The Winter-Hawk Memorial Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Winter-Hawk Memorial Observatory clear sky chart from 2005-11-06 to 2024-11-12.

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	13% 8% 3 7% 5% 5% 5% 4 6% 7% 37%	101147
	Night	15% 9% 3 7% 4 4 4 4 6% 7% 38%	97966
Transparency	Day	42% 10% 12% 20% 13% 3	104915
	Night	42% 9% 12% 20% 14% 3	102337
Seeing	Day	18% 13% 23% 24% 16% 6%	14999
	Night	17% 10% 22% 31% 17% 2	25042

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	13% 16% 6% 10% 5% 3 4 3 6% 7% 28%	2836
	11th to 20th	Day	14% 15% 7% 9% 7% 5% 3 3 4 5% 28%	2840
	21st to end	Day	18% 17% 4 7% 4 3 3 3 5% 5% 31%	3124
February	1st to 10th	Day	17% 13% 3 8% 5% 4 4 4 4 5% 33%	1809
	11th to 20th	Day	20% 13% 4 9% 4 3 4 3 4 5% 32%	1848
	21st to end	Day	20% 12% 2 7% 3 4 4 3 5% 5% 35%	1570
March	1st to 10th	Day	19% 13% 3 6% 4 4 4 3 4 6% 34%	3309
	11th to 20th	Day	14% 8% 3 5% 3 4 3 3 5% 5% 47%	3480
	21st to end	Day	16% 10% 2 6% 4 4 4 4 6% 6% 38%	3815
April	1st to 10th	Day	12% 8% 2 6% 4 5% 4 4 7% 7% 42%	2090
	11th to 20th	Day	15% 8% 2 5% 5% 4 4 4 5% 7% 43%	2304
	21st to end	Day	15% 7% 3 6% 5% 5% 4 4 5% 7% 40%	2470
May	1st to 10th	Day	17% 7% 3 8% 6% 5% 5% 4 6% 7% 32%	4082
	11th to 20th	Day	17% 8% 3 8% 6% 5% 5% 4 6% 6% 32%	4081
	21st to end	Day	10% 6% 2 6% 5% 5% 5% 5% 8% 10% 38%	4476
June	1st to 10th	Day	10% 6% 2 6% 6% 6% 7% 5% 7% 10% 35%	2470
	11th to 20th	Day	6% 5% 3 7% 7% 6% 8% 6% 9% 9% 35%	2470
	21st to end	Day	9% 5% 2 6% 6% 6% 7% 6% 8% 11% 36%	2470
July	1st to 10th	Day	7% 4 2 6% 6% 6% 6% 5% 9% 12% 36%	4120
	11th to 20th	Day	11% 6% 2 6% 5% 5% 6% 5% 7% 9% 38%	4120
	21st to end	Day	15% 9% 3 11% 8% 7% 8% 5% 7% 8% 19%	4466
August	1st to 10th	Day	11% 6% 2 7% 6% 6% 7% 5% 7% 11% 33%	4104
	11th to 20th	Day	10% 6% 2 7% 5% 5% 6% 5% 8% 10% 35%	4044
	21st to end	Day	6% 4 2 5% 4 4 5% 4 7% 8% 52%	4179
September	1st to 10th	Day	11% 6% 2 6% 5% 5% 6% 4 6% 8% 42%	2090
	11th to 20th	Day	15% 5% 2 7% 4 4 4 4 5% 8% 41%	2090
	21st to end	Day	14% 5% 3 5% 5% 4 4 5% 6% 7% 43%	2090
October	1st to 10th	Day	12% 6% 2 5% 3 3 3 3 5% 6% 51%	2077
	11th to 20th	Day	14% 6% 2 5% 3 3 3 2 5% 6% 52%	1900
	21st to end	Day	15% 7% 2 4 3 4 3 3 4 5% 51%	2090
November	1st to 10th	Day	13% 5% 1 5% 3 3 4 3 4 6% 53%	1817
	11th to 20th	Day	12% 8% 3 4 3 3 4 4 5% 7% 46%	1719
	21st to end	Day	13% 10% 4 6% 3 3 3 3 5% 6% 44%	1710
December	1st to 10th	Day	19% 12% 4 6% 4 3 4 4 6% 5% 33%	1710
	11th to 20th	Day	14% 14% 3 7% 3 2 4 4 7% 7% 35%	2153
	21st to end	Day	14% 17% 3 7% 5% 5% 4 3 4 5% 31%	3124
January	1st to 10th	Night	19% 15% 6% 8% 4 4 4 3 4 5% 29%	4109
	11th to 20th	Night	19% 11% 3 9% 6% 4 3 2 3 5% 34%	4120
	21st to end	Night	21% 13% 4 7% 4 3 3 3 4 5% 34%	4532
February	1st to 10th	Night	17% 11% 4 7% 4 4 4 4 5% 6% 37%	2366
	11th to 20th	Night	21% 12% 3 7% 4 4 4 3 5% 4 33%	2218
	21st to end	Night	20% 12% 3 6% 4 4 4 4 6% 6% 31%	1884
March	1st to 10th	Night	24% 12% 3 6% 4 4 3 3 4 6% 32%	3542
	11th to 20th	Night	15% 6% 2 5% 3 3 4 3 5% 8% 45%	3480
	21st to end	Night	15% 7% 2 5% 5% 4 4 5% 6% 7% 41%	3817
April	1st to 10th	Night	13% 8% 2 5% 4 3 4 4 6% 7% 42%	2090
	11th to 20th	Night	14% 9% 2 6% 5% 4 3 3 5% 7% 42%	1839
	21st to end	Night	15% 6% 2 6% 4 4 4 4 6% 7% 43%	1710
May	1st to 10th	Night	16% 8% 2 7% 5% 5% 5% 4 7% 9% 32%	2813
	11th to 20th	Night	19% 7% 3 6% 6% 5% 4 4 7% 8% 33%	2812
	21st to end	Night	11% 6% 3 7% 5% 5% 5% 5% 7% 9% 37%	3079
June	1st to 10th	Night	11% 6% 3 5% 6% 5% 6% 5% 8% 11% 35%	1710
	11th to 20th	Night	5% 5% 3 5% 5% 5% 6% 4 8% 12% 41%	1710
	21st to end	Night	8% 6% 2 6% 6% 6% 6% 4 6% 11% 39%	1710
July	1st to 10th	Night	12% 6% 2 7% 5% 5% 6% 6% 9% 10% 32%	2840
	11th to 20th	Night	8% 5% 2 7% 5% 4 6% 5% 8% 11% 39%	2840
	21st to end	Night	13% 9% 4 11% 7% 7% 6% 5% 7% 9% 21%	3087
August	1st to 10th	Night	10% 5% 2 8% 5% 5% 5% 6% 7% 10% 36%	2825
	11th to 20th	Night	13% 6% 2 7% 5% 5% 5% 4 7% 8% 38%	2785
	21st to end	Night	6% 4 1 5% 4 4 6% 4 7% 8% 49%	3412
September	1st to 10th	Night	11% 7% 2 7% 4 4 4 4 6% 6% 43%	2090
	11th to 20th	Night	15% 6% 2 7% 4 4 4 4 7% 8% 40%	2090
	21st to end	Night	13% 5% 2 6% 3 4 4 3 6% 7% 47%	2090
October	1st to 10th	Night	14% 5% 2 5% 3 3 3 2 5% 6% 51%	2101
	11th to 20th	Night	15% 6% 2 5% 3 3 3 3 4 6% 51%	2280
	21st to end	Night	14% 6% 2 4 3 3 3 3 5% 6% 50%	2508
November	1st to 10th	Night	15% 7% 2 5% 3 3 3 3 4 5% 50%	2479
	11th to 20th	Night	14% 8% 2 4 3 4 3 3 5% 7% 46%	2484
	21st to end	Night	14% 9% 2 5% 3 4 3 3 5% 6% 46%	2470
December	1st to 10th	Night	18% 13% 4 8% 4 4 3 3 5% 6% 31%	2470
	11th to 20th	Night	18% 11% 4 9% 4 3 3 3 4 6% 35%	3042
	21st to end	Night	14% 16% 4 8% 5% 5% 5% 4 6% 8% 26%	4532

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	48% 10% 9% 18% 13% 2	2837
	11th to 20th	Day	54% 8% 8% 14% 15% 1	2840
	21st to end	Day	55% 5% 7% 16% 16% 1	3124
February	1st to 10th	Day	53% 5% 8% 15% 16% 2	1809
	11th to 20th	Day	55% 6% 8% 15% 14% 2	1858
	21st to end	Day	50% 6% 9% 14% 16% 5%	1570
March	1st to 10th	Day	49% 7% 9% 17% 14% 4	3309
	11th to 20th	Day	37% 7% 8% 22% 19% 6%	3480
	21st to end	Day	45% 7% 10% 25% 11% 2	3815
April	1st to 10th	Day	39% 8% 12% 21% 17% 3	2090
	11th to 20th	Day	40% 8% 9% 18% 20% 5%	2304
	21st to end	Day	43% 7% 11% 24% 13% 2	2470
May	1st to 10th	Day	46% 13% 12% 19% 8% 1	4120
	11th to 20th	Day	49% 11% 11% 21% 7% 1	4085
	21st to end	Day	36% 14% 16% 19% 13% 2	4489
June	1st to 10th	Day	41% 13% 17% 18% 10% 1	2470
	11th to 20th	Day	39% 14% 17% 16% 13% 1	2470
	21st to end	Day	40% 13% 14% 18% 12% 3	2470
July	1st to 10th	Day	36% 16% 21% 17% 9% 1	4055
	11th to 20th	Day	40% 12% 18% 21% 6% 2	4051
	21st to end	Day	60% 12% 12% 11% 4	4324
August	1st to 10th	Day	42% 13% 18% 20% 7%	4091
	11th to 20th	Day	37% 14% 21% 19% 8% 1	4083
	21st to end	Day	28% 10% 15% 35% 10% 2	4179
September	1st to 10th	Day	38% 11% 14% 18% 15% 4	2090
	11th to 20th	Day	41% 10% 13% 19% 16% 2	2090
	21st to end	Day	39% 8% 15% 19% 14% 4	2090
October	1st to 10th	Day	27% 7% 10% 18% 28% 10%	3454
	11th to 20th	Day	25% 5% 7% 25% 20% 18%	3140
	21st to end	Day	26% 5% 7% 28% 24% 10%	3428
November	1st to 10th	Day	33% 6% 9% 20% 26% 6%	1817
	11th to 20th	Day	36% 6% 9% 21% 23% 5%	1719
	21st to end	Day	40% 6% 8% 22% 20% 4	1710
December	1st to 10th	Day	51% 8% 8% 20% 12% 2	1710
	11th to 20th	Day	44% 8% 11% 17% 17% 3	2150
	21st to end	Day	51% 9% 8% 22% 9% 1	3124
January	1st to 10th	Night	55% 8% 7% 14% 13% 2	4109
	11th to 20th	Night	50% 7% 9% 14% 18% 2	4120
	21st to end	Night	53% 6% 7% 14% 18% 1	4532
February	1st to 10th	Night	48% 6% 10% 18% 16% 2	2366
	11th to 20th	Night	54% 5% 8% 16% 13% 4	2219
	21st to end	Night	51% 6% 9% 16% 13% 4	1884
March	1st to 10th	Night	53% 8% 10% 14% 13% 2	3542
	11th to 20th	Night	36% 8% 11% 22% 15% 8%	3480
	21st to end	Night	39% 9% 12% 24% 14% 3	3817
April	1st to 10th	Night	39% 8% 13% 21% 15% 3	2090
	11th to 20th	Night	40% 7% 10% 20% 19% 4	1839
	21st to end	Night	39% 8% 12% 26% 13% 1	1710
May	1st to 10th	Night	44% 12% 16% 19% 7% 1	2840
	11th to 20th	Night	45% 12% 15% 22% 6%	2813
	21st to end	Night	35% 15% 16% 23% 10% 1	3087
June	1st to 10th	Night	38% 13% 19% 18% 11% 1	1710
	11th to 20th	Night	33% 13% 21% 21% 11% 1	1710
	21st to end	Night	37% 12% 17% 20% 11% 4	1710
July	1st to 10th	Night	42% 14% 19% 17% 7% 1	2795
	11th to 20th	Night	34% 13% 24% 21% 6% 2	2786
	21st to end	Night	54% 14% 15% 13% 4	2988
August	1st to 10th	Night	37% 14% 21% 21% 6%	2814
	11th to 20th	Night	39% 12% 19% 21% 8%	2812
	21st to end	Night	27% 11% 17% 32% 12% 1	3412
September	1st to 10th	Night	39% 9% 14% 20% 14% 4	2090
	11th to 20th	Night	39% 11% 15% 18% 16% 1	2090
	21st to end	Night	36% 9% 11% 22% 18% 3	2090
October	1st to 10th	Night	31% 7% 10% 17% 28% 7%	3504
	11th to 20th	Night	27% 5% 8% 21% 23% 17%	3779
	21st to end	Night	25% 5% 7% 28% 22% 13%	4120
November	1st to 10th	Night	36% 6% 10% 19% 22% 7%	2479
	11th to 20th	Night	38% 6% 8% 20% 22% 6%	2484
	21st to end	Night	39% 5% 7% 26% 18% 4	2470
December	1st to 10th	Night	54% 8% 10% 16% 10% 2	2470
	11th to 20th	Night	50% 7% 8% 15% 18% 3	3044
	21st to end	Night	50% 11% 12% 16% 10% 1	4532

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	23% 29% 30% 15% 3	270
	11th to 20th	Day	37% 22% 26% 13% 2	270
	21st to end	Day	25% 29% 32% 11% 3	297
February	1st to 10th	Day	22% 27% 34% 14% 2	270
	11th to 20th	Day	37% 29% 25% 8% 1	270
	21st to end	Day	39% 24% 29% 7% 1	225
March	1st to 10th	Day	26% 19% 29% 18% 7%	381
	11th to 20th	Day	26% 20% 33% 17% 4 1	460
	21st to end	Day	26% 21% 26% 20% 7%	506
April	1st to 10th	Day	22% 20% 25% 23% 9% 1	460
	11th to 20th	Day	19% 20% 25% 23% 11% 2	452
	21st to end	Day	18% 17% 26% 22% 14% 3	460
May	1st to 10th	Day	20% 15% 27% 23% 11% 4	463
	11th to 20th	Day	16% 11% 23% 29% 14% 7%	487
	21st to end	Day	14% 7% 23% 26% 20% 10%	529
June	1st to 10th	Day	11% 7% 24% 29% 22% 8%	490
	11th to 20th	Day	6% 6% 20% 30% 27% 11%	490
	21st to end	Day	10% 6% 27% 28% 18% 11%	490
July	1st to 10th	Day	12% 4 15% 27% 30% 14%	485
	11th to 20th	Day	11% 5% 14% 29% 26% 15%	484
	21st to end	Day	13% 3 17% 27% 28% 12%	532
August	1st to 10th	Day	13% 6% 17% 26% 24% 13%	486
	11th to 20th	Day	11% 5% 17% 29% 27% 11%	479
	21st to end	Day	11% 4 11% 26% 32% 16%	539
September	1st to 10th	Day	11% 5% 13% 28% 31% 12%	490
	11th to 20th	Day	14% 5% 16% 25% 31% 8%	490
	21st to end	Day	17% 7% 17% 31% 24% 4	490
October	1st to 10th	Day	16% 7% 23% 29% 19% 6%	490
	11th to 20th	Day	15% 14% 23% 29% 18% 2	490
	21st to end	Day	21% 11% 22% 31% 13% 2	539
November	1st to 10th	Day	15% 14% 30% 28% 11% 2	355
	11th to 20th	Day	18% 18% 34% 23% 7%	273
	21st to end	Day	19% 15% 37% 20% 8% 1	270
December	1st to 10th	Day	29% 21% 31% 16% 3	270
	11th to 20th	Day	24% 18% 32% 22% 4	270
	21st to end	Day	22% 27% 33% 13% 4 1	297
January	1st to 10th	Night	23% 21% 28% 23% 5%	760
	11th to 20th	Night	25% 17% 30% 23% 5%	760
	21st to end	Night	23% 18% 33% 25% 3	836
February	1st to 10th	Night	23% 14% 28% 31% 4	760
	11th to 20th	Night	27% 20% 32% 20% 1	743
	21st to end	Night	27% 22% 29% 21% 1	628
March	1st to 10th	Night	24% 15% 29% 27% 5%	760
	11th to 20th	Night	23% 16% 31% 23% 6% 1	760
	21st to end	Night	21% 14% 30% 27% 8%	836
April	1st to 10th	Night	18% 17% 29% 28% 8% 1	760
	11th to 20th	Night	18% 14% 27% 29% 12% 1	606
	21st to end	Night	16% 9% 25% 38% 11% 1	570
May	1st to 10th	Night	16% 11% 24% 31% 16% 1	570
	11th to 20th	Night	13% 8% 21% 37% 19% 2	561
	21st to end	Night	9% 2 17% 35% 32% 4	617
June	1st to 10th	Night	9% 4 15% 42% 27% 4	570
	11th to 20th	Night	5% 2 16% 36% 33% 7%	570
	21st to end	Night	8% 2 14% 38% 33% 5%	570
July	1st to 10th	Night	12% 3 7% 35% 37% 6%	555
	11th to 20th	Night	9% 3 7% 32% 41% 8%	552
	21st to end	Night	8% 3 9% 32% 40% 8%	624
August	1st to 10th	Night	8% 3 8% 35% 40% 7%	567
	11th to 20th	Night	10% 4 9% 33% 40% 3	564
	21st to end	Night	10% 2 10% 33% 38% 7%	646
September	1st to 10th	Night	13% 3 11% 32% 36% 6%	760
	11th to 20th	Night	16% 4 12% 33% 30% 4	760
	21st to end	Night	13% 5% 18% 36% 26% 3	760
October	1st to 10th	Night	14% 7% 17% 31% 26% 6%	760
	11th to 20th	Night	16% 8% 25% 32% 16% 2	760
	21st to end	Night	16% 10% 23% 36% 13% 2	836
November	1st to 10th	Night	18% 8% 21% 35% 16% 3	780
	11th to 20th	Night	18% 13% 22% 35% 10% 1	765
	21st to end	Night	19% 11% 25% 31% 13% 1	760
December	1st to 10th	Night	25% 14% 28% 27% 6%	760
	11th to 20th	Night	23% 13% 25% 31% 7% 1	760
	21st to end	Night	23% 15% 30% 28% 4	836

Page generated at 2024-11-08 22:45:40. Version ac07

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