Those are shown on the charts with groups of 6 blockes linked together The far future ECMWF cloud forecasts are still usable.īut note that the furthest out forecasts may be for 6-hour blocks. So like many civil forecasts "clear sky" might still mean "some cirrus".Īccuracy Summary: The ECMWF forecast is more accurate than the CMC cloud forecast when predicting mostly clear, but less accurate when This isn't an astronomy-specific forecast. Which is different than when the CMC forecasts update. It's here for comparison with the CMC cloud cover forecast.New data becomes available around 13:00 and 01:00 local time. It's data form the "european" forecast model ECMWF. It's always wise to click on a colored block for the hour you want to observe and see if your location is close to a cloud edge.ĬMC's text page explaining this forecast is Is 76% and the mostly-cloudy accuracy is 89%. When the forecast is predicting 36 to 48 hours into the future, the mostly-clear accuracy Mostly-clear forecasts (cloud75%) have been When the forecast is clear, the sky may still be hazy, if the transparency forecast is poor.Īccuracy averaged over North America for a 30 day period: when the forecast is predicting less than 12 hours into the future, This forecast may miss low cloud and afternoon thunderstorms. Lighter shades of blue are increasing cloudiness and white is overcast. The colors are picked from what color the sky is likely to be, with The line, labeled Cloud Cover forecasts total cloud cover. Connected blocks mean one forecast calculation for several hours. (Local time for Seattle is -8.0 hours from GMT.) Single blocks mean separate forecast data for each hour. A digit 1 on top of a 3 means 13:00 or 1pm. The two numbers at the top of a column is the time. The colors of the blocks are the colors from CMC's forecast maps for that hour. Summary: In the rows labeled "Sky", find a column of blue blocks. Summarizes CMC's forecast images just for SeattleĪnd the surroundings out to about 10 miles. So, Attilla Danko wrote a script to generate the images like the one above It can be a chore to find the one map that tells you if you can observe tonight. CMC's numerical weather forecasts are unique because they are specifically designed for astronomers.īut they have 1180 forecast maps. The data comes from a forecast model developed by Allan Rahill of theĬanadian Meteorological Centre. It's a prediction of when Seattle, WA, will have good weather for astronomical observing. At a glance, it shows when it will be cloudy or clear for the This likely leading to initially unsettled conditions with transitory settled periods and typically average temperatures in the Atlantic flow, cooler at times in northern regions, before increasing likelihood of colder and drier than average conditions from mid-month.Home of the Seattle Astronomical Society and theīoeing Employees' Astronomical Society (BEAS). Saturday 2 Mar - Saturday 16 Marįirst half of March liable to see a slightly higher than normal likelihood of winds from the west then edging northerly later in the period. Occasional strong winds especially in north-western areas, with more settled conditions across the south and east where driest and brightest conditions more likely. From Saturday conditions expected to remain unsettled with occasional bands of rain or showers, heaviest rainfall affecting the northwest, although most areas likely to see some rainfall. Conditions turn unsettled with northwest winds carrying showery conditions over the British Isles from Thursday with clearer conditions in the east through the remainder of the week, returning the UK to more average temperatures for the time of year, though sometimes cooler in northwest areas. Most likely wet and mild in the south to start Wednesday with a brighter but cooler start in northern areas before rain moves in from the west for all.
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