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 2024-01-12.

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	12% 7% 3 6% 5% 3 5% 4 5% 7% 42%	74731
	Night	11% 7% 3 6% 5% 3 4 4 5% 7% 45%	74989
Transparency	Day	41% 6% 14% 25% 13% 2	74438
	Night	38% 6% 14% 26% 15% 2	74802
Seeing	Day	15% 10% 31% 29% 13% 2	14748
	Night	14% 8% 34% 34% 10% 1	24781

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	7% 9% 5% 9% 9% 5% 10% 7% 5% 6% 29%	1465
	11th to 20th	Day	7% 13% 6% 10% 7% 4 7% 5% 6% 7% 28%	1522
	21st to end	Day	10% 13% 6% 12% 8% 5% 7% 6% 5% 6% 24%	1782
February	1st to 10th	Day	10% 9% 5% 9% 9% 5% 7% 6% 6% 7% 28%	1620
	11th to 20th	Day	9% 10% 4 8% 8% 5% 6% 5% 5% 6% 35%	1596
	21st to end	Day	12% 10% 4 9% 5% 3 6% 5% 5% 8% 34%	1480
March	1st to 10th	Day	15% 9% 5% 8% 5% 2 3 3 4 7% 38%	1898
	11th to 20th	Day	13% 9% 3 8% 6% 3 5% 5% 5% 8% 36%	1980
	21st to end	Day	19% 12% 4 7% 6% 2 5% 5% 6% 6% 29%	2178
April	1st to 10th	Day	17% 8% 2 7% 6% 3 5% 4 5% 7% 37%	2035
	11th to 20th	Day	20% 8% 3 5% 5% 2 5% 4 4 6% 37%	2312
	21st to end	Day	21% 7% 2 5% 4 3 3 3 5% 6% 39%	2340
May	1st to 10th	Day	18% 7% 3 5% 6% 4 5% 4 5% 7% 37%	2340
	11th to 20th	Day	17% 7% 3 5% 5% 3 6% 5% 5% 7% 37%	2302
	21st to end	Day	18% 6% 2 5% 5% 3 5% 4 6% 8% 37%	2704
June	1st to 10th	Day	12% 5% 2 4 5% 2 4 4 5% 9% 48%	2613
	11th to 20th	Day	13% 5% 3 5% 4 3 5% 5% 5% 8% 44%	2700
	21st to end	Day	8% 5% 2 4 4 3 4 5% 7% 8% 50%	2700
July	1st to 10th	Day	6% 3 2 4 4 2 5% 5% 6% 9% 53%	2687
	11th to 20th	Day	6% 3 1 4 3 2 3 4 5% 8% 60%	2489
	21st to end	Day	6% 3 2 3 4 3 5% 4 6% 10% 55%	2546
August	1st to 10th	Day	10% 5% 2 5% 5% 3 5% 6% 7% 9% 43%	2328
	11th to 20th	Day	9% 5% 3 5% 4 3 5% 5% 7% 8% 48%	2301
	21st to end	Day	8% 3 2 4 4 3 4 4 5% 7% 57%	2574
September	1st to 10th	Day	14% 5% 2 4 3 3 4 3 4 6% 52%	2094
	11th to 20th	Day	11% 4 2 4 5% 2 3 3 4 6% 55%	1980
	21st to end	Day	11% 4 2 4 4 3 3 4 6% 6% 52%	1980
October	1st to 10th	Day	17% 6% 2 4 4 3 3 3 5% 5% 48%	1859
	11th to 20th	Day	13% 7% 2 4 3 2 3 4 4 5% 53%	1800
	21st to end	Day	16% 7% 3 6% 4 2 2 3 5% 5% 47%	1902
November	1st to 10th	Day	10% 7% 2 5% 5% 2 3 4 6% 8% 47%	1673
	11th to 20th	Day	9% 7% 3 10% 7% 4 5% 4 4 6% 41%	1582
	21st to end	Day	12% 8% 3 6% 4 3 5% 5% 5% 7% 41%	1520
December	1st to 10th	Day	8% 9% 3 9% 8% 3 5% 5% 7% 7% 36%	1520
	11th to 20th	Day	7% 13% 5% 9% 8% 5% 6% 6% 5% 7% 31%	1887
	21st to end	Day	17% 6% 6% 14% 6% 3 4 5% 6% 7% 26%	2442
January	1st to 10th	Night	8% 7% 3 8% 8% 4 7% 5% 6% 8% 35%	2695
	11th to 20th	Night	7% 10% 6% 10% 8% 4 5% 4 5% 8% 33%	2474
	21st to end	Night	9% 12% 4 9% 7% 4 6% 5% 5% 8% 32%	2574
February	1st to 10th	Night	10% 10% 4 9% 7% 4 5% 4 5% 6% 38%	2340
	11th to 20th	Night	9% 9% 3 8% 6% 4 5% 4 5% 7% 41%	2266
	21st to end	Night	9% 9% 3 7% 7% 3 5% 5% 5% 6% 42%	1776
March	1st to 10th	Night	11% 7% 4 7% 5% 3 4 4 5% 8% 43%	2061
	11th to 20th	Night	12% 9% 4 6% 5% 4 4 4 5% 7% 41%	1980
	21st to end	Night	15% 11% 3 6% 5% 3 5% 3 5% 6% 36%	2178
April	1st to 10th	Night	14% 8% 2 5% 5% 3 5% 5% 5% 7% 40%	1921
	11th to 20th	Night	18% 8% 3 5% 4 2 4 3 4 7% 43%	1599
	21st to end	Night	17% 6% 3 5% 5% 3 4 4 6% 7% 41%	1620
May	1st to 10th	Night	14% 5% 2 4 5% 2 3 4 6% 8% 44%	1620
	11th to 20th	Night	15% 7% 2 3 4 3 4 3 4 8% 46%	1593
	21st to end	Night	15% 6% 2 5% 5% 3 5% 5% 6% 9% 40%	1570
June	1st to 10th	Night	8% 5% 1 4 3 2 5% 4 5% 8% 55%	1342
	11th to 20th	Night	7% 3 2 5% 4 3 4 5% 6% 9% 54%	1260
	21st to end	Night	7% 3 1 3 4 2 4 5% 5% 7% 59%	1260
July	1st to 10th	Night	4 3 2 4 3 2 4 4 6% 8% 60%	1268
	11th to 20th	Night	4 1 1 3 3 2 4 3 5% 7% 67%	1470
	21st to end	Night	4 2 2 3 3 2 5% 5% 6% 10% 59%	1772
August	1st to 10th	Night	6% 3 2 5% 4 3 6% 7% 6% 9% 50%	1611
	11th to 20th	Night	8% 4 1 3 3 2 4 4 6% 7% 59%	1600
	21st to end	Night	5% 2 1 3 4 2 3 4 5% 8% 63%	1782
September	1st to 10th	Night	9% 3 2 4 4 2 3 4 6% 7% 57%	1862
	11th to 20th	Night	9% 4 2 3 4 2 2 4 5% 7% 58%	1980
	21st to end	Night	9% 4 2 3 3 2 3 4 4 7% 58%	1980
October	1st to 10th	Night	16% 5% 2 3 4 1 4 3 5% 6% 52%	2083
	11th to 20th	Night	12% 5% 3 4 3 3 4 3 4 5% 53%	2160
	21st to end	Night	14% 7% 2 4 4 2 3 3 4 6% 51%	2452
November	1st to 10th	Night	9% 5% 2 4 4 2 5% 5% 4 7% 53%	2405
	11th to 20th	Night	9% 6% 3 7% 5% 3 4 4 5% 8% 45%	2597
	21st to end	Night	9% 8% 3 5% 5% 3 3 4 5% 7% 48%	2660
December	1st to 10th	Night	8% 9% 4 8% 6% 4 5% 4 6% 8% 40%	2660
	11th to 20th	Night	10% 8% 3 7% 6% 3 5% 5% 5% 8% 40%	3293
	21st to end	Night	18% 9% 5% 13% 6% 3 4 4 4 6% 28%	5225

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	54% 7% 15% 16% 8% 1	1466
	11th to 20th	Day	54% 6% 14% 18% 8%	1522
	21st to end	Day	61% 7% 13% 14% 5%	1782
February	1st to 10th	Day	55% 6% 14% 15% 9% 1	1620
	11th to 20th	Day	50% 6% 14% 19% 10% 1	1605
	21st to end	Day	48% 8% 12% 20% 11% 1	1480
March	1st to 10th	Day	48% 5% 14% 24% 8% 1	1898
	11th to 20th	Day	47% 6% 12% 25% 9%	1980
	21st to end	Day	55% 8% 14% 17% 5% 1	2178
April	1st to 10th	Day	47% 5% 12% 23% 11% 1	2035
	11th to 20th	Day	49% 6% 9% 22% 12% 2	2312
	21st to end	Day	46% 5% 12% 25% 11% 1	2340
May	1st to 10th	Day	46% 7% 12% 22% 13%	2340
	11th to 20th	Day	44% 7% 14% 23% 11% 1	2306
	21st to end	Day	45% 7% 12% 22% 13% 1	2704
June	1st to 10th	Day	33% 7% 16% 29% 13% 2	2613
	11th to 20th	Day	37% 7% 13% 25% 15% 3	2700
	21st to end	Day	30% 8% 14% 30% 15% 3	2700
July	1st to 10th	Day	26% 7% 18% 32% 15% 1	2613
	11th to 20th	Day	22% 6% 13% 30% 22% 6%	2414
	21st to end	Day	24% 7% 15% 32% 18% 3	2405
August	1st to 10th	Day	35% 9% 16% 27% 11% 2	2314
	11th to 20th	Day	32% 8% 13% 33% 12% 1	2301
	21st to end	Day	27% 6% 12% 32% 19% 4	2574
September	1st to 10th	Day	35% 5% 11% 29% 18% 2	2094
	11th to 20th	Day	30% 6% 15% 33% 15% 1	1980
	21st to end	Day	31% 6% 10% 32% 20% 1	1980
October	1st to 10th	Day	39% 4 12% 27% 17% 1	1859
	11th to 20th	Day	34% 4 12% 29% 18% 3	1800
	21st to end	Day	41% 4 12% 25% 16% 2	1902
November	1st to 10th	Day	34% 5% 17% 26% 14% 3	1673
	11th to 20th	Day	43% 6% 14% 23% 13% 1	1582
	21st to end	Day	41% 7% 15% 24% 13% 1	1520
December	1st to 10th	Day	45% 5% 17% 22% 10% 1	1520
	11th to 20th	Day	51% 6% 18% 20% 5%	1884
	21st to end	Day	57% 5% 13% 17% 7% 1	2442
January	1st to 10th	Night	46% 6% 14% 22% 12% 1	2695
	11th to 20th	Night	50% 6% 16% 21% 7% 1	2474
	21st to end	Night	50% 6% 14% 19% 9% 1	2574
February	1st to 10th	Night	46% 5% 12% 24% 11% 1	2340
	11th to 20th	Night	43% 5% 12% 23% 13% 3	2267
	21st to end	Night	43% 5% 12% 24% 14% 3	1776
March	1st to 10th	Night	40% 6% 16% 26% 9% 2	2061
	11th to 20th	Night	44% 5% 10% 26% 13% 1	1980
	21st to end	Night	49% 6% 13% 22% 8% 2	2178
April	1st to 10th	Night	41% 7% 14% 24% 14% 1	1921
	11th to 20th	Night	44% 4 10% 23% 17% 2	1599
	21st to end	Night	42% 6% 11% 24% 13% 2	1620
May	1st to 10th	Night	36% 7% 15% 25% 15% 1	1620
	11th to 20th	Night	38% 6% 13% 25% 17% 2	1594
	21st to end	Night	40% 8% 13% 22% 14% 2	1571
June	1st to 10th	Night	26% 8% 15% 29% 19% 2	1342
	11th to 20th	Night	27% 7% 15% 27% 20% 5%	1260
	21st to end	Night	22% 6% 17% 30% 22% 2	1260
July	1st to 10th	Night	22% 6% 15% 35% 20% 2	1233
	11th to 20th	Night	18% 6% 15% 31% 23% 7%	1422
	21st to end	Night	20% 7% 15% 31% 22% 5%	1673
August	1st to 10th	Night	30% 9% 15% 28% 16% 2	1601
	11th to 20th	Night	24% 8% 13% 35% 18% 3	1600
	21st to end	Night	20% 6% 14% 28% 25% 6%	1782
September	1st to 10th	Night	26% 7% 13% 28% 22% 4	1862
	11th to 20th	Night	27% 4 14% 34% 18% 2	1980
	21st to end	Night	26% 5% 11% 34% 23% 2	1980
October	1st to 10th	Night	35% 4 11% 28% 21% 1	2083
	11th to 20th	Night	34% 4 11% 28% 21% 4	2160
	21st to end	Night	36% 4 13% 24% 20% 2	2452
November	1st to 10th	Night	31% 5% 15% 24% 21% 4	2405
	11th to 20th	Night	36% 5% 15% 26% 16% 2	2597
	21st to end	Night	35% 5% 15% 28% 16% 1	2660
December	1st to 10th	Night	42% 5% 18% 25% 9%	2660
	11th to 20th	Night	43% 6% 21% 24% 7%	3295
	21st to end	Night	58% 4 11% 19% 7% 1	5225

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% 11% 34% 26% 12% 2	270
	11th to 20th	Day	18% 9% 36% 29% 7% 1	245
	21st to end	Day	18% 11% 40% 25% 6% 1	264
February	1st to 10th	Day	12% 18% 39% 30% 2	240
	11th to 20th	Day	16% 15% 41% 23% 5% 1	240
	21st to end	Day	21% 14% 41% 18% 5% 1	198
March	1st to 10th	Day	20% 18% 36% 20% 5% 1	240
	11th to 20th	Day	22% 8% 40% 17% 11% 1	240
	21st to end	Day	28% 13% 33% 19% 6% 2	264
April	1st to 10th	Day	25% 17% 36% 18% 4	295
	11th to 20th	Day	26% 14% 31% 23% 5% 1	590
	21st to end	Day	27% 13% 27% 22% 10% 2	600
May	1st to 10th	Day	19% 13% 31% 27% 9% 1	603
	11th to 20th	Day	21% 12% 29% 25% 11% 3	625
	21st to end	Day	21% 6% 28% 31% 11% 2	679
June	1st to 10th	Day	8% 7% 25% 35% 21% 4	630
	11th to 20th	Day	13% 8% 36% 25% 15% 3	630
	21st to end	Day	9% 7% 32% 35% 16% 2	630
July	1st to 10th	Day	7% 4 20% 42% 24% 5%	621
	11th to 20th	Day	6% 6% 29% 36% 19% 3	618
	21st to end	Day	6% 4 25% 41% 22% 3	684
August	1st to 10th	Day	9% 3 25% 38% 22% 4	626
	11th to 20th	Day	10% 5% 25% 35% 21% 5%	615
	21st to end	Day	8% 5% 28% 35% 22% 4	693
September	1st to 10th	Day	18% 7% 27% 28% 16% 3	384
	11th to 20th	Day	9% 5% 37% 30% 15% 3	270
	21st to end	Day	14% 17% 32% 26% 10% 2	270
October	1st to 10th	Day	21% 9% 29% 27% 10% 5%	270
	11th to 20th	Day	17% 18% 32% 24% 8% 1	270
	21st to end	Day	23% 15% 35% 19% 7%	297
November	1st to 10th	Day	20% 10% 36% 21% 9% 3	270
	11th to 20th	Day	13% 19% 41% 22% 5%	270
	21st to end	Day	21% 16% 33% 21% 9%	270
December	1st to 10th	Day	11% 11% 45% 24% 8% 1	270
	11th to 20th	Day	18% 11% 41% 26% 5%	270
	21st to end	Day	23% 15% 35% 25% 3	297
January	1st to 10th	Night	13% 9% 37% 31% 10% 1	950
	11th to 20th	Night	13% 10% 35% 34% 7% 1	910
	21st to end	Night	15% 10% 38% 31% 6%	990
February	1st to 10th	Night	15% 10% 39% 30% 5% 1	900
	11th to 20th	Night	13% 10% 39% 29% 8% 1	872
	21st to end	Night	14% 7% 37% 31% 9% 1	592
March	1st to 10th	Night	14% 8% 40% 32% 6% 1	621
	11th to 20th	Night	16% 9% 38% 33% 4	540
	21st to end	Night	20% 9% 35% 27% 8% 1	594
April	1st to 10th	Night	18% 12% 40% 27% 3	540
	11th to 20th	Night	22% 13% 32% 26% 6% 1	533
	21st to end	Night	19% 13% 34% 25% 9% 1	540
May	1st to 10th	Night	17% 7% 36% 30% 10%	540
	11th to 20th	Night	17% 10% 31% 30% 11% 1	531
	21st to end	Night	18% 7% 32% 30% 13%	584
June	1st to 10th	Night	10% 6% 24% 43% 16% 1	540
	11th to 20th	Night	8% 4 35% 41% 12% 1	540
	21st to end	Night	8% 3 27% 46% 15%	540
July	1st to 10th	Night	6% 2 24% 42% 26% 1	525
	11th to 20th	Night	4 2 27% 50% 16%	522
	21st to end	Night	5% 3 23% 53% 16% 1	591
August	1st to 10th	Night	6% 3 24% 46% 20% 1	537
	11th to 20th	Night	9% 3 24% 38% 25% 1	534
	21st to end	Night	5% 2 28% 44% 19% 1	594
September	1st to 10th	Night	10% 5% 26% 43% 14% 2	540
	11th to 20th	Night	10% 5% 33% 36% 13% 3	540
	21st to end	Night	14% 6% 33% 35% 11% 1	540
October	1st to 10th	Night	17% 10% 32% 28% 12%	643
	11th to 20th	Night	16% 12% 36% 28% 8%	720
	21st to end	Night	18% 11% 34% 28% 9%	868
November	1st to 10th	Night	11% 10% 36% 33% 9% 1	925
	11th to 20th	Night	13% 11% 39% 30% 7%	950
	21st to end	Night	13% 9% 38% 33% 7%	950
December	1st to 10th	Night	13% 9% 38% 32% 7%	950
	11th to 20th	Night	17% 7% 36% 31% 8%	950
	21st to end	Night	21% 11% 34% 28% 6%	1045

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