Blue Heron Cove Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Blue Heron Cove Observatory clear sky chart from 2005-11-06 to 2024-12-02.

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	17% 10% 4 9% 5% 5% 5% 4 5% 7% 29%	101700
	Night	17% 11% 4 9% 5% 5% 4 4 5% 6% 30%	97947
Transparency	Day	51% 5% 12% 21% 10% 1	105182
	Night	51% 4 12% 21% 10% 1	102554
Seeing	Day	26% 13% 28% 20% 9% 3	14809
	Night	24% 14% 27% 25% 9% 1	23918

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	13% 15% 9% 15% 6% 6% 4 4 4 4 20%	2517
	11th to 20th	Day	15% 19% 7% 16% 7% 8% 4 3 4 4 15%	2520
	21st to end	Day	17% 18% 9% 13% 7% 5% 4 4 4 5% 16%	2904
February	1st to 10th	Day	14% 16% 5% 12% 9% 6% 5% 4 5% 5% 19%	1710
	11th to 20th	Day	12% 15% 7% 15% 7% 5% 5% 4 5% 4 22%	1774
	21st to end	Day	19% 15% 5% 10% 6% 4 4 3 5% 5% 23%	1570
March	1st to 10th	Day	24% 16% 5% 10% 5% 4 4 2 5% 4 23%	3116
	11th to 20th	Day	12% 16% 8% 12% 6% 5% 4 3 5% 4 25%	3371
	21st to end	Day	18% 13% 4 10% 5% 4 4 2 3 5% 33%	4116
April	1st to 10th	Day	19% 15% 3 8% 4 4 4 3 4 5% 31%	2280
	11th to 20th	Day	18% 11% 3 7% 5% 4 4 4 4 6% 32%	2254
	21st to end	Day	20% 12% 4 8% 4 4 4 4 4 5% 30%	2341
May	1st to 10th	Day	25% 9% 3 8% 4 4 4 3 5% 6% 29%	4294
	11th to 20th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 29%	4398
	21st to end	Day	14% 6% 2 7% 5% 5% 5% 4 6% 8% 38%	4837
June	1st to 10th	Day	17% 8% 3 8% 6% 5% 5% 4 6% 9% 28%	2660
	11th to 20th	Day	18% 6% 3 7% 5% 4 5% 5% 7% 9% 30%	2660
	21st to end	Day	19% 7% 3 8% 6% 5% 5% 5% 6% 7% 30%	2660
July	1st to 10th	Day	13% 7% 3 7% 6% 5% 5% 5% 7% 9% 35%	4440
	11th to 20th	Day	12% 7% 2 7% 5% 6% 6% 5% 8% 11% 32%	4440
	21st to end	Day	16% 6% 3 7% 6% 6% 6% 4 6% 7% 33%	4814
August	1st to 10th	Day	17% 6% 2 7% 4 5% 5% 4 7% 8% 33%	4360
	11th to 20th	Day	18% 8% 2 7% 5% 6% 6% 5% 7% 9% 27%	3800
	21st to end	Day	17% 5% 2 6% 4 5% 6% 4 7% 8% 36%	4180
September	1st to 10th	Day	15% 6% 2 6% 5% 5% 5% 4 6% 7% 39%	2280
	11th to 20th	Day	16% 5% 3 5% 4 4 4 4 6% 7% 43%	2223
	21st to end	Day	18% 7% 3 6% 5% 5% 4 4 6% 6% 36%	2090
October	1st to 10th	Day	24% 10% 3 8% 4 5% 5% 3 4 5% 29%	1933
	11th to 20th	Day	18% 10% 4 8% 4 4 4 3 5% 7% 33%	1900
	21st to end	Day	24% 14% 3 7% 4 4 5% 4 5% 5% 26%	1915
November	1st to 10th	Day	14% 12% 3 6% 6% 5% 4 4 6% 7% 33%	1761
	11th to 20th	Day	16% 12% 5% 9% 4 4 3 3 5% 7% 30%	1776
	21st to end	Day	18% 15% 5% 10% 6% 5% 4 3 4 7% 24%	1600
December	1st to 10th	Day	19% 20% 8% 10% 6% 4 4 3 4 4 17%	1528
	11th to 20th	Day	23% 13% 6% 11% 6% 3 4 3 5% 6% 21%	1906
	21st to end	Day	20% 19% 7% 14% 6% 4 3 2 3 4 16%	2772
January	1st to 10th	Night	15% 14% 7% 13% 8% 6% 5% 3 5% 5% 20%	4429
	11th to 20th	Night	13% 12% 9% 15% 13% 7% 4 4 4 4 14%	4440
	21st to end	Night	18% 17% 7% 12% 6% 5% 5% 4 4 4 18%	4748
February	1st to 10th	Night	13% 13% 5% 13% 8% 6% 6% 4 6% 5% 21%	2470
	11th to 20th	Night	12% 11% 5% 13% 7% 6% 5% 5% 6% 6% 24%	2291
	21st to end	Night	15% 12% 5% 12% 7% 5% 4 4 5% 8% 24%	1884
March	1st to 10th	Night	21% 14% 4 9% 5% 5% 5% 4 5% 5% 24%	3724
	11th to 20th	Night	15% 14% 7% 10% 6% 5% 4 3 4 5% 28%	3585
	21st to end	Night	16% 11% 5% 13% 5% 4 4 3 4 5% 31%	3514
April	1st to 10th	Night	20% 12% 4 6% 4 4 4 3 5% 8% 30%	1900
	11th to 20th	Night	18% 9% 3 7% 6% 3 5% 3 6% 6% 34%	1875
	21st to end	Night	20% 9% 4 7% 5% 3 4 4 4 5% 35%	1838
May	1st to 10th	Night	25% 10% 3 8% 4 4 4 3 5% 7% 29%	2674
	11th to 20th	Night	18% 11% 3 9% 5% 4 4 3 5% 6% 33%	2495
	21st to end	Night	13% 9% 3 7% 5% 5% 5% 4 6% 7% 37%	2738
June	1st to 10th	Night	17% 6% 2 6% 5% 5% 5% 3 6% 8% 37%	1520
	11th to 20th	Night	18% 6% 2 5% 4 4 4 4 5% 9% 40%	1520
	21st to end	Night	17% 6% 2 6% 4 4 5% 4 5% 8% 39%	1520
July	1st to 10th	Night	11% 7% 4 8% 5% 5% 5% 5% 6% 6% 38%	2520
	11th to 20th	Night	17% 6% 2 6% 4 3 4 4 6% 7% 41%	2520
	21st to end	Night	15% 6% 2 6% 5% 5% 4 4 5% 6% 41%	2739
August	1st to 10th	Night	24% 8% 2 6% 4 4 4 3 5% 6% 35%	2564
	11th to 20th	Night	20% 9% 2 6% 3 3 3 3 5% 5% 40%	2997
	21st to end	Night	13% 6% 2 5% 4 4 4 4 6% 8% 45%	3476
September	1st to 10th	Night	13% 6% 2 5% 4 4 5% 4 6% 8% 43%	1900
	11th to 20th	Night	15% 6% 2 5% 3 3 4 3 4 6% 49%	1956
	21st to end	Night	18% 6% 2 5% 4 4 5% 4 5% 7% 40%	2090
October	1st to 10th	Night	20% 9% 3 8% 5% 4 5% 3 5% 6% 32%	2244
	11th to 20th	Night	19% 10% 3 8% 4 5% 3 3 5% 7% 35%	2280
	21st to end	Night	22% 11% 3 7% 5% 4 5% 4 6% 6% 27%	2681
November	1st to 10th	Night	13% 10% 4 9% 5% 5% 4 4 6% 5% 37%	2537
	11th to 20th	Night	18% 12% 4 8% 5% 4 4 4 5% 6% 30%	2620
	21st to end	Night	15% 14% 4 9% 5% 5% 4 3 6% 7% 27%	2800
December	1st to 10th	Night	18% 18% 5% 10% 6% 4 4 4 5% 6% 20%	2686
	11th to 20th	Night	20% 14% 5% 11% 6% 6% 5% 4 5% 5% 20%	3288
	21st to end	Night	26% 14% 5% 11% 5% 4 4 3 5% 5% 18%	4884

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	64% 3 10% 16% 6% 1	2518
	11th to 20th	Day	71% 4 9% 11% 4 2	2520
	21st to end	Day	70% 3 10% 12% 4 1	2904
February	1st to 10th	Day	64% 4 11% 15% 5% 1	1710
	11th to 20th	Day	63% 4 8% 15% 9% 1	1783
	21st to end	Day	61% 3 11% 16% 9%	1570
March	1st to 10th	Day	64% 2 10% 14% 8% 1	3119
	11th to 20th	Day	58% 4 15% 13% 9% 2	3371
	21st to end	Day	54% 3 6% 18% 17% 2	4116
April	1st to 10th	Day	54% 4 7% 20% 12% 2	2280
	11th to 20th	Day	52% 4 10% 21% 12% 1	2254
	21st to end	Day	55% 4 8% 18% 12% 3	2341
May	1st to 10th	Day	56% 3 9% 21% 10% 1	4308
	11th to 20th	Day	52% 4 12% 22% 8% 1	4402
	21st to end	Day	42% 5% 13% 28% 11% 1	4837
June	1st to 10th	Day	50% 6% 13% 21% 11%	2660
	11th to 20th	Day	47% 5% 15% 22% 10% 1	2660
	21st to end	Day	48% 6% 14% 23% 9% 1	2660
July	1st to 10th	Day	41% 7% 15% 25% 12%	4370
	11th to 20th	Day	39% 7% 16% 29% 9%	4365
	21st to end	Day	45% 6% 14% 25% 9%	4661
August	1st to 10th	Day	45% 6% 16% 21% 12%	4346
	11th to 20th	Day	47% 7% 18% 23% 5%	3838
	21st to end	Day	40% 7% 14% 31% 9%	4180
September	1st to 10th	Day	41% 6% 12% 29% 11% 1	2280
	11th to 20th	Day	38% 4 13% 27% 17% 1	2223
	21st to end	Day	46% 4 11% 25% 12% 1	2090
October	1st to 10th	Day	46% 7% 10% 24% 12% 1	3206
	11th to 20th	Day	41% 4 14% 25% 15% 2	3140
	21st to end	Day	40% 6% 15% 27% 11% 1	3127
November	1st to 10th	Day	45% 5% 14% 23% 12% 1	1761
	11th to 20th	Day	52% 4 11% 18% 14% 1	1776
	21st to end	Day	58% 4 15% 16% 6% 1	1600
December	1st to 10th	Day	65% 3 11% 15% 4 1	1528
	11th to 20th	Day	62% 4 15% 14% 4 1	1906
	21st to end	Day	72% 3 6% 12% 6%	2772
January	1st to 10th	Night	62% 3 13% 14% 8%	4429
	11th to 20th	Night	67% 5% 10% 11% 6% 1	4440
	21st to end	Night	66% 3 10% 14% 5% 1	4748
February	1st to 10th	Night	60% 3 12% 17% 7% 1	2470
	11th to 20th	Night	56% 3 11% 20% 9% 1	2293
	21st to end	Night	56% 3 13% 18% 9% 1	1884
March	1st to 10th	Night	61% 3 8% 18% 10% 1	3734
	11th to 20th	Night	56% 3 11% 21% 7% 1	3586
	21st to end	Night	55% 3 6% 18% 15% 2	3514
April	1st to 10th	Night	52% 3 10% 22% 11% 1	1900
	11th to 20th	Night	49% 4 11% 22% 13% 1	1875
	21st to end	Night	50% 3 10% 19% 14% 3	1838
May	1st to 10th	Night	56% 3 11% 17% 11% 2	2680
	11th to 20th	Night	52% 4 13% 22% 8% 1	2496
	21st to end	Night	45% 5% 12% 21% 16% 1	2739
June	1st to 10th	Night	43% 5% 13% 25% 12% 2	1520
	11th to 20th	Night	41% 4 16% 25% 13% 1	1520
	21st to end	Night	41% 7% 14% 26% 12%	1520
July	1st to 10th	Night	41% 7% 15% 21% 15% 1	2480
	11th to 20th	Night	39% 7% 15% 24% 14%	2472
	21st to end	Night	39% 7% 12% 29% 12% 1	2651
August	1st to 10th	Night	47% 7% 13% 24% 9%	2554
	11th to 20th	Night	45% 5% 15% 27% 8%	3025
	21st to end	Night	33% 5% 16% 35% 10%	3476
September	1st to 10th	Night	37% 5% 14% 30% 13% 1	1900
	11th to 20th	Night	36% 3 12% 28% 19% 1	1956
	21st to end	Night	42% 4 13% 26% 14% 2	2090
October	1st to 10th	Night	48% 6% 12% 22% 11% 1	3751
	11th to 20th	Night	37% 4 15% 23% 15% 5%	3779
	21st to end	Night	44% 5% 14% 28% 8% 1	4419
November	1st to 10th	Night	45% 4 13% 23% 14% 2	2537
	11th to 20th	Night	51% 4 10% 21% 12% 2	2620
	21st to end	Night	52% 4 17% 20% 7% 1	2800
December	1st to 10th	Night	61% 4 12% 16% 6%	2686
	11th to 20th	Night	61% 5% 12% 15% 8% 1	3288
	21st to end	Night	67% 2 11% 14% 5%	4884

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	32% 12% 35% 15% 5% 1	180
	11th to 20th	Day	39% 20% 29% 9% 2 1	180
	21st to end	Day	27% 21% 34% 14% 4	236
February	1st to 10th	Day	37% 23% 30% 9% 2	270
	11th to 20th	Day	34% 25% 30% 10% 2	382
	21st to end	Day	36% 17% 30% 15% 2	382
March	1st to 10th	Day	29% 18% 34% 15% 4 1	460
	11th to 20th	Day	35% 20% 27% 13% 3 1	460
	21st to end	Day	35% 17% 28% 13% 6% 2	506
April	1st to 10th	Day	35% 19% 24% 15% 6% 1	460
	11th to 20th	Day	34% 18% 21% 17% 8% 2	452
	21st to end	Day	33% 14% 31% 14% 5% 2	460
May	1st to 10th	Day	35% 13% 28% 15% 7% 3	463
	11th to 20th	Day	21% 13% 34% 22% 8% 2	487
	21st to end	Day	20% 10% 29% 25% 12% 4	529
June	1st to 10th	Day	22% 14% 27% 23% 12% 2	490
	11th to 20th	Day	20% 12% 31% 24% 11% 2	490
	21st to end	Day	22% 14% 29% 23% 8% 2	490
July	1st to 10th	Day	17% 8% 28% 26% 18% 3	485
	11th to 20th	Day	18% 5% 31% 29% 14% 4	484
	21st to end	Day	18% 7% 37% 25% 12% 2	532
August	1st to 10th	Day	14% 9% 26% 27% 18% 7%	486
	11th to 20th	Day	20% 8% 24% 27% 13% 8%	479
	21st to end	Day	17% 10% 27% 27% 13% 7%	539
September	1st to 10th	Day	19% 8% 22% 24% 19% 9%	490
	11th to 20th	Day	15% 6% 25% 23% 19% 12%	490
	21st to end	Day	21% 7% 28% 24% 15% 5%	490
October	1st to 10th	Day	30% 11% 24% 17% 13% 5%	490
	11th to 20th	Day	23% 17% 27% 23% 9% 1	490
	21st to end	Day	33% 11% 27% 22% 6%	446
November	1st to 10th	Day	30% 14% 26% 19% 11% 1	395
	11th to 20th	Day	31% 19% 27% 17% 4 1	376
	21st to end	Day	41% 14% 29% 15% 2	200
December	1st to 10th	Day	36% 19% 28% 12% 5%	182
	11th to 20th	Day	39% 15% 32% 8% 5%	180
	21st to end	Day	38% 16% 29% 14% 2 1	198
January	1st to 10th	Night	28% 20% 32% 18% 2	760
	11th to 20th	Night	28% 22% 28% 19% 3	760
	21st to end	Night	22% 21% 31% 23% 3	836
February	1st to 10th	Night	26% 19% 35% 19% 2	760
	11th to 20th	Night	25% 23% 35% 15% 2	743
	21st to end	Night	29% 18% 32% 18% 3	628
March	1st to 10th	Night	25% 18% 34% 20% 3	760
	11th to 20th	Night	30% 16% 32% 19% 3	760
	21st to end	Night	26% 18% 30% 21% 5% 1	836
April	1st to 10th	Night	27% 15% 34% 20% 4	760
	11th to 20th	Night	26% 14% 31% 22% 6% 1	751
	21st to end	Night	27% 15% 27% 23% 8%	698
May	1st to 10th	Night	32% 10% 26% 21% 11% 1	475
	11th to 20th	Night	20% 13% 29% 29% 8% 1	374
	21st to end	Night	18% 5% 26% 35% 15% 1	411
June	1st to 10th	Night	18% 9% 24% 33% 14% 2	380
	11th to 20th	Night	19% 9% 22% 36% 15%	380
	21st to end	Night	18% 6% 25% 39% 12% 1	380
July	1st to 10th	Night	13% 3 22% 41% 20% 1	370
	11th to 20th	Night	15% 4 18% 42% 20% 1	368
	21st to end	Night	13% 4 25% 43% 15% 1	416
August	1st to 10th	Night	14% 3 20% 39% 23% 1	410
	11th to 20th	Night	19% 4 18% 35% 21% 3	686
	21st to end	Night	16% 5% 19% 38% 20% 2	836
September	1st to 10th	Night	16% 6% 21% 35% 21% 1	760
	11th to 20th	Night	17% 6% 20% 30% 23% 5%	760
	21st to end	Night	20% 6% 24% 31% 17% 2	760
October	1st to 10th	Night	25% 12% 22% 24% 15% 2	760
	11th to 20th	Night	23% 12% 26% 28% 10% 1	760
	21st to end	Night	28% 14% 31% 21% 6%	836
November	1st to 10th	Night	21% 15% 27% 28% 8%	780
	11th to 20th	Night	26% 18% 26% 23% 7% 1	800
	21st to end	Night	27% 18% 27% 22% 6% 1	800
December	1st to 10th	Night	29% 18% 32% 18% 3	768
	11th to 20th	Night	33% 18% 27% 17% 4 1	760
	21st to end	Night	34% 22% 26% 16% 3	836

Page generated at 2024-11-29 10:43:11. Version ac07

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