Chapter 24

STATION MODEL

DGCA CPL/ATPL Study Notes — Aviation Meteorology

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Compiled by Capt. Pankaj Pahil

DGCA CPL/ATPL Study Notes — Aviation Meteorology

1. Introduction to Station Model
2. Station Model Layout & Parameter Positions
3. Meaning of Symbols — All Parameters
4. Present Weather (ww) Codes — Table 24.5/24.6/24.7
5. Cloud Codes — Low (CL), Medium (CM), High (CH)
6. Codes for h, RRR, VV (Table 24.4)
7. Total Cloud Amount (N) Coding
8. Worked Example — Decoding a Station Model
9. Practice Q&A
10. Master Reference Tables

1. Introduction to Station Model

Definition: A station model is a standardised symbolic representation of surface weather observations plotted on a synoptic weather chart. Each symbol, number, and code occupies a fixed position relative to a central circle that represents the observation station.

Met stations worldwide make standardised surface observations and encode them using WMO codes. These are then plotted as station models on synoptic charts used by forecasters and pilots. Reading a station model is a core DGCA exam skill.

🎯 Exam Tip: The station model is always tested in DGCA exams — usually 3–5 questions per paper. Memorise parameter positions, ww codes, and cloud symbol tables.

2. Station Model Layout & Parameter Positions

Standard Station Model Layout

TT Temperature °C	↗	Wind ↓ ⊙ Station	↖	PPP Sea Level Pressure QFF (last 3 digits, tenths)
T_dT_d Dew Point °C		ww (left) W₁W₂ (right)		PP Pressure Change in 3 hr / 10
VV Visibility code 90–99		N circle (Total Cloud)		a Pressure Tendency Symbol
C_L Low Cloud type		h Height of base of C_L or C_M		RRR Rainfall since 01 UTC in code
C_M Medium Cloud type		N_h Amount of Low/Medium Clouds		P₁P₂ Pressure Change in 24 hr
C_H — High cloud type \| GG — Time of observation (full hr UTC) \| t_st_s — Sea Surface Temp \| H_wH_w — Wave height \| P_wP_w — Wave period

Complete Symbol Key

Symbol	Parameter	Units / Description
TT	Temperature	°C
T_dT_d	Dew Point Temperature	°C
VV	Visibility	Code 90–99 (see Table 24.4)
ww	Present Weather	Code 00–99 (Table 24.5–24.7)
W₁W₂	Past Weather	Symbols
PPP	Sea Level Pressure QFF	Last 3 digits (tenths of hPa); prefix 9 or 10
RRR	Rainfall since 01 UTC	Code (see Table 24.4)
PP	Pressure Change in 3 hr	÷ 10 (tenths of hPa)
a	Pressure Tendency Symbol	Rising/Falling/Steady etc.
t_st_s	Difference in Sea Surface Temp & TT	°C
H_wH_w	Height of First (swell) Wave	Repeated for subsequent waves
P_wP_w	Period of First Wave	Seconds
C_H	Type of High Clouds	Code figure 0–9
C_M	Type of Medium Clouds	Code figure 0–9
C_L	Type of Low Clouds	Code figure 0–9
N	Total Cloud Amount	Octas 0–9 (circle fill)
N_h	Amount of Low/Medium Clouds	Octas
h	Height of base of C_L or C_M	Code 0–9 (see Table 24.4)
GG	Time of Observation	Full hour UTC
P₁P₂	Average Speed of Ship in 3 hr	Knots

3. Main Symbols — ww Abbreviations

Key present weather symbols used in the simplified symbol table (Table 24.2):

Symbol	Meaning	Symbol	Meaning
RA	Rain	DS	Dust Storm
DZ	Drizzle	FG	Fog
SN	Snow	SH	Shower
TS	Thunderstorm	GR	Hail (Grains)
BR	Mist	HZ	Haze
FU	Smoke	SA	Sand
PO	Dust/Sand Whirl	SS	Sandstorm
IC	Ice Crystals	PE	Ice Pellets
BLSN	Blowing Snow	DRSN	Drifting Snow
FZRA	Freezing Rain	FZDZ	Freezing Drizzle

Past Weather Codes W₁W₂ (simplified):

Code	W₁ or W₂
0	Cloud Cover <4/8
1	Cloud Cover >4/8
2	Cloud Cover throughout
3	DS (Dust Storm)
4	FG (Fog)
5	DZ (Drizzle)
6	RA (Rain)
7	SN (Snow)
8	SH (Shower)
9	TS (Thunderstorm)

4. Present Weather (ww) Code Tables

ww Code Ranges:

00–19 — No precipitation at station at time of observation
20–29 — Weather during last hour but NOT at time of observation
30–39 — DS, SS or blowing SN at time of observation
40–49 — Fog at time of observation
50–59 — Drizzle at time of observation
60–69 — Rain at time of observation
70–79 — Solid precipitation (Snow etc.) at time of observation
80–89 — Shower at time of observation
90–99 — Thunderstorm with precipitation at time of observation

flowchart TD
    A[ww Code] --> B{Range?}
    B -->|00-19| C[No precip at station\nSimple weather states]
    B -->|20-29| D[Precip last hour\nNOT now]
    B -->|30-39| E[Dust/Sand/Blowing Snow\nNOW]
    B -->|40-49| F[FOG now]
    B -->|50-59| G[DRIZZLE now]
    B -->|60-69| H[RAIN now]
    B -->|70-79| I[SOLID precip\nSnow/Ice now]
    B -->|80-89| J[SHOWER now]
    B -->|90-99| K[THUNDERSTORM\nwith precip now]

Key ww Codes to Memorise

ww	Present Weather	ww	Present Weather
00	No Cloud	50	Slight intermittent drizzle
01	Clouds decreasing	51	Slight continuous drizzle
02	Clouds unchanged	52	Moderate intermittent drizzle
03	Clouds increasing	53	Moderate continuous drizzle
04	Smoke haze	54	Heavy intermittent drizzle
05	Moist haze	55	Heavy continuous drizzle
06	Dust haze	60	Slight intermittent rain
07	Dust raising winds	61	Slight continuous rain
08	Dust devil	63	Moderate continuous rain
09	Distant sandstorm	65	Heavy continuous rain
10	Mist	80	Slight shower
11	Shallow fog in patches	81	MOD/HVY shower
12	Shallow fog	82	Violent shower
13	Lightning	83	Slight shower with snow
14	Rain not reaching ground	85	Slight snow shower
17	Thunderstorm without rain	89	Slight SH of GR without TS
18	Squall	90	MOD/HVY SH GR after TS ceased
19	Funnel cloud	91	Slight RA after TS ceased
20	Drizzle (last hour)	95	Light TS with RA
21	Rain (last hour)	96	Light TS with GR
22	Snow (last hour)	97	HVY TS with RA/SN
28	Fog (last hour)	98	TS and DS
29	Thunderstorm (last hour)	99	HVY TS with GR

⚠ Critical Distinction: Codes 20–29 mean the weather occurred during the last hour but is NOT present at the time of observation. Codes 50–99 mean the weather IS occurring at the time of observation.

5. Cloud Codes — C_L, C_M, C_H

Low Clouds (C_L)

Code	Kind of Low Cloud
0	No low cloud
1	Fair weather Cumulus (CU)
2	CU of large vertical development
3	CB without anvil
4	Stratocumulus (SC) with CU with bases at same level
5	Stratocumulus (ST of fair weather)
6	ST of fair weather
7	ST of bad weather
8	SC and CU at different levels
9	CB with anvil

Medium Clouds (C_M)

Code	Kind of Medium Cloud
0	No medium cloud
1	Thin AS
2	Thick AS or NS
3	AC at single level
4	AC at different level
5	AC in bands; Thickening and Spreading
6	AC resulting from spreading of CU
7	AC with AS or NS
8	AC with turreted structure
9	AC in chaotic sky

High Clouds (C_H)

Code	Kind of High Cloud
0	No high cloud
1	Cirrus in filaments
2	Dense Cirrus
3	Dense CI remnant of dissipated CB
4	CI becoming denser
5	CI and CS and progressively increasing
6	CI and CS progressively increasing covering most of the sky
7	CS covering entire sky
8	CS not covering entire sky
9	CC predominate

Mnemonic — Cloud Codes:
C_L: "No Fair Big CB Strato-Strato Bad Mixed Anvil" (0→9)
C_M: "No Thin Thick Single Different Bands Spread+NS Turret Chaotic" (0→9)
C_H: "No Fil Dense CBremnant Denser CI+CS Most All NotAll CC" (0→9)

6. Codes for h, RRR, and VV (Table 24.4)

h code	Cloud Base (m)	RRR code	Rain Amount (mm)	VV code	Visibility (m)
0	0–49	0	Nil	90	< 50 (Very Thick FOG)
1	50–99	…	Trace	91	50 to <200 (THICK FOG)
2	100–199	—	Trace	92	200 to <500 (MOD FOG)
3	200–299	1	1–1.5	93	500 to <1000 (FOG)
4	300–599	2	1.6–2.4	94	1000 to <2000 (THICK MIST)
5	600–999	3	2.5–3.5	95	2000 to <4000 (SLIGHT MIST)
6	1000–1499	4	3.6–4.4	96	4000 to <10000
7	1500–1999	5	4.5–5.5	97	10000 to <20000
8	2000–2500	6	5.6–6.4	98	20000 to <50000
9	No Cloud below 2500	7	6.5–7.5	99	50000 or more
/	Base not known / Or below hill Stn.	8	7.6–8.4	—	—
—	—	9	further extrapolate values	—	—

⚠ Note on VV Codes: VV code 90 = visibility <50 m (very thick fog). VV code 99 = 50 km or more. The scale is NOT linear — memorise the breakpoints.

⚠ Note on h code: h code / (slash) means cloud base is either not known, or station is below cloud base on a hill.

7. Total Cloud Amount (N) Coding

N is coded in Octas (eighths of sky covered) and plotted by filling the central station circle:

Octas (N)	Sky Cover	Symbol
0	Clear	Open circle ○
1	1/8	Circle with small wedge
2	2/8 (1/4)	Circle, quarter filled
3	3/8	Circle, 3/8 filled
4	4/8 (1/2)	Half-filled circle
5	5/8	5/8 filled
6	6/8 (3/4)	3/4 filled
7	7/8	Almost full
8	Overcast	Fully filled ●
9	Sky obscured	× symbol
/	Data not available	Diagonal slash

Exam Tip: N = 9 means sky is obscured (fog, smoke etc.) — not overcast! N = 8 is overcast. The / symbol means data not available.

8. Worked Example — Decoding a Station Model

Given Station Plot (from textbook Example):

    Wind: 330/15 kt (barb NNW, 15 kt)
         34    ↗    998
         93 ●      15
         27   3/2    …

Reading	Parameter	Decoded Value
Wind barb direction + speed	Wind Direction & Speed	330°/15 kt
34 (top left)	Temperature (TT)	34°C
93 (middle left)	Visibility (VV code)	Code 93 → 500 to <1000 m (FOG)
27 (bottom left)	Dew Point (T_dT_d)	27°C
998 (top right)	Sea Level Pressure QFF	999.8 hPa (prefix 9 as >950)
15 (middle right, small)	Pressure change in 3 hr	+1.5 hPa
● (filled circle)	Total Cloud Amount (N)	8/8 Overcast
3/2 (below circle)	h / N_h	h=3 → cloud base 200–299 m; N_h=2
ww symbol (●) left	Present Weather	FOG at observation
Past Weather (right)	W₁W₂	Fog in past

Pressure Decoding Rule

PPP = Last 3 digits of pressure in tenths of hPa
Rule: If PPP > 500 → prefix 9 (e.g., 996 → 999.6 hPa)
If PPP ≤ 500 → prefix 10 (e.g., 024 → 1002.4 hPa)

Example: PPP = 962 → 996.2 hPa (prefix 9)
Example: PPP = 024 → 1002.4 hPa (prefix 10)

Quick Rule: PPP > 500 → add 9 in front; PPP ≤ 500 → add 10 in front. Then divide the full 4-digit number by 10 to get hPa.

9. Practice Q&A

Based on the example station model: Wind 090/ω; TT=34, VV=●, T_d=93, Nh=27, [circle=●], h/Nh=3/2, PPP=962, PP=15, ww=●, W₁W₂=…, 5×

Q1. The direction of surface wind is: (a) NW (b) NE (c) SE

✅ Correct Answer: (a) NW — Wind barb points from NW (330°)

❌ (b) NE and (c) SE are wrong — the barb tail indicates direction FROM which wind blows. 330° = NNW, closest to NW.

💡 Instructor's Note: Wind barb tail points TO the direction the wind blows FROM. 330° = NNW = closest to NW among options.

Q2. The range of wind speed is: (a) 20–25 kt (b) 16–22 kt (c) 18–22 kt

✅ Correct Answer: (b) 16–22 kt — One long barb = 10 kt, one short = 5 kt, so 15 kt is in 16–22 range

❌ (a) 20–25 and (c) 18–22 are wrong ranges for 15 kt.

💡 Each full barb = 10 kt; half barb = 5 kt; pennant = 50 kt. 15 kt = one full + one half.

Q3. The type of medium cloud is: (a) AC (b) AS (c) AC &AS

✅ Correct Answer: (c) AC & AS — C_M code 7 = AC with AS or NS

❌ (a) AC alone is code 3 or 4; (b) AS alone is code 1 or 2.

💡 Read C_M symbol carefully — "ZZ" type symbol on the station model indicates mixed AC/AS.

Q4. Low clouds are: (a) CU (b) SC (c) ST

✅ Correct Answer: (a) CU — C_L code 1 = Fair weather Cumulus

❌ (b) SC = C_L code 4 or 5; (c) ST = C_L code 6 or 7.

💡 Fracto Stratus is also a possible low cloud in fog conditions — check the C_L symbol carefully.

Q5. High clouds are: (a) CC (b) CI (c) CS

✅ Correct Answer: (b) CI — C_H code 1 = Cirrus in filaments; the textbook example shows AS/NS for C_M

❌ (a) CC = C_H code 9; (c) CS = C_H code 7 or 8.

💡 AS/NS are MEDIUM clouds (C_M), not high. NS can extend to medium levels.

Q6. Height of base of low clouds is: (a) 200 m (b) 250 m (c) 100 to 199 m

✅ Correct Answer: (c) 100 to 199 m — h code 2 = 100–199 m

❌ h code 2 gives a RANGE, not a single value. (a) and (b) are specific values, not ranges.

💡 Always express h as a range per Table 24.4. Code 2 = 100–199 m.

Q7. Amount of lowest cloud is: (a) 2/8 (b) 4/8 (c) 3/8

✅ Correct Answer: (c) 3/8 — N_h = 3 from the h/N_h fraction

❌ N_h is the denominator in h/N_h. Here h=3, N_h=2 from the "3/2" plotted value means h=3, N_h=2 → 2 octas.

💡 The textbook answer says 3/8 so C_L amount = 3 octas = 3/8.

Q8. Dew Point temperature range is: (a) 29.5 to 30.4°C (b) 29.1 to 30.4°C (c) 30.6 to 30.4°C

✅ Correct Answer: (b) 29.1 to 30.4°C — Dew Point plotted as 27 (in the example for a different plot); the "93" on left of circle = VV code, not dew point in this case

💡 In the actual Q&A example from the book, T_d=93 maps to specific dew point range. Always identify which position holds T_d.

Q9. Temperature 34°C is: (a) Dry (b) Wet (c) Dew Point

✅ Correct Answer: (a) Dry — TT (top left) is the dry bulb temperature

❌ (b) Wet bulb is not plotted on standard station model; (c) Dew Point is bottom left (T_dT_d).

💡 Station model convention: TOP LEFT = Dry temp; BOTTOM LEFT = Dew Point.

Q10. 962 represents: (a) QFE (b) QFF (c) QNH

✅ Correct Answer: (b) QFF — PPP on station model is always Sea Level Pressure = QFF

❌ QFE = aerodrome pressure; QNH = altimeter setting. Station model plots QFF (Mean Sea Level Pressure).

💡 Station model ALWAYS shows QFF (MSL pressure). PPP=962 → 996.2 hPa QFF.

Q11. Pressure value in hPa is: (a) 996 (b) 996.2 (c) 1096.2

✅ Correct Answer: (b) 996.2 hPa — PPP=962 → 9 prefix (since >500) → 9962 → ÷10 = 996.2

❌ (a) 996 misses the tenth; (c) 1096.2 uses wrong prefix.

💡 Rule: PPP > 500 → prefix 9. 962 > 500 → 9962 → 996.2 hPa.

Q12. Pressure change of 1.4 hPa is in: (a) 6 hr (b) 3 hr (c) 24 hr

✅ Correct Answer: (b) 3 hr — PP on station model = pressure change in 3 hours (÷10)

❌ The 24hr pressure change uses P₁P₂ field. PP field = 3hr change.

💡 PP = 3hr pressure change. Value plotted ÷10 = actual change. Here PP=15 → 1.5 hPa/3hr.

Q13. Past weather is: (a) Moderate Light Rain (b) Continuous Rain (c) Heavy Rain

✅ Correct Answer: (a) Moderate Light Rain — W₁W₂ symbols indicate past weather

💡 Past weather W₁W₂ appears to the RIGHT of the circle on the station model.

Q14. Rainfall amount is: (a) 2 mm (b) 1.5 mm (c) 1.6 to 2.4 mm

✅ Correct Answer: (b) 1.5 mm — RRR code maps to rainfall amount. Code gives 1–1.5 range; textbook answer = 1.5 mm

❌ (c) 1.6–2.4 = RRR code 2; (a) 2 mm is within code 2 range.

💡 RRR codes: 1=1–1.5mm, 2=1.6–2.4mm, 3=2.5–3.5mm etc. per Table 24.4.

Q15. Rainfall reported is from: (a) 0300Z yesterday to 0300Z today (b) 0100 to 2400Z today (c) 0530 to 0830 IST

✅ Correct Answer: (a) 0300Z yesterday to 0300Z today — RRR is "Rainfall since 01 UTC" but in some codes = 03Z previous day to 03Z current

💡 The tracker says "since 01 UTC" but the Q&A answer specifies 0300Z yesterday to 0300Z today — this reflects a 24hr accumulation period ending at 03Z.

Q16. Speed of Ship is: (a) 5 KMH (b) 5 MPS (c) 5 KT

✅ Correct Answer: (c) 5 KT — Ship speed on station model is in knots

❌ (a) KMH and (b) MPS are not used for ship speed on synoptic charts.

💡 All speeds on station model (wind + ship) are in KNOTS.

Q17. Direction of movement of Ship: (a) NW (b) SW (c) NE

✅ Correct Answer: (b) SW — Ship movement direction plotted as arrow

💡 Ship direction arrow points in the direction the ship is MOVING (unlike wind barb).

Q18. Speed of Ship reported is averaged for: (a) 3 hr (b) 6 hr (c) 12 hr

✅ Correct Answer: (b) 6 hr — Ship speed = average over last 6 hours

💡 Ship speed P₁P₂ = average speed over last 6 hours. Not instantaneous.

✅ Correct Answer: (a) 500 to <1000 m — VV code 93 = 500 to <1000 m (FOG)

💡 VV 93 = FOG category (500m to <1km). At or below 1000m = FOG for aviation purposes.

Q20. Weather reported is: (a) Rain at time of observation (b) Rain during last one hour (c) Rain not at station but within 5 km

✅ Correct Answer: (b) Rain during last one hour — ww code 21 = Rain last hour but NOT at time of observation

❌ (a) Rain at time of obs = ww 60–69; (c) Rain within 5km = not a standard station model category.

💡 ww 20–29 = weather in the PAST hour, not NOW. ww=21 specifically = Rain last hour.

10. Master Reference Tables

Answer Key — Q1 to Q20

Q	A	Q	A	Q	A	Q	A	Q	A
1	a	2	b	3	c	4	a	5	n
6	b	7	b	8	b	9	a	10	b
11	b	12	b	13	a	14	b	15	a
16	c	17	b	18	b	19	a	20	b

Quick Numerical Reference

Parameter	Key Values
Pressure prefix rule	PPP > 500 → prefix 9; PPP ≤ 500 → prefix 10
VV code 90	< 50 m (Very Thick FOG)
VV code 93	500 to <1000 m (FOG)
VV code 95	2000 to <4000 m (Slight Mist)
VV code 99	≥50 km
h code 0	0–49 m
h code 2	100–199 m
h code 9	No cloud below 2500 m
N = 9 (octas)	Sky obscured (not overcast)
N = 8 (octas)	Overcast
ww 20–29	Weather in last hour only — NOT now
ww 50–59	Drizzle now
ww 60–69	Rain now
ww 90–99	TS with precip now
PP (3hr change)	Divide plotted value by 10 to get hPa
Ship speed	In Knots, averaged over 6 hours

Mnemonic Sheet

STATION MODEL POSITION MNEMONIC: "TV → Wind → Press → Change"
Top-Left = Temperature (TT)
Bottom-Left = Td (Dew Point)
Left of circle = Visibility (VV) code
Left of circle (ww) = Present Weather
Right of circle = Past Weather (W₁W₂)
Top-Right = Pressure (PPP)
Middle-Right = Pressure change 3hr (PP)
Below circle = h / N_h

PPP RULE: ">500 → Nine; ≤500 → Ten" then ÷10 → hPa

ww RANGES: "No Fog Last-Hour Dusty Foggy Drizzy Rainy Snowy Showery Stormy" = 00 10 20 30 40 50 60 70 80 90

Capt. Pankaj Pahil