UND Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the UND Observatory clear sky chart from 2005-11-06 to 2024-12-09.

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	11% 8% 3 8% 5% 5% 5% 4 6% 7% 38%	105707
	Night	10% 9% 3 9% 6% 5% 5% 4 6% 7% 38%	102735
Transparency	Day	45% 5% 15% 26% 9% 1	105434
	Night	46% 5% 14% 25% 10% 1	102597
Seeing	Day	14% 9% 31% 28% 14% 3	16263
	Night	14% 8% 32% 33% 11% 1	26234

By Month

Percentage Cloud Cover SW (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	5% 13% 6% 15% 8% 7% 6% 5% 7% 6% 22%	2218
	11th to 20th	Day	4 8% 4 13% 13% 13% 13% 6% 6% 4 15%	2384
	21st to end	Day	7% 12% 8% 18% 7% 5% 5% 4 5% 5% 24%	2794
February	1st to 10th	Day	8% 15% 5% 10% 8% 6% 7% 5% 6% 5% 25%	1691
	11th to 20th	Day	6% 11% 4 12% 9% 7% 8% 5% 6% 6% 25%	1664
	21st to end	Day	7% 11% 4 13% 8% 8% 5% 4 5% 6% 27%	1532
March	1st to 10th	Day	12% 12% 3 8% 7% 5% 5% 3 5% 7% 32%	3217
	11th to 20th	Day	8% 9% 5% 13% 9% 5% 5% 5% 6% 8% 27%	3480
	21st to end	Day	15% 12% 5% 12% 5% 4 5% 3 5% 6% 27%	3814
April	1st to 10th	Day	11% 12% 3 9% 6% 5% 5% 5% 5% 6% 33%	2273
	11th to 20th	Day	17% 11% 4 8% 4 4 5% 4 5% 6% 32%	2439
	21st to end	Day	20% 9% 3 8% 5% 4 4 4 6% 6% 31%	2470
May	1st to 10th	Day	18% 8% 2 5% 5% 4 5% 5% 6% 8% 34%	4120
	11th to 20th	Day	15% 8% 3 6% 4 4 5% 4 6% 8% 36%	4467
	21st to end	Day	17% 8% 3 7% 5% 5% 4 4 5% 7% 35%	5173
June	1st to 10th	Day	14% 5% 2 6% 5% 4 5% 4 7% 9% 40%	2850
	11th to 20th	Day	14% 5% 2 6% 5% 4 4 4 6% 8% 41%	2850
	21st to end	Day	11% 5% 3 7% 5% 5% 5% 5% 7% 9% 40%	2850
July	1st to 10th	Day	7% 4 1 4 4 4 5% 4 7% 11% 47%	4750
	11th to 20th	Day	5% 3 1 5% 3 5% 4 4 7% 9% 54%	4750
	21st to end	Day	5% 4 1 5% 4 5% 5% 4 7% 9% 51%	4906
August	1st to 10th	Day	9% 4 2 6% 4 4 5% 4 6% 8% 48%	4147
	11th to 20th	Day	14% 5% 2 5% 4 4 4 3 6% 9% 44%	4041
	21st to end	Day	9% 5% 2 6% 4 4 4 3 4 7% 51%	4532
September	1st to 10th	Day	11% 5% 2 4 4 4 4 3 5% 7% 51%	2311
	11th to 20th	Day	12% 6% 2 6% 4 4 4 3 4 7% 46%	2090
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 8% 45%	2090
October	1st to 10th	Day	12% 6% 2 4 3 3 4 3 4 6% 54%	3238
	11th to 20th	Day	13% 8% 2 6% 4 3 4 3 4 5% 47%	3124
	21st to end	Day	11% 10% 3 9% 5% 4 5% 3 5% 8% 37%	3091
November	1st to 10th	Day	13% 13% 5% 10% 4 4 4 3 4 5% 34%	1664
	11th to 20th	Day	10% 16% 6% 12% 6% 6% 5% 3 5% 6% 27%	1600
	21st to end	Day	10% 13% 5% 13% 8% 5% 5% 4 3 5% 30%	1576
December	1st to 10th	Day	9% 13% 5% 13% 8% 7% 6% 5% 5% 6% 23%	1386
	11th to 20th	Day	9% 14% 6% 12% 7% 7% 5% 5% 7% 7% 22%	1683
	21st to end	Day	14% 15% 5% 12% 7% 8% 5% 3 4 4 23%	2442
January	1st to 10th	Night	5% 12% 6% 13% 8% 8% 7% 4 6% 7% 25%	4737
	11th to 20th	Night	5% 10% 5% 15% 11% 10% 9% 6% 7% 6% 16%	4582
	21st to end	Night	8% 13% 7% 16% 7% 5% 4 4 5% 5% 26%	4873
February	1st to 10th	Night	8% 11% 4 13% 6% 6% 5% 4 5% 6% 30%	2487
	11th to 20th	Night	7% 10% 3 9% 7% 7% 8% 5% 6% 7% 31%	2403
	21st to end	Night	7% 12% 4 11% 7% 5% 4 3 5% 7% 35%	1941
March	1st to 10th	Night	8% 11% 4 8% 7% 5% 5% 4 5% 6% 38%	3643
	11th to 20th	Night	8% 10% 3 9% 7% 6% 4 4 6% 7% 37%	3480
	21st to end	Night	13% 14% 5% 11% 5% 4 4 3 5% 6% 29%	3817
April	1st to 10th	Night	11% 9% 3 7% 4 4 4 4 6% 6% 41%	1904
	11th to 20th	Night	16% 11% 4 7% 4 5% 3 4 5% 6% 36%	1689
	21st to end	Night	16% 9% 3 7% 5% 4 4 3 5% 6% 37%	1710
May	1st to 10th	Night	16% 7% 3 6% 5% 4 4 4 5% 6% 38%	2850
	11th to 20th	Night	14% 6% 2 6% 4 4 6% 3 6% 7% 42%	2433
	21st to end	Night	15% 7% 2 4 4 3 3 4 5% 7% 45%	2414
June	1st to 10th	Night	10% 5% 1 5% 3 4 5% 4 6% 9% 48%	1330
	11th to 20th	Night	10% 6% 2 5% 4 3 4 4 7% 8% 47%	1330
	21st to end	Night	7% 3 2 5% 4 4 6% 4 6% 10% 50%	1330
July	1st to 10th	Night	7% 4 1 5% 3 3 4 4 8% 9% 53%	2220
	11th to 20th	Night	4 3 1 3 2 3 3 3 5% 8% 63%	2220
	21st to end	Night	6% 3 1 5% 4 4 5% 5% 8% 10% 48%	2656
August	1st to 10th	Night	6% 3 1 6% 4 4 5% 4 7% 8% 54%	2790
	11th to 20th	Night	11% 4 1 4 4 4 4 4 6% 10% 48%	2798
	21st to end	Night	11% 6% 2 5% 4 3 3 2 5% 6% 54%	3135
September	1st to 10th	Night	8% 4 2 4 3 3 4 3 5% 7% 57%	1864
	11th to 20th	Night	9% 5% 2 5% 3 3 4 3 6% 8% 53%	2090
	21st to end	Night	13% 6% 2 5% 4 3 4 3 4 6% 51%	2090
October	1st to 10th	Night	10% 4 1 6% 4 3 4 3 5% 7% 52%	3689
	11th to 20th	Night	10% 9% 2 6% 4 4 4 4 5% 8% 44%	3795
	21st to end	Night	14% 9% 3 8% 4 4 4 3 5% 7% 40%	4467
November	1st to 10th	Night	11% 10% 4 10% 6% 5% 5% 4 5% 7% 33%	2632
	11th to 20th	Night	9% 14% 6% 11% 6% 5% 4 4 4 6% 31%	2800
	21st to end	Night	11% 12% 4 10% 6% 5% 4 4 5% 5% 33%	2820
December	1st to 10th	Night	8% 13% 4 13% 9% 7% 6% 4 5% 6% 25%	2977
	11th to 20th	Night	10% 15% 5% 13% 8% 5% 5% 5% 5% 6% 23%	3514
	21st to end	Night	17% 13% 4 11% 7% 5% 4 3 5% 5% 26%	5225

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	60% 6% 12% 18% 4	2219
	11th to 20th	Day	69% 4 12% 12% 3	2384
	21st to end	Day	62% 3 9% 20% 6%	2794
February	1st to 10th	Day	59% 4 12% 16% 8%	1691
	11th to 20th	Day	55% 6% 12% 19% 7% 1	1673
	21st to end	Day	56% 6% 13% 20% 6%	1532
March	1st to 10th	Day	52% 4 13% 23% 7%	3217
	11th to 20th	Day	53% 5% 15% 23% 4	3480
	21st to end	Day	57% 6% 13% 20% 4	3814
April	1st to 10th	Day	49% 6% 12% 22% 10% 1	2273
	11th to 20th	Day	53% 5% 12% 19% 11% 1	2442
	21st to end	Day	52% 5% 14% 22% 6% 1	2470
May	1st to 10th	Day	45% 6% 13% 26% 10% 1	4120
	11th to 20th	Day	44% 5% 12% 27% 10% 1	4471
	21st to end	Day	48% 5% 12% 27% 8% 1	5173
June	1st to 10th	Day	39% 5% 19% 27% 9% 1	2850
	11th to 20th	Day	39% 6% 18% 26% 10% 1	2850
	21st to end	Day	39% 6% 17% 28% 9% 1	2850
July	1st to 10th	Day	30% 7% 23% 31% 8%	4676
	11th to 20th	Day	24% 6% 19% 39% 12% 1	4669
	21st to end	Day	28% 5% 21% 35% 10% 1	4751
August	1st to 10th	Day	33% 5% 17% 29% 15% 1	4132
	11th to 20th	Day	36% 5% 16% 33% 10%	4080
	21st to end	Day	33% 4 19% 35% 10%	4531
September	1st to 10th	Day	34% 4 15% 33% 13% 1	2311
	11th to 20th	Day	39% 5% 19% 28% 9% 1	2090
	21st to end	Day	35% 6% 16% 33% 9% 1	2090
October	1st to 10th	Day	33% 3 12% 35% 17% 1	3238
	11th to 20th	Day	39% 4 10% 31% 16%	3124
	21st to end	Day	47% 3 14% 26% 9%	3091
November	1st to 10th	Day	52% 4 15% 18% 10% 1	1664
	11th to 20th	Day	59% 5% 14% 17% 6% 1	1600
	21st to end	Day	57% 6% 14% 17% 6%	1576
December	1st to 10th	Day	61% 5% 14% 16% 4	1386
	11th to 20th	Day	60% 5% 15% 14% 5%	1680
	21st to end	Day	66% 4 6% 19% 5%	2442
January	1st to 10th	Night	58% 5% 14% 18% 5%	4737
	11th to 20th	Night	67% 4 11% 14% 4	4582
	21st to end	Night	61% 4 11% 20% 5%	4873
February	1st to 10th	Night	54% 4 14% 20% 8%	2487
	11th to 20th	Night	50% 7% 12% 19% 11%	2404
	21st to end	Night	49% 4 14% 25% 8% 1	1941
March	1st to 10th	Night	46% 6% 13% 27% 9%	3643
	11th to 20th	Night	45% 5% 14% 26% 10% 1	3480
	21st to end	Night	55% 4 14% 20% 7% 1	3817
April	1st to 10th	Night	42% 6% 12% 26% 13% 2	1904
	11th to 20th	Night	49% 4 12% 20% 13% 3	1689
	21st to end	Night	48% 4 13% 24% 10% 2	1710
May	1st to 10th	Night	45% 5% 12% 27% 10% 1	2850
	11th to 20th	Night	40% 4 11% 29% 13% 3	2434
	21st to end	Night	40% 4 12% 31% 12% 1	2414
June	1st to 10th	Night	32% 6% 17% 32% 11% 2	1330
	11th to 20th	Night	34% 5% 16% 28% 14% 3	1330
	21st to end	Night	30% 7% 19% 34% 8% 1	1330
July	1st to 10th	Night	27% 6% 25% 31% 10% 1	2185
	11th to 20th	Night	19% 5% 15% 48% 12% 1	2178
	21st to end	Night	28% 6% 23% 30% 12% 1	2572
August	1st to 10th	Night	27% 5% 15% 35% 17% 2	2782
	11th to 20th	Night	31% 5% 19% 31% 12% 1	2825
	21st to end	Night	32% 4 16% 32% 16% 1	3135
September	1st to 10th	Night	27% 5% 14% 36% 17% 1	1864
	11th to 20th	Night	29% 5% 19% 32% 14% 1	2090
	21st to end	Night	35% 3 13% 32% 16% 1	2090
October	1st to 10th	Night	31% 4 12% 34% 15% 3	3689
	11th to 20th	Night	39% 4 11% 29% 16% 1	3795
	21st to end	Night	45% 4 12% 27% 12%	4467
November	1st to 10th	Night	49% 6% 13% 19% 10% 2	2632
	11th to 20th	Night	56% 5% 14% 18% 7% 1	2800
	21st to end	Night	52% 5% 16% 20% 7%	2820
December	1st to 10th	Night	59% 5% 15% 16% 4	2977
	11th to 20th	Night	61% 6% 16% 14% 4	3516
	21st to end	Night	62% 3 11% 17% 6%	5225

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	10% 9% 39% 30% 10% 3	270
	11th to 20th	Day	13% 7% 38% 31% 11% 1	270
	21st to end	Day	16% 7% 36% 29% 11% 2	297
February	1st to 10th	Day	15% 14% 36% 29% 7% 1	270
	11th to 20th	Day	12% 11% 42% 23% 11% 1	270
	21st to end	Day	8% 8% 45% 28% 11%	225
March	1st to 10th	Day	16% 14% 28% 30% 10% 1	270
	11th to 20th	Day	15% 10% 36% 24% 11% 3	270
	21st to end	Day	14% 12% 31% 29% 11% 2	297
April	1st to 10th	Day	18% 17% 31% 23% 10% 2	453
	11th to 20th	Day	24% 14% 28% 24% 9% 2	640
	21st to end	Day	23% 10% 29% 25% 11% 2	650
May	1st to 10th	Day	18% 12% 29% 28% 11% 2	653
	11th to 20th	Day	17% 10% 28% 29% 12% 4	675
	21st to end	Day	15% 9% 30% 26% 18% 2	734
June	1st to 10th	Day	12% 11% 29% 29% 15% 5%	680
	11th to 20th	Day	14% 9% 39% 23% 13% 2	680
	21st to end	Day	11% 11% 29% 26% 19% 5%	680
July	1st to 10th	Day	6% 4 28% 32% 21% 10%	671
	11th to 20th	Day	10% 6% 28% 29% 21% 5%	668
	21st to end	Day	5% 3 26% 36% 22% 8%	739
August	1st to 10th	Day	7% 4 26% 35% 22% 5%	676
	11th to 20th	Day	13% 5% 22% 32% 19% 10%	665
	21st to end	Day	11% 8% 28% 31% 19% 4	748
September	1st to 10th	Day	11% 7% 31% 30% 17% 3	521
	11th to 20th	Day	15% 10% 30% 30% 12% 3	300
	21st to end	Day	15% 13% 36% 24% 10% 2	300
October	1st to 10th	Day	18% 10% 30% 27% 11% 3	300
	11th to 20th	Day	14% 12% 38% 26% 9% 1	300
	21st to end	Day	18% 15% 36% 22% 8% 2	330
November	1st to 10th	Day	22% 11% 27% 29% 10% 1	300
	11th to 20th	Day	16% 10% 39% 25% 9%	300
	21st to end	Day	16% 14% 38% 25% 8%	300
December	1st to 10th	Day	12% 9% 36% 31% 10% 2	294
	11th to 20th	Day	16% 10% 40% 30% 4	270
	21st to end	Day	17% 7% 35% 27% 12% 2	297
January	1st to 10th	Night	12% 9% 34% 33% 11% 1	950
	11th to 20th	Night	14% 8% 36% 32% 9% 1	950
	21st to end	Night	14% 8% 36% 32% 9%	1045
February	1st to 10th	Night	13% 9% 33% 34% 10% 1	950
	11th to 20th	Night	11% 9% 37% 30% 10% 2	929
	21st to end	Night	12% 8% 33% 34% 11% 2	685
March	1st to 10th	Night	14% 9% 37% 28% 11% 2	708
	11th to 20th	Night	13% 8% 39% 30% 9% 1	570
	21st to end	Night	15% 9% 32% 31% 12% 2	627
April	1st to 10th	Night	15% 9% 35% 31% 10%	570
	11th to 20th	Night	19% 10% 29% 30% 11%	563
	21st to end	Night	21% 6% 25% 36% 11% 1	570
May	1st to 10th	Night	20% 8% 29% 33% 10% 1	570
	11th to 20th	Night	15% 8% 32% 30% 15% 1	561
	21st to end	Night	15% 7% 33% 31% 13% 1	617
June	1st to 10th	Night	13% 6% 29% 38% 14% 1	570
	11th to 20th	Night	11% 6% 35% 35% 12%	570
	21st to end	Night	8% 4 28% 44% 16% 1	570
July	1st to 10th	Night	6% 3 24% 45% 20% 2	555
	11th to 20th	Night	7% 3 27% 44% 18% 1	552
	21st to end	Night	6% 3 22% 49% 19% 2	624
August	1st to 10th	Night	6% 3 24% 47% 19% 1	567
	11th to 20th	Night	9% 3 24% 40% 21% 2	564
	21st to end	Night	10% 5% 26% 38% 19% 1	627
September	1st to 10th	Night	9% 4 30% 39% 16% 2	570
	11th to 20th	Night	11% 5% 31% 38% 15% 1	570
	21st to end	Night	15% 6% 31% 36% 12%	570
October	1st to 10th	Night	18% 8% 33% 33% 8%	688
	11th to 20th	Night	19% 11% 34% 29% 7%	764
	21st to end	Night	20% 10% 33% 28% 8%	1045
November	1st to 10th	Night	15% 10% 37% 28% 10% 1	975
	11th to 20th	Night	16% 10% 36% 27% 10% 1	1000
	21st to end	Night	17% 13% 39% 25% 6% 1	1000
December	1st to 10th	Night	15% 8% 34% 33% 9% 1	993
	11th to 20th	Night	18% 11% 33% 30% 7% 1	950
	21st to end	Night	22% 8% 33% 27% 9% 1	1045

Page generated at 2024-12-06 02:54:47. Version ac07

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