Camp Delany
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Camp Delany clear sky chart from 2005-11-06 to 2024-11-05.

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% 3 6% 4 4 4 4 5% 7% 50%	105323
	Night	8% 9% 3 7% 4 4 4 4 5% 7% 45%	102331
Transparency	Day	34% 5% 10% 23% 19% 9%	105092
	Night	38% 6% 11% 22% 16% 7%	102208
Seeing	Day	10% 8% 21% 29% 22% 9%	14300
	Night	13% 5% 19% 37% 22% 3	23297

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	15% 21% 6% 11% 6% 5% 4 3 4 4 20%	2539
	11th to 20th	Day	18% 14% 5% 10% 7% 5% 4 4 5% 5% 24%	2516
	21st to end	Day	24% 24% 9% 10% 3 4 3 2 4 4 14%	2794
February	1st to 10th	Day	12% 14% 5% 11% 7% 5% 5% 5% 7% 5% 26%	1618
	11th to 20th	Day	9% 13% 4 10% 5% 4 4 4 7% 8% 33%	1695
	21st to end	Day	7% 13% 4 10% 6% 5% 6% 4 5% 7% 34%	1570
March	1st to 10th	Day	7% 9% 3 7% 4 4 6% 5% 6% 9% 40%	3138
	11th to 20th	Day	5% 7% 2 5% 3 3 4 4 5% 7% 55%	3321
	21st to end	Day	8% 8% 3 8% 6% 5% 5% 5% 6% 8% 37%	4129
April	1st to 10th	Day	9% 8% 3 7% 7% 5% 4 5% 6% 9% 37%	2280
	11th to 20th	Day	6% 8% 2 6% 5% 5% 6% 5% 7% 8% 43%	2252
	21st to end	Day	5% 7% 3 8% 6% 5% 4 4 6% 9% 44%	2503
May	1st to 10th	Day	7% 6% 2 5% 3 3 3 4 5% 9% 54%	4420
	11th to 20th	Day	4 3 1 5% 3 4 4 4 7% 9% 56%	4377
	21st to end	Day	6% 7% 3 8% 6% 5% 6% 5% 6% 7% 40%	4813
June	1st to 10th	Day	8% 6% 2 7% 6% 5% 4 4 6% 8% 44%	2660
	11th to 20th	Day	7% 4 2 6% 4 5% 5% 4 7% 8% 48%	2660
	21st to end	Day	4 3 1 5% 3 3 3 3 5% 7% 61%	2660
July	1st to 10th	Day	1 1 1 2 1 2 2 2 3 4 80%	4420
	11th to 20th	Day	1 2 1 2 2 2 2 2 3 3 79%	4420
	21st to end	Day	1 1 1 2 2 2 2 2 3 5% 79%	4790
August	1st to 10th	Day	2 2 1 3 2 3 3 3 4 5% 72%	4401
	11th to 20th	Day	1 2 1 3 2 3 3 3 5% 6% 70%	4167
	21st to end	Day	3 4 2 5% 3 3 3 3 4 6% 64%	4180
September	1st to 10th	Day	3 3 1 3 2 3 3 3 4 7% 70%	2280
	11th to 20th	Day	4 3 2 6% 4 4 5% 4 6% 7% 56%	2247
	21st to end	Day	6% 5% 1 4 4 4 4 4 5% 7% 56%	2090
October	1st to 10th	Day	5% 4 2 3 3 4 3 3 5% 8% 61%	3187
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 5% 6% 7% 47%	3106
	21st to end	Day	9% 6% 2 6% 4 5% 5% 4 6% 7% 46%	3101
November	1st to 10th	Day	15% 10% 3 8% 6% 5% 5% 4 6% 7% 32%	1710
	11th to 20th	Day	12% 15% 4 9% 6% 4 4 4 5% 5% 32%	1520
	21st to end	Day	12% 14% 5% 11% 7% 5% 6% 4 5% 7% 25%	1520
December	1st to 10th	Day	12% 17% 4 11% 7% 4 5% 5% 5% 7% 24%	1520
	11th to 20th	Day	18% 18% 9% 15% 6% 5% 5% 3 4 5% 13%	1925
	21st to end	Day	12% 21% 7% 13% 6% 6% 4 4 4 6% 16%	2794
January	1st to 10th	Night	16% 19% 6% 11% 6% 5% 5% 4 5% 6% 18%	4406
	11th to 20th	Night	17% 13% 4 11% 5% 4 3 3 5% 9% 26%	4382
	21st to end	Night	20% 22% 10% 11% 4 4 3 3 4 5% 14%	4862
February	1st to 10th	Night	10% 13% 4 9% 6% 5% 4 4 6% 8% 30%	2561
	11th to 20th	Night	9% 10% 4 9% 5% 4 5% 5% 6% 7% 36%	2371
	21st to end	Night	8% 12% 4 8% 5% 6% 5% 4 6% 8% 33%	1884
March	1st to 10th	Night	7% 9% 2 6% 5% 4 5% 5% 8% 11% 38%	3736
	11th to 20th	Night	6% 6% 2 4 4 3 4 3 5% 6% 58%	3656
	21st to end	Night	7% 8% 3 9% 7% 6% 6% 6% 7% 9% 31%	3523
April	1st to 10th	Night	8% 9% 3 8% 6% 5% 4 4 6% 8% 40%	1900
	11th to 20th	Night	6% 9% 2 6% 5% 4 5% 4 6% 6% 46%	1879
	21st to end	Night	6% 6% 2 7% 6% 6% 5% 5% 6% 8% 44%	1674
May	1st to 10th	Night	4 5% 2 6% 4 4 4 4 5% 8% 54%	2540
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 7% 63%	2516
	21st to end	Night	5% 4 2 5% 4 4 5% 4 6% 9% 52%	2762
June	1st to 10th	Night	7% 6% 2 5% 6% 4 5% 4 6% 8% 47%	1520
	11th to 20th	Night	5% 4 1 5% 4 4 5% 5% 7% 8% 52%	1520
	21st to end	Night	3 3 1 5% 4 4 4 3 4 6% 62%	1520
July	1st to 10th	Night	1 1 1 2 1 2 2 2 3 4 82%	2540
	11th to 20th	Night	1 1 1 1 1 1 2 2 2 4 84%	2540
	21st to end	Night	1 1 1 1 1 2 2 2 4 4 82%	2762
August	1st to 10th	Night	2 3 1 3 2 2 2 3 3 6% 73%	2529
	11th to 20th	Night	1 3 1 4 3 3 4 3 5% 6% 68%	2662
	21st to end	Night	2 4 2 5% 3 3 3 3 5% 6% 66%	3498
September	1st to 10th	Night	2 2 1 2 3 3 3 2 5% 8% 68%	1900
	11th to 20th	Night	4 4 2 5% 4 3 4 3 6% 7% 59%	1933
	21st to end	Night	5% 3 1 4 4 4 4 3 5% 8% 57%	2090
October	1st to 10th	Night	5% 3 1 3 3 3 4 3 6% 8% 61%	3790
	11th to 20th	Night	6% 4 2 5% 4 5% 6% 5% 6% 8% 49%	3828
	21st to end	Night	11% 7% 2 6% 5% 4 4 4 5% 6% 44%	4457
November	1st to 10th	Night	14% 10% 3 6% 5% 4 4 3 6% 8% 36%	2469
	11th to 20th	Night	11% 12% 3 8% 6% 5% 5% 4 6% 5% 35%	2659
	21st to end	Night	13% 13% 4 10% 6% 5% 5% 4 5% 6% 29%	2660
December	1st to 10th	Night	12% 14% 5% 10% 6% 5% 5% 4 6% 7% 26%	2660
	11th to 20th	Night	16% 15% 8% 16% 6% 5% 5% 4 5% 5% 14%	3280
	21st to end	Night	15% 20% 5% 10% 6% 5% 5% 4 5% 6% 20%	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	67% 6% 6% 12% 8% 1	2539
	11th to 20th	Day	63% 5% 13% 16% 2 1	2540
	21st to end	Day	75% 4 11% 7% 3	2794
February	1st to 10th	Day	55% 9% 16% 14% 5%	1618
	11th to 20th	Day	47% 7% 17% 18% 10% 1	1704
	21st to end	Day	47% 8% 15% 19% 9% 1	1570
March	1st to 10th	Day	38% 7% 12% 24% 17% 1	3138
	11th to 20th	Day	28% 6% 12% 43% 11% 1	3321
	21st to end	Day	41% 10% 17% 19% 11% 3	4129
April	1st to 10th	Day	42% 6% 14% 23% 12% 2	2280
	11th to 20th	Day	35% 7% 14% 22% 17% 5%	2252
	21st to end	Day	35% 6% 12% 25% 18% 4	2503
May	1st to 10th	Day	25% 4 8% 24% 33% 6%	4420
	11th to 20th	Day	22% 5% 10% 33% 24% 7%	4380
	21st to end	Day	38% 8% 14% 25% 13% 2	4814
June	1st to 10th	Day	37% 6% 10% 22% 20% 5%	2660
	11th to 20th	Day	30% 6% 10% 27% 21% 6%	2660
	21st to end	Day	22% 4 7% 30% 28% 9%	2660
July	1st to 10th	Day	9% 2 4 14% 29% 41%	4351
	11th to 20th	Day	11% 2 3 11% 24% 49%	4345
	21st to end	Day	10% 1 3 19% 35% 31%	4639
August	1st to 10th	Day	15% 3 4 17% 37% 24%	4384
	11th to 20th	Day	16% 2 6% 38% 31% 8%	4209
	21st to end	Day	23% 2 8% 28% 30% 8%	4179
September	1st to 10th	Day	15% 4 9% 27% 32% 12%	2280
	11th to 20th	Day	26% 6% 11% 24% 26% 8%	2247
	21st to end	Day	27% 6% 16% 30% 17% 6%	2090
October	1st to 10th	Day	24% 3 12% 36% 24% 2	3187
	11th to 20th	Day	36% 4 17% 25% 17% 1	3106
	21st to end	Day	38% 4 14% 27% 13% 4	3101
November	1st to 10th	Day	50% 8% 13% 18% 9% 2	1710
	11th to 20th	Day	53% 6% 15% 18% 7% 1	1520
	21st to end	Day	58% 8% 14% 12% 6% 2	1520
December	1st to 10th	Day	59% 6% 14% 14% 6%	1520
	11th to 20th	Day	74% 7% 7% 7% 4 1	1928
	21st to end	Day	69% 6% 11% 10% 4	2794
January	1st to 10th	Night	66% 6% 11% 12% 4	4406
	11th to 20th	Night	56% 6% 14% 19% 5%	4420
	21st to end	Night	73% 6% 11% 7% 2 1	4862
February	1st to 10th	Night	50% 9% 17% 16% 7% 1	2561
	11th to 20th	Night	44% 8% 18% 18% 11% 1	2373
	21st to end	Night	46% 8% 13% 20% 11% 1	1884
March	1st to 10th	Night	35% 8% 13% 26% 16% 2	3736
	11th to 20th	Night	27% 5% 12% 41% 15% 1	3657
	21st to end	Night	43% 11% 16% 24% 6%	3523
April	1st to 10th	Night	41% 5% 13% 28% 11% 2	1900
	11th to 20th	Night	35% 6% 11% 25% 18% 5%	1879
	21st to end	Night	35% 7% 11% 25% 18% 4	1674
May	1st to 10th	Night	28% 4 6% 20% 36% 6%	2540
	11th to 20th	Night	20% 5% 8% 32% 32% 4	2516
	21st to end	Night	26% 7% 16% 37% 12% 2	2762
June	1st to 10th	Night	33% 6% 10% 23% 22% 6%	1520
	11th to 20th	Night	27% 6% 9% 29% 23% 5%	1520
	21st to end	Night	24% 4 7% 28% 28% 9%	1520
July	1st to 10th	Night	8% 2 3 13% 29% 44%	2500
	11th to 20th	Night	7% 2 3 11% 23% 55%	2492
	21st to end	Night	7% 1 2 15% 37% 37%	2674
August	1st to 10th	Night	15% 2 3 13% 38% 29%	2521
	11th to 20th	Night	19% 2 4 34% 32% 9%	2686
	21st to end	Night	20% 2 6% 28% 31% 13%	3498
September	1st to 10th	Night	15% 3 7% 26% 32% 17%	1900
	11th to 20th	Night	24% 4 9% 25% 27% 10%	1933
	21st to end	Night	24% 6% 11% 32% 19% 8%	2090
October	1st to 10th	Night	22% 3 7% 41% 25% 1	3790
	11th to 20th	Night	32% 4 15% 27% 19% 3	3828
	21st to end	Night	40% 4 11% 28% 15% 3	4457
November	1st to 10th	Night	45% 7% 17% 19% 10% 2	2469
	11th to 20th	Night	49% 9% 14% 17% 9% 2	2659
	21st to end	Night	55% 7% 13% 16% 8% 1	2660
December	1st to 10th	Night	56% 8% 14% 18% 5%	2660
	11th to 20th	Night	71% 7% 10% 8% 3	3276
	21st to end	Night	63% 8% 11% 10% 7% 1	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	24% 9% 23% 26% 16% 2	180
	11th to 20th	Day	27% 6% 16% 29% 17% 6%	180
	21st to end	Day	27% 3 16% 37% 14% 3	198
February	1st to 10th	Day	16% 5% 26% 35% 15% 3	278
	11th to 20th	Day	17% 7% 23% 32% 16% 4	380
	21st to end	Day	11% 8% 26% 30% 20% 4	382
March	1st to 10th	Day	14% 7% 26% 30% 17% 6%	460
	11th to 20th	Day	14% 11% 18% 30% 19% 8%	460
	21st to end	Day	15% 11% 27% 27% 15% 4	506
April	1st to 10th	Day	16% 12% 21% 31% 15% 5%	460
	11th to 20th	Day	9% 20% 28% 24% 13% 6%	452
	21st to end	Day	7% 13% 26% 25% 21% 8%	460
May	1st to 10th	Day	7% 11% 24% 33% 18% 6%	463
	11th to 20th	Day	13% 9% 18% 24% 23% 13%	488
	21st to end	Day	9% 9% 18% 25% 26% 13%	529
June	1st to 10th	Day	8% 10% 23% 29% 20% 11%	490
	11th to 20th	Day	10% 10% 28% 30% 16% 7%	490
	21st to end	Day	3 6% 20% 28% 30% 12%	490
July	1st to 10th	Day	2 6% 16% 37% 29% 9%	486
	11th to 20th	Day	1 4 20% 30% 31% 14%	484
	21st to end	Day	1 4 15% 29% 35% 16%	531
August	1st to 10th	Day	3 5% 14% 30% 29% 20%	487
	11th to 20th	Day	2 3 15% 26% 31% 22%	477
	21st to end	Day	4 5% 17% 31% 26% 17%	539
September	1st to 10th	Day	5% 5% 16% 29% 29% 17%	490
	11th to 20th	Day	6% 7% 17% 28% 31% 11%	490
	21st to end	Day	10% 9% 18% 30% 26% 7%	490
October	1st to 10th	Day	9% 6% 26% 29% 22% 8%	490
	11th to 20th	Day	11% 8% 20% 26% 27% 8%	460
	21st to end	Day	16% 10% 24% 32% 15% 3	330
November	1st to 10th	Day	20% 10% 18% 36% 16% 1	282
	11th to 20th	Day	20% 12% 24% 22% 17% 5%	180
	21st to end	Day	17% 6% 21% 31% 24% 1	180
December	1st to 10th	Day	20% 7% 19% 28% 19% 6%	180
	11th to 20th	Day	19% 8% 26% 29% 16% 2	180
	21st to end	Day	20% 7% 18% 37% 16% 4	198
January	1st to 10th	Night	27% 5% 21% 31% 14% 2	760
	11th to 20th	Night	22% 5% 20% 31% 18% 4	760
	21st to end	Night	21% 5% 16% 40% 17% 3	836
February	1st to 10th	Night	18% 4 28% 34% 15% 2	760
	11th to 20th	Night	14% 5% 24% 35% 19% 2	744
	21st to end	Night	14% 8% 21% 37% 17% 4	628
March	1st to 10th	Night	15% 6% 19% 37% 19% 3	760
	11th to 20th	Night	11% 6% 22% 38% 22% 2	760
	21st to end	Night	11% 7% 24% 39% 16% 3	836
April	1st to 10th	Night	12% 8% 19% 36% 22% 3	760
	11th to 20th	Night	12% 9% 27% 33% 17% 4	751
	21st to end	Night	8% 10% 26% 34% 19% 3	534
May	1st to 10th	Night	7% 8% 25% 36% 21% 3	380
	11th to 20th	Night	10% 6% 17% 34% 28% 5%	374
	21st to end	Night	8% 4 18% 38% 28% 5%	411
June	1st to 10th	Night	7% 7% 23% 38% 23% 3	380
	11th to 20th	Night	7% 9% 24% 38% 20% 2	380
	21st to end	Night	6% 4 22% 36% 28% 4	380
July	1st to 10th	Night	2 4 16% 43% 33% 3	370
	11th to 20th	Night	2 4 18% 42% 33% 2	368
	21st to end	Night	1 3 15% 39% 40% 2	416
August	1st to 10th	Night	3 3 13% 36% 39% 8%	378
	11th to 20th	Night	3 1 12% 36% 37% 10%	463
	21st to end	Night	3 4 15% 38% 35% 5%	836
September	1st to 10th	Night	2 4 15% 40% 33% 6%	760
	11th to 20th	Night	5% 5% 13% 33% 37% 8%	760
	21st to end	Night	7% 4 17% 36% 31% 4	760
October	1st to 10th	Night	12% 4 16% 40% 26% 3	760
	11th to 20th	Night	11% 5% 17% 38% 25% 4	760
	21st to end	Night	16% 5% 19% 39% 17% 4	836
November	1st to 10th	Night	19% 5% 16% 46% 12% 1	760
	11th to 20th	Night	18% 8% 24% 33% 14% 3	760
	21st to end	Night	19% 5% 16% 36% 21% 2	760
December	1st to 10th	Night	18% 5% 19% 37% 18% 3	760
	11th to 20th	Night	23% 5% 18% 39% 14% 1	760
	21st to end	Night	24% 6% 20% 39% 11% 1	836

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