When the forecast is predicting from 60 to 64 hours into the future, the mostly-clear accuracy To remind that the time resolution is much lower.Īccuracy details: Averaged over North America for a 30 day period: when the forecast is predicting less than 12 hours into the future, 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 17:00 and 05:00 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 Boston is -4.0 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 BostonĪnd 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 Boston, MA, will have good weather for astronomical observing. At a glance, it shows when it will be cloudy or clear for the While the far southeast will remain with plain rain, we’ll already be dealing with slick conditions for many across I-495, I-95, Routes 2 and needless to say that much of the north.The Harvard College Observatory of Harvard University. This could cause flash freezing in some areas. While the temperatures will remain in the upper 30s early in the morning, the earlier commuters won’t suffer from freezing just yet, but by 7 a.m., we’ll see those temperatures reaching near 32 in Worcester, northern Essex County and Middlesex counties. from the lakes region north of the Merrimack Valley and towards western Mass. Freezing Temperatures Hit During Morning Commuteįrom being in the 40s today, our temperatures will take a dramatic drop to the 20s by tomorrow morning north and drop slowly south through the early afternoon into the evening. While northern New England has already received its share of snow today in the far northern country, scattered rain has filled in for much of western New England and more fragmented rain has affected eastern New England. Timing of the transition, as well as the snowfall amounts depend on location. A cold front drops south through New England and is bringing a transition to a wintry mix of freezing rain, sleet and snow from north to south late tonight into Friday morning as cold air pushes in.
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