BoonHill Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the BoonHill Observatory clear sky chart from 2005-11-06 to 2024-11-10.

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% 12% 4 10% 6% 5% 4 4 5% 6% 31%	101169
	Night	13% 13% 5% 11% 6% 5% 4 3 5% 5% 30%	98013
Transparency	Day	52% 6% 10% 19% 12% 1	104714
	Night	55% 6% 11% 18% 9% 1	102596
Seeing	Day	20% 14% 30% 22% 10% 3	15823
	Night	20% 11% 31% 28% 9% 1	25800

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	11% 23% 12% 22% 8% 6% 3 2 3 2 8%	2527
	11th to 20th	Day	12% 17% 8% 21% 14% 11% 5% 2 2 2 4	2530
	21st to end	Day	17% 22% 11% 15% 9% 5% 5% 3 3 3 7%	2783
February	1st to 10th	Day	9% 18% 7% 13% 15% 8% 6% 3 3 5% 13%	1656
	11th to 20th	Day	9% 16% 7% 18% 12% 8% 4 4 4 4 15%	1848
	21st to end	Day	10% 18% 9% 15% 7% 5% 4 3 4 4 20%	1570
March	1st to 10th	Day	11% 15% 6% 10% 6% 5% 4 4 5% 5% 29%	3120
	11th to 20th	Day	9% 9% 6% 18% 8% 5% 3 3 5% 6% 27%	3378
	21st to end	Day	18% 13% 5% 16% 7% 5% 3 3 4 4 23%	3967
April	1st to 10th	Day	16% 18% 5% 8% 5% 4 4 3 5% 6% 27%	2280
	11th to 20th	Day	19% 14% 4 8% 4 3 4 3 4 5% 32%	2333
	21st to end	Day	15% 12% 4 9% 6% 5% 4 4 6% 6% 30%	2470
May	1st to 10th	Day	14% 9% 3 7% 4 4 4 3 5% 7% 39%	4082
	11th to 20th	Day	11% 8% 2 6% 5% 5% 5% 4 5% 7% 43%	4199
	21st to end	Day	12% 7% 3 6% 4 4 5% 4 6% 7% 42%	4824
June	1st to 10th	Day	11% 7% 2 7% 5% 4 5% 4 6% 7% 41%	2660
	11th to 20th	Day	12% 8% 2 7% 5% 4 4 3 7% 8% 40%	2660
	21st to end	Day	13% 6% 3 6% 5% 5% 5% 4 7% 8% 38%	2660
July	1st to 10th	Day	14% 7% 3 7% 4 5% 5% 4 7% 9% 35%	4440
	11th to 20th	Day	7% 5% 2 4 4 4 5% 4 8% 11% 46%	4440
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 4 7% 8% 42%	4813
August	1st to 10th	Day	10% 6% 2 7% 5% 6% 6% 5% 8% 8% 38%	4231
	11th to 20th	Day	13% 6% 3 6% 4 4 4 4 6% 7% 43%	4044
	21st to end	Day	11% 7% 2 8% 5% 5% 5% 4 5% 8% 41%	4292
September	1st to 10th	Day	14% 5% 2 6% 6% 5% 6% 4 5% 7% 40%	2256
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 7% 46%	2090
	21st to end	Day	14% 9% 3 7% 5% 4 5% 4 5% 8% 36%	2090
October	1st to 10th	Day	17% 9% 2 7% 4 5% 3 3 4 6% 39%	2090
	11th to 20th	Day	20% 16% 3 10% 6% 5% 4 4 5% 6% 21%	1811
	21st to end	Day	21% 16% 4 10% 6% 5% 4 4 5% 6% 19%	1881
November	1st to 10th	Day	14% 17% 5% 7% 5% 3 4 4 6% 7% 28%	1753
	11th to 20th	Day	12% 21% 9% 14% 6% 5% 4 3 5% 6% 17%	1710
	21st to end	Day	16% 23% 9% 14% 5% 4 3 2 2 5% 16%	1687
December	1st to 10th	Day	14% 22% 11% 19% 6% 4 4 2 3 4 11%	1385
	11th to 20th	Day	13% 21% 9% 17% 9% 6% 4 3 4 5% 10%	1826
	21st to end	Day	17% 25% 9% 17% 7% 5% 4 2 2 3 8%	2783
January	1st to 10th	Night	13% 21% 11% 18% 7% 6% 3 3 3 3 12%	4428
	11th to 20th	Night	11% 17% 8% 22% 11% 13% 5% 2 3 3 7%	4440
	21st to end	Night	15% 21% 9% 20% 8% 7% 5% 3 4 3 7%	4884
February	1st to 10th	Night	10% 15% 6% 16% 13% 9% 5% 4 3 4 15%	2523
	11th to 20th	Night	11% 13% 6% 16% 10% 6% 6% 4 5% 5% 17%	2218
	21st to end	Night	13% 15% 5% 14% 8% 5% 5% 3 4 5% 21%	1884
March	1st to 10th	Night	15% 10% 5% 9% 4 4 4 3 4 5% 36%	3733
	11th to 20th	Night	8% 13% 6% 10% 6% 4 3 4 6% 6% 35%	3581
	21st to end	Night	14% 13% 6% 13% 6% 4 5% 3 4 6% 26%	3693
April	1st to 10th	Night	15% 13% 5% 8% 5% 5% 4 4 5% 5% 30%	1900
	11th to 20th	Night	20% 11% 3 7% 3 3 5% 3 5% 7% 33%	1795
	21st to end	Night	16% 10% 3 8% 5% 4 3 3 6% 5% 37%	1710
May	1st to 10th	Night	14% 9% 3 6% 5% 5% 4 4 5% 7% 39%	2813
	11th to 20th	Night	13% 8% 3 6% 4 4 4 3 6% 8% 40%	2695
	21st to end	Night	17% 7% 2 6% 4 4 3 3 6% 6% 43%	2743
June	1st to 10th	Night	14% 8% 2 6% 5% 3 4 4 6% 8% 41%	1520
	11th to 20th	Night	10% 6% 2 8% 5% 4 4 4 6% 9% 43%	1520
	21st to end	Night	11% 7% 2 6% 4 4 5% 4 5% 7% 45%	1520
July	1st to 10th	Night	11% 9% 3 6% 4 4 5% 4 6% 7% 40%	2530
	11th to 20th	Night	6% 4 2 5% 3 4 4 4 6% 7% 55%	2530
	21st to end	Night	6% 6% 2 6% 4 4 4 4 6% 7% 50%	2750
August	1st to 10th	Night	11% 5% 3 7% 4 5% 5% 4 7% 8% 41%	2699
	11th to 20th	Night	12% 7% 2 5% 3 3 3 3 5% 6% 51%	2785
	21st to end	Night	8% 7% 2 6% 4 5% 4 4 5% 6% 48%	3348
September	1st to 10th	Night	11% 6% 2 6% 4 3 3 3 6% 6% 50%	1904
	11th to 20th	Night	12% 5% 2 6% 3 3 4 4 6% 6% 50%	2090
	21st to end	Night	15% 8% 3 7% 4 4 5% 3 6% 7% 39%	2090
October	1st to 10th	Night	15% 9% 3 7% 4 4 3 2 5% 6% 42%	2090
	11th to 20th	Night	18% 14% 3 8% 5% 4 4 4 5% 5% 30%	2365
	21st to end	Night	22% 14% 4 8% 5% 4 4 3 5% 5% 26%	2717
November	1st to 10th	Night	11% 17% 5% 9% 6% 4 4 3 5% 7% 30%	2530
	11th to 20th	Night	13% 19% 6% 15% 6% 5% 5% 3 4 5% 19%	2470
	21st to end	Night	16% 19% 7% 13% 5% 5% 4 4 4 5% 18%	2491
December	1st to 10th	Night	13% 21% 9% 18% 8% 4 5% 3 3 4 12%	2785
	11th to 20th	Night	12% 22% 8% 19% 8% 5% 4 4 3 3 12%	3355
	21st to end	Night	20% 26% 9% 15% 5% 4 3 2 3 3 10%	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	85% 4 5% 4 2	2528
	11th to 20th	Day	89% 3 3 3 1	2530
	21st to end	Day	83% 6% 7% 3 1	2783
February	1st to 10th	Day	74% 5% 7% 11% 3	1656
	11th to 20th	Day	73% 5% 8% 10% 4	1858
	21st to end	Day	68% 5% 10% 14% 4 1	1570
March	1st to 10th	Day	56% 6% 11% 19% 9%	3120
	11th to 20th	Day	56% 5% 13% 17% 7% 2	3378
	21st to end	Day	64% 5% 9% 15% 6% 1	3967
April	1st to 10th	Day	58% 5% 10% 17% 11%	2280
	11th to 20th	Day	54% 5% 8% 17% 15% 2	2333
	21st to end	Day	52% 7% 11% 14% 15% 2	2470
May	1st to 10th	Day	43% 6% 10% 22% 18% 2	4120
	11th to 20th	Day	38% 7% 11% 25% 17% 2	4203
	21st to end	Day	38% 7% 12% 21% 19% 3	4837
June	1st to 10th	Day	40% 7% 11% 24% 17% 2	2660
	11th to 20th	Day	40% 6% 12% 22% 19% 2	2660
	21st to end	Day	42% 7% 13% 23% 15% 1	2660
July	1st to 10th	Day	44% 5% 13% 22% 14% 2	4371
	11th to 20th	Day	29% 7% 12% 32% 18% 2	4365
	21st to end	Day	36% 7% 11% 24% 19% 1	4662
August	1st to 10th	Day	40% 7% 11% 27% 14% 1	4216
	11th to 20th	Day	39% 5% 12% 27% 16% 1	4083
	21st to end	Day	40% 5% 13% 27% 13% 1	4291
September	1st to 10th	Day	43% 6% 12% 24% 14% 1	2256
	11th to 20th	Day	36% 7% 13% 28% 15% 1	2090
	21st to end	Day	45% 6% 13% 24% 11%	2090
October	1st to 10th	Day	32% 4 8% 34% 20% 1	3480
	11th to 20th	Day	54% 5% 10% 19% 12%	2975
	21st to end	Day	62% 5% 13% 16% 4	3081
November	1st to 10th	Day	55% 7% 11% 18% 9%	1753
	11th to 20th	Day	69% 5% 11% 11% 4	1710
	21st to end	Day	73% 4 12% 8% 3	1687
December	1st to 10th	Day	80% 5% 6% 7% 2	1385
	11th to 20th	Day	78% 5% 9% 6% 1	1823
	21st to end	Day	83% 4 6% 5% 2	2783
January	1st to 10th	Night	77% 5% 8% 9% 1	4428
	11th to 20th	Night	83% 5% 5% 5% 2	4440
	21st to end	Night	81% 6% 7% 4 1	4884
February	1st to 10th	Night	73% 6% 6% 11% 4	2523
	11th to 20th	Night	68% 5% 10% 12% 4	2219
	21st to end	Night	64% 5% 12% 13% 4 1	1884
March	1st to 10th	Night	48% 7% 15% 21% 9%	3733
	11th to 20th	Night	47% 6% 14% 22% 10% 1	3581
	21st to end	Night	58% 7% 9% 19% 7% 1	3693
April	1st to 10th	Night	53% 6% 9% 18% 12% 1	1900
	11th to 20th	Night	52% 4 10% 19% 14% 2	1795
	21st to end	Night	49% 4 10% 20% 14% 3	1710
May	1st to 10th	Night	43% 6% 13% 18% 16% 3	2840
	11th to 20th	Night	41% 7% 9% 28% 14% 2	2696
	21st to end	Night	41% 6% 11% 21% 16% 5%	2751
June	1st to 10th	Night	39% 7% 11% 26% 16% 1	1520
	11th to 20th	Night	38% 7% 12% 23% 19% 2	1520
	21st to end	Night	38% 8% 10% 27% 15% 2	1520
July	1st to 10th	Night	42% 4 12% 23% 13% 5%	2490
	11th to 20th	Night	26% 7% 15% 33% 18% 1	2482
	21st to end	Night	32% 7% 14% 25% 20% 1	2662
August	1st to 10th	Night	39% 6% 15% 26% 13% 1	2690
	11th to 20th	Night	34% 4 14% 31% 15% 1	2812
	21st to end	Night	37% 5% 13% 24% 20% 2	3348
September	1st to 10th	Night	34% 6% 13% 27% 18% 2	1904
	11th to 20th	Night	33% 7% 13% 32% 14% 1	2090
	21st to end	Night	44% 6% 13% 26% 11% 1	2090
October	1st to 10th	Night	36% 5% 9% 36% 13% 1	3480
	11th to 20th	Night	47% 4 10% 23% 14%	3927
	21st to end	Night	53% 4 12% 24% 7%	4467
November	1st to 10th	Night	55% 6% 12% 18% 8% 1	2530
	11th to 20th	Night	68% 5% 11% 10% 5% 1	2470
	21st to end	Night	69% 6% 13% 10% 2 1	2491
December	1st to 10th	Night	78% 5% 7% 8% 2	2785
	11th to 20th	Night	77% 6% 9% 6% 2	3357
	21st to end	Night	80% 6% 8% 4 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	19% 20% 34% 20% 6%	270
	11th to 20th	Day	28% 18% 38% 14% 2	270
	21st to end	Day	25% 20% 33% 20% 3	297
February	1st to 10th	Day	23% 26% 33% 13% 4 1	270
	11th to 20th	Day	21% 27% 36% 14% 1	270
	21st to end	Day	26% 33% 35% 5%	225
March	1st to 10th	Day	23% 28% 36% 11% 2	270
	11th to 20th	Day	25% 15% 30% 22% 7% 1	397
	21st to end	Day	30% 16% 26% 21% 6%	506
April	1st to 10th	Day	28% 17% 36% 15% 3 1	460
	11th to 20th	Day	32% 16% 29% 13% 6% 3	452
	21st to end	Day	25% 15% 28% 23% 7% 2	460
May	1st to 10th	Day	24% 20% 30% 17% 6% 2	463
	11th to 20th	Day	20% 14% 30% 23% 9% 3	553
	21st to end	Day	15% 13% 31% 28% 11% 3	734
June	1st to 10th	Day	13% 15% 36% 24% 10% 2	680
	11th to 20th	Day	19% 13% 34% 22% 10% 3	680
	21st to end	Day	18% 11% 33% 26% 10% 3	680
July	1st to 10th	Day	11% 8% 29% 31% 16% 5%	671
	11th to 20th	Day	12% 9% 28% 32% 14% 5%	668
	21st to end	Day	11% 7% 32% 31% 14% 6%	739
August	1st to 10th	Day	12% 6% 27% 28% 20% 7%	562
	11th to 20th	Day	14% 6% 23% 28% 18% 11%	479
	21st to end	Day	16% 7% 25% 29% 17% 5%	539
September	1st to 10th	Day	19% 7% 23% 28% 17% 6%	490
	11th to 20th	Day	11% 7% 24% 32% 18% 8%	490
	21st to end	Day	22% 10% 24% 25% 14% 5%	490
October	1st to 10th	Day	23% 14% 27% 21% 12% 2	490
	11th to 20th	Day	32% 15% 30% 20% 4	372
	21st to end	Day	33% 22% 29% 12% 3 1	330
November	1st to 10th	Day	32% 14% 34% 12% 7%	297
	11th to 20th	Day	25% 26% 35% 11% 3	270
	21st to end	Day	28% 23% 35% 10% 4	270
December	1st to 10th	Day	29% 21% 29% 16% 2 2	205
	11th to 20th	Day	26% 24% 35% 12% 2 1	227
	21st to end	Day	30% 25% 31% 12% 1 1	297
January	1st to 10th	Night	23% 15% 35% 21% 6% 1	950
	11th to 20th	Night	23% 17% 33% 21% 6%	950
	21st to end	Night	18% 12% 38% 27% 5% 1	1045
February	1st to 10th	Night	19% 14% 37% 25% 4 1	836
	11th to 20th	Night	20% 16% 36% 24% 5%	743
	21st to end	Night	22% 18% 37% 19% 3	628
March	1st to 10th	Night	17% 14% 37% 23% 8% 1	760
	11th to 20th	Night	18% 14% 38% 24% 6%	760
	21st to end	Night	21% 12% 33% 27% 5% 1	763
April	1st to 10th	Night	22% 12% 38% 22% 5% 1	570
	11th to 20th	Night	25% 14% 32% 21% 7%	563
	21st to end	Night	19% 12% 32% 29% 7% 1	570
May	1st to 10th	Night	19% 10% 35% 29% 8% 1	570
	11th to 20th	Night	19% 8% 33% 29% 9% 1	561
	21st to end	Night	16% 7% 29% 36% 12% 1	617
June	1st to 10th	Night	15% 7% 31% 36% 10% 1	570
	11th to 20th	Night	13% 8% 28% 35% 14% 1	570
	21st to end	Night	16% 5% 25% 39% 14% 1	570
July	1st to 10th	Night	12% 3 22% 40% 21% 2	555
	11th to 20th	Night	8% 4 26% 40% 21% 2	552
	21st to end	Night	11% 4 21% 41% 22% 1	624
August	1st to 10th	Night	10% 3 21% 45% 20% 1	567
	11th to 20th	Night	10% 4 19% 38% 24% 5%	564
	21st to end	Night	15% 5% 21% 38% 20% 1	627
September	1st to 10th	Night	16% 3 22% 37% 18% 5%	574
	11th to 20th	Night	13% 4 24% 37% 19% 3	760
	21st to end	Night	18% 9% 24% 31% 14% 3	760
October	1st to 10th	Night	21% 9% 26% 31% 12% 1	760
	11th to 20th	Night	27% 11% 29% 26% 6% 1	760
	21st to end	Night	33% 12% 27% 21% 6%	836
November	1st to 10th	Night	23% 13% 32% 25% 6% 1	779
	11th to 20th	Night	25% 14% 38% 19% 4	760
	21st to end	Night	25% 14% 35% 22% 4	781
December	1st to 10th	Night	24% 14% 36% 22% 4	950
	11th to 20th	Night	24% 16% 37% 17% 4 1	950
	21st to end	Night	28% 15% 35% 20% 2	1045

Page generated at 2024-11-07 06:55:47. Version ac07

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