Whitin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Whitin Observatory 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	19% 6% 5% 5% 5% 7% 35%	16488
	Night	19% 6% 5% 6% 37%	16449
Cloud Cover	Day	19% 6% 5% 5% 7% 35%	16497
	Night	19% 6% 6% 37%	16470
Transparency	Day	7% 15% 24% 15%	12754
	Night	6% 16% 24% 15%	13016
Seeing	Day	11% 33% 25% 10%	1119
	Night	15% 37% 24% 6%	4768

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	19% 6% 6% 6% 6% 37%	979
	Night	17% 8% 5% 5% 6% 36%	1720
February	Day	13% 8% 5% 5% 6% 6% 6% 35%	1067
	Night	16% 7% 5% 5% 5% 5% 39%	1339
March	Day	18% 6% 7% 40%	1310
	Night	16% 6% 5% 5% 39%	1369
April	Day	21% 5% 6% 5% 35%	1461
	Night	23% 7% 5% 6% 36%	1143
May	Day	24% 7% 5% 6% 34%	1653
	Night	24% 6% 6% 31%	1060
June	Day	28% 7% 5% 6% 5% 8% 23%	1663
	Night	28% 6% 5% 5% 6% 7% 24%	956
July	Day	13% 7% 6% 8% 6% 6% 8% 28%	1716
	Night	15% 6% 5% 5% 8% 5% 6% 8% 30%	974
August	Day	13% 5% 5% 5% 5% 5% 7% 7% 38%	1560
	Night	12% 5% 5% 6% 7% 7% 39%	1154
September	Day	14% 6% 48%	1342
	Night	16% 7% 49%	1262
October	Day	17% 5% 5% 7% 42%	1210
	Night	18% 5% 6% 41%	1484
November	Day	24% 7% 5% 5% 35%	1299
	Night	24% 7% 5% 5% 35%	1873
December	Day	20% 7% 5% 7% 36%	1228
	Night	19% 7% 5% 6% 39%	2115

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	19% 6% 5% 6% 7% 37%	977
	Night	18% 8% 5% 6% 36%	1721
February	Day	13% 9% 5% 6% 5% 5% 6% 35%	1064
	Night	16% 6% 5% 6% 39%	1331
March	Day	19% 5% 6% 39%	1331
	Night	16% 7% 7% 38%	1393
April	Day	21% 6% 6% 5% 35%	1460
	Night	22% 8% 5% 7% 35%	1143
May	Day	23% 7% 6% 34%	1647
	Night	24% 7% 5% 7% 31%	1054
June	Day	28% 6% 6% 5% 5% 8% 23%	1672
	Night	28% 6% 5% 5% 5% 5% 6% 25%	958
July	Day	12% 6% 6% 6% 8% 5% 7% 9% 28%	1716
	Night	15% 5% 5% 5% 5% 7% 6% 6% 8% 29%	975
August	Day	13% 6% 5% 6% 5% 5% 9% 37%	1554
	Night	12% 5% 5% 5% 6% 5% 5% 9% 38%	1157
September	Day	14% 5% 6% 48%	1341
	Night	17% 7% 49%	1263
October	Day	16% 6% 6% 42%	1210
	Night	19% 5% 5% 6% 41%	1484
November	Day	23% 7% 5% 35%	1297
	Night	24% 7% 5% 5% 35%	1872
December	Day	20% 7% 5% 6% 37%	1228
	Night	19% 8% 5% 6% 39%	2119

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	10% 17% 29% 15%	729
	Night	6% 18% 25% 15%	1256
February	Day	8% 16% 27% 11%	825
	Night	7% 16% 30% 12%	1052
March	Day	5% 15% 27% 17%	1014
	Night	5% 14% 26% 19%	1073
April	Day	5% 13% 23% 18% 7%	1050
	Night	11% 25% 21% 5%	831
May	Day	6% 15% 24% 14%	1212
	Night	8% 18% 18% 13%	800
June	Day	12% 21% 18% 6%	1174
	Night	11% 20% 16% 8%	659
July	Day	10% 16% 22% 11%	1094
	Night	9% 18% 27% 8%	625
August	Day	8% 13% 23% 18%	1375
	Night	7% 16% 26% 15%	1020
September	Day	10% 26% 27%	1187
	Night	10% 24% 28%	1127
October	Day	5% 15% 26% 15%	1095
	Night	5% 15% 24% 15%	1336
November	Day	5% 14% 26% 14%	1012
	Night	6% 17% 20% 15%	1473
December	Day	5% 20% 19% 16%	987
	Night	5% 18% 25% 13%	1764

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	20% 46% 19%	431
February	Day	20% 36% 24%	91
	Night	21% 39% 20%	403
March	Day	21% 33% 18% 11%	117
	Night	22% 44% 16%	461
April	Day	16% 36% 21% 10%	104
	Night	21% 36% 21% 7%	375
May	Day	13% 34% 23% 6%	109
	Night	18% 36% 23%	284
June	Day	6% 31% 28% 8%	103
	Night	9% 29% 33% 7%	205
July	Day	34% 38% 12%	106
	Night	33% 41% 9%	214
August	Day	26% 37% 11% 5%	117
	Night	30% 40% 12%	386
September	Day	6% 35% 21% 11% 13%	113
	Night	6% 32% 31% 13%	446
October	Day	11% 31% 25% 12%	116
	Night	12% 35% 24% 9%	461
November	Day	15% 32% 17% 11%	132
	Night	15% 32% 23% 7%	523
December	Day	36% 27% 9%	11
	Night	20% 42% 13%	579

Page generated at 2009-12-30 05:20:36. Version ab11