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Weather Guides

Understanding the Weather

Original guides to aviation meteorology, the Indian monsoon and severe weather — written from operational experience, for people who need to make decisions.

18Guides
5Subjects
11+Years IAF

Weather information is abundant. Weather understanding is considerably less so. These guides are written to close that gap — explaining not merely what the instruments report, but what the reports mean for someone who has to act upon them.

They are drawn from over eleven years of operational aviation meteorology with the Indian Air Force, where the difference between decoding a report and interpreting one was frequently the difference that mattered. Each guide is written to be read by a non-specialist and to remain useful to a professional.

Monalisa Dutta, Founder, Sky Watch Weather India

Aviation Weather

Operational weather for flight crew, dispatchers and anyone who plans against the sky.

ANATOMY OF A METARMETARVIDP191200Z09008KT4000HZSCT02034/24Q1004Report typeStationDay / time UTCWindVisibility (m)WeatherCloudTemp / dewpointQNH
Aviation Weather

How to Read a METAR: A Practical Guide to Aviation Weather Reports

Every element of the standard aerodrome weather report explained in sequence, with the operational judgement that decoding alone does not provide.

Read the guide → 9 min
TAF CHANGE GROUPSBECMGPermanent changeOccurs gradually withinthe stated windowTEMPOTemporary fluctuationEach under 1 hour,less than half the periodPROB30/40Probability30% or 40% chanceof the stated conditionFMFromRapid, complete changeat the stated timeA TAF describes expected conditions within roughly 8 km of the aerodrome reference point.
Aviation Weather

Understanding the TAF: How to Read an Aerodrome Forecast

The TAF tells you what an aerodrome is expected to do over the coming hours. Understanding its change groups is what separates reading a forecast from planning against one.

Read the guide → 8 min
FLIGHT CATEGORY THRESHOLDSVFRCEILINGCeiling > 3000 ftVISIBILITYVisibility > 5 smMVFRCEILING1000 - 3000 ftVISIBILITY3 - 5 smIFRCEILING500 - 1000 ftVISIBILITY1 - 3 smLIFRCEILINGBelow 500 ftVISIBILITYBelow 1 smThe worse of the two values determines the category. Indian operations apply DGCA and aerodrome-specific minima.
Aviation Weather

VFR, MVFR, IFR and LIFR: What Flight Categories Actually Mean

The four colour-coded flight categories summarise ceiling and visibility into a single indication. Understanding how they are derived is essential to using them sensibly.

Read the guide → 6 min
ANATOMY OF A CUMULONIMBUSAnvil / overshooting topSevere icing layerHail & severe turbulenceDowndraught / microburstLightning & staticExtreme vertical shearGust front outflow
Aviation Weather

The Cumulonimbus: Why a Single Cloud Outweighs an Entire Weather Report

Every significant hazard in aviation meteorology is present simultaneously within one cloud type. Understanding its structure explains why avoidance, rather than penetration, is the only acceptable strategy.

Read the guide → 8 min
THE MICROBURST ENCOUNTERDescending core1. Headwind increase2. Downdraught3. Tailwind, lift lossThe initial performance gain is the trap — it is immediately followed by loss.
Aviation Weather

Windshear and Microbursts: The Hazard That Begins by Helping You

A microburst encounter starts with improving performance. Understanding why that initial gain is the most dangerous part of the sequence is central to recognising and surviving it.

Read the guide → 7 min
CLOUD COVER IN OKTASFEW1/8 sky coveredSCT4/8 sky coveredBKN6/8 sky coveredOVC8/8 sky coveredA ceiling is defined only by a BKN or OVC layer — FEW and SCT layers never form a ceiling.
Aviation Weather

Cloud Cover, Oktas and Ceilings: How Sky Condition Is Actually Measured

Cloud reporting appears simple until it matters. The distinction between a low layer and a ceiling changes the operational picture entirely.

Read the guide → 6 min

Indian Monsoon

How the season actually works, from onset criteria to the breaks that decide the outcome.

THE THREE ONSET CRITERIA01RAINFALL60% of 14 designatedstations recording2.5 mm or more ontwo consecutive days02WIND FIELDWesterlies maintainedup to 600 hPa;15-20 kt zonal windat 925 hPa03CLOUD (OLR)Outgoing longwaveradiation below200 W/m2 over theSE Arabian SeaAll three must be satisfied together — heavy rain alone does not constitute onset.
Indian Monsoon

How the IMD Declares Monsoon Onset Over Kerala

Onset is not declared because it rained. Three independent conditions must be satisfied together, and understanding them changes how the season is read.

Read the guide → 8 min
THE MONSOON AS A REVERSING WIND SYSTEMIndian Ocean — cooler, moistIndian landmass — strongly heatedLOWPRESSUREDeep, moisture-laden south-westerliesRain is the symptom. The seasonal reversal of the wind is the mechanism.
Indian Monsoon

Understanding the Indian Monsoon: The Mechanism Behind the Season

The monsoon is a seasonal reversal of wind driven by the differential heating of land and ocean, shaped by the Earth's rotation and the position of the jet streams.

Read the guide → 8 min
ACTIVE AND BREAK MONSOON PHASESACTIVE PHASEMonsoon trough lies overits normal position across the plainsWidespread rain over central IndiaBREAK PHASETrough shifts north to theHimalayan foothillsPlains dry and hot; foothills floodProlonged breaks in July and August do more to determine the season total than the onset date.
Indian Monsoon

Break Monsoon: Why the Rain Stops in the Middle of the Season

Extended dry spells during July and August do more to determine whether a monsoon season succeeds or fails than the onset date ever does.

Read the guide → 6 min

Climate Drivers

The ocean and atmosphere patterns that shape an entire monsoon season.

Weather Observation

Reading the instruments — radar, satellite and lightning detection.

RADAR REFLECTIVITY SCALE (dBZ)5152532384450566270Light rainModerateHeavy rainVery heavy / hailLarge hail likelyReturned power scales with the sixth power of droplet diameter.This is why hail dominates the high end of the scale — and why heavy warm rain can look modest.
Weather Observation

Doppler Radar Colours Explained: What Green, Yellow and Red Actually Mean

Radar colour measures how strongly the atmosphere reflects a pulse, not how much rain is coming. The difference explains most of the misreading seen in public commentary.

Read the guide → 8 min
THE THREE SATELLITE CHANNELSVISIBLEReflected sunlightDaytime onlyShows cloud textureand thicknessINFRAREDEmitted heatDay and nightCold tops = tall,deep convectionWATER VAPOURMid-level moistureDay and nightReveals jets, troughsand dry intrusionsForecasters rarely rely on one channel alone — the three are read together.
Weather Observation

Reading Weather Satellite Imagery: Visible, Infrared and Water Vapour

Three satellite channels answer three different questions. Knowing which to consult, and when, is the difference between looking at cloud and understanding it.

Read the guide → 7 min
CHARGE SEPARATION IN A THUNDERSTORM+++++++++Positive charge in ice crystals near the topNegative charge in graupel lower downInduced positive charge at the surface
Weather Observation

How Lightning Detection Works, and Why It Matters in India

Lightning networks locate strikes to within a few hundred metres in real time. In a country where lightning causes substantial loss of life each year, that capability has genuine value.

Read the guide → 6 min

Severe Weather

Cyclones, heat, fog and the warning systems built around them.

IMD CYCLONE INTENSITY SCALE (KNOTS)17-27Depression28-33DeepDepression34-47CyclonicStorm48-63Severe64-89VerySevere90-119ExtremelySevere120+SuperCyclone3-minute sustained surface wind speed, as classified by the India Meteorological Department.
Severe Weather

Cyclone Categories in the North Indian Ocean: The IMD Classification

The IMD uses a seven-stage intensity scale based on three-minute sustained winds, which is why the same storm may be described differently by different agencies.

Read the guide → 7 min
IMD COLOUR-CODED WARNING SYSTEMGREENNo actionNo adverse weatherYELLOWBe updatedWatch the situationORANGEBe preparedDisruption likelyREDTake actionSevere impact expectedThe colour reflects expected impact, not simply rainfall quantity.
Severe Weather

IMD Colour-Coded Weather Warnings: What Each Level Requires

Green, yellow, orange and red describe expected impact and the action required, not simply the quantity of rain forecast.

Read the guide → 5 min
IMD HEATWAVE CRITERIAPlains40 °C or aboveHilly regions30 °C or aboveCoastal areas37 °C or aboveMinimum threshold before any departure is consideredDeparture from normalHeatwave — 4.5 to 6.4 °C above normalSevere heatwave — above 6.4 °COr 45 °C absolute (heatwave) / 47 °C (severe)
Severe Weather

Heatwaves in India: The Criteria, and Why Humidity Changes Everything

The IMD declares a heatwave using both absolute thresholds and departure from normal. Understanding the criteria explains why coastal warnings arrive at lower temperatures.

Read the guide → 6 min
CONDITIONS FOR RADIATION FOG1Clear skiesHeat escapes to space2Light wind3-7 kt mixes gently3Moist airSmall dewpoint spread4Long nightExtended cooling5Cooling surfaceAir chills to dewpointThe classic North Indian winter sequence — and the reason Delhi fog forms overnight, not by day.
Severe Weather

Winter Fog in North India: Why It Forms and Why It Persists

The Indo-Gangetic plain experiences some of the most persistent fog anywhere in the world. The reasons are partly meteorological and partly geographical.

Read the guide → 7 min