FMI contribution to WGii first report Requirements from the forecasters and from the cuntomers Janne Kotro Jukka Julkunen Juha Kilpinen

Models, observations and basic recuirements Essential part of short range forecasting of fog, visibility and stratus clouds is observation network - including remote sensing (northern latitudes polar satellites and weather radars) observation network for needed purposes is nor good enough

Nowcasting methods have not been the main interest of weather forecasting in Finland (FMI) Nowcasting mainly based on weather radars, polar satellites and ground based observations the only ones have been have been radar extrapolation of radar echoes by FMI

FMI has not meso-scale NWP with enough horizontal and vertical or time resolution (HIRLAM in every 6 hours, not enough model levels in the boundary layer, horiz. Rez. 0.2 deg)

meteorologist do not not enough time to synoptical or meso analysis synoptical analysis is done in 4 offices simultaneously which would be improved by better communication network and other methods -> one meteorologist should do analysis, the others should discuss about the analysis Objective meso-scale analysis has taken in to testing use in FMI (originally by SMHI, Sverige), resolution deg. and update cycle 1 hour

For the aviation forecasting purposes obs. Cycle of every 30 min. is not enough (compared with the the speed of formation of the fog), obs. Cycle should be 10 minutes real time obs. of cloud ceiling anf horiz. visibility from the surrounding of an aerodrome should be very important

Air mass soundings are done in every 12 hours in Finland, should be done in every 6 hours real time stability measurement of boundary layer should be taken in to use this requires automated numerical analysis of sounding or mast observations (need more numerical coding resources)

Minimum reqiurement for forecasting ICAO manual ANNEX 3 (International Standards and Recommended Practices for Meteorological Service for International Air Navigation) gives the minimum accuracy of the observation (metar) and aviation forecasts (TAF)

according to ANNEX3: minimum time scale is given to be one (1) hour cloud base at minimum at minimum 100 feet (about 30 meters) visibility at minimum 150 meters

For visibility the limits are: 000m - 150m- 350m - 600m - 800m m -3000m -5000m m And for cloud base (cloud amount more than 4/8 octas): 000 ft ft ft ft ft-1500 ft - There are some national differences in these limits. The Finnish Air Forces have even more accurate requirements than the ones mentioned above.

These requirements are far too beyond the actual possibilities of accuracy limits of the numerical weather forecasting models.

Real time observation are at least as or maybe more important than the output of reduced scale NWP’s. The requirements of other end users (road traffic, marine meteorological services, offshore services) mainly concern visibility and these limits are not so tight. These requirements for visibility are given in WMO Handbook of offshore forecasting services, WMO/TD-N 850.