Halfmoon Observatory
Clear Sky Chart
History

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

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	13% 8% 3 7% 5% 4 4 4 5% 7% 41%	100997
	Night	14% 8% 3 6% 4 4 4 3 5% 6% 43%	98140
Transparency	Day	40% 5% 10% 24% 17% 3	104685
	Night	39% 5% 9% 24% 19% 4	102592
Seeing	Day	16% 12% 25% 24% 16% 7%	15400
	Night	18% 10% 25% 28% 16% 2	25171

By Month

Percentage Cloud Cover SE (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% 14% 6% 10% 5% 4 5% 3 4 4 32%	2527
	11th to 20th	Day	18% 9% 3 9% 6% 4 6% 2 4 4 33%	2530
	21st to end	Day	24% 13% 5% 7% 4 4 4 3 4 5% 28%	3240
February	1st to 10th	Day	18% 12% 4 6% 4 3 3 3 5% 6% 37%	1900
	11th to 20th	Day	19% 10% 3 7% 5% 4 3 3 5% 4 37%	1848
	21st to end	Day	17% 11% 3 8% 4 4 4 3 4 6% 34%	1570
March	1st to 10th	Day	21% 15% 4 7% 4 3 3 3 4 5% 32%	3120
	11th to 20th	Day	15% 7% 2 6% 3 3 2 3 4 6% 49%	3250
	21st to end	Day	12% 8% 3 8% 5% 4 4 4 5% 6% 41%	4159
April	1st to 10th	Day	14% 6% 2 6% 5% 4 4 4 5% 7% 43%	2280
	11th to 20th	Day	15% 7% 3 7% 5% 5% 4 3 5% 6% 40%	2254
	21st to end	Day	16% 7% 2 5% 5% 4 4 3 5% 8% 40%	2289
May	1st to 10th	Day	17% 8% 3 7% 5% 5% 5% 4 6% 9% 31%	4082
	11th to 20th	Day	18% 7% 3 6% 4 4 4 4 6% 7% 37%	4081
	21st to end	Day	12% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	4498
June	1st to 10th	Day	10% 5% 2 5% 5% 4 4 4 6% 8% 46%	2660
	11th to 20th	Day	5% 4 2 5% 5% 5% 6% 5% 7% 10% 47%	2660
	21st to end	Day	5% 5% 2 5% 6% 5% 5% 5% 7% 11% 44%	2660
July	1st to 10th	Day	9% 5% 2 7% 5% 6% 6% 5% 7% 10% 38%	4440
	11th to 20th	Day	7% 5% 2 5% 4 4 5% 5% 7% 11% 46%	4440
	21st to end	Day	11% 10% 4 10% 6% 6% 6% 4 6% 8% 28%	4638
August	1st to 10th	Day	5% 4 2 4 4 4 4 4 6% 9% 54%	3852
	11th to 20th	Day	8% 6% 2 7% 4 5% 6% 5% 8% 10% 40%	3729
	21st to end	Day	5% 4 2 5% 4 4 4 3 6% 9% 56%	4180
September	1st to 10th	Day	10% 6% 2 6% 5% 4 5% 5% 6% 8% 44%	2280
	11th to 20th	Day	11% 5% 2 6% 5% 5% 4 4 5% 7% 47%	2111
	21st to end	Day	12% 6% 2 7% 4 3 4 3 5% 6% 49%	2090
October	1st to 10th	Day	9% 5% 2 5% 3 3 3 3 4 7% 57%	2090
	11th to 20th	Day	12% 5% 1 6% 4 4 4 2 4 6% 52%	1961
	21st to end	Day	19% 7% 2 5% 3 3 2 2 5% 5% 47%	1929
November	1st to 10th	Day	10% 6% 2 6% 3 3 3 2 4 5% 55%	1735
	11th to 20th	Day	16% 7% 2 4 4 3 4 2 5% 6% 48%	1710
	21st to end	Day	17% 8% 3 6% 4 3 4 3 4 5% 43%	1710
December	1st to 10th	Day	19% 10% 3 6% 4 3 4 3 4 6% 36%	1710
	11th to 20th	Day	15% 13% 4 7% 5% 4 4 4 5% 5% 34%	2001
	21st to end	Day	16% 14% 5% 8% 5% 5% 5% 3 4 6% 29%	2783
January	1st to 10th	Night	18% 12% 4 6% 3 3 4 4 5% 5% 36%	4428
	11th to 20th	Night	16% 13% 4 10% 5% 5% 5% 2 3 4 32%	4440
	21st to end	Night	24% 13% 5% 6% 4 3 3 2 4 5% 31%	4418
February	1st to 10th	Night	21% 11% 4 8% 5% 4 4 3 4 5% 33%	2280
	11th to 20th	Night	19% 8% 4 8% 5% 4 4 3 3 5% 38%	2218
	21st to end	Night	21% 9% 4 7% 5% 4 4 3 4 5% 34%	1884
March	1st to 10th	Night	23% 11% 3 7% 3 3 3 3 4 5% 35%	3733
	11th to 20th	Night	13% 8% 2 5% 4 3 3 3 4 6% 49%	3709
	21st to end	Night	14% 8% 3 7% 5% 4 3 3 5% 6% 42%	3500
April	1st to 10th	Night	12% 6% 2 5% 4 3 4 4 6% 7% 47%	1900
	11th to 20th	Night	15% 6% 3 5% 4 3 4 4 4 6% 46%	1875
	21st to end	Night	14% 8% 3 5% 5% 4 4 4 6% 8% 39%	1891
May	1st to 10th	Night	20% 7% 2 6% 4 4 4 3 5% 7% 37%	2813
	11th to 20th	Night	15% 7% 2 6% 5% 4 3 4 6% 8% 41%	2812
	21st to end	Night	8% 6% 2 5% 5% 5% 6% 4 7% 9% 44%	3053
June	1st to 10th	Night	12% 6% 2 6% 3 3 5% 3 6% 8% 46%	1520
	11th to 20th	Night	5% 3 2 4 4 4 4 4 8% 8% 55%	1520
	21st to end	Night	2 3 1 4 5% 4 5% 4 8% 13% 50%	1520
July	1st to 10th	Night	7% 4 2 6% 4 4 5% 4 6% 10% 46%	2530
	11th to 20th	Night	6% 4 2 5% 3 3 4 4 6% 9% 55%	2530
	21st to end	Night	9% 7% 4 10% 6% 6% 6% 5% 7% 9% 31%	2916
August	1st to 10th	Night	5% 3 1 5% 3 3 3 3 5% 8% 60%	3073
	11th to 20th	Night	4 4 2 5% 4 5% 5% 4 7% 9% 51%	3100
	21st to end	Night	4 3 1 4 3 3 3 4 6% 8% 61%	3476
September	1st to 10th	Night	10% 5% 2 5% 4 3 3 3 5% 6% 53%	1900
	11th to 20th	Night	9% 6% 2 6% 4 3 5% 3 5% 6% 51%	2049
	21st to end	Night	11% 5% 2 4 4 3 3 3 5% 6% 53%	2090
October	1st to 10th	Night	7% 5% 2 5% 3 2 4 2 3 6% 61%	2090
	11th to 20th	Night	15% 5% 2 5% 3 3 3 2 4 4 54%	2215
	21st to end	Night	17% 7% 2 5% 3 3 4 3 4 6% 47%	2669
November	1st to 10th	Night	13% 6% 2 5% 3 3 3 3 4 6% 53%	2504
	11th to 20th	Night	13% 6% 2 5% 3 3 4 3 5% 6% 50%	2470
	21st to end	Night	17% 8% 2 4 4 3 3 3 5% 5% 46%	2470
December	1st to 10th	Night	20% 11% 3 6% 3 4 4 3 5% 5% 36%	2470
	11th to 20th	Night	17% 10% 3 7% 4 4 4 3 4 5% 40%	3190
	21st to end	Night	18% 14% 4 9% 5% 5% 5% 4 4 6% 27%	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	54% 4 7% 23% 9% 2	2528
	11th to 20th	Day	55% 3 7% 22% 11% 2	2530
	21st to end	Day	59% 4 8% 20% 9% 1	3240
February	1st to 10th	Day	49% 3 9% 24% 13% 2	1900
	11th to 20th	Day	51% 3 8% 21% 12% 4	1858
	21st to end	Day	52% 4 8% 16% 15% 5%	1570
March	1st to 10th	Day	56% 3 5% 18% 12% 6%	3120
	11th to 20th	Day	38% 4 8% 28% 17% 4	3250
	21st to end	Day	43% 5% 10% 24% 17% 1	4159
April	1st to 10th	Day	40% 4 11% 24% 19% 2	2280
	11th to 20th	Day	45% 4 8% 21% 18% 3	2254
	21st to end	Day	43% 5% 10% 27% 13% 2	2289
May	1st to 10th	Day	47% 9% 12% 21% 11% 1	4120
	11th to 20th	Day	45% 8% 10% 24% 13% 1	4085
	21st to end	Day	41% 7% 10% 19% 21% 1	4511
June	1st to 10th	Day	34% 6% 13% 24% 20% 3	2660
	11th to 20th	Day	30% 7% 13% 27% 20% 3	2660
	21st to end	Day	32% 9% 15% 23% 16% 5%	2660
July	1st to 10th	Day	40% 7% 13% 27% 11% 2	4371
	11th to 20th	Day	31% 6% 14% 36% 12% 2	4365
	21st to end	Day	53% 6% 13% 20% 8% 1	4491
August	1st to 10th	Day	26% 6% 14% 32% 22% 1	3839
	11th to 20th	Day	37% 6% 11% 27% 18% 1	3765
	21st to end	Day	26% 5% 11% 36% 20% 3	4179
September	1st to 10th	Day	37% 6% 10% 23% 20% 4	2280
	11th to 20th	Day	37% 5% 11% 23% 22% 3	2111
	21st to end	Day	36% 4 7% 25% 23% 5%	2090
October	1st to 10th	Day	18% 3 6% 18% 48% 7%	3480
	11th to 20th	Day	24% 3 6% 27% 31% 9%	3240
	21st to end	Day	30% 3 5% 28% 28% 6%	3154
November	1st to 10th	Day	33% 3 9% 25% 25% 5%	1735
	11th to 20th	Day	38% 4 8% 23% 21% 6%	1710
	21st to end	Day	44% 4 6% 26% 16% 4	1710
December	1st to 10th	Day	49% 4 10% 22% 12% 2	1710
	11th to 20th	Day	51% 4 9% 22% 13% 2	1998
	21st to end	Day	56% 6% 11% 17% 10%	2783
January	1st to 10th	Night	49% 3 8% 26% 12% 1	4428
	11th to 20th	Night	57% 3 6% 20% 11% 2	4440
	21st to end	Night	56% 4 8% 22% 10% 1	4418
February	1st to 10th	Night	56% 3 9% 19% 13% 1	2280
	11th to 20th	Night	50% 3 6% 23% 15% 3	2219
	21st to end	Night	53% 4 8% 16% 16% 4	1884
March	1st to 10th	Night	53% 4 6% 14% 18% 4	3733
	11th to 20th	Night	38% 5% 11% 23% 15% 9%	3709
	21st to end	Night	43% 4 10% 25% 16% 1	3500
April	1st to 10th	Night	35% 5% 10% 27% 20% 3	1900
	11th to 20th	Night	39% 5% 9% 20% 21% 6%	1875
	21st to end	Night	41% 5% 10% 24% 17% 2	1891
May	1st to 10th	Night	45% 8% 12% 23% 10% 1	2840
	11th to 20th	Night	40% 8% 12% 24% 14% 1	2813
	21st to end	Night	34% 10% 14% 23% 18% 2	3061
June	1st to 10th	Night	35% 5% 12% 24% 21% 3	1520
	11th to 20th	Night	24% 7% 15% 25% 25% 4	1520
	21st to end	Night	23% 9% 17% 27% 19% 6%	1520
July	1st to 10th	Night	33% 6% 13% 29% 15% 3	2490
	11th to 20th	Night	25% 5% 13% 37% 16% 3	2482
	21st to end	Night	48% 8% 14% 20% 9% 1	2823
August	1st to 10th	Night	23% 6% 12% 37% 21% 1	3062
	11th to 20th	Night	28% 6% 16% 30% 19% 1	3130
	21st to end	Night	21% 5% 9% 37% 24% 3	3476
September	1st to 10th	Night	31% 6% 9% 26% 23% 5%	1900
	11th to 20th	Night	33% 5% 8% 27% 24% 4	2049
	21st to end	Night	32% 4 9% 22% 26% 7%	2090
October	1st to 10th	Night	18% 3 5% 15% 48% 11%	3480
	11th to 20th	Night	22% 2 5% 23% 39% 10%	3675
	21st to end	Night	29% 2 7% 23% 28% 10%	4394
November	1st to 10th	Night	35% 3 7% 24% 25% 6%	2504
	11th to 20th	Night	35% 4 6% 24% 22% 9%	2470
	21st to end	Night	40% 3 8% 25% 20% 4	2470
December	1st to 10th	Night	50% 4 10% 21% 13% 2	2470
	11th to 20th	Night	46% 3 8% 22% 18% 3	3192
	21st to end	Night	58% 5% 8% 17% 10% 2	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% 25% 32% 14% 4	270
	11th to 20th	Day	29% 26% 33% 10% 2	270
	21st to end	Day	23% 27% 39% 10% 1	297
February	1st to 10th	Day	28% 26% 31% 11% 2 1	270
	11th to 20th	Day	33% 27% 32% 7% 1	270
	21st to end	Day	35% 24% 30% 10% 2	225
March	1st to 10th	Day	27% 25% 34% 11% 3	270
	11th to 20th	Day	28% 24% 32% 12% 3	321
	21st to end	Day	28% 18% 34% 15% 6%	506
April	1st to 10th	Day	20% 21% 29% 23% 6% 1	460
	11th to 20th	Day	23% 18% 28% 21% 9% 2	452
	21st to end	Day	21% 17% 30% 21% 8% 3	460
May	1st to 10th	Day	21% 17% 29% 22% 8% 3	463
	11th to 20th	Day	17% 10% 24% 30% 13% 5%	487
	21st to end	Day	11% 7% 27% 28% 17% 10%	538
June	1st to 10th	Day	12% 5% 22% 28% 22% 10%	680
	11th to 20th	Day	5% 4 23% 35% 24% 9%	680
	21st to end	Day	6% 5% 25% 35% 19% 10%	680
July	1st to 10th	Day	10% 3 17% 27% 24% 18%	671
	11th to 20th	Day	8% 4 18% 30% 29% 12%	668
	21st to end	Day	9% 3 17% 31% 26% 14%	639
August	1st to 10th	Day	13% 2 14% 33% 24% 14%	486
	11th to 20th	Day	14% 3 16% 32% 27% 7%	479
	21st to end	Day	9% 3 12% 28% 33% 16%	539
September	1st to 10th	Day	10% 4 17% 29% 30% 11%	490
	11th to 20th	Day	9% 3 14% 27% 33% 13%	490
	21st to end	Day	17% 9% 20% 25% 21% 9%	490
October	1st to 10th	Day	9% 6% 26% 32% 21% 6%	490
	11th to 20th	Day	14% 13% 34% 23% 11% 4	361
	21st to end	Day	25% 17% 30% 20% 6% 2	330
November	1st to 10th	Day	16% 11% 39% 21% 11% 1	291
	11th to 20th	Day	18% 20% 33% 23% 4 1	270
	21st to end	Day	23% 17% 31% 21% 8% 1	270
December	1st to 10th	Day	23% 23% 29% 18% 6% 1	270
	11th to 20th	Day	24% 17% 34% 20% 4	270
	21st to end	Day	26% 25% 33% 14% 2	297
January	1st to 10th	Night	25% 19% 31% 22% 3	950
	11th to 20th	Night	27% 18% 34% 17% 3	950
	21st to end	Night	24% 18% 35% 21% 2	960
February	1st to 10th	Night	26% 17% 33% 21% 2	760
	11th to 20th	Night	27% 18% 34% 18% 2	743
	21st to end	Night	27% 19% 34% 18% 1	628
March	1st to 10th	Night	23% 18% 31% 24% 5%	760
	11th to 20th	Night	22% 16% 34% 22% 5%	760
	21st to end	Night	23% 13% 29% 29% 6%	648
April	1st to 10th	Night	16% 13% 34% 28% 7% 1	570
	11th to 20th	Night	20% 12% 30% 26% 13%	563
	21st to end	Night	18% 11% 32% 28% 10% 1	570
May	1st to 10th	Night	21% 7% 32% 24% 14% 2	570
	11th to 20th	Night	14% 6% 22% 35% 20% 3	561
	21st to end	Night	8% 4 21% 35% 29% 4	617
June	1st to 10th	Night	13% 3 17% 34% 29% 4	570
	11th to 20th	Night	5% 1 15% 44% 31% 3	570
	21st to end	Night	3 2 18% 40% 33% 4	570
July	1st to 10th	Night	9% 1 10% 33% 37% 10%	555
	11th to 20th	Night	9% 3 10% 30% 42% 7%	552
	21st to end	Night	9% 2 13% 35% 33% 9%	624
August	1st to 10th	Night	8% 2 9% 33% 41% 7%	567
	11th to 20th	Night	7% 2 11% 40% 35% 4	564
	21st to end	Night	9% 1 7% 33% 41% 8%	627
September	1st to 10th	Night	13% 2 14% 31% 35% 5%	570
	11th to 20th	Night	11% 3 11% 30% 39% 6%	719
	21st to end	Night	12% 5% 22% 29% 27% 5%	760
October	1st to 10th	Night	11% 6% 18% 33% 28% 5%	760
	11th to 20th	Night	17% 7% 26% 31% 16% 2	760
	21st to end	Night	22% 9% 30% 26% 12% 1	836
November	1st to 10th	Night	16% 9% 28% 32% 14% 1	771
	11th to 20th	Night	16% 13% 32% 28% 10%	760
	21st to end	Night	22% 13% 28% 25% 10% 1	760
December	1st to 10th	Night	26% 11% 32% 24% 6%	760
	11th to 20th	Night	25% 11% 31% 26% 6%	861
	21st to end	Night	29% 14% 30% 24% 3	1045

Page generated at 2024-11-05 07:15:52. Version ac07

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