Halfmoon Stream Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Halfmoon Stream Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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	18% 9% 3 6% 4 4 4 4 5% 7% 36%	104422
	Night	17% 9% 3 7% 4 4 4 3 5% 6% 37%	104642
Transparency	Day	47% 3 11% 23% 13% 2	107961
	Night	47% 3 11% 23% 14% 2	109193
Seeing	Day	24% 18% 32% 18% 6% 1	15747
	Night	23% 16% 33% 22% 6% 1	24300

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	16% 9% 3 6% 4 4 4 3 5% 6% 39%	2565
	11th to 20th	Day	16% 7% 3 6% 4 4 4 3 5% 5% 42%	2520
	21st to end	Day	16% 12% 4 8% 4 3 3 4 5% 5% 36%	2773
February	1st to 10th	Day	17% 10% 3 6% 5% 5% 4 4 5% 6% 35%	1710
	11th to 20th	Day	13% 10% 3 8% 6% 5% 5% 4 5% 5% 36%	1790
	21st to end	Day	14% 10% 3 9% 5% 5% 5% 4 5% 5% 35%	1570
March	1st to 10th	Day	24% 14% 3 7% 4 4 4 3 4 4 29%	3116
	11th to 20th	Day	17% 11% 3 9% 5% 4 4 2 4 5% 34%	3471
	21st to end	Day	24% 10% 3 8% 4 3 3 4 6% 6% 29%	3833
April	1st to 10th	Day	21% 12% 3 7% 5% 4 3 4 4 5% 32%	2280
	11th to 20th	Day	18% 9% 2 6% 5% 3 4 4 6% 8% 36%	2397
	21st to end	Day	22% 9% 3 7% 4 4 4 3 4 6% 33%	2470
May	1st to 10th	Day	21% 10% 3 7% 5% 4 5% 4 5% 6% 29%	4106
	11th to 20th	Day	18% 9% 3 8% 5% 5% 5% 5% 5% 6% 31%	4095
	21st to end	Day	15% 6% 2 6% 5% 4 5% 5% 7% 9% 35%	4887
June	1st to 10th	Day	23% 8% 3 6% 5% 4 5% 3 5% 7% 31%	2850
	11th to 20th	Day	19% 7% 3 6% 4 4 5% 4 6% 7% 36%	2850
	21st to end	Day	24% 9% 3 6% 4 4 4 4 6% 7% 29%	2850
July	1st to 10th	Day	14% 6% 2 7% 4 5% 5% 5% 7% 10% 34%	4452
	11th to 20th	Day	14% 6% 2 6% 5% 5% 5% 4 7% 10% 37%	4440
	21st to end	Day	19% 6% 3 7% 4 4 4 4 6% 8% 35%	4788
August	1st to 10th	Day	18% 7% 3 7% 5% 5% 5% 4 6% 8% 33%	4105
	11th to 20th	Day	16% 9% 3 8% 5% 5% 4 4 6% 8% 32%	4045
	21st to end	Day	10% 6% 2 5% 4 4 5% 4 5% 9% 44%	4454
September	1st to 10th	Day	11% 5% 2 5% 4 4 4 4 6% 7% 49%	2204
	11th to 20th	Day	13% 4 2 4 4 4 4 2 4 6% 52%	2090
	21st to end	Day	16% 6% 2 5% 4 3 4 3 5% 8% 44%	2090
October	1st to 10th	Day	16% 7% 3 7% 5% 4 4 3 5% 6% 39%	2057
	11th to 20th	Day	18% 6% 2 6% 4 4 4 2 4 7% 41%	1862
	21st to end	Day	20% 10% 3 7% 4 4 3 3 5% 5% 36%	1881
November	1st to 10th	Day	16% 8% 2 6% 4 4 5% 3 5% 7% 41%	1761
	11th to 20th	Day	19% 8% 2 4 4 3 4 3 6% 6% 41%	1800
	21st to end	Day	19% 10% 2 5% 4 3 4 3 3 5% 42%	1615
December	1st to 10th	Day	16% 12% 2 4 4 3 3 3 5% 7% 40%	2379
	11th to 20th	Day	19% 8% 3 5% 3 4 3 3 4 6% 42%	2618
	21st to end	Day	21% 12% 4 6% 3 4 4 3 4 4 35%	3648
January	1st to 10th	Night	14% 10% 3 7% 5% 4 4 3 5% 6% 39%	4514
	11th to 20th	Night	13% 9% 3 9% 6% 5% 4 4 6% 6% 36%	4440
	21st to end	Night	15% 12% 4 9% 5% 4 4 4 5% 6% 32%	4880
February	1st to 10th	Night	15% 9% 4 7% 6% 5% 6% 4 5% 6% 33%	2470
	11th to 20th	Night	13% 9% 4 8% 6% 5% 4 3 5% 5% 38%	2274
	21st to end	Night	13% 12% 2 8% 6% 4 4 3 5% 6% 38%	1884
March	1st to 10th	Night	28% 14% 3 6% 3 4 3 2 3 4 30%	3724
	11th to 20th	Night	13% 11% 3 8% 6% 5% 6% 4 6% 7% 29%	3485
	21st to end	Night	25% 10% 2 7% 4 4 4 4 6% 5% 27%	3795
April	1st to 10th	Night	21% 11% 3 6% 4 4 3 3 5% 5% 33%	1900
	11th to 20th	Night	18% 7% 3 7% 5% 4 4 4 6% 7% 34%	1730
	21st to end	Night	22% 10% 3 6% 4 3 4 3 5% 6% 34%	1710
May	1st to 10th	Night	22% 9% 3 6% 3 3 4 3 6% 9% 32%	2834
	11th to 20th	Night	18% 7% 3 8% 6% 5% 6% 4 7% 9% 27%	2813
	21st to end	Night	15% 7% 2 6% 5% 5% 5% 3 6% 8% 38%	2701
June	1st to 10th	Night	21% 8% 2 7% 4 5% 4 4 6% 8% 30%	1330
	11th to 20th	Night	16% 8% 3 5% 5% 4 4 3 5% 8% 39%	1330
	21st to end	Night	22% 9% 3 7% 5% 4 4 4 6% 8% 29%	1330
July	1st to 10th	Night	12% 7% 2 7% 5% 5% 6% 5% 7% 9% 34%	2503
	11th to 20th	Night	15% 6% 2 7% 5% 4 4 4 6% 8% 38%	2520
	21st to end	Night	14% 7% 2 6% 4 4 5% 4 5% 8% 41%	2739
August	1st to 10th	Night	20% 8% 3 7% 6% 5% 5% 4 5% 7% 30%	2820
	11th to 20th	Night	14% 10% 3 7% 4 5% 6% 4 6% 7% 34%	2782
	21st to end	Night	10% 6% 2 6% 4 4 4 4 6% 8% 46%	3186
September	1st to 10th	Night	13% 5% 2 5% 3 3 4 4 5% 7% 50%	1976
	11th to 20th	Night	15% 6% 2 4 3 2 3 2 4 7% 53%	2090
	21st to end	Night	15% 8% 2 4 4 4 4 3 4 7% 45%	2090
October	1st to 10th	Night	18% 5% 2 7% 4 4 4 4 5% 6% 41%	2122
	11th to 20th	Night	17% 6% 2 5% 4 4 4 3 5% 7% 43%	2316
	21st to end	Night	22% 10% 2 6% 4 4 4 3 4 5% 37%	2717
November	1st to 10th	Night	17% 7% 3 6% 4 3 3 4 5% 6% 42%	2537
	11th to 20th	Night	17% 6% 3 5% 4 4 4 3 5% 7% 40%	2600
	21st to end	Night	17% 9% 3 5% 5% 4 4 3 5% 6% 40%	2782
December	1st to 10th	Night	16% 11% 3 6% 4 4 5% 4 6% 7% 36%	4809
	11th to 20th	Night	22% 9% 2 4 4 3 3 3 4 5% 40%	5591
	21st to end	Night	20% 12% 3 7% 3 3 3 3 4 5% 37%	7318

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	47% 1 12% 28% 10% 1	2566
	11th to 20th	Day	43% 3 10% 28% 13% 2	2520
	21st to end	Day	50% 2 13% 20% 14% 1	2773
February	1st to 10th	Day	50% 3 10% 20% 14% 3	1710
	11th to 20th	Day	49% 4 9% 21% 15% 2	1799
	21st to end	Day	50% 3 9% 21% 11% 5%	1570
March	1st to 10th	Day	60% 3 7% 13% 14% 3	3119
	11th to 20th	Day	53% 2 9% 20% 13% 3	3471
	21st to end	Day	56% 2 4 16% 17% 4	3833
April	1st to 10th	Day	55% 3 7% 16% 15% 4	2280
	11th to 20th	Day	47% 3 8% 23% 16% 2	2397
	21st to end	Day	53% 3 7% 19% 14% 4	2470
May	1st to 10th	Day	56% 3 11% 19% 9% 2	4120
	11th to 20th	Day	53% 2 12% 21% 10% 1	4099
	21st to end	Day	46% 3 14% 22% 15% 1	4887
June	1st to 10th	Day	53% 4 11% 23% 9% 1	2850
	11th to 20th	Day	46% 4 12% 20% 15% 2	2850
	21st to end	Day	54% 5% 11% 19% 9% 1	2850
July	1st to 10th	Day	43% 5% 13% 27% 11%	4382
	11th to 20th	Day	41% 5% 15% 27% 11% 1	4365
	21st to end	Day	47% 5% 11% 23% 14% 1	4635
August	1st to 10th	Day	49% 4 14% 26% 6%	4092
	11th to 20th	Day	49% 5% 16% 22% 8%	4084
	21st to end	Day	36% 4 12% 28% 19% 1	4454
September	1st to 10th	Day	34% 4 14% 28% 18% 1	2204
	11th to 20th	Day	34% 3 9% 30% 21% 3	2090
	21st to end	Day	40% 3 10% 29% 17% 1	2090
October	1st to 10th	Day	53% 3 9% 23% 12% 1	3421
	11th to 20th	Day	35% 2 10% 32% 21%	3078
	21st to end	Day	37% 2 13% 25% 19% 3	3081
November	1st to 10th	Day	44% 3 13% 23% 15% 2	1761
	11th to 20th	Day	43% 4 9% 23% 19% 4	1800
	21st to end	Day	45% 3 15% 24% 12% 1	1615
December	1st to 10th	Day	44% 3 14% 26% 12% 1	2379
	11th to 20th	Day	44% 2 11% 18% 17% 7%	2618
	21st to end	Day	53% 2 9% 19% 12% 4	3648
January	1st to 10th	Night	47% 2 11% 28% 10% 2	4514
	11th to 20th	Night	49% 3 12% 21% 12% 3	4440
	21st to end	Night	54% 2 8% 21% 13% 1	4880
February	1st to 10th	Night	51% 3 11% 20% 13% 2	2470
	11th to 20th	Night	48% 3 8% 22% 16% 3	2276
	21st to end	Night	47% 3 9% 21% 15% 5%	1884
March	1st to 10th	Night	60% 2 7% 16% 11% 4	3734
	11th to 20th	Night	54% 2 11% 20% 11% 2	3486
	21st to end	Night	58% 2 4 16% 17% 2	3795
April	1st to 10th	Night	53% 3 6% 17% 18% 3	1900
	11th to 20th	Night	48% 3 8% 24% 16% 1	1730
	21st to end	Night	52% 3 11% 17% 15% 3	1710
May	1st to 10th	Night	51% 2 17% 21% 8% 1	2840
	11th to 20th	Night	54% 3 13% 22% 7% 1	2814
	21st to end	Night	46% 2 16% 23% 12% 1	2702
June	1st to 10th	Night	52% 4 11% 23% 9% 1	1330
	11th to 20th	Night	45% 3 14% 23% 12% 2	1330
	21st to end	Night	54% 4 12% 19% 9% 2	1330
July	1st to 10th	Night	45% 5% 16% 23% 12%	2463
	11th to 20th	Night	44% 4 15% 28% 9%	2472
	21st to end	Night	42% 4 14% 28% 12% 1	2651
August	1st to 10th	Night	54% 5% 13% 21% 7%	2809
	11th to 20th	Night	48% 4 16% 21% 10%	2809
	21st to end	Night	36% 4 14% 27% 17% 1	3186
September	1st to 10th	Night	34% 4 14% 32% 16% 1	1976
	11th to 20th	Night	33% 2 11% 31% 20% 2	2090
	21st to end	Night	40% 3 9% 30% 16% 2	2090
October	1st to 10th	Night	43% 3 14% 26% 14% 1	3538
	11th to 20th	Night	34% 2 10% 31% 22% 1	3839
	21st to end	Night	39% 3 11% 29% 16% 2	4467
November	1st to 10th	Night	42% 4 11% 27% 15% 1	2537
	11th to 20th	Night	43% 4 9% 24% 18% 3	2600
	21st to end	Night	45% 4 14% 21% 15% 2	2782
December	1st to 10th	Night	47% 2 9% 30% 12%	4809
	11th to 20th	Night	47% 3 10% 19% 19% 2	5592
	21st to end	Night	51% 2 10% 19% 17% 2	7318

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	31% 26% 27% 13% 3	192
	11th to 20th	Day	30% 25% 31% 10% 3 1	180
	21st to end	Day	23% 27% 35% 14% 2	199
February	1st to 10th	Day	27% 22% 31% 16% 3	370
	11th to 20th	Day	28% 30% 31% 9% 2	429
	21st to end	Day	24% 27% 31% 15% 3	382
March	1st to 10th	Day	29% 26% 31% 12% 1	460
	11th to 20th	Day	23% 30% 32% 12% 3 1	460
	21st to end	Day	31% 24% 27% 13% 4 1	506
April	1st to 10th	Day	33% 25% 28% 10% 3 1	460
	11th to 20th	Day	31% 27% 25% 12% 4 1	452
	21st to end	Day	30% 22% 31% 12% 5% 1	460
May	1st to 10th	Day	30% 20% 33% 12% 3 1	463
	11th to 20th	Day	21% 21% 35% 18% 4 1	487
	21st to end	Day	21% 21% 35% 18% 5%	553
June	1st to 10th	Day	25% 15% 33% 18% 8% 1	680
	11th to 20th	Day	21% 13% 34% 20% 11% 1	680
	21st to end	Day	29% 11% 30% 22% 7% 1	680
July	1st to 10th	Day	20% 12% 37% 22% 8% 1	497
	11th to 20th	Day	19% 9% 40% 21% 9% 2	484
	21st to end	Day	17% 10% 37% 25% 9% 2	532
August	1st to 10th	Day	17% 9% 36% 28% 8% 1	486
	11th to 20th	Day	19% 10% 30% 29% 10% 2	479
	21st to end	Day	18% 12% 32% 27% 9% 2	539
September	1st to 10th	Day	14% 13% 35% 26% 11% 2	490
	11th to 20th	Day	19% 12% 30% 21% 12% 7%	490
	21st to end	Day	19% 16% 31% 20% 9% 5%	490
October	1st to 10th	Day	21% 16% 28% 23% 9% 3	473
	11th to 20th	Day	24% 18% 31% 17% 8% 2	390
	21st to end	Day	31% 15% 35% 14% 4	429
November	1st to 10th	Day	24% 20% 29% 20% 6% 2	395
	11th to 20th	Day	28% 21% 31% 17% 3 1	400
	21st to end	Day	30% 24% 26% 16% 5%	400
December	1st to 10th	Day	28% 22% 29% 16% 4	260
	11th to 20th	Day	35% 28% 26% 9% 3	200
	21st to end	Day	30% 27% 25% 15% 2	220
January	1st to 10th	Night	24% 22% 35% 17% 3	785
	11th to 20th	Night	26% 23% 30% 17% 3	760
	21st to end	Night	18% 26% 35% 18% 3	836
February	1st to 10th	Night	22% 22% 35% 18% 3	760
	11th to 20th	Night	22% 25% 36% 14% 2	743
	21st to end	Night	23% 23% 33% 18% 3	628
March	1st to 10th	Night	26% 20% 38% 14% 1	760
	11th to 20th	Night	22% 24% 32% 16% 5%	760
	21st to end	Night	24% 20% 33% 18% 5%	836
April	1st to 10th	Night	29% 18% 33% 17% 3	760
	11th to 20th	Night	25% 18% 35% 18% 4	606
	21st to end	Night	31% 16% 31% 19% 3	570
May	1st to 10th	Night	26% 11% 33% 25% 4	570
	11th to 20th	Night	24% 12% 38% 21% 4	562
	21st to end	Night	23% 9% 33% 28% 6%	424
June	1st to 10th	Night	27% 9% 31% 29% 5%	380
	11th to 20th	Night	18% 9% 33% 30% 9%	380
	21st to end	Night	28% 4 33% 31% 4	380
July	1st to 10th	Night	18% 5% 33% 37% 7%	370
	11th to 20th	Night	17% 3 31% 37% 11% 1	368
	21st to end	Night	18% 4 32% 35% 11% 1	416
August	1st to 10th	Night	16% 3 35% 37% 9%	563
	11th to 20th	Night	16% 6% 31% 34% 12% 1	562
	21st to end	Night	16% 7% 29% 35% 12% 1	663
September	1st to 10th	Night	15% 7% 36% 31% 10% 1	760
	11th to 20th	Night	19% 9% 28% 28% 13% 4	760
	21st to end	Night	21% 9% 32% 26% 11% 2	760
October	1st to 10th	Night	22% 10% 30% 25% 13%	760
	11th to 20th	Night	21% 14% 32% 23% 9% 1	760
	21st to end	Night	29% 17% 32% 19% 4	836
November	1st to 10th	Night	23% 17% 30% 21% 6% 1	780
	11th to 20th	Night	21% 20% 33% 20% 6% 1	800
	21st to end	Night	25% 24% 29% 18% 4	892
December	1st to 10th	Night	26% 20% 32% 16% 6%	900
	11th to 20th	Night	26% 24% 31% 16% 3	900
	21st to end	Night	29% 21% 31% 16% 3	950

Page generated at 2025-01-04 03:23:58. Version ac07

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