Heavy precipitation in Southeastern Norway during

Summer 2007

How well was it predicted?

Prec. Summer 2007Prec. Summer 2007

• The situation was quite unusual • Much wetter than the summer 2006• Normally 12-15 days with precipitation

each month – June till August • This summer: Up to 25 days each month• Types of prec.: Heavy showers and frontal

Prec. Summer 2007Prec. Summer 2007

• Several places got more than 300 % of the normal

• Several records were beaten • Highest daily prec.: June 90,3 mm July 76,5 mm

• Max. monthly prec.: Around 300 mm

These events resulted in several floods

Some place in England

West of Oslo

Camping?

Kongsberg – west of Oslo

North of Oslo

Oslo 24.6

Several situations like this one

June 24. 2007June 24. 2007

• 1445 – 1600 hrs: 56,1 mm (84 min)

• 49,3 mm (60 min) • 38,6 mm (30 min)

Radar and UM1 24.6

15 utc

12 utc

Conclusion 1:Conclusion 1:

All models had too much precipitation

Highest deviation: Hirlam20/10 followed by UM4 and EC

In spite of this: Hirlam underestimated the strongest prec. events.

Conclusion 2:Conclusion 2:

• Showery prec.: - The models give prec.

but - Seldom at wright place and time - Too low values compared with obs. - Too bad in the most intense and local incidents

• Frontal prec.: - You never know – either too much or too little

prec.

• Local prec.: Described best in models with the lowest resolution

• We are dependent of the models, but do we know when we can trust in them and when we should be more skeptical.

• The answer is both yes and no – depending of situation and person (knowledge).

• But in several cases we won’t be able to tell the “truth”.

We can NOT trust completely in the models.

The human knowledge and criticism is for the time being very important –

but for how long?

Precipitation in percentage of the normal

NWPThe HIRLAM models

ModelsModels

• EC: Resolution appr. 25x25 km², or 0,25° lat. and long.• Hirlam20: Resolution appr. 20x20 km², or 0,2°. • Hirlam10: Resolution appr. 10x10 km², or 0,1°.• UM4 - Unified Modell (MetOffice). Resolution of 4x4 km².• UM1: Resolution 1x1 km².