3 Herons Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the 3 Herons Observatory clear sky chart from 2005-11-06 to 2024-08-30.

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	17% 12% 4 9% 6% 5% 5% 4 5% 6% 27%	95742
	Night	18% 14% 5% 11% 6% 5% 4 3 4 5% 26%	93319
Transparency	Day	57% 5% 11% 19% 8% 1	95461
	Night	61% 4 10% 16% 8% 1	93154
Seeing	Day	27% 16% 29% 19% 8% 2	14459
	Night	26% 13% 24% 26% 10% 1	23360

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	14% 17% 9% 18% 8% 5% 5% 3 3 3 15%	2517
	11th to 20th	Day	13% 16% 8% 20% 10% 5% 5% 3 4 4 14%	2520
	21st to end	Day	12% 22% 9% 14% 6% 6% 5% 3 4 4 13%	2772
February	1st to 10th	Day	13% 16% 5% 16% 10% 6% 4 3 5% 4 18%	1648
	11th to 20th	Day	11% 17% 7% 17% 10% 6% 4 4 3 4 17%	1825
	21st to end	Day	12% 17% 6% 13% 8% 6% 5% 3 4 4 21%	1570
March	1st to 10th	Day	21% 17% 5% 10% 7% 4 4 4 3 4 20%	3116
	11th to 20th	Day	13% 22% 7% 13% 6% 4 4 2 4 4 21%	3247
	21st to end	Day	17% 14% 5% 12% 5% 4 3 3 3 4 30%	4166
April	1st to 10th	Day	19% 17% 5% 10% 5% 4 3 2 4 5% 26%	2280
	11th to 20th	Day	18% 14% 3 7% 5% 4 4 3 4 5% 32%	2254
	21st to end	Day	23% 12% 3 9% 5% 4 4 3 5% 5% 28%	2456
May	1st to 10th	Day	25% 12% 3 8% 5% 5% 4 3 5% 5% 26%	4218
	11th to 20th	Day	18% 10% 4 8% 6% 5% 6% 5% 5% 7% 27%	4398
	21st to end	Day	15% 7% 3 7% 5% 5% 5% 5% 7% 8% 33%	4837
June	1st to 10th	Day	26% 8% 3 6% 5% 4 5% 4 6% 6% 27%	2660
	11th to 20th	Day	18% 7% 2 7% 5% 5% 4 4 7% 8% 33%	2660
	21st to end	Day	23% 8% 3 7% 5% 5% 4 5% 6% 7% 27%	2660
July	1st to 10th	Day	13% 6% 2 7% 6% 5% 6% 5% 8% 10% 32%	4440
	11th to 20th	Day	12% 7% 3 7% 6% 6% 6% 6% 7% 9% 31%	4440
	21st to end	Day	14% 7% 3 7% 5% 5% 5% 4 6% 7% 36%	4814
August	1st to 10th	Day	17% 8% 3 7% 4 5% 5% 5% 6% 7% 33%	2646
	11th to 20th	Day	16% 7% 3 6% 5% 5% 6% 4 6% 9% 33%	2374
	21st to end	Day	15% 7% 3 6% 5% 4 5% 5% 5% 9% 36%	2486
September	1st to 10th	Day	18% 7% 2 6% 4 3 4 4 6% 6% 40%	2160
	11th to 20th	Day	18% 7% 1 5% 4 4 4 2 4 7% 45%	2047
	21st to end	Day	17% 8% 2 6% 5% 3 5% 3 6% 7% 36%	1980
October	1st to 10th	Day	25% 10% 3 8% 4 4 4 4 4 7% 27%	1920
	11th to 20th	Day	19% 12% 4 8% 5% 4 5% 4 5% 5% 29%	1735
	21st to end	Day	26% 20% 4 6% 5% 5% 3 2 3 4 22%	1782
November	1st to 10th	Day	16% 19% 4 8% 4 5% 4 3 3 5% 28%	1671
	11th to 20th	Day	17% 18% 6% 9% 7% 4 5% 3 5% 4 23%	1710
	21st to end	Day	17% 18% 5% 13% 4 6% 4 4 4 5% 19%	1535
December	1st to 10th	Day	18% 22% 8% 14% 6% 4 4 2 4 4 14%	1520
	11th to 20th	Day	19% 18% 7% 12% 6% 4 4 2 4 4 20%	1906
	21st to end	Day	20% 16% 7% 16% 8% 6% 5% 3 3 3 14%	2772
January	1st to 10th	Night	13% 18% 7% 21% 7% 6% 5% 3 3 3 14%	4429
	11th to 20th	Night	10% 16% 7% 22% 11% 6% 5% 3 4 4 12%	4440
	21st to end	Night	15% 20% 8% 14% 8% 6% 4 3 3 3 15%	4884
February	1st to 10th	Night	13% 17% 6% 17% 9% 7% 4 3 4 4 16%	2529
	11th to 20th	Night	12% 16% 6% 16% 10% 6% 5% 3 4 3 19%	2239
	21st to end	Night	13% 15% 6% 13% 7% 6% 5% 3 4 4 23%	1884
March	1st to 10th	Night	21% 17% 5% 9% 6% 4 3 2 4 4 24%	3724
	11th to 20th	Night	14% 20% 7% 12% 5% 5% 3 2 4 4 25%	3707
	21st to end	Night	16% 19% 5% 12% 5% 4 3 2 3 2 29%	3466
April	1st to 10th	Night	20% 15% 5% 10% 4 4 4 2 4 5% 27%	1900
	11th to 20th	Night	22% 11% 4 9% 5% 4 4 2 4 5% 29%	1875
	21st to end	Night	22% 13% 4 6% 5% 4 4 3 4 5% 31%	1722
May	1st to 10th	Night	25% 13% 4 6% 4 4 4 3 4 6% 26%	2752
	11th to 20th	Night	20% 11% 4 7% 5% 4 4 3 4 6% 32%	2495
	21st to end	Night	17% 6% 2 7% 5% 5% 5% 4 6% 8% 36%	2738
June	1st to 10th	Night	27% 8% 3 6% 4 4 4 4 4 7% 29%	1520
	11th to 20th	Night	18% 7% 3 7% 4 4 5% 4 6% 8% 34%	1520
	21st to end	Night	22% 9% 3 6% 4 4 5% 5% 6% 7% 30%	1520
July	1st to 10th	Night	15% 7% 3 7% 5% 5% 6% 5% 7% 7% 33%	2520
	11th to 20th	Night	16% 9% 3 7% 5% 5% 4 3 5% 8% 35%	2520
	21st to end	Night	16% 7% 3 7% 6% 6% 5% 4 5% 7% 35%	2739
August	1st to 10th	Night	15% 7% 3 6% 4 4 4 3 6% 9% 38%	1512
	11th to 20th	Night	15% 7% 3 8% 4 4 4 4 5% 6% 39%	1724
	21st to end	Night	16% 8% 3 6% 4 4 4 4 6% 7% 39%	2080
September	1st to 10th	Night	17% 6% 2 6% 4 4 5% 4 5% 7% 41%	1800
	11th to 20th	Night	17% 7% 2 6% 3 3 3 3 5% 7% 45%	1912
	21st to end	Night	19% 8% 2 5% 4 4 4 3 5% 6% 41%	1980
October	1st to 10th	Night	23% 8% 2 7% 4 5% 4 3 5% 6% 32%	2038
	11th to 20th	Night	22% 12% 3 7% 5% 5% 6% 3 3 6% 29%	2223
	21st to end	Night	26% 16% 3 8% 5% 4 3 3 4 5% 22%	2574
November	1st to 10th	Night	19% 16% 4 8% 5% 5% 4 3 4 5% 29%	2407
	11th to 20th	Night	17% 16% 6% 11% 5% 3 3 3 4 5% 26%	2470
	21st to end	Night	17% 18% 6% 14% 5% 5% 3 3 4 4 20%	2644
December	1st to 10th	Night	19% 23% 7% 13% 7% 5% 4 3 4 3 12%	2660
	11th to 20th	Night	19% 21% 7% 14% 6% 5% 3 3 3 3 15%	3288
	21st to end	Night	20% 19% 6% 18% 7% 4 4 2 3 3 14%	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	75% 4 9% 10% 2	2518
	11th to 20th	Day	74% 6% 7% 9% 4 1	2520
	21st to end	Day	74% 3 10% 8% 3 1	2772
February	1st to 10th	Day	70% 4 6% 14% 5% 1	1648
	11th to 20th	Day	71% 4 7% 12% 5% 1	1834
	21st to end	Day	66% 4 8% 12% 8% 2	1570
March	1st to 10th	Day	69% 3 8% 10% 7% 1	3119
	11th to 20th	Day	67% 4 9% 10% 9% 1	3247
	21st to end	Day	58% 4 5% 16% 16% 1	4166
April	1st to 10th	Day	62% 3 7% 18% 9% 1	2280
	11th to 20th	Day	55% 5% 7% 19% 13% 1	2254
	21st to end	Day	59% 4 9% 16% 9% 3	2456
May	1st to 10th	Day	61% 5% 8% 19% 7% 1	4232
	11th to 20th	Day	54% 7% 13% 17% 8% 1	4402
	21st to end	Day	45% 7% 12% 26% 10% 1	4837
June	1st to 10th	Day	55% 5% 11% 19% 9%	2660
	11th to 20th	Day	47% 6% 11% 23% 12% 1	2660
	21st to end	Day	55% 5% 11% 20% 8% 1	2660
July	1st to 10th	Day	44% 6% 16% 25% 10%	4370
	11th to 20th	Day	44% 7% 16% 29% 5%	4365
	21st to end	Day	46% 5% 11% 29% 7%	4661
August	1st to 10th	Day	48% 6% 16% 23% 7%	2632
	11th to 20th	Day	47% 5% 17% 22% 9%	2374
	21st to end	Day	44% 6% 13% 24% 12%	2486
September	1st to 10th	Day	43% 4 12% 28% 12% 1	2160
	11th to 20th	Day	42% 4 10% 30% 14% 1	2047
	21st to end	Day	46% 5% 14% 23% 9% 2	1980
October	1st to 10th	Day	58% 4 10% 19% 9%	1920
	11th to 20th	Day	55% 5% 14% 18% 7%	1735
	21st to end	Day	69% 3 7% 14% 6% 2	1782
November	1st to 10th	Day	59% 4 11% 18% 8%	1671
	11th to 20th	Day	66% 4 10% 12% 7% 2	1710
	21st to end	Day	67% 5% 13% 12% 3	1535
December	1st to 10th	Day	75% 4 9% 9% 3	1520
	11th to 20th	Day	69% 3 8% 15% 5%	1906
	21st to end	Day	76% 4 6% 11% 3	2772
January	1st to 10th	Night	75% 6% 11% 7% 2	4429
	11th to 20th	Night	76% 4 9% 8% 3	4440
	21st to end	Night	75% 3 8% 9% 4 1	4884
February	1st to 10th	Night	72% 4 8% 11% 5%	2529
	11th to 20th	Night	70% 3 7% 13% 7%	2241
	21st to end	Night	64% 4 7% 15% 8% 1	1884
March	1st to 10th	Night	64% 4 8% 14% 9% 1	3734
	11th to 20th	Night	64% 4 7% 15% 10% 1	3708
	21st to end	Night	61% 5% 5% 15% 13% 1	3466
April	1st to 10th	Night	61% 3 8% 17% 10% 1	1900
	11th to 20th	Night	57% 3 8% 20% 11% 1	1875
	21st to end	Night	56% 4 9% 15% 13% 2	1722
May	1st to 10th	Night	60% 4 9% 18% 8% 1	2758
	11th to 20th	Night	53% 6% 12% 19% 9% 1	2496
	21st to end	Night	45% 6% 14% 19% 15% 1	2739
June	1st to 10th	Night	55% 4 10% 21% 9% 1	1520
	11th to 20th	Night	46% 7% 13% 22% 10% 2	1520
	21st to end	Night	52% 6% 13% 20% 9%	1520
July	1st to 10th	Night	47% 6% 15% 21% 11%	2480
	11th to 20th	Night	46% 5% 14% 28% 7%	2472
	21st to end	Night	48% 6% 12% 23% 10%	2651
August	1st to 10th	Night	41% 5% 20% 26% 8%	1502
	11th to 20th	Night	45% 5% 16% 23% 11%	1724
	21st to end	Night	44% 5% 15% 24% 12%	2080
September	1st to 10th	Night	42% 5% 15% 27% 10% 1	1800
	11th to 20th	Night	39% 4 14% 31% 11% 1	1912
	21st to end	Night	44% 4 12% 25% 12% 2	1980
October	1st to 10th	Night	53% 4 12% 21% 9% 1	2038
	11th to 20th	Night	57% 5% 12% 19% 7%	2223
	21st to end	Night	65% 4 9% 13% 7% 1	2574
November	1st to 10th	Night	58% 4 11% 18% 8% 1	2407
	11th to 20th	Night	62% 4 9% 15% 7% 2	2470
	21st to end	Night	69% 3 10% 14% 4	2644
December	1st to 10th	Night	78% 4 7% 9% 2	2660
	11th to 20th	Night	76% 4 6% 9% 5%	3288
	21st to end	Night	77% 3 6% 10% 3	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	26% 22% 30% 19% 4	180
	11th to 20th	Day	33% 22% 31% 10% 4 1	180
	21st to end	Day	25% 19% 39% 14% 4	198
February	1st to 10th	Day	33% 30% 28% 8% 2	240
	11th to 20th	Day	29% 27% 32% 10% 3	433
	21st to end	Day	31% 19% 32% 15% 3	382
March	1st to 10th	Day	34% 17% 30% 17% 3	460
	11th to 20th	Day	29% 24% 29% 13% 4	460
	21st to end	Day	34% 20% 26% 11% 8% 1	506
April	1st to 10th	Day	37% 14% 25% 16% 5% 1	460
	11th to 20th	Day	36% 18% 23% 15% 5% 2	452
	21st to end	Day	33% 17% 28% 13% 8% 1	460
May	1st to 10th	Day	34% 16% 27% 15% 6% 2	463
	11th to 20th	Day	24% 15% 33% 18% 8% 2	487
	21st to end	Day	23% 18% 30% 22% 6% 1	529
June	1st to 10th	Day	30% 13% 32% 17% 7% 1	490
	11th to 20th	Day	23% 13% 31% 23% 9% 2	490
	21st to end	Day	26% 17% 31% 18% 7% 1	490
July	1st to 10th	Day	19% 9% 33% 25% 12% 2	485
	11th to 20th	Day	17% 9% 38% 25% 9% 3	484
	21st to end	Day	17% 10% 35% 26% 9% 2	532
August	1st to 10th	Day	20% 10% 28% 28% 12% 3	486
	11th to 20th	Day	20% 8% 30% 23% 15% 5%	479
	21st to end	Day	21% 13% 25% 23% 13% 5%	532
September	1st to 10th	Day	20% 10% 26% 22% 14% 6%	450
	11th to 20th	Day	21% 12% 23% 20% 16% 8%	450
	21st to end	Day	18% 10% 30% 23% 12% 6%	450
October	1st to 10th	Day	29% 10% 25% 18% 14% 4	450
	11th to 20th	Day	29% 16% 24% 20% 10% 1	417
	21st to end	Day	39% 15% 22% 19% 4	396
November	1st to 10th	Day	33% 15% 21% 23% 8% 1	365
	11th to 20th	Day	31% 22% 24% 15% 8% 1	370
	21st to end	Day	35% 14% 31% 18% 1	195
December	1st to 10th	Day	30% 20% 31% 16% 4	180
	11th to 20th	Day	34% 20% 32% 11% 2	180
	21st to end	Day	31% 23% 30% 13% 2 1	198
January	1st to 10th	Night	26% 21% 29% 21% 3	760
	11th to 20th	Night	28% 19% 28% 20% 4	760
	21st to end	Night	20% 17% 32% 25% 4 1	836
February	1st to 10th	Night	23% 19% 33% 22% 3	760
	11th to 20th	Night	23% 23% 30% 21% 3	743
	21st to end	Night	23% 20% 30% 24% 3	628
March	1st to 10th	Night	29% 14% 29% 24% 4 1	760
	11th to 20th	Night	29% 18% 25% 21% 7%	760
	21st to end	Night	29% 15% 25% 21% 8% 1	836
April	1st to 10th	Night	31% 14% 25% 23% 6%	760
	11th to 20th	Night	30% 15% 24% 22% 8%	751
	21st to end	Night	30% 14% 25% 22% 8%	582
May	1st to 10th	Night	30% 11% 25% 22% 10% 1	527
	11th to 20th	Night	22% 8% 28% 31% 9% 2	374
	21st to end	Night	19% 9% 23% 36% 12%	411
June	1st to 10th	Night	30% 6% 22% 30% 11% 1	380
	11th to 20th	Night	22% 5% 22% 33% 17% 1	380
	21st to end	Night	24% 7% 18% 38% 12% 1	380
July	1st to 10th	Night	16% 4 22% 38% 19% 1	370
	11th to 20th	Night	12% 3 20% 44% 19% 1	368
	21st to end	Night	17% 4 17% 45% 17%	416
August	1st to 10th	Night	19% 4 14% 42% 21% 1	378
	11th to 20th	Night	18% 4 20% 32% 23% 2	600
	21st to end	Night	20% 5% 17% 35% 22% 2	832
September	1st to 10th	Night	18% 6% 19% 36% 19% 2	720
	11th to 20th	Night	21% 5% 18% 31% 22% 3	720
	21st to end	Night	23% 7% 22% 27% 17% 3	720
October	1st to 10th	Night	28% 11% 17% 27% 15% 2	720
	11th to 20th	Night	29% 11% 21% 27% 11% 1	720
	21st to end	Night	34% 13% 25% 23% 5%	792
November	1st to 10th	Night	30% 15% 23% 24% 8% 1	740
	11th to 20th	Night	29% 14% 26% 21% 8% 1	760
	21st to end	Night	31% 17% 25% 19% 7% 1	760
December	1st to 10th	Night	32% 19% 25% 19% 4	760
	11th to 20th	Night	28% 21% 26% 20% 5%	760
	21st to end	Night	31% 21% 24% 20% 3	836

Page generated at 2024-08-27 09:49:40. Version ac07

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