Freedom of the Hills Chapter 27

1. Mountain Weather Freedom of the Hills Chapter 27 1

2. Weather Basics Mountain weather can change rapidly!! • Weather is objective hazard, one you have no control over • In winter, temperatures can drop 40º or more the instant the sun sets • HOW you prepare to deal with changing weather is a subjective hazard, YOU have total control • BE prepared to function in any weather: • Rain, wind, snow, thunderstorms - often more than one • Carry protective gear and clothing layers • Bivy sack in Summer that is weatherproof to keep you dry • Tent in Winter that can withstand heavy snow and high winds • Clothing that protects you from wind and rain • Mental strength to cope with inclement weather 2

3. Forces that create weather • Sun • Air Movement • Earth’s Rotation • Fronts: • Cold Front: Cold air is replacing warm air • Characterized by puffy, cotton candy like clouds • Warm Fronts: Warm air is replacing cold air • Characterized by layered, sheet-like clouds Precipitation and wind are associated with both fronts, but cold fronts usually bring more severe weather Supported by the United Way 3

4. Thunder and Lightning • Thunderstorms usually set off by: • Collision of different air masses or • Rapid heating of air when in contact with sun-warmed slopes • Thunderstorms CAN and DO KILL • Lightning strikes • Forest fires • Flash floods • If Thunderstorms are forecast: • Obtain updated reports before hitting the trail • Don’t camp or climb in narrow valleys/gullies • Don’t climb or hike in high, exposed areas • Summit early and descend by afternoon • Watch small cumulus clouds for strong, upward growth or color changed from white to dark grey/black Supported by the United Way 4

5. Thunder and Lightning Use the flash to bang test to estimate storm’s approach • Count seconds between flash of lightning until the bang of the thunder clap. Five seconds per mile. • If the interval gets shorter, the storm is getting closer. If you get caught in a thunderstorm… • Get off ridges and peaks and away from water • MOVE IMMEDIATELY if your hair stands on end or you hear buzzing • Seek shelter (not in tents that may become lightning rods) • Crouch to minimize your height and cover your head and ears • Insulate yourself from the ground (sit on pack or foam pad) • Do not lie down (minimize contact with ground) • Do NOT remain near, touch or wear metal or graphite material • Do NOT get under lone trees or lookout points. • Look for a stand of even height trees. 5

6. Mountain Winds Understanding localized patterns is critical • Gap Winds - Winds between peaks and passes can blow twice as fast as surrounding wind • Valley & Gravity winds – Typically blow uphill during the day and downhill during the night • Chinook Winds – High “downhill” winds, heated by rapid compression, increases avalanche and flood hazards 6

7. Field ForecastingPredicting changes in the weather pattern Major indicators of approaching storm are changes in: • Cloud cover • Air pressure • Wind direction • Wind speed Watch for changes in overnight altimeter readings (barometric pressure) • Increased altitude indicates a lowering of pressure  worsening weather • Decreased altitude indicates an increase in pressure  improving weather 7

8. Weather Briefings • Create your own weather report • Seek input from weather forecasts, websites, locals • Plug latitude and longitude into http://forecast.weather.gov/MapClick.php?lon=XXX&lat=YYY • Or just click through weather link at peak page at http://www.peakbagger.com • Be sure to check surrounding areas! • Watch the weather pattern daily for several days prior to a planned trip • Pay attention to the trend in weather changes • Watch the positions of highs, lows, and fronts which can indicate what you might expect • Each day, check the accuracy of the previous day’s weather forecast 8

9. Expect the unexpected! 9