Chapter 1 Meteorology

Blizzards then

Monumental advances in monitoring of weather, 1888, 4 nor’easters hit the mid-Atlantic during the winter of 2009-2010, January 2016 snowstorm rated a rare extreme for NE US

Blizzards now

not exact, much better monitoring for forecasting weather, understanding oc coastal winter storms, satellites/radar, radiosondes, surface observations

Weather

state of the atmosphere at some place and time, quantitative variables

Examples of quantitative variables

temperature, humidity, cloudiness, precipitation, wind speed, wind direction

Meteorology

study of the atmosphere, processes that cause weather, and the life cycle of weather systems

Climate

weather conditions at some locality averages over a specified time period, climate is averages weather computed for last 30-years and updated every decade, locale’s climate also includes weather extremes

Climatology

study of climate, its controls, and spatial and temporal variability, has expanded with a system as a whole

Accessing weather information

smartphones, online, television, radio, weather apps

Radio

NOAA weather radio with continuous broadcasts repeated every 4-6 min, interrupted with warnings and watches

Time keeping

time zones measured east/west of the prime meridian (0 longitude), UTC, surface observations taken 4+ times per 24 hrs, upper air takes measurements taken at 0000Z and 1200Z

UTC

based on atomic clock, expressed as 24-hr clock (7:45 = 0745), no daylight savings time

What are the 2 types of pressure systems?

high and low air pressure systems

High pressure

fair weather, clockwise rotation of sinking air (northern hemisphere), generally track toward the east and southeast, outward

Low pressure

stormy weather, counterclockwise rotation of rising air (northern hemisphere), generally track toward the east and northeast, lows tracking across the N US/S Canada produce less moisture than lows tracking across the southern US, inward

What’s the weather like usually to the west and north?

cold

What’s the weather like to the south and east?

warm

Air masses

huge volume of air covering hundreds of thousands of square kilometers, uniform temperature and humidity, gather characteristics from source region

What are the characteristics of the source region?

cold dry air masses form over continents, cold humid air masses form at higher latitudes over maritime surfaces, warm dry air masses form over continents in subtropical regions, warm humid air masses form near the equator or in the subtropics over maritime surfaces

What are different air mass tendencies in different areas of the world?

polar air masses are colder in winter and milder in summer, tropical air masses have less seasonal variation due to nearly uniform sunlight duration and intensity, modify as they move away from source region (take on characteristics of the area they pass over)

Weather systems

fronts are 3D, warm front clouds and precipitation occur over a wide band (12-24 hrs/longer, usually light precipitation), cold front clouds and precipitation occur over a narrow band (occur over minutes to hours, heavy precipitation), wind directions are different on the 2 sides of a front, some fronts have no clouds/precipitation (wind shift, temperature/humidity changes), summer temp can be same on both sides of a cold front (difference in humidity), fronts anchored to lows on a weather map, thunderstorms/severe weather often occur in warm, humid air mass located between cold and warm fronts

What is shown where the front intersects?

earth’s surface with the front symbol on the map

What does counterclockwise flow bring in?

contrasting air masses together to form fronts

Coastal areas weather systems

lake/sea breezes lower summer temperatures, push 10-50 km inland from the shore

Great Lakes/Great Salt Lake weather systems

heavy lake-effect snow, late fall and winter, downwind

Central US weather systems

most common location of tornadoes in the spring

Thunderstorm weather system

common in FL, western High Plains and eastern slopes of the Rockies, rare along Pacific Coast and in HI

Tropical storm and hurricanes in the coast weather systems

mostly August through October, rare on west coast

State of the atmosphere

maximum temperature (early to mid-afternoon), minimum temperature (occurs around sunrise), dew point/frost point (temperature when air is cooled at constant pressure it’s saturated with water vapor and dew/frost forms), relative humidity, precipitation amount (10 in of snow = 1 in of precipitation), air pressure (tendency, falling indicates cold front coming), wind direction and speed (direction blow from west toward east), sky cover (fraction of the sky covered in clouds), weather watch (NWS when hazardous weather is considered possible), weather warning (NWS when hazardous weather is imminent or happening)

Relative humidity

percentage/ratio of actual water vapor concentration fo air vs water vapor concentration if air was saturated, relative humidity changes through the day as temperature varies, generally highest around sunrise and lowest when warmest

Weather satellite imagery

geostationary, polar orbiting, visible satellite image, infrared satellite image, water vapor satellite image

Geostationary

high orbits (36000 km high), orbits plant at same rate as Earth’s rotation in same direction, currently 2 provide a view of North US and adjacent oceans to latitudes of ~60, positioned over equator at 75 W and 135 W longitude

Polar orbiting

low orbits 800-1000 km high, provides overlapping north-south strips of images, passes over the same point twice every 24 hrs

Visible satellite image

black and white image of the planet, only available during daylight hours, highly reflective surfaces appear bright white and less reflective surfaces are darker

Infrared satellite image

available anytime, provides temperature comparison of features, higher cloud tops appear white because they’re colder, color scale used to enhance certain temperature areas

Water vapor satellite image

enables tracking of plumes of moisture, whiter masses have increasing moisture, upper-level clouds appear milky to bright white, color scale can be used to enhance

Weather radar

complements satellite surveillance, doppler radar detects movement, excellent for forecasting tornadoes, composite of infrared satellite image and radar echoes

Clouds

aggregates of tiny water droplets, ice crystals/both, relatively low cumulus clouds are composed of tiny water droplets with more sharply defined edges, high thin cirrus clouds appear fibrous because they are composed of mostly tiny ice crystals

Fog

cloud in contact with ground

What are the different types of clouds that can form?

stratiform clouds, cumuliform clouds

Stratiform clouds

sheet-like clouds formed in horizontal laters, form where air ascends gradually over a broad region

Cumuliform clouds

puffy like cotton balls, fair weather cumulus usually vaporize after sunset, most common during warmest time of day, form with vigorous ascent of air over small area, under the right conditions can build vertically into a cumulonimbus/thunderstorm cloud

What does it mean when high wispy clouds are in the western sky?

first sign of approaching warm front

Clouds of vertical development

merging vertically growing cumuls clouds

Cumulonimbus clouids

vertically grown, nimbo is nimbus prefix/suffix = rain producing, produces lightning, heavy rain, hail, strong and gusty surface winds

What does it mean when clouds move in different directions at different altitudes?

indicates horizontal wind shifts with altitude

What is a good habit to have?

watch the sky for changing conditions and monitor weather instruments