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 2024-11-30.

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	8% 8% 2 6% 4 4 4 3 5% 6% 51%	105533
	Night	9% 9% 3 6% 4 4 4 3 5% 6% 46%	102771
Transparency	Day	34% 4 11% 23% 19% 9%	105285
	Night	39% 4 12% 22% 16% 7%	102608
Seeing	Day	17% 13% 28% 27% 11% 4	15020
	Night	16% 7% 17% 32% 24% 4	24096

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	12% 18% 6% 11% 6% 5% 5% 4 6% 7% 20%	2539
	11th to 20th	Day	19% 15% 4 8% 6% 5% 4 4 5% 6% 23%	2714
	21st to end	Day	14% 13% 4 10% 5% 6% 4 4 6% 7% 28%	3146
February	1st to 10th	Day	7% 13% 4 9% 6% 5% 6% 7% 6% 7% 30%	1710
	11th to 20th	Day	10% 12% 4 8% 6% 5% 4 4 6% 7% 35%	1665
	21st to end	Day	11% 17% 4 10% 6% 5% 3 3 6% 6% 29%	1522
March	1st to 10th	Day	12% 16% 4 12% 6% 5% 4 4 5% 5% 25%	3379
	11th to 20th	Day	8% 9% 3 6% 4 4 4 3 5% 5% 48%	3490
	21st to end	Day	11% 15% 5% 11% 6% 6% 6% 5% 6% 8% 22%	3853
April	1st to 10th	Day	11% 14% 5% 11% 7% 5% 4 4 6% 6% 28%	2280
	11th to 20th	Day	13% 14% 4 8% 5% 5% 5% 3 6% 7% 31%	2249
	21st to end	Day	12% 11% 3 7% 5% 3 4 3 7% 9% 37%	2393
May	1st to 10th	Day	10% 10% 3 7% 4 4 3 3 4 7% 46%	4136
	11th to 20th	Day	6% 7% 2 4 3 2 3 3 4 6% 61%	4377
	21st to end	Day	10% 8% 2 4 3 3 4 3 5% 7% 51%	4813
June	1st to 10th	Day	11% 8% 3 5% 5% 4 3 4 6% 8% 44%	2660
	11th to 20th	Day	7% 6% 2 5% 3 4 4 3 4 7% 55%	2660
	21st to end	Day	4 3 1 3 2 2 3 2 4 5% 70%	2660
July	1st to 10th	Day	1 2 1 1 1 1 1 2 3 87%	4420
	11th to 20th	Day	2 2 1 2 2 2 2 2 2 3 79%	4420
	21st to end	Day	1 1 1 1 1 2 2 2 2 86%	4525
August	1st to 10th	Day	2 2 1 2 2 2 2 2 3 5% 76%	4091
	11th to 20th	Day	1 1 1 2 1 2 2 2 3 4 79%	4026
	21st to end	Day	2 2 1 3 2 2 2 2 3 4 77%	4223
September	1st to 10th	Day	2 2 1 2 2 2 2 2 4 5% 77%	2280
	11th to 20th	Day	5% 4 2 4 3 3 4 4 5% 6% 60%	2256
	21st to end	Day	6% 3 2 4 3 2 3 3 4 7% 63%	2010
October	1st to 10th	Day	5% 3 1 3 3 2 3 2 3 5% 70%	3180
	11th to 20th	Day	5% 6% 2 6% 4 4 4 3 6% 9% 51%	3161
	21st to end	Day	11% 8% 3 7% 6% 4 5% 4 5% 7% 40%	3448
November	1st to 10th	Day	14% 9% 3 8% 6% 4 4 4 6% 8% 33%	1810
	11th to 20th	Day	13% 9% 2 10% 6% 5% 5% 4 8% 9% 27%	1600
	21st to end	Day	11% 12% 4 6% 5% 5% 5% 5% 5% 8% 35%	1595
December	1st to 10th	Day	9% 10% 2 6% 5% 5% 4 5% 7% 8% 38%	1520
	11th to 20th	Day	13% 13% 4 9% 6% 5% 5% 4 6% 8% 26%	1928
	21st to end	Day	13% 14% 4 9% 7% 6% 6% 4 7% 8% 20%	2794
January	1st to 10th	Night	13% 14% 5% 11% 7% 6% 6% 6% 6% 7% 19%	4406
	11th to 20th	Night	16% 16% 5% 9% 5% 4 4 3 5% 6% 25%	4234
	21st to end	Night	17% 16% 4 10% 5% 5% 5% 3 5% 5% 25%	4521
February	1st to 10th	Night	9% 14% 3 8% 5% 4 4 4 7% 8% 33%	2470
	11th to 20th	Night	10% 15% 5% 8% 5% 5% 5% 3 6% 6% 33%	2402
	21st to end	Night	8% 15% 4 8% 5% 5% 5% 5% 7% 8% 30%	1932
March	1st to 10th	Night	12% 15% 4 8% 6% 6% 6% 4 6% 7% 25%	3491
	11th to 20th	Night	7% 11% 3 7% 5% 4 4 3 4 5% 49%	3490
	21st to end	Night	10% 14% 4 11% 7% 7% 6% 4 6% 6% 24%	3798
April	1st to 10th	Night	12% 17% 4 8% 5% 5% 5% 4 5% 7% 30%	1900
	11th to 20th	Night	10% 14% 3 8% 5% 4 4 5% 6% 6% 34%	1879
	21st to end	Night	15% 11% 2 6% 3 3 4 4 7% 9% 36%	1784
May	1st to 10th	Night	12% 11% 4 9% 4 3 3 3 4 5% 43%	2832
	11th to 20th	Night	6% 5% 2 6% 3 4 3 3 4 4 59%	2516
	21st to end	Night	15% 8% 2 5% 3 3 3 2 4 5% 50%	2762
June	1st to 10th	Night	12% 7% 2 4 4 5% 5% 4 7% 6% 45%	1520
	11th to 20th	Night	9% 6% 2 5% 4 2 3 2 5% 6% 55%	1520
	21st to end	Night	5% 3 1 3 2 2 2 2 4 4 73%	1520
July	1st to 10th	Night	1 1 1 2 2 2 1 2 3 85%	2540
	11th to 20th	Night	2 1 1 2 2 2 2 2 2 4 82%	2540
	21st to end	Night	1 1 1 1 1 2 1 2 3 86%	3032
August	1st to 10th	Night	2 1 1 2 2 2 2 2 3 4 80%	2848
	11th to 20th	Night	1 1 2 2 2 2 2 4 6% 78%	2812
	21st to end	Night	4 3 1 3 2 2 2 2 3 3 75%	3452
September	1st to 10th	Night	3 2 1 2 1 1 1 1 4 5% 81%	1900
	11th to 20th	Night	5% 4 1 4 3 2 3 3 6% 7% 63%	1920
	21st to end	Night	8% 4 1 4 3 3 3 2 4 6% 63%	2169
October	1st to 10th	Night	5% 3 1 3 3 3 3 2 3 3 72%	3800
	11th to 20th	Night	9% 6% 2 5% 3 3 3 3 5% 6% 55%	3777
	21st to end	Night	8% 9% 3 8% 5% 5% 5% 4 5% 8% 40%	4121
November	1st to 10th	Night	14% 12% 3 7% 6% 4 5% 4 6% 6% 34%	2485
	11th to 20th	Night	14% 10% 3 8% 6% 6% 6% 4 7% 8% 28%	2800
	21st to end	Night	13% 11% 3 6% 5% 5% 4 3 5% 7% 38%	2800
December	1st to 10th	Night	11% 10% 3 6% 4 4 4 4 7% 8% 38%	2660
	11th to 20th	Night	11% 13% 4 10% 6% 7% 6% 5% 7% 8% 24%	3276
	21st to end	Night	13% 15% 4 9% 6% 6% 5% 4 6% 6% 25%	4862

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	63% 3 14% 14% 4 1	2539
	11th to 20th	Day	61% 3 10% 14% 7% 5%	2714
	21st to end	Day	55% 2 16% 16% 7% 3	3146
February	1st to 10th	Day	51% 5% 17% 15% 10% 2	1710
	11th to 20th	Day	49% 4 15% 21% 9% 2	1674
	21st to end	Day	57% 4 10% 17% 10% 2	1522
March	1st to 10th	Day	61% 3 10% 19% 7%	3379
	11th to 20th	Day	39% 3 13% 19% 24% 2	3490
	21st to end	Day	60% 4 16% 17% 3	3853
April	1st to 10th	Day	57% 5% 13% 15% 8% 2	2280
	11th to 20th	Day	53% 5% 16% 15% 8% 4	2252
	21st to end	Day	44% 5% 16% 22% 11% 1	2393
May	1st to 10th	Day	40% 3 12% 27% 15% 3	4136
	11th to 20th	Day	25% 4 8% 31% 27% 5%	4380
	21st to end	Day	33% 5% 20% 34% 8%	4814
June	1st to 10th	Day	40% 4 16% 29% 11%	2660
	11th to 20th	Day	30% 4 12% 35% 16% 2	2660
	21st to end	Day	18% 2 11% 34% 26% 8%	2660
July	1st to 10th	Day	7% 2 5% 16% 23% 48%	4351
	11th to 20th	Day	11% 2 3 16% 29% 38%	4345
	21st to end	Day	7% 2 3 21% 46% 21%	4382
August	1st to 10th	Day	13% 2 6% 19% 41% 19%	4076
	11th to 20th	Day	10% 3 6% 36% 34% 11%	4065
	21st to end	Day	12% 3 7% 32% 36% 10%	4222
September	1st to 10th	Day	12% 2 4 24% 35% 23%	2280
	11th to 20th	Day	24% 4 10% 28% 25% 10%	2256
	21st to end	Day	22% 3 11% 26% 24% 14%	2010
October	1st to 10th	Day	19% 3 11% 16% 24% 26%	3180
	11th to 20th	Day	30% 4 18% 29% 14% 4	3161
	21st to end	Day	41% 7% 10% 22% 15% 6%	3448
November	1st to 10th	Day	49% 3 13% 19% 13% 3	1810
	11th to 20th	Day	50% 6% 14% 16% 9% 4	1600
	21st to end	Day	47% 6% 11% 17% 12% 7%	1595
December	1st to 10th	Day	42% 4 14% 21% 16% 3	1520
	11th to 20th	Day	57% 3 17% 13% 8% 1	1928
	21st to end	Day	59% 3 15% 17% 5% 2	2794
January	1st to 10th	Night	63% 5% 13% 13% 5% 2	4406
	11th to 20th	Night	60% 4 10% 14% 8% 5%	4234
	21st to end	Night	62% 2 10% 14% 9% 3	4521
February	1st to 10th	Night	48% 4 15% 18% 12% 2	2470
	11th to 20th	Night	52% 4 12% 21% 9% 2	2404
	21st to end	Night	51% 7% 15% 16% 8% 2	1932
March	1st to 10th	Night	57% 4 13% 21% 5%	3491
	11th to 20th	Night	39% 4 12% 23% 19% 3	3490
	21st to end	Night	60% 4 17% 16% 3	3798
April	1st to 10th	Night	54% 4 17% 17% 6% 1	1900
	11th to 20th	Night	49% 6% 17% 17% 8% 3	1879
	21st to end	Night	43% 8% 20% 22% 6% 1	1784
May	1st to 10th	Night	43% 6% 13% 26% 11% 2	2832
	11th to 20th	Night	26% 7% 10% 42% 13% 2	2516
	21st to end	Night	37% 5% 27% 29% 3	2762
June	1st to 10th	Night	39% 6% 19% 31% 6%	1520
	11th to 20th	Night	31% 5% 15% 35% 13% 1	1520
	21st to end	Night	18% 2 12% 41% 21% 5%	1520
July	1st to 10th	Night	8% 2 5% 19% 22% 44%	2500
	11th to 20th	Night	10% 1 4 19% 35% 31%	2492
	21st to end	Night	6% 2 5% 23% 48% 17%	2937
August	1st to 10th	Night	11% 2 5% 23% 51% 9%	2839
	11th to 20th	Night	9% 3 9% 41% 27% 10%	2839
	21st to end	Night	16% 3 7% 34% 31% 9%	3452
September	1st to 10th	Night	10% 1 5% 28% 37% 19%	1900
	11th to 20th	Night	21% 3 11% 31% 26% 8%	1920
	21st to end	Night	25% 2 12% 26% 19% 16%	2169
October	1st to 10th	Night	20% 3 7% 20% 26% 24%	3800
	11th to 20th	Night	31% 3 14% 35% 12% 6%	3777
	21st to end	Night	42% 5% 12% 20% 14% 7%	4121
November	1st to 10th	Night	50% 4 13% 16% 12% 5%	2485
	11th to 20th	Night	52% 6% 14% 15% 9% 5%	2800
	21st to end	Night	46% 4 12% 14% 16% 8%	2800
December	1st to 10th	Night	43% 5% 11% 22% 15% 3	2660
	11th to 20th	Night	56% 4 13% 15% 11% 1	3276
	21st to end	Night	58% 4 13% 17% 6% 2	4862

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	33% 12% 27% 20% 5% 2	180
	11th to 20th	Day	26% 14% 28% 18% 10% 3	289
	21st to end	Day	26% 15% 23% 21% 14% 1	407
February	1st to 10th	Day	22% 15% 31% 23% 8% 1	370
	11th to 20th	Day	26% 20% 27% 19% 7% 1	365
	21st to end	Day	28% 18% 27% 23% 4	359
March	1st to 10th	Day	31% 18% 25% 18% 7%	460
	11th to 20th	Day	24% 16% 28% 22% 10% 1	460
	21st to end	Day	29% 19% 28% 18% 6%	506
April	1st to 10th	Day	24% 20% 28% 20% 7% 1	460
	11th to 20th	Day	28% 19% 26% 20% 5% 2	452
	21st to end	Day	24% 17% 27% 21% 8% 2	460
May	1st to 10th	Day	21% 15% 32% 20% 9% 3	463
	11th to 20th	Day	22% 14% 27% 25% 8% 4	488
	21st to end	Day	21% 11% 25% 28% 9% 6%	529
June	1st to 10th	Day	18% 15% 28% 23% 12% 5%	490
	11th to 20th	Day	13% 19% 29% 26% 10% 3	490
	21st to end	Day	4 10% 35% 33% 11% 7%	490
July	1st to 10th	Day	6% 11% 33% 28% 15% 6%	486
	11th to 20th	Day	3 9% 37% 30% 13% 8%	484
	21st to end	Day	3 6% 34% 33% 14% 10%	531
August	1st to 10th	Day	3 8% 31% 34% 15% 8%	487
	11th to 20th	Day	3 11% 27% 35% 16% 8%	477
	21st to end	Day	6% 10% 27% 37% 15% 6%	539
September	1st to 10th	Day	4 9% 27% 39% 16% 5%	490
	11th to 20th	Day	9% 11% 28% 35% 16% 2	490
	21st to end	Day	11% 9% 29% 33% 15% 3	490
October	1st to 10th	Day	13% 10% 27% 33% 16% 2	490
	11th to 20th	Day	14% 9% 27% 30% 18% 2	490
	21st to end	Day	18% 12% 29% 25% 13% 3	539
November	1st to 10th	Day	21% 10% 25% 28% 14% 2	352
	11th to 20th	Day	21% 11% 26% 25% 15% 4	200
	21st to end	Day	19% 10% 30% 24% 16% 2	199
December	1st to 10th	Day	22% 10% 28% 23% 13% 4	180
	11th to 20th	Day	28% 9% 22% 28% 9% 4	180
	21st to end	Day	34% 6% 23% 23% 12% 2	198
January	1st to 10th	Night	23% 10% 27% 26% 11% 3	760
	11th to 20th	Night	19% 11% 26% 28% 12% 4	760
	21st to end	Night	20% 7% 23% 31% 16% 3	836
February	1st to 10th	Night	19% 9% 22% 36% 14% 1	760
	11th to 20th	Night	22% 9% 22% 31% 14% 2	744
	21st to end	Night	17% 12% 22% 33% 14% 1	628
March	1st to 10th	Night	24% 12% 20% 29% 12% 3	760
	11th to 20th	Night	19% 8% 21% 31% 18% 2	760
	21st to end	Night	22% 15% 20% 29% 14% 1	836
April	1st to 10th	Night	23% 9% 20% 31% 16% 2	760
	11th to 20th	Night	20% 8% 21% 30% 16% 5%	751
	21st to end	Night	23% 6% 15% 31% 23% 3	644
May	1st to 10th	Night	19% 6% 14% 33% 23% 5%	555
	11th to 20th	Night	15% 5% 13% 34% 30% 3	374
	21st to end	Night	18% 5% 12% 30% 29% 4	411
June	1st to 10th	Night	15% 6% 9% 33% 33% 4	380
	11th to 20th	Night	15% 4 12% 41% 26% 3	380
	21st to end	Night	6% 3 7% 38% 43% 3	380
July	1st to 10th	Night	3 1 7% 32% 54% 3	370
	11th to 20th	Night	4 1 5% 38% 48% 3	368
	21st to end	Night	2 1 3 27% 57% 9%	573
August	1st to 10th	Night	3 1 3 29% 55% 10%	567
	11th to 20th	Night	2 5% 32% 51% 10%	564
	21st to end	Night	4 2 13% 33% 42% 7%	803
September	1st to 10th	Night	4 3 11% 33% 43% 6%	760
	11th to 20th	Night	6% 3 12% 34% 37% 9%	760
	21st to end	Night	12% 3 11% 34% 31% 9%	760
October	1st to 10th	Night	9% 3 14% 40% 30% 5%	760
	11th to 20th	Night	12% 5% 14% 37% 27% 6%	760
	21st to end	Night	15% 4 17% 36% 20% 8%	836
November	1st to 10th	Night	22% 5% 19% 34% 17% 4	780
	11th to 20th	Night	20% 8% 25% 33% 12% 2	800
	21st to end	Night	20% 9% 21% 33% 16% 1	800
December	1st to 10th	Night	20% 10% 21% 32% 15% 2	760
	11th to 20th	Night	22% 11% 27% 26% 12% 3	760
	21st to end	Night	28% 12% 25% 26% 8% 1	836

Page generated at 2024-11-27 14:30:52. Version ac07

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