Milk River
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Milk River clear sky chart from 2005-11-06 to 2026-07-01.

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	7% 7% 3 7% 4 4 5% 4 6% 8% 44%	146884
	Night	6% 8% 3 7% 5% 5% 5% 4 6% 8% 43%	142768
Transparency	Day	36% 6% 14% 26% 15% 3	141512
	Night	38% 5% 16% 25% 13% 3	139151
Seeing	Day	13% 10% 29% 29% 16% 4	17601
	Night	11% 10% 35% 32% 11% 1	26827

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	4 13% 5% 10% 5% 5% 5% 5% 7% 9% 32%	4124
	11th to 20th	Day	2 9% 4 10% 5% 5% 7% 6% 6% 8% 36%	4237
	21st to end	Day	2 8% 4 10% 5% 5% 5% 3 5% 7% 46%	5187
February	1st to 10th	Day	6% 13% 4 12% 6% 5% 5% 3 6% 9% 31%	1832
	11th to 20th	Day	6% 13% 5% 8% 6% 6% 6% 5% 7% 7% 32%	1845
	21st to end	Day	3 11% 5% 10% 7% 5% 4 3 6% 8% 38%	1630
March	1st to 10th	Day	4 9% 3 8% 5% 6% 5% 4 6% 9% 42%	4748
	11th to 20th	Day	4 7% 4 9% 6% 5% 5% 4 6% 9% 41%	5110
	21st to end	Day	8% 15% 6% 13% 6% 5% 6% 5% 6% 7% 23%	5607
April	1st to 10th	Day	7% 12% 4 8% 6% 5% 5% 4 7% 8% 33%	2543
	11th to 20th	Day	10% 12% 4 8% 6% 4 4 4 6% 7% 35%	2697
	21st to end	Day	10% 10% 3 7% 5% 5% 5% 5% 7% 7% 36%	2730
May	1st to 10th	Day	11% 9% 2 6% 4 4 4 4 6% 8% 42%	7802
	11th to 20th	Day	10% 8% 3 7% 5% 6% 6% 5% 7% 9% 34%	8471
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 5% 7% 9% 39%	9648
June	1st to 10th	Day	13% 7% 2 6% 5% 5% 5% 4 7% 8% 38%	3150
	11th to 20th	Day	14% 6% 2 7% 4 5% 5% 5% 7% 8% 35%	3150
	21st to end	Day	8% 3 1 4 4 5% 4 3 7% 9% 51%	3150
July	1st to 10th	Day	5% 3 1 4 3 3 4 3 5% 9% 59%	6780
	11th to 20th	Day	6% 3 1 4 3 3 4 3 6% 10% 57%	6780
	21st to end	Day	5% 3 1 3 2 3 4 3 5% 7% 63%	7215
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 4 6% 10% 46%	5936
	11th to 20th	Day	4 3 1 4 3 4 5% 4 6% 10% 55%	5798
	21st to end	Day	7% 4 1 4 3 2 3 3 5% 6% 63%	6468
September	1st to 10th	Day	10% 4 1 4 3 3 4 3 5% 6% 56%	2465
	11th to 20th	Day	10% 7% 2 5% 3 3 5% 3 5% 6% 51%	2200
	21st to end	Day	10% 5% 2 5% 3 3 4 3 4 8% 52%	2200
October	1st to 10th	Day	7% 6% 2 6% 3 3 4 3 6% 8% 51%	3355
	11th to 20th	Day	5% 7% 2 6% 4 4 4 4 6% 8% 51%	3207
	21st to end	Day	6% 6% 3 6% 4 4 5% 4 7% 8% 47%	3200
November	1st to 10th	Day	11% 13% 4 8% 5% 4 3 4 6% 6% 35%	1694
	11th to 20th	Day	5% 8% 2 8% 7% 6% 4 4 7% 9% 39%	1680
	21st to end	Day	4 12% 4 9% 5% 3 5% 4 6% 10% 38%	1595
December	1st to 10th	Day	2 8% 5% 10% 6% 5% 5% 5% 6% 8% 40%	2360
	11th to 20th	Day	3 11% 4 9% 7% 6% 6% 4 7% 7% 36%	2715
	21st to end	Day	4 11% 5% 9% 5% 5% 5% 3 6% 6% 41%	3575
January	1st to 10th	Night	3 12% 5% 10% 5% 4 4 4 7% 10% 35%	8768
	11th to 20th	Night	2 9% 5% 9% 5% 6% 7% 4 6% 8% 39%	8780
	21st to end	Night	3 6% 4 9% 5% 6% 5% 4 6% 8% 44%	8994
February	1st to 10th	Night	5% 12% 4 10% 6% 5% 6% 5% 6% 7% 33%	2786
	11th to 20th	Night	4 13% 4 10% 6% 6% 6% 5% 7% 8% 32%	2662
	21st to end	Night	3 13% 5% 10% 6% 5% 5% 4 5% 7% 36%	2174
March	1st to 10th	Night	3 8% 4 9% 6% 5% 5% 4 6% 10% 39%	5366
	11th to 20th	Night	3 7% 4 9% 5% 5% 5% 5% 7% 9% 43%	5110
	21st to end	Night	10% 17% 6% 10% 5% 4 5% 4 7% 9% 24%	5610
April	1st to 10th	Night	7% 11% 3 8% 5% 4 5% 4 6% 8% 37%	2074
	11th to 20th	Night	9% 11% 3 8% 6% 5% 5% 4 6% 7% 37%	1871
	21st to end	Night	11% 11% 3 7% 6% 5% 6% 5% 5% 7% 35%	1890
May	1st to 10th	Night	13% 10% 3 6% 4 4 4 3 6% 7% 41%	5143
	11th to 20th	Night	8% 7% 2 8% 5% 6% 7% 6% 7% 9% 34%	4388
	21st to end	Night	12% 5% 2 6% 4 4 5% 4 7% 9% 42%	4525
June	1st to 10th	Night	11% 6% 2 5% 4 4 4 5% 8% 8% 42%	1470
	11th to 20th	Night	13% 6% 2 5% 4 4 4 4 8% 9% 41%	1470
	21st to end	Night	7% 4 1 4 3 4 4 4 7% 9% 52%	1470
July	1st to 10th	Night	5% 2 1 3 2 3 4 4 5% 8% 64%	3180
	11th to 20th	Night	6% 2 1 3 2 3 3 3 6% 8% 62%	3180
	21st to end	Night	5% 3 1 3 3 3 3 3 5% 7% 62%	3619
August	1st to 10th	Night	9% 5% 2 6% 4 4 5% 4 6% 9% 46%	3869
	11th to 20th	Night	4 3 2 5% 5% 4 5% 4 8% 11% 50%	4051
	21st to end	Night	8% 4 1 3 3 3 2 3 4 6% 63%	4509
September	1st to 10th	Night	10% 4 2 4 3 3 3 3 5% 8% 55%	1931
	11th to 20th	Night	9% 7% 1 5% 4 3 4 3 5% 8% 51%	2200
	21st to end	Night	9% 6% 2 4 3 4 4 3 5% 7% 54%	2200
October	1st to 10th	Night	7% 5% 2 5% 4 4 4 3 5% 7% 53%	3824
	11th to 20th	Night	7% 7% 2 5% 4 4 4 4 6% 7% 51%	3928
	21st to end	Night	5% 7% 3 7% 4 5% 5% 4 6% 7% 47%	4600
November	1st to 10th	Night	9% 11% 4 8% 4 4 5% 4 6% 8% 36%	2803
	11th to 20th	Night	4 9% 4 7% 6% 6% 5% 4 6% 8% 41%	2940
	21st to end	Night	4 12% 4 8% 5% 5% 4 4 6% 8% 41%	3024
December	1st to 10th	Night	3 8% 3 7% 5% 5% 5% 6% 8% 9% 40%	5040
	11th to 20th	Night	4 10% 5% 10% 6% 5% 5% 4 6% 8% 37%	5696
	21st to end	Night	3 10% 4 8% 5% 4 4 4 6% 8% 43%	7623

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	46% 5% 15% 25% 8% 1	4125
	11th to 20th	Day	45% 5% 17% 18% 12% 4	4237
	21st to end	Day	38% 5% 17% 29% 11% 1	5187
February	1st to 10th	Day	51% 5% 16% 18% 10% 2	1832
	11th to 20th	Day	47% 7% 15% 20% 9% 1	1854
	21st to end	Day	44% 5% 15% 23% 11% 1	1630
March	1st to 10th	Day	36% 6% 14% 27% 15% 1	4748
	11th to 20th	Day	38% 6% 19% 24% 13% 1	5110
	21st to end	Day	57% 6% 18% 13% 6%	5607
April	1st to 10th	Day	46% 7% 15% 23% 8%	2543
	11th to 20th	Day	47% 7% 10% 25% 10% 2	2700
	21st to end	Day	43% 7% 13% 26% 10% 1	2730
May	1st to 10th	Day	39% 5% 10% 27% 16% 4	7802
	11th to 20th	Day	40% 8% 12% 26% 11% 2	8475
	21st to end	Day	37% 8% 13% 28% 13%	9650
June	1st to 10th	Day	41% 7% 16% 21% 14% 1	3150
	11th to 20th	Day	43% 6% 13% 22% 14% 2	3150
	21st to end	Day	28% 5% 15% 35% 14% 2	3150
July	1st to 10th	Day	22% 5% 15% 24% 27% 8%	6707
	11th to 20th	Day	23% 5% 15% 29% 21% 7%	6699
	21st to end	Day	20% 5% 12% 26% 23% 15%	7005
August	1st to 10th	Day	30% 5% 14% 26% 22% 3	4316
	11th to 20th	Day	23% 5% 14% 36% 19% 3	4197
	21st to end	Day	23% 3 10% 37% 23% 4	4663
September	1st to 10th	Day	28% 4 12% 27% 19% 9%	2465
	11th to 20th	Day	33% 6% 13% 28% 16% 4	2200
	21st to end	Day	32% 6% 11% 31% 16% 4	2200
October	1st to 10th	Day	30% 4 12% 35% 16% 2	3355
	11th to 20th	Day	31% 4 15% 32% 17% 1	3207
	21st to end	Day	33% 5% 13% 32% 16% 1	3200
November	1st to 10th	Day	49% 6% 13% 22% 8% 3	1694
	11th to 20th	Day	39% 8% 19% 24% 10% 1	1680
	21st to end	Day	41% 6% 21% 21% 10% 2	1595
December	1st to 10th	Day	42% 6% 16% 29% 6% 2	2360
	11th to 20th	Day	45% 6% 21% 24% 4 1	2714
	21st to end	Day	42% 4 13% 23% 15% 3	3575
January	1st to 10th	Night	43% 5% 16% 25% 10% 1	8769
	11th to 20th	Night	43% 4 18% 19% 13% 2	8780
	21st to end	Night	38% 5% 17% 28% 11% 1	8994
February	1st to 10th	Night	48% 6% 15% 17% 12% 2	2786
	11th to 20th	Night	47% 7% 15% 20% 11% 1	2663
	21st to end	Night	47% 5% 15% 21% 10% 2	2174
March	1st to 10th	Night	39% 5% 17% 24% 12% 3	5366
	11th to 20th	Night	35% 7% 18% 28% 12%	5110
	21st to end	Night	56% 5% 18% 14% 6%	5610
April	1st to 10th	Night	42% 8% 16% 26% 8% 1	2074
	11th to 20th	Night	44% 6% 13% 23% 12% 1	1871
	21st to end	Night	46% 6% 13% 25% 9% 1	1890
May	1st to 10th	Night	42% 4 12% 29% 10% 3	5141
	11th to 20th	Night	41% 7% 12% 26% 13% 1	4388
	21st to end	Night	36% 6% 14% 30% 13% 1	4526
June	1st to 10th	Night	37% 6% 16% 28% 13% 1	1470
	11th to 20th	Night	37% 6% 15% 26% 14% 2	1470
	21st to end	Night	26% 6% 16% 31% 18% 3	1470
July	1st to 10th	Night	18% 5% 16% 27% 24% 11%	3145
	11th to 20th	Night	20% 4 15% 32% 20% 9%	3138
	21st to end	Night	22% 4 15% 25% 20% 14%	3517
August	1st to 10th	Night	27% 5% 11% 27% 21% 8%	2816
	11th to 20th	Night	26% 6% 18% 30% 17% 3	2928
	21st to end	Night	26% 3 9% 36% 20% 6%	3245
September	1st to 10th	Night	28% 4 11% 30% 18% 9%	1931
	11th to 20th	Night	31% 4 13% 30% 16% 5%	2200
	21st to end	Night	30% 4 14% 31% 18% 3	2200
October	1st to 10th	Night	31% 4 11% 32% 18% 4	3824
	11th to 20th	Night	32% 5% 13% 30% 17% 3	3928
	21st to end	Night	34% 5% 11% 32% 16% 1	4600
November	1st to 10th	Night	45% 7% 14% 22% 11% 2	2803
	11th to 20th	Night	40% 5% 19% 22% 13% 1	2940
	21st to end	Night	40% 5% 23% 19% 10% 2	3024
December	1st to 10th	Night	38% 7% 22% 21% 10% 1	5040
	11th to 20th	Night	44% 6% 25% 19% 6% 1	5697
	21st to end	Night	38% 5% 12% 25% 16% 4	7623

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	13% 8% 35% 24% 14% 6%	220
	11th to 20th	Day	10% 14% 41% 24% 9% 3	220
	21st to end	Day	9% 12% 39% 27% 10% 3	242
February	1st to 10th	Day	15% 14% 41% 21% 8% 1	300
	11th to 20th	Day	10% 12% 41% 28% 8% 2	330
	21st to end	Day	13% 13% 37% 28% 7% 2	346
March	1st to 10th	Day	12% 14% 34% 25% 12% 3	540
	11th to 20th	Day	12% 13% 36% 26% 9% 3	540
	21st to end	Day	14% 14% 32% 27% 9% 3	594
April	1st to 10th	Day	15% 14% 34% 27% 8% 1	540
	11th to 20th	Day	15% 13% 35% 25% 10% 2	532
	21st to end	Day	15% 14% 26% 28% 15% 2	540
May	1st to 10th	Day	16% 10% 24% 27% 19% 4	604
	11th to 20th	Day	19% 9% 21% 28% 18% 5%	775
	21st to end	Day	19% 7% 19% 28% 21% 5%	844
June	1st to 10th	Day	16% 13% 26% 26% 15% 4	780
	11th to 20th	Day	18% 12% 30% 26% 12% 2	780
	21st to end	Day	10% 6% 28% 32% 19% 5%	780
July	1st to 10th	Day	7% 5% 22% 36% 22% 7%	722
	11th to 20th	Day	7% 5% 24% 37% 22% 3	718
	21st to end	Day	5% 5% 22% 37% 26% 6%	728
August	1st to 10th	Day	6% 6% 21% 35% 26% 5%	527
	11th to 20th	Day	7% 4 20% 38% 22% 8%	517
	21st to end	Day	10% 5% 23% 32% 24% 7%	583
September	1st to 10th	Day	12% 7% 24% 31% 21% 5%	530
	11th to 20th	Day	11% 8% 25% 33% 18% 5%	530
	21st to end	Day	13% 9% 33% 31% 10% 4	530
October	1st to 10th	Day	13% 8% 32% 23% 20% 4	389
	11th to 20th	Day	12% 9% 36% 27% 14% 2	330
	21st to end	Day	16% 17% 36% 20% 10% 1	363
November	1st to 10th	Day	23% 9% 40% 22% 5% 1	330
	11th to 20th	Day	11% 10% 48% 21% 9% 1	330
	21st to end	Day	12% 13% 39% 27% 7% 2	285
December	1st to 10th	Day	14% 12% 44% 21% 8% 1	220
	11th to 20th	Day	13% 19% 43% 15% 10% 1	220
	21st to end	Day	13% 13% 33% 29% 8% 5%	242
January	1st to 10th	Night	10% 14% 42% 25% 7% 2	1050
	11th to 20th	Night	9% 15% 42% 24% 8% 1	1036
	21st to end	Night	8% 15% 42% 27% 6% 2	924
February	1st to 10th	Night	11% 15% 36% 26% 10% 2	840
	11th to 20th	Night	11% 10% 39% 31% 9% 1	824
	21st to end	Night	9% 11% 36% 28% 13% 2	692
March	1st to 10th	Night	8% 10% 38% 32% 12% 1	840
	11th to 20th	Night	9% 12% 39% 30% 9% 1	840
	21st to end	Night	13% 13% 34% 29% 11% 1	924
April	1st to 10th	Night	14% 10% 34% 31% 10% 1	730
	11th to 20th	Night	14% 9% 41% 27% 8% 1	623
	21st to end	Night	17% 10% 31% 32% 11%	630
May	1st to 10th	Night	15% 7% 28% 34% 15%	630
	11th to 20th	Night	13% 7% 26% 38% 13% 2	517
	21st to end	Night	20% 7% 21% 34% 16% 2	455
June	1st to 10th	Night	15% 10% 29% 33% 13%	420
	11th to 20th	Night	16% 10% 32% 31% 10%	420
	21st to end	Night	9% 7% 25% 43% 15% 1	420
July	1st to 10th	Night	7% 4 24% 47% 17% 1	390
	11th to 20th	Night	7% 2 26% 46% 17% 2	388
	21st to end	Night	6% 3 21% 47% 21% 1	438
August	1st to 10th	Night	9% 3 22% 44% 20% 2	522
	11th to 20th	Night	7% 2 25% 43% 22% 1	594
	21st to end	Night	8% 5% 27% 42% 18%	660
September	1st to 10th	Night	12% 2 25% 42% 17% 1	627
	11th to 20th	Night	11% 5% 22% 41% 20% 2	800
	21st to end	Night	13% 6% 31% 36% 13% 1	800
October	1st to 10th	Night	14% 6% 30% 35% 15% 1	800
	11th to 20th	Night	14% 10% 35% 29% 11% 2	800
	21st to end	Night	11% 12% 42% 27% 8%	880
November	1st to 10th	Night	16% 11% 41% 27% 4	958
	11th to 20th	Night	10% 15% 45% 24% 6% 1	1050
	21st to end	Night	9% 11% 43% 28% 9% 1	1050
December	1st to 10th	Night	10% 13% 38% 30% 8% 2	1050
	11th to 20th	Night	10% 11% 44% 27% 7% 1	1050
	21st to end	Night	11% 12% 44% 26% 6% 1	1155

Page generated at 2026-06-28 00:10:45. Version ac07

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