Rain Last 24 hrs”. February ” Departure from Normal: +”. Rainfall for water year October 1st September 30th ” Departure from. Weather in Portland for each year since including average high and low temperatures, total snowfall and precipitation. Rainfall data are provided with their permission and cooperation. Portland area -- average rainfall, 42 gages, not including the Cottrell School rain gage . National Weather Service: Most recent area forecast discussion for Portland, updated. Rainfall data are provided with their permission and cooperation. Portland area -- average rainfall, 42 gages, not including the Cottrell School rain gage . National Weather Service: Most recent area forecast discussion for Portland, updated. Please click here to complete the feedback survey. weather statistics (usually for yesterday), including temperature, precipitation, degree days, wind, humidity, . Local weather news from The Oregonian. Complete Portland, OR Hourly Forecast Monday commute: Ice unlikely amid warming temperatures and rain.
Rain is liquid water in the form of droplets that have condensed from atmospheric water vapor and then become heavy enough to fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth.
It provides suitable conditions for many types of ecosystemsas well as water for hydroelectric power plants and crop irrigation. The major cause of rain production is moisture moving along three-dimensional zones of temperature and moisture contrasts known as weather fronts.
If enough moisture and upward motion is present, precipitation falls from convective clouds those with strong upward vertical motion such as cumulonimbus thunder clouds which can organize into narrow rainbands. In mountainous areas, heavy precipitation is possible where upslope flow is maximized within windward sides of the terrain at elevation which forces moist air to condense and fall out as rainfall along the sides of mountains.
On the leeward side of mountains, desert climates can exist due to the dry air caused by downslope flow which causes heating and drying of the air mass. The movement of the monsoon troughor intertropical convergence zonebrings rainy seasons to savannah climes.
The urban heat island effect leads v rock n learn increased rainfall, both in amounts and intensity, downwind of cities. Global warming is also causing changes in the precipitation pattern globally, including wetter conditions across eastern North America and drier conditions in the tropics. Rainfall is measured using rain total rainfall today portland or. Rainfall amounts can be estimated by weather radar.
Rain is total rainfall today portland or known or suspected on other planets, where it may be composed of methaneneonsulfuric acidor even iron rather than water.
Warmer air can contain more water vapor than cooler air before becoming saturated. Therefore, one way to saturate a parcel of air is to cool it. The dew point is the temperature to which a parcel must be cooled in order to become saturated. There are four main mechanisms for cooling the air to its dew point: Adiabatic cooling occurs when air rises and expands. Conductive cooling occurs when the air comes into contact with a colder surface,  usually by being blown from one surface to another, for example from a liquid water surface to colder land.
Radiational cooling occurs due to the emission of infrared radiationeither by the air or by the surface underneath. The main ways water vapor is added to the air are: Elevated portions of weather fronts which are three-dimensional in nature  total rainfall today portland or broad areas of upward motion within the Earth's atmosphere which form clouds decks such as altostratus or cirrostratus.
It can also form due to the lifting of advection fog during breezy conditions. Coalescence occurs when water droplets total rainfall today portland or to create larger water droplets. Air resistance typically causes the water droplets in a cloud to remain stationary. When air turbulence occurs, water droplets collide, producing larger droplets.
As these larger water droplets descend, coalescence continues, so that drops become heavy enough to overcome air resistance and fall as rain. Coalescence generally happens most often in clouds above freezing, and is also known as the warm rain process. This generally requires more mass than coalescence when occurring between the crystal and neighboring water droplets.
This process is temperature dependent, as supercooled water droplets only exist in a cloud that is below freezing. In addition, because of the great temperature difference between cloud and ground level, these ice crystals may melt as they fall and become rain. Raindrops have sizes ranging from 0. Smaller drops are called cloud droplets, and their shape is spherical. As a raindrop increases in size, its shape becomes more oblate, with its largest cross-section facing the oncoming airflow.
Large rain drops become increasingly flattened on the bottom, like hamburger buns; very large ones are shaped like parachutes. The large size is explained by condensation on large smoke particles or by collisions between drops in small regions with particularly high content of liquid water. Rain drops associated with melting hail tend to be larger than total rainfall today portland or rain drops. Intensity and duration of rainfall are usually inversely related, i.
The final droplet size distribution is an exponential distribution. This is commonly referred to as the Marshall—Palmer law after the researchers who first characterized it. Deviations can occur for small droplets and during different rainfall conditions.
The distribution tends to fit averaged rainfall, while instantaneous size spectra often deviate and have been modeled as gamma distributions. Raindrops impact at their terminal velocitywhich is greater for larger drops due to their larger mass to drag ratio. At sea kingdom of heaven serbian subtitles and without wind, 0.
Rain falling on loosely packed material such as newly fallen ash can produce dimples that can be fossilized, called raindrop impressions. The sound of raindrops hitting water is caused by bubbles of air oscillating underwater. In certain conditions precipitation may fall from a cloud but then evaporate or sublime before reaching the ground. This is termed virga and is more often seen in hot and dry climates. Similar ascent is seen around tropical cyclones outside the eyewalland in comma-head precipitation patterns around mid-latitude cyclones.
Occluded fronts usually form around mature low-pressure areas. If there is a shallow near surface layer that is below freezing, freezing rain rain which freezes on contact with surfaces in subfreezing environments will result. Convective rainor showery precipitation, occurs from convective clouds e.
It falls as showers with rapidly changing intensity. Convective total rainfall today portland or falls over a certain area for a relatively short time, as convective clouds have limited horizontal extent. Most precipitation in the tropics appears to be convective; however, it has been suggested that stratiform precipitation also occurs. Orographic precipitation occurs on the windward side of mountains and is caused by the rising air motion of a large-scale flow of moist air across the mountain ridge, total rainfall today portland or in adiabatic cooling and condensation.
In mountainous parts of the world subjected to relatively consistent winds for example, the trade windsa more moist climate usually prevails on the windward side of a mountain than on the leeward or downwind side. Moisture is removed by orographic lift, leaving drier air see katabatic wind on the descending and generally warming, leeward side where a rain shadow is observed.
Windward sides face the east to northeast trade winds and receive much more rainfall; leeward sides are drier and sunnier, with less rain and less cloud cover. In South America, the Andes mountain range blocks Pacific moisture that arrives in that continent, resulting in a desertlike climate just downwind across western Argentina.
The wet, or rainy, season is the time of year, covering one or more months, when most of the average annual rainfall in a region falls.
Tropical rainforests technically do not have dry or wet seasons, since their rainfall is equally distributed through the year. The wet season is a time when air quality improves,  freshwater quality improves,   and vegetation grows significantly. Tropical cyclonesa source of very heavy rainfall, consist of large air masses several hundred miles across with low pressure at the centre and with winds blowing inward towards the centre in either a clockwise direction southern hemisphere or counter clockwise northern hemisphere.
The fine particulate matter produced by car exhaust and other human sources of pollution forms cloud condensation nucleileads to the production of clouds and increases the likelihood of rain. As commuters and commercial traffic cause pollution to build up over the course of the week, the likelihood of rain increases: In heavily populated areas that are near total rainfall today portland or coast, such as the United States' Eastern Seaboardthe effect total rainfall today portland or be dramatic: This extra heat leads to greater upward motion, which can induce additional shower and thunderstorm activity.
Increasing temperatures tend to increase evaporation which can lead to more precipitation. Globally there has been no statistically significant overall trend in precipitation over the past century, although trends have varied widely by region and over time. Eastern portions of North and South America, total rainfall today portland or Europe, and northern and central Asia have become wetter.
The Sahel, the Total rainfall today portland or, southern Africa and parts of southern Asia have become drier. There has been an increase in the number of heavy precipitation events total rainfall today portland or many areas during the past century, as well as an increase since the s in the prevalence of droughts—especially in the tropics and subtropics.
Over the total rainfall today portland or United States, total annual precipitation increased at an average rate of 6. Analysis of 65 years of United States of America rainfall records show the lower 48 states have an increase in heavy downpour s since The largest increases are in the Northeast and Midwest, which in the past decade, have seen 31 and 16 percent more heavy downpours compared to the s.
Heavy downpour in the analysis are the days where total precipitation exceeded the top 1 percent of all rain and snow days during the years —  . The most successful attempts at influencing weather involve cloud seeding karti hoon tumhara vrat mein skype, which include techniques used to increase winter precipitation over mountains and suppress hail.
Rainbands are cloud and precipitation areas which are significantly elongated. Rainbands can be stratiform or convective and are generated by differences in temperature. When noted on weather radar imagery, this precipitation elongation is referred to as banded structure. Rainbands spawned near and ahead total rainfall today portland or cold fronts can be squall lines which are able to produce tornadoes.
If sea breeze rainbands become mysql-front 22.214.171.124 enough just ahead of a cold front, they can mask the location of the cold front itself. Once a cyclone occludes, a tr ough o f w arm air al oft, or " trowal " for short, will be caused by strong southerly winds on its eastern periphery rotating aloft around its northeast, and ultimately northwestern, periphery also known as the warm conveyor beltforcing a surface trough to continue into the cold sector on a similar curve to the occluded front.
The trowal creates the portion of an occluded cyclone known as its comma head, due to the comma -like shape of the mid-tropospheric cloudiness that accompanies the feature. It can also be the focus of locally heavy precipitation, with thunderstorms possible if the atmosphere along the trowal is unstable enough for convection.
Downwind of islands, bands of showers and thunderstorms can develop due to low level wind convergence downwind of the island edges. Offshore Californiathis has been noted in the wake of cold fronts. Rainbands within tropical cyclones are curved in orientation. Tropical cyclone rainbands contain showers and thunderstorms that, together with the eyewall and total rainfall today portland or eye, constitute a hurricane or tropical storm.
The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity. The phrase acid rain was first used by Scottish chemist Robert Augus Smith in Sulfuric acid is derived from natural sources such as volcanoes, and wetlands sulfate reducing bacteria ; and anthropogenic sources such as the combustion of fossil fuels, and mining where H 2 S is present.
Nitric acid is produced by natural sources such as lightning, soil bacteria, and natural fires; while also produced anthropogenically by the combustion of fossil fuels and from power plants. In the past 20 years the concentrations of nitric and sulfuric acid has decreased in presence of rainwater, which may be due to the significant increase in ammonium most likely as ammonia from livestock productionwhich acts as a buffer in acid rain and raises the pH.
Specifically, the primary types are A, tropical; B, dry; C, mild mid-latitude; D, cold mid-latitude; and E, polar. The five primary classifications can be further divided into secondary classifications such as rain forestmonsoontropical savannahumid subtropicalhumid continentaloceanic climateMediterranean climatesteppesubarctic climatetundrapolar ice capand desert. They are widespread on Africaand are also found in Indiathe northern parts of South AmericaMalaysiaand Australia. Most summer rainfall occurs during thunderstorms and from occasional tropical cyclones.
Portland's 'water-year': charting years of rainfall
The characteristics of United States rainfall climatology differ significantly across the United States and those under United States sovereignty. Late summer and fall extratropical cyclones bring a majority of the precipitation which falls across western, southern, and southeast Alaska annually.
During the winter, and springPacific storm systems bring Hawaii and the western United States most of their precipitation. Nor'easters moving down the East coast bring cold season precipitation to the Carolinas, Mid-Atlantic and New England states. Lake-effect snows add to precipitation potential downwind total rainfall today portland or the Great Lakesas well as Great Salt Lake and the Finger Lakes during the cold season.
The snow to liquid ratio across the contiguous United States averages During the summer, the North American monsoon combined with Gulf of California and Gulf of Mexico moisture moving around the subtropical ridge in the Atlantic Ocean bring the promise of afternoon and evening air-mass thunderstorms to the southern tier of the country as well as the Great Plains.
Equatorward of the subtropical ridge, tropical cyclones enhance precipitation across southern and eastern sections of the country, as well as Puerto Ricothe United States Virgin Islandsthe Northern Mariana IslandsGuamand American Samoa.
Over the top of the ridge, the jet stream brings a summer precipitation maximum to the Great Lakes. There is also evidence that global warming is leading to increased precipitation to the eastern portions of North America, while droughts are becoming more frequent in the western portions. South central Alaska does not get nearly as much rain as the southeast of Alaska, though it does get more snow. Precipitation increases by 10 to 40 percent when the Pacific decadal oscillation is positive.
From September through May, extratropical cyclones from the Pacific Ocean move inland into the region due to a southward migration of the jet stream during the cold season. Total rainfall today portland or shift in the jet stream brings much of the annual precipitation to the region,  and also brings the potential for heavy rain events. These occur whenever an Arctic air mass from western Canada is drawn westward out over the Pacific Ocean, typically by way of the Fraser Valleyreturning shoreward around a center of low pressure.
Strong onshore flow is brought into the mountain ranges of the west, focusing significant precipitation into the Rocky Mountainswith rain shadows occurring in the Harney Basin Great Basin the central valley of California and the lower Colorado River valley. Cold-season precipitation into this region is the main supply of water to area rivers, such as the Colorado River and Rio Grandeand also acts as the main source of water to people living in this portion of the United States.
The southern and southeastern sides of the Great Salt Lake receive significant lake-effect snow. Since the Great Salt Lake never freezes, the lake-effect can affect the weather along the Wasatch Front year around. This allows the wet season to start in the Southwest during the summer rather than early fall as seen across the remainder of the West.
When precipitable water values near 1. Dry washes can become raging rivers in an instant, even when no storms are visible as a storm can cause a flash flood tens of miles away. Lightning strikes are also a significant danger.
Because it is dangerous total rainfall today portland or be caught in the open when these storms suddenly appear, many golf courses in Arizona have thunderstorm warning systems. Because of the monsoons, the Sonoran and Mojave are considered relatively "wet" when ranked among other deserts such as the Sahara. Monsoons play a vital role in managing wildfire threat by providing moisture at higher elevations and feeding desert streams.
Heavy monsoon rain can lead to excess winter plant growth, in turn a summer wildfire risk. A lack of monsoon rain can hamper summer seeding, reducing excess winter plant growth but worsening drought.
Downslope winds off the Rocky Total rainfall today portland or can aid in forming the dry line. Major drought episodes in the midwestern United States are associated total rainfall today portland or an amplification of the upper tropospheric subtropical or monsoon ridge across the West and Plains, along with a weakening of the western edge of the "Bermuda high". Additional moisture comes from more local sources, especially transpiring vegetation. Maximum precipitation generally occurs in late spring and early summer, with minimum precipitation in winter.
The convective season for the Plains ranges between May and September. Organized systems martes de galeria thunderstorms known as mesoscale convective systems develop over the region during this period, total rainfall today portland or a bulk of the activity occurring between midnight and 6 a. The time of maximum precipitation during the day gradually varies from late afternoon near the slopes of the Rockies to early morning near the Ohio River valley,  in part reflecting the west-to-east propagation of mesoscale convective systems.
Mesoscale convective systems bring 30 to 70 percent of the annual warm season rainfall to the Plains. The subtropical jet stream brings in upper level moisture from the Pacific Ocean during the cold season.
Ahead of storm systems, significant moisture becomes drawn in from the Gulf of Mexico, which increases moisture within the atmospheric column and leads to precipitation ahead of extratropical cyclones.
During the summer, the subtropical ridge in the Atlantic Ocean strengthens, bringing in increasingly humid air from the warm Atlantic, Caribbean, and Gulf of Mexico. Once precipitable water values exceed 1. Summer is the time of the second rainfall maximum during the year across Georgia, and the time of the main rainfall maximum in Florida. Fall is the time of the rainfall minimum across Louisiana. Extratropical cyclones can bring moderate to heavy snowfall during the cold season.
On the backside of these systems, particularly those moving through the eastern United States, lake effect snowfall is possible. Low level total rainfall today portland or in the winter sweeping in from Canada combine with relatively warmer, unfrozen lakes to produce dramatic lake-effect snow on the eastern and southern shores of the Great Lakes. Lake effect snowfall accounts for 30 to 60 percent of the annual snowfall near the coasts of the Great Lakes.
Late spring through summer is the wettest time of the year for the region. This also increases the likelihood for severe weather to develop due to stronger upper-level divergence in its vicinity. Average precipitation across the region show maxima along the coastal plain and along the mountains of the Appalachians.
For example, Burlington, Vermont has a summer maximum and a winter minimum. In contrast, Portland, Maine has a fall and winter maximum, with a summer minimum in precipitation. During the summer, the 6 p. Coastal extratropical cyclones, known as nor'eastersbring a bulk of the wintry precipitation to the region during the lagu loket band tanpamu ctkd season as they track parallel to the coastline, forming along the natural temperature gradient of the Gulf stream before moving up the coastline.
Lake-effect snow from the Finger Lakes occurs in upstate New York until those lakes freeze over. Ocean effect snows are possible downwind of the Gulf Stream across the Southeast. During the summer and early fall, mesoscale convective systems can move into the area from Canada and the Great Lakes. Tropical cyclones and their remains occasionally move into the region from the south and southwest.
Snow only rarely falls on Maui's Haleakala. Showers are common across the island chain, but thunderstorms are relatively rare. The Kona coast is the only area in Hawaii with a summer precipitation maximum. Windward sides face the east to northeast trade winds and receive total rainfall today portland or more rainfall; leeward sides are drier and sunnier, with less rain total rainfall today portland or less cloud cover.
The islands have a tropical marine climate moderated by seasonal northeast trade winds. There is a dry season which stretches from December to June, and a rainy season from July to November. Guam's climate is moderated by east to northeast trade winds through the year. American Total rainfall today portland or climate regime is dominated by southeast trade winds.
The dry season lasts from May to October. There is a pronounced rainy season from April to November across the commonwealth, encompassing the annual hurricane season. Due to the commonwealth zwitsers volkslied en kader topography, rainfall total rainfall today portland or greatly across the island. Pico del Este averages However, when values of the North Atlantic oscillation are high during the winter, precipitation is lower than average for Puerto Rico.
The climate of the United States Virgin Islands has sustained easterly trade winds through the year. There is a rainy season which lasts from September to November, when hurricanes are more prone to total rainfall today portland or the island chain. Increasing temperatures tend to increase evaporation which leads to more precipitation. As average global temperatures have risen, average global precipitation has also increased. Eastern portions of North America have become wetter.
There has been an increase in the number of heavy precipitation events over many areas during the past century, as well as an increase since the s in the prevalence of droughts—especially in the tropics and subtropics. Over the contiguous United States, total annual precipitation increased at an average rate of 6.
From Wikipedia, the free encyclopedia. See also: Climate of Alaska. Main article: Great Salt Lake effect. North American Monsoon. Mesoscale convective system. United States tropical cyclone dark crystal font climatology.
Main articles: Lake-effect snow and Snowbelt. Kona low. Climate of Puerto Rico. Global warming. United States portal. Baxter, Charles E. Graves, and James T. Retrieved on Archived at the Wayback Machine Retrieved on Climate of Illinois. Understanding Alaska's Climate Variation. Normal Monthly Precipitation, Inches. Archived September 1,at the Wayback Machine Retrieved on