Rochester
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rochester clear sky chart from 2005-11-05 to 2008-11-27.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	18% 8% 5% 6% 5% 5% 5% 6% 29%	12238
	Night	20% 9% 6% 7% 5% 5% 6% 25%	12156
Cloud Cover	Day	18% 9% 6% 7% 5% 5% 5% 5% 6% 27%	12257
	Night	19% 10% 6% 7% 5% 5% 5% 6% 25%	12179
Transparency	Day	8% 18% 22% 13%	7979
	Night	8% 18% 21% 11%	7808
Seeing	Day	10% 30% 24% 16% 6%	686
	Night	20% 30% 25% 9%	3349

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	20% 14% 11% 10% 7% 5% 12%	782
	Night	28% 14% 9% 10% 7% 11%	1258
February	Day	20% 14% 11% 12% 10% 6% 5% 9%	749
	Night	17% 13% 11% 10% 8% 7% 5% 6% 10%	1042
March	Day	19% 12% 9% 7% 7% 6% 5% 20%	994
	Night	17% 13% 8% 8% 5% 5% 26%	1002
April	Day	20% 8% 5% 5% 6% 37%	1098
	Night	20% 9% 5% 6% 35%	882
May	Day	13% 7% 5% 5% 6% 7% 38%	1284
	Night	11% 5% 5% 8% 45%	762
June	Day	12% 5% 5% 6% 6% 6% 8% 37%	1251
	Night	13% 5% 5% 8% 6% 6% 7% 33%	718
July	Day	12% 5% 5% 8% 5% 7% 9% 34%	1290
	Night	9% 5% 6% 5% 6% 10% 40%	751
August	Day	14% 6% 5% 6% 40%	1169
	Night	13% 6% 6% 5% 7% 40%	863
September	Day	23% 6% 5% 5% 35%	1032
	Night	22% 6% 5% 38%	945
October	Day	27% 8% 6% 5% 5% 5% 6% 25%	922
	Night	26% 9% 7% 6% 7% 24%	1112
November	Day	20% 12% 6% 8% 8% 5% 21%	923
	Night	24% 11% 6% 7% 6% 5% 5% 5% 18%	1524
December	Day	23% 22% 12% 9% 11%	744
	Night	24% 15% 8% 8% 5% 7% 5% 11%	1297

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	20% 14% 10% 10% 8% 6% 11%	781
	Night	26% 15% 9% 9% 6% 6% 10%	1259
February	Day	19% 14% 10% 14% 9% 6% 5% 8%	747
	Night	17% 13% 11% 10% 10% 7% 5% 5% 6% 8%	1033
March	Day	19% 13% 9% 7% 6% 6% 19%	1017
	Night	18% 13% 9% 7% 5% 24%	1024
April	Day	20% 8% 5% 5% 6% 37%	1097
	Night	20% 9% 5% 5% 5% 35%	882
May	Day	15% 6% 5% 5% 6% 8% 37%	1283
	Night	11% 5% 5% 8% 45%	762
June	Day	12% 5% 5% 6% 6% 6% 10% 35%	1260
	Night	12% 5% 5% 7% 6% 7% 6% 34%	720
July	Day	12% 5% 5% 8% 6% 7% 8% 33%	1290
	Night	7% 6% 6% 5% 6% 11% 39%	752
August	Day	15% 5% 5% 5% 5% 5% 7% 39%	1164
	Night	13% 6% 6% 9% 39%	865
September	Day	21% 5% 6% 6% 5% 5% 5% 34%	1031
	Night	20% 8% 38%	946
October	Day	25% 9% 6% 5% 6% 5% 25%	922
	Night	23% 10% 7% 6% 6% 24%	1112
November	Day	19% 12% 7% 9% 6% 6% 5% 19%	921
	Night	23% 11% 7% 7% 5% 5% 5% 6% 17%	1523
December	Day	22% 22% 13% 9% 11%	744
	Night	23% 15% 9% 9% 6% 7% 5% 10%	1301

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	13% 24% 7%	375
	Night	6% 23% 10%	579
February	Day	11% 14% 11%	345
	Night	8% 21% 14%	526
March	Day	7% 21% 20% 9%	566
	Night	9% 19% 26% 7%	604
April	Day	7% 19% 22% 29%	670
	Night	10% 16% 23% 20% 5%	568
May	Day	7% 19% 30% 17%	949
	Night	6% 19% 30% 20%	594
June	Day	11% 24% 28% 13%	871
	Night	10% 22% 28% 12%	493
July	Day	10% 22% 28% 9%	706
	Night	10% 22% 34% 12%	410
August	Day	5% 14% 25% 19%	994
	Night	6% 16% 25% 18%	719
September	Day	6% 12% 25% 17%	787
	Night	10% 31% 15%	743
October	Day	7% 11% 20% 9%	728
	Night	7% 13% 18% 11%	864
November	Day	11% 18% 14% 5%	624
	Night	11% 20% 12% 6%	1057
December	Day	8% 21% 10%	364
	Night	15% 22% 9%	651

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	33% 35% 14%	295
February	Day	23% 38% 30%	13
	Night	35% 34% 15%	270
March	Day	23% 37% 18% 7%	85
	Night	26% 35% 18% 6%	331
April	Day	23% 27% 20% 18%	80
	Night	22% 28% 33% 7%	297
May	Day	11% 31% 24% 15% 12%	86
	Night	7% 31% 34% 20%	193
June	Day	28% 38% 24%	75
	Night	7% 35% 37% 16%	153
July	Day	5% 32% 30% 20% 5%	73
	Night	31% 41% 18%	167
August	Day	19% 26% 21% 14%	84
	Night	6% 23% 40% 18%	280
September	Day	7% 20% 25% 15% 12%	80
	Night	12% 21% 28% 21%	320
October	Day	7% 40% 18% 12%	80
	Night	10% 30% 29% 8%	330
November	Day	13% 50% 20% 13%	30
	Night	23% 30% 20% 6%	400
December	Night	40% 30% 15%	313

Page generated at 2008-11-27 13:47:38. Version ab11