Chipman
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Chipman clear sky chart from 2005-11-06 to 2026-05-02.

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	19% 10% 3 8% 5% 4 4 3 5% 6% 32%	131620
	Night	19% 11% 3 7% 4 4 4 3 5% 6% 33%	131036
Transparency	Day	53% 3 11% 22% 10% 1	135120
	Night	53% 3 11% 21% 11% 1	135610
Seeing	Day	29% 14% 30% 19% 6% 1	18402
	Night	27% 13% 30% 23% 6%	26289

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% 19% 5% 12% 4 4 4 2 4 5% 27%	4093
	11th to 20th	Day	14% 16% 7% 13% 7% 5% 3 3 3 4 26%	4401
	21st to end	Day	8% 10% 3 8% 5% 4 5% 4 6% 7% 39%	5641
February	1st to 10th	Day	14% 13% 5% 7% 6% 5% 5% 4 5% 6% 31%	1890
	11th to 20th	Day	15% 14% 3 7% 6% 4 4 4 5% 6% 32%	1843
	21st to end	Day	11% 13% 4 8% 6% 5% 4 4 5% 6% 35%	1640
March	1st to 10th	Day	23% 13% 4 12% 5% 3 3 2 4 4 26%	4890
	11th to 20th	Day	21% 13% 4 8% 5% 4 5% 3 5% 6% 26%	5090
	21st to end	Day	26% 14% 3 8% 5% 4 3 3 4 6% 24%	5587
April	1st to 10th	Day	23% 14% 4 7% 5% 4 3 4 4 5% 27%	2457
	11th to 20th	Day	21% 10% 3 7% 4 4 4 4 5% 5% 32%	2702
	21st to end	Day	25% 10% 4 7% 4 3 3 3 5% 6% 31%	2730
May	1st to 10th	Day	26% 15% 3 8% 4 4 4 3 5% 5% 24%	5899
	11th to 20th	Day	24% 10% 2 7% 5% 4 4 3 4 6% 30%	6315
	21st to end	Day	21% 10% 3 7% 4 4 4 4 6% 8% 29%	7104
June	1st to 10th	Day	26% 9% 3 7% 5% 4 4 3 5% 6% 27%	3000
	11th to 20th	Day	22% 7% 2 6% 5% 5% 5% 4 5% 7% 32%	3000
	21st to end	Day	27% 9% 2 6% 4 4 4 3 5% 6% 28%	3000
July	1st to 10th	Day	16% 7% 3 7% 5% 5% 6% 5% 7% 9% 28%	6820
	11th to 20th	Day	16% 6% 2 5% 4 5% 5% 3 6% 8% 39%	6820
	21st to end	Day	14% 6% 2 6% 4 4 5% 5% 6% 8% 38%	6687
August	1st to 10th	Day	20% 6% 3 7% 5% 5% 5% 4 6% 6% 33%	4235
	11th to 20th	Day	14% 7% 3 8% 5% 5% 6% 5% 6% 8% 34%	4175
	21st to end	Day	15% 5% 2 5% 4 4 5% 4 6% 8% 44%	4656
September	1st to 10th	Day	14% 5% 2 5% 4 5% 4 4 6% 7% 44%	2400
	11th to 20th	Day	16% 7% 2 6% 4 4 3 2 4 6% 47%	2210
	21st to end	Day	20% 6% 2 6% 4 4 3 3 5% 6% 43%	2200
October	1st to 10th	Day	15% 8% 3 7% 5% 4 3 3 5% 5% 42%	2010
	11th to 20th	Day	20% 7% 3 6% 4 4 6% 3 4 6% 37%	2000
	21st to end	Day	21% 9% 3 8% 5% 4 4 4 5% 7% 31%	2097
November	1st to 10th	Day	22% 8% 2 7% 5% 4 5% 3 5% 5% 34%	1730
	11th to 20th	Day	20% 9% 3 9% 6% 4 4 3 4 5% 34%	1680
	21st to end	Day	20% 12% 4 8% 5% 4 4 2 5% 6% 30%	1680
December	1st to 10th	Day	18% 13% 3 9% 5% 3 3 3 4 6% 33%	2690
	11th to 20th	Day	22% 11% 3 9% 5% 3 3 2 3 4 34%	2695
	21st to end	Day	19% 14% 4 8% 4 4 3 3 5% 4 34%	3553
January	1st to 10th	Night	15% 16% 4 9% 4 4 4 3 5% 6% 31%	8831
	11th to 20th	Night	19% 14% 5% 11% 6% 4 4 3 4 5% 24%	8492
	21st to end	Night	8% 13% 3 7% 5% 5% 5% 3 5% 7% 40%	8538
February	1st to 10th	Night	14% 13% 4 8% 5% 4 4 4 5% 6% 32%	2730
	11th to 20th	Night	16% 13% 4 9% 6% 5% 5% 3 4 5% 31%	2663
	21st to end	Night	14% 14% 4 7% 5% 5% 4 4 4 5% 35%	2165
March	1st to 10th	Night	25% 14% 4 8% 5% 5% 4 3 3 3 27%	5169
	11th to 20th	Night	22% 13% 4 8% 5% 4 4 4 5% 6% 25%	5089
	21st to end	Night	31% 12% 3 6% 4 3 3 3 4 5% 26%	5587
April	1st to 10th	Night	25% 12% 3 8% 5% 4 4 2 4 5% 28%	2159
	11th to 20th	Night	23% 11% 3 6% 4 4 4 3 5% 5% 33%	1868
	21st to end	Night	22% 11% 3 7% 5% 4 3 3 5% 5% 30%	1890
May	1st to 10th	Night	28% 12% 3 6% 3 4 4 3 4 6% 27%	4064
	11th to 20th	Night	25% 8% 2 5% 4 4 4 3 5% 6% 33%	3596
	21st to end	Night	18% 10% 3 7% 4 4 4 3 5% 7% 35%	3821
June	1st to 10th	Night	24% 9% 3 7% 4 5% 4 4 5% 6% 29%	1400
	11th to 20th	Night	20% 7% 2 6% 5% 4 4 5% 5% 5% 36%	1400
	21st to end	Night	27% 9% 3 6% 5% 4 3 2 5% 5% 31%	1400
July	1st to 10th	Night	18% 7% 3 7% 5% 5% 5% 4 7% 8% 31%	3160
	11th to 20th	Night	19% 5% 2 7% 4 4 5% 4 6% 8% 36%	3160
	21st to end	Night	16% 6% 2 6% 5% 5% 4 4 6% 8% 39%	4123
August	1st to 10th	Night	18% 7% 3 9% 5% 5% 5% 4 6% 7% 30%	2915
	11th to 20th	Night	12% 8% 3 9% 4 4 5% 4 6% 8% 37%	2872
	21st to end	Night	16% 5% 2 5% 4 3 3 3 5% 7% 47%	3241
September	1st to 10th	Night	17% 5% 2 6% 4 4 3 4 5% 7% 44%	2000
	11th to 20th	Night	16% 6% 2 5% 3 3 4 3 4 7% 47%	2187
	21st to end	Night	19% 6% 2 5% 3 3 4 3 5% 6% 44%	2200
October	1st to 10th	Night	19% 6% 2 7% 3 2 4 3 5% 6% 42%	2390
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 5% 7% 38%	2400
	21st to end	Night	23% 9% 2 8% 4 4 4 2 4 6% 35%	2740
November	1st to 10th	Night	22% 8% 3 6% 5% 3 4 4 4 6% 35%	2788
	11th to 20th	Night	21% 9% 3 6% 5% 5% 4 4 4 7% 32%	2940
	21st to end	Night	23% 10% 4 8% 4 4 4 3 5% 5% 30%	2940
December	1st to 10th	Night	16% 11% 4 8% 5% 4 4 3 4 6% 35%	4720
	11th to 20th	Night	23% 10% 3 7% 4 3 3 3 4 5% 36%	5731
	21st to end	Night	20% 14% 4 9% 4 3 4 2 4 5% 31%	7667

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	62% 2 11% 15% 10%	4094
	11th to 20th	Day	65% 2 10% 14% 9% 1	4430
	21st to end	Day	45% 3 9% 24% 17% 2	5641
February	1st to 10th	Day	54% 4 10% 20% 10% 2	1890
	11th to 20th	Day	54% 3 10% 21% 12% 1	1851
	21st to end	Day	50% 3 9% 23% 13% 2	1640
March	1st to 10th	Day	63% 2 8% 14% 11% 2	4894
	11th to 20th	Day	61% 3 12% 16% 7% 2	5090
	21st to end	Day	63% 2 4 19% 10% 2	5587
April	1st to 10th	Day	61% 3 6% 16% 12% 2	2457
	11th to 20th	Day	54% 3 8% 22% 12% 1	2702
	21st to end	Day	55% 3 8% 17% 13% 4	2730
May	1st to 10th	Day	64% 2 6% 17% 10% 1	5910
	11th to 20th	Day	57% 2 11% 22% 6% 2	6319
	21st to end	Day	54% 4 11% 19% 12%	7104
June	1st to 10th	Day	57% 4 10% 19% 9% 1	3000
	11th to 20th	Day	50% 4 11% 21% 12% 1	3000
	21st to end	Day	57% 4 11% 17% 10% 1	3000
July	1st to 10th	Day	52% 3 17% 20% 8%	6745
	11th to 20th	Day	43% 3 16% 28% 9% 1	6739
	21st to end	Day	44% 4 15% 30% 8%	6497
August	1st to 10th	Day	52% 3 13% 25% 6%	4222
	11th to 20th	Day	47% 4 15% 27% 7%	4214
	21st to end	Day	38% 3 15% 28% 16%	4656
September	1st to 10th	Day	39% 4 15% 29% 14%	2400
	11th to 20th	Day	40% 3 12% 28% 15% 2	2210
	21st to end	Day	44% 3 9% 28% 15% 1	2200
October	1st to 10th	Day	47% 3 12% 28% 10%	3270
	11th to 20th	Day	47% 4 10% 32% 8%	3240
	21st to end	Day	44% 2 15% 22% 17%	3360
November	1st to 10th	Day	53% 3 10% 23% 11% 1	1730
	11th to 20th	Day	54% 3 13% 18% 12% 1	1680
	21st to end	Day	58% 4 14% 18% 7%	1680
December	1st to 10th	Day	56% 2 15% 20% 6%	2690
	11th to 20th	Day	57% 3 8% 20% 10% 3	2695
	21st to end	Day	55% 2 11% 18% 11% 2	3553
January	1st to 10th	Night	56% 2 11% 22% 8% 1	8831
	11th to 20th	Night	64% 3 8% 18% 7%	8538
	21st to end	Night	46% 2 10% 23% 17% 2	8538
February	1st to 10th	Night	54% 3 10% 19% 13% 2	2730
	11th to 20th	Night	57% 3 8% 19% 12% 1	2666
	21st to end	Night	53% 2 8% 21% 13% 2	2165
March	1st to 10th	Night	65% 2 5% 13% 12% 3	5178
	11th to 20th	Night	60% 3 13% 14% 9% 1	5090
	21st to end	Night	63% 2 4 17% 13% 2	5587
April	1st to 10th	Night	61% 2 5% 16% 11% 4	2159
	11th to 20th	Night	54% 3 8% 21% 13% 1	1868
	21st to end	Night	55% 3 9% 17% 14% 2	1890
May	1st to 10th	Night	60% 3 10% 17% 10% 1	4070
	11th to 20th	Night	53% 3 11% 24% 8% 2	3597
	21st to end	Night	49% 4 17% 21% 8%	3822
June	1st to 10th	Night	55% 4 10% 21% 9% 1	1400
	11th to 20th	Night	49% 4 12% 24% 9% 2	1400
	21st to end	Night	57% 4 12% 18% 10% 1	1400
July	1st to 10th	Night	51% 3 15% 21% 10%	3125
	11th to 20th	Night	47% 3 17% 27% 6%	3118
	21st to end	Night	45% 4 15% 26% 10%	3999
August	1st to 10th	Night	54% 5% 13% 21% 7%	2903
	11th to 20th	Night	45% 3 19% 26% 7%	2899
	21st to end	Night	38% 2 18% 26% 14% 2	3240
September	1st to 10th	Night	41% 4 11% 31% 14% 1	2000
	11th to 20th	Night	39% 3 13% 29% 15% 1	2187
	21st to end	Night	42% 3 11% 29% 14% 1	2200
October	1st to 10th	Night	49% 2 12% 26% 11%	3910
	11th to 20th	Night	42% 3 11% 31% 13%	3899
	21st to end	Night	46% 2 14% 24% 14%	4414
November	1st to 10th	Night	52% 4 12% 21% 10% 1	2788
	11th to 20th	Night	55% 3 11% 20% 10% 1	2940
	21st to end	Night	58% 3 13% 16% 10%	2940
December	1st to 10th	Night	53% 2 11% 25% 9%	4720
	11th to 20th	Night	54% 2 9% 21% 13% 1	5732
	21st to end	Night	58% 2 9% 19% 11% 1	7667

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	34% 14% 33% 18% 2	220
	11th to 20th	Day	40% 15% 29% 9% 6%	220
	21st to end	Day	22% 18% 36% 18% 5% 1	424
February	1st to 10th	Day	29% 16% 32% 15% 6% 1	430
	11th to 20th	Day	30% 21% 30% 14% 3 2	426
	21st to end	Day	28% 22% 32% 14% 5%	399
March	1st to 10th	Day	33% 20% 31% 12% 3 1	540
	11th to 20th	Day	34% 19% 28% 15% 3 1	540
	21st to end	Day	38% 17% 28% 12% 4 2	594
April	1st to 10th	Day	42% 19% 26% 10% 3	540
	11th to 20th	Day	36% 18% 28% 12% 4 1	532
	21st to end	Day	36% 18% 26% 13% 6% 1	540
May	1st to 10th	Day	38% 15% 26% 15% 5% 1	507
	11th to 20th	Day	32% 12% 30% 19% 5% 2	721
	21st to end	Day	30% 15% 31% 19% 4 1	790
June	1st to 10th	Day	32% 13% 30% 19% 6% 1	730
	11th to 20th	Day	30% 14% 28% 21% 6% 1	730
	21st to end	Day	32% 11% 29% 21% 7%	730
July	1st to 10th	Day	23% 11% 35% 21% 9% 1	720
	11th to 20th	Day	23% 6% 33% 28% 9% 2	718
	21st to end	Day	20% 8% 37% 24% 10% 1	642
August	1st to 10th	Day	18% 8% 36% 28% 9% 2	526
	11th to 20th	Day	22% 9% 27% 28% 13% 2	519
	21st to end	Day	21% 11% 28% 27% 10% 3	583
September	1st to 10th	Day	15% 13% 35% 26% 9% 2	530
	11th to 20th	Day	24% 8% 30% 23% 12% 3	530
	21st to end	Day	22% 13% 35% 17% 8% 4	530
October	1st to 10th	Day	23% 12% 28% 22% 14% 2	425
	11th to 20th	Day	29% 13% 26% 20% 10% 2	420
	21st to end	Day	30% 16% 31% 16% 5% 1	462
November	1st to 10th	Day	34% 14% 32% 15% 4 1	425
	11th to 20th	Day	34% 16% 29% 15% 6%	430
	21st to end	Day	34% 19% 27% 16% 4	430
December	1st to 10th	Day	33% 12% 31% 18% 5%	430
	11th to 20th	Day	40% 23% 27% 9% 1	227
	21st to end	Day	33% 15% 35% 14% 2	242
January	1st to 10th	Night	28% 17% 30% 21% 4	950
	11th to 20th	Night	29% 16% 27% 22% 5%	887
	21st to end	Night	22% 17% 35% 21% 5%	924
February	1st to 10th	Night	26% 17% 31% 21% 5%	840
	11th to 20th	Night	25% 20% 33% 17% 4 1	823
	21st to end	Night	24% 17% 33% 22% 5%	692
March	1st to 10th	Night	29% 14% 34% 20% 2	840
	11th to 20th	Night	27% 16% 31% 20% 5%	840
	21st to end	Night	29% 15% 32% 19% 5%	924
April	1st to 10th	Night	35% 16% 28% 18% 3	713
	11th to 20th	Night	32% 16% 31% 17% 4	624
	21st to end	Night	31% 15% 31% 19% 5%	630
May	1st to 10th	Night	32% 13% 28% 22% 5%	604
	11th to 20th	Night	31% 12% 30% 22% 5%	592
	21st to end	Night	22% 13% 40% 20% 4	600
June	1st to 10th	Night	28% 7% 33% 29% 4	400
	11th to 20th	Night	24% 9% 30% 30% 7% 1	400
	21st to end	Night	34% 5% 25% 31% 5%	400
July	1st to 10th	Night	20% 4 39% 30% 6%	390
	11th to 20th	Night	22% 3 30% 36% 9%	388
	21st to end	Night	24% 6% 31% 31% 8% 1	583
August	1st to 10th	Night	18% 2 33% 35% 11%	598
	11th to 20th	Night	19% 5% 29% 35% 12% 1	592
	21st to end	Night	18% 8% 27% 34% 14% 1	660
September	1st to 10th	Night	21% 6% 37% 26% 9%	600
	11th to 20th	Night	21% 7% 25% 31% 14% 1	787
	21st to end	Night	24% 9% 30% 27% 11% 1	800
October	1st to 10th	Night	25% 10% 28% 27% 10% 1	800
	11th to 20th	Night	25% 10% 32% 23% 9% 1	800
	21st to end	Night	30% 15% 30% 20% 5%	880
November	1st to 10th	Night	31% 14% 27% 22% 6%	883
	11th to 20th	Night	31% 15% 29% 18% 6% 1	950
	21st to end	Night	31% 17% 28% 20% 4 1	950
December	1st to 10th	Night	33% 11% 29% 21% 4	950
	11th to 20th	Night	33% 19% 27% 17% 3	950
	21st to end	Night	32% 16% 27% 21% 4 1	1045

Page generated at 2026-04-29 03:21:47. Version ac07

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