SNOW SEEDSNOWMAKING

Can I Make Snow Today?

Your local forecast, hour by hour, colored by the kind of snow you can make. Plus a wet bulb calculator and a printable chart for any conditions.

Your Forecast

Enter a US ZIP code or use your location.

Forecast from the National Weather Service, about seven days out, US only. Wet bulb is worked out from the forecast temperature and humidity with the same equation as the calculator below. A forecast is a forecast: check the real numbers before you fire up the pump. New to snowmaking? Read how to make snow at home.

Wet Bulb Calculator

Air temperature and humidity in. Wet bulb and a straight answer out.

Wet Bulb

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Wet Bulb Chart

Find your air temperature on the left and your humidity across the top. The color tells you what kind of snow you can make.

  • Above 28° No Snow
  • 27–28° Threshold
  • 24–27° Wet
  • 20–24° Good
  • 15–20° Optimal
  • Below 15° Excellent
Wet bulb in °F by air temperature and relative humidity
Air °F10%20%30%40%50%60%70%80%90%95%
4028293031333435373839
3928293031323334363738
3827282930313233353637
3727272829303132343536
3626272728293031333435
3525262727282931323334
3425252627272830313233
3324252526272829303132
3224242425262728293031
3123232424252627282930
3022222323242526272829
2922222222232425262728
2821212122222324252627
2721202021212223242526
2620202020212122232425
2520191919202021222324
2419181818191920212223
2318181718181919202122
2218171717171818192021
2117161616161718181920
2016161515151617171919
1916151414151516171818
1815141414141415161717
1714141313131314151616
1613131212121213141515
1512121111111112131414
1411121110101011121313
1391110991010111212
1281099999101111
11798888891010
106987777899

Values rounded to the nearest degree; colors use the unrounded value. Sea-level pressure.

This table runs 1 to 2 °F colder than the wet bulb chart most home snowmaking sites circulate. That is not an error on either side. This one is computed directly from Stull, whose stated error band is roughly −1.8 to +1.2 °F, which covers the gap. The widely copied chart is a secondary source with no published derivation.

Practical effect: if you are within a couple of degrees of the 27 °F threshold, treat it as marginal either way and go by what actually comes out of the gun. Do not bet a night on the last degree from any chart.

What the Numbers Mean

Wet BulbSnow
Above 28 °FNothing. Below 28 is the floor for making snow at all.
27 to 28 °FThreshold. Possible with good equipment, very wet and slushy.
24 to 27 °FWet. Home guns typically make slush through the mid 20s.
20 to 24 °FGood. Dries out steadily through the low 20s.
15 to 20 °FOptimal. Under 20 is the accepted sweet spot. Dry snow.
Below 15 °FExcellent. Dry and powdery.

Thresholds from Snow State, Stratton Mountain, and TechnoAlpin. Snow State puts the working threshold at 27 °F, notes that good equipment can work up toward 29 °F but only produces slush there, and that home guns improve from mid-20s slush to dry powder in the teens. Stratton puts the optimum under 20 °F.

These bands describe conditions, not your gun. Water temperature, nozzle sizing, hang time, and air supply all move the real result. A well-set-up gun at 23 °F will beat a badly set-up one at 18 °F.

Why the Low-to-Mid 20s Matters Most

TechnoAlpin looked at about 30,000 snow producers worldwide and found 71.5% of all snowmaking hours happen between −2.5 °C and −6.4 °C wet bulb, roughly 23 to 27 °F. That same band produced 63.2% of annual snow volume.

Making snow at 10 °F is easy and rare. The low-to-mid 20s is where equipment actually earns its keep.

What This Is Doing

It uses the Stull (2011) equation, a closed-form approximation for wet bulb from air temperature and relative humidity.

Tw = T·atan[0.151977·(RH+8.313659)0.5] + atan(T+RH) − atan(RH−1.676331) + 0.00391838·RH1.5·atan(0.023101·RH) − 4.686035

T in °C, RH in percent. This page converts °F to °C and back for you.

Its limits, stated honestly. Stull is valid for 5 to 99% relative humidity and −20 to 50 °C. Stated error runs roughly −1 to +0.65 °C. It assumes sea-level pressure, which is fine in Connecticut and less fine at elevation.

It is an approximation, not a measurement. A sling psychrometer beats it.