Hawkeye Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hawkeye Observatory clear sky chart from 2005-11-06 to 2025-10-04.

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% 9% 3 7% 5% 4 4 4 5% 7% 38%	126712
	Night	13% 9% 4 8% 4 4 4 3 5% 6% 39%	122919
Transparency	Day	44% 6% 12% 24% 13% 1	130206
	Night	45% 5% 11% 23% 15% 2	127498
Seeing	Day	17% 11% 29% 25% 13% 5%	17160
	Night	17% 9% 31% 30% 11% 1	26932

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	9% 12% 7% 15% 7% 6% 5% 4 4 5% 26%	3617
	11th to 20th	Day	9% 11% 5% 12% 4 4 4 7% 6% 6% 30%	3620
	21st to end	Day	13% 16% 8% 9% 4 3 3 3 4 5% 33%	4230
February	1st to 10th	Day	12% 13% 7% 9% 6% 5% 5% 4 4 6% 30%	1800
	11th to 20th	Day	13% 11% 3 9% 6% 5% 4 3 4 6% 36%	1898
	21st to end	Day	13% 14% 4 10% 5% 4 4 3 4 5% 33%	1650
March	1st to 10th	Day	16% 8% 2 6% 3 3 3 2 4 6% 44%	4480
	11th to 20th	Day	12% 6% 3 7% 4 4 4 3 5% 8% 44%	4796
	21st to end	Day	20% 12% 5% 10% 6% 5% 5% 3 4 5% 26%	5911
April	1st to 10th	Day	18% 12% 4 8% 5% 4 3 4 5% 6% 31%	2400
	11th to 20th	Day	17% 10% 3 7% 5% 4 5% 4 5% 7% 34%	2374
	21st to end	Day	19% 10% 3 7% 5% 4 4 4 4 6% 34%	2455
May	1st to 10th	Day	15% 8% 3 7% 4 4 5% 4 5% 7% 37%	5995
	11th to 20th	Day	15% 5% 2 6% 5% 4 5% 4 5% 8% 42%	6319
	21st to end	Day	14% 6% 2 6% 4 5% 5% 4 6% 9% 38%	6935
June	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 8% 43%	2800
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 3 6% 9% 44%	2800
	21st to end	Day	11% 6% 2 6% 5% 4 4 5% 7% 10% 39%	2800
July	1st to 10th	Day	10% 7% 3 7% 5% 5% 6% 4 7% 9% 38%	6360
	11th to 20th	Day	9% 5% 2 6% 4 4 5% 4 6% 9% 45%	6360
	21st to end	Day	10% 6% 3 7% 5% 5% 5% 4 6% 9% 39%	6924
August	1st to 10th	Day	10% 5% 2 6% 4 5% 6% 4 7% 9% 42%	4466
	11th to 20th	Day	11% 5% 2 5% 4 3 4 4 6% 8% 47%	3897
	21st to end	Day	9% 6% 2 6% 4 4 4 4 6% 9% 47%	4312
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 3 5% 8% 47%	2400
	11th to 20th	Day	12% 3 1 4 3 4 3 3 5% 8% 52%	2330
	21st to end	Day	11% 6% 4 6% 4 4 4 4 5% 7% 45%	2200
October	1st to 10th	Day	14% 6% 2 4 4 4 3 3 4 7% 49%	1981
	11th to 20th	Day	19% 8% 3 6% 4 5% 3 4 5% 6% 37%	1900
	21st to end	Day	19% 10% 3 5% 5% 3 4 3 3 7% 39%	1920
November	1st to 10th	Day	12% 9% 3 6% 4 3 4 3 4 5% 45%	1762
	11th to 20th	Day	14% 13% 3 9% 5% 5% 4 3 5% 6% 33%	1800
	21st to end	Day	16% 14% 3 9% 4 3 3 3 4 6% 36%	1620
December	1st to 10th	Day	8% 10% 4 8% 5% 4 4 3 5% 7% 42%	2610
	11th to 20th	Day	14% 15% 5% 12% 5% 5% 5% 4 5% 6% 24%	3008
	21st to end	Day	21% 22% 10% 11% 5% 4 4 3 3 5% 12%	3982
January	1st to 10th	Night	10% 13% 7% 15% 6% 4 4 3 3 4 33%	6348
	11th to 20th	Night	11% 14% 6% 13% 6% 5% 5% 6% 6% 5% 23%	6360
	21st to end	Night	14% 15% 6% 10% 5% 4 4 3 4 5% 31%	6746
February	1st to 10th	Night	13% 14% 5% 8% 6% 5% 4 3 4 5% 33%	2600
	11th to 20th	Night	12% 11% 4 7% 5% 4 4 3 4 6% 38%	2388
	21st to end	Night	17% 11% 3 7% 4 4 3 3 5% 5% 37%	1980
March	1st to 10th	Night	17% 9% 4 6% 4 3 4 3 4 5% 43%	5373
	11th to 20th	Night	9% 6% 2 6% 5% 4 4 3 4 8% 49%	5193
	21st to end	Night	22% 12% 5% 10% 5% 4 4 3 4 5% 28%	5018
April	1st to 10th	Night	17% 10% 3 5% 5% 4 4 3 5% 5% 39%	2000
	11th to 20th	Night	18% 9% 3 8% 4 3 4 3 5% 5% 39%	1975
	21st to end	Night	17% 8% 2 7% 4 4 5% 4 7% 6% 36%	1945
May	1st to 10th	Night	18% 6% 3 7% 4 4 4 4 5% 7% 38%	3903
	11th to 20th	Night	12% 5% 2 6% 4 4 5% 4 6% 8% 45%	3596
	21st to end	Night	14% 7% 3 7% 4 4 4 4 6% 7% 40%	3942
June	1st to 10th	Night	9% 4 1 5% 4 5% 5% 4 7% 9% 47%	1600
	11th to 20th	Night	11% 5% 2 5% 4 4 4 4 6% 9% 45%	1600
	21st to end	Night	9% 6% 2 7% 4 4 5% 4 5% 7% 46%	1600
July	1st to 10th	Night	12% 6% 2 6% 4 4 4 4 6% 9% 41%	3618
	11th to 20th	Night	7% 5% 2 5% 3 3 5% 3 6% 8% 53%	3617
	21st to end	Night	9% 6% 2 6% 4 4 5% 4 6% 8% 46%	3947
August	1st to 10th	Night	7% 3 2 6% 4 4 4 4 5% 10% 51%	2690
	11th to 20th	Night	9% 5% 2 5% 4 4 4 4 5% 7% 51%	3140
	21st to end	Night	9% 4 2 5% 4 5% 4 3 5% 8% 51%	3586
September	1st to 10th	Night	8% 5% 2 5% 4 3 4 3 4 6% 56%	2000
	11th to 20th	Night	10% 4 1 5% 4 3 5% 3 5% 7% 53%	2050
	21st to end	Night	11% 5% 2 6% 4 4 4 3 5% 6% 50%	2200
October	1st to 10th	Night	12% 6% 2 6% 3 3 4 3 4 6% 51%	2262
	11th to 20th	Night	17% 7% 2 6% 4 3 4 2 4 6% 45%	2280
	21st to end	Night	19% 8% 3 6% 4 4 4 3 5% 7% 37%	2676
November	1st to 10th	Night	12% 8% 3 6% 3 3 4 3 4 5% 50%	2536
	11th to 20th	Night	15% 11% 3 8% 5% 4 4 4 5% 6% 36%	2600
	21st to end	Night	18% 10% 4 8% 5% 3 4 3 4 6% 36%	2775
December	1st to 10th	Night	9% 9% 3 8% 5% 5% 5% 4 5% 6% 41%	4580
	11th to 20th	Night	17% 16% 5% 9% 5% 4 4 3 5% 5% 29%	5199
	21st to end	Night	22% 18% 7% 11% 5% 5% 4 3 4 4 17%	6996

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	60% 4 11% 18% 7%	3618
	11th to 20th	Day	52% 5% 12% 10% 19% 3	3620
	21st to end	Day	54% 3 14% 18% 10%	4230
February	1st to 10th	Day	55% 4 13% 16% 11% 1	1800
	11th to 20th	Day	50% 4 11% 24% 9% 2	1908
	21st to end	Day	53% 6% 8% 20% 11% 2	1650
March	1st to 10th	Day	42% 5% 11% 28% 10% 4	4480
	11th to 20th	Day	39% 4 12% 32% 12% 1	4796
	21st to end	Day	61% 5% 11% 14% 8% 1	5913
April	1st to 10th	Day	54% 6% 10% 20% 10%	2400
	11th to 20th	Day	50% 6% 9% 21% 11% 2	2374
	21st to end	Day	51% 5% 13% 18% 12% 2	2455
May	1st to 10th	Day	45% 6% 9% 21% 18% 1	6030
	11th to 20th	Day	40% 7% 10% 28% 15% 1	6323
	21st to end	Day	40% 7% 11% 26% 12% 3	6949
June	1st to 10th	Day	37% 8% 13% 25% 16% 1	2800
	11th to 20th	Day	36% 7% 13% 24% 18% 2	2800
	21st to end	Day	39% 8% 13% 24% 13% 2	2800
July	1st to 10th	Day	40% 7% 14% 27% 11% 1	6291
	11th to 20th	Day	35% 6% 14% 29% 15% 1	6285
	21st to end	Day	40% 7% 16% 20% 15% 2	6728
August	1st to 10th	Day	36% 8% 15% 27% 13% 1	4451
	11th to 20th	Day	34% 6% 13% 33% 14% 1	3933
	21st to end	Day	34% 6% 12% 30% 16% 1	4311
September	1st to 10th	Day	36% 6% 10% 27% 19% 2	2400
	11th to 20th	Day	29% 6% 12% 33% 18% 2	2330
	21st to end	Day	38% 6% 9% 27% 19% 1	2200
October	1st to 10th	Day	24% 4 7% 38% 26% 1	3267
	11th to 20th	Day	34% 3 10% 27% 24% 2	3140
	21st to end	Day	42% 3 9% 29% 14% 3	3145
November	1st to 10th	Day	41% 5% 14% 24% 14% 2	1762
	11th to 20th	Day	52% 5% 13% 19% 10% 1	1800
	21st to end	Day	51% 5% 13% 23% 8%	1620
December	1st to 10th	Day	41% 5% 20% 26% 7% 1	2610
	11th to 20th	Day	60% 4 12% 16% 6% 2	3005
	21st to end	Day	75% 4 7% 9% 5%	3982
January	1st to 10th	Night	55% 4 10% 20% 10% 1	6348
	11th to 20th	Night	60% 4 10% 10% 15% 1	6360
	21st to end	Night	56% 3 12% 17% 11% 1	6746
February	1st to 10th	Night	54% 4 10% 19% 12% 2	2600
	11th to 20th	Night	47% 5% 11% 22% 14% 1	2389
	21st to end	Night	49% 4 12% 19% 12% 3	1980
March	1st to 10th	Night	45% 4 11% 22% 11% 6%	5373
	11th to 20th	Night	35% 4 11% 34% 13% 3	5193
	21st to end	Night	60% 4 9% 17% 9% 1	5018
April	1st to 10th	Night	46% 6% 10% 23% 14% 2	2000
	11th to 20th	Night	47% 4 8% 20% 18% 3	1975
	21st to end	Night	45% 7% 13% 22% 12% 2	1945
May	1st to 10th	Night	44% 6% 12% 18% 18% 2	3930
	11th to 20th	Night	36% 8% 14% 23% 16% 3	3597
	21st to end	Night	40% 8% 12% 23% 15% 2	3950
June	1st to 10th	Night	31% 8% 14% 26% 20% 1	1600
	11th to 20th	Night	34% 7% 10% 24% 23% 3	1600
	21st to end	Night	36% 7% 13% 22% 19% 3	1600
July	1st to 10th	Night	39% 6% 14% 25% 14% 2	3580
	11th to 20th	Night	29% 5% 15% 30% 20% 1	3572
	21st to end	Night	34% 6% 16% 24% 17% 3	3832
August	1st to 10th	Night	30% 6% 14% 30% 19% 2	2681
	11th to 20th	Night	32% 6% 13% 31% 17% 1	3169
	21st to end	Night	31% 6% 13% 30% 17% 4	3586
September	1st to 10th	Night	30% 5% 11% 27% 24% 2	2000
	11th to 20th	Night	31% 6% 10% 32% 19% 3	2050
	21st to end	Night	34% 6% 10% 29% 20% 2	2200
October	1st to 10th	Night	25% 4 6% 35% 29% 1	3756
	11th to 20th	Night	33% 4 8% 26% 26% 3	3779
	21st to end	Night	43% 4 9% 26% 15% 3	4401
November	1st to 10th	Night	38% 5% 9% 27% 18% 3	2536
	11th to 20th	Night	48% 5% 12% 21% 12% 1	2600
	21st to end	Night	50% 5% 12% 23% 11% 1	2775
December	1st to 10th	Night	43% 5% 14% 28% 10% 1	4580
	11th to 20th	Night	58% 4 12% 16% 9% 1	5201
	21st to end	Night	71% 4 8% 12% 5%	6996

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	18% 16% 31% 29% 6%	300
	11th to 20th	Day	19% 18% 38% 20% 4 1	300
	21st to end	Day	23% 13% 40% 19% 4 1	330
February	1st to 10th	Day	19% 21% 37% 17% 5%	300
	11th to 20th	Day	21% 23% 33% 20% 3	300
	21st to end	Day	25% 19% 41% 11% 3	249
March	1st to 10th	Day	20% 20% 42% 14% 4	300
	11th to 20th	Day	25% 17% 37% 14% 5% 1	300
	21st to end	Day	29% 15% 32% 17% 6% 2	520
April	1st to 10th	Day	26% 16% 32% 22% 5%	500
	11th to 20th	Day	25% 20% 25% 19% 8% 2	492
	21st to end	Day	24% 13% 31% 23% 7% 2	500
May	1st to 10th	Day	20% 13% 32% 23% 8% 3	558
	11th to 20th	Day	22% 9% 30% 23% 12% 3	725
	21st to end	Day	18% 10% 28% 22% 15% 7%	789
June	1st to 10th	Day	10% 8% 31% 30% 17% 5%	730
	11th to 20th	Day	12% 7% 32% 29% 15% 5%	730
	21st to end	Day	14% 7% 29% 29% 16% 4	730
July	1st to 10th	Day	10% 2 17% 32% 25% 13%	721
	11th to 20th	Day	10% 6% 27% 29% 19% 9%	718
	21st to end	Day	9% 4 24% 36% 21% 7%	794
August	1st to 10th	Day	7% 3 22% 34% 24% 10%	726
	11th to 20th	Day	13% 5% 20% 26% 22% 15%	555
	21st to end	Day	11% 5% 19% 30% 25% 9%	583
September	1st to 10th	Day	15% 6% 24% 26% 23% 7%	530
	11th to 20th	Day	10% 3 21% 29% 25% 12%	530
	21st to end	Day	14% 11% 25% 25% 17% 8%	530
October	1st to 10th	Day	15% 10% 27% 28% 18% 3	360
	11th to 20th	Day	26% 19% 31% 16% 7%	300
	21st to end	Day	28% 15% 31% 19% 6%	330
November	1st to 10th	Day	19% 16% 36% 19% 9% 2	300
	11th to 20th	Day	21% 20% 35% 17% 6% 1	300
	21st to end	Day	28% 12% 36% 20% 4	300
December	1st to 10th	Day	16% 21% 41% 16% 4 2	300
	11th to 20th	Day	20% 14% 40% 19% 7% 1	300
	21st to end	Day	26% 17% 38% 16% 3	330
January	1st to 10th	Night	18% 14% 36% 26% 6% 1	1000
	11th to 20th	Night	20% 13% 37% 24% 5% 1	1000
	21st to end	Night	21% 12% 37% 25% 5%	1100
February	1st to 10th	Night	21% 14% 37% 24% 5%	1000
	11th to 20th	Night	19% 14% 38% 24% 5%	833
	21st to end	Night	25% 13% 38% 20% 4	660
March	1st to 10th	Night	21% 12% 37% 23% 6%	800
	11th to 20th	Night	16% 13% 36% 28% 7%	696
	21st to end	Night	24% 10% 34% 25% 6% 1	660
April	1st to 10th	Night	22% 12% 37% 25% 4	600
	11th to 20th	Night	21% 15% 29% 28% 7%	593
	21st to end	Night	21% 9% 34% 28% 8% 1	600
May	1st to 10th	Night	18% 8% 34% 32% 9% 1	600
	11th to 20th	Night	19% 6% 31% 32% 12%	591
	21st to end	Night	13% 5% 31% 34% 16% 1	650
June	1st to 10th	Night	9% 6% 26% 43% 15% 1	600
	11th to 20th	Night	11% 5% 31% 40% 13%	600
	21st to end	Night	10% 5% 28% 41% 16% 1	600
July	1st to 10th	Night	8% 3 15% 42% 29% 3	585
	11th to 20th	Night	9% 3 20% 43% 24% 3	582
	21st to end	Night	9% 2 17% 46% 24% 1	657
August	1st to 10th	Night	5% 2 16% 46% 28% 3	597
	11th to 20th	Night	10% 3 14% 38% 30% 6%	594
	21st to end	Night	9% 2 17% 42% 27% 2	660
September	1st to 10th	Night	10% 3 23% 34% 26% 4	600
	11th to 20th	Night	10% 3 21% 36% 26% 3	650
	21st to end	Night	12% 8% 25% 31% 22% 2	800
October	1st to 10th	Night	14% 6% 30% 32% 17% 1	773
	11th to 20th	Night	20% 11% 32% 27% 10%	760
	21st to end	Night	22% 11% 33% 25% 8% 1	836
November	1st to 10th	Night	16% 10% 41% 23% 10% 1	780
	11th to 20th	Night	20% 14% 36% 25% 6%	800
	21st to end	Night	23% 12% 34% 23% 7%	975
December	1st to 10th	Night	21% 12% 38% 23% 6% 1	1000
	11th to 20th	Night	24% 11% 33% 26% 5% 1	1000
	21st to end	Night	28% 12% 34% 23% 3	1100

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