weather on the summit..
I am curious.. what's the most consecutive days the Summit of Mount Washington has seen without any precipitation? I know it can be too terribly long. What's the normal length of clement weather before another storm sends conditions down the tubes again?
along with this.. which month is best to hike to the summit presuming one wants it relatively warm and sunny?
Maybe one of the Obs people could find some stats, but I would think either July or August is about as warm as you will get. I think the record high is around 72 degrees. I don't think you can predict the weather for a warm & sunny hike more than a couple of days in advance. Remember, it has snowed & many people have died of hypothermia on MW in the summer months. Use some common sense & pack clothing for cold weather & rain.
A couple of years ago in July I went from the Summit of MW to Jefferson & back on what was supposed to be a good day. It was very warm in the valley, probably mid eighties & nice on the summits. While at Jefferson I noticed clouds in the distance that looked like they could bring rain in later in the day. I hiked back & as I was getting closer to MW the clouds has already obscured the summit & it was closing in fast from the south. As I was passing the Great Gulf & almost back to my car the clouds arrived & the visibility was near zero. I walked toward the auto road hoping that I would come out near where my car was parked. I was a little nervous because even if I got to the auto road, I was hoping I knew which way I would have to go in order to get to the car. As I was within just a few feet of my car it started to rain & the wind really picked up. I threw off my pack & hopped into my car & within the next 30 seconds it was like being in a hurricane with rapidly dropping temps. My car rocked like crazy from the wind gusts & I watched the temp dropped over 20 degrees per my cars thermometer within just a few more minutes. Even being prepared I was sure glad that I was not out in it. I went into the Observatory & saw that winds had gusted to over 65 mph & the temp had actually dropped more than 25 degrees. A recipe for disaster if you don't have the proper clothing.
I don't want to scare you with the story, but relay that there are no guarantees on MW. You might have a nice warm, sunny, humid day & hike in shorts & a tee shirt, but be prepared if you venture any distance from the summit.
I will start by working backwards. The warmest month, statistically is July followed by August. This can be seen on our Normals, Means and Extremes page (http://www.mountwashington.org/weather/normals.php). It should be noted though that this page is currently under an update, so some of the numbers are a bit dated.
You can also check out our WS Form F-6 page: http://www.mountwashington.org/weather/f6/ which holds at least 7+ years of data that we have made public out of our 80+ year history. On this page, just click on any given month and you will see the past highs, lows, averages, etc for each month and day. This is very useful in planning as the best way to know what the weather will be in the future is to look at the past. But, with that being said, and like whitemtnvisitor mentioned, just because we are statistically warm and dry on any particular day, it will not be like that every year. And just because it is hot and sunny in the valley doesn't mean you will encounter similar weather as you ascend. Always pack for the unexpected even if the forecast is calling for great weather. I am talking from experience, that just because I and/or other meteorologists may call for awesome weather, on occasion, as you may know, we are not exact. So, always pack some extra gear to stay warm or dry in those one off occasions. It is easy to pack a layer or two for those just in case moments in life. Think of it like carrying jumper cables in your car. Most of the time you won't need them but it's safer to have them than not; same as warm/dry clothing.
As far as precipitation goes, I can't readily look that up as I would have to think about how to do that inquiry in our database. But I know in my time here, the longest time without precipitation of any form that I have experienced is about 8 days. I am sure, looking at our monthly means and extremes though, with some of the minimum months we have my guess would be one of those months holds the record. But, New England is called the tailpipe of weather for the US, so that means if something forms anywhere in the lower 48, odds are at some point it will impact us. Unfortunately though, there is no rule of thumb like if it is raining today it will be dry and clear for three days after. Nor is it similar to conditions in the west that fit a Gaussian curve where summer is nearly bone dry and all the precipitation comes down in the winter; precipitation in New England is a year round affair as you can see from the normal totals on the page referenced above. While some months during any particular year, it rains every single day, other times we'll just get bursts of rain then nothing for days. So, this stat will not help in planning any hikes per say. I think the better thing to look at is our snowfall stats since snow takes a whole different set of equipment and mind set than just rain would. The least snowiest months are July and August with a mean of a trace for July and 0.3 inches for August. That's not to say it won't snow more than those numbers, but on average, these would be the least likely months to have to worry about snow and ice on the summit. But like everything else I keep driving home, it still can happen and you should be able to dress for those events. But, statistically, when telling my friends when to hike this mountain, I will tell them to aim for July or early August to get the best and safest possible conditions. And if your plans don't pan out, go as far as is safe and try again another day. The mountain's not going anywhere.
" The mountain is not going anywhere." These may be the most pertinent words I've ever heard (read) regarding hiking. Slow down and enjoy and don't be ashamed to not make the summit. Turning back is OK if weather doesn't look good, or even if you are simply tired. The mountain will still be there in the future.
Many people have died on Mount Everest needlessly. Simply put, they kept going when they should have turned back. Yeah they may have made the summit but they ran into trouble on the way down. I think this was the case in "In to Thin Air."
From a purely meteorological point, I bet the longest dry stretches are in the winter...coinciding with really cold temperatures, when the storm track is over NC and DC.