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Flagstaff
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Flagstaff clear sky chart from 2003-08-01 to 2005-11-07.

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	9% 5% 5% 49%	8687
	Night	8% 5% 5% 5% 52%	8481
Transparency	Day	6% 9% 25% 36% 22%	5877
	Night	5% 10% 26% 34% 22%	5851
Seeing	Day	21% 34% 35% 8%	484
	Night	16% 20% 29% 28%	2809

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% 10% 8% 5% 5% 34%	549
	Night	13% 8% 10% 7% 5% 34%	804
February	Day	21% 11% 10% 5% 6% 29%	543
	Night	15% 9% 11% 7% 6% 31%	701
March	Day	13% 6% 5% 51%	681
	Night	11% 6% 5% 52%	681
April	Day	9% 5% 5% 55%	716
	Night	6% 6% 8% 58%	603
May	Day	6% 7% 8% 59%	806
	Night	5% 5% 5% 63%	558
June	Day	5% 72%	780
	Night	78%	537
July	Day	5% 5% 9% 7% 6% 6% 43%	795
	Night	5% 10% 6% 6% 53%	558
August	Day	16% 6% 6% 6% 6% 9% 5% 6% 27%	1183
	Night	8% 7% 6% 5% 7% 5% 6% 43%	859
September	Day	6% 5% 5% 60%	969
	Night	6% 64%	977
October	Day	7% 6% 54%	633
	Night	7% 7% 5% 5% 56%	731
November	Day	12% 5% 6% 52%	483
	Night	11% 7% 7% 48%	682
December	Day	6% 5% 6% 6% 59%	549
	Night	11% 5% 6% 49%	790

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	8% 15% 54% 14% 7%	252
	Night	8% 14% 44% 27% 5%	379
February	Day	13% 15% 42% 23%	238
	Night	12% 18% 37% 24% 7%	304
March	Day	5% 9% 29% 40% 14%	418
	Night	5% 15% 29% 33% 16%	424
April	Day	7% 8% 19% 44% 19%	488
	Night	6% 11% 24% 38% 19%	433
May	Day	14% 23% 35% 24%	652
	Night	12% 20% 40% 23%	439
June	Day	5% 16% 40% 36%	654
	Night	23% 43% 27%	462
July	Day	11% 14% 28% 40%	505
	Night	9% 5% 15% 23% 46%	372
August	Day	17% 10% 31% 25% 15%	537
	Night	13% 15% 21% 29% 20%	505
September	Day	20% 43% 27%	730
	Night	6% 20% 40% 30%	739
October	Day	9% 25% 44% 16%	665
	Night	11% 30% 37% 19%	801
November	Day	5% 17% 27% 38% 11%	362
	Night	10% 15% 26% 30% 17%	499
December	Day	7% 26% 40% 23%	376
	Night	5% 30% 36% 23%	494

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	27% 20% 25% 24%	222
February	Day	46% 23% 30%	26
	Night	35% 23% 24% 15%	208
March	Day	29% 29% 29% 9%	54
	Night	19% 29% 27% 20%	231
April	Day	29% 38% 29%	47
	Night	23% 23% 34% 17%	193
May	Day	27% 44% 24%	54
	Night	17% 29% 31% 20%	181
June	Day	12% 54% 33%	57
	Night	5% 24% 43% 25%	177
July	Day	11% 27% 47% 13%	61
	Night	10% 38% 45%	183
August	Day	14% 24% 42% 15%	82
	Night	8% 7% 23% 51% 8%	273
September	Day	19% 33% 36% 10%	83
	Night	8% 15% 30% 38% 6%	345
October	Day	20% 25% 45% 10%	20
	Night	12% 19% 32% 30% 5%	349
November	Night	26% 22% 25% 21%	227
December	Night	20% 29% 25% 20%	220

Page generated at 2008-05-11 01:45:37. Version ab11