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Northern Prairie Star Party
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northern Prairie Star Party clear sky chart from 2005-11-06 to 2025-11-03.

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	9% 9% 3 9% 5% 5% 5% 4 6% 8% 36%	131222
	Night	8% 9% 4 10% 6% 5% 6% 5% 6% 8% 34%	127518
Transparency	Day	44% 7% 17% 23% 8% 1	130919
	Night	46% 7% 16% 21% 9% 1	127401
Seeing	Day	12% 7% 25% 31% 18% 6%	16822
	Night	12% 6% 29% 36% 16% 2	25763

By Month

Percentage Cloud Cover NW (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% 11% 5% 12% 7% 8% 6% 5% 6% 8% 27%	3179
	11th to 20th	Day	3 10% 3 9% 8% 7% 7% 5% 10% 9% 28%	3159
	21st to end	Day	8% 11% 4 9% 6% 5% 4 4 6% 8% 35%	3700
February	1st to 10th	Day	8% 14% 5% 13% 7% 5% 6% 4 7% 7% 25%	1600
	11th to 20th	Day	6% 13% 5% 11% 7% 6% 6% 6% 6% 7% 27%	1744
	21st to end	Day	5% 13% 4 10% 8% 6% 7% 5% 7% 8% 27%	1504
March	1st to 10th	Day	3 9% 5% 12% 8% 6% 6% 5% 7% 10% 30%	4553
	11th to 20th	Day	6% 13% 5% 12% 6% 6% 5% 3 5% 9% 31%	4999
	21st to end	Day	9% 14% 5% 16% 6% 4 4 3 5% 8% 25%	5486
April	1st to 10th	Day	8% 12% 4 8% 6% 6% 7% 4 6% 8% 31%	2517
	11th to 20th	Day	12% 12% 4 9% 5% 4 5% 4 6% 7% 31%	2570
	21st to end	Day	13% 11% 3 8% 6% 5% 5% 3 6% 8% 33%	2600
May	1st to 10th	Day	12% 8% 3 8% 6% 5% 5% 4 5% 7% 38%	6582
	11th to 20th	Day	15% 11% 3 8% 6% 6% 5% 5% 6% 8% 27%	6734
	21st to end	Day	10% 7% 3 8% 5% 5% 5% 4 6% 7% 41%	7405
June	1st to 10th	Day	14% 8% 3 8% 5% 6% 6% 5% 6% 7% 33%	3000
	11th to 20th	Day	19% 10% 3 7% 6% 7% 5% 4 6% 7% 25%	3000
	21st to end	Day	10% 7% 2 7% 5% 5% 6% 5% 7% 10% 35%	3000
July	1st to 10th	Day	7% 4 2 5% 4 5% 5% 4 7% 9% 47%	6780
	11th to 20th	Day	10% 6% 2 6% 4 5% 5% 4 7% 8% 42%	6780
	21st to end	Day	10% 6% 2 6% 5% 4 5% 4 6% 9% 44%	7376
August	1st to 10th	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	4716
	11th to 20th	Day	8% 5% 2 6% 5% 4 5% 5% 7% 10% 43%	4218
	21st to end	Day	10% 5% 2 5% 4 3 5% 5% 7% 10% 45%	4664
September	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 6% 8% 45%	2549
	11th to 20th	Day	13% 8% 3 6% 3 4 3 3 5% 8% 43%	2200
	21st to end	Day	8% 7% 2 6% 4 4 4 4 6% 9% 46%	2200
October	1st to 10th	Day	8% 9% 3 8% 6% 5% 4 4 5% 7% 40%	3346
	11th to 20th	Day	10% 8% 4 7% 4 5% 5% 4 6% 10% 38%	3045
	21st to end	Day	7% 11% 3 7% 5% 5% 5% 3 6% 8% 40%	3109
November	1st to 10th	Day	9% 15% 5% 10% 6% 6% 5% 4 6% 7% 27%	1584
	11th to 20th	Day	6% 11% 6% 15% 6% 5% 6% 4 4 7% 30%	1493
	21st to end	Day	5% 11% 6% 14% 6% 6% 5% 4 6% 8% 30%	1400
December	1st to 10th	Day	9% 14% 5% 13% 8% 6% 6% 4 7% 7% 22%	2290
	11th to 20th	Day	9% 13% 4 12% 6% 7% 7% 5% 8% 9% 20%	2642
	21st to end	Day	3 7% 3 9% 7% 6% 5% 4 6% 7% 42%	3498
January	1st to 10th	Night	4 9% 5% 13% 9% 8% 8% 6% 7% 8% 25%	6766
	11th to 20th	Night	3 10% 4 10% 8% 6% 6% 5% 5% 6% 37%	6739
	21st to end	Night	7% 12% 4 11% 6% 5% 5% 4 6% 7% 35%	7298
February	1st to 10th	Night	5% 10% 4 13% 9% 7% 6% 6% 6% 7% 27%	2800
	11th to 20th	Night	6% 11% 4 10% 7% 7% 6% 4 8% 7% 30%	2542
	21st to end	Night	4 10% 4 10% 8% 7% 6% 5% 7% 9% 31%	2125
March	1st to 10th	Night	4 9% 5% 11% 6% 5% 6% 5% 7% 11% 30%	5341
	11th to 20th	Night	3 10% 4 12% 8% 6% 6% 5% 6% 8% 32%	5000
	21st to end	Night	10% 13% 6% 14% 7% 5% 6% 4 6% 6% 24%	5489
April	1st to 10th	Night	6% 11% 3 8% 6% 5% 6% 5% 8% 8% 35%	1880
	11th to 20th	Night	10% 11% 5% 9% 6% 6% 6% 5% 6% 7% 28%	1781
	21st to end	Night	12% 10% 3 8% 5% 5% 5% 5% 7% 7% 35%	1800
May	1st to 10th	Night	16% 6% 2 6% 4 4 4 4 5% 6% 41%	3382
	11th to 20th	Night	12% 10% 4 10% 6% 7% 6% 5% 7% 7% 25%	3159
	21st to end	Night	11% 8% 2 9% 6% 6% 6% 5% 6% 8% 34%	3470
June	1st to 10th	Night	15% 8% 3 8% 6% 6% 5% 5% 6% 8% 32%	1400
	11th to 20th	Night	17% 9% 3 8% 7% 7% 6% 6% 7% 8% 24%	1400
	21st to end	Night	10% 6% 3 6% 5% 5% 7% 6% 7% 10% 37%	1400
July	1st to 10th	Night	6% 6% 2 6% 5% 5% 5% 5% 7% 8% 44%	3180
	11th to 20th	Night	11% 5% 2 7% 5% 4 6% 5% 6% 9% 40%	3180
	21st to end	Night	10% 5% 3 6% 4 4 5% 4 7% 10% 43%	3467
August	1st to 10th	Night	16% 5% 2 6% 4 5% 4 4 6% 7% 42%	2433
	11th to 20th	Night	9% 6% 3 6% 5% 5% 6% 4 7% 9% 41%	2839
	21st to end	Night	9% 5% 1 7% 4 5% 5% 5% 6% 9% 45%	3245
September	1st to 10th	Night	11% 5% 2 6% 3 3 4 4 6% 9% 47%	1847
	11th to 20th	Night	13% 7% 2 5% 3 4 4 4 5% 6% 48%	2200
	21st to end	Night	8% 7% 2 6% 4 5% 5% 4 5% 7% 47%	2200
October	1st to 10th	Night	9% 7% 3 8% 4 5% 5% 4 6% 8% 42%	3846
	11th to 20th	Night	9% 7% 3 6% 4 4 5% 4 7% 9% 42%	4088
	21st to end	Night	6% 10% 3 8% 5% 5% 6% 4 6% 9% 38%	4659
November	1st to 10th	Night	12% 15% 6% 8% 6% 5% 4 4 6% 6% 29%	2759
	11th to 20th	Night	7% 13% 4 11% 8% 6% 5% 5% 6% 7% 28%	2905
	21st to end	Night	5% 12% 4 13% 9% 6% 6% 4 5% 8% 29%	3000
December	1st to 10th	Night	10% 15% 5% 14% 8% 6% 6% 4 5% 7% 21%	4890
	11th to 20th	Night	7% 14% 5% 14% 7% 6% 6% 5% 7% 8% 20%	5550
	21st to end	Night	2 6% 3 10% 6% 6% 5% 5% 6% 8% 43%	7458

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% 6% 10% 21% 8%	3179
	11th to 20th	Day	47% 7% 13% 14% 18% 1	3180
	21st to end	Day	47% 7% 19% 21% 5%	3700
February	1st to 10th	Day	58% 5% 13% 15% 9%	1600
	11th to 20th	Day	53% 7% 16% 15% 9%	1753
	21st to end	Day	51% 7% 13% 21% 8%	1504
March	1st to 10th	Day	48% 6% 19% 19% 8%	4553
	11th to 20th	Day	50% 6% 15% 20% 8%	5000
	21st to end	Day	56% 7% 10% 21% 6%	5486
April	1st to 10th	Day	48% 9% 14% 19% 8% 1	2517
	11th to 20th	Day	48% 7% 15% 21% 9%	2570
	21st to end	Day	48% 7% 14% 22% 8% 1	2600
May	1st to 10th	Day	44% 6% 11% 24% 14% 2	6582
	11th to 20th	Day	51% 8% 12% 22% 7%	6738
	21st to end	Day	38% 9% 19% 21% 12% 1	7406
June	1st to 10th	Day	47% 9% 13% 20% 10% 1	3000
	11th to 20th	Day	56% 8% 15% 17% 4 1	3000
	21st to end	Day	40% 12% 20% 20% 7% 1	3000
July	1st to 10th	Day	31% 7% 23% 30% 9%	6706
	11th to 20th	Day	37% 7% 18% 28% 10%	6699
	21st to end	Day	36% 7% 22% 27% 8%	7169
August	1st to 10th	Day	38% 8% 19% 33% 3	4698
	11th to 20th	Day	33% 8% 25% 27% 7%	4258
	21st to end	Day	32% 8% 26% 28% 5% 1	4663
September	1st to 10th	Day	36% 8% 19% 26% 8% 2	2549
	11th to 20th	Day	38% 7% 17% 30% 7% 1	2200
	21st to end	Day	34% 9% 19% 28% 8% 2	2200
October	1st to 10th	Day	44% 5% 21% 25% 6%	3346
	11th to 20th	Day	42% 6% 15% 27% 10%	3045
	21st to end	Day	42% 6% 19% 28% 4	3109
November	1st to 10th	Day	55% 7% 15% 15% 6% 1	1584
	11th to 20th	Day	53% 7% 17% 19% 4	1493
	21st to end	Day	51% 8% 17% 18% 5% 1	1400
December	1st to 10th	Day	60% 7% 18% 11% 4 1	2290
	11th to 20th	Day	57% 7% 18% 14% 4	2644
	21st to end	Day	41% 5% 12% 29% 12% 1	3498
January	1st to 10th	Night	55% 7% 14% 15% 9% 1	6766
	11th to 20th	Night	47% 6% 13% 17% 16% 1	6780
	21st to end	Night	48% 6% 18% 22% 5%	7298
February	1st to 10th	Night	55% 6% 13% 17% 9% 1	2800
	11th to 20th	Night	49% 7% 14% 17% 12% 1	2543
	21st to end	Night	47% 7% 13% 22% 9% 1	2125
March	1st to 10th	Night	45% 7% 18% 22% 8%	5341
	11th to 20th	Night	47% 7% 16% 21% 9% 1	5000
	21st to end	Night	56% 9% 10% 17% 8%	5489
April	1st to 10th	Night	43% 8% 15% 20% 14%	1880
	11th to 20th	Night	51% 7% 12% 18% 9% 2	1781
	21st to end	Night	44% 8% 13% 21% 12% 2	1800
May	1st to 10th	Night	41% 6% 9% 24% 16% 3	3382
	11th to 20th	Night	51% 10% 14% 18% 7%	3159
	21st to end	Night	44% 10% 15% 22% 9% 1	3470
June	1st to 10th	Night	47% 9% 12% 21% 9% 1	1400
	11th to 20th	Night	55% 11% 12% 15% 6%	1400
	21st to end	Night	38% 12% 21% 22% 6% 1	1400
July	1st to 10th	Night	34% 6% 25% 21% 14% 1	3145
	11th to 20th	Night	39% 7% 14% 30% 9% 1	3138
	21st to end	Night	34% 8% 25% 27% 7%	3369
August	1st to 10th	Night	38% 8% 20% 31% 2	2426
	11th to 20th	Night	38% 7% 23% 24% 7%	2865
	21st to end	Night	34% 7% 22% 31% 6%	3245
September	1st to 10th	Night	32% 9% 19% 26% 11% 3	1847
	11th to 20th	Night	35% 7% 17% 29% 10% 2	2200
	21st to end	Night	34% 9% 16% 26% 13% 3	2200
October	1st to 10th	Night	39% 5% 21% 27% 7%	3846
	11th to 20th	Night	37% 6% 15% 34% 8% 1	4088
	21st to end	Night	42% 6% 21% 25% 5%	4659
November	1st to 10th	Night	54% 7% 12% 19% 7% 1	2759
	11th to 20th	Night	55% 8% 13% 17% 6% 1	2905
	21st to end	Night	53% 8% 16% 17% 6% 1	3000
December	1st to 10th	Night	62% 6% 15% 11% 5% 1	4890
	11th to 20th	Night	61% 7% 17% 10% 5%	5547
	21st to end	Night	39% 6% 15% 22% 16% 2	7458

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% 5% 29% 37% 17% 4	200
	11th to 20th	Day	12% 9% 26% 36% 16% 3	200
	21st to end	Day	10% 9% 34% 30% 14% 4	220
February	1st to 10th	Day	10% 8% 31% 36% 13% 3	200
	11th to 20th	Day	9% 7% 30% 35% 15% 4	295
	21st to end	Day	8% 8% 28% 33% 16% 7%	268
March	1st to 10th	Day	9% 9% 27% 35% 18% 2	500
	11th to 20th	Day	9% 6% 31% 32% 16% 6%	500
	21st to end	Day	13% 6% 29% 30% 19% 4	550
April	1st to 10th	Day	9% 11% 29% 35% 12% 4	500
	11th to 20th	Day	15% 10% 24% 30% 17% 4	492
	21st to end	Day	17% 9% 26% 30% 14% 4	500
May	1st to 10th	Day	14% 9% 23% 33% 17% 5%	689
	11th to 20th	Day	11% 6% 25% 32% 19% 7%	725
	21st to end	Day	16% 6% 22% 27% 20% 9%	789
June	1st to 10th	Day	16% 11% 25% 32% 14% 3	730
	11th to 20th	Day	20% 7% 25% 24% 17% 7%	730
	21st to end	Day	11% 4 22% 30% 23% 10%	730
July	1st to 10th	Day	11% 4 17% 34% 27% 8%	721
	11th to 20th	Day	12% 4 19% 31% 24% 9%	718
	21st to end	Day	10% 5% 18% 31% 27% 10%	794
August	1st to 10th	Day	12% 5% 17% 30% 24% 13%	637
	11th to 20th	Day	9% 5% 23% 31% 24% 7%	517
	21st to end	Day	11% 7% 19% 30% 24% 9%	583
September	1st to 10th	Day	12% 8% 25% 29% 19% 7%	530
	11th to 20th	Day	17% 5% 24% 32% 18% 5%	530
	21st to end	Day	13% 13% 29% 28% 14% 3	530
October	1st to 10th	Day	15% 8% 27% 29% 16% 4	380
	11th to 20th	Day	12% 10% 32% 30% 15% 2	330
	21st to end	Day	12% 11% 39% 23% 11% 3	363
November	1st to 10th	Day	19% 7% 30% 30% 12% 2	306
	11th to 20th	Day	11% 9% 37% 33% 10% 1	245
	21st to end	Day	7% 9% 35% 34% 13% 4	200
December	1st to 10th	Day	10% 9% 32% 31% 14% 5%	200
	11th to 20th	Day	10% 9% 29% 36% 16% 1	200
	21st to end	Day	8% 6% 23% 40% 17% 5%	220
January	1st to 10th	Night	10% 7% 32% 36% 13% 2	1000
	11th to 20th	Night	9% 9% 33% 35% 11% 2	1000
	21st to end	Night	13% 10% 34% 32% 10% 2	1031
February	1st to 10th	Night	8% 9% 27% 36% 18% 2	800
	11th to 20th	Night	9% 6% 31% 37% 16% 1	784
	21st to end	Night	7% 6% 28% 36% 19% 5%	660
March	1st to 10th	Night	9% 5% 28% 41% 15% 2	800
	11th to 20th	Night	10% 4 32% 36% 15% 3	800
	21st to end	Night	13% 6% 26% 36% 16% 3	880
April	1st to 10th	Night	7% 9% 28% 34% 19% 3	670
	11th to 20th	Night	13% 6% 31% 35% 13% 1	593
	21st to end	Night	16% 6% 24% 39% 15% 1	600
May	1st to 10th	Night	15% 7% 24% 35% 18% 2	485
	11th to 20th	Night	12% 5% 24% 39% 19% 2	394
	21st to end	Night	18% 6% 22% 35% 18% 2	433
June	1st to 10th	Night	16% 8% 25% 35% 15% 2	400
	11th to 20th	Night	18% 6% 24% 31% 19% 3	400
	21st to end	Night	12% 4 18% 37% 24% 5%	400
July	1st to 10th	Night	11% 3 18% 42% 25% 1	390
	11th to 20th	Night	11% 3 18% 47% 19% 2	388
	21st to end	Night	10% 3 18% 38% 28% 3	438
August	1st to 10th	Night	13% 2 17% 35% 29% 4	398
	11th to 20th	Night	12% 6% 16% 38% 26% 2	556
	21st to end	Night	10% 3 23% 37% 26% 1	660
September	1st to 10th	Night	12% 3 20% 39% 24% 2	602
	11th to 20th	Night	15% 4 20% 40% 20% 1	800
	21st to end	Night	11% 5% 32% 38% 14% 1	800
October	1st to 10th	Night	15% 5% 28% 37% 15% 1	800
	11th to 20th	Night	13% 5% 32% 35% 13% 1	800
	21st to end	Night	13% 6% 37% 33% 11%	915
November	1st to 10th	Night	18% 7% 32% 33% 8% 1	986
	11th to 20th	Night	13% 7% 35% 31% 11% 3	1000
	21st to end	Night	9% 5% 39% 35% 11% 1	1000
December	1st to 10th	Night	13% 8% 34% 29% 13% 3	1000
	11th to 20th	Night	12% 7% 34% 35% 12% 1	1000
	21st to end	Night	9% 4 31% 38% 15% 3	1100

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