Bear Creek Observatory
Clear Sky Chart
History

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

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	22% 9% 3 7% 5% 4 4 3 5% 6% 33%	105733
	Night	25% 10% 3 7% 5% 4 4 3 4 5% 30%	101873
Transparency	Day	54% 3 13% 19% 9% 1	105491
	Night	59% 3 12% 18% 7% 1	101761
Seeing	Day	27% 8% 17% 26% 17% 5%	15061
	Night	32% 6% 10% 26% 21% 4	23419

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	39% 17% 4 8% 5% 4 4 2 3 4 11%	2295
	11th to 20th	Day	27% 13% 4 8% 5% 4 4 3 5% 6% 21%	2516
	21st to end	Day	41% 14% 3 8% 5% 4 3 3 4 4 11%	2840
February	1st to 10th	Day	33% 12% 5% 9% 5% 4 5% 4 4 5% 16%	1710
	11th to 20th	Day	29% 14% 4 8% 5% 4 4 3 4 5% 20%	1665
	21st to end	Day	29% 15% 4 7% 6% 4 4 4 4 4 20%	1484
March	1st to 10th	Day	21% 14% 4 9% 7% 5% 5% 4 5% 6% 20%	3194
	11th to 20th	Day	20% 10% 3 7% 4 4 5% 3 4 5% 35%	3490
	21st to end	Day	27% 12% 4 10% 6% 5% 5% 4 5% 7% 15%	3969
April	1st to 10th	Day	27% 13% 4 8% 6% 5% 4 4 5% 6% 18%	2280
	11th to 20th	Day	23% 11% 3 7% 6% 5% 5% 4 5% 6% 25%	2265
	21st to end	Day	22% 11% 3 9% 7% 5% 5% 4 5% 6% 22%	2525
May	1st to 10th	Day	18% 8% 3 5% 5% 4 4 4 5% 7% 37%	4420
	11th to 20th	Day	19% 7% 2 6% 4 4 4 4 5% 10% 35%	4377
	21st to end	Day	30% 10% 4 9% 6% 5% 4 3 4 6% 20%	4813
June	1st to 10th	Day	23% 8% 3 7% 5% 5% 5% 3 6% 7% 28%	2689
	11th to 20th	Day	25% 10% 3 7% 6% 5% 5% 4 5% 6% 24%	2850
	21st to end	Day	14% 7% 2 7% 5% 4 5% 4 6% 7% 39%	2850
July	1st to 10th	Day	8% 4 2 4 3 2 3 3 4 5% 63%	4740
	11th to 20th	Day	6% 3 1 3 2 3 2 3 4 5% 68%	4501
	21st to end	Day	12% 4 2 5% 2 3 3 3 4 5% 58%	4790
August	1st to 10th	Day	7% 3 1 3 2 3 3 3 5% 7% 63%	4350
	11th to 20th	Day	10% 6% 3 7% 5% 4 5% 4 6% 9% 41%	4026
	21st to end	Day	17% 8% 3 7% 4 3 3 3 4 7% 42%	4318
September	1st to 10th	Day	11% 5% 2 7% 4 4 3 2 4 7% 49%	2280
	11th to 20th	Day	16% 7% 3 9% 5% 4 4 4 5% 7% 37%	2280
	21st to end	Day	20% 7% 3 6% 5% 4 5% 3 5% 6% 37%	2013
October	1st to 10th	Day	16% 7% 2 6% 4 5% 5% 4 6% 10% 36%	3180
	11th to 20th	Day	31% 9% 3 8% 4 4 4 3 4 6% 24%	3161
	21st to end	Day	30% 11% 3 9% 5% 5% 4 3 6% 6% 18%	3233
November	1st to 10th	Day	39% 10% 3 6% 4 4 3 4 4 6% 17%	1578
	11th to 20th	Day	34% 12% 2 6% 4 4 4 3 4 4 22%	1520
	21st to end	Day	36% 10% 3 6% 5% 4 3 3 5% 5% 20%	1520
December	1st to 10th	Day	30% 13% 3 8% 5% 5% 3 3 4 5% 23%	1520
	11th to 20th	Day	33% 14% 4 7% 5% 5% 5% 3 4 5% 15%	1925
	21st to end	Day	29% 12% 5% 11% 6% 5% 5% 4 4 5% 14%	2566
January	1st to 10th	Night	39% 14% 4 9% 5% 4 4 3 4 3 11%	4629
	11th to 20th	Night	29% 13% 4 7% 4 3 3 3 4 7% 23%	4382
	21st to end	Night	38% 13% 4 8% 5% 4 4 3 4 5% 13%	4800
February	1st to 10th	Night	33% 12% 4 8% 6% 4 3 3 4 5% 18%	2470
	11th to 20th	Night	28% 14% 3 7% 5% 5% 4 3 4 6% 22%	2402
	21st to end	Night	30% 14% 4 7% 5% 3 4 3 4 6% 21%	1970
March	1st to 10th	Night	19% 14% 4 9% 7% 5% 6% 5% 6% 6% 18%	3679
	11th to 20th	Night	20% 9% 2 6% 4 3 4 2 4 6% 39%	3489
	21st to end	Night	30% 14% 4 9% 5% 5% 4 3 5% 4 16%	3684
April	1st to 10th	Night	26% 11% 3 8% 6% 5% 6% 5% 7% 6% 18%	1900
	11th to 20th	Night	21% 10% 3 8% 5% 5% 4 4 5% 5% 29%	1862
	21st to end	Night	25% 11% 4 8% 5% 5% 3 4 5% 6% 25%	1653
May	1st to 10th	Night	20% 8% 3 7% 4 3 4 3 4 4 40%	2540
	11th to 20th	Night	19% 7% 3 7% 4 4 4 3 4 7% 38%	2516
	21st to end	Night	29% 11% 3 9% 6% 5% 5% 3 4 4 21%	2762
June	1st to 10th	Night	21% 7% 3 7% 6% 5% 5% 3 6% 5% 31%	1486
	11th to 20th	Night	25% 11% 4 8% 5% 4 4 3 6% 5% 26%	1330
	21st to end	Night	14% 5% 2 7% 6% 4 4 3 6% 7% 43%	1330
July	1st to 10th	Night	11% 5% 2 4 3 2 2 2 3 4 61%	2220
	11th to 20th	Night	5% 3 1 3 2 2 2 2 3 4 73%	2444
	21st to end	Night	12% 4 2 4 3 3 3 3 5% 6% 56%	2762
August	1st to 10th	Night	6% 2 1 3 3 2 3 2 4 5% 69%	2578
	11th to 20th	Night	15% 5% 2 5% 3 3 3 3 4 7% 50%	2812
	21st to end	Night	19% 6% 2 5% 4 3 3 2 3 4 48%	3356
September	1st to 10th	Night	10% 5% 2 6% 3 3 3 3 4 6% 54%	1900
	11th to 20th	Night	17% 8% 3 7% 5% 3 4 3 5% 5% 41%	1900
	21st to end	Night	19% 7% 2 6% 4 5% 3 3 4 5% 39%	2165
October	1st to 10th	Night	17% 7% 2 6% 5% 4 4 3 6% 9% 37%	3800
	11th to 20th	Night	29% 8% 2 7% 3 5% 4 3 4 6% 29%	3777
	21st to end	Night	32% 12% 3 8% 4 4 4 3 4 5% 21%	4327
November	1st to 10th	Night	35% 10% 3 7% 5% 4 4 3 5% 5% 20%	2620
	11th to 20th	Night	35% 9% 3 7% 5% 4 4 2 4 3 23%	2660
	21st to end	Night	34% 9% 3 8% 5% 4 4 3 4 5% 22%	2660
December	1st to 10th	Night	31% 11% 3 7% 5% 4 4 3 4 5% 24%	2660
	11th to 20th	Night	31% 14% 4 8% 5% 5% 5% 3 5% 3 16%	3280
	21st to end	Night	30% 15% 4 11% 6% 5% 4 3 4 4 14%	5068

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	81% 1 6% 9% 2 1	2295
	11th to 20th	Day	65% 2 10% 15% 6% 1	2540
	21st to end	Day	78% 2 8% 9% 3	2840
February	1st to 10th	Day	71% 4 11% 10% 3 1	1710
	11th to 20th	Day	70% 3 9% 10% 7% 1	1674
	21st to end	Day	70% 2 10% 12% 5%	1484
March	1st to 10th	Day	67% 1 10% 17% 5%	3194
	11th to 20th	Day	54% 2 15% 26% 3 1	3490
	21st to end	Day	72% 2 13% 12% 1	3969
April	1st to 10th	Day	70% 4 14% 11% 1	2280
	11th to 20th	Day	64% 3 12% 13% 7% 1	2265
	21st to end	Day	65% 4 12% 13% 5% 1	2525
May	1st to 10th	Day	52% 2 11% 23% 12%	4420
	11th to 20th	Day	48% 4 23% 21% 4	4380
	21st to end	Day	69% 2 18% 10% 1	4814
June	1st to 10th	Day	60% 4 17% 14% 5%	2689
	11th to 20th	Day	65% 3 15% 13% 4	2850
	21st to end	Day	47% 4 21% 20% 8% 1	2850
July	1st to 10th	Day	27% 3 9% 23% 25% 13%	4666
	11th to 20th	Day	23% 3 9% 31% 33% 3	4423
	21st to end	Day	30% 3 17% 34% 15% 2	4639
August	1st to 10th	Day	23% 4 13% 42% 16% 1	4333
	11th to 20th	Day	41% 7% 21% 22% 7% 2	4065
	21st to end	Day	44% 3 13% 29% 11% 1	4317
September	1st to 10th	Day	38% 3 15% 27% 12% 5%	2280
	11th to 20th	Day	49% 3 13% 19% 13% 2	2280
	21st to end	Day	49% 4 16% 19% 9% 2	2013
October	1st to 10th	Day	43% 4 15% 31% 6%	3180
	11th to 20th	Day	62% 3 11% 16% 7%	3161
	21st to end	Day	67% 4 11% 9% 8% 1	3233
November	1st to 10th	Day	71% 3 11% 11% 4	1578
	11th to 20th	Day	69% 3 9% 11% 7% 2	1520
	21st to end	Day	68% 3 7% 12% 8% 2	1520
December	1st to 10th	Day	66% 5% 8% 12% 8% 1	1520
	11th to 20th	Day	71% 3 10% 13% 3 1	1928
	21st to end	Day	73% 2 11% 11% 3	2566
January	1st to 10th	Night	80% 2 6% 8% 2 1	4629
	11th to 20th	Night	64% 2 8% 19% 6% 1	4420
	21st to end	Night	76% 1 9% 9% 4 1	4800
February	1st to 10th	Night	71% 3 10% 10% 5% 1	2470
	11th to 20th	Night	65% 3 12% 11% 7% 1	2404
	21st to end	Night	68% 3 10% 13% 5% 1	1970
March	1st to 10th	Night	66% 2 11% 16% 5%	3679
	11th to 20th	Night	50% 3 19% 25% 3 1	3490
	21st to end	Night	72% 2 15% 10% 1	3684
April	1st to 10th	Night	66% 5% 14% 12% 3	1900
	11th to 20th	Night	59% 3 14% 14% 9% 1	1862
	21st to end	Night	64% 4 12% 14% 5% 1	1653
May	1st to 10th	Night	51% 2 11% 27% 8% 1	2540
	11th to 20th	Night	50% 3 21% 22% 4	2516
	21st to end	Night	71% 4 15% 9% 1	2762
June	1st to 10th	Night	58% 3 16% 19% 5%	1486
	11th to 20th	Night	63% 5% 14% 15% 2	1330
	21st to end	Night	43% 4 23% 21% 7% 2	1330
July	1st to 10th	Night	31% 2 9% 21% 21% 17%	2185
	11th to 20th	Night	20% 2 8% 29% 40% 1	2399
	21st to end	Night	32% 4 12% 30% 20% 3	2674
August	1st to 10th	Night	20% 3 13% 42% 20% 2	2570
	11th to 20th	Night	39% 6% 21% 25% 8% 2	2839
	21st to end	Night	43% 3 16% 30% 9% 1	3356
September	1st to 10th	Night	35% 3 16% 29% 13% 4	1900
	11th to 20th	Night	48% 3 12% 20% 13% 4	1900
	21st to end	Night	47% 4 15% 21% 11% 2	2165
October	1st to 10th	Night	44% 5% 19% 29% 4	3800
	11th to 20th	Night	58% 3 13% 19% 7%	3777
	21st to end	Night	66% 5% 10% 12% 7%	4327
November	1st to 10th	Night	67% 3 13% 12% 3 1	2620
	11th to 20th	Night	68% 3 10% 11% 5% 2	2660
	21st to end	Night	68% 3 8% 12% 9% 1	2660
December	1st to 10th	Night	65% 4 10% 12% 8% 1	2660
	11th to 20th	Night	72% 2 11% 11% 3 1	3276
	21st to end	Night	75% 2 10% 11% 3	5068

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	40% 11% 10% 17% 12% 10%	180
	11th to 20th	Day	38% 8% 13% 17% 20% 4	180
	21st to end	Day	47% 12% 8% 16% 11% 6%	231
February	1st to 10th	Day	44% 7% 16% 19% 9% 4	370
	11th to 20th	Day	43% 11% 19% 16% 10% 2	365
	21st to end	Day	38% 12% 21% 19% 9% 2	341
March	1st to 10th	Day	36% 12% 20% 18% 11% 2	460
	11th to 20th	Day	32% 12% 17% 20% 15% 5%	460
	21st to end	Day	39% 10% 22% 19% 10% 1	506
April	1st to 10th	Day	36% 11% 20% 19% 12% 2	460
	11th to 20th	Day	29% 12% 25% 18% 10% 6%	452
	21st to end	Day	29% 10% 23% 22% 13% 2	460
May	1st to 10th	Day	20% 8% 21% 34% 14% 2	463
	11th to 20th	Day	27% 8% 16% 25% 16% 7%	488
	21st to end	Day	30% 8% 17% 24% 16% 5%	529
June	1st to 10th	Day	26% 8% 20% 26% 15% 4	519
	11th to 20th	Day	26% 11% 20% 26% 14% 3	680
	21st to end	Day	15% 5% 19% 35% 20% 5%	680
July	1st to 10th	Day	13% 4 17% 34% 27% 4	671
	11th to 20th	Day	9% 4 17% 35% 29% 6%	536
	21st to end	Day	11% 3 13% 39% 27% 7%	531
August	1st to 10th	Day	12% 4 12% 36% 24% 12%	487
	11th to 20th	Day	9% 2 15% 34% 30% 10%	477
	21st to end	Day	17% 6% 19% 31% 19% 8%	539
September	1st to 10th	Day	14% 8% 19% 34% 19% 5%	490
	11th to 20th	Day	20% 8% 14% 28% 25% 5%	490
	21st to end	Day	21% 8% 17% 29% 20% 6%	490
October	1st to 10th	Day	25% 8% 17% 25% 18% 8%	490
	11th to 20th	Day	34% 8% 13% 22% 15% 7%	490
	21st to end	Day	37% 10% 14% 21% 13% 4	412
November	1st to 10th	Day	43% 12% 10% 18% 15% 2	216
	11th to 20th	Day	42% 12% 10% 8% 19% 9%	180
	21st to end	Day	37% 8% 12% 19% 13% 11%	180
December	1st to 10th	Day	46% 7% 8% 13% 13% 14%	180
	11th to 20th	Day	42% 12% 11% 22% 12% 2	180
	21st to end	Day	41% 9% 11% 20% 16% 4	198
January	1st to 10th	Night	48% 9% 10% 16% 13% 3	822
	11th to 20th	Night	42% 8% 9% 20% 18% 4	760
	21st to end	Night	41% 6% 10% 25% 16% 3	836
February	1st to 10th	Night	43% 6% 10% 26% 12% 2	760
	11th to 20th	Night	39% 7% 11% 27% 15% 1	744
	21st to end	Night	41% 8% 11% 25% 12% 3	628
March	1st to 10th	Night	36% 7% 13% 26% 16% 2	760
	11th to 20th	Night	34% 9% 13% 26% 15% 3	760
	21st to end	Night	38% 8% 14% 28% 11% 2	836
April	1st to 10th	Night	35% 7% 15% 25% 16% 3	760
	11th to 20th	Night	29% 7% 15% 29% 16% 3	734
	21st to end	Night	32% 9% 11% 29% 16% 3	513
May	1st to 10th	Night	23% 10% 12% 31% 22% 2	380
	11th to 20th	Night	21% 7% 9% 27% 31% 5%	374
	21st to end	Night	27% 6% 12% 22% 28% 5%	411
June	1st to 10th	Night	24% 6% 11% 31% 25% 3	380
	11th to 20th	Night	31% 7% 10% 29% 21% 3	380
	21st to end	Night	16% 4 12% 31% 31% 6%	380
July	1st to 10th	Night	15% 4 9% 26% 40% 6%	370
	11th to 20th	Night	11% 3 6% 33% 43% 5%	368
	21st to end	Night	12% 1 6% 28% 45% 7%	416
August	1st to 10th	Night	10% 2 5% 24% 48% 11%	401
	11th to 20th	Night	11% 2 5% 24% 43% 15%	564
	21st to end	Night	18% 4 7% 27% 36% 8%	746
September	1st to 10th	Night	13% 4 7% 32% 37% 8%	760
	11th to 20th	Night	20% 5% 7% 24% 35% 10%	760
	21st to end	Night	24% 4 9% 28% 28% 7%	760
October	1st to 10th	Night	25% 4 9% 27% 30% 5%	760
	11th to 20th	Night	31% 7% 10% 24% 21% 7%	760
	21st to end	Night	38% 6% 12% 25% 15% 4	836
November	1st to 10th	Night	41% 7% 15% 25% 12% 1	764
	11th to 20th	Night	40% 8% 11% 23% 14% 3	760
	21st to end	Night	41% 7% 11% 22% 14% 5%	760
December	1st to 10th	Night	38% 6% 10% 26% 18% 3	760
	11th to 20th	Night	45% 8% 12% 23% 10% 2	760
	21st to end	Night	50% 8% 11% 20% 10% 1	896

Page generated at 2024-11-03 10:19:06. Version ac07

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