Critter Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Critter Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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	7% 7% 2 6% 4 4 4 3 5% 6% 53%	140016
	Night	9% 9% 3 6% 4 4 4 3 5% 6% 47%	138232
Transparency	Day	33% 4 11% 24% 19% 9%	134846
	Night	39% 4 11% 23% 16% 7%	134396
Seeing	Day	17% 13% 28% 27% 12% 4	16491
	Night	16% 7% 17% 32% 24% 4	25671

By Month

Percentage Cloud Cover SW (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	13% 14% 5% 11% 6% 6% 6% 4 6% 7% 21%	4722
	11th to 20th	Day	10% 8% 3 5% 4 3 3 3 4 5% 52%	5082
	21st to end	Day	8% 9% 3 8% 5% 5% 5% 3 5% 7% 42%	5843
February	1st to 10th	Day	8% 13% 3 9% 6% 5% 6% 6% 6% 7% 31%	1890
	11th to 20th	Day	10% 12% 4 9% 6% 5% 4 4 6% 7% 33%	1801
	21st to end	Day	11% 16% 4 9% 6% 5% 3 3 6% 6% 31%	1600
March	1st to 10th	Day	11% 16% 4 10% 5% 5% 4 4 5% 7% 29%	4863
	11th to 20th	Day	8% 12% 4 10% 6% 5% 5% 4 5% 5% 36%	5000
	21st to end	Day	11% 13% 5% 11% 6% 6% 6% 4 6% 8% 25%	5527
April	1st to 10th	Day	11% 14% 5% 11% 7% 5% 4 4 6% 6% 28%	2400
	11th to 20th	Day	13% 14% 3 7% 5% 5% 5% 3 5% 7% 34%	2369
	21st to end	Day	12% 11% 3 7% 5% 4 4 3 7% 9% 37%	2519
May	1st to 10th	Day	8% 7% 2 5% 3 3 3 2 4 6% 54%	5919
	11th to 20th	Day	6% 8% 2 6% 4 3 4 3 5% 6% 50%	6277
	21st to end	Day	7% 6% 2 4 3 3 3 3 5% 7% 59%	6902
June	1st to 10th	Day	10% 8% 3 5% 5% 4 3 3 5% 8% 46%	2800
	11th to 20th	Day	7% 6% 2 5% 3 4 4 3 4 7% 55%	2800
	21st to end	Day	4 3 1 4 2 2 3 2 4 5% 70%	2800
July	1st to 10th	Day	1 1 1 1 1 2 1 2 3 85%	6319
	11th to 20th	Day	1 1 1 2 1 2 2 2 2 3 84%	6320
	21st to end	Day	1 1 1 1 1 2 2 3 4 83%	6498
August	1st to 10th	Day	2 2 1 2 1 2 2 2 4 5% 76%	5777
	11th to 20th	Day	3 2 1 2 2 2 2 2 3 4 78%	5796
	21st to end	Day	2 2 1 2 2 2 3 3 4 5% 75%	6040
September	1st to 10th	Day	3 2 1 2 2 2 2 2 4 5% 76%	2400
	11th to 20th	Day	5% 3 2 4 3 3 3 5% 6% 6% 60%	2375
	21st to end	Day	6% 3 2 4 2 2 3 3 4 6% 63%	2116
October	1st to 10th	Day	5% 3 1 4 3 3 3 1 4 5% 69%	3280
	11th to 20th	Day	5% 6% 2 6% 4 4 4 3 6% 9% 51%	3261
	21st to end	Day	11% 8% 3 7% 6% 4 5% 4 5% 7% 40%	3558
November	1st to 10th	Day	14% 9% 3 8% 6% 4 4 4 6% 8% 33%	1902
	11th to 20th	Day	13% 10% 2 10% 6% 6% 5% 4 8% 9% 27%	1680
	21st to end	Day	10% 12% 4 6% 5% 5% 5% 5% 5% 8% 35%	1680
December	1st to 10th	Day	7% 7% 2 5% 4 4 4 4 7% 10% 47%	2700
	11th to 20th	Day	17% 13% 5% 10% 6% 5% 5% 4 6% 7% 22%	3108
	21st to end	Day	15% 14% 5% 11% 7% 6% 6% 5% 7% 7% 16%	4092
January	1st to 10th	Night	17% 14% 4 10% 6% 5% 6% 4 5% 7% 21%	8172
	11th to 20th	Night	9% 10% 4 7% 3 3 3 2 4 6% 50%	7878
	21st to end	Night	11% 10% 3 9% 5% 5% 5% 4 5% 6% 38%	8371
February	1st to 10th	Night	9% 14% 3 8% 6% 4 4 4 6% 8% 33%	2730
	11th to 20th	Night	11% 15% 5% 8% 5% 5% 5% 3 6% 6% 32%	2597
	21st to end	Night	9% 15% 4 8% 5% 5% 5% 5% 6% 8% 31%	2030
March	1st to 10th	Night	12% 16% 4 8% 6% 6% 5% 4 6% 7% 27%	5027
	11th to 20th	Night	7% 12% 3 9% 5% 5% 5% 4 5% 6% 39%	5000
	21st to end	Night	10% 14% 5% 11% 6% 6% 5% 4 6% 7% 26%	5446
April	1st to 10th	Night	11% 17% 4 8% 5% 5% 5% 4 6% 7% 29%	2000
	11th to 20th	Night	10% 14% 3 7% 5% 3 4 4 6% 6% 36%	1979
	21st to end	Night	15% 11% 2 6% 3 3 4 3 7% 9% 37%	1878
May	1st to 10th	Night	10% 10% 3 7% 3 3 2 3 4 5% 50%	4058
	11th to 20th	Night	9% 12% 3 7% 4 4 3 3 4 4 47%	3616
	21st to end	Night	10% 6% 1 4 3 2 3 2 4 6% 59%	3972
June	1st to 10th	Night	11% 6% 2 4 4 4 5% 4 7% 6% 48%	1600
	11th to 20th	Night	9% 6% 2 5% 4 2 3 2 5% 6% 56%	1600
	21st to end	Night	5% 3 1 3 2 2 2 2 3 4 72%	1600
July	1st to 10th	Night	1 1 1 2 2 2 3 2 3 3 79%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 1 3 87%	3640
	21st to end	Night	2 1 1 1 1 2 2 2 2 4 83%	4367
August	1st to 10th	Night	2 1 1 2 1 2 2 3 3 4 79%	4035
	11th to 20th	Night	4 3 1 3 1 1 2 2 3 4 76%	4052
	21st to end	Night	3 3 1 3 2 2 2 2 3 5% 73%	4955
September	1st to 10th	Night	3 2 1 2 1 1 2 1 4 5% 79%	2000
	11th to 20th	Night	5% 4 1 4 3 2 3 3 6% 7% 63%	2021
	21st to end	Night	7% 4 1 4 3 3 3 2 4 6% 63%	2283
October	1st to 10th	Night	5% 3 1 3 3 3 3 2 3 3 71%	3920
	11th to 20th	Night	9% 6% 2 5% 3 3 3 3 5% 6% 55%	3897
	21st to end	Night	8% 9% 3 8% 5% 5% 5% 4 6% 8% 40%	4253
November	1st to 10th	Night	14% 12% 3 7% 5% 4 4 4 6% 7% 34%	2613
	11th to 20th	Night	14% 10% 3 8% 6% 6% 6% 4 7% 8% 28%	2940
	21st to end	Night	12% 10% 3 6% 5% 5% 4 3 5% 8% 39%	2940
December	1st to 10th	Night	8% 8% 2 5% 3 3 4 3 6% 8% 50%	4700
	11th to 20th	Night	13% 13% 4 11% 7% 7% 6% 5% 6% 7% 22%	5316
	21st to end	Night	16% 13% 4 10% 6% 6% 5% 4 6% 7% 24%	7106

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	59% 6% 12% 17% 5% 1	4723
	11th to 20th	Day	36% 3 7% 20% 19% 17%	5082
	21st to end	Day	42% 3 11% 15% 18% 11%	5843
February	1st to 10th	Day	50% 5% 15% 17% 11% 2	1890
	11th to 20th	Day	51% 4 14% 20% 9% 2	1810
	21st to end	Day	55% 4 10% 18% 11% 2	1600
March	1st to 10th	Day	55% 3 9% 25% 8%	4863
	11th to 20th	Day	49% 5% 13% 15% 17% 1	5000
	21st to end	Day	55% 6% 15% 20% 4	5527
April	1st to 10th	Day	57% 5% 13% 16% 7% 2	2400
	11th to 20th	Day	51% 5% 15% 15% 10% 3	2372
	21st to end	Day	44% 5% 16% 22% 12% 1	2519
May	1st to 10th	Day	32% 3 9% 30% 23% 2	5919
	11th to 20th	Day	32% 6% 11% 27% 20% 3	6280
	21st to end	Day	25% 4 18% 43% 9%	6904
June	1st to 10th	Day	38% 4 15% 30% 12% 1	2800
	11th to 20th	Day	30% 4 12% 35% 17% 2	2800
	21st to end	Day	18% 2 12% 34% 26% 8%	2800
July	1st to 10th	Day	8% 2 4 26% 26% 33%	6251
	11th to 20th	Day	8% 1 3 16% 34% 37%	6245
	21st to end	Day	8% 2 4 36% 36% 14%	6310
August	1st to 10th	Day	13% 2 6% 21% 40% 18%	4206
	11th to 20th	Day	10% 3 7% 36% 34% 11%	4195
	21st to end	Day	12% 3 7% 31% 37% 10%	4355
September	1st to 10th	Day	13% 2 5% 25% 34% 22%	2400
	11th to 20th	Day	23% 4 10% 28% 25% 10%	2375
	21st to end	Day	22% 3 10% 26% 25% 15%	2116
October	1st to 10th	Day	20% 3 11% 16% 24% 25%	3280
	11th to 20th	Day	30% 4 18% 30% 14% 4	3261
	21st to end	Day	40% 7% 10% 22% 15% 6%	3558
November	1st to 10th	Day	49% 3 13% 19% 13% 2	1902
	11th to 20th	Day	51% 6% 14% 16% 9% 4	1680
	21st to end	Day	46% 5% 12% 18% 12% 7%	1680
December	1st to 10th	Day	32% 4 11% 25% 19% 8%	2700
	11th to 20th	Day	60% 4 15% 13% 7% 1	3108
	21st to end	Day	63% 5% 12% 16% 4 1	4092
January	1st to 10th	Night	62% 5% 12% 15% 5% 1	8172
	11th to 20th	Night	37% 3 7% 18% 19% 16%	7878
	21st to end	Night	47% 3 8% 14% 16% 13%	8371
February	1st to 10th	Night	49% 4 14% 18% 13% 3	2730
	11th to 20th	Night	52% 4 13% 20% 9% 2	2599
	21st to end	Night	50% 7% 15% 17% 9% 2	2030
March	1st to 10th	Night	55% 4 14% 20% 6% 1	5027
	11th to 20th	Night	45% 5% 11% 22% 15% 2	5000
	21st to end	Night	57% 4 17% 17% 4	5446
April	1st to 10th	Night	54% 5% 18% 17% 6% 1	2000
	11th to 20th	Night	47% 6% 16% 18% 9% 3	1979
	21st to end	Night	43% 7% 19% 22% 7% 1	1878
May	1st to 10th	Night	37% 5% 10% 28% 19% 2	4055
	11th to 20th	Night	37% 8% 10% 34% 10% 1	3616
	21st to end	Night	27% 4 26% 37% 5%	3972
June	1st to 10th	Night	37% 6% 18% 32% 7%	1600
	11th to 20th	Night	30% 5% 15% 36% 14% 1	1600
	21st to end	Night	18% 2 12% 41% 21% 5%	1600
July	1st to 10th	Night	11% 3 5% 29% 22% 30%	3600
	11th to 20th	Night	7% 1 3 18% 39% 32%	3592
	21st to end	Night	9% 2 6% 38% 34% 12%	4243
August	1st to 10th	Night	11% 2 5% 24% 49% 8%	2929
	11th to 20th	Night	9% 3 9% 41% 27% 10%	2929
	21st to end	Night	16% 3 6% 34% 31% 9%	3561
September	1st to 10th	Night	11% 2 6% 28% 35% 18%	2000
	11th to 20th	Night	21% 3 11% 31% 25% 8%	2021
	21st to end	Night	25% 2 11% 27% 19% 16%	2283
October	1st to 10th	Night	21% 3 7% 20% 26% 23%	3920
	11th to 20th	Night	31% 3 15% 34% 12% 6%	3897
	21st to end	Night	41% 5% 12% 21% 14% 6%	4253
November	1st to 10th	Night	50% 4 14% 16% 12% 5%	2613
	11th to 20th	Night	53% 5% 14% 14% 9% 5%	2940
	21st to end	Night	45% 4 12% 15% 16% 8%	2940
December	1st to 10th	Night	33% 4 10% 23% 23% 7%	4700
	11th to 20th	Night	59% 5% 13% 14% 7% 1	5316
	21st to end	Night	58% 5% 13% 18% 5% 1	7106

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	31% 13% 27% 21% 5% 2	220
	11th to 20th	Day	22% 12% 27% 22% 11% 5%	341
	21st to end	Day	23% 14% 24% 23% 15% 2	473
February	1st to 10th	Day	23% 15% 30% 23% 8% 1	430
	11th to 20th	Day	26% 19% 28% 19% 7% 1	411
	21st to end	Day	28% 17% 28% 23% 5%	389
March	1st to 10th	Day	29% 19% 26% 19% 7%	500
	11th to 20th	Day	26% 16% 28% 21% 9% 1	500
	21st to end	Day	29% 18% 28% 18% 6% 1	550
April	1st to 10th	Day	24% 20% 28% 20% 7% 1	500
	11th to 20th	Day	26% 19% 27% 20% 6% 2	492
	21st to end	Day	24% 16% 27% 22% 9% 2	500
May	1st to 10th	Day	20% 16% 32% 20% 10% 3	503
	11th to 20th	Day	22% 15% 27% 24% 7% 4	528
	21st to end	Day	21% 11% 26% 27% 9% 6%	573
June	1st to 10th	Day	17% 15% 27% 25% 12% 5%	530
	11th to 20th	Day	13% 19% 29% 26% 10% 3	530
	21st to end	Day	5% 10% 35% 33% 11% 7%	530
July	1st to 10th	Day	6% 11% 33% 29% 15% 6%	526
	11th to 20th	Day	3 9% 36% 31% 14% 8%	524
	21st to end	Day	3 6% 34% 33% 14% 10%	575
August	1st to 10th	Day	3 8% 30% 35% 15% 9%	527
	11th to 20th	Day	3 10% 27% 35% 16% 9%	517
	21st to end	Day	5% 10% 27% 36% 14% 7%	583
September	1st to 10th	Day	5% 9% 28% 38% 16% 5%	530
	11th to 20th	Day	9% 10% 27% 36% 15% 3	530
	21st to end	Day	11% 9% 28% 34% 15% 3	530
October	1st to 10th	Day	14% 10% 27% 32% 15% 2	530
	11th to 20th	Day	14% 8% 28% 31% 17% 2	530
	21st to end	Day	18% 12% 29% 26% 13% 3	583
November	1st to 10th	Day	21% 10% 25% 27% 14% 2	384
	11th to 20th	Day	20% 10% 25% 26% 15% 4	220
	21st to end	Day	17% 10% 30% 25% 15% 2	220
December	1st to 10th	Day	19% 8% 28% 25% 14% 5%	220
	11th to 20th	Day	26% 11% 23% 26% 9% 5%	220
	21st to end	Day	31% 8% 25% 22% 11% 2	242
January	1st to 10th	Night	23% 10% 27% 27% 10% 3	840
	11th to 20th	Night	18% 10% 25% 30% 14% 4	840
	21st to end	Night	19% 7% 24% 32% 16% 2	924
February	1st to 10th	Night	19% 9% 22% 35% 13% 1	840
	11th to 20th	Night	22% 10% 24% 30% 13% 2	804
	21st to end	Night	18% 12% 22% 33% 14% 1	660
March	1st to 10th	Night	25% 12% 20% 29% 12% 3	800
	11th to 20th	Night	20% 9% 22% 30% 17% 2	800
	21st to end	Night	22% 15% 19% 29% 14% 1	880
April	1st to 10th	Night	22% 10% 21% 31% 15% 2	800
	11th to 20th	Night	20% 8% 21% 31% 16% 4	791
	21st to end	Night	23% 6% 15% 32% 22% 3	678
May	1st to 10th	Night	19% 6% 14% 34% 23% 5%	584
	11th to 20th	Night	17% 5% 13% 34% 28% 3	394
	21st to end	Night	18% 5% 12% 31% 30% 4	433
June	1st to 10th	Night	14% 5% 9% 34% 34% 4	400
	11th to 20th	Night	14% 5% 12% 42% 25% 3	400
	21st to end	Night	6% 4 7% 38% 42% 3	400
July	1st to 10th	Night	3 1 7% 33% 53% 3	390
	11th to 20th	Night	4 1 5% 37% 49% 3	388
	21st to end	Night	2 1 3 27% 58% 9%	604
August	1st to 10th	Night	3 1 4 29% 54% 9%	597
	11th to 20th	Night	2 1 5% 32% 51% 9%	594
	21st to end	Night	3 2 13% 34% 41% 7%	846
September	1st to 10th	Night	4 3 11% 34% 42% 6%	800
	11th to 20th	Night	7% 3 12% 34% 36% 8%	800
	21st to end	Night	12% 3 11% 35% 31% 8%	800
October	1st to 10th	Night	10% 3 14% 40% 29% 5%	800
	11th to 20th	Night	12% 5% 15% 37% 26% 6%	800
	21st to end	Night	15% 5% 17% 36% 20% 7%	880
November	1st to 10th	Night	22% 5% 19% 33% 17% 4	820
	11th to 20th	Night	21% 8% 25% 33% 12% 2	840
	21st to end	Night	19% 8% 21% 34% 15% 1	840
December	1st to 10th	Night	19% 9% 21% 33% 16% 2	840
	11th to 20th	Night	22% 11% 27% 25% 12% 3	840
	21st to end	Night	28% 11% 26% 26% 8% 1	924

Page generated at 2026-02-12 22:42:11. Version ac07

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