Windy Hill 5 Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Windy Hill 5 Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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% 4 2 6% 5% 5% 6% 5% 8% 10% 43%	131160
	Night	7% 5% 2 6% 5% 5% 5% 4 7% 10% 44%	129690
Transparency	Day	32% 10% 19% 21% 13% 4	134933
	Night	34% 9% 17% 21% 14% 5%	133987
Seeing	Day	8% 5% 19% 28% 25% 14%	17152
	Night	8% 4 18% 33% 27% 9%	27249

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	6% 5% 2 5% 4 3 4 4 6% 8% 53%	5258
	11th to 20th	Day	18% 9% 3 8% 4 4 4 4 5% 7% 34%	5280
	21st to end	Day	12% 6% 2 6% 3 3 4 3 6% 8% 47%	6409
February	1st to 10th	Day	9% 5% 2 6% 3 4 5% 4 6% 8% 48%	2100
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 5% 7% 56%	1998
	21st to end	Day	7% 3 2 5% 4 3 3 4 6% 8% 55%	1694
March	1st to 10th	Day	7% 4 2 6% 4 5% 5% 4 6% 8% 49%	4935
	11th to 20th	Day	4 3 2 4 3 3 3 3 6% 9% 61%	4980
	21st to end	Day	7% 4 2 5% 4 3 4 4 7% 9% 52%	5465
April	1st to 10th	Day	6% 2 1 4 4 4 4 4 7% 10% 53%	2200
	11th to 20th	Day	7% 4 2 6% 4 4 4 4 6% 8% 51%	2176
	21st to end	Day	4 2 1 4 3 4 4 5% 6% 8% 58%	2369
May	1st to 10th	Day	2 2 1 3 3 3 4 4 7% 11% 60%	5862
	11th to 20th	Day	8% 3 1 5% 4 4 4 4 7% 10% 51%	5861
	21st to end	Day	3 3 1 3 3 4 4 4 7% 12% 56%	6433
June	1st to 10th	Day	10% 6% 3 7% 5% 5% 6% 6% 9% 11% 33%	2600
	11th to 20th	Day	6% 5% 2 6% 5% 7% 8% 6% 11% 13% 32%	2600
	21st to end	Day	7% 4 2 7% 7% 6% 7% 7% 10% 11% 31%	2600
July	1st to 10th	Day	5% 4 2 8% 6% 7% 8% 8% 11% 15% 25%	5900
	11th to 20th	Day	3 4 2 7% 6% 8% 10% 9% 12% 14% 25%	5900
	21st to end	Day	3 3 2 6% 6% 7% 9% 8% 12% 15% 30%	6424
August	1st to 10th	Day	6% 4 2 9% 7% 7% 8% 7% 10% 14% 26%	4111
	11th to 20th	Day	3 4 2 6% 5% 6% 7% 6% 10% 13% 38%	3849
	21st to end	Day	5% 4 2 8% 6% 7% 9% 7% 12% 14% 25%	3953
September	1st to 10th	Day	7% 5% 3 8% 7% 7% 9% 7% 10% 11% 26%	2200
	11th to 20th	Day	8% 6% 3 7% 6% 7% 7% 6% 8% 12% 30%	2200
	21st to end	Day	6% 5% 2 8% 5% 6% 7% 5% 9% 12% 35%	2200
October	1st to 10th	Day	8% 5% 2 8% 6% 6% 5% 5% 7% 10% 37%	2200
	11th to 20th	Day	6% 4 2 4 5% 5% 4 4 6% 9% 52%	2066
	21st to end	Day	7% 5% 2 5% 3 4 5% 3 6% 9% 52%	2200
November	1st to 10th	Day	7% 4 2 6% 4 4 4 4 6% 8% 52%	2057
	11th to 20th	Day	7% 5% 1 6% 4 4 5% 4 5% 7% 51%	2100
	21st to end	Day	7% 5% 2 4 4 5% 5% 4 5% 9% 51%	1932
December	1st to 10th	Day	4 3 1 4 3 3 4 3 5% 9% 60%	3020
	11th to 20th	Day	7% 6% 3 6% 5% 4 4 4 6% 7% 49%	3463
	21st to end	Day	9% 7% 3 9% 6% 5% 5% 4 6% 8% 39%	4565
January	1st to 10th	Night	6% 5% 2 6% 4 4 4 3 5% 9% 51%	7635
	11th to 20th	Night	16% 10% 4 9% 5% 5% 4 3 6% 7% 32%	7680
	21st to end	Night	12% 5% 2 6% 4 4 4 4 6% 7% 45%	7768
February	1st to 10th	Night	9% 8% 2 7% 4 4 4 3 5% 8% 47%	2520
	11th to 20th	Night	9% 6% 2 5% 3 3 4 4 6% 7% 51%	2399
	21st to end	Night	6% 4 2 5% 4 4 4 5% 6% 8% 52%	1934
March	1st to 10th	Night	8% 5% 2 6% 4 4 4 4 6% 7% 49%	4918
	11th to 20th	Night	4 3 1 4 4 4 4 4 7% 10% 57%	4980
	21st to end	Night	8% 6% 2 6% 4 4 4 4 5% 7% 51%	5467
April	1st to 10th	Night	5% 3 1 4 4 3 4 4 7% 9% 55%	2200
	11th to 20th	Night	6% 3 1 5% 4 4 4 5% 6% 9% 52%	2173
	21st to end	Night	4 3 1 4 4 4 4 4 5% 8% 58%	2045
May	1st to 10th	Night	2 2 1 5% 3 4 5% 5% 7% 10% 55%	4033
	11th to 20th	Night	7% 4 2 5% 4 4 4 3 6% 8% 54%	4032
	21st to end	Night	2 3 1 4 4 4 5% 4 6% 10% 58%	4421
June	1st to 10th	Night	10% 5% 3 6% 4 6% 5% 4 7% 12% 39%	1800
	11th to 20th	Night	5% 5% 1 5% 5% 6% 6% 6% 9% 13% 38%	1800
	21st to end	Night	6% 5% 2 6% 5% 6% 7% 6% 8% 14% 35%	1800
July	1st to 10th	Night	4 5% 3 9% 7% 7% 9% 7% 11% 14% 24%	4058
	11th to 20th	Night	3 4 2 8% 6% 8% 8% 7% 12% 14% 28%	4057
	21st to end	Night	3 5% 3 11% 8% 8% 9% 7% 10% 13% 24%	4427
August	1st to 10th	Night	5% 5% 2 6% 5% 6% 7% 6% 11% 14% 34%	3032
	11th to 20th	Night	3 3 2 6% 5% 6% 7% 7% 11% 16% 34%	3200
	21st to end	Night	6% 4 2 8% 6% 8% 8% 7% 11% 14% 25%	3911
September	1st to 10th	Night	5% 6% 3 7% 7% 7% 8% 7% 9% 13% 29%	2200
	11th to 20th	Night	8% 6% 3 9% 6% 8% 6% 6% 7% 11% 30%	2200
	21st to end	Night	8% 6% 3 9% 6% 7% 7% 4 8% 10% 33%	2200
October	1st to 10th	Night	8% 6% 3 6% 5% 6% 6% 5% 8% 8% 39%	2200
	11th to 20th	Night	6% 5% 2 5% 5% 4 5% 3 5% 8% 51%	2331
	21st to end	Night	8% 5% 2 6% 4 4 4 3 7% 9% 49%	2640
November	1st to 10th	Night	6% 4 2 6% 5% 4 4 4 5% 8% 51%	2461
	11th to 20th	Night	7% 7% 2 5% 4 4 3 4 5% 8% 50%	2520
	21st to end	Night	7% 5% 2 6% 4 4 4 4 6% 9% 48%	2683
December	1st to 10th	Night	5% 3 2 4 3 3 3 3 5% 8% 61%	4380
	11th to 20th	Night	10% 6% 2 5% 4 4 4 3 5% 8% 49%	4952
	21st to end	Night	11% 8% 3 8% 5% 5% 5% 4 6% 9% 36%	6633

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	27% 7% 11% 24% 25% 7%	5259
	11th to 20th	Day	49% 5% 7% 17% 14% 8%	5280
	21st to end	Day	34% 5% 10% 29% 14% 9%	6409
February	1st to 10th	Day	32% 6% 12% 20% 19% 11%	2100
	11th to 20th	Day	25% 7% 13% 21% 25% 9%	2008
	21st to end	Day	27% 5% 13% 20% 26% 8%	1694
March	1st to 10th	Day	31% 9% 13% 21% 21% 6%	4935
	11th to 20th	Day	20% 7% 13% 25% 20% 16%	4980
	21st to end	Day	27% 5% 11% 30% 21% 6%	5465
April	1st to 10th	Day	23% 8% 20% 24% 18% 6%	2200
	11th to 20th	Day	29% 7% 15% 18% 23% 8%	2176
	21st to end	Day	20% 7% 15% 27% 27% 4	2369
May	1st to 10th	Day	16% 7% 29% 30% 15% 3	5897
	11th to 20th	Day	26% 9% 20% 29% 16% 1	5865
	21st to end	Day	19% 8% 23% 35% 13% 1	6447
June	1st to 10th	Day	39% 13% 25% 19% 4	2600
	11th to 20th	Day	37% 14% 27% 19% 3	2600
	21st to end	Day	40% 17% 27% 14% 3	2600
July	1st to 10th	Day	41% 17% 34% 7% 1	5835
	11th to 20th	Day	41% 18% 33% 8%	5831
	21st to end	Day	35% 19% 28% 16% 1	6240
August	1st to 10th	Day	41% 17% 30% 9% 3	4098
	11th to 20th	Day	30% 17% 30% 18% 4	3885
	21st to end	Day	41% 18% 30% 10% 1	3953
September	1st to 10th	Day	45% 18% 25% 11% 1	2200
	11th to 20th	Day	44% 14% 25% 14% 4	2200
	21st to end	Day	38% 13% 19% 19% 9% 2	2200
October	1st to 10th	Day	50% 13% 14% 10% 8% 4	3590
	11th to 20th	Day	26% 6% 9% 22% 33% 4	3345
	21st to end	Day	27% 6% 8% 26% 27% 7%	3538
November	1st to 10th	Day	28% 7% 13% 23% 19% 10%	2057
	11th to 20th	Day	32% 6% 11% 22% 21% 9%	2100
	21st to end	Day	30% 7% 13% 22% 19% 9%	1932
December	1st to 10th	Day	22% 5% 16% 29% 20% 8%	3020
	11th to 20th	Day	33% 6% 10% 19% 21% 10%	3460
	21st to end	Day	41% 7% 12% 21% 15% 3	4565
January	1st to 10th	Night	29% 6% 10% 26% 24% 5%	7636
	11th to 20th	Night	51% 5% 9% 15% 13% 7%	7680
	21st to end	Night	35% 7% 11% 22% 16% 8%	7768
February	1st to 10th	Night	34% 5% 11% 19% 21% 9%	2520
	11th to 20th	Night	31% 6% 12% 21% 22% 9%	2400
	21st to end	Night	28% 7% 13% 21% 26% 7%	1934
March	1st to 10th	Night	31% 8% 13% 22% 18% 8%	4918
	11th to 20th	Night	20% 7% 17% 21% 19% 16%	4980
	21st to end	Night	31% 5% 10% 27% 22% 4	5467
April	1st to 10th	Night	23% 7% 19% 27% 17% 7%	2200
	11th to 20th	Night	24% 9% 16% 21% 23% 6%	2173
	21st to end	Night	22% 7% 14% 27% 26% 4	2045
May	1st to 10th	Night	19% 11% 24% 29% 14% 4	4060
	11th to 20th	Night	26% 9% 18% 31% 15%	4033
	21st to end	Night	20% 7% 21% 35% 16% 1	4429
June	1st to 10th	Night	37% 10% 26% 21% 6%	1800
	11th to 20th	Night	33% 13% 29% 21% 4	1800
	21st to end	Night	36% 17% 27% 15% 5%	1800
July	1st to 10th	Night	45% 17% 31% 7% 1	4015
	11th to 20th	Night	39% 19% 35% 7%	4006
	21st to end	Night	46% 15% 25% 13%	4297
August	1st to 10th	Night	36% 16% 31% 11% 6%	3021
	11th to 20th	Night	30% 16% 35% 17% 1	3230
	21st to end	Night	42% 19% 28% 9% 1	3911
September	1st to 10th	Night	41% 20% 25% 13% 2	2200
	11th to 20th	Night	46% 14% 24% 15% 2	2200
	21st to end	Night	42% 13% 19% 18% 8% 1	2200
October	1st to 10th	Night	54% 11% 13% 11% 8% 4	3590
	11th to 20th	Night	26% 6% 9% 28% 25% 5%	3791
	21st to end	Night	29% 6% 9% 26% 25% 5%	4252
November	1st to 10th	Night	29% 7% 13% 21% 20% 10%	2461
	11th to 20th	Night	32% 7% 11% 22% 20% 8%	2520
	21st to end	Night	31% 7% 12% 23% 19% 8%	2683
December	1st to 10th	Night	21% 5% 18% 29% 16% 11%	4380
	11th to 20th	Night	33% 6% 11% 21% 21% 8%	4954
	21st to end	Night	42% 9% 14% 18% 15% 3	6633

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	10% 14% 39% 29% 8% 1	330
	11th to 20th	Day	12% 17% 33% 27% 9% 2	330
	21st to end	Day	16% 12% 46% 22% 4	363
February	1st to 10th	Day	8% 11% 32% 33% 14% 1	330
	11th to 20th	Day	7% 9% 37% 30% 14% 2	315
	21st to end	Day	7% 11% 30% 37% 14% 1	293
March	1st to 10th	Day	6% 10% 40% 33% 11% 1	500
	11th to 20th	Day	8% 10% 31% 32% 18% 1	500
	21st to end	Day	6% 8% 35% 32% 16% 3	550
April	1st to 10th	Day	5% 8% 37% 33% 15% 1	500
	11th to 20th	Day	8% 9% 28% 37% 15% 3	492
	21st to end	Day	4 4 23% 42% 24% 4	500
May	1st to 10th	Day	4 5% 23% 38% 23% 8%	503
	11th to 20th	Day	9% 4 19% 33% 27% 9%	527
	21st to end	Day	6% 2 13% 29% 33% 17%	573
June	1st to 10th	Day	14% 4 9% 30% 28% 16%	530
	11th to 20th	Day	7% 2 9% 27% 33% 22%	530
	21st to end	Day	5% 1 6% 17% 34% 37%	530
July	1st to 10th	Day	5% 2 3 15% 37% 38%	525
	11th to 20th	Day	4 1 4 14% 37% 40%	524
	21st to end	Day	9% 1 5% 13% 37% 35%	576
August	1st to 10th	Day	7% 1 5% 16% 36% 35%	526
	11th to 20th	Day	6% 1 4 13% 36% 39%	519
	21st to end	Day	8% 2 6% 19% 34% 32%	583
September	1st to 10th	Day	9% 2 4 20% 35% 31%	530
	11th to 20th	Day	9% 2 6% 28% 31% 24%	530
	21st to end	Day	6% 1 7% 27% 35% 25%	530
October	1st to 10th	Day	11% 4 15% 34% 30% 7%	530
	11th to 20th	Day	8% 2 19% 34% 28% 9%	530
	21st to end	Day	8% 4 21% 37% 25% 4	583
November	1st to 10th	Day	8% 6% 21% 36% 25% 4	535
	11th to 20th	Day	11% 5% 23% 37% 20% 4	540
	21st to end	Day	8% 7% 30% 33% 20% 2	372
December	1st to 10th	Day	6% 10% 35% 32% 13% 4	330
	11th to 20th	Day	7% 8% 37% 32% 15% 1	330
	21st to end	Day	5% 12% 31% 35% 14% 3	363
January	1st to 10th	Night	10% 8% 27% 37% 17% 1	840
	11th to 20th	Night	13% 9% 25% 37% 15% 1	840
	21st to end	Night	12% 12% 30% 35% 11%	924
February	1st to 10th	Night	12% 7% 30% 33% 17%	840
	11th to 20th	Night	11% 8% 25% 38% 18% 1	804
	21st to end	Night	8% 5% 24% 45% 17%	660
March	1st to 10th	Night	5% 7% 34% 42% 11% 1	800
	11th to 20th	Night	6% 7% 25% 41% 20% 1	800
	21st to end	Night	7% 5% 27% 40% 19% 1	880
April	1st to 10th	Night	5% 8% 25% 43% 19% 1	800
	11th to 20th	Night	6% 6% 27% 42% 17% 2	791
	21st to end	Night	5% 3 25% 47% 19% 1	775
May	1st to 10th	Night	3 1 14% 46% 32% 4	600
	11th to 20th	Night	7% 2 14% 40% 31% 6%	591
	21st to end	Night	4 1 10% 36% 42% 7%	650
June	1st to 10th	Night	11% 1 5% 25% 45% 14%	600
	11th to 20th	Night	6% 2 5% 17% 45% 25%	600
	21st to end	Night	7% 1 5% 12% 43% 32%	600
July	1st to 10th	Night	6% 1 4 8% 44% 37%	585
	11th to 20th	Night	4 1 3 10% 40% 42%	582
	21st to end	Night	5% 1 3 11% 45% 36%	657
August	1st to 10th	Night	5% 1 3 12% 44% 36%	597
	11th to 20th	Night	6% 3 11% 38% 42%	594
	21st to end	Night	11% 1 5% 21% 39% 23%	855
September	1st to 10th	Night	6% 2 7% 20% 43% 23%	800
	11th to 20th	Night	9% 2 7% 27% 37% 17%	800
	21st to end	Night	10% 2 8% 30% 38% 13%	800
October	1st to 10th	Night	12% 2 16% 36% 29% 5%	800
	11th to 20th	Night	7% 5% 16% 37% 32% 4	800
	21st to end	Night	8% 5% 24% 38% 23% 3	880
November	1st to 10th	Night	7% 4 27% 40% 19% 2	820
	11th to 20th	Night	9% 5% 22% 41% 22% 2	840
	21st to end	Night	8% 6% 25% 42% 19% 1	840
December	1st to 10th	Night	8% 6% 24% 38% 23% 2	840
	11th to 20th	Night	9% 6% 27% 36% 20% 2	840
	21st to end	Night	10% 7% 25% 36% 20% 2	924

Page generated at 2026-02-13 01:42:16. Version ac07

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