Hidden Loft Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hidden Loft Observatory 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	6% 6% 62%	12277
	Night	5% 6% 64%	12154
Transparency	Day	6% 12% 28% 38%	10519
	Night	7% 12% 28% 38%	10488
Seeing	Day	13% 35% 39% 8%	669
	Night	16% 39% 32% 6%	3883

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	9% 5% 5% 59%	835
	Night	9% 5% 5% 57%	1203
February	Day	9% 6% 60%	798
	Night	7% 5% 7% 58%	980
March	Day	7% 5% 6% 62%	1020
	Night	9% 64%	1020
April	Day	74%	1044
	Night	75%	930
May	Day	78%	1209
	Night	7% 78%	837
June	Day	74%	1170
	Night	5% 74%	810
July	Day	12% 7% 6% 7% 10% 33%	1208
	Night	7% 5% 5% 7% 8% 8% 11% 37%	833
August	Day	10% 6% 8% 6% 7% 8% 34%	1163
	Night	5% 7% 8% 12% 40%	873
September	Day	5% 6% 65%	985
	Night	6% 68%	990
October	Day	78%	936
	Night	79%	1097
November	Day	5% 7% 68%	1072
	Night	5% 5% 66%	1374
December	Day	8% 6% 67%	837
	Night	7% 67%	1207

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	9% 19% 28% 28%	708
	Night	5% 9% 19% 24% 29%	1022
February	Day	7% 17% 34% 28%	679
	Night	5% 5% 17% 34% 28%	851
March	Day	6% 7% 36% 41%	826
	Night	5% 11% 35% 40%	809
April	Day	5% 29% 56%	923
	Night	6% 30% 55%	796
May	Day	8% 27% 52%	1134
	Night	10% 30% 49%	798
June	Day	5% 18% 67%	1039
	Night	14% 73%	687
July	Day	9% 13% 18% 20% 12%	716
	Night	14% 20% 14% 19% 13%	506
August	Day	11% 16% 17% 20% 5%	946
	Night	12% 20% 17% 17% 11%	749
September	Day	6% 13% 34% 31%	891
	Night	5% 13% 35% 31%	915
October	Day	6% 23% 58%	877
	Night	23% 60%	1023
November	Day	5% 12% 31% 40%	1032
	Night	13% 30% 38%	1286
December	Day	5% 19% 39% 26%	748
	Night	7% 17% 37% 27%	1046

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	29% 42% 17%	364
February	Day	16% 45% 28%	53
	Night	20% 41% 24% 5%	313
March	Day	31% 43% 14% 8%	85
	Night	23% 43% 22%	351
April	Day	28% 47% 15%	82
	Night	7% 22% 48% 19%	297
May	Day	14% 52% 28%	91
	Night	18% 42% 31%	279
June	Day	7% 34% 51% 5%	90
	Night	10% 33% 47% 5%	252
July	Day	19% 66% 5%	77
	Night	6% 25% 56% 8%	241
August	Day	15% 53% 23%	88
	Night	17% 58% 17%	269
September	Day	6% 32% 48% 10%	87
	Night	14% 36% 39% 7%	349
October	Day	6% 25% 56% 6%	16
	Night	12% 43% 30% 9%	363
November	Night	11% 42% 35% 6%	444
December	Night	14% 45% 27% 6%	361

Page generated at 2008-11-27 11:47:41. Version ab11