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 2024-09-29.

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% 8% 3 7% 5% 4 5% 4 6% 8% 44%	101401
	Night	7% 9% 3 7% 5% 4 5% 4 6% 8% 43%	96981
Transparency	Day	36% 6% 15% 26% 14% 3	101125
	Night	38% 6% 16% 24% 13% 3	96846
Seeing	Day	13% 9% 29% 29% 16% 4	15334
	Night	11% 9% 35% 32% 12% 1	24486

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	3 13% 4 10% 6% 5% 5% 5% 7% 9% 33%	2219
	11th to 20th	Day	4 10% 4 11% 6% 5% 9% 7% 5% 6% 32%	2261
	21st to end	Day	2 8% 4 9% 5% 5% 5% 4 6% 8% 46%	2794
February	1st to 10th	Day	6% 14% 4 12% 6% 5% 5% 3 5% 8% 31%	1657
	11th to 20th	Day	6% 13% 5% 8% 6% 6% 5% 5% 7% 6% 31%	1665
	21st to end	Day	3 12% 5% 11% 7% 4 4 4 5% 8% 36%	1479
March	1st to 10th	Day	3 10% 3 9% 6% 7% 5% 4 6% 8% 38%	3226
	11th to 20th	Day	4 7% 3 7% 5% 4 5% 4 6% 9% 47%	3490
	21st to end	Day	10% 15% 6% 13% 6% 4 5% 4 5% 7% 25%	3825
April	1st to 10th	Day	7% 12% 4 8% 7% 6% 6% 4 7% 8% 31%	2301
	11th to 20th	Day	10% 12% 4 8% 6% 4 4 4 6% 8% 34%	2437
	21st to end	Day	10% 10% 3 7% 5% 5% 5% 5% 7% 7% 36%	2470
May	1st to 10th	Day	18% 14% 3 8% 4 4 4 4 4 6% 31%	4204
	11th to 20th	Day	9% 7% 3 7% 5% 6% 6% 5% 8% 9% 35%	4538
	21st to end	Day	15% 8% 3 8% 6% 5% 6% 5% 6% 8% 31%	5161
June	1st to 10th	Day	13% 7% 2 6% 5% 5% 5% 4 7% 8% 38%	2850
	11th to 20th	Day	15% 7% 2 7% 5% 5% 6% 5% 7% 8% 35%	2850
	21st to end	Day	7% 3 1 4 4 5% 4 3 8% 9% 52%	2850
July	1st to 10th	Day	4 3 1 4 3 4 4 4 6% 9% 58%	4740
	11th to 20th	Day	3 2 1 3 2 3 3 3 6% 10% 65%	4740
	21st to end	Day	2 1 1 2 2 2 3 3 5% 7% 71%	5027
August	1st to 10th	Day	7% 4 2 6% 4 4 5% 4 6% 9% 50%	4198
	11th to 20th	Day	4 3 1 4 3 4 5% 4 6% 10% 56%	4028
	21st to end	Day	6% 3 1 4 3 3 3 3 5% 7% 61%	4521
September	1st to 10th	Day	10% 4 1 5% 3 3 4 3 5% 6% 56%	2342
	11th to 20th	Day	10% 7% 2 5% 3 3 5% 3 6% 6% 50%	2090
	21st to end	Day	10% 5% 2 5% 3 3 4 3 4 8% 51%	2069
October	1st to 10th	Day	11% 9% 3 7% 3 4 4 3 6% 6% 44%	1854
	11th to 20th	Day	6% 10% 3 8% 5% 6% 4 4 6% 6% 43%	1782
	21st to end	Day	9% 8% 3 7% 4 4 5% 4 8% 8% 40%	1782
November	1st to 10th	Day	12% 14% 4 8% 5% 4 3 3 5% 6% 35%	1530
	11th to 20th	Day	5% 8% 3 8% 7% 6% 4 4 7% 9% 39%	1520
	21st to end	Day	3 12% 4 8% 5% 3 5% 4 6% 10% 39%	1444
December	1st to 10th	Day	3 12% 5% 11% 6% 4 5% 4 6% 8% 36%	1330
	11th to 20th	Day	4 11% 4 9% 7% 6% 6% 5% 7% 8% 34%	1685
	21st to end	Day	3 8% 3 7% 4 4 5% 3 6% 7% 48%	2442
January	1st to 10th	Night	3 11% 5% 9% 6% 4 5% 4 7% 10% 35%	4726
	11th to 20th	Night	3 12% 6% 9% 5% 7% 7% 4 5% 7% 34%	4728
	21st to end	Night	3 8% 3 9% 5% 4 5% 4 5% 8% 45%	4862
February	1st to 10th	Night	6% 13% 5% 10% 6% 5% 6% 5% 5% 7% 34%	2522
	11th to 20th	Night	4 14% 4 9% 6% 6% 6% 5% 7% 8% 32%	2402
	21st to end	Night	3 13% 5% 11% 6% 6% 5% 4 5% 7% 34%	1974
March	1st to 10th	Night	3 8% 5% 11% 8% 6% 5% 4 6% 8% 37%	3648
	11th to 20th	Night	3 7% 3 7% 5% 4 4 4 6% 9% 48%	3490
	21st to end	Night	11% 19% 7% 12% 6% 4 4 3 5% 6% 23%	3828
April	1st to 10th	Night	8% 11% 4 8% 5% 4 5% 4 7% 8% 37%	1876
	11th to 20th	Night	10% 11% 3 8% 6% 4 5% 4 6% 7% 37%	1691
	21st to end	Night	11% 11% 3 6% 5% 5% 6% 4 5% 8% 36%	1710
May	1st to 10th	Night	17% 13% 3 7% 5% 4 4 3 5% 5% 32%	2764
	11th to 20th	Night	9% 5% 2 7% 4 5% 5% 5% 6% 9% 43%	2344
	21st to end	Night	16% 7% 2 8% 5% 4 5% 4 7% 10% 33%	2414
June	1st to 10th	Night	11% 6% 2 5% 4 4 4 5% 8% 8% 43%	1330
	11th to 20th	Night	14% 6% 2 5% 4 4 4 4 7% 8% 41%	1330
	21st to end	Night	6% 3 1 4 3 4 4 4 7% 9% 54%	1330
July	1st to 10th	Night	3 2 1 4 3 3 4 4 6% 8% 62%	2220
	11th to 20th	Night	4 2 1 2 2 3 3 3 7% 8% 66%	2220
	21st to end	Night	3 2 1 2 2 3 3 3 4 6% 69%	2522
August	1st to 10th	Night	9% 4 1 4 3 3 4 3 5% 9% 54%	2738
	11th to 20th	Night	4 3 2 4 5% 4 5% 4 8% 12% 49%	2811
	21st to end	Night	8% 5% 1 4 3 3 3 3 4 7% 59%	3146
September	1st to 10th	Night	11% 4 2 4 3 3 3 3 5% 8% 54%	1834
	11th to 20th	Night	9% 7% 2 5% 4 3 4 3 5% 8% 51%	2090
	21st to end	Night	9% 6% 2 4 3 3 4 4 5% 7% 53%	2079
October	1st to 10th	Night	12% 6% 2 6% 4 4 4 3 6% 8% 46%	2106
	11th to 20th	Night	9% 8% 3 6% 4 4 3 3 6% 8% 46%	2177
	21st to end	Night	7% 8% 3 8% 5% 5% 5% 4 7% 8% 40%	2574
November	1st to 10th	Night	10% 11% 3 8% 4 4 4 4 6% 8% 36%	2529
	11th to 20th	Night	4 9% 4 7% 6% 6% 5% 4 6% 8% 41%	2660
	21st to end	Night	4 12% 4 8% 5% 4 4 4 6% 8% 41%	2736
December	1st to 10th	Night	5% 10% 5% 9% 6% 6% 5% 5% 6% 8% 35%	2850
	11th to 20th	Night	4 8% 4 10% 6% 5% 5% 4 5% 9% 39%	3506
	21st to end	Night	3 9% 3 7% 5% 4 4 4 6% 7% 47%	5214

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	45% 6% 16% 24% 6% 1	2219
	11th to 20th	Day	51% 7% 13% 13% 13% 3	2261
	21st to end	Day	35% 7% 21% 31% 5%	2794
February	1st to 10th	Day	51% 5% 16% 19% 7% 2	1657
	11th to 20th	Day	48% 7% 16% 20% 7% 1	1674
	21st to end	Day	46% 6% 15% 22% 10% 1	1479
March	1st to 10th	Day	39% 8% 17% 26% 10%	3226
	11th to 20th	Day	32% 7% 25% 26% 9% 1	3490
	21st to end	Day	57% 6% 18% 14% 5%	3825
April	1st to 10th	Day	48% 7% 15% 22% 8%	2301
	11th to 20th	Day	48% 7% 10% 24% 10% 2	2440
	21st to end	Day	44% 7% 13% 25% 10% 1	2470
May	1st to 10th	Day	53% 6% 11% 24% 6%	4204
	11th to 20th	Day	36% 11% 14% 28% 10% 1	4542
	21st to end	Day	44% 11% 15% 21% 9% 1	5162
June	1st to 10th	Day	41% 7% 18% 20% 13% 1	2850
	11th to 20th	Day	44% 7% 14% 20% 13% 2	2850
	21st to end	Day	27% 5% 16% 35% 15% 3	2850
July	1st to 10th	Day	22% 5% 14% 28% 24% 7%	4666
	11th to 20th	Day	16% 4 11% 34% 26% 10%	4659
	21st to end	Day	12% 4 8% 24% 31% 21%	4868
August	1st to 10th	Day	30% 5% 13% 26% 23% 3	4182
	11th to 20th	Day	23% 5% 14% 36% 19% 2	4067
	21st to end	Day	23% 3 10% 38% 22% 4	4520
September	1st to 10th	Day	29% 4 12% 26% 20% 10%	2342
	11th to 20th	Day	33% 6% 14% 28% 15% 4	2090
	21st to end	Day	32% 6% 12% 31% 15% 4	2069
October	1st to 10th	Day	40% 6% 17% 26% 11% 1	1854
	11th to 20th	Day	41% 5% 16% 24% 12% 2	1782
	21st to end	Day	39% 8% 18% 24% 10% 1	1782
November	1st to 10th	Day	50% 6% 12% 21% 8% 3	1530
	11th to 20th	Day	40% 8% 19% 23% 9% 1	1520
	21st to end	Day	39% 6% 21% 20% 11% 2	1444
December	1st to 10th	Day	45% 7% 15% 21% 8% 3	1330
	11th to 20th	Day	45% 7% 20% 24% 3 1	1684
	21st to end	Day	34% 5% 16% 26% 15% 4	2442
January	1st to 10th	Night	42% 7% 19% 24% 7% 1	4726
	11th to 20th	Night	49% 5% 14% 15% 14% 2	4728
	21st to end	Night	37% 7% 19% 28% 9%	4862
February	1st to 10th	Night	49% 7% 16% 16% 11% 2	2522
	11th to 20th	Night	47% 7% 15% 19% 10% 1	2403
	21st to end	Night	49% 5% 15% 20% 10% 2	1974
March	1st to 10th	Night	44% 6% 17% 23% 10%	3648
	11th to 20th	Night	31% 9% 24% 26% 10%	3490
	21st to end	Night	63% 6% 14% 13% 4	3828
April	1st to 10th	Night	43% 8% 16% 25% 8%	1876
	11th to 20th	Night	45% 7% 12% 23% 13% 1	1691
	21st to end	Night	46% 6% 14% 25% 9% 1	1710
May	1st to 10th	Night	52% 5% 14% 21% 8% 1	2764
	11th to 20th	Night	32% 10% 15% 29% 13% 1	2344
	21st to end	Night	44% 7% 17% 23% 9%	2414
June	1st to 10th	Night	36% 7% 17% 29% 11% 1	1330
	11th to 20th	Night	39% 5% 15% 25% 14% 2	1330
	21st to end	Night	24% 6% 17% 30% 19% 3	1330
July	1st to 10th	Night	18% 5% 14% 30% 27% 5%	2185
	11th to 20th	Night	16% 4 12% 32% 24% 13%	2178
	21st to end	Night	16% 3 7% 26% 28% 20%	2443
August	1st to 10th	Night	27% 5% 11% 27% 22% 8%	2730
	11th to 20th	Night	26% 5% 18% 30% 17% 3	2838
	21st to end	Night	26% 4 9% 36% 19% 6%	3146
September	1st to 10th	Night	28% 4 11% 29% 18% 10%	1834
	11th to 20th	Night	32% 4 13% 29% 17% 5%	2090
	21st to end	Night	30% 4 15% 31% 17% 3	2079
October	1st to 10th	Night	36% 5% 16% 26% 14% 2	2106
	11th to 20th	Night	36% 6% 16% 27% 13% 3	2177
	21st to end	Night	40% 7% 16% 25% 11% 1	2574
November	1st to 10th	Night	45% 7% 15% 21% 10% 2	2529
	11th to 20th	Night	40% 6% 18% 23% 13% 1	2660
	21st to end	Night	39% 5% 23% 19% 11% 2	2736
December	1st to 10th	Night	44% 7% 15% 22% 10% 2	2850
	11th to 20th	Night	41% 7% 24% 22% 6% 1	3507
	21st to end	Night	34% 6% 14% 25% 16% 5%	5214

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	12% 7% 37% 23% 13% 8%	180
	11th to 20th	Day	9% 11% 38% 27% 11% 4	180
	21st to end	Day	10% 11% 37% 28% 11% 4	198
February	1st to 10th	Day	16% 13% 44% 19% 7% 1	245
	11th to 20th	Day	10% 12% 39% 27% 9% 3	270
	21st to end	Day	12% 10% 36% 32% 8% 2	291
March	1st to 10th	Day	12% 14% 35% 25% 12% 3	460
	11th to 20th	Day	10% 12% 37% 28% 11% 3	460
	21st to end	Day	14% 13% 31% 29% 10% 3	506
April	1st to 10th	Day	15% 15% 36% 27% 6% 1	460
	11th to 20th	Day	15% 12% 36% 26% 10% 2	452
	21st to end	Day	17% 14% 27% 27% 13% 2	460
May	1st to 10th	Day	18% 9% 24% 26% 19% 4	518
	11th to 20th	Day	19% 7% 19% 30% 19% 6%	675
	21st to end	Day	20% 7% 18% 27% 22% 5%	734
June	1st to 10th	Day	15% 13% 25% 27% 16% 4	680
	11th to 20th	Day	19% 12% 30% 25% 12% 3	680
	21st to end	Day	8% 7% 28% 31% 20% 6%	680
July	1st to 10th	Day	7% 4 21% 37% 23% 8%	671
	11th to 20th	Day	6% 5% 25% 36% 24% 3	668
	21st to end	Day	4 5% 22% 37% 26% 6%	677
August	1st to 10th	Day	6% 6% 22% 36% 26% 5%	487
	11th to 20th	Day	7% 4 19% 38% 23% 9%	477
	21st to end	Day	10% 6% 24% 32% 23% 7%	539
September	1st to 10th	Day	13% 7% 24% 30% 21% 4	490
	11th to 20th	Day	12% 8% 27% 33% 15% 5%	490
	21st to end	Day	14% 10% 31% 31% 10% 5%	483
October	1st to 10th	Day	14% 8% 31% 22% 21% 4	324
	11th to 20th	Day	14% 9% 34% 26% 16% 2	270
	21st to end	Day	18% 16% 35% 19% 10% 2	297
November	1st to 10th	Day	24% 9% 38% 23% 4 1	270
	11th to 20th	Day	12% 9% 47% 22% 9% 1	270
	21st to end	Day	9% 12% 41% 28% 7% 3	234
December	1st to 10th	Day	13% 11% 47% 18% 9% 2	180
	11th to 20th	Day	13% 14% 46% 14% 11% 1	180
	21st to end	Day	13% 13% 30% 31% 8% 5%	198
January	1st to 10th	Night	11% 14% 42% 25% 7% 2	950
	11th to 20th	Night	9% 13% 43% 25% 9% 1	938
	21st to end	Night	8% 15% 41% 27% 7% 3	836
February	1st to 10th	Night	11% 16% 35% 25% 11% 2	760
	11th to 20th	Night	12% 10% 38% 29% 10% 1	744
	21st to end	Night	9% 10% 36% 29% 14% 2	628
March	1st to 10th	Night	7% 10% 39% 31% 12% 1	760
	11th to 20th	Night	9% 11% 38% 31% 10% 1	760
	21st to end	Night	13% 11% 32% 31% 12% 1	836
April	1st to 10th	Night	14% 10% 34% 31% 10% 1	660
	11th to 20th	Night	15% 9% 40% 27% 9% 1	563
	21st to end	Night	17% 10% 31% 31% 11%	570
May	1st to 10th	Night	15% 7% 28% 32% 17% 1	570
	11th to 20th	Night	13% 5% 26% 39% 15% 2	467
	21st to end	Night	21% 7% 21% 32% 16% 2	411
June	1st to 10th	Night	14% 9% 29% 34% 14%	380
	11th to 20th	Night	18% 11% 31% 30% 11%	380
	21st to end	Night	8% 7% 26% 43% 16% 1	380
July	1st to 10th	Night	7% 4 24% 47% 18% 1	370
	11th to 20th	Night	7% 2 26% 46% 18% 2	368
	21st to end	Night	6% 3 22% 48% 21% 1	416
August	1st to 10th	Night	9% 3 21% 45% 21% 2	496
	11th to 20th	Night	7% 2 25% 43% 22% 1	564
	21st to end	Night	8% 5% 27% 41% 18%	627
September	1st to 10th	Night	13% 2 26% 41% 16% 1	595
	11th to 20th	Night	11% 5% 23% 40% 19% 2	760
	21st to end	Night	13% 6% 31% 36% 12% 1	756
October	1st to 10th	Night	14% 7% 29% 35% 15% 1	720
	11th to 20th	Night	14% 10% 35% 28% 12% 2	720
	21st to end	Night	12% 11% 40% 27% 8% 1	792
November	1st to 10th	Night	17% 11% 40% 27% 4	864
	11th to 20th	Night	10% 15% 46% 23% 6% 1	950
	21st to end	Night	10% 10% 45% 26% 9% 1	950
December	1st to 10th	Night	10% 12% 37% 31% 9% 2	950
	11th to 20th	Night	9% 11% 43% 28% 8% 1	950
	21st to end	Night	11% 11% 42% 28% 6% 1	1045

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