Kendrick Astro Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kendrick Astro Observatory clear sky chart from 2005-11-06 to 2025-03-12.

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	14% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	108958
	Night	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	110019
Transparency	Day	46% 8% 15% 20% 10% 1	112596
	Night	47% 8% 14% 20% 11% 1	114544
Seeing	Day	17% 9% 27% 28% 15% 5%	14772
	Night	18% 8% 29% 30% 13% 2	24341

By Month

Percentage Cloud Cover NE (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	12% 10% 4 12% 7% 6% 5% 4 7% 7% 25%	3597
	11th to 20th	Day	11% 16% 7% 17% 9% 6% 5% 3 5% 5% 17%	3916
	21st to end	Day	18% 16% 6% 12% 6% 5% 5% 4 5% 5% 20%	4466
February	1st to 10th	Day	15% 14% 4 12% 7% 5% 5% 4 5% 6% 23%	1800
	11th to 20th	Day	12% 14% 6% 11% 7% 6% 5% 4 4 6% 25%	1753
	21st to end	Day	17% 12% 4 10% 6% 5% 4 4 5% 5% 26%	1545
March	1st to 10th	Day	19% 9% 4 8% 5% 4 4 4 5% 6% 31%	3542
	11th to 20th	Day	11% 14% 4 9% 6% 5% 5% 5% 6% 6% 29%	3491
	21st to end	Day	16% 9% 3 7% 5% 5% 5% 3 5% 6% 37%	3815
April	1st to 10th	Day	16% 13% 3 8% 6% 5% 4 4 5% 6% 30%	2242
	11th to 20th	Day	19% 9% 3 6% 5% 4 4 3 5% 7% 35%	2323
	21st to end	Day	20% 8% 2 8% 4 5% 5% 4 5% 6% 33%	2470
May	1st to 10th	Day	17% 8% 3 8% 4 4 4 4 6% 8% 33%	4108
	11th to 20th	Day	14% 10% 3 7% 6% 5% 4 4 6% 8% 32%	4363
	21st to end	Day	12% 5% 2 5% 4 4 4 4 6% 8% 46%	4837
June	1st to 10th	Day	14% 6% 2 6% 6% 4 5% 4 7% 8% 38%	2660
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 8% 10% 40%	2660
	21st to end	Day	13% 5% 2 6% 4 5% 5% 5% 7% 10% 40%	2660
July	1st to 10th	Day	9% 4 2 5% 5% 5% 5% 5% 7% 11% 42%	4440
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 7% 9% 47%	4440
	21st to end	Day	7% 5% 2 7% 4 5% 6% 5% 8% 10% 42%	4500
August	1st to 10th	Day	16% 7% 2 6% 4 4 5% 4 6% 8% 39%	4104
	11th to 20th	Day	10% 7% 3 7% 5% 6% 5% 4 8% 9% 37%	4044
	21st to end	Day	9% 6% 2 6% 4 4 5% 5% 6% 9% 45%	4351
September	1st to 10th	Day	13% 5% 2 6% 4 4 5% 4 6% 8% 42%	2280
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 3 6% 7% 47%	2167
	21st to end	Day	13% 6% 2 7% 6% 5% 5% 4 6% 9% 37%	2052
October	1st to 10th	Day	18% 8% 2 6% 4 4 4 3 6% 7% 36%	1900
	11th to 20th	Day	19% 8% 3 8% 5% 5% 5% 4 5% 7% 30%	1900
	21st to end	Day	23% 10% 3 8% 6% 5% 5% 4 7% 6% 23%	2090
November	1st to 10th	Day	14% 8% 4 8% 6% 5% 6% 3 6% 8% 33%	1696
	11th to 20th	Day	15% 12% 3 9% 6% 5% 5% 6% 5% 8% 26%	1600
	21st to end	Day	19% 13% 4 9% 6% 4 5% 3 7% 7% 23%	1600
December	1st to 10th	Day	19% 14% 4 10% 7% 6% 6% 4 6% 6% 17%	2600
	11th to 20th	Day	21% 15% 4 9% 5% 5% 4 4 6% 6% 22%	2986
	21st to end	Day	27% 15% 6% 10% 6% 4 4 3 4 5% 15%	3960
January	1st to 10th	Night	14% 11% 4 9% 6% 6% 6% 5% 6% 7% 25%	6349
	11th to 20th	Night	13% 13% 5% 14% 10% 7% 6% 4 5% 6% 18%	5954
	21st to end	Night	17% 13% 5% 10% 6% 5% 5% 4 5% 6% 23%	6490
February	1st to 10th	Night	15% 15% 5% 9% 6% 5% 5% 3 6% 7% 25%	2600
	11th to 20th	Night	15% 14% 4 9% 7% 5% 4 5% 5% 6% 26%	2533
	21st to end	Night	15% 11% 4 10% 6% 5% 5% 3 6% 5% 29%	2080
March	1st to 10th	Night	19% 9% 4 8% 5% 5% 5% 3 5% 6% 32%	3518
	11th to 20th	Night	13% 10% 3 9% 5% 4 4 4 6% 7% 36%	3497
	21st to end	Night	17% 8% 2 5% 4 3 3 3 5% 5% 44%	3817
April	1st to 10th	Night	19% 9% 3 7% 6% 4 4 3 5% 6% 33%	1936
	11th to 20th	Night	16% 8% 3 7% 5% 4 5% 3 4 7% 38%	1821
	21st to end	Night	17% 7% 3 7% 4 4 5% 5% 5% 7% 36%	1710
May	1st to 10th	Night	18% 8% 2 7% 4 4 4 3 5% 6% 39%	2833
	11th to 20th	Night	15% 8% 3 7% 4 4 5% 3 6% 8% 35%	2527
	21st to end	Night	10% 4 2 5% 4 4 3 4 5% 8% 50%	2738
June	1st to 10th	Night	13% 4 2 6% 5% 5% 5% 4 6% 8% 42%	1520
	11th to 20th	Night	10% 5% 2 6% 4 4 5% 4 6% 10% 42%	1520
	21st to end	Night	12% 5% 2 7% 5% 4 4 4 6% 8% 44%	1520
July	1st to 10th	Night	6% 5% 2 5% 4 4 5% 4 6% 9% 51%	2520
	11th to 20th	Night	12% 3 2 5% 3 4 3 3 5% 9% 51%	2520
	21st to end	Night	8% 4 2 4 4 3 4 3 8% 7% 52%	3049
August	1st to 10th	Night	10% 5% 2 6% 5% 5% 5% 3 6% 7% 46%	2825
	11th to 20th	Night	11% 4 1 6% 3 3 4 3 5% 8% 50%	2785
	21st to end	Night	10% 5% 2 5% 4 4 4 4 6% 8% 47%	3272
September	1st to 10th	Night	10% 5% 2 6% 3 4 5% 3 6% 8% 47%	1900
	11th to 20th	Night	10% 4 2 5% 4 3 3 3 5% 6% 56%	2009
	21st to end	Night	15% 6% 3 7% 5% 4 4 3 6% 7% 42%	2128
October	1st to 10th	Night	15% 7% 2 7% 5% 3 4 4 5% 6% 40%	2280
	11th to 20th	Night	18% 9% 3 8% 5% 3 4 4 4 6% 36%	2280
	21st to end	Night	21% 9% 3 8% 4 5% 4 4 6% 6% 31%	2508
November	1st to 10th	Night	16% 7% 3 7% 5% 4 4 4 5% 7% 38%	2596
	11th to 20th	Night	16% 10% 4 8% 5% 5% 5% 5% 6% 6% 31%	2800
	21st to end	Night	20% 11% 3 8% 5% 5% 5% 4 6% 7% 27%	2800
December	1st to 10th	Night	19% 13% 4 10% 6% 5% 6% 5% 6% 6% 20%	4580
	11th to 20th	Night	17% 17% 4 9% 5% 5% 5% 4 6% 6% 23%	5208
	21st to end	Night	26% 14% 7% 10% 6% 4 4 4 4 5% 16%	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	51% 11% 18% 12% 8%	3598
	11th to 20th	Day	69% 6% 13% 9% 3	3950
	21st to end	Day	64% 7% 12% 10% 6%	4466
February	1st to 10th	Day	60% 8% 14% 14% 3 1	1800
	11th to 20th	Day	58% 8% 13% 14% 6% 1	1762
	21st to end	Day	56% 8% 15% 14% 6% 1	1545
March	1st to 10th	Day	51% 9% 14% 17% 8%	3545
	11th to 20th	Day	49% 10% 13% 18% 8% 1	3491
	21st to end	Day	42% 9% 15% 20% 13% 2	3815
April	1st to 10th	Day	52% 6% 13% 18% 10% 1	2242
	11th to 20th	Day	47% 7% 11% 20% 14% 1	2323
	21st to end	Day	48% 9% 11% 18% 12% 3	2470
May	1st to 10th	Day	44% 8% 15% 17% 14% 1	4120
	11th to 20th	Day	47% 11% 16% 18% 8% 1	4367
	21st to end	Day	32% 9% 14% 24% 17% 4	4837
June	1st to 10th	Day	40% 10% 14% 21% 14% 1	2660
	11th to 20th	Day	36% 9% 15% 23% 15% 1	2660
	21st to end	Day	36% 9% 15% 25% 14% 1	2660
July	1st to 10th	Day	31% 8% 18% 25% 15% 2	4370
	11th to 20th	Day	30% 7% 15% 35% 12% 1	4365
	21st to end	Day	34% 10% 16% 22% 18% 1	4356
August	1st to 10th	Day	41% 7% 15% 21% 15% 1	4091
	11th to 20th	Day	38% 9% 18% 24% 11% 1	4083
	21st to end	Day	32% 9% 15% 34% 10% 1	4351
September	1st to 10th	Day	36% 10% 15% 27% 11% 1	2280
	11th to 20th	Day	33% 7% 17% 28% 14% 1	2167
	21st to end	Day	41% 10% 16% 25% 9%	2052
October	1st to 10th	Day	35% 7% 17% 28% 13% 1	3160
	11th to 20th	Day	37% 6% 17% 26% 13%	3140
	21st to end	Day	50% 8% 15% 20% 6%	3428
November	1st to 10th	Day	46% 9% 16% 20% 8% 1	1696
	11th to 20th	Day	53% 9% 16% 15% 7%	1600
	21st to end	Day	57% 10% 16% 14% 2	1600
December	1st to 10th	Day	65% 9% 16% 8% 3	2600
	11th to 20th	Day	61% 9% 14% 10% 7%	2986
	21st to end	Day	69% 8% 10% 8% 5%	3960
January	1st to 10th	Night	52% 10% 15% 19% 4	6349
	11th to 20th	Night	65% 10% 13% 9% 3	5995
	21st to end	Night	59% 8% 13% 10% 8% 1	6490
February	1st to 10th	Night	57% 7% 15% 16% 4 1	2600
	11th to 20th	Night	57% 8% 13% 15% 7% 1	2535
	21st to end	Night	53% 7% 15% 17% 7%	2080
March	1st to 10th	Night	51% 8% 13% 21% 6% 1	3528
	11th to 20th	Night	43% 9% 16% 19% 10% 2	3498
	21st to end	Night	38% 7% 10% 25% 18% 2	3817
April	1st to 10th	Night	50% 6% 12% 18% 13% 1	1936
	11th to 20th	Night	46% 6% 10% 20% 15% 2	1821
	21st to end	Night	45% 8% 11% 19% 15% 2	1710
May	1st to 10th	Night	43% 8% 13% 17% 16% 2	2840
	11th to 20th	Night	43% 13% 15% 17% 10% 2	2528
	21st to end	Night	29% 9% 14% 24% 22% 3	2739
June	1st to 10th	Night	38% 7% 13% 23% 16% 2	1520
	11th to 20th	Night	36% 7% 13% 22% 21% 2	1520
	21st to end	Night	37% 8% 13% 24% 18% 1	1520
July	1st to 10th	Night	29% 6% 15% 24% 22% 3	2480
	11th to 20th	Night	30% 6% 15% 33% 15% 1	2472
	21st to end	Night	28% 8% 16% 29% 17% 2	2952
August	1st to 10th	Night	35% 7% 13% 27% 15% 2	2814
	11th to 20th	Night	32% 6% 17% 33% 12% 1	2812
	21st to end	Night	32% 8% 14% 31% 14% 1	3272
September	1st to 10th	Night	33% 9% 16% 27% 15% 1	1900
	11th to 20th	Night	29% 6% 14% 33% 17%	2009
	21st to end	Night	41% 8% 13% 26% 11%	2128
October	1st to 10th	Night	33% 7% 11% 25% 23% 1	3800
	11th to 20th	Night	41% 7% 15% 26% 10%	3779
	21st to end	Night	39% 8% 17% 26% 9% 1	4120
November	1st to 10th	Night	44% 7% 15% 22% 11% 1	2596
	11th to 20th	Night	49% 9% 15% 17% 9% 1	2800
	21st to end	Night	55% 9% 19% 14% 3	2800
December	1st to 10th	Night	61% 10% 15% 12% 3	4580
	11th to 20th	Night	60% 8% 12% 13% 7%	5208
	21st to end	Night	67% 9% 11% 8% 4	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	19% 15% 36% 22% 8% 2	200
	11th to 20th	Day	21% 20% 36% 14% 7% 1	277
	21st to end	Day	22% 14% 35% 22% 5%	330
February	1st to 10th	Day	21% 18% 40% 18% 4	300
	11th to 20th	Day	23% 17% 40% 18% 2	300
	21st to end	Day	25% 23% 29% 21% 2	269
March	1st to 10th	Day	19% 12% 39% 24% 6%	500
	11th to 20th	Day	17% 18% 32% 25% 8% 1	464
	21st to end	Day	24% 9% 33% 26% 7% 1	506
April	1st to 10th	Day	18% 12% 33% 28% 8%	460
	11th to 20th	Day	24% 10% 34% 20% 10% 3	452
	21st to end	Day	21% 8% 33% 27% 10% 2	460
May	1st to 10th	Day	17% 9% 27% 29% 13% 5%	463
	11th to 20th	Day	15% 5% 24% 33% 18% 5%	487
	21st to end	Day	13% 3 21% 34% 22% 7%	529
June	1st to 10th	Day	12% 6% 26% 36% 17% 3	490
	11th to 20th	Day	12% 5% 24% 34% 22% 3	490
	21st to end	Day	14% 7% 22% 34% 19% 5%	490
July	1st to 10th	Day	7% 4 16% 34% 28% 10%	485
	11th to 20th	Day	13% 3 18% 34% 24% 9%	484
	21st to end	Day	7% 3 18% 41% 24% 7%	532
August	1st to 10th	Day	11% 5% 17% 29% 27% 12%	486
	11th to 20th	Day	9% 5% 16% 33% 25% 12%	479
	21st to end	Day	11% 5% 19% 31% 24% 10%	539
September	1st to 10th	Day	13% 4 21% 29% 21% 12%	490
	11th to 20th	Day	9% 4 18% 27% 27% 16%	490
	21st to end	Day	13% 6% 29% 27% 16% 8%	490
October	1st to 10th	Day	20% 9% 26% 24% 15% 7%	490
	11th to 20th	Day	18% 12% 34% 24% 10% 2	490
	21st to end	Day	26% 11% 29% 25% 8% 1	539
November	1st to 10th	Day	18% 16% 27% 27% 11% 1	291
	11th to 20th	Day	21% 19% 33% 21% 7% 1	200
	21st to end	Day	23% 15% 38% 21% 3 1	200
December	1st to 10th	Day	25% 16% 34% 20% 6% 1	200
	11th to 20th	Day	27% 22% 30% 18% 4	200
	21st to end	Day	26% 15% 37% 18% 3	220
January	1st to 10th	Night	22% 14% 38% 20% 6%	800
	11th to 20th	Night	26% 13% 33% 24% 4	800
	21st to end	Night	20% 10% 38% 25% 7%	880
February	1st to 10th	Night	21% 14% 39% 22% 3	800
	11th to 20th	Night	22% 13% 37% 23% 4	783
	21st to end	Night	19% 12% 41% 24% 4	660
March	1st to 10th	Night	18% 11% 38% 26% 7%	800
	11th to 20th	Night	20% 13% 36% 24% 7% 1	767
	21st to end	Night	20% 9% 30% 31% 10% 1	836
April	1st to 10th	Night	22% 8% 33% 30% 6%	760
	11th to 20th	Night	18% 9% 33% 28% 10% 2	697
	21st to end	Night	20% 7% 26% 34% 13%	570
May	1st to 10th	Night	17% 4 27% 32% 17% 3	570
	11th to 20th	Night	15% 3 23% 41% 18%	393
	21st to end	Night	9% 3 23% 38% 25% 2	411
June	1st to 10th	Night	13% 2 21% 43% 19% 1	380
	11th to 20th	Night	11% 3 26% 38% 22% 1	380
	21st to end	Night	10% 4 20% 43% 23% 1	380
July	1st to 10th	Night	6% 2 15% 48% 26% 2	370
	11th to 20th	Night	11% 2 18% 39% 26% 3	368
	21st to end	Night	8% 2 15% 46% 27% 3	599
August	1st to 10th	Night	9% 3 13% 40% 31% 4	567
	11th to 20th	Night	8% 2 14% 39% 32% 5%	564
	21st to end	Night	11% 2 19% 36% 29% 4	710
September	1st to 10th	Night	11% 5% 20% 33% 24% 6%	760
	11th to 20th	Night	12% 3 16% 31% 31% 7%	760
	21st to end	Night	16% 5% 21% 32% 21% 5%	760
October	1st to 10th	Night	18% 6% 25% 28% 20% 3	760
	11th to 20th	Night	20% 9% 30% 29% 11% 1	760
	21st to end	Night	24% 8% 31% 30% 6% 1	836
November	1st to 10th	Night	20% 9% 28% 30% 12% 1	780
	11th to 20th	Night	20% 11% 36% 25% 8% 2	800
	21st to end	Night	24% 11% 35% 25% 6%	800
December	1st to 10th	Night	27% 12% 35% 20% 6%	800
	11th to 20th	Night	22% 13% 41% 20% 4	800
	21st to end	Night	29% 11% 34% 23% 2	880

Page generated at 2025-03-09 08:08:43. Version ac07

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