Koper weather in April

In April, Koper sees average daytime highs of 16°C and overnight lows near 9°C, with 95 mm of precipitation across 11.2 wet days and about 13.2 hours of daylight. It is the 7th-warmest and 6th-wettest month of the year here.

Highs climb over the month, from about 14°C in the first days to 18°C by the end. The sky is clear or mostly clear about 36% of the time in April, and the air most often feels dry.

Daylight stretches from about 12 h 30 min at the start of April to 14 hours by month's end. Set against the rest of the year, April is Koper's 9th-clearest and 7th-windiest month. For the whole year in context, see Koper's year-round climate.

Daytime high
16°
7th warmest
Overnight low
6th coldest
Precipitation
95 mm
11.2 wet days
Daylight
13 h 18 min
5:27 AM – 6:44 PM
Cloud cover
56%
9th clearest
Wind
10 km/h
7th windiest
Solar energy
4.92 kWh/m²
Travel score
4.8
out of 10

Koper is city in southwest Slovenia.

Air quality
Good
PM10 16.8 µg/m³ · 2019
Density
1,981/km²
people per km²

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in April

Average highAverage lowShaded bands: 10–90% of days

Highs climb over the month, from about 14°C in the first days to 18°C by the end.

A typical April day in Koper reaches about 16°C in the afternoon and slips back to 9°C overnight — a 6°C spread between the day's warmth and the night's chill. On most days the high lands between 12°C and 20°C. Set against its neighbours, April runs about 4°C warmer than March and about 5°C cooler than May.

10°15°20°25°151015202530
Avg high (°C)Avg low (°C)
1147
2148
3148
4148
5148
6148
7148
8158
9158
10158
11159
12159
13159
14159
15159
16169
17169
181610
191610
201610
211610
221710
231710
241711
251711
261711
271811
281811
291812
301812

How April really feels in Koper

Once humidity and wind are folded in, April averages 0 days that feel above 32°C and 0 that feel at or below 0°C — the comfort signal a plain temperature reading hides.

Days feeling ≥ 32°C
0
heat index over the day's high
Days feeling ≤ C
0
wind chill below the day's low

April sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.

Koper weather by month

How April compares with the rest of the year at a glance. April is the 7th-warmest and 6th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°C)Rainfall (mm)Wet daysSnow daysDaylight (hours)Travel score
Jan / 779.10.98.91.1
Feb / 858.51.510.11.6
Mar12° / 869.30.711.63.3
Apr16° / 9511.20.213.24.8
May20° / 14°10311.7014.76.2
Jun24° / 18°8510.1015.47.0
Jul27° / 20°628.2015.17.2
Aug27° / 20°898.5013.97.1
Sep22° / 16°14710.3012.36.8
Oct18° / 12°15712.2010.75.5
Nov12° / 16712.70.39.33.1
Dec / 1129.90.98.61.5

Cloud cover in April

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 36% of the time in April.

Beyond those clear spells, partly cloudy skies cover about 16% of April, with mostly cloudy or overcast conditions the remaining 48%.

0%25%50%75%100%151015202530
Clearer (%)Cloudier (%)
15347
25347
35347
45347
55446
65347
75347
85347
95347
105347
115347
125347
135347
145347
155347
165347
175248
185248
195248
205248
215149
225149
235149
245149
255050
265050
275149
285149
295050
305149

Chance of precipitation in April

Any precipitation

Koper gets around 95 mm of rain and snow over 11.2 wet days in April. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable precipitation averages around 37% and peaks near 39% on the wettest days, and about 0 day brings snow.

0%10%20%30%40%50%151015202530
Rain chance (%)
135
236
336
436
537
637
737
838
938
1038
1139
1239
1338
1438
1538
1638
1737
1837
1937
2037
2137
2237
2337
2437
2537
2637
2737
2838
2938
3039

Humidity in April

DryComfortableHumidMuggyOppressiveMiserable

Most of April feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, April lands in the dry band about 98% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202530
Dry (%)Comfortable (%)
11000
21000
31000
41000
51000
61000
71000
81000
91000
101000
111000
121000
131000
141000
151000
161000
171000
18991
19991
20991
21991
22982
23982
24973
25973
26964
27955
28946
29937
30919

Wind in April

Winds average 10 km/h in April.

Across April, daily wind ranges from about 9 km/h on the calmest days to 11 km/h at its breeziest. It stays fairly steady from day to day.

051015151015202530
Wind speed (km/h)Feels
111calm
211calm
311calm
411calm
510calm
610calm
710calm
810calm
910calm
1010calm
1110calm
1210calm
1310calm
1410calm
1510calm
1610calm
1710calm
1810calm
1910calm
2010calm
2110calm
2210calm
2310calm
249calm
259calm
269calm
279calm
289calm
299calm
309calm

Sunrise & sunset in April

DaylightNight

Daylight runs from about 12 h 30 min at the start of April to 14 hours by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 90 minutes over April. Sunrise moves from 5:55 AM to 5:03 AM, and sunset from 6:24 PM to 7:02 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202530
Daylight (h)Sunrise (AM)Sunset (PM)
112.55:556:24
212.55:536:25
312.65:516:27
412.65:506:28
512.75:486:29
612.85:466:31
712.85:446:32
812.95:426:33
912.95:406:35
1013.05:386:36
1113.05:366:37
1213.15:346:39
1313.15:326:40
1413.25:306:41
1513.25:296:43
1613.35:276:44
1713.35:256:45
1813.45:236:46
1913.45:216:48
2013.55:206:49
2113.55:186:50
2213.65:166:52
2313.65:146:53
2413.75:136:54
2513.75:116:56
2613.85:096:57
2713.85:086:58
2813.95:067:00
2913.95:047:01
3014.05:037:02

Solar energy in April

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in April, about 4.92 kWh/m².

For context, solar energy here swings from a low near 1.2 kWh/m² to a high of 6.47 kWh/m² in July across the year — April's 4.92 kWh/m² falls in the middle.

0246151015202530
Solar energy (kWh/m²)Level
14.3Bright
24.4Bright
34.4Bright
44.5Bright
54.5Bright
64.6Bright
74.6Bright
84.6Bright
94.7Bright
104.7Bright
114.8Bright
124.8Bright
134.8Bright
144.9Bright
154.9Bright
165.0Bright
175.0Bright
185.0Bright
195.1Bright
205.1Bright
215.1Bright
225.2Bright
235.2Bright
245.2Bright
255.3Bright
265.3Bright
275.3Bright
285.3Bright
295.3Bright
305.4Bright
Planning a trip in April

Is April a good time to visit Koper?

Our two travel scores rate April for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

4.8
Sightseeing
7th-best month of the year
0.6
Beach & pool
7th-best month of the year

April is a reasonable time to visit Koper for sightseeing.

What to pack for Koper in April

From April's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In April, Koper sees daytime highs around 16°C and nights near 9°C. Worth packing: a warm layer, rain gear and sun protection. About 11 days see rain.

a warm layerrain gearsun protection

Sea temperature near Koper in April

The nearest coast averages about 13°C in April — the other half of the beach question. The full-year curve and swim-comfort zones are below.

The sea offshore is warmest in August at about 25°C and coldest in February near 10°C.

It's comfortable for a long swim from May 31 to Oct 9 — about 4.3 months when the water holds above 20°C.

10°20°30°JanFebMarAprMayJunJulAugSepOctNovDecbracingcoolrefreshingwarmtropicalcomfortable to swim
Sea temperature (°C)Comfort
Jan11Bracing
Feb10Bracing
Mar10Bracing
Apr13Bracing
May18Cool
Jun23Refreshing
Jul25Warm
Aug25Warm
Sep23Refreshing
Oct19Cool
Nov16Cool
Dec13Bracing

UV index in Koper in April

LowModerateHighVery highExtreme

Clear-sky midday UV in April peaks around 7 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.

Under clear skies, the midday UV index in Koper peaks around July 15 at about 8 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near January 1 at about 1 (low).

The index reaches 3 or more — the level where the WHO recommends sun protection — in 7 months of the year.

025710JanFebMarAprMayJunJulAugSepOctNovDecLowModerateHighVery highHighModerateLowJul 15UV 8Jan 1UV 1
UV index (midday)Level
Jan1Low
Feb2Moderate
Mar4Moderate
Apr7High
May7High
Jun8Very high
Jul8Very high
Aug7Very high
Sep5Moderate
Oct3Moderate
Nov2Low
Dec1Low

Air quality in Koper in April

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where April falls, not just the annual average.

Air quality in Koper is worst in January — around 22 µg/m³ PM2.5 (moderate), about 1.8× the cleanest month (September, 12 µg/m³).

Modeled monthly averages (CAMS reanalysis, 2015–2024).

0102030JanFebMarAprMayJunJulAugSepOctNovDecModerateJan 1822 µg/m³Sep 1412 µg/m³
PM2.5 (µg/m³)Level
Jan22Moderate
Feb20Moderate
Mar20Moderate
Apr19Moderate
May16Moderate
Jun16Moderate
Jul16Moderate
Aug13Moderate
Sep12Moderate
Oct14Moderate
Nov14Moderate
Dec18Moderate
Location & terrain

Where is Koper?

Koper sits at 45.5°N, 13.7°E, 12 m above sea level, in Slovenia. The nearest listed city is Trieste, 12 km away.

DivačaMonfalconeGoriziaPostojnaNova Gorica

Topography around Koper

How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Koper.

Within 3 km, the terrain around Koper has only modest variations in elevation — a maximum elevation change of 238 m around an average of 24 m above sea level; within 16 km, significant variations in elevation — a maximum elevation change of 575 m; within 80 km, very significant variations in elevation — a maximum elevation change of 2,150 m.

The land around Koper is covered by water (34%) and artificial surfaces (23%) within 3 km, trees (46%) and water (34%) within 16 km, and trees (48%) and water (29%) within 80 km.

3 km
238 m
16 km
575 m
80 km
2,150 m
treesshrubsgrasslandcroplandartificial surfaceswaterwetland
April weather nearby: Trieste 12 km · Piran 13 km · Divača 24 km · Monfalcone 32 km · Gorizia 44 km · Postojna 45 km · Nova Gorica 46 km · Rovinj 52 km

Slovenia travel facts

Travel advisory
Level 1
Exercise Normal Precautions
Power plugs
Type C / F
230 V · 50 Hz
Prices
≈ 63% of US
price level, 2025
GDP per capita
$37,376
2025
Happiness
6.9 / 10
World Happiness, 2025
Safe drinking water
100%
of population, 2024
Homicide rate
0.6
per 100k, 2023
Road deaths
5.1
per 100k/yr, 2019
Income group
High
World Bank
Religion
Catholic 69%atheist 14%Orthodox 4%non-believer/agnostic 4%

Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.

Data sources

Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Koper (45.5482°, 13.7296°, elevation 12 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google. Sea temperatures are the NOAA OISST v2.1 1991–2020 monthly climatology (public domain), sampled at the nearest ocean point. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).