Henning Gisselø Danish Meteorological Institute in Copenhagen Operational forecaster for 17 years

S03 HIRLAM (NWP) has problems when predicting 2mTemp (max and min) in cases with no or just a few clouds.

S03 HIRLAM 3.3km * 3.3km * 40 layers * 90sek +54 h Hydrostatic Introduced spring 2009

In situations with only a few clouds the model is predicting too low max temp in day time and too high min temp in night time.

CASE The night between the 13 th and 14 th October 2009

Analysis, 14 th Oct. 00 UTC

NOAA, 14 th Oct. 02:43 UTC

S03 2mT Min, wind, cloudcover

Possible explainations from The HIRLAM Developing Group

DAYTIME CLOUDCOVER MODEL: many clouds ACTUALLY: few clouds RESULT: higher temp observed than predicted by model

DAYTIME EVAPORATION MODEL: high evaporation (moist soil) ACTUALLY: low evaporation (dry soil) RESULT: higher temp observed than predicted by model

NIGHT TIME CLOUDCOVER MODEL: many clouds ACTUALLY: few clouds RESULT: lower temp observed than predicted by model

NIGHT TIME HEAT CONDUCTION FROM GROUND MODEL: high heat conduction from ground ACTUALLY: low heat conduction from ground RESULT: lower temp observed than predicted by model

NIGHT TIME VEGETATION MODEL: low vegetation ACTUALLY: high vegetation High vegetation cools more efficient than low vegetation, producing a cooler surface layer. RESULT: lower temp observed than predicted by model Growing through spring and summer

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