Hawk Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hawk Observatory clear sky chart from 2005-11-06 to 2025-09-19.

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	12% 7% 3 7% 5% 4 4 4 6% 7% 42%	126274
	Night	10% 7% 3 7% 4 4 4 3 5% 7% 45%	123028
Transparency	Day	40% 6% 13% 25% 14% 2	129852
	Night	38% 5% 13% 26% 16% 2	127518
Seeing	Day	15% 10% 31% 29% 13% 2	17185
	Night	13% 8% 34% 34% 10% 1	26984

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	10% 13% 4 16% 9% 8% 7% 4 5% 5% 19%	3518
	11th to 20th	Day	5% 11% 5% 10% 7% 6% 8% 4 8% 9% 26%	3814
	21st to end	Day	5% 10% 5% 12% 7% 6% 6% 4 5% 5% 35%	4488
February	1st to 10th	Day	9% 12% 4 11% 8% 7% 7% 4 6% 6% 27%	1800
	11th to 20th	Day	9% 10% 4 10% 7% 6% 6% 4 5% 6% 35%	1779
	21st to end	Day	11% 10% 3 9% 5% 4 5% 4 5% 7% 37%	1650
March	1st to 10th	Day	11% 7% 3 8% 4 3 3 3 4 6% 48%	4754
	11th to 20th	Day	8% 7% 2 6% 4 3 3 3 5% 8% 51%	4980
	21st to end	Day	22% 12% 4 9% 5% 4 4 4 5% 6% 25%	5462
April	1st to 10th	Day	16% 8% 2 7% 5% 4 4 3 5% 6% 38%	2263
	11th to 20th	Day	18% 8% 3 6% 4 3 5% 4 5% 6% 37%	2572
	21st to end	Day	21% 8% 2 6% 3 4 3 3 5% 6% 38%	2600
May	1st to 10th	Day	12% 4 2 4 4 4 4 4 5% 7% 49%	5862
	11th to 20th	Day	17% 6% 2 5% 3 3 3 3 4 5% 48%	5862
	21st to end	Day	19% 8% 2 7% 4 4 4 4 5% 6% 36%	6886
June	1st to 10th	Day	12% 5% 2 5% 4 3 4 3 5% 8% 48%	2904
	11th to 20th	Day	14% 6% 2 6% 4 4 4 4 5% 8% 44%	3000
	21st to end	Day	9% 5% 2 4 4 4 4 4 7% 8% 49%	3000
July	1st to 10th	Day	8% 4 2 6% 5% 5% 5% 5% 7% 10% 44%	6759
	11th to 20th	Day	9% 5% 2 5% 3 3 4 3 5% 7% 54%	6257
	21st to end	Day	6% 4 2 6% 4 5% 5% 4 8% 10% 46%	6422
August	1st to 10th	Day	8% 5% 2 6% 4 5% 5% 4 6% 9% 45%	4234
	11th to 20th	Day	16% 7% 2 6% 4 4 5% 4 6% 7% 37%	4171
	21st to end	Day	9% 4 2 6% 4 4 4 3 5% 7% 52%	4675
September	1st to 10th	Day	13% 5% 2 4 3 3 3 3 4 6% 53%	2325
	11th to 20th	Day	10% 4 2 4 4 3 3 3 5% 7% 55%	2178
	21st to end	Day	10% 4 2 5% 4 3 4 3 6% 6% 54%	2090
October	1st to 10th	Day	16% 6% 1 5% 3 3 2 3 5% 6% 49%	1962
	11th to 20th	Day	13% 7% 2 4 3 2 3 3 4 5% 53%	1900
	21st to end	Day	16% 7% 3 7% 3 3 2 2 5% 5% 46%	2007
November	1st to 10th	Day	11% 7% 2 6% 4 3 4 4 6% 8% 45%	1763
	11th to 20th	Day	9% 8% 3 11% 5% 5% 4 4 4 6% 41%	1665
	21st to end	Day	11% 8% 3 8% 4 4 5% 4 5% 7% 40%	1600
December	1st to 10th	Day	4 8% 3 10% 7% 5% 5% 5% 7% 7% 39%	2610
	11th to 20th	Day	8% 14% 5% 11% 6% 6% 6% 4 6% 6% 28%	2964
	21st to end	Day	17% 8% 5% 16% 5% 4 4 4 6% 7% 25%	3498
January	1st to 10th	Night	8% 11% 4 13% 10% 7% 6% 4 5% 6% 25%	6442
	11th to 20th	Night	3 8% 4 10% 6% 5% 7% 4 8% 8% 35%	6149
	21st to end	Night	4 9% 5% 10% 4 5% 5% 4 5% 7% 41%	6490
February	1st to 10th	Night	9% 11% 3 10% 6% 5% 3 4 6% 6% 37%	2600
	11th to 20th	Night	8% 10% 4 9% 5% 5% 4 3 5% 7% 41%	2525
	21st to end	Night	8% 8% 3 7% 6% 4 4 4 6% 6% 44%	1980
March	1st to 10th	Night	11% 7% 2 5% 3 3 3 3 4 6% 53%	5107
	11th to 20th	Night	10% 6% 2 5% 3 3 4 3 6% 9% 49%	4980
	21st to end	Night	19% 11% 3 7% 5% 4 4 3 5% 6% 34%	5467
April	1st to 10th	Night	14% 8% 2 6% 4 5% 4 4 5% 7% 40%	2133
	11th to 20th	Night	17% 7% 2 6% 4 3 4 2 4 6% 45%	1779
	21st to end	Night	17% 7% 2 7% 4 3 4 3 6% 6% 40%	1800
May	1st to 10th	Night	13% 4 2 4 3 2 3 3 4 7% 55%	4053
	11th to 20th	Night	12% 6% 2 4 3 3 4 3 4 6% 51%	4053
	21st to end	Night	19% 6% 2 6% 4 4 4 3 5% 7% 41%	3989
June	1st to 10th	Night	8% 5% 2 5% 2 4 4 3 5% 8% 55%	1490
	11th to 20th	Night	7% 4 2 5% 4 4 4 4 6% 9% 52%	1400
	21st to end	Night	8% 4 1 4 3 2 4 4 6% 8% 56%	1400
July	1st to 10th	Night	8% 4 2 5% 3 3 4 4 6% 9% 51%	3214
	11th to 20th	Night	9% 3 2 4 3 3 4 3 4 7% 58%	3719
	21st to end	Night	7% 3 1 4 3 3 4 4 6% 10% 54%	4449
August	1st to 10th	Night	6% 4 2 6% 4 4 6% 5% 6% 8% 49%	2926
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 5% 8% 49%	2888
	21st to end	Night	8% 3 1 4 3 4 4 3 6% 8% 56%	3234
September	1st to 10th	Night	8% 3 2 4 3 2 3 3 6% 7% 59%	2070
	11th to 20th	Night	9% 4 2 4 3 3 2 3 6% 7% 57%	2178
	21st to end	Night	9% 5% 1 3 2 3 3 4 4 7% 59%	2090
October	1st to 10th	Night	15% 5% 1 4 3 3 3 2 4 6% 54%	2199
	11th to 20th	Night	12% 5% 3 5% 3 3 4 3 4 5% 54%	2280
	21st to end	Night	14% 7% 2 5% 3 3 3 3 4 6% 50%	2589
November	1st to 10th	Night	10% 5% 2 5% 4 3 5% 4 4 7% 52%	2535
	11th to 20th	Night	9% 6% 3 8% 4 4 4 3 6% 8% 46%	2734
	21st to end	Night	8% 8% 2 7% 4 4 4 3 6% 7% 47%	2800
December	1st to 10th	Night	5% 7% 4 10% 5% 5% 4 3 5% 7% 44%	4580
	11th to 20th	Night	10% 9% 4 8% 7% 6% 5% 5% 5% 7% 35%	5226
	21st to end	Night	15% 13% 4 13% 5% 4 4 4 5% 6% 27%	7480

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	65% 5% 12% 13% 4	3519
	11th to 20th	Day	52% 4 11% 18% 14%	3814
	21st to end	Day	50% 6% 14% 19% 11% 1	4488
February	1st to 10th	Day	56% 6% 14% 15% 9% 1	1800
	11th to 20th	Day	49% 6% 13% 19% 11% 1	1788
	21st to end	Day	45% 8% 13% 21% 12% 1	1650
March	1st to 10th	Day	39% 4 11% 34% 10% 2	4754
	11th to 20th	Day	32% 4 10% 33% 18% 2	4980
	21st to end	Day	60% 7% 12% 17% 4 1	5464
April	1st to 10th	Day	46% 5% 12% 23% 12% 1	2263
	11th to 20th	Day	47% 6% 9% 23% 12% 2	2572
	21st to end	Day	46% 6% 12% 24% 12% 1	2600
May	1st to 10th	Day	32% 6% 9% 27% 26%	5900
	11th to 20th	Day	37% 5% 11% 23% 15% 9%	5866
	21st to end	Day	47% 6% 9% 24% 14% 1	6900
June	1st to 10th	Day	34% 7% 15% 29% 13% 2	2904
	11th to 20th	Day	38% 7% 14% 25% 14% 3	3000
	21st to end	Day	31% 8% 14% 29% 16% 3	3000
July	1st to 10th	Day	33% 7% 18% 29% 12% 1	6685
	11th to 20th	Day	30% 5% 13% 32% 18% 3	6182
	21st to end	Day	30% 8% 18% 26% 16% 1	6240
August	1st to 10th	Day	34% 7% 15% 29% 13% 2	4220
	11th to 20th	Day	44% 7% 14% 25% 9% 1	4210
	21st to end	Day	31% 7% 16% 28% 16% 3	4674
September	1st to 10th	Day	33% 5% 11% 31% 18% 2	2325
	11th to 20th	Day	30% 6% 16% 33% 15% 1	2178
	21st to end	Day	30% 6% 10% 31% 21% 2	2090
October	1st to 10th	Day	25% 3 8% 27% 33% 4	3261
	11th to 20th	Day	29% 4 15% 27% 21% 4	3140
	21st to end	Day	39% 4 13% 24% 18% 2	3288
November	1st to 10th	Day	36% 5% 17% 26% 14% 3	1763
	11th to 20th	Day	43% 5% 14% 24% 13% 1	1665
	21st to end	Day	42% 6% 15% 23% 12% 1	1600
December	1st to 10th	Day	42% 5% 17% 27% 9% 1	2610
	11th to 20th	Day	54% 5% 17% 18% 6%	2961
	21st to end	Day	57% 4 14% 18% 6%	3498
January	1st to 10th	Night	58% 6% 11% 17% 8%	6442
	11th to 20th	Night	44% 5% 15% 18% 16% 2	6149
	21st to end	Night	42% 7% 13% 25% 13%	6490
February	1st to 10th	Night	47% 5% 12% 23% 12% 1	2600
	11th to 20th	Night	44% 5% 12% 23% 13% 3	2526
	21st to end	Night	39% 5% 13% 25% 14% 3	1980
March	1st to 10th	Night	33% 4 10% 33% 19% 1	5107
	11th to 20th	Night	31% 5% 10% 31% 21% 2	4980
	21st to end	Night	52% 6% 13% 22% 6% 1	5467
April	1st to 10th	Night	42% 7% 14% 23% 14% 1	2133
	11th to 20th	Night	42% 4 10% 23% 19% 2	1779
	21st to end	Night	43% 6% 11% 24% 14% 2	1800
May	1st to 10th	Night	30% 5% 11% 28% 24% 2	4080
	11th to 20th	Night	34% 5% 10% 21% 20% 9%	4054
	21st to end	Night	42% 6% 9% 28% 14% 1	3997
June	1st to 10th	Night	27% 8% 14% 29% 18% 3	1490
	11th to 20th	Night	28% 7% 15% 26% 19% 4	1400
	21st to end	Night	25% 6% 17% 29% 21% 2	1400
July	1st to 10th	Night	30% 5% 18% 31% 14% 2	3181
	11th to 20th	Night	28% 5% 12% 37% 15% 3	3674
	21st to end	Night	25% 7% 20% 29% 16% 2	4320
August	1st to 10th	Night	31% 8% 14% 29% 16% 2	2916
	11th to 20th	Night	33% 7% 16% 30% 13% 1	2915
	21st to end	Night	26% 7% 16% 25% 22% 4	3234
September	1st to 10th	Night	25% 7% 13% 30% 22% 3	2070
	11th to 20th	Night	26% 4 16% 34% 18% 2	2178
	21st to end	Night	25% 5% 10% 33% 24% 3	2090
October	1st to 10th	Night	20% 3 6% 24% 43% 4	3667
	11th to 20th	Night	26% 3 13% 29% 26% 3	3779
	21st to end	Night	38% 4 12% 30% 16% 1	4263
November	1st to 10th	Night	32% 5% 15% 24% 21% 4	2535
	11th to 20th	Night	36% 5% 15% 26% 16% 2	2734
	21st to end	Night	36% 5% 15% 28% 15% 1	2800
December	1st to 10th	Night	39% 4 16% 31% 9%	4580
	11th to 20th	Night	47% 6% 18% 22% 7%	5228
	21st to end	Night	58% 4 11% 20% 6%	7480

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	14% 10% 36% 25% 12% 3	300
	11th to 20th	Day	17% 12% 35% 29% 7% 1	300
	21st to end	Day	15% 11% 39% 25% 9% 1	330
February	1st to 10th	Day	12% 19% 39% 27% 3	300
	11th to 20th	Day	13% 15% 41% 24% 6% 1	300
	21st to end	Day	19% 13% 42% 20% 5%	249
March	1st to 10th	Day	19% 15% 40% 21% 4 1	300
	11th to 20th	Day	20% 11% 40% 18% 11% 1	300
	21st to end	Day	28% 13% 34% 18% 5% 1	330
April	1st to 10th	Day	25% 17% 36% 18% 4	363
	11th to 20th	Day	25% 16% 31% 22% 5% 1	690
	21st to end	Day	27% 14% 27% 20% 10% 1	700
May	1st to 10th	Day	17% 13% 31% 26% 12% 2	703
	11th to 20th	Day	21% 11% 28% 25% 12% 2	725
	21st to end	Day	21% 7% 29% 30% 11% 2	789
June	1st to 10th	Day	10% 7% 27% 34% 19% 4	730
	11th to 20th	Day	14% 7% 36% 26% 14% 3	730
	21st to end	Day	11% 7% 34% 32% 14% 2	730
July	1st to 10th	Day	7% 4 22% 40% 23% 5%	721
	11th to 20th	Day	7% 6% 28% 37% 19% 3	718
	21st to end	Day	6% 3 25% 42% 21% 4	794
August	1st to 10th	Day	9% 3 27% 38% 20% 4	726
	11th to 20th	Day	11% 4 26% 33% 21% 5%	715
	21st to end	Day	8% 4 26% 37% 21% 4	803
September	1st to 10th	Day	16% 8% 27% 29% 17% 3	455
	11th to 20th	Day	9% 6% 37% 31% 15% 2	324
	21st to end	Day	13% 16% 31% 25% 12% 3	300
October	1st to 10th	Day	19% 9% 29% 27% 10% 5%	300
	11th to 20th	Day	15% 18% 32% 26% 8% 1	300
	21st to end	Day	22% 15% 36% 21% 7%	330
November	1st to 10th	Day	21% 11% 35% 22% 9% 3	300
	11th to 20th	Day	14% 19% 41% 21% 5%	300
	21st to end	Day	19% 16% 33% 22% 9%	300
December	1st to 10th	Day	11% 11% 44% 24% 9% 1	300
	11th to 20th	Day	19% 12% 40% 25% 4	300
	21st to end	Day	22% 14% 34% 25% 5% 1	330
January	1st to 10th	Night	12% 9% 37% 31% 10% 1	1000
	11th to 20th	Night	13% 11% 36% 33% 7% 1	1000
	21st to end	Night	14% 10% 39% 30% 7%	1100
February	1st to 10th	Night	14% 12% 39% 29% 5% 1	1000
	11th to 20th	Night	13% 10% 39% 30% 7% 1	971
	21st to end	Night	12% 7% 39% 32% 8% 1	660
March	1st to 10th	Night	14% 8% 40% 32% 6% 1	689
	11th to 20th	Night	15% 12% 38% 32% 4	600
	21st to end	Night	21% 10% 35% 27% 8%	660
April	1st to 10th	Night	18% 14% 39% 27% 3	600
	11th to 20th	Night	21% 14% 32% 26% 5% 1	593
	21st to end	Night	19% 14% 32% 26% 8% 1	600
May	1st to 10th	Night	17% 7% 35% 30% 11%	600
	11th to 20th	Night	17% 10% 30% 31% 10% 1	591
	21st to end	Night	18% 7% 32% 30% 13% 1	650
June	1st to 10th	Night	10% 7% 25% 43% 15% 1	600
	11th to 20th	Night	8% 5% 35% 41% 11% 1	600
	21st to end	Night	10% 4 28% 45% 14%	600
July	1st to 10th	Night	6% 2 24% 42% 25% 1	585
	11th to 20th	Night	5% 2 26% 50% 16%	582
	21st to end	Night	6% 2 23% 53% 16% 1	657
August	1st to 10th	Night	6% 4 24% 46% 19% 1	597
	11th to 20th	Night	9% 3 23% 39% 24% 1	594
	21st to end	Night	6% 3 28% 44% 19% 1	660
September	1st to 10th	Night	9% 6% 25% 44% 15% 2	600
	11th to 20th	Night	9% 5% 33% 37% 13% 3	594
	21st to end	Night	13% 6% 32% 35% 12% 1	570
October	1st to 10th	Night	16% 9% 33% 29% 12% 1	679
	11th to 20th	Night	16% 11% 37% 29% 7%	760
	21st to end	Night	17% 12% 35% 27% 9%	917
November	1st to 10th	Night	12% 10% 36% 33% 9% 1	975
	11th to 20th	Night	13% 11% 39% 29% 7%	1000
	21st to end	Night	13% 9% 38% 33% 7%	1000
December	1st to 10th	Night	13% 10% 39% 32% 6%	1000
	11th to 20th	Night	17% 8% 36% 31% 8%	1000
	21st to end	Night	21% 11% 33% 29% 6% 1	1100

Page generated at 2025-09-16 00:49:12. Version ac07

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