and structured clays with a high winter water table are the most prone, and well-drained gravelly or sandy soils the least. That’s why a patio heaves and settles when it sits on wet, silty ground with a thin base.

• Base and drainage: a compacted aggregate base, thicker on wet or weak soil, and a surface sloped so water runs off. The Concrete Masonry and Hardscapes Association (CMHA) calls for slopes of at least 1.5% in its paver construction guide (PAV-TEC-002). See PA gravel sizes for which stone to use.
• The pavers themselves: ASTM C936, the standard for concrete pavers, includes freeze-thaw and deicing-salt durability criteria, tested under ASTM C1645. The standard also has an optional colder test for regions with severe freezing (CMHA PAV-FAQ-001). Ask which test your paver line passed.
• Ice melt: CMHA calls rock salt the least damaging, says to use calcium chloride only when you need something faster, and to avoid magnesium chloride and CMA. Don’t over-apply, follow the recommended dosage, and promptly clear loosened snow, ice and excess salt.

What about retaining walls and asphalt?

Block walls. Dry-cast segmental retaining wall block is tested for freeze-thaw under ASTM C1262, in plain water or a 3% salt solution depending on how the block will be used. A wall beside a salted driveway or walk is the salt case, so ask for block tested that way. Behind the wall, frost action needs water, so the clean drainage stone and drain pipe matter as much as the block.

Asphalt. The University of Michigan’s Great Lakes climate program, GLISA, notes that repeated freezing and thawing damages roads, including by forming potholes, and NRCS lists pavements among what frost heave and thaw weakening damage. Our advice for driveways: keep water off and out of the base. That means crown or slope the surface, keep the edges from ponding, and fill cracks before winter.

Is a freeze-thaw day the same as frost depth?

No. Freeze-thaw days count how often the air crosses 32°F at the weather station. Frost depth is how far freezing reaches into the ground, and it’s what sets footing depth for decks, additions and walls. In Pennsylvania that number comes from your municipality or its code agency. See frost line depth in Pennsylvania.

Is Pennsylvania getting fewer freeze-thaw cycles?

Probably, with a lot of uncertainty. GLISA finds that freeze-thaw cycles have dropped across the Great Lakes region, most between 2000 and 2020, and projects fewer cycles in places like Ohio, Illinois and Pennsylvania as winters warm. It stresses that the projections depend on the time period and the definition used. The normals here are 30-year averages, so any single winter can run well above or below them.

How we counted

NOAA’s annual normals give each station’s average number of days with a minimum temperature at or below 32°F and with a maximum at or below 32°F (NCEI documentation). A day that stays frozen is counted in both, so the difference is the days that freeze and thaw. NOAA doesn’t publish a freeze-thaw count; the subtraction is ours. GLISA counts freeze-thaw a little differently, by counting how often temperature readings cross 32°F (two crossings make one cycle), so its numbers won’t match ours exactly. Our count misses days that cross freezing twice, the gap between air temperature and a sunny pavement surface, and whether anything was wet when it froze.

Sources

• NOAA NCEI, U.S. Climate Normals 1991–2020, annual day counts by station: Lock Haven, Williamsport · State College, Philadelphia, Pittsburgh, Harrisburg · Erie, Allentown, Wilkes-Barre, Bradford · Renovo, Linesville, Clarion, Franklin Institute, Clarence · comparison cities
• NCEI, annual/seasonal normals documentation (PDF)
• PennDOT Publication 408/2020, Section 704 (PDF)
• NRMCA, CIP 2: Scaling Concrete Surfaces (PDF, hosted by the Tennessee Concrete Association)
• USDA NRCS, Field Office Technical Guide: soil engineering interpretations (frost action)
• CMHA, PAV-FAQ-001: freeze-thaw and deicers for concrete pavers
• CMHA, Construction of Interlocking Concrete Pavements (PAV-TEC-002)
• ASTM C1262/C1262M-24, scope
• GLISA, Freeze-Thaw Cycles

Last checked November 14, 2026.

Common questions

How many freeze-thaw cycles does Pennsylvania get a year?

At the NOAA stations we checked, from about 50 a year at Philadelphia’s Franklin Institute to about 131 at Clarence in Centre County, using 1991 to 2020 normals. Central Pennsylvania towns fall in between: State College about 87, Williamsport about 95 and Lock Haven about 109.

Why does State College have fewer freeze-thaw days than Lock Haven?

More of State College’s winter days stay below freezing all day, about 35 a year against 29 in Lock Haven. A day that never thaws isn’t a freeze-thaw day, so the colder station ends up with fewer cycles.

Do I need air-entrained concrete in Pennsylvania?

For anything outside that will freeze wet, yes. PennDOT designs its concrete at 6 percent air, 7 percent for paving and bridge decks, and the National Ready Mixed Concrete Association recommends about 6 percent air for exterior concrete with three-quarter-inch or one-inch stone to resist scaling.

What ice melt is safest for pavers and concrete?

Rock salt, used sparingly. The Concrete Masonry and Hardscapes Association calls it the least damaging for pavers and says to avoid magnesium chloride and CMA. NRMCA says to keep deicers off new concrete the first winter and never use ammonium sulfate, ammonium nitrate or magnesium-based salts.

Is a freeze-thaw day the same as frost depth?

No. Freeze-thaw days count how often the air crosses 32 degrees. Frost depth is how deep freezing reaches into the ground, and in Pennsylvania your municipality or its code agency sets it for footings.

See every Pennsylvania building, digging and contractor rule on our Pennsylvania guide. Compare every state in freeze-thaw cycles by state and ZIP code, and see rainfall and snowfall by Pennsylvania town.