KepCo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the KepCo Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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	9% 10% 3 7% 5% 4 5% 4 5% 7% 40%	108655
	Night	11% 12% 4 7% 4 4 4 3 5% 6% 38%	108955
Transparency	Day	23% 46% 7% 12% 9% 3	108423
	Night	26% 44% 7% 13% 8% 2	108833
Seeing	Day	17% 13% 28% 25% 13% 3	15015
	Night	18% 8% 20% 33% 18% 3	23988

By Month

Percentage Cloud Cover NW (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	16% 25% 7% 13% 6% 5% 4 3 4 5% 14%	2587
	11th to 20th	Day	15% 15% 4 8% 6% 5% 4 3 5% 6% 29%	2516
	21st to end	Day	23% 27% 5% 7% 3 3 3 3 3 5% 17%	2794
February	1st to 10th	Day	13% 16% 4 8% 5% 4 5% 4 5% 7% 28%	1562
	11th to 20th	Day	10% 16% 5% 10% 5% 4 5% 4 6% 5% 30%	1678
	21st to end	Day	10% 14% 4 11% 8% 6% 5% 5% 6% 6% 26%	1570
March	1st to 10th	Day	10% 16% 5% 9% 5% 5% 5% 4 5% 7% 28%	3138
	11th to 20th	Day	7% 10% 3 6% 4 3 4 3 5% 6% 49%	3293
	21st to end	Day	12% 15% 4 9% 6% 6% 6% 5% 7% 7% 24%	4152
April	1st to 10th	Day	11% 12% 5% 11% 7% 6% 6% 5% 5% 7% 25%	2280
	11th to 20th	Day	9% 12% 4 9% 7% 5% 6% 4 6% 8% 29%	2273
	21st to end	Day	9% 13% 4 10% 6% 4 5% 5% 6% 8% 31%	2555
May	1st to 10th	Day	9% 8% 3 7% 6% 5% 6% 4 6% 8% 38%	4420
	11th to 20th	Day	7% 8% 3 8% 5% 5% 5% 4 8% 10% 37%	4377
	21st to end	Day	13% 11% 4 10% 6% 6% 6% 5% 7% 7% 26%	4813
June	1st to 10th	Day	15% 9% 3 8% 6% 5% 5% 5% 6% 7% 31%	2816
	11th to 20th	Day	11% 9% 4 8% 6% 6% 6% 6% 7% 7% 29%	2850
	21st to end	Day	7% 6% 3 7% 5% 4 5% 4 8% 7% 45%	3012
July	1st to 10th	Day	3 3 1 3 2 2 3 3 4 7% 70%	4425
	11th to 20th	Day	2 3 1 3 2 2 2 2 3 4 74%	4420
	21st to end	Day	3 2 1 3 3 2 3 3 5% 7% 69%	4790
August	1st to 10th	Day	2 3 1 3 3 3 4 4 5% 8% 64%	4401
	11th to 20th	Day	3 3 1 4 4 4 5% 4 6% 8% 59%	4293
	21st to end	Day	5% 5% 2 6% 5% 4 5% 3 5% 7% 54%	4180
September	1st to 10th	Day	5% 4 1 5% 4 3 3 2 4 7% 60%	2280
	11th to 20th	Day	9% 6% 3 5% 4 4 4 3 6% 8% 48%	2242
	21st to end	Day	10% 6% 2 7% 3 4 4 3 5% 7% 49%	2090
October	1st to 10th	Day	7% 6% 3 7% 4 3 4 3 5% 7% 50%	3190
	11th to 20th	Day	10% 9% 3 8% 5% 6% 5% 4 5% 6% 39%	3048
	21st to end	Day	13% 11% 7% 9% 4 4 3 3 4 6% 35%	3101
November	1st to 10th	Day	19% 13% 3 8% 5% 5% 5% 4 6% 7% 26%	1719
	11th to 20th	Day	16% 18% 4 8% 5% 4 4 3 4 5% 29%	1600
	21st to end	Day	17% 16% 6% 10% 6% 3 4 4 5% 6% 23%	1512
December	1st to 10th	Day	10% 10% 3 8% 5% 4 3 5% 7% 10% 34%	2290
	11th to 20th	Day	14% 24% 8% 11% 5% 4 5% 4 5% 4 17%	2642
	21st to end	Day	14% 23% 7% 14% 6% 4 5% 4 5% 5% 13%	3746
January	1st to 10th	Night	17% 26% 8% 12% 5% 4 4 3 3 4 15%	4490
	11th to 20th	Night	16% 16% 4 7% 5% 4 3 3 5% 7% 32%	4382
	21st to end	Night	22% 26% 9% 9% 4 3 4 3 3 3 14%	4862
February	1st to 10th	Night	14% 15% 5% 9% 6% 5% 5% 3 5% 6% 27%	2616
	11th to 20th	Night	10% 13% 4 8% 6% 4 4 4 5% 6% 34%	2388
	21st to end	Night	9% 16% 6% 9% 5% 6% 5% 4 6% 8% 27%	1884
March	1st to 10th	Night	7% 13% 4 10% 5% 5% 5% 4 6% 9% 32%	3736
	11th to 20th	Night	8% 10% 3 5% 4 3 4 3 5% 5% 50%	3685
	21st to end	Night	11% 17% 5% 10% 6% 4 5% 4 6% 7% 26%	3500
April	1st to 10th	Night	11% 11% 3 7% 5% 5% 6% 5% 6% 7% 34%	1900
	11th to 20th	Night	8% 9% 4 8% 6% 5% 6% 4 6% 6% 38%	1857
	21st to end	Night	7% 10% 4 7% 6% 5% 5% 4 6% 7% 38%	1622
May	1st to 10th	Night	7% 8% 3 6% 5% 4 5% 4 5% 8% 45%	2540
	11th to 20th	Night	6% 5% 1 6% 5% 5% 5% 4 6% 9% 48%	2516
	21st to end	Night	10% 7% 3 8% 6% 5% 6% 4 7% 7% 37%	2762
June	1st to 10th	Night	12% 7% 2 5% 5% 5% 5% 5% 7% 8% 38%	1363
	11th to 20th	Night	9% 7% 3 7% 5% 6% 6% 5% 6% 8% 38%	1330
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 6% 9% 49%	1150
July	1st to 10th	Night	2 2 1 2 2 2 2 2 4 4 76%	2522
	11th to 20th	Night	1 2 1 2 1 2 3 2 4 5% 77%	2540
	21st to end	Night	1 1 1 3 2 4 3 3 5% 5% 71%	2762
August	1st to 10th	Night	2 3 2 5% 3 3 4 3 5% 6% 65%	2529
	11th to 20th	Night	2 2 1 3 4 3 3 3 7% 10% 61%	2532
	21st to end	Night	6% 5% 2 5% 3 3 4 3 6% 7% 56%	3498
September	1st to 10th	Night	3 4 2 4 2 3 3 4 6% 7% 62%	1900
	11th to 20th	Night	8% 5% 1 5% 3 3 4 3 5% 8% 54%	1938
	21st to end	Night	8% 6% 3 6% 4 4 4 3 5% 8% 50%	2090
October	1st to 10th	Night	7% 5% 2 5% 4 5% 5% 4 5% 6% 51%	3787
	11th to 20th	Night	12% 11% 3 8% 4 4 4 3 6% 6% 41%	3886
	21st to end	Night	16% 9% 3 7% 4 4 4 3 5% 5% 40%	4457
November	1st to 10th	Night	20% 15% 3 7% 4 4 4 3 5% 6% 28%	2575
	11th to 20th	Night	20% 15% 3 8% 4 4 4 4 5% 6% 27%	2800
	21st to end	Night	18% 17% 4 11% 5% 4 5% 3 4 5% 24%	2865
December	1st to 10th	Night	9% 10% 3 8% 5% 5% 4 3 5% 8% 38%	4890
	11th to 20th	Night	17% 23% 5% 11% 6% 5% 4 3 4 5% 16%	5550
	21st to end	Night	16% 25% 6% 10% 5% 4 5% 4 5% 4 17%	7251

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	46% 38% 5% 7% 4	2587
	11th to 20th	Day	36% 37% 9% 10% 2 5%	2540
	21st to end	Day	52% 39% 4 3 1	2794
February	1st to 10th	Day	21% 66% 3 5% 3 1	1562
	11th to 20th	Day	21% 65% 4 7% 3	1687
	21st to end	Day	17% 66% 4 8% 5%	1570
March	1st to 10th	Day	34% 42% 5% 9% 10%	3138
	11th to 20th	Day	15% 41% 13% 27% 3	3293
	21st to end	Day	35% 43% 9% 8% 6%	4152
April	1st to 10th	Day	18% 67% 6% 7% 2	2280
	11th to 20th	Day	16% 67% 4 9% 3	2273
	21st to end	Day	17% 66% 4 7% 5%	2555
May	1st to 10th	Day	22% 43% 6% 14% 13% 1	4420
	11th to 20th	Day	22% 42% 9% 19% 9%	4380
	21st to end	Day	34% 41% 9% 13% 3	4814
June	1st to 10th	Day	16% 66% 4 8% 4 1	2816
	11th to 20th	Day	16% 67% 4 9% 4 1	2850
	21st to end	Day	14% 64% 4 10% 7% 1	3012
July	1st to 10th	Day	7% 37% 3 9% 23% 21%	4356
	11th to 20th	Day	7% 36% 2 6% 23% 26%	4345
	21st to end	Day	10% 37% 5% 16% 21% 11%	4639
August	1st to 10th	Day	9% 38% 3 17% 26% 8%	4384
	11th to 20th	Day	14% 41% 9% 27% 6% 1	4335
	21st to end	Day	19% 39% 9% 17% 13% 3	4179
September	1st to 10th	Day	12% 60% 6% 13% 8% 1	2280
	11th to 20th	Day	16% 62% 4 10% 6% 1	2242
	21st to end	Day	16% 61% 7% 10% 5% 1	2090
October	1st to 10th	Day	18% 39% 13% 24% 6%	3190
	11th to 20th	Day	29% 41% 5% 18% 7%	3048
	21st to end	Day	31% 40% 7% 16% 7%	3101
November	1st to 10th	Day	24% 58% 8% 8% 2	1719
	11th to 20th	Day	26% 58% 6% 6% 3 1	1600
	21st to end	Day	26% 58% 5% 6% 4 1	1512
December	1st to 10th	Day	27% 39% 19% 13% 2	2290
	11th to 20th	Day	49% 34% 7% 6% 4	2644
	21st to end	Day	57% 29% 7% 6% 2	3746
January	1st to 10th	Night	50% 36% 5% 6% 2	4490
	11th to 20th	Night	34% 37% 6% 12% 7% 4	4420
	21st to end	Night	53% 40% 4 2 1	4862
February	1st to 10th	Night	22% 66% 3 4 3 1	2616
	11th to 20th	Night	21% 65% 4 7% 2 1	2390
	21st to end	Night	16% 66% 4 8% 6%	1884
March	1st to 10th	Night	30% 43% 5% 12% 10% 1	3736
	11th to 20th	Night	16% 41% 11% 26% 6%	3686
	21st to end	Night	37% 42% 8% 10% 4	3500
April	1st to 10th	Night	16% 67% 6% 8% 2 1	1900
	11th to 20th	Night	16% 67% 4 8% 5%	1857
	21st to end	Night	15% 66% 3 9% 7%	1622
May	1st to 10th	Night	20% 43% 6% 15% 16%	2540
	11th to 20th	Night	16% 40% 10% 24% 6% 2	2516
	21st to end	Night	23% 41% 14% 17% 4	2762
June	1st to 10th	Night	12% 66% 6% 12% 5% 1	1363
	11th to 20th	Night	15% 66% 5% 8% 5% 1	1330
	21st to end	Night	12% 64% 4 13% 6% 1	1150
July	1st to 10th	Night	6% 35% 2 10% 31% 16%	2482
	11th to 20th	Night	7% 35% 3 5% 23% 26%	2492
	21st to end	Night	10% 36% 3 19% 22% 11%	2674
August	1st to 10th	Night	12% 37% 3 15% 28% 5%	2521
	11th to 20th	Night	11% 40% 11% 27% 10% 1	2556
	21st to end	Night	18% 38% 9% 22% 11% 1	3498
September	1st to 10th	Night	10% 61% 6% 13% 9% 1	1900
	11th to 20th	Night	14% 61% 4 12% 7%	1938
	21st to end	Night	15% 61% 7% 12% 5%	2090
October	1st to 10th	Night	16% 38% 14% 23% 8%	3787
	11th to 20th	Night	27% 38% 7% 18% 10%	3886
	21st to end	Night	26% 39% 10% 21% 5%	4457
November	1st to 10th	Night	25% 58% 7% 8% 2	2575
	11th to 20th	Night	24% 58% 6% 6% 4 2	2800
	21st to end	Night	25% 58% 6% 5% 4 1	2865
December	1st to 10th	Night	24% 38% 15% 19% 5%	4890
	11th to 20th	Night	48% 34% 8% 6% 4	5547
	21st to end	Night	49% 28% 8% 10% 5%	7251

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	29% 11% 21% 27% 9% 3	192
	11th to 20th	Day	32% 4 24% 24% 12% 3	180
	21st to end	Day	29% 10% 27% 23% 9% 2	198
February	1st to 10th	Day	18% 16% 34% 26% 4 1	222
	11th to 20th	Day	21% 16% 31% 23% 8% 1	371
	21st to end	Day	15% 13% 35% 27% 9% 1	382
March	1st to 10th	Day	24% 19% 29% 16% 10% 1	460
	11th to 20th	Day	23% 15% 26% 21% 15% 2	460
	21st to end	Day	23% 19% 25% 19% 11% 2	506
April	1st to 10th	Day	26% 15% 31% 19% 8% 1	460
	11th to 20th	Day	22% 19% 27% 18% 9% 4	452
	21st to end	Day	19% 19% 27% 20% 10% 4	460
May	1st to 10th	Day	17% 16% 30% 24% 10% 3	463
	11th to 20th	Day	22% 10% 26% 27% 11% 4	488
	21st to end	Day	20% 9% 26% 24% 16% 5%	529
June	1st to 10th	Day	20% 11% 29% 26% 11% 3	646
	11th to 20th	Day	18% 13% 26% 26% 13% 3	680
	21st to end	Day	11% 12% 26% 28% 19% 4	842
July	1st to 10th	Day	8% 11% 30% 34% 13% 3	491
	11th to 20th	Day	6% 16% 29% 31% 14% 4	484
	21st to end	Day	6% 8% 30% 32% 18% 5%	531
August	1st to 10th	Day	6% 8% 28% 35% 17% 6%	487
	11th to 20th	Day	5% 9% 27% 31% 18% 9%	477
	21st to end	Day	11% 13% 26% 28% 16% 5%	539
September	1st to 10th	Day	11% 11% 29% 29% 16% 5%	490
	11th to 20th	Day	18% 11% 25% 27% 17% 3	490
	21st to end	Day	18% 14% 29% 23% 13% 3	490
October	1st to 10th	Day	14% 16% 28% 26% 13% 2	490
	11th to 20th	Day	18% 14% 28% 24% 13% 2	428
	21st to end	Day	27% 8% 32% 22% 10% 2	330
November	1st to 10th	Day	24% 13% 27% 25% 9% 1	277
	11th to 20th	Day	27% 18% 23% 20% 13%	200
	21st to end	Day	22% 10% 32% 20% 14% 4	200
December	1st to 10th	Day	23% 5% 22% 23% 21% 7%	200
	11th to 20th	Day	21% 12% 31% 26% 9% 3	200
	21st to end	Day	23% 11% 24% 30% 10% 2	220
January	1st to 10th	Night	30% 10% 20% 27% 10% 2	784
	11th to 20th	Night	27% 7% 20% 31% 12% 2	760
	21st to end	Night	24% 6% 19% 36% 14% 1	836
February	1st to 10th	Night	21% 9% 24% 31% 11% 3	760
	11th to 20th	Night	17% 8% 23% 36% 14% 2	744
	21st to end	Night	18% 7% 22% 32% 18% 3	628
March	1st to 10th	Night	19% 9% 19% 33% 17% 3	760
	11th to 20th	Night	18% 9% 22% 33% 16% 2	760
	21st to end	Night	19% 11% 22% 30% 15% 3	836
April	1st to 10th	Night	18% 8% 18% 34% 20% 3	760
	11th to 20th	Night	13% 10% 24% 33% 16% 3	729
	21st to end	Night	12% 10% 24% 35% 17% 2	482
May	1st to 10th	Night	11% 10% 21% 36% 21% 3	380
	11th to 20th	Night	13% 6% 17% 35% 25% 4	374
	21st to end	Night	14% 8% 18% 30% 25% 5%	411
June	1st to 10th	Night	16% 7% 21% 35% 19% 2	380
	11th to 20th	Night	15% 7% 24% 32% 19% 2	380
	21st to end	Night	9% 7% 21% 33% 27% 3	380
July	1st to 10th	Night	5% 7% 21% 33% 31% 4	370
	11th to 20th	Night	5% 8% 19% 41% 24% 3	368
	21st to end	Night	4 6% 14% 39% 31% 5%	416
August	1st to 10th	Night	2 6% 16% 33% 35% 8%	378
	11th to 20th	Night	3 4 17% 34% 37% 6%	385
	21st to end	Night	7% 6% 16% 38% 28% 5%	836
September	1st to 10th	Night	5% 6% 18% 38% 27% 7%	760
	11th to 20th	Night	13% 5% 13% 31% 30% 8%	760
	21st to end	Night	12% 6% 18% 37% 23% 5%	760
October	1st to 10th	Night	18% 6% 17% 32% 25% 2	760
	11th to 20th	Night	20% 8% 19% 32% 19% 3	760
	21st to end	Night	24% 7% 21% 32% 13% 3	836
November	1st to 10th	Night	29% 7% 24% 31% 7% 1	780
	11th to 20th	Night	29% 10% 20% 25% 15% 1	800
	21st to end	Night	27% 7% 19% 31% 13% 3	865
December	1st to 10th	Night	21% 8% 20% 36% 14% 2	1000
	11th to 20th	Night	28% 9% 21% 32% 10% 1	1000
	21st to end	Night	29% 7% 26% 29% 9% 1	1010

Page generated at 2025-01-04 00:24:00. Version ac07

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