The Big Bear Valley is a small mountain community near San Bernardino, high above the smog, at an elevation of 6,750 feet with an estimated population of about 12,000 residents. Each year, Big Bear is blessed with an average of 320 days of sun with blue skies by day and star-filled skies at night, making it perfect for stargazing.
Big Bear’s environment is dominated by pine and oak forest. It sits in a mecca of sunshine and clear air. Average annual temperatures range from a pleasant 56 to 80 degrees in the summer months to 30 degrees in the winter. Precipitation averages about 20 inches per year and snowfall is common during winter months. Big Bear provides habitats for 30 wintering Bald Eagles and 29 species of rare plants.
Geography
We inhabit a valley at the top of the only transverse mountain range on the entire Pacific Rim. This range which stretches east of us to include Mt. San Gorgonio and west all the way to the Pacific ocean in Malibu. Generally all other mountina ranges, the Cascades, Rockies, Poconos, Appalachians and the like all run in a north/south orientation. Usually this would mean very much to our weather systems if it was not for the fact that this range cuts directly through a coastal plain above the 30th parallel. This is significant since, in the northern hemisphere the weather patterns above 30° N come in from the west borne on winds known as the prevailing westerlies. Add to this our friend the Polar Front Jet Stream that peaks in winter and we have interesting enough weather on the west coast let alone at 7000 ft. of elevation.
Big Bear Mountain in summerMeterology
The regional weather systems come in from the west borne on the prevailing westerlies. The area also has a large body of water, in addition to the Pacific Ocean just over 100 miles to the west. In winter, the Polar Front Jet Stream brings roaring, high altitude winds across the west coast from over the Pacific Ocean. This jet stream circles the North Pole in a counter-clockwise rotation if you were to look directly down on the North Pole. It can expand or contract in size, and when it does, it greatly influences the amount and type of moisture brought to bear on us. In its contracted form, the jet stream will pull Pacific moisture across the Pacific Northwest, hence Seattle’s generally gloomy winter weather. When expanded however, it will stream sub-tropical moisture from the Pacific Ocean off the Mexican coast right across Southern California. We saw a good example of this on Christmas day, 2003 when locations in the LA basin received 5" of rain per hour and terrible flash floods claimed lives at the base of our mountains. On that day the jet stream was roaring directly across Los Angeles from the West South West. It drew rising moist air from the warmer sub-tropical ocean off Mexico and combined with an intense low pressure system just off our coast.
… and in winterThe Christmas day storm
Thanks to the nature of the moisture brought in by the jet stream. The freezing level in any storm system determines where precipitation will be seen as rain or snow. In that particular storm, the freezing level didn't begin until around 8,500' since the moist air was sub-tropical and warmer than usual. So we in the valley, living below 8,500' saw rain and high winds. Anyone who happened to be Christmas camping above Onyx Summit (8,500' ASL) saw the storm as heavy wet snow showers and freezing winds. Finally, as the low pressure system, fed by the jet stream and strengthen by the warm sub-tropical moisture circled closer to the coast, air temperatures began to fall. In Los Angeles all the way up to Blue Jay, this made little difference. Here we finally saw the rain turn to snow at the tail end of the storm as the freezing level dropped to 5,00 feet.
The area gets the benefit of its location not only in winter but also in the summer monsoonal season. This is a time when the temperature of the land is much greater than that of the ocean. Thus the air mass above the land is rising rapidly, drawing in moist air from just over the ocean surface. Coastal communities of the Los Angeles basin see this as coastal foggy conditions.
Here in the mountains the story is much different. As the inrushing air hits the mountains it is forced to rise. When this happens, it expands and cools causing severe evaporation. We see this as incredibly clear late summer mornings followed by massive early afternoon thunderheads building directly over the mountain ridges themselves, as solar radiation heats the land forcing air above it to rise rapidly. As the evaporating air within the cumulus clouds reaches the dew point and can no longer remain as cloud moisture, the area gets drenching thunderstorms.