Days 1-14 are a real forecast from global weather models. Days 15-30 are season-typical values based on climate normals 1991-2020 (MET) — good for planning, NOT an exact forecast that far ahead.
The forecast for Porsgrunn and the places around it comes from the same weather models as the place pages. Radar: RainViewer, images from the last two hours.
30 days — Porsgrunn
14 real + 16 synthesised
Fri · Today Showers
+15°+8°4,7 mm
Sat · Tomorrow Clear
+15°+8°2,4 mm
Sunday 4/10 Cloudy
+14°+7°0,3 mm
Monday 5/10 Clear
+16°+10°0,1 mm
Tuesday 6/10 Clear
+15°+6°5%
Wednesday 7/10 Cloudy
+13°+4°8%
Thursday 8/10 Cloudy
+11°+5°11%
Friday 9/10 Cloudy
+10°+3°2,8 mm
Saturday 10/10 Showers
+13°+9°3,0 mm
Sunday 11/10 Cloudy
+12°+5°10%
Monday 12/10 Clear
+9°+1°4%
Tuesday 13/10 Cloudy
+9°0°19%
Wednesday 14/10 Cloudy
+13°+7°26%
Thursday 15/10 Fog
+11°+5°23%
Friday 16/10 Rain (climate normal)
+10°+4°5,3 mm
Saturday 17/10 Partly cloudy (climate normal)
+13°+6°20%
Sunday 18/10 Partly cloudy (climate normal)
+11°+5°20%
Monday 19/10 Rain (climate normal)
+12°+5°5,9 mm
Tuesday 20/10 Partly cloudy (climate normal)
+9°+3°20%
Wednesday 21/10 Partly cloudy (climate normal)
+7°+2°20%
Thursday 22/10 Rain (climate normal)
+8°+3°5,3 mm
Friday 23/10 Partly cloudy (climate normal)
+10°+4°20%
Saturday 24/10 Partly cloudy (climate normal)
+11°+4°20%
Sunday 25/10 Rain (climate normal)
+12°+5°7,8 mm
Monday 26/10 Partly cloudy (climate normal)
+12°+5°20%
Tuesday 27/10 Partly cloudy (climate normal)
+10°+4°20%
Wednesday 28/10 Rain (climate normal)
+6°+2°7,6 mm
Thursday 29/10 Partly cloudy (climate normal)
+7°+2°20%
Friday 30/10 Partly cloudy (climate normal)
+10°+4°20%
Saturday 31/10 Rain (climate normal)
+13°+6°10,1 mm
How does the long-range forecast work?
Days 1-14: Fetched live from global weather models (ECMWF, GFS) with statistical correction. Reliability about 85 % for days 1-3, about 60 % for days 7-10, about 45 % for days 11-14.
Days 15-30: A real forecast does not exist that far ahead (chaotic system). Instead we show season-typical values: the monthly average Tmax/Tmin from climate normals 1991-2020, with mild weekly variation.
Use: «About how warm is it usually in Oslo the last week of July?» — a good question for days 15-30. «Will it rain on 27 May?» — no serious forecast can answer that.