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 2024-02-05.

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	8% 8% 3 6% 5% 3 5% 5% 6% 8% 43%	77749
	Night	7% 8% 4 6% 6% 3 5% 5% 6% 8% 42%	81129
Transparency	Day	38% 6% 15% 25% 13% 3	77433
	Night	39% 6% 16% 24% 13% 3	80966
Seeing	Day	13% 9% 29% 29% 16% 4	14325
	Night	11% 9% 35% 31% 12% 1	23774

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 12% 5% 10% 6% 4 5% 7% 7% 9% 33%	2219
	11th to 20th	Day	4 9% 5% 9% 7% 4 8% 9% 5% 7% 32%	2261
	21st to end	Day	2 8% 4 8% 6% 3 5% 5% 5% 8% 46%	2794
February	1st to 10th	Day	6% 13% 4 10% 7% 3 6% 4 5% 9% 31%	1603
	11th to 20th	Day	7% 13% 5% 7% 7% 4 6% 7% 7% 7% 30%	1575
	21st to end	Day	4 11% 7% 9% 8% 3 4 4 5% 7% 36%	1394
March	1st to 10th	Day	4 11% 5% 10% 8% 4 5% 4 5% 8% 36%	1849
	11th to 20th	Day	7% 10% 4 7% 6% 3 5% 6% 6% 8% 38%	1980
	21st to end	Day	6% 11% 5% 9% 7% 3 6% 6% 7% 9% 31%	2178
April	1st to 10th	Day	7% 10% 6% 7% 8% 5% 6% 6% 7% 8% 32%	2179
	11th to 20th	Day	11% 12% 5% 8% 6% 4 4 5% 5% 7% 34%	2307
	21st to end	Day	11% 10% 3 6% 6% 3 6% 6% 6% 7% 35%	2340
May	1st to 10th	Day	11% 9% 3 6% 7% 4 5% 5% 6% 7% 36%	2392
	11th to 20th	Day	12% 7% 2 6% 5% 4 6% 5% 6% 9% 39%	2563
	21st to end	Day	21% 8% 3 5% 5% 3 5% 4 5% 8% 31%	2917
June	1st to 10th	Day	14% 7% 3 5% 5% 3 6% 5% 7% 8% 38%	2700
	11th to 20th	Day	15% 6% 3 6% 5% 3 5% 7% 7% 9% 34%	2700
	21st to end	Day	6% 3 1 3 5% 3 5% 4 7% 9% 52%	2700
July	1st to 10th	Day	5% 3 2 4 4 3 4 5% 5% 10% 56%	2700
	11th to 20th	Day	5% 2 1 3 4 3 4 4 6% 9% 57%	2700
	21st to end	Day	4 2 1 2 3 2 4 5% 5% 8% 63%	2880
August	1st to 10th	Day	6% 3 1 3 3 2 3 4 5% 9% 59%	2396
	11th to 20th	Day	6% 4 1 4 4 2 4 5% 6% 9% 55%	2299
	21st to end	Day	8% 3 1 4 5% 2 4 4 6% 8% 55%	2574
September	1st to 10th	Day	11% 4 1 4 4 2 4 4 5% 6% 55%	2220
	11th to 20th	Day	11% 7% 2 4 4 2 4 4 5% 6% 52%	1980
	21st to end	Day	11% 5% 2 5% 4 2 4 4 4 8% 50%	1980
October	1st to 10th	Day	11% 8% 3 7% 4 3 5% 4 6% 6% 44%	1854
	11th to 20th	Day	7% 9% 3 6% 6% 4 5% 5% 5% 6% 43%	1782
	21st to end	Day	9% 8% 3 6% 5% 3 4 6% 8% 8% 40%	1782
November	1st to 10th	Day	12% 13% 5% 7% 5% 3 3 4 5% 7% 35%	1530
	11th to 20th	Day	5% 8% 3 7% 8% 5% 5% 5% 7% 9% 39%	1520
	21st to end	Day	4 10% 5% 8% 5% 2 5% 5% 6% 10% 39%	1444
December	1st to 10th	Day	3 11% 5% 10% 7% 3 5% 5% 5% 8% 36%	1330
	11th to 20th	Day	4 10% 4 8% 8% 4 6% 6% 6% 8% 35%	1685
	21st to end	Day	3 8% 4 6% 5% 4 5% 4 6% 7% 48%	2442
January	1st to 10th	Night	4 11% 5% 8% 7% 3 5% 6% 7% 10% 35%	4726
	11th to 20th	Night	3 12% 6% 8% 6% 5% 7% 6% 5% 8% 34%	4728
	21st to end	Night	3 8% 4 8% 6% 3 5% 5% 5% 8% 45%	4862
February	1st to 10th	Night	6% 11% 5% 8% 7% 4 6% 6% 5% 7% 34%	2450
	11th to 20th	Night	5% 13% 4 7% 7% 4 6% 5% 8% 8% 31%	2272
	21st to end	Night	4 12% 7% 10% 8% 4 5% 5% 5% 6% 34%	1861
March	1st to 10th	Night	5% 7% 5% 8% 9% 4 5% 6% 6% 10% 34%	2111
	11th to 20th	Night	5% 9% 4 7% 7% 3 6% 6% 8% 10% 36%	1980
	21st to end	Night	7% 10% 5% 7% 8% 4 6% 5% 7% 8% 33%	2178
April	1st to 10th	Night	7% 9% 4 8% 6% 3 5% 6% 6% 9% 37%	1778
	11th to 20th	Night	10% 10% 4 7% 6% 3 5% 5% 5% 7% 37%	1601
	21st to end	Night	12% 10% 3 6% 6% 4 7% 5% 5% 8% 36%	1620
May	1st to 10th	Night	9% 9% 3 7% 6% 3 4 5% 7% 8% 40%	1566
	11th to 20th	Night	11% 3 2 5% 4 3 5% 5% 5% 7% 48%	1328
	21st to end	Night	20% 7% 2 7% 5% 3 5% 4 4 8% 34%	1358
June	1st to 10th	Night	11% 6% 2 4 4 3 4 6% 7% 9% 43%	1260
	11th to 20th	Night	15% 6% 3 5% 5% 3 3 5% 7% 8% 41%	1260
	21st to end	Night	6% 3 2 4 4 3 4 5% 7% 9% 54%	1260
July	1st to 10th	Night	5% 3 1 3 3 2 4 4 5% 7% 63%	1260
	11th to 20th	Night	6% 2 2 3 3 3 4 5% 7% 8% 58%	1260
	21st to end	Night	4 2 1 2 3 2 4 4 4 8% 67%	1435
August	1st to 10th	Night	7% 3 1 3 4 2 3 4 5% 9% 57%	1543
	11th to 20th	Night	6% 3 2 3 4 2 4 3 6% 11% 55%	1602
	21st to end	Night	6% 5% 2 4 4 3 4 4 5% 7% 56%	1782
September	1st to 10th	Night	11% 4 2 4 3 2 3 4 5% 8% 54%	1736
	11th to 20th	Night	9% 6% 2 4 4 3 4 4 5% 8% 52%	1980
	21st to end	Night	10% 6% 2 4 3 3 4 4 5% 8% 52%	1980
October	1st to 10th	Night	12% 5% 3 5% 5% 3 4 4 6% 8% 46%	2106
	11th to 20th	Night	9% 7% 3 5% 5% 3 4 4 6% 8% 46%	2177
	21st to end	Night	7% 8% 3 7% 6% 3 5% 6% 6% 8% 41%	2574
November	1st to 10th	Night	11% 11% 4 7% 5% 3 5% 5% 6% 8% 36%	2529
	11th to 20th	Night	4 8% 4 6% 6% 4 5% 5% 6% 9% 42%	2660
	21st to end	Night	4 10% 5% 7% 5% 4 4 5% 6% 9% 42%	2736
December	1st to 10th	Night	5% 9% 5% 8% 7% 4 6% 6% 6% 9% 36%	2850
	11th to 20th	Night	4 8% 4 9% 6% 4 5% 5% 5% 9% 40%	3506
	21st to end	Night	3 8% 4 6% 6% 3 5% 5% 6% 7% 48%	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	50% 5% 17% 19% 7% 2	1603
	11th to 20th	Day	48% 7% 16% 20% 7% 1	1584
	21st to end	Day	46% 6% 14% 21% 11% 2	1394
March	1st to 10th	Day	47% 5% 17% 23% 7%	1849
	11th to 20th	Day	42% 7% 17% 24% 8% 2	1980
	21st to end	Day	47% 8% 17% 19% 8%	2178
April	1st to 10th	Day	48% 7% 15% 22% 8%	2179
	11th to 20th	Day	49% 7% 10% 23% 10% 2	2310
	21st to end	Day	45% 7% 13% 24% 8% 1	2340
May	1st to 10th	Day	44% 7% 15% 24% 10% 1	2392
	11th to 20th	Day	40% 7% 15% 26% 11% 1	2567
	21st to end	Day	50% 6% 14% 21% 8%	2918
June	1st to 10th	Day	42% 7% 18% 20% 12% 1	2700
	11th to 20th	Day	44% 7% 14% 20% 14% 1	2700
	21st to end	Day	27% 5% 16% 35% 14% 3	2700
July	1st to 10th	Day	22% 7% 16% 30% 19% 5%	2626
	11th to 20th	Day	23% 6% 14% 28% 24% 7%	2619
	21st to end	Day	18% 6% 11% 27% 30% 9%	2720
August	1st to 10th	Day	23% 5% 16% 28% 23% 6%	2379
	11th to 20th	Day	25% 5% 14% 32% 20% 4	2299
	21st to end	Day	26% 4 13% 28% 22% 6%	2574
September	1st to 10th	Day	30% 4 11% 26% 19% 9%	2220
	11th to 20th	Day	32% 6% 13% 29% 16% 4	1980
	21st to end	Day	33% 6% 12% 31% 15% 4	1980
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	48% 7% 16% 17% 11% 2	2450
	11th to 20th	Night	48% 7% 16% 20% 10%	2273
	21st to end	Night	50% 5% 13% 19% 10% 2	1861
March	1st to 10th	Night	45% 6% 18% 23% 7% 1	2111
	11th to 20th	Night	42% 8% 18% 22% 10% 1	1980
	21st to end	Night	47% 8% 18% 19% 7% 1	2178
April	1st to 10th	Night	42% 8% 16% 25% 8%	1778
	11th to 20th	Night	46% 7% 12% 22% 13% 1	1601
	21st to end	Night	47% 5% 14% 25% 8% 1	1620
May	1st to 10th	Night	40% 5% 17% 26% 10% 1	1566
	11th to 20th	Night	34% 5% 16% 28% 16% 2	1328
	21st to end	Night	49% 5% 16% 21% 9%	1358
June	1st to 10th	Night	36% 6% 17% 29% 11% 1	1260
	11th to 20th	Night	39% 5% 16% 25% 14% 1	1260
	21st to end	Night	24% 6% 17% 30% 19% 3	1260
July	1st to 10th	Night	19% 5% 12% 32% 24% 7%	1225
	11th to 20th	Night	22% 5% 13% 28% 23% 9%	1218
	21st to end	Night	17% 4 9% 26% 31% 14%	1355
August	1st to 10th	Night	24% 5% 12% 28% 23% 7%	1535
	11th to 20th	Night	24% 4 13% 28% 24% 5%	1602
	21st to end	Night	28% 5% 9% 25% 26% 9%	1782
September	1st to 10th	Night	29% 4 11% 29% 17% 9%	1736
	11th to 20th	Night	31% 4 12% 29% 17% 6%	1980
	21st to end	Night	31% 4 15% 30% 16% 3	1980
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% 45% 18% 7% 1	227
	11th to 20th	Day	11% 13% 43% 25% 6% 2	240
	21st to end	Day	13% 8% 36% 32% 8% 2	260
March	1st to 10th	Day	12% 15% 36% 23% 12% 2	420
	11th to 20th	Day	10% 12% 37% 26% 10% 4	420
	21st to end	Day	13% 14% 32% 28% 10% 3	462
April	1st to 10th	Day	14% 15% 36% 28% 7% 1	420
	11th to 20th	Day	16% 12% 35% 25% 9% 2	412
	21st to end	Day	17% 14% 26% 27% 14% 2	420
May	1st to 10th	Day	17% 8% 25% 27% 19% 4	475
	11th to 20th	Day	19% 8% 19% 29% 19% 6%	625
	21st to end	Day	22% 7% 17% 28% 22% 5%	679
June	1st to 10th	Day	15% 13% 25% 27% 17% 4	630
	11th to 20th	Day	19% 12% 31% 25% 12% 3	630
	21st to end	Day	7% 6% 26% 32% 22% 6%	630
July	1st to 10th	Day	7% 5% 21% 37% 22% 8%	621
	11th to 20th	Day	7% 6% 26% 36% 22% 3	618
	21st to end	Day	4 4 23% 38% 26% 5%	626
August	1st to 10th	Day	6% 6% 23% 36% 25% 5%	447
	11th to 20th	Day	8% 4 18% 37% 23% 9%	437
	21st to end	Day	10% 5% 23% 33% 23% 7%	495
September	1st to 10th	Day	14% 8% 25% 30% 20% 3	450
	11th to 20th	Day	12% 8% 25% 34% 15% 5%	450
	21st to end	Day	15% 9% 31% 30% 10% 5%	450
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% 15% 36% 25% 11% 2	738
	11th to 20th	Night	12% 11% 38% 28% 10% 1	704
	21st to end	Night	9% 10% 34% 30% 15% 2	592
March	1st to 10th	Night	7% 9% 39% 31% 12% 1	720
	11th to 20th	Night	9% 11% 38% 30% 10% 2	720
	21st to end	Night	12% 12% 34% 30% 11% 1	792
April	1st to 10th	Night	13% 10% 34% 32% 11% 1	626
	11th to 20th	Night	15% 8% 40% 26% 9% 1	533
	21st to end	Night	18% 9% 30% 32% 11%	540
May	1st to 10th	Night	14% 7% 29% 32% 18% 1	540
	11th to 20th	Night	14% 5% 26% 37% 15% 2	443
	21st to end	Night	22% 7% 21% 32% 16% 2	389
June	1st to 10th	Night	13% 8% 30% 34% 14%	360
	11th to 20th	Night	18% 11% 31% 30% 10%	360
	21st to end	Night	8% 7% 26% 43% 16% 1	360
July	1st to 10th	Night	7% 4 23% 47% 18% 1	350
	11th to 20th	Night	7% 2 27% 46% 16% 2	348
	21st to end	Night	5% 3 22% 47% 21% 2	394
August	1st to 10th	Night	9% 3 21% 45% 21% 2	469
	11th to 20th	Night	7% 2 25% 42% 22% 1	534
	21st to end	Night	8% 5% 27% 42% 19%	594
September	1st to 10th	Night	13% 2 27% 40% 16% 1	563
	11th to 20th	Night	11% 5% 23% 40% 20% 2	720
	21st to end	Night	14% 6% 31% 35% 13% 2	720
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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