Harken Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harken Observatory clear sky chart from 2005-11-06 to 2024-12-24.

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% 9% 3 8% 5% 4 5% 4 6% 7% 37%	101788
	Night	13% 10% 4 7% 5% 4 4 3 5% 6% 38%	98398
Transparency	Day	44% 6% 12% 24% 13% 1	105332
	Night	45% 5% 11% 23% 14% 2	102995
Seeing	Day	16% 12% 30% 26% 12% 4	16041
	Night	17% 11% 31% 28% 12% 1	25964

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% 15% 8% 13% 5% 4 5% 3 4 5% 28%	2527
	11th to 20th	Day	10% 14% 6% 16% 5% 4 4 8% 6% 7% 20%	2530
	21st to end	Day	17% 18% 10% 12% 5% 3 3 3 4 5% 20%	2797
February	1st to 10th	Day	10% 14% 6% 10% 5% 6% 5% 4 5% 6% 30%	1710
	11th to 20th	Day	13% 12% 3 8% 5% 5% 5% 3 5% 5% 35%	1843
	21st to end	Day	11% 15% 5% 11% 5% 5% 5% 4 4 6% 29%	1570
March	1st to 10th	Day	12% 9% 3 8% 5% 4 4 3 5% 6% 41%	3120
	11th to 20th	Day	10% 7% 3 8% 6% 4 5% 4 5% 6% 42%	3272
	21st to end	Day	21% 13% 4 10% 4 4 4 3 4 6% 28%	4165
April	1st to 10th	Day	18% 13% 4 8% 5% 4 4 4 5% 6% 29%	2280
	11th to 20th	Day	15% 11% 3 7% 5% 5% 4 4 5% 6% 34%	2254
	21st to end	Day	17% 11% 3 6% 5% 4 5% 4 6% 7% 33%	2403
May	1st to 10th	Day	15% 8% 2 8% 4 5% 4 4 6% 7% 37%	4100
	11th to 20th	Day	13% 7% 2 6% 4 5% 4 4 6% 7% 43%	4399
	21st to end	Day	13% 7% 2 7% 5% 4 5% 4 6% 9% 38%	4824
June	1st to 10th	Day	9% 5% 2 6% 4 5% 4 4 7% 8% 45%	2660
	11th to 20th	Day	11% 6% 2 5% 5% 4 4 3 8% 9% 43%	2660
	21st to end	Day	11% 7% 2 6% 5% 4 5% 5% 6% 10% 40%	2660
July	1st to 10th	Day	12% 8% 3 8% 5% 5% 6% 5% 7% 9% 34%	4440
	11th to 20th	Day	5% 3 2 5% 4 5% 6% 5% 7% 10% 49%	4440
	21st to end	Day	7% 7% 3 7% 5% 5% 5% 4 7% 9% 42%	4813
August	1st to 10th	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 40%	4405
	11th to 20th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 8% 42%	3797
	21st to end	Day	9% 7% 3 6% 4 4 4 4 6% 8% 44%	4180
September	1st to 10th	Day	12% 6% 3 7% 4 4 3 4 6% 8% 44%	2280
	11th to 20th	Day	12% 5% 2 5% 3 4 3 3 5% 8% 49%	2171
	21st to end	Day	12% 7% 3 6% 5% 4 4 3 6% 7% 43%	2090
October	1st to 10th	Day	13% 7% 3 6% 4 3 3 4 5% 7% 46%	2014
	11th to 20th	Day	18% 10% 3 7% 4 4 4 4 5% 7% 33%	1876
	21st to end	Day	17% 10% 3 7% 4 5% 4 2 5% 5% 37%	1881
November	1st to 10th	Day	11% 10% 3 6% 5% 4 5% 3 5% 5% 43%	1762
	11th to 20th	Day	11% 12% 5% 10% 5% 5% 5% 4 5% 7% 30%	1800
	21st to end	Day	18% 12% 3 7% 5% 3 3 2 4 6% 35%	1660
December	1st to 10th	Day	12% 12% 5% 10% 7% 6% 4 4 5% 7% 29%	1600
	11th to 20th	Day	12% 14% 5% 10% 5% 5% 5% 4 6% 7% 27%	1998
	21st to end	Day	17% 21% 9% 13% 5% 4 4 4 4 4 15%	2807
January	1st to 10th	Night	14% 14% 7% 10% 5% 4 4 3 5% 4 31%	4428
	11th to 20th	Night	12% 15% 7% 14% 6% 5% 5% 5% 6% 5% 19%	4440
	21st to end	Night	15% 18% 8% 11% 5% 4 5% 3 4 5% 21%	4852
February	1st to 10th	Night	11% 14% 5% 9% 6% 4 4 3 5% 6% 33%	2470
	11th to 20th	Night	12% 10% 3 8% 5% 4 5% 4 5% 6% 40%	2222
	21st to end	Night	17% 11% 4 7% 5% 4 4 3 5% 6% 34%	1884
March	1st to 10th	Night	17% 9% 3 5% 4 3 4 3 5% 5% 41%	3733
	11th to 20th	Night	9% 7% 2 5% 4 4 5% 4 6% 8% 45%	3715
	21st to end	Night	20% 12% 5% 9% 5% 5% 4 3 4 5% 29%	3466
April	1st to 10th	Night	17% 10% 2 7% 5% 5% 5% 4 5% 7% 35%	1900
	11th to 20th	Night	19% 10% 3 7% 5% 4 3 3 5% 5% 38%	1875
	21st to end	Night	17% 9% 3 6% 4 4 3 4 6% 7% 38%	1777
May	1st to 10th	Night	15% 8% 3 8% 4 4 4 3 6% 8% 37%	2793
	11th to 20th	Night	14% 7% 2 6% 4 5% 5% 4 7% 7% 40%	2506
	21st to end	Night	12% 10% 3 7% 4 3 4 3 5% 7% 41%	2743
June	1st to 10th	Night	9% 6% 2 5% 4 4 4 4 6% 8% 47%	1520
	11th to 20th	Night	11% 5% 2 5% 5% 3 5% 5% 6% 8% 45%	1520
	21st to end	Night	9% 7% 2 6% 4 5% 4 3 6% 8% 47%	1520
July	1st to 10th	Night	12% 7% 3 7% 5% 4 5% 4 5% 7% 41%	2530
	11th to 20th	Night	4 3 1 4 4 4 4 3 7% 9% 56%	2530
	21st to end	Night	5% 4 2 5% 4 5% 5% 4 7% 10% 47%	2750
August	1st to 10th	Night	10% 5% 2 5% 3 5% 5% 3 7% 8% 48%	2532
	11th to 20th	Night	10% 6% 2 6% 4 4 4 3 6% 8% 48%	3029
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 9% 50%	3476
September	1st to 10th	Night	8% 5% 3 5% 4 3 4 3 5% 7% 54%	1900
	11th to 20th	Night	11% 4 2 5% 3 3 4 3 4 7% 54%	1990
	21st to end	Night	12% 6% 2 6% 4 5% 4 3 5% 7% 47%	2090
October	1st to 10th	Night	12% 6% 2 6% 5% 4 3 3 5% 5% 48%	2162
	11th to 20th	Night	16% 8% 2 6% 3 4 4 3 4 7% 43%	2304
	21st to end	Night	19% 9% 3 7% 4 4 3 3 6% 7% 36%	2717
November	1st to 10th	Night	13% 7% 3 6% 4 4 4 3 5% 6% 45%	2536
	11th to 20th	Night	14% 10% 4 8% 6% 5% 5% 3 5% 7% 34%	2600
	21st to end	Night	16% 11% 3 7% 5% 5% 4 3 5% 6% 36%	2736
December	1st to 10th	Night	14% 12% 5% 8% 5% 5% 5% 4 5% 6% 32%	2800
	11th to 20th	Night	15% 14% 4 9% 7% 5% 6% 4 5% 5% 28%	3419
	21st to end	Night	20% 19% 5% 10% 6% 5% 4 3 5% 5% 20%	4933

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 12% 17% 6%	2528
	11th to 20th	Day	61% 6% 11% 17% 6%	2530
	21st to end	Day	67% 4 8% 17% 5%	2797
February	1st to 10th	Day	55% 4 11% 19% 10% 1	1710
	11th to 20th	Day	49% 5% 10% 24% 11% 2	1853
	21st to end	Day	55% 5% 10% 17% 10% 2	1570
March	1st to 10th	Day	44% 4 10% 26% 12% 3	3120
	11th to 20th	Day	41% 5% 11% 28% 13% 2	3272
	21st to end	Day	59% 4 11% 17% 6% 2	4165
April	1st to 10th	Day	55% 6% 11% 18% 10%	2280
	11th to 20th	Day	50% 5% 10% 20% 12% 3	2254
	21st to end	Day	49% 6% 13% 18% 12% 1	2403
May	1st to 10th	Day	45% 5% 11% 24% 15% 1	4138
	11th to 20th	Day	40% 6% 11% 29% 14% 1	4403
	21st to end	Day	40% 7% 12% 22% 16% 3	4837
June	1st to 10th	Day	35% 7% 13% 26% 17% 2	2660
	11th to 20th	Day	36% 6% 13% 25% 18% 1	2660
	21st to end	Day	39% 7% 14% 23% 15% 2	2660
July	1st to 10th	Day	43% 7% 13% 25% 9% 2	4371
	11th to 20th	Day	27% 8% 17% 30% 17% 1	4365
	21st to end	Day	36% 8% 16% 19% 19% 2	4662
August	1st to 10th	Day	37% 7% 15% 28% 11% 1	4390
	11th to 20th	Day	36% 8% 13% 31% 12% 1	3835
	21st to end	Day	36% 6% 13% 25% 19% 1	4179
September	1st to 10th	Day	37% 7% 11% 27% 17% 2	2280
	11th to 20th	Day	33% 5% 11% 32% 18% 1	2171
	21st to end	Day	39% 6% 11% 30% 14%	2090
October	1st to 10th	Day	24% 3 6% 40% 25% 1	3352
	11th to 20th	Day	36% 4 11% 27% 22% 1	3092
	21st to end	Day	41% 4 11% 28% 13% 2	3081
November	1st to 10th	Day	42% 4 13% 25% 14% 1	1762
	11th to 20th	Day	53% 5% 13% 19% 10% 1	1800
	21st to end	Day	51% 4 13% 24% 7%	1660
December	1st to 10th	Day	55% 4 14% 18% 7% 1	1600
	11th to 20th	Day	54% 6% 14% 17% 7% 2	1995
	21st to end	Day	72% 5% 7% 10% 5%	2807
January	1st to 10th	Night	57% 5% 9% 19% 10% 1	4428
	11th to 20th	Night	66% 4 10% 13% 7%	4440
	21st to end	Night	65% 5% 10% 14% 6%	4852
February	1st to 10th	Night	52% 4 10% 19% 12% 2	2470
	11th to 20th	Night	44% 6% 11% 22% 15% 1	2223
	21st to end	Night	50% 4 11% 20% 12% 3	1884
March	1st to 10th	Night	46% 4 12% 25% 9% 4	3733
	11th to 20th	Night	35% 5% 12% 27% 18% 3	3715
	21st to end	Night	59% 5% 8% 17% 10% 2	3466
April	1st to 10th	Night	48% 6% 9% 20% 16% 1	1900
	11th to 20th	Night	49% 4 6% 20% 18% 3	1875
	21st to end	Night	45% 5% 12% 21% 15% 2	1777
May	1st to 10th	Night	44% 6% 12% 19% 17% 2	2820
	11th to 20th	Night	41% 6% 12% 28% 12% 1	2507
	21st to end	Night	41% 6% 10% 18% 17% 8%	2751
June	1st to 10th	Night	34% 6% 13% 27% 18% 2	1520
	11th to 20th	Night	35% 7% 10% 24% 22% 2	1520
	21st to end	Night	36% 5% 15% 24% 18% 2	1520
July	1st to 10th	Night	42% 5% 13% 22% 12% 4	2490
	11th to 20th	Night	23% 6% 17% 35% 17% 2	2482
	21st to end	Night	29% 8% 15% 21% 23% 3	2662
August	1st to 10th	Night	32% 6% 15% 26% 19% 1	2523
	11th to 20th	Night	32% 6% 13% 32% 15% 1	3057
	21st to end	Night	30% 6% 13% 28% 21% 3	3476
September	1st to 10th	Night	30% 6% 12% 27% 24% 2	1900
	11th to 20th	Night	31% 5% 10% 34% 18% 2	1990
	21st to end	Night	37% 4 9% 32% 16% 1	2090
October	1st to 10th	Night	26% 4 6% 38% 24% 1	3604
	11th to 20th	Night	34% 4 12% 26% 21% 2	3827
	21st to end	Night	42% 5% 9% 26% 17% 1	4467
November	1st to 10th	Night	40% 4 10% 27% 17% 2	2536
	11th to 20th	Night	49% 5% 13% 21% 11% 2	2600
	21st to end	Night	49% 5% 14% 21% 10% 1	2736
December	1st to 10th	Night	53% 5% 12% 20% 9% 1	2800
	11th to 20th	Night	57% 5% 10% 17% 9% 1	3421
	21st to end	Night	67% 5% 9% 14% 5%	4933

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	16% 20% 33% 25% 5% 1	270
	11th to 20th	Day	20% 16% 37% 22% 3 1	270
	21st to end	Day	22% 15% 39% 21% 4	297
February	1st to 10th	Day	13% 23% 41% 16% 6% 1	270
	11th to 20th	Day	20% 24% 37% 16% 3	270
	21st to end	Day	18% 25% 41% 13% 2	225
March	1st to 10th	Day	14% 28% 41% 13% 3	270
	11th to 20th	Day	23% 21% 30% 18% 6% 1	287
	21st to end	Day	26% 14% 29% 22% 6% 1	506
April	1st to 10th	Day	26% 14% 35% 20% 5%	460
	11th to 20th	Day	20% 22% 26% 20% 9% 2	452
	21st to end	Day	22% 15% 28% 23% 12% 1	460
May	1st to 10th	Day	22% 12% 32% 25% 7% 2	468
	11th to 20th	Day	20% 12% 32% 25% 9% 3	675
	21st to end	Day	16% 10% 29% 27% 12% 5%	734
June	1st to 10th	Day	9% 8% 33% 30% 14% 5%	680
	11th to 20th	Day	13% 10% 30% 30% 12% 5%	680
	21st to end	Day	14% 8% 30% 32% 13% 4	680
July	1st to 10th	Day	8% 3 24% 31% 24% 9%	671
	11th to 20th	Day	8% 7% 26% 34% 18% 7%	668
	21st to end	Day	7% 3 29% 37% 17% 7%	739
August	1st to 10th	Day	8% 4 23% 36% 19% 10%	671
	11th to 20th	Day	12% 4 18% 31% 22% 13%	479
	21st to end	Day	9% 8% 21% 30% 24% 8%	539
September	1st to 10th	Day	13% 9% 23% 27% 21% 7%	490
	11th to 20th	Day	12% 3 22% 31% 23% 10%	490
	21st to end	Day	16% 13% 23% 26% 16% 6%	490
October	1st to 10th	Day	17% 11% 27% 26% 14% 5%	414
	11th to 20th	Day	23% 19% 29% 21% 7%	300
	21st to end	Day	28% 15% 35% 17% 4 1	330
November	1st to 10th	Day	16% 18% 36% 20% 8% 1	300
	11th to 20th	Day	18% 21% 39% 16% 6%	300
	21st to end	Day	26% 16% 37% 18% 3	300
December	1st to 10th	Day	16% 22% 40% 16% 5% 1	300
	11th to 20th	Day	19% 20% 37% 17% 7%	300
	21st to end	Day	24% 24% 35% 15% 2	306
January	1st to 10th	Night	19% 17% 35% 22% 6%	950
	11th to 20th	Night	21% 15% 37% 21% 6% 1	950
	21st to end	Night	18% 12% 38% 26% 5%	1045
February	1st to 10th	Night	19% 15% 38% 24% 5%	950
	11th to 20th	Night	17% 18% 35% 25% 4	747
	21st to end	Night	24% 14% 39% 18% 4	628
March	1st to 10th	Night	21% 12% 34% 24% 8% 1	760
	11th to 20th	Night	17% 14% 36% 26% 8%	732
	21st to end	Night	21% 10% 30% 31% 6% 1	627
April	1st to 10th	Night	21% 12% 36% 24% 7%	570
	11th to 20th	Night	23% 13% 31% 24% 7% 1	563
	21st to end	Night	21% 11% 31% 26% 10% 1	570
May	1st to 10th	Night	19% 8% 33% 33% 6% 1	570
	11th to 20th	Night	19% 6% 30% 32% 12%	561
	21st to end	Night	14% 6% 24% 36% 19% 2	617
June	1st to 10th	Night	10% 6% 26% 41% 16% 1	570
	11th to 20th	Night	13% 5% 31% 35% 15% 1	570
	21st to end	Night	11% 5% 25% 40% 18% 1	570
July	1st to 10th	Night	9% 2 17% 39% 29% 4	555
	11th to 20th	Night	6% 4 22% 41% 24% 4	552
	21st to end	Night	5% 4 18% 46% 26% 2	624
August	1st to 10th	Night	8% 2 16% 47% 25% 2	567
	11th to 20th	Night	9% 3 15% 39% 28% 5%	564
	21st to end	Night	10% 3 18% 40% 26% 3	627
September	1st to 10th	Night	9% 4 22% 34% 25% 5%	570
	11th to 20th	Night	10% 5% 23% 30% 28% 4	660
	21st to end	Night	15% 8% 26% 27% 20% 4	760
October	1st to 10th	Night	14% 9% 28% 30% 18% 2	760
	11th to 20th	Night	21% 11% 32% 26% 8% 1	760
	21st to end	Night	24% 11% 31% 25% 9% 1	836
November	1st to 10th	Night	17% 12% 36% 24% 10% 1	780
	11th to 20th	Night	19% 17% 35% 22% 7%	800
	21st to end	Night	21% 16% 35% 22% 6%	936
December	1st to 10th	Night	21% 17% 37% 20% 5%	1000
	11th to 20th	Night	23% 14% 35% 22% 5% 1	1000
	21st to end	Night	26% 16% 36% 19% 3	1063

Page generated at 2024-12-21 03:13:49. Version ac07

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