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Mount Washington is known as "The Home of the World's Worst Weather." Most of that occurs in winter, but life-threatening conditions can occur in summer, too.

Here are some summit weather statistics for May through October- temperatures are in degrees F.

  May June July August September October
Normal Max temp 42 50 54 53 46 36
Normal Min temp 30 39 43 42 35 24
Record Max temp 66 72 71 72 69 59
Record Min temp -2 8 24 20 9 -5
Average Wind, miles per hour 30 27 26 25 29 34
Max Wind, miles per hour 164 136 154 142 174 161
Average Snowfall, inches 12.5 1.1 Trace .2 2.2 13.7
Average Precipitation, inches 8.21 8.36 8.02 8.08 8.55 7.66
Days with .01 inch or more of precipitation 17 16 16 15 15 17
% of Possible Sunshine 36 32 30 31 35 38
Days with Heavy Fog 24 25 27 27 26 25
Days with Thunderstorms 1.8 3.5 4.4 2.9 .9 .6

The figures in the table show that cold, wet, and windy weather is commonplace on the mountain. While sunny, warm and dry days, with light winds, do occur from time to time, they are definitely in the minority. If you get a day like that for your visit, be grateful, and realize that less cooperative weather is far more likely.

Here's a rundown of typical conditions:

As a very rough rule of thumb, expect the temperature at the summit of Mount Washington to be about 20 degrees colder than at its base. Even in mid-summer, a typical daily high temperature does not exceed the low 50's. Occasionally the temperature can reach the 60's – practically a heat wave for the summit! Maximum temperature for the summit since 1932 is 72 degrees, and that's only been experienced on two occasions! Temperatures certainly can get below freezing, even in mid-summer. Be prepared for cold conditions!

In addition to cool or cold temperatures, the wind can have a major effect on your comfort and safety. Average mid-summer winds are about 25 miles per hour, which significantly adds to the cooling effect of the environment. You'll need a good wind-proof layer to maintain the value of your insulating layers.

Even a light breeze can be significantly chilling! Light breezes, and especially stronger winds, can make it hard to stay dry in foggy conditions and in rainy weather, too. Extreme winds can occur on the mountain even in summer – one July day saw average winds of about 100 miles per hour and a peak gust to 154 miles per hour! Winds like that can knock you down instantly. Even less forceful winds – say, 50 or 60 miles per hour – can slow your progress, tire you, and make a stumble on rough rocks much more likely.

If you are hiking up the mountain, once you reach the treeline you are fully exposed to the wind. If you experience tiring or troubling winds as you ascend the mountain, be prepared to turn back and descend to the relative protection of the trees.

About 60% of the time, the summit of Mount Washington is in a fog bank, actually within the clouds. Sometimes the fog is thin, but more typically it is thick and wet, with visibility limited – sometimes allowing you to see a hundred or two hundred feet, but sometimes limiting visibility to less than 10 feet. Finding your way, especially on a trail above treeline, can be very difficult at such times. You might be struggling to remain on the trail, paying extra attention to the footway and to the rockpiles (called "cairns") that mark the trails.

Even when the summit is NOT in the clouds, clouds over the mountain are common, preventing the cheering and warming sunshine from reaching you. The summit only receives about a third of the theoretically possible sunshine.

Thick fog can also be very wet fog, requiring extra care to stay dry and warm. You may need to wear rain gear even if it's not raining – for all practical purposes, there is no difference in this regard between wet, wind-driven fog and actual rain.

Precipitation is a regular occurrence on the mountain, especially its upper reaches. Usually in summer that precipitation falls in the form of rain or drizzle, but frozen precipitation – in the form of hail, sleet, or snow – can fall in any month. Be prepared for wet weather with good raingear and good footwear.

A particular hazard is lightning, which can occur as part of small-scale, more localized thunderstorm activity, or as part of a frontal system. Be alert to the possibility of a thunderstorm – through checking the weather forecast ahead of time, and by being attuned to the sights and sounds of the weather during your trip – and do your best to avoid being caught out in a thunderstorm, especially in the open areas above treeline.

If a thunderstorms threatens, being in the open above treeline is very, very dangerous.

In sum – if you are planning a trip to Mount Washington, be prepared for uncomfortable, and possibly dangerous, weather. The better prepared you are for cold, wet, windy weather – both psychologically and in terms of fitness, clothing and equipment – the safer and more enjoyable your trip can be.

Be aware, too, that weather can have an impact on your trip through not only what is in the air but also through what weather puts on the ground. Early and late in the season, ice and snow can make walking (and sometimes route finding) difficult. In some spots, the previous winter's snow can linger into July and even into August. Steep snowy areas (such as the headwall of Tuckerman Ravine) can be treacherous and are best avoided – travel in these areas, if at all, only if you have the special equipment and knowledge needed.

Spring snowmelt, as well as heavy rains at any time of year, can cause streams to run very high. While most streams on the mountain can be straightforward to cross at low levels, when running high they can be difficult, dangerous, and perhaps even impossible to cross safely. People have drowned trying to cross rain-swollen streams on the lower reaches of the mountain. Be prepared to change your plans should you come upon hazardous stream crossings.

Home of the World's Worst Weather
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