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Weather Wise: Air Masses and Fronts

Lift the curtain on air masses, fronts, regional weather, and high- and low-pressure systems to come to the right decision about flying in weather.

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Weather RegionsWeather Regions

Safety SPOTLIGHT: Air Masses and Fronts

View from beyond the control panel of a cessna airplane with no roof or side windows in the frame to achieve an open canopy effect.  All text is generic warning notes and instrument readings. Clipping path for control panel embedded.

Different regions in the United States have unique weather characteristics. These are the most common, prevalent weather patterns and potential flying hazards that can be expected in each.

Northwest

Spring and summer—Prevalent high pressure systems bring good flying weather.

Fall, winter, and spring— Onshore flow of moisture can bring severe icing conditions.

Winter—Moisture off the Pacific Ocean causes rain on the windward side of the mountains and snow on the leeward side. The coast can be cool and wet with fog and low ceilings.

Northern Rockies—Tend to have strong winds and turbulence. Summers can produce thunderstorms and prolonged heat waves. High density altitude is a major concern. Fall offers the best flying weather, though the snow tends to begin in mid-October.

Southwest

Rising hot air causes many strong low pressure systems to form in this region and move east.

Summers—Generally warm and dry in the desert, although thunderstorms and hail may be encountered. High density altitude is a major concern. Moisture from the Pacific Ocean, the Gulf of California, and the Gulf of Mexico triggers rain in the mountains. Many of these thunderstorms can be "dry thunderstorms" that produce lightning but no rain. In some cases these can produce nasty dry microbursts.

Desert winters—Cool and dry.

Mountain winters—Expect strong downslope winds, mixed icing in clouds, and blizzards.

California—Coastal fog forms over land in the winter and migrates from the ocean in the summer.

Southern California—Has smog, onshore flow, and temperature inversions. October to April is rainy. Fall and spring bring the Santa Ana winds, which are a turbulent line between moist oceanic air and dry desert air.

Observing weather patterns for several days before you fly helps to provide the big picture on how frontal and pressure systems expect to be moving.

South Central

Summer—High heat and humidity mixed with heavy rain showers, thunderstorms, squall lines, and possibly tornadoes. Drylines can form when moist Gulf of Mexico air and dry, hot desert air meet.

Summer and fall—Threat of hurricane landfall.

Winters—Near the Gulf, are mild with rain and morning fog due to low temperature-dewpoint spreads.

North Central

Summers—Warm and dry. Moisture from the Gulf of Mexico triggers occasional thunderstorms.

Winters—Very cold and dry. Blizzards are common due to cold air from the north and moisture from the Gulf of Mexico mixing in this region.

Midwest/Ohio Valley

Low pressure systems form on the lee side of the Rocky Mountains and grow as they head east and are fed by moisture from the Gulf of Mexico.

Summers—Usually hot, humid, and rainy with air mass thunderstorms. The southern portion of this region is part of Tornado Alley.

Fall— High dewpoints cause night and morning fog.

Winter—Can be cold with lake effect snow near the Great Lakes. A low pressure system can bring heavy rain in the southern portion of the region and heavy snow in the northern portion. 

Southeast

Summers— Moisture from the Gulf of Mexico and the Atlantic Ocean causes hot and humid weather with rain and thunderstorms. Thunderstorms are typically pulse-type (single cell) that do not produce severe weather and usually last 20 to 30 minutes.

Summer and Fall—Hurricanes can pose a threat.

Winters—Cool and mild with occasional heavy rain showers.

Florida—Surrounding water triggers morning fog, afternoon thunderstorms, sea breezes, and turbulence. Some of the Gulf Coast states and Florida can have thunderstorms triggered by sea breeze fronts.

New England/Mid-Atlantic

This region’s weather is influenced by its location between mountains and the ocean.

Summers—Warm and humid with heavy rain showers and thunderstorms. Expect low visibility due to haze. Morning fog forms due to easterly flow off the Atlantic Ocean and up the rising terrain of the Appalachian Mountains.

Winter—Can bring heavy snow and rain due to upper-level lows from the west and south. Instrument meteorological conditions and icing are common. Areas near the Great Lakes experience lake effect snow.

ATC, flight service, and onboard technology like weather radar and datalink are excellent in-flight weather resources to help assess if and how conditions are changing.

Alaska

Alaska Southeast/Gulf of Alaska (Juneau, Ketchikan): Plenty of moisture along the coast causes low ceilings and lots of rain the entire year.

Alaska Cook Inlet/Kenai Peninsula (Anchorage, Kenai, Homer): VFR conditions are common year-round, although occasional coastal morning fog and/or low ceilings could be encountered in summer. In winter, expect occasional ice fog and blowing snow. In the spring and fall, look for icing in clouds, freezing rain, and snow. Occasional radical pressure changes will cause high winds.

Central Alaska (Fairbanks): Summer features extended daylight hours, very high temperatures, haze, and thunderstorms with hail. In the fall, look for snow, freezing rain, and ice fog as the temperatures begin to drop. Winter brings very little sunlight, extremely low temperatures, and more ice fog. The snow, freezing rain, and ice fog continue into the spring months.

Seward Peninsula (Nome, Kotzebue, Bethel): High humidity brings low clouds during summer months. In the fall, look for more low clouds along with ice fog, blowing snow, and freezing rain. These conditions continue into winter with colder temperatures. Rising temperatures in the springtime add freezing rain to the mix of snow and low clouds.

Western Aleutian Island Chain (Cold Bay, Dutch Harbor, Adak): Low clouds and windy conditions throughout the year.

Far North (70 degrees latitude, Barrow): Cold conditions, low clouds, ice fog, and blowing snow most of the year.

In-Flight Weather Assistance

Forecasts are imperfect, but you can extract a lot of truth from them to make the best go/no-go decisions. When flying, compare the forecast to actual conditions and pay attention to trends. ATC, flight service, and onboard technology like weather radar and datalink are excellent in-flight weather resources to help assess if and how conditions are changing. Depending on your datalink provider and in-cockpit equipment, you can pull up graphical and textual weather that offer a clear picture of wind shifts, pressure changes, and temperature changes at altitude and at your destination. This together with what you hear from ATC or flight service and what you see outside the cockpit, greatly improves your situational weather picture aloft.

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