Harrington Beach State Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harrington Beach State Park 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	15% 5% 5% 6% 5% 5% 8% 34%	8742
	Night	18% 5% 5% 6% 5% 7% 34%	8433
Transparency	Day	23% 20% 40% 13%	4734
	Night	20% 18% 41% 18%	4355
Seeing	Day	14% 39% 32% 9%	594
	Night	10% 23% 37% 24%	2560

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	28% 11% 8% 7% 22%	489
	Night	28% 7% 6% 6% 26%	864
February	Day	21% 6% 6% 6% 5% 6% 9% 26%	548
	Night	23% 8% 6% 5% 6% 5% 29%	706
March	Day	21% 9% 7% 6% 6% 8% 5% 23%	670
	Night	19% 8% 6% 5% 6% 5% 5% 34%	696
April	Day	11% 6% 6% 6% 6% 8% 38%	736
	Night	16% 6% 7% 6% 5% 39%	583
May	Day	23% 6% 5% 5% 7% 6% 6% 27%	844
	Night	20% 5% 6% 8% 9% 30%	509
June	Day	12% 6% 5% 6% 10% 39%	840
	Night	11% 5% 5% 7% 11% 42%	476
July	Day	9% 5% 6% 6% 7% 12% 35%	866
	Night	7% 5% 9% 7% 7% 9% 40%	496
August	Day	8% 5% 8% 5% 6% 11% 41%	1187
	Night	9% 7% 6% 7% 47%	855
September	Day	7% 5% 6% 8% 53%	1011
	Night	6% 9% 54%	931
October	Day	19% 5% 7% 5% 7% 34%	604
	Night	20% 7% 6% 5% 5% 5% 5% 32%	758
November	Day	28% 6% 5% 7% 5% 6% 25%	460
	Night	29% 7% 5% 5% 5% 7% 5% 5% 20%	707
December	Day	21% 7% 8% 5% 8% 7% 6% 22%	487
	Night	21% 7% 8% 6% 9% 5% 6% 21%	852

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	37% 17% 34% 11%	135
	Night	34% 15% 40% 8%	312
February	Day	32% 27% 35% 5%	247
	Night	30% 22% 34% 12%	276
March	Day	33% 30% 32%	244
	Night	17% 19% 50% 13%	325
April	Day	29% 16% 38% 11%	429
	Night	23% 11% 38% 21% 5%	308
May	Day	20% 29% 44% 5%	341
	Night	24% 19% 44% 10%	254
June	Day	21% 19% 36% 20%	499
	Night	18% 19% 42% 19%	297
July	Day	19% 12% 47% 17%	518
	Night	20% 14% 41% 18% 6%	299
August	Day	19% 20% 43% 15%	729
	Night	16% 19% 39% 23%	535
September	Day	12% 20% 43% 19%	707
	Night	7% 17% 40% 29%	660
October	Day	27% 24% 36% 11%	525
	Night	15% 22% 44% 16%	536
November	Day	19% 30% 45%	222
	Night	18% 22% 45% 13%	287
December	Day	38% 7% 34% 18%	138
	Night	39% 12% 32% 15%	266

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	10% 47% 28% 10%	223
February	Night	7% 27% 45% 15%	185
March	Day	5% 30% 35% 20% 10%	20
	Night	11% 29% 43% 13%	191
April	Day	7% 20% 39% 28%	53
	Night	7% 16% 47% 24%	161
May	Day	7% 15% 51% 20%	82
	Night	6% 11% 57% 24%	149
June	Day	11% 46% 32% 7%	109
	Night	8% 42% 39% 6%	161
July	Day	9% 40% 34% 13%	114
	Night	9% 9% 31% 40% 9%	181
August	Day	10% 30% 41% 14%	112
	Night	6% 12% 34% 37% 8%	258
September	Day	7% 16% 33% 34% 8%	84
	Night	7% 12% 40% 36% 5%	300
October	Day	5% 25% 30% 35% 5%	20
	Night	11% 26% 30% 29%	317
November	Night	17% 43% 29% 8%	188
December	Night	23% 37% 30% 7%	246

Page generated at 2008-05-11 03:45:47. Version ab11