MET 11- Precipitation

A rain shadow area is the leeward (downwind) side of a mountain barrier, characterized by significantly reduced precipitation because the air has lost most of its moisture rising over the windward side.
1. Barrier Orientation: The Western Ghats run along the west coast of India.
2. Moisture Flow: During the Southwest (SW) Monsoon (June to September), which is the principal rainy season for the region, the moisture-laden winds approach the Indian Peninsula from the west/southwest. These winds strike the Western Ghats (the windward side).
3. Precipitation Distribution: The upwind (western) slopes receive abundant, heavy rainfall. The air then descends, warming and drying adiabatically, causing precipitation to decrease drastically on the opposite side.
4. Conclusion: The areas to the East of the Western Ghats are the leeward, dry, rain shadow areas.

Key Data to Remember:
• Rain Shadow: Leeward side of mountains.
• Western Ghats Windward Side: West Coast (wettest due to SW Monsoon).
• Western Ghats Leeward Side: East (rain shadow).

The “Giant Nucleus Theory,” which is synonymous with the Coalescence Theory ( that explains the occurrence of precipitation in clouds where temperatures are above zero (warm clouds). This process relies on larger droplets combining with smaller ones until they become heavy enough to fall as rain ).

The “Giant Nucleus Theory is particularly relevant to Maritime Areas (over the sea) because large hygroscopic nuclei, such as salt particles (derived from ocean spray), are present. These nuclei allow water vapor to condense easily, forming larger droplets that trigger the coalescence process and subsequent rainfall common over sea and coastal areas.

Key Data to Remember:
• Theory Name: Coalescence Theory or Giant Nucleus Theory.
• Location: Maritime Area (over the sea) and coastline area.
• Mechanism: Requires the presence of large hygroscopic nuclei (salt) to initiate the growth of droplets in warm clouds (>0 ∘C).
• Precipitation Type: Primarily drizzle or rain.

Clouds whose vertical extent includes temperatures below 0 ∘ C are fundamentally important, particularly due to the presence of supercooled water droplets and associated icing hazards.

Cold Cloud Definition: Cold clouds are those that extend into atmospheric layers where temperatures are below freezing (0 ∘C).
Composition: Cold clouds contain a mixture of ice crystals and liquid water droplets. Water droplets that exist at temperatures below freezing are known as supercooled water droplets (SWD). SWD are abundant in the temperature range of 0 ∘ C to −15 ∘C.
Vertical Extent: Clouds of great vertical extension, such as Cumulonimbus (CB) and Towering Cumulus (TCU), contain SWD above the freezing level. CB clouds are the ultimate manifestation of instability and can extend from the surface up to the tropopause (up to 45,000 ft or higher in low latitudes).
Layer Clouds: Certain layer clouds, such as Nimbostratus (NS) and Altostratus (AS), are classified as cold clouds because their tops and sometimes substantial portions contain water droplets and ice crystals, causing light to severe icing hazards.

Aviation Significance (Icing and Precipitation)
1. Icing Hazard: The existence of SWD poses a significant icing threat to aircraft.
◦ Icing risk is highest where the concentration of SWD is high, such as near the base of the cloud where temperatures are highest (closest to 0 ∘C).
◦ CB and CU clouds, due to strong updrafts, support a high concentration of liquid water well above the freezing level, leading to moderate to severe icing conditions.
◦ Even stratified cold clouds (AS, NS) present serious icing conditions for protracted flights, typically in a layer 2,000 ft to 5,000 ft above the freezing level.
2. Precipitation Process: Precipitation formation in cold clouds in middle and high latitudes is often explained by the Ice-Crystal (Bergeron) process. This process relies on the co-existence of ice crystals and supercooled water droplets, where ice crystals grow rapidly at the expense of liquid droplets through deposition.

A rain shadow area is the leeward (downwind) side of a mountain barrier where descending air is relatively dry, resulting in noticeably lower precipitation.
The Eastern Ghats, which run near the eastern coast of India, function as a barrier primarily during the Northeast (NE) Monsoon (October to December).
1. Wind Flow: During the NE Monsoon, the surface winds blow from the Northeast, often having picked up considerable moisture after crossing the Bay of Bengal.
2. Rainfall Distribution: This moist flow strikes the eastern coast and the seaward (eastern) slopes of the Eastern Ghats, resulting in significant rainfall along the coastal areas (Tamil Nadu and Andhra Pradesh).
3. Rain Shadow: As the air continues westward over the Eastern Ghats and descends into the interior, it warms and dries, causing the rainfall amounts to decrease significantly inland (to the interior/west).
Therefore, the areas to the West (W) of the Eastern Ghats are the rain shadow regions associated with this mountain range during the NE Monsoon.

Key Data to Remember:
• Rain Shadow Location: Always the leeward side (downwind side) of the barrier.
• Eastern Ghats Dominant Season: NE Monsoon (Oct−Dec).
• Wind Direction: NE (onshore).
• Result: West (W) side is the rain shadow area.

A rain shadow area is consistently located on the leeward side (downwind side) of a mountain range. This phenomenon is the result of orographic uplift. As moist air is forced to ascend the windward side, cooling leads to condensation and precipitation, removing moisture from the air mass. When the now-dry air descends the leeward side, it warms adiabatically (known as the Foehn effect). This warming and drying process inhibits cloud formation and precipitation, resulting in a region characterized by noticeably low rainfall.

Key Data to Remember:
• Rain Shadow Location: Leeward/Downwind side of a mountain.
• Windward Side: Characterized by rising, cooling, moist air, and abundant precipitation.
• Leeward Side: Characterized by descending, warming, dry air, resulting in low precipitation and often a lower relative humidity.

Fog dispersal, or “thinning,” through artificial stimulation has been achieved, although usually only for specific types of fog and often only for short durations.
The most reasonably successful method to date is the seeding of cold fog (supercooled fog). Cold fog forms when the air temperature is below freezing, and the fog droplets remain liquid (supercooled).
• Mechanism: Introducing substances like dry ice (solid carbon dioxide) into the cold fog causes the supercooled droplets to freeze into ice crystals. These ice crystals then grow and fall out, leaving a clear area for aircraft operations.
• Duration/Feasibility: Although successful for cold fog, methods attempted for warm fog (such as heating or hygroscopic particle injection) are typically short-lived, expensive, or not very effective, clearing the area for only a short time.

Convective clouds, typically Cumulus (CU), form when the surface is heated, causing thermals to rise.
1. Cloud Base Height (LCL): As the day progresses, the maximum surface temperature (T) increases, causing the spread between the temperature and the dew point (T−Td) to increase. This larger spread means the air must be lifted to a greater altitude before saturation occurs (LCL), resulting in a rising cloud base.
2. Vertical Development: The increased surface heating also destabilizes the atmosphere (especially if conditionally unstable). If instability is deep, small-early morning CU clouds can develop vertically throughout the day into large Towering Cumulus (TCU) or Cumulonimbus (CB) clouds by the afternoon.

Key Data to Remember:
• Mechanism: Convection (free convection/thermals) requires surface heating and instability.
• Diurnal Pattern: T max (around 1500 LMT) leads to maximum instability and maximum cloud growth, often converting CU to CB.
• Cloud Type: CU and CB are the primary convective cloud types, characterized by vertical development.

Anticyclonic conditions are characterized by divergence of air at the surface and general subsidence (sinking air) throughout the system.

1. Subsidence Effect: Sinking air is compressed and warms adiabatically. This warming effect stabilizes the atmosphere, inhibiting lifting and preventing the formation of vertically developed clouds (CU or CB). Therefore, cloud formation is generally suppressed, leading to clear skies or good weather above the subsidence inversion.
2. Turbulence Cloud Exception: The main exception to cloudlessness occurs at low levels, beneath the subsidence inversion, where moisture and pollutants are trapped. Here, local turbulence or cooling can cause stratified clouds, specifically Stratus (ST) and Stratocumulus (SC), to form. Since these low, layered clouds (ST, SC) are generated by mechanical mixing/turbulence within the friction layer, they are often referred to as turbulence clouds.

Conclusion: Apart from these low, stratiform (turbulence) clouds and clouds potentially found only at the edge of the system, the stabilizing influence of the anticyclone makes the formation of other cloud types highly unlikely.

Key Data to Remember:
• Vertical Motion: Subsidence/Descending air.
• Stability: Atmosphere is stabilized and warming, inhibiting convection.
• Cloud Type (Likely): ST or SC (turbulence cloud) forming below the subsidence inversion, or no cloud at all.
• Visibility: Haze/mist/fog are likely below the inversion due to trapped contaminants and light winds.

Anticyclonic conditions are characterized by divergence of air at the surface and general subsidence (sinking air) throughout the system.

1. Subsidence Effect: Sinking air is compressed and warms adiabatically. This warming effect stabilizes the atmosphere, inhibiting lifting and preventing the formation of vertically developed clouds (CU or CB). Therefore, cloud formation is generally suppressed, leading to clear skies or good weather above the subsidence inversion.
2. Turbulence Cloud Exception: The main exception to cloudlessness occurs at low levels, beneath the subsidence inversion, where moisture and pollutants are trapped. Here, local turbulence or cooling can cause stratified clouds, specifically Stratus (ST) and Stratocumulus (SC), to form. Since these low, layered clouds (ST, SC) are generated by mechanical mixing/turbulence within the friction layer, they are often referred to as turbulence clouds.

Conclusion: Apart from these low, stratiform (turbulence) clouds and clouds potentially found only at the edge of the system, the stabilizing influence of the anticyclone makes the formation of other cloud types highly unlikely.

Key Data to Remember:
• Vertical Motion: Subsidence/Descending air.
• Stability: Atmosphere is stabilized and warming, inhibiting convection.
• Cloud Type (Likely): ST or SC (turbulence cloud) forming below the subsidence inversion, or no cloud at all.
• Visibility: Haze/mist/fog are likely below the inversion due to trapped contaminants and light winds.

A Cloudburst is the term used in popular meteorology to describe any sudden and excessively heavy fall of rain, almost always of the shower type. Showers are characterized by suddenness of beginning and ending, and rapid change of intensity, and they originate from cumuliform clouds, such as Cumulus (CU) or Cumulonimbus (CB). Since heavy showers originate from clouds with strong vertical upcurrents (convective clouds), the intensity can be extreme over a short duration.

Key Data to Remember:
• Definition: Excessively heavy rain shower.
• Cloud Type: Associated with convective clouds (CU, CB).
• Duration: Short and sporadic, typical of showers.
• Contrast: Continuous rain falls from layer clouds (stratiform, e.g., Nimbostratus).

Artificial rainmaking is formally termed Cloud Seeding. This process involves introducing artificial substances, such as silver iodide or dry ice, into a cloud. The goal is to provide artificial nuclei to stimulate the growth of cloud particles, causing them to fall as precipitation. This technique is used to increase precipitation or, in the case of cold fog, to initiate freezing and subsequent dispersal.

Key Data to Remember:
• Definition: Introduction of artificial nuclei (AgI or dry ice) into clouds to enhance or modify precipitation.
• Mechanism: Utilizes the collision-coalescence process (in warm clouds) or the ice-crystal/Bergeron process (in cold, supercooled clouds).
• Agents: Silver iodide (AgI) and dry ice (solid carbon dioxide).

This phenomenon is the fundamental premise of the Ice-Crystal Process (also known as the Bergeron process), which explains precipitation formation in cold clouds (T<0 ∘ C) where supercooled water droplets (SWD) and ice crystals coexist.
At the same subfreezing temperature, the Saturation Vapour Pressure (SVP) over a supercooled liquid water surface is greater than the SVP over an ice surface.
This pressure differential causes water vapor molecules to move (diffuse) continuously from the area of higher SVP (around the water droplet) to the area of lower SVP (around the ice crystal). Consequently, the supercooled water droplets evaporate, and the water vapor deposits directly onto the ice crystals (sublimation), causing the ice crystals to grow rapidly at the expense of the liquid droplets.

Key Data to Remember:
• Process: Ice-Crystal (Bergeron) Process.
• Condition: T<0 ∘C (Cold Cloud).
• Vapor Pressure Rule: SVP Water > SVP Ice (at subfreezing temperatures).
• Result: Ice crystals grow through deposition (sublimation).

Rainfall in the temperate latitudes (approximately 40 ∘ to 65 ∘ N and S) is primarily controlled by the activity of travelling frontal depressions forming along the Polar Front.
1. Frontal Frequency: Polar Front lows are generally more frequent and vigorous in winter than in summer because the temperature contrast between polar air and tropical air masses is greatest during the cold season.
2. Precipitation Type: These active frontal systems lead to the greatest amount of precipitation (rain or snow) during the winter months in temperate maritime areas. This results in “wet” winters, such as those found in Western Europe.
3. Mediterranean Climate: Coastal regions within the transitional temperate zone (Mediterranean climate, 35∘to 40 ∘latitude) are specifically characterized by mild, wet winters and dry summers.

Key Data to Remember:
• Controlling Factor: Traveling Frontal Depressions (Polar Front Lows).
• Seasonal Maxima: Polar Front Lows are most frequent and intense in winter.
• Result: Precipitation (rain or snow) is maximal in winter in temperate oceanic and western regions. (Note: Inland continental areas may see a summer precipitation maximum due to intense thermal lows and convection).

For snow to reach the surface without completely melting, the surface temperature must generally be less than +4 ∘ C.
Although the freezing point of water is 0∘C, snowflakes falling into air warmer than 0 ∘C melt slowly. If the air is relatively dry, partial melting allows evaporation to occur, which absorbs latent heat and cools the snowflake, retarding the overall rate of melting. This mechanism allows snow to survive for a distance (approximately 300 m or 1000 ft) below the freezing level.
Therefore, the critical surface temperature threshold for accumulated snow is 4∘C (39.2 ∘F), above which falling snow is highly likely to melt completely before or immediately upon reaching the ground.

Key Data to Remember (Snow Survival):
• Surface Temperature Threshold: Less than +4∘ C.
• Melting: Snowflakes can fall about 1000 ft below the 0 ∘C level before completely melting, especially if the air is relatively dry.
• Aviation Context: Wet (melting) snow can lead to “pack snow,” obstructing engine intakes and degrading runway braking action.

The type of precipitation that is likely to reduce visibility the most is snow, particularly when it is heavy, blowing, or drifting. While heavy drizzle can reduce visibility significantly (down to 500 m) due to the large number of small droplets, heavy snow can result in extremely low horizontal visibility, sometimes reducing it to 50 m or even less.

Key Data to Remember (Visibility in Heavy Precipitation):
• Heavy Snow: Visibility can be reduced to 50 m to 200 m.
• Drizzle: Visibility typically ranges from 500 m to 3000 m.
• Operational Context: Poor visibility is listed as a major hazard associated with CBs and CUs, where precipitation often falls as heavy snow or rain showers. The worst type of precipitation for visibility reduction is snow.

The Coalescence Theory, also known as the Collision-Coalescence Process (or Capture Effect), is primarily used to explain the formation of precipitation in Warm Clouds.
1. Warm Clouds: These are clouds where the temperature throughout their entire depth, including the cloud tops, remains above freezing (0 ∘C). They are commonly found in tropical and lower latitudes.
2. Mechanism: This theory posits that precipitation forms when larger cloud droplets fall faster and collide (coalesce) with smaller droplets in their path. The combining droplets grow until they are heavy enough to overcome upward air currents and fall as drizzle or rain.
3. Contrast: This process is crucial because the Ice-Crystal (Bergeron) process, which dominates precipitation formation in middle and high latitudes, requires sub-zero conditions and the coexistence of ice crystals and supercooled water droplets. Where the cloud is entirely above 0 ∘C, the Coalescence Theory must be invoked to account for the precipitation.

Key Data to Remember:
• Theory Name: Coalescence Theory or Collision-Coalescence Process.
• Cloud Type: Warm Clouds (>0 ∘C throughout).
• Location: Primarily lower/tropical latitudes.
• Precipitation Type: Drizzle or rain.

The precipitation over Jammu and Kashmir (J&K) and the Western Himalayas is maximal during the Winter Season (Cold Weather Season, typically January and February). This region is an exception to the general Indian climate pattern where the Southwest (SW) Monsoon brings maximum rainfall in summer. The precipitation in the Western Himalayas during winter is primarily associated with the passage of Western Disturbances (WDs).

Key Data to Remember:
• Controlling System: Western Disturbances (WDs).
• Nature of WDs: Synoptic systems in mid-latitude westerly winds, often occluded fronts, bringing precipitation from the west.
• Precipitation Type: The higher reaches of the Western Himalayas often receive snowfall.
• Rainfall Amount: Kashmir and neighborhood receive greater than 20 cm of rainfall during the winter season, distinguishing this area from the typically dry winter conditions elsewhere in India.

Turbulence clouds, such as Stratus (ST) and Stratocumulus (SC), are layer clouds characterized by little vertical extension (typically 1000 to 2000 ft thick) and a flat top.
1. Mechanism: These clouds form in stable air, within the friction layer, where there is sufficient wind (W/V>10 kt) to create mechanical turbulence and vertical mixing.
2. Lapse Rate Change: Turbulent mixing causes the Environmental Lapse Rate (ELR) within the mixed layer to steepen towards the Dry Adiabatic Lapse Rate (DALR).
3. Flat Top: The vertical growth of this cloud is sharply limited by a highly stable layer or a temperature inversion that acts as a “lid,” usually located just above the friction layer. The rising air is immediately stopped upon encountering the warmer, more stable air of the inversion, which results in the characteristic flat top.

Key Data to Remember:
• Cloud Types: ST, SC, and AC are formed by turbulence.
• Structure: Characterized by large horizontal extent and a flat top caused by a capping inversion.
• Process: Turbulence mixes the layer below the inversion, steepening the lapse rate until condensation occurs.

In tropical regions (especially the transitional climatic zone between 10 ∘ and 20 ∘ latitude), precipitation is maximized during the summer season (or high-sun period).
1. Mechanism: The global atmospheric circulation features, particularly the Intertropical Convergence Zone (ITCZ), follow the sun’s seasonal movement (the thermal equator).
2. Rainy Season: When the ITCZ migrates poleward into the respective hemisphere during its summer, it brings strong surface convergence and widespread lifting of warm, moist air. This leads to the development of huge cumulonimbus (CB) clouds, heavy showers, and thunderstorms, characteristic of the wet season.
3. Contrast: During the winter (low-sun period), these regions fall under the influence of the dry trade winds and the sinking air associated with the subtropical highs, resulting in the dry season.

Key Data to Remember:
• Maximum Rainfall: High-sun period or summer season.
• Cause: Seasonal migration of the Intertropical Convergence Zone (ITCZ).
• Weather: Convective activity, heavy showers, and thunderstorms.

In the tropics, high temperatures and humidity favor convective activity, resulting in heavy showers and thunderstorms.
1. Convective Mechanism: Over tropical land areas, the surface receives maximum insolation, leading to the greatest surface heating and resulting instability.
2. Timing: Due to the time lag between peak insolation (noon) and maximum air temperature/instability, towering Cumulus (CU) clouds and Cumulonimbus (CB) clouds typically form and produce heavy, localized showers by early afternoon. Maximum intensity and frequency of these Air Mass thunderstorms usually occur during the middle and late afternoon.
3. Note on Coastal Areas: While generalized tropical rainfall maximizes in the afternoon over land, rainfall over many tropical coastal areas and near islands can reach a maximum during the night or early morning due to convergence associated with the land breeze effect. However, the primary diurnal maximum associated with the tropical wet climate is generally the afternoon.

Key Data to Remember:
• Mechanism: Convection (surface heating/instability).
• Timing (Land): Maximum precipitation/TS activity in the afternoon.
• Cloud Type: CU and CB (Showers).

The cloud type most likely to produce continuous moderate or heavy rain is Nimbostratus (NS).
1. Cloud Type and Mechanism: Nimbostratus is a stratiform (layer) cloud. Layer clouds form in stable air and are associated with precipitation that is widespread and of long duration. NS is specifically defined as a dense, dark-gray, stratiform cloud producing extensive and long-lasting continuous or intermittent precipitation.
2. Convective Contrast: This contrasts sharply with Cumulonimbus (CB) and large Cumulus (CU) clouds, which are cumuliform (heap) clouds forming in unstable air and are characterized by precipitation that falls as showers. Showers are of short duration.
3. Intensity: Nimbostratus precipitation intensity is typically described as light to moderate or moderate to heavy. When associated with a slow-moving front, NS precipitation can cover thousands of square miles.

Key Data to Remember:
• Nimbostratus (NS): Stratiform (Layer) cloud, characteristic of stable air and frontal uplift (Warm Fronts).
• Precipitation Type: Continuous or intermittent.
• Hazard: Can pose a serious icing problem if temperatures are near or below freezing, and visibility is poor in precipitation.
• Cumulonimbus (CB)/CU: Cumuliform (Heap) clouds. Precipitation is always showery.

Rainfall maximization over many coastal areas, particularly in tropical regions, frequently occurs during the night and early morning hours. This timing contrasts with the afternoon maximum typical of convection over continental landmasses.
The mechanism for this nocturnal coastal precipitation maximum involves thermally driven circulation and the diurnal heating cycle:
1. Land Breeze/Katabatic Effect: At night, the land cools more rapidly than the adjacent sea surface. This cooling creates higher surface pressure over the land, leading to a land breeze blowing offshore. In coastal areas with mountainous terrain (like Sumatra/Malaysia), this effect is amplified by katabatic flow (cold air drainage down slopes).
2. Convergence over Water: This cold air flow moves over the relatively warm sea surface. Convergence occurs offshore where the flow meets, or as the cold air destabilizes over the warm water.
3. Convective Activity: The passage of cool air over warm water rapidly takes in moisture and becomes unstable. This instability and upward motion generate convective clouds (CU and CB) and associated heavy showers over the water, which often drift toward the coast.
A notable example supporting this pattern is the violent thundery squalls known as Sumatras in the Malacca Straits, which form at night due to katabatic flow meeting over the warm sea, reaching maximum development by dawn.

The movement of cool (Polar) air over a significantly warmer surface (such as a warmer ocean or land) is a classic mechanism for atmospheric destabilization and convection.
1. Heating from Below: When cool air moves over a warmer surface, the lower layers of the air mass are heated by conduction.
2. Instability: This heating from below steepens the Environmental Lapse Rate (ELR), generating instability and increasing buoyancy.
3. Convective Cloud Formation: If the air is sufficiently moist, this instability leads to the development of vertical air currents (thermals or convection currents) which rise and cool adiabatically until condensation occurs. This process results in the formation of heap-type clouds.
4. Cloud Types: Typical convective clouds formed by this process are Cumulus (CU) and, if the instability is deep and moisture is abundant, Cumulonimbus (CB). This often leads to showers. A prime example is Polar maritime air moving south over a warmer sea, which becomes unstable and produces CU and CB activity.
This process contrasts with advection fog, which requires warm, moist air moving over a colder surface.

The term Sleet is used in different contexts. In popular terminology, Sleet is defined as a mixture of snow and rain. It occurs when snow partially melts while falling through air slightly above freezing temperatures, typically between +5 ∘C to +6 ∘ C. This mixture is similar to freezing rain in its ability to lead to ‘pack snow’ which can block air intakes.

Key Data to Remember (Terminology Note):
• Sleet (as a mixture): Rain and Snow.
• Sleet (ICAO Definition): Tiny transparent ice pellets (PE). These form when a partially melted snowflake or cold raindrop refreezes into an ice pellet before reaching the ground.

A day is defined as a Rainy day when the total rainfall amount measured in a 24-hour period is 2.5 mm or more.

Key Data to Remember:
• Rainy Day Threshold: ≥2.5 mm of rainfall in a day.
• Context: This is a specific meteorological criterion used for defining and reporting days with significant precipitation.

Drizzle, characterized by very small water drops (diameter 0.2 to 0.5 mm) that appear to float, primarily falls from low, sheet-like clouds.
• Stratus (ST): This cloud type is explicitly associated with drizzle. ST is a layer cloud with large horizontal extent but little vertical development, and drizzle is characteristic of the minimal precipitation produced by such clouds.
• Contrast: Continuous rain or snow falls from Nimbostratus (NS). Showers of rain or snow fall from Cumulus (CU) and Cumulonimbus (CB) clouds.

Key Data to Remember:
• Drizzle Definition: Very small water drops, <0.5 mm in diameter.
• Cloud Type: Stratus (ST) or sometimes Stratocumulus (SC).
• Visibility: Drizzle reduces visibility significantly, potentially to 500 m.
• Continuity: Drizzle falls continuously or intermittently, typical of layer clouds (stratiform).

In the tropics, high temperatures and humidity favor convective activity, resulting in heavy showers and thunderstorms.
1. Convective Mechanism: Over tropical land areas, the surface receives maximum insolation, leading to the greatest surface heating and resulting instability.
2. Timing: Due to the time lag between peak insolation (noon) and maximum air temperature/instability, towering Cumulus (CU) clouds and Cumulonimbus (CB) clouds typically form and produce heavy, localized showers by early afternoon. Maximum intensity and frequency of these Air Mass thunderstorms usually occur during the middle and late afternoon.
3. Note on Coastal Areas: While generalized tropical rainfall maximizes in the afternoon over land, rainfall over many tropical coastal areas and near islands can reach a maximum during the night or early morning due to convergence associated with the land breeze effect. However, the primary diurnal maximum associated with the tropical wet climate is generally the afternoon.

Key Data to Remember:
• Mechanism: Convection (surface heating/instability).
• Timing (Land): Maximum precipitation/TS activity in the afternoon.
• Cloud Type: CU and CB (Showers).

Showery precipitation is characterized by its suddenness of beginning and ending, rapid change of intensity, and short duration. This type of precipitation is exclusively associated with convective clouds or heap type cloud (Cumulus and Cumulonimbus (CB)) that form in unstable air. Cumulonimbus clouds have great vertical development and contain strong upcurrents necessary to support the large water droplets, hail, or snow that fall as heavy showers.

Key Data to Remember:
• Showers: Short duration, variable intensity.
• Cloud Type: CB or CU (Cumuliform/Heap clouds).
• Continuous/Intermittent Precipitation: Falls from layer clouds (Stratiform), such as Nimbostratus (NS).
• Associated Hazards (CB): Heavy showers, hail, severe icing, severe turbulence.

The intensity of precipitation—which refers to the rate of fall—is typically described using the categories Slight, Moderate, or Heavy.
• This classification distinguishes the quantitative rate of precipitation (e.g., mm per hour).
• In aviation reports (such as METAR/TAF), moderate intensity is indicated by no qualifying symbol, light intensity by a ‘–’, and heavy intensity by a ‘+’.

Key Data to Remember:
• Intensity: Refers to the rate of precipitation (Slight, Moderate, Heavy).
• Continuity: Refers to the duration (Showers, Intermittent, Continuous).
• Types: Refer to the form (Drizzle, Rain, Snow, Hail).

The Ice-Crystal Process, also known as the Bergeron Theory, is the mechanism that explains the formation of precipitation in cold clouds. Cold clouds are those clouds where the temperature, at least partially (or entirely, in the upper levels), is below freezing (0 ∘C).
1. Requirement: This process requires the simultaneous existence of supercooled liquid water droplets and ice crystals within the cloud.
2. Mechanism: At the same subfreezing temperature, the saturation vapor pressure (SVP) over water is greater than the SVP over ice. This differential causes water vapor to continuously diffuse from the supercooled water droplets (which evaporate) to the ice crystals (which grow rapidly by deposition or sublimation).
3. Context: This process is crucial in middle and high latitudes where clouds frequently extend to levels where temperatures are below freezing.

Key Data to Remember:
• Theory Name: Ice-Crystal (Bergeron) Process.
• Cloud Type: Cold Clouds (T<0 ∘C).
• Condition: Co-existence of ice crystals and supercooled water droplets.
• Premise: Saturation vapor pressure over water is greater than over ice at subfreezing temperatures.
• Contrast: The Coalescence Theory explains precipitation in Warm Clouds where temperatures are entirely above 0 ∘C.

Stratocumulus (SC) clouds are low-level, stratiform (layer) clouds resulting from turbulence. The composition of SC is primarily water droplets. Since the cloud base often extends from 1000 ft to 6500 ft, its vertical profile frequently includes regions where temperatures are below freezing.
If the air temperature is 0 ∘ C or colder, these water droplets often become supercooled (remaining liquid below 0 ∘C). This is the condition necessary for aircraft structural icing. Stratocumulus clouds can contain small supercooled droplets from 0 ∘ C to −40 ∘C.
Precipitation from SC is typically limited to drizzle, freezing drizzle, or snow grains. The vertical currents in SC are light to moderate turbulence, not the strong upcurrents required to support large water droplets characteristic of Cumulonimbus (CB).

Key Data to Remember:
• Cloud Type: Stratiform/Turbulence cloud.
• Composition: Water droplets, capable of being supercooled.
• Icing: Light to moderate Rime Ice risk when supercooled.
• Precipitation: Drizzle, freezing drizzle, snow grains.

fair weather cumulus in morning the you can expect thunderstorm activity in afternoon.
in morning you may experience turbulence in the same region ( specially at lower level).