Mountain Weather and how to stay safe

Mountain WeatherMountain Weatherand how to stay safeand how to stay safe

Joe GrimJoe Grim

Let’s try to make this as interactive Let’s try to make this as interactive as possibleas possible

• If you have any questions along the way, please ask

• If you have any personal experiences to share that go along with the presentation, please feel free to do so

• I know a lot about the theory, but many have you have had more experience up in the mountains

Dangers of Mountain WeatherDangers of Mountain Weather

• Thunderstorms– Lightning– Strong winds– Hail

• Snowstorms

• Hypothermia and Frost Bite

• Strong Non-thunderstorm Winds

• Fog

How to prepare for your hikeHow to prepare for your hike

• Check the weather forecast for where you plan to hike (NOT Ft. Collins)– Know that forecasts can be wrong

• Be prepared for any type of weather possible– There is never a 0% chance of thunderstorms in the summer– Small, puffy cumulus can explode into

thunderstorms within a half hour– At high elevations, you can be caught in a

whiteout snowstorm any month of the year

Good weather forecast sitesGood weather forecast sites

• Colorado Avalanche Information Center (winter)– http://avalanche.state.co.us/

• National Weather Service– www.nws.noaa.gov– www.weather.gov/view/states.php?state=CO

• look for the county and elevation under “Zone Forecast”

• Private forecast sites usually give more generic forecasts– e.g. The Weather Channel, Accuweather– give one forecast for a whole area

• e.g. one forecast for ALL of RMNP

Good sites for current conditionsGood sites for current conditions

• Snotel automated sites– www.wcc.nrcs.usda.gov/snotel/Colorado/colorado.html

• Denver NWS weather radar– radar.weather.gov/radar.php?rid=ftg

• For many other websites– see my website

Other Weather Information LinksOther Weather Information Links

• I have many additional weather links online at

http://www.atmos.uiuc.edu/~jgrim/wx_bookmarks.htm

• This presentation is also online athttp://www.atmos.uiuc.edu/~jgrim/Mountain_Weather.ppt

Keep an eye on the weather during your hikeKeep an eye on the weather during your hike

In thunderstorm season, In thunderstorm season, what should you look for?what should you look for?

• Watch cloud development• Note wind direction• If you have a psychrometer, monitor dew point

– not a strong indicator, but can be helpful

• Look for vertical development

How to recognize potential How to recognize potential thunderstorm cloudsthunderstorm clouds

• Look for cauliflower cloud sides and/or tops

How to recognize potential How to recognize potential thunderstorm cloudsthunderstorm clouds

• When the clouds get tall, look for the formation of a wispy “anvil” at the top

– An “anvil” indicates that the top of the storm is high in the atmosphere where ice is present

How to recognize potential How to recognize potential thunderstorm cloudsthunderstorm clouds

How to recognize potential How to recognize potential thunderstorm cloudsthunderstorm clouds

• Look for rain streaks coming from the bottom

• Look for dark cloud bases

How to recognize potential How to recognize potential thunderstorm cloudsthunderstorm clouds

How to recognize potential How to recognize potential thunderstorm cloudsthunderstorm clouds

1. Look for vertical development

2. Look for cauliflower cloud sides and/or tops

3. When the clouds get very tall, look for the formation of a wispy “anvil” at the top

– An “anvil” indicates that the top of the storm is high in the atmosphere where ice is present

4. Look for dark cloud bases

5. Look for rain streaks coming from the bottom

lightning can strike at any time if #1, but the more of these characteristics you see, the more likely it is for there to be lightning

tall {

Do the skies look threatening?

wispy top

rain streaks

cauliflower sides

dark base

Do the skies look threatening?

Do the skies look threatening?

Do the skies look threatening?

Later that afternoon

Do the skies look threatening?

Do the skies look threatening?

20 minutes later at the summit, looking the opposite direction

Do the skies look threatening?

Wind directionWind direction

• Is the wind upslope or downslope?– upslope winds indicate upward motions that

could result in later thunderstorms

Thunderstorms and LightningThunderstorms and Lightning

• No place outside is entirely safe!

• There are some places that are more dangerous than others– Above timberline– By or below lone or tall trees– Anywhere in the open– In or on the water

*The average lightning flash would light a 100 watt light bulb for 3 months!

Uh oh, you’re caught in a Uh oh, you’re caught in a thunderstorm anyway!thunderstorm anyway!

What should you do now?What should you do now?• DO NOT PANIC

– Head to a safer area at a brisk but SAFE pace• You’ll go a lot slower if you twist an ankle!

• If possible, get out of the open and away from any tall objects ASAP

• If with a group, spread out >15 ft.

• If descent is not possible crouch down in a low spot with only your feet touching the ground

What to be aware of while on your What to be aware of while on your hikehike

• Get back below timberline before storms form – NOT once they do!– A significant minority of strike victims are struck by

the first bolt from a storm

• Even if a nearby storm appears to be moving away, don’t push your luck– Movement of clouds within a storm are often

different than the movement of the entire storm– The complex flow within the mountains can make

for erratic storm motions and winds– Ongoing storms can quickly trigger new storms

nearby

What about “Bolts from the Blue”?What about “Bolts from the Blue”?

• “Bolts from the Blue” are actually bolts from a storm that strike well off to the side appear to be “out of the blue”

When is lightning most likely?When is lightning most likely?

• The time of highest lightning strikes in Colorado is usually between 4 and 5 pm

• However, the average first lightning strike of the day in Colorado is 11 AM.

• It depends on the day, as to when thunderstorms are likely to begin– check weather forecast– don’t use “rule of thumb” (e.g., 3 pm)

United States Lightning DensityUnited States Lightning Density

Fort Collins

Colorado Lightning DensityColorado Lightning Density

Fort Collins

What to be aware of while on your What to be aware of while on your hike (cont.)hike (cont.)

• You can get hypothermia at any time of the year– Cool Air + Wet You + Wind = Hypothermia– The wet-bulb temperature (Tw) indicates how

cool it feels if you’re wet.

– A temperature of 45 and a RH of 50% makes a wet you feel like: 45-0.25x(100-50)=32

– Before a storm it might be 65, but after it could be 45 and feel like 32!

– Adding a 25 mph wind, it can feel like 19!

Humidity Relative-100%*0.25-eTemperatureTemperatur bulb-Wet

Hiking in the “winter”Hiking in the “winter”(pretty much anytime outside of summer)(pretty much anytime outside of summer)

• At high elevations, you can be caught in a whiteout snowstorm any month of the year

• What starts out as a clear calm day can quickly change to a blizzard

• Check the weather forecast for where you plan to hike (NOT Ft. Collins)– Good sources: CAIC, NWS– Know that forecasts can be wrong

so be prepared for anything

Hiking in the “winter”Hiking in the “winter”(cont.)(cont.)

• Bring along gear as if you might have to spend the night– e.g., plenty of extra clothing layers,

emergency blanket, water, food, lighter, etc.– If ever you do get stuck in a freak storm, you’ll

be glad you were prepared!

• Always be aware of potential avalanches in avalanche country

Low Avalanche Danger ≠ NO Avalanche Danger

Other potentially dangerous Other potentially dangerous mountain weathermountain weather

• Strong winds– Winds can be particularly variable and gusty in the mountains (Chinook winds are common in

winter, while thunderstorm winds are common in summer)

– i.e., be careful near edges

• Fog– With low visibility, you can quickly become lost even

with a map and compass– You can accidentally wander into dangerous terrain

(steep rocky slopes, crevasse fields, etc.)

• Hail – rarely is it dangerous, but it sure can hurt!

Ever see pretty clouds like these?Ever see pretty clouds like these?

They’re called “lenticular” clouds for their lens-type shapeThey often indicate very high winds up high

Questions?Questions?Personal experiences?Personal experiences?