NWP models. Strengths and weaknesses. Morten Køltzow, met.no NOMEK

Norwegian Meteorological Institute met.no Outline Models employed at met.no Models ability to forecast: –Precipitation. –2m air temperature. –Extreme weather (wind).

Norwegian Meteorological Institute met.no Models employed at met.no Hirlam, 12km, 8km, 4km –(NOR)LAMEPS 12km UM, 4km -> 1km ECMWF (approximately 16km) Simra, turbulence model, 100m -> 50m AirQUIS, urban air quality model Wave and ocean models SNAP, (nuclear accident) transport model EMEP, chemical transport model

Norwegian Meteorological Institute met.no Hirlam - hydrostatic model. –Assumes that the vertical acceleration is much smaller than g. The vertical velocity is found by diagnostics. Good approximation for coarse models. UM – non hydrostatic model. Non-hydrostatic models are important when features with large vertical velocities is resolved (i.e. convection or flow around steep orography).

Norwegian Meteorological Institute met.no H12, H08, H4, UM4: H12 H08 4km

Norwegian Meteorological Institute met.no

Precipitation

Norwegian Meteorological Institute met.no Seasonal mean, 24h precipitation: JJASON UM4km HIRLAM 8km

Norwegian Meteorological Institute met.no Precipitation from a fine scale model (left), a global model (mid) and observations (right). From Ebert (2009).

Norwegian Meteorological Institute met.no Verification of precipitation DJF: (models ability to forecast correctly 24h precipitation above a certain threshold) HIT RATE FALSE ALARM RATIO

Norwegian Meteorological Institute met.no Binary approach: –Each coloured grid cell precipitation > 0.0mm Compare fraction of occurences from forecast and radar for different areas. On which spatial scales are the fractions similar? ForecastRadar At what spatial scales show the models useful information?

Norwegian Meteorological Institute met.no Spin-up, cloud cover. HIRLAM 4 HIRLAM 8 HIRLAM 12 UM4 9months june - February JJA DJF

Norwegian Meteorological Institute met.no Spin-up of precipitation (mm/h) HIRLAM 4 HIRLAM 8 HIRLAM 12 UM4 JJA DJF 9mnd June - Februay

Norwegian Meteorological Institute met.no Near surface temperature (T2m). Coastlines. Heightcorrection of T2m.

Norwegian Meteorological Institute met.no T2m bias, coastal stations. WINTER SUMMER Warm bias in winter and cold bias in summer due to too high influence by the sea surface temperature on T2m. BIAS

Norwegian Meteorological Institute met.no Coast “coarse model” ECMWF. B

Norwegian Meteorological Institute met.no Interpolation: bi-linear Nearest grid point Nearest land grid point (B is a ocean grid point in the model) B

Norwegian Meteorological Institute met.no Bi-linear interpolation: 22°

Norwegian Meteorological Institute met.no Observed 28.7° Nearest land point “interpolation”

Norwegian Meteorological Institute met.no Difference in topography 8km and 500m horizontal resolution Blue – real topo less than model topo

Norwegian Meteorological Institute met.no Height corrections of T2m is necessary! BIAS Model topography – real topography HIRLAM8 T2m

Norwegian Meteorological Institute met.no ALNA BLINDERN TRYVANN BJØRNHOLT HAKADAL KJELLER

Norwegian Meteorological Institute met.no Variasjon i tid og rom: Nov.Dec.Jan.Feb. Sort – mean Stiplet – stdev Varsel;T+0->T+48

Norwegian Meteorological Institute met.no Modelling wind in Norway

Norwegian Meteorological Institute met.no Low pressure system 1000 hPa, Newfoundland kl. 00 Utc. From Karsten Eitrheim, VpV, met.no

Norwegian Meteorological Institute met.no Analysis 18 Utc From Karsten Eitrheim, VpV, met.no

Norwegian Meteorological Institute met.no Analysis 00 UTC From Karsten Eitrheim, VpV, met.no

Norwegian Meteorological Institute met.no Analysis Kl. 06 UTC From Karsten Eitrheim, VpV, met.no

Norwegian Meteorological Institute met.no From Trygve Aspenes

Norwegian Meteorological Institute met.no Maksvind ~33.5m/s From Karsten Eitrheim, VpV, met.no

Norwegian Meteorological Institute met.no The new year storm, observed wind strength: Færder to Bodø: More than strong gale (>20.8m/s). Hardangerfjorden to Sklinna Fyr: More than violent storm (>28.5m/s). Stad to Vikna: More than hurricane force (>32.6m/s). Maximum wind strength (10min average) at Svinøy and Skalmen Fyr. Most probably the most severe storm in Norway the last 110 years. Skalmen Svinøy

Norwegian Meteorological Institute met.no

A rerun with a state of the art NWP model (HIRLAM, 8km) valid: 09UTC h +21h Green > 20m/s, Yellow > 24m/s, Red > 30m/s Maximum 35m/s Initial and lateral boundaries from ERA-interim.

Norwegian Meteorological Institute met.no Probability based on the Norwegian Ensemble Prediction System (NORLAMEPS) +60h valid 06UTC Probabilities for more than 25m/s (green) Probabilities for more than 30m/s (red) NORLAMEPS

Norwegian Meteorological Institute met.no Ulrik, 2008 Black: Analysis HIRLAM 00UTC 26.October. Red : HIRLAM forecast +48h

Norwegian Meteorological Institute met.no Ulrik, 2008 Black: Analysis HIRLAM8 00UTC 26.October Red: HIRLAM forecast +24h

Norwegian Meteorological Institute met.no Vera, Polar low, November 2008:

Norwegian Meteorological Institute met.no Vera – “offshore”: Observations - black curve

Norwegian Meteorological Institute met.no Vera – “outer coast line”: ECMWF Observations - black curve

Norwegian Meteorological Institute met.no Vera – “inner coast line”: Observations - black curve

Norwegian Meteorological Institute met.no Model Verification of wind (+0 to +60) at 6 Norwegian offshore stations December February 2010 Observation Observations are originally taken approximately 100masl and reduced to 10masl assuming neutral conditions.

Norwegian Meteorological Institute met.no Observation Model Verification of wind (+0 to +60) at 28 Norwegian coast stations (lighthouses). December February 2010.

Norwegian Meteorological Institute met.no Model Observation Verification of wind (+0 to +60) at 9 Norwegian mountain stations (>930masl) December February 2010

Norwegian Meteorological Institute met.no Thank you for your attention!