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 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	19% 10% 3 7% 5% 4 4 3 5% 6% 33%	104940
	Night	19% 10% 3 7% 4 4 4 3 5% 6% 33%	104211
Transparency	Day	52% 3 12% 22% 10% 1	108455
	Night	52% 3 11% 22% 10% 1	108772
Seeing	Day	29% 14% 30% 19% 7% 1	16663
	Night	27% 13% 30% 23% 6%	24533

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% 14% 5% 11% 4 4 4 2 4 6% 33%	2249
	11th to 20th	Day	15% 14% 5% 8% 6% 5% 3 3 4 4 34%	2374
	21st to end	Day	12% 10% 3 8% 6% 4 5% 4 6% 7% 35%	3040
February	1st to 10th	Day	16% 13% 4 6% 6% 5% 5% 4 5% 5% 31%	1710
	11th to 20th	Day	16% 14% 3 7% 5% 5% 4 4 5% 7% 30%	1663
	21st to end	Day	11% 13% 4 8% 6% 5% 4 3 5% 6% 35%	1488
March	1st to 10th	Day	22% 15% 4 8% 5% 3 3 3 4 5% 27%	3326
	11th to 20th	Day	19% 17% 5% 10% 6% 5% 5% 3 4 5% 23%	3480
	21st to end	Day	29% 13% 4 8% 5% 4 3 3 4 6% 23%	3816
April	1st to 10th	Day	22% 15% 4 7% 5% 5% 3 4 4 5% 26%	2223
	11th to 20th	Day	20% 10% 3 7% 4 4 4 4 4 6% 34%	2442
	21st to end	Day	26% 11% 3 6% 3 3 3 3 5% 6% 31%	2470
May	1st to 10th	Day	21% 15% 3 8% 5% 4 4 3 5% 6% 28%	4106
	11th to 20th	Day	19% 9% 2 8% 5% 4 4 3 5% 7% 33%	4395
	21st to end	Day	18% 8% 3 7% 5% 5% 5% 5% 7% 8% 30%	4950
June	1st to 10th	Day	26% 9% 3 7% 5% 4 4 3 5% 6% 26%	2850
	11th to 20th	Day	22% 7% 2 6% 5% 5% 5% 4 5% 7% 33%	2850
	21st to end	Day	27% 9% 2 7% 4 4 4 3 5% 6% 28%	2850
July	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 5% 7% 9% 32%	4760
	11th to 20th	Day	19% 7% 2 5% 4 5% 5% 4 7% 8% 34%	4760
	21st to end	Day	16% 7% 2 6% 4 5% 5% 5% 6% 8% 35%	4645
August	1st to 10th	Day	21% 7% 3 7% 5% 5% 5% 4 6% 6% 31%	4105
	11th to 20th	Day	14% 7% 3 8% 5% 5% 6% 5% 6% 8% 33%	4045
	21st to end	Day	15% 5% 2 5% 4 4 4 4 6% 8% 44%	4514
September	1st to 10th	Day	14% 5% 2 6% 4 5% 5% 4 6% 7% 44%	2280
	11th to 20th	Day	17% 7% 2 6% 4 4 4 3 4 6% 46%	2100
	21st to end	Day	20% 6% 2 6% 4 4 3 3 4 6% 42%	2090
October	1st to 10th	Day	16% 8% 3 7% 5% 4 4 4 6% 5% 40%	1910
	11th to 20th	Day	20% 7% 3 6% 4 4 6% 3 4 6% 38%	1900
	21st to end	Day	21% 9% 3 7% 5% 4 4 4 5% 7% 31%	1992
November	1st to 10th	Day	22% 8% 2 6% 5% 4 4 3 4 5% 34%	1646
	11th to 20th	Day	20% 9% 3 9% 6% 4 4 3 4 5% 34%	1600
	21st to end	Day	20% 12% 4 8% 5% 4 4 2 5% 6% 30%	1600
December	1st to 10th	Day	18% 13% 3 9% 5% 3 3 3 4 6% 32%	2610
	11th to 20th	Day	22% 11% 3 9% 5% 4 3 2 4 4 34%	2625
	21st to end	Day	19% 14% 4 8% 4 4 3 3 5% 4 34%	3476
January	1st to 10th	Night	14% 10% 4 9% 5% 4 5% 4 6% 7% 33%	4839
	11th to 20th	Night	17% 11% 4 10% 6% 4 4 3 5% 6% 29%	4586
	21st to end	Night	13% 13% 4 7% 5% 4 5% 3 6% 7% 33%	4614
February	1st to 10th	Night	15% 13% 3 8% 5% 4 4 4 6% 6% 32%	2470
	11th to 20th	Night	17% 13% 4 9% 6% 4 5% 3 4 5% 30%	2403
	21st to end	Night	14% 14% 4 7% 6% 5% 4 4 4 5% 34%	1965
March	1st to 10th	Night	22% 15% 3 8% 5% 6% 4 3 3 3 27%	3513
	11th to 20th	Night	21% 15% 4 8% 6% 4 5% 4 5% 6% 22%	3479
	21st to end	Night	31% 11% 3 6% 5% 3 3 3 5% 4 25%	3816
April	1st to 10th	Night	25% 12% 3 8% 4 4 5% 2 4 5% 28%	1953
	11th to 20th	Night	22% 11% 3 6% 4 4 4 3 5% 5% 34%	1688
	21st to end	Night	23% 11% 3 7% 4 4 3 3 5% 5% 31%	1710
May	1st to 10th	Night	22% 11% 3 6% 4 4 5% 3 4 6% 31%	2834
	11th to 20th	Night	20% 8% 2 5% 4 4 5% 3 6% 7% 36%	2506
	21st to end	Night	16% 8% 3 7% 5% 4 5% 4 6% 8% 33%	2664
June	1st to 10th	Night	25% 8% 3 8% 4 5% 4 4 5% 6% 28%	1330
	11th to 20th	Night	20% 8% 3 6% 5% 4 4 5% 5% 5% 36%	1330
	21st to end	Night	27% 9% 3 6% 4 4 3 2 5% 5% 31%	1330
July	1st to 10th	Night	16% 7% 3 6% 5% 5% 5% 4 7% 8% 34%	2210
	11th to 20th	Night	22% 6% 2 7% 3 4 5% 3 6% 8% 34%	2210
	21st to end	Night	19% 6% 3 6% 5% 5% 4 4 5% 7% 36%	2877
August	1st to 10th	Night	19% 7% 3 9% 5% 5% 5% 4 6% 7% 28%	2825
	11th to 20th	Night	12% 8% 3 9% 4 4 4 4 6% 8% 36%	2782
	21st to end	Night	16% 5% 2 4 4 3 3 3 5% 7% 47%	3142
September	1st to 10th	Night	16% 5% 2 6% 4 4 3 4 5% 7% 43%	1900
	11th to 20th	Night	17% 7% 2 5% 3 3 4 3 4 7% 46%	2077
	21st to end	Night	20% 6% 2 5% 3 3 3 3 5% 6% 44%	2090
October	1st to 10th	Night	20% 7% 2 7% 3 2 4 3 5% 6% 40%	2270
	11th to 20th	Night	17% 8% 3 7% 4 4 4 4 4 8% 38%	2280
	21st to end	Night	23% 8% 2 7% 4 4 4 2 3 6% 35%	2603
November	1st to 10th	Night	22% 8% 3 6% 5% 3 3 3 4 6% 36%	2652
	11th to 20th	Night	21% 9% 3 6% 5% 5% 4 4 4 7% 32%	2800
	21st to end	Night	23% 10% 3 8% 4 4 4 3 5% 6% 30%	2800
December	1st to 10th	Night	17% 11% 4 8% 5% 3 4 3 4 6% 35%	4580
	11th to 20th	Night	23% 11% 3 7% 4 3 3 3 4 4 36%	5581
	21st to end	Night	21% 14% 4 9% 4 3 4 2 4 5% 31%	7502

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	55% 2 15% 18% 10%	2250
	11th to 20th	Day	56% 3 5% 21% 14% 1	2374
	21st to end	Day	48% 3 13% 21% 14% 1	3040
February	1st to 10th	Day	54% 4 11% 19% 10% 2	1710
	11th to 20th	Day	54% 4 10% 19% 12% 1	1671
	21st to end	Day	50% 3 9% 23% 12% 3	1488
March	1st to 10th	Day	61% 2 10% 18% 7% 3	3330
	11th to 20th	Day	66% 3 8% 15% 7% 2	3480
	21st to end	Day	65% 2 5% 17% 9% 2	3816
April	1st to 10th	Day	61% 3 7% 16% 11% 3	2223
	11th to 20th	Day	52% 3 8% 23% 12% 1	2442
	21st to end	Day	55% 3 9% 17% 13% 4	2470
May	1st to 10th	Day	59% 2 7% 22% 9% 1	4120
	11th to 20th	Day	52% 2 13% 24% 8% 1	4399
	21st to end	Day	50% 5% 13% 19% 12%	4950
June	1st to 10th	Day	58% 4 10% 18% 9%	2850
	11th to 20th	Day	51% 4 11% 20% 12% 1	2850
	21st to end	Day	57% 4 11% 17% 10% 1	2850
July	1st to 10th	Day	48% 3 18% 21% 11%	4685
	11th to 20th	Day	48% 3 15% 24% 9%	4679
	21st to end	Day	47% 5% 15% 25% 8%	4496
August	1st to 10th	Day	53% 3 13% 25% 6%	4092
	11th to 20th	Day	47% 4 15% 26% 7%	4084
	21st to end	Day	38% 3 15% 27% 16%	4514
September	1st to 10th	Day	40% 4 15% 28% 13%	2280
	11th to 20th	Day	41% 3 11% 28% 14% 2	2100
	21st to end	Day	44% 3 9% 28% 14% 1	2090
October	1st to 10th	Day	47% 3 12% 27% 10%	3170
	11th to 20th	Day	47% 4 10% 32% 8%	3140
	21st to end	Day	43% 3 15% 22% 17%	3255
November	1st to 10th	Day	53% 3 10% 23% 11% 1	1646
	11th to 20th	Day	54% 3 13% 17% 13% 1	1600
	21st to end	Day	58% 4 14% 18% 7%	1600
December	1st to 10th	Day	56% 2 15% 20% 5%	2610
	11th to 20th	Day	57% 3 7% 20% 10% 3	2625
	21st to end	Day	55% 2 11% 18% 11% 2	3476
January	1st to 10th	Night	51% 2 15% 24% 8% 1	4839
	11th to 20th	Night	57% 4 9% 21% 9% 1	4586
	21st to end	Night	52% 3 11% 23% 10% 1	4614
February	1st to 10th	Night	54% 3 11% 18% 13% 2	2470
	11th to 20th	Night	58% 3 8% 17% 13% 2	2406
	21st to end	Night	54% 3 8% 21% 13% 2	1965
March	1st to 10th	Night	64% 2 7% 18% 8% 2	3522
	11th to 20th	Night	65% 3 9% 14% 8% 1	3480
	21st to end	Night	63% 2 4 18% 11% 2	3816
April	1st to 10th	Night	61% 3 5% 16% 11% 4	1953
	11th to 20th	Night	53% 3 8% 21% 14% 1	1688
	21st to end	Night	55% 3 9% 17% 14% 2	1710
May	1st to 10th	Night	55% 3 13% 19% 8% 1	2840
	11th to 20th	Night	48% 2 15% 27% 8% 1	2507
	21st to end	Night	49% 5% 17% 21% 7% 1	2665
June	1st to 10th	Night	55% 4 10% 20% 9% 1	1330
	11th to 20th	Night	50% 4 11% 24% 9% 2	1330
	21st to end	Night	57% 4 12% 18% 9% 1	1330
July	1st to 10th	Night	46% 4 16% 22% 11%	2175
	11th to 20th	Night	50% 3 16% 24% 7%	2168
	21st to end	Night	49% 4 13% 25% 9% 1	2786
August	1st to 10th	Night	55% 5% 13% 20% 7%	2813
	11th to 20th	Night	45% 3 19% 26% 7%	2809
	21st to end	Night	38% 2 17% 26% 15% 2	3141
September	1st to 10th	Night	41% 4 11% 30% 13% 1	1900
	11th to 20th	Night	40% 3 13% 29% 15% 1	2077
	21st to end	Night	43% 3 11% 28% 14% 1	2090
October	1st to 10th	Night	50% 2 11% 26% 10%	3790
	11th to 20th	Night	42% 3 10% 32% 13%	3779
	21st to end	Night	46% 2 14% 24% 14%	4277
November	1st to 10th	Night	51% 4 12% 22% 10% 1	2652
	11th to 20th	Night	55% 3 11% 20% 10% 1	2800
	21st to end	Night	58% 4 13% 16% 10%	2800
December	1st to 10th	Night	53% 2 12% 25% 8%	4580
	11th to 20th	Night	54% 2 9% 21% 13% 1	5582
	21st to end	Night	58% 2 9% 19% 11% 1	7502

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% 31% 19% 2	192
	11th to 20th	Day	42% 17% 27% 10% 3 1	180
	21st to end	Day	22% 17% 36% 19% 6% 1	362
February	1st to 10th	Day	32% 16% 32% 15% 6% 1	370
	11th to 20th	Day	30% 22% 30% 14% 2 2	366
	21st to end	Day	28% 21% 31% 15% 5%	343
March	1st to 10th	Day	33% 19% 32% 13% 3 1	460
	11th to 20th	Day	31% 19% 29% 16% 4 1	460
	21st to end	Day	37% 17% 29% 12% 4 2	506
April	1st to 10th	Day	40% 18% 27% 11% 3	460
	11th to 20th	Day	33% 19% 29% 13% 5% 1	452
	21st to end	Day	37% 18% 26% 12% 6% 2	460
May	1st to 10th	Day	37% 15% 27% 16% 5% 1	463
	11th to 20th	Day	31% 12% 29% 20% 6% 2	671
	21st to end	Day	29% 15% 32% 19% 4 1	735
June	1st to 10th	Day	32% 13% 29% 19% 6% 1	680
	11th to 20th	Day	29% 13% 28% 23% 7% 1	680
	21st to end	Day	32% 11% 29% 21% 7%	680
July	1st to 10th	Day	23% 11% 36% 21% 9% 1	670
	11th to 20th	Day	23% 6% 33% 28% 9% 2	668
	21st to end	Day	21% 8% 36% 25% 10% 1	595
August	1st to 10th	Day	19% 8% 35% 28% 8% 1	486
	11th to 20th	Day	22% 9% 28% 27% 13% 1	479
	21st to end	Day	22% 10% 27% 27% 11% 3	539
September	1st to 10th	Day	14% 13% 36% 27% 8% 2	490
	11th to 20th	Day	25% 8% 30% 22% 12% 3	490
	21st to end	Day	23% 13% 34% 17% 9% 4	490
October	1st to 10th	Day	23% 12% 28% 20% 15% 2	395
	11th to 20th	Day	29% 14% 26% 19% 9% 2	390
	21st to end	Day	29% 17% 32% 17% 5% 1	429
November	1st to 10th	Day	33% 13% 33% 15% 4 1	395
	11th to 20th	Day	34% 17% 28% 15% 6% 1	400
	21st to end	Day	35% 18% 28% 17% 3	400
December	1st to 10th	Day	33% 11% 32% 18% 6% 1	400
	11th to 20th	Day	41% 20% 28% 10% 1	207
	21st to end	Day	34% 14% 35% 15% 2	220
January	1st to 10th	Night	27% 17% 30% 21% 4	881
	11th to 20th	Night	29% 16% 28% 22% 5%	799
	21st to end	Night	22% 16% 35% 22% 6%	836
February	1st to 10th	Night	27% 17% 31% 20% 4	760
	11th to 20th	Night	26% 21% 33% 16% 3 1	743
	21st to end	Night	24% 16% 32% 22% 5%	628
March	1st to 10th	Night	28% 13% 36% 21% 2	760
	11th to 20th	Night	26% 16% 31% 21% 5% 1	760
	21st to end	Night	28% 15% 32% 19% 5%	836
April	1st to 10th	Night	34% 16% 28% 20% 3	645
	11th to 20th	Night	30% 16% 31% 17% 5%	564
	21st to end	Night	31% 15% 31% 18% 5%	570
May	1st to 10th	Night	31% 14% 28% 22% 5%	570
	11th to 20th	Night	31% 12% 30% 23% 5%	562
	21st to end	Night	21% 14% 40% 20% 4	570
June	1st to 10th	Night	28% 7% 33% 29% 4	380
	11th to 20th	Night	24% 9% 29% 30% 7% 1	380
	21st to end	Night	33% 4 25% 32% 6%	380
July	1st to 10th	Night	21% 5% 39% 29% 6%	370
	11th to 20th	Night	22% 3 29% 36% 10%	368
	21st to end	Night	25% 5% 30% 30% 8% 1	554
August	1st to 10th	Night	18% 2 34% 35% 10%	568
	11th to 20th	Night	20% 5% 28% 35% 12%	562
	21st to end	Night	18% 8% 26% 33% 14% 1	627
September	1st to 10th	Night	21% 7% 37% 26% 9%	570
	11th to 20th	Night	22% 7% 25% 31% 14% 1	747
	21st to end	Night	24% 8% 30% 26% 11% 1	760
October	1st to 10th	Night	26% 9% 28% 27% 10% 1	760
	11th to 20th	Night	25% 11% 33% 22% 9% 1	760
	21st to end	Night	30% 15% 30% 20% 4	836
November	1st to 10th	Night	30% 14% 27% 23% 6%	837
	11th to 20th	Night	31% 15% 29% 18% 6% 1	900
	21st to end	Night	31% 17% 27% 20% 4	900
December	1st to 10th	Night	34% 11% 29% 21% 5%	900
	11th to 20th	Night	33% 18% 27% 18% 3	900
	21st to end	Night	33% 15% 27% 21% 4 1	990

Page generated at 2025-01-04 04:23:59. Version ac07

Copyright © 2025 Attilla Danko.