Flight Forecast T-3 and Cross-section T-4

Meteorology · Chapter 29 · DGCA CPL and ATPL

The two forms a forecaster fills in for a route when charts cannot be sent: a table for short routes and a side-on picture for long ones.

Remember

Met T-3: tabular, routes up to 500 NM, heights in feet amsl. Met T-4: cross-section, routes beyond 500 NM, heights in flight levels.
Both give the synoptic situation and surface pressure, en-route outlook, cloud amount and type, upper winds and temperatures, freezing level, tropopause, and surface visibility for flights below FL100.
ISOL under 50% of the area, OCNL 50-75%, FRQ over 75%. EMBD: embedded in other cloud. Cloud is written base/top.
In a T-4 the wind and temperature are given at each end of the route for each level; read between them. Veering: turning clockwise; backing: anticlockwise.
Read a T-3 or T-4 in order: route and validity, special features (the reason), winds and temperatures, cloud, hazards, 0 °C level, surface boxes (visibility, QNH or lowest MSL pressure).

What does a table of numbers look like as weather?

The T-3, drawn

A sample T-3 (Kolkata to Delhi, 4 April 2023) turned into a side view of the route, box by box. Heights to scale. Tap Next.

The heading The route is Kolkata (VECC) to Delhi (VIDP) via Lucknow (VILK), on 4 April 2023. The forecast is for a take-off between 0300 and 0500 UTC and a landing between 0600 and 0800 UTC. All heights on a T-3 are in feet above mean sea level (amsl), not flight levels.
Why the weather First the forecaster names the system behind the weather. Here it is a western disturbance (WD) over west Rajasthan, beyond Delhi. With it goes an upper-air cyclonic circulation (CYCIR): winds turning round a low, up to 20 000 ft. So expect cloud and storms towards the Delhi end.
Winds and temperatures There are four heights: 5000, 10 000, 20 000 and 30 000 ft. Each row gives the Kolkata end and the Delhi end. At 30 000 ft: 300/60 kt and −33 °C at Kolkata, 270/70 kt and −30 °C at Delhi. M means minus. Low down the wind is easterly; high up it is westerly. That turn with height is normal ahead of a WD.
Cloud Scattered stratus at 1000 ft, a few stratocumulus at 2500 ft, scattered altocumulus at 12 000 ft and broken cirrostratus at 35 000 ft. Then one isolated CB from 2000 to 35 000 ft. It is embedded (EMBD): hidden in the layer cloud, so you may not see it to avoid it.
Hazards and freezing level Isolated thunderstorms, with icing and turbulence in the CB between 15 000 and 25 000 ft. Careful: the CB is written base/top (2000/35000), but the icing top/base (25000/15000). The bigger number is always the top. The 0 °C level is at 15 000 ft at Kolkata and 14 000 ft at Delhi. Above it, cloud means ice.
At the surface Visibility 6 km, 3000 m in rain and 1500 m in a thunderstorm. The forecast QNH is 1006 hPa at Kolkata and 1008 hPa at Delhi: the pressure setting for your altimeter, so it reads your height above sea level on landing.

Memory hook: T-3: a table, feet amsl, a column per place.

Takeaway: Read a T-3 from top to bottom. First the route and times. Then the reason for the weather, winds and temperatures at fixed heights for each end, cloud with bases and tops, surface visibility, significant weather, the 0 °C level and the forecast QNH. Every height is in feet above mean sea level.

What does this Kolkata-Delhi T-3 say?

Read a T-3

A tabular forecast, line by line. Tap each.

Kolkata to Delhi via Lucknow VECC TO VIDP VIA VILK The route, with a column for each point along it.
Feet above mean sea level HEIGHTS IN FEET AMSL T-3 heights are in feet amsl; T-4 uses flight levels.
Valid departure and arrival windows DEP 0300-0500 UTC · ARR 0600-0800 UTC The forecast holds for a departure and arrival inside these times.
Synoptic situation A WD LIES OVER W RAJASTHAN WITH UPPER AIR CYCIR UP TO 20,000 FT A western disturbance with an upper-air cyclonic circulation: the reason for the weather at the Delhi end.
Wind and temperature at 30,000 ft 30,000 FT: 300/60 M33 … 270/70 M30 Kolkata end 300°/60 kt −33 °C, Delhi end 270°/70 kt −30 °C. Lower rows give 20,000, 10,000 and 5000 ft.
Layer cloud and bases (ft) SCT ST 1000 FEW SC 2500 SCT AC 12000 Scattered stratus at 1000 ft, a few stratocumulus at 2500 ft, scattered altocumulus at 12,000 ft.
Isolated embedded CB, base 2000, top 35,000 ft ISOL EMBD CB 2000/35000 Base/top. Embedded means hidden inside layer cloud.
Broken cirrostratus at 35,000 ft BKN CS 35000 High cloud.
Surface visibility 6 KM · 3000 M IN RAIN · 1500 M IN TS Given because part of the information is for flights below FL100.
Significant weather ISOL TS · ICING, TURB IN CB Isolated thunderstorms, with icing and turbulence in the CB.
Freezing level 15,000 and 14,000 ft 0 °C ISOTHERM 15000 · 14000 Along the route.
Forecast QNH, hPa QNH 1006 · 1008 To set on the altimeter at each end.

Memory hook: T-3 is a table: feet above sea level, and a column for each place on the route.

Takeaway: A T-3 gives the route and validity, the synoptic situation, winds and temperatures by height, cloud, visibility, weather, the 0 °C isotherm and QNH, in a table. Heights in feet amsl.