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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 2009-12-29.

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	17% 9% 5% 7% 6% 5% 5% 6% 28%	16443
	Night	19% 10% 5% 7% 6% 5% 6% 26%	16492
Cloud Cover	Day	17% 9% 5% 7% 6% 5% 5% 5% 6% 27%	16456
	Night	18% 10% 6% 7% 6% 5% 6% 25%	16509
Transparency	Day	7% 16% 20% 12%	12178
	Night	7% 16% 19% 10%	12142
Seeing	Day	9% 29% 25% 14% 6%	937
	Night	18% 30% 24% 9%	4701

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	18% 16% 10% 11% 9% 5% 11%	1035
	Night	25% 15% 8% 11% 8% 11%	1664
February	Day	18% 13% 10% 14% 10% 5% 10%	1007
	Night	15% 15% 10% 12% 8% 6% 5% 12%	1400
March	Day	17% 12% 7% 7% 6% 5% 5% 24%	1334
	Night	17% 11% 7% 9% 6% 28%	1344
April	Day	20% 8% 6% 36%	1445
	Night	19% 10% 5% 5% 5% 6% 34%	1163
May	Day	13% 6% 5% 6% 6% 39%	1702
	Night	13% 5% 5% 5% 5% 7% 43%	1008
June	Day	13% 5% 5% 5% 6% 6% 6% 8% 36%	1663
	Night	14% 5% 5% 5% 7% 6% 7% 7% 32%	956
July	Day	13% 6% 5% 7% 6% 6% 9% 32%	1701
	Night	10% 5% 5% 5% 6% 9% 40%	989
August	Day	14% 5% 6% 5% 7% 39%	1561
	Night	13% 5% 6% 5% 7% 42%	1151
September	Day	21% 6% 5% 5% 5% 35%	1361
	Night	21% 5% 5% 5% 41%	1242
October	Day	27% 8% 7% 6% 5% 6% 23%	1221
	Night	28% 9% 7% 6% 6% 22%	1473
November	Day	17% 13% 5% 8% 7% 5% 5% 24%	1196
	Night	21% 11% 5% 7% 5% 5% 5% 6% 23%	1976
December	Day	21% 19% 9% 12% 6% 11%	1217
	Night	22% 16% 7% 10% 6% 6% 10%	2126

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	17% 16% 9% 11% 9% 5% 5% 10%	1033
	Night	23% 16% 9% 11% 7% 6% 11%	1665
February	Day	17% 13% 10% 16% 10% 5% 9%	1005
	Night	15% 14% 10% 12% 9% 6% 5% 11%	1391
March	Day	17% 13% 7% 7% 6% 6% 24%	1357
	Night	17% 11% 7% 9% 6% 26%	1366
April	Day	20% 8% 5% 6% 35%	1444
	Night	19% 10% 5% 5% 5% 5% 34%	1163
May	Day	15% 6% 6% 5% 6% 7% 38%	1696
	Night	12% 5% 5% 7% 42%	1002
June	Day	13% 6% 5% 5% 6% 5% 6% 9% 34%	1672
	Night	13% 5% 5% 5% 7% 5% 7% 7% 32%	958
July	Day	13% 6% 5% 7% 6% 7% 8% 31%	1701
	Night	9% 5% 6% 5% 5% 6% 9% 40%	990
August	Day	15% 5% 6% 5% 5% 5% 5% 8% 37%	1556
	Night	13% 5% 6% 9% 41%	1153
September	Day	20% 5% 5% 5% 5% 6% 34%	1360
	Night	20% 7% 5% 41%	1243
October	Day	26% 10% 7% 5% 5% 5% 5% 23%	1221
	Night	26% 11% 6% 5% 6% 23%	1473
November	Day	17% 13% 6% 9% 6% 5% 6% 22%	1194
	Night	21% 11% 6% 7% 5% 5% 7% 22%	1975
December	Day	20% 17% 11% 13% 6% 12%	1217
	Night	21% 16% 8% 11% 7% 6% 5% 9%	2130

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 20% 6%	628
	Night	17% 8%	985
February	Day	7% 13% 12%	603
	Night	6% 18% 12%	884
March	Day	5% 17% 21% 11%	898
	Night	7% 17% 21% 10%	946
April	Day	6% 15% 21% 24%	1017
	Night	8% 12% 23% 17%	846
May	Day	5% 15% 26% 17%	1367
	Night	6% 14% 25% 19%	841
June	Day	9% 20% 25% 14%	1283
	Night	9% 17% 27% 12%	731
July	Day	9% 19% 26% 7%	1117
	Night	9% 19% 30% 12%	648
August	Day	6% 14% 23% 17%	1386
	Night	7% 14% 28% 17%	1007
September	Day	6% 11% 25% 16%	1116
	Night	10% 30% 16%	1040
October	Day	7% 12% 17% 7%	1029
	Night	6% 13% 16% 8%	1225
November	Day	10% 16% 15% 7%	897
	Night	9% 19% 14% 7%	1509
December	Day	7% 14% 9%	837
	Night	9% 15% 7%	1480

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	31% 35% 13%	415
February	Day	26% 42% 26%	19
	Night	30% 35% 16%	382
March	Day	21% 34% 22% 7%	116
	Night	23% 35% 21% 5%	455
April	Day	20% 24% 25% 15%	109
	Night	19% 31% 29% 7%	405
May	Day	10% 33% 25% 12% 10%	115
	Night	6% 33% 31% 17%	257
June	Day	30% 36% 19%	104
	Night	5% 33% 37% 15%	212
July	Day	31% 30% 19%	102
	Night	29% 42% 17%	229
August	Day	20% 26% 17% 15%	115
	Night	24% 38% 17%	382
September	Day	8% 18% 21% 16% 15%	108
	Night	9% 19% 26% 25%	433
October	Day	7% 38% 18% 11%	110
	Night	10% 29% 25% 7%	450
November	Day	10% 46% 23% 15%	39
	Night	20% 29% 22% 6%	531
December	Night	34% 29% 13%	550

Page generated at 2009-12-30 05:21:03. Version ab11