Missoula
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Missoula clear sky chart from 2005-11-06 to 2024-11-05.

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% 10% 3 8% 5% 4 5% 4 5% 7% 41%	105285
	Night	8% 12% 4 8% 5% 5% 5% 4 5% 7% 37%	102406
Transparency	Day	40% 5% 14% 22% 13% 5%	105018
	Night	43% 6% 16% 22% 10% 4	102261
Seeing	Day	16% 14% 25% 28% 15% 3	15184
	Night	15% 7% 21% 39% 17% 1	24444

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	6% 22% 10% 14% 8% 7% 5% 4 5% 6% 13%	2326
	11th to 20th	Day	8% 18% 6% 16% 7% 5% 4 3 5% 5% 22%	2540
	21st to end	Day	10% 18% 6% 13% 8% 5% 6% 4 5% 6% 20%	2794
February	1st to 10th	Day	8% 23% 7% 14% 7% 5% 5% 3 4 5% 18%	1638
	11th to 20th	Day	6% 19% 8% 12% 7% 5% 5% 4 5% 6% 22%	1711
	21st to end	Day	8% 19% 5% 12% 9% 6% 5% 4 5% 7% 20%	1570
March	1st to 10th	Day	6% 13% 5% 10% 7% 6% 5% 5% 7% 8% 28%	3138
	11th to 20th	Day	7% 11% 4 9% 5% 5% 5% 3 5% 7% 39%	3484
	21st to end	Day	7% 18% 5% 14% 8% 6% 6% 5% 7% 7% 16%	3825
April	1st to 10th	Day	9% 16% 6% 12% 6% 6% 5% 4 6% 7% 23%	2277
	11th to 20th	Day	11% 15% 5% 10% 6% 5% 5% 4 6% 6% 28%	2437
	21st to end	Day	12% 17% 4 10% 6% 4 4 4 5% 6% 27%	2470
May	1st to 10th	Day	14% 14% 4 9% 6% 6% 5% 4 5% 6% 27%	4110
	11th to 20th	Day	8% 7% 3 6% 4 5% 6% 5% 8% 11% 38%	4270
	21st to end	Day	14% 11% 3 8% 6% 5% 6% 4 7% 8% 29%	5161
June	1st to 10th	Day	16% 9% 3 7% 5% 5% 5% 4 6% 8% 32%	2850
	11th to 20th	Day	16% 10% 3 7% 5% 5% 5% 4 6% 6% 33%	2850
	21st to end	Day	6% 5% 2 5% 5% 4 5% 4 6% 7% 52%	2850
July	1st to 10th	Day	2 1 1 3 3 3 4 3 6% 7% 69%	4740
	11th to 20th	Day	2 2 1 2 1 2 2 2 3 4 78%	4527
	21st to end	Day	2 2 1 2 2 3 3 3 4 5% 73%	4790
August	1st to 10th	Day	3 3 1 4 3 4 5% 4 6% 9% 59%	4220
	11th to 20th	Day	3 2 1 3 3 3 4 4 7% 8% 60%	4028
	21st to end	Day	4 3 1 4 3 3 4 3 5% 7% 65%	4521
September	1st to 10th	Day	6% 4 2 4 4 3 3 3 4 7% 60%	2252
	11th to 20th	Day	7% 7% 2 6% 5% 4 5% 4 5% 7% 46%	2090
	21st to end	Day	9% 6% 3 5% 4 3 3 3 6% 7% 49%	2090
October	1st to 10th	Day	8% 6% 2 6% 3 3 2 3 4 7% 54%	3404
	11th to 20th	Day	8% 8% 3 7% 4 3 4 3 5% 7% 48%	3032
	21st to end	Day	10% 11% 5% 10% 5% 4 5% 4 4 6% 35%	3101
November	1st to 10th	Day	14% 19% 5% 10% 4 5% 5% 3 5% 7% 23%	1710
	11th to 20th	Day	12% 18% 5% 10% 5% 5% 4 4 5% 6% 25%	1564
	21st to end	Day	8% 17% 5% 9% 6% 5% 5% 4 5% 7% 28%	1458
December	1st to 10th	Day	9% 17% 6% 13% 6% 5% 5% 4 4 7% 23%	1330
	11th to 20th	Day	9% 21% 5% 13% 6% 5% 6% 4 6% 7% 18%	1685
	21st to end	Day	7% 15% 6% 12% 7% 7% 7% 4 7% 7% 21%	2442
January	1st to 10th	Night	8% 23% 7% 13% 8% 7% 6% 4 5% 6% 13%	4648
	11th to 20th	Night	9% 17% 6% 14% 7% 6% 5% 3 5% 7% 23%	4420
	21st to end	Night	11% 21% 6% 13% 8% 5% 4 4 5% 7% 17%	4862
February	1st to 10th	Night	10% 24% 8% 11% 5% 5% 3 4 4 6% 20%	2542
	11th to 20th	Night	7% 20% 6% 12% 7% 5% 4 4 6% 5% 24%	2355
	21st to end	Night	7% 18% 6% 12% 7% 6% 6% 4 4 6% 23%	1884
March	1st to 10th	Night	5% 13% 5% 11% 6% 6% 5% 5% 6% 8% 31%	3736
	11th to 20th	Night	7% 11% 3 9% 4 4 4 3 4 6% 44%	3495
	21st to end	Night	11% 20% 6% 11% 6% 6% 7% 5% 7% 6% 17%	3828
April	1st to 10th	Night	9% 15% 4 7% 7% 5% 6% 4 6% 8% 29%	1900
	11th to 20th	Night	11% 12% 4 10% 6% 5% 6% 4 6% 5% 32%	1691
	21st to end	Night	10% 12% 4 8% 5% 5% 4 4 6% 8% 34%	1710
May	1st to 10th	Night	14% 12% 4 9% 5% 5% 5% 4 5% 6% 31%	2860
	11th to 20th	Night	7% 6% 2 5% 4 5% 5% 5% 8% 10% 45%	2609
	21st to end	Night	14% 10% 4 9% 5% 5% 6% 5% 7% 8% 28%	2414
June	1st to 10th	Night	16% 9% 3 6% 6% 4 4 4 6% 8% 36%	1330
	11th to 20th	Night	16% 8% 3 5% 5% 4 4 4 5% 7% 38%	1330
	21st to end	Night	5% 4 1 4 4 4 4 3 6% 9% 57%	1330
July	1st to 10th	Night	3 2 1 2 2 1 3 3 5% 7% 71%	2220
	11th to 20th	Night	2 2 1 2 3 2 2 2 4 5% 75%	2430
	21st to end	Night	2 1 1 2 2 3 2 2 5% 6% 74%	2761
August	1st to 10th	Night	3 3 1 3 3 3 3 4 6% 10% 63%	2713
	11th to 20th	Night	2 3 1 4 3 4 5% 4 6% 7% 60%	2811
	21st to end	Night	4 3 1 2 2 2 3 3 5% 6% 68%	3146
September	1st to 10th	Night	6% 5% 2 4 3 2 3 3 5% 6% 61%	1923
	11th to 20th	Night	10% 5% 1 5% 4 4 5% 4 6% 7% 50%	2090
	21st to end	Night	10% 6% 2 6% 3 3 3 2 5% 7% 53%	2090
October	1st to 10th	Night	8% 7% 3 7% 4 3 3 3 4 5% 54%	3573
	11th to 20th	Night	8% 7% 2 6% 4 3 5% 4 5% 7% 49%	3894
	21st to end	Night	9% 11% 3 8% 5% 4 4 4 5% 8% 39%	4457
November	1st to 10th	Night	15% 15% 4 8% 5% 4 4 4 4 7% 29%	2469
	11th to 20th	Night	11% 18% 5% 10% 5% 5% 4 3 5% 6% 27%	2594
	21st to end	Night	8% 13% 4 10% 5% 5% 5% 4 7% 8% 31%	2721
December	1st to 10th	Night	9% 19% 6% 9% 6% 5% 5% 4 5% 7% 25%	2850
	11th to 20th	Night	8% 20% 7% 12% 6% 5% 5% 3 5% 9% 20%	3506
	21st to end	Night	7% 14% 6% 12% 6% 8% 7% 6% 7% 8% 18%	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	64% 7% 18% 10% 1	2326
	11th to 20th	Day	61% 5% 15% 16% 3 1	2540
	21st to end	Day	59% 6% 20% 12% 3 1	2794
February	1st to 10th	Day	65% 6% 15% 12% 2	1638
	11th to 20th	Day	59% 5% 17% 13% 5%	1720
	21st to end	Day	59% 5% 10% 18% 6% 1	1570
March	1st to 10th	Day	45% 8% 15% 21% 11%	3138
	11th to 20th	Day	41% 6% 21% 29% 3	3484
	21st to end	Day	61% 9% 16% 11% 3	3825
April	1st to 10th	Day	56% 6% 17% 17% 4	2277
	11th to 20th	Day	53% 5% 13% 21% 8% 1	2440
	21st to end	Day	55% 6% 13% 20% 6%	2470
May	1st to 10th	Day	54% 5% 13% 19% 8%	4110
	11th to 20th	Day	34% 7% 18% 28% 12% 1	4273
	21st to end	Day	48% 7% 19% 20% 5%	5162
June	1st to 10th	Day	48% 7% 17% 19% 7%	2850
	11th to 20th	Day	48% 5% 12% 21% 12% 3	2850
	21st to end	Day	29% 4 13% 32% 19% 3	2850
July	1st to 10th	Day	15% 4 7% 19% 34% 22%	4666
	11th to 20th	Day	11% 2 5% 13% 25% 43%	4448
	21st to end	Day	13% 3 4 20% 36% 24%	4639
August	1st to 10th	Day	20% 5% 8% 28% 28% 12%	4204
	11th to 20th	Day	19% 5% 12% 36% 24% 5%	4067
	21st to end	Day	19% 3 9% 34% 28% 6%	4520
September	1st to 10th	Day	24% 4 10% 31% 22% 9%	2252
	11th to 20th	Day	35% 5% 14% 28% 15% 3	2090
	21st to end	Day	33% 4 19% 28% 14% 2	2090
October	1st to 10th	Day	31% 4 12% 39% 14%	3404
	11th to 20th	Day	35% 4 21% 32% 9%	3032
	21st to end	Day	48% 4 12% 27% 8% 1	3101
November	1st to 10th	Day	58% 6% 16% 16% 4	1710
	11th to 20th	Day	55% 7% 19% 15% 3	1564
	21st to end	Day	47% 6% 24% 18% 4	1458
December	1st to 10th	Day	58% 7% 18% 13% 5%	1330
	11th to 20th	Day	61% 6% 21% 11% 2	1684
	21st to end	Day	55% 8% 16% 14% 7%	2442
January	1st to 10th	Night	65% 10% 14% 10% 1	4648
	11th to 20th	Night	59% 5% 15% 17% 3 1	4420
	21st to end	Night	64% 8% 14% 11% 3	4862
February	1st to 10th	Night	64% 5% 15% 13% 3	2542
	11th to 20th	Night	58% 5% 19% 15% 2	2356
	21st to end	Night	57% 5% 13% 18% 6% 1	1884
March	1st to 10th	Night	42% 7% 16% 23% 12%	3736
	11th to 20th	Night	38% 6% 23% 29% 4	3495
	21st to end	Night	61% 9% 16% 12% 3	3828
April	1st to 10th	Night	48% 7% 20% 21% 4	1900
	11th to 20th	Night	50% 6% 15% 22% 7% 1	1691
	21st to end	Night	45% 6% 17% 24% 8%	1710
May	1st to 10th	Night	50% 6% 14% 24% 6%	2860
	11th to 20th	Night	30% 7% 18% 31% 13%	2609
	21st to end	Night	47% 7% 22% 18% 5%	2414
June	1st to 10th	Night	45% 6% 18% 23% 8%	1330
	11th to 20th	Night	44% 5% 15% 21% 11% 3	1330
	21st to end	Night	23% 5% 15% 33% 21% 3	1330
July	1st to 10th	Night	12% 4 7% 26% 30% 20%	2185
	11th to 20th	Night	12% 2 6% 16% 19% 45%	2386
	21st to end	Night	12% 2 5% 22% 26% 32%	2674
August	1st to 10th	Night	18% 3 9% 31% 27% 12%	2705
	11th to 20th	Night	21% 4 13% 36% 21% 5%	2838
	21st to end	Night	17% 3 11% 36% 28% 5%	3146
September	1st to 10th	Night	24% 3 11% 27% 24% 11%	1923
	11th to 20th	Night	31% 5% 14% 28% 18% 4	2090
	21st to end	Night	31% 4 17% 29% 16% 2	2090
October	1st to 10th	Night	33% 3 13% 33% 17% 1	3573
	11th to 20th	Night	34% 5% 22% 30% 9%	3894
	21st to end	Night	41% 5% 18% 27% 8% 1	4457
November	1st to 10th	Night	53% 5% 18% 19% 4 1	2469
	11th to 20th	Night	54% 6% 20% 16% 4	2594
	21st to end	Night	46% 5% 23% 21% 5%	2721
December	1st to 10th	Night	55% 7% 16% 17% 5%	2850
	11th to 20th	Night	59% 8% 19% 13% 1	3507
	21st to end	Night	55% 10% 15% 13% 7%	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	16% 12% 23% 30% 18% 2	180
	11th to 20th	Day	19% 6% 22% 32% 15% 6%	180
	21st to end	Day	17% 13% 25% 31% 11% 3	198
February	1st to 10th	Day	24% 17% 29% 24% 6%	236
	11th to 20th	Day	15% 21% 24% 28% 12% 1	316
	21st to end	Day	22% 15% 25% 29% 9% 1	382
March	1st to 10th	Day	20% 18% 28% 27% 7% 1	460
	11th to 20th	Day	17% 15% 25% 24% 17% 2	460
	21st to end	Day	20% 18% 30% 24% 7% 1	506
April	1st to 10th	Day	21% 18% 30% 22% 9%	460
	11th to 20th	Day	22% 19% 32% 19% 7% 1	452
	21st to end	Day	24% 21% 25% 19% 9% 2	460
May	1st to 10th	Day	13% 18% 29% 29% 9% 2	463
	11th to 20th	Day	22% 13% 25% 24% 14% 2	511
	21st to end	Day	21% 13% 19% 26% 17% 4	734
June	1st to 10th	Day	17% 14% 22% 25% 18% 4	680
	11th to 20th	Day	23% 17% 25% 21% 12% 2	680
	21st to end	Day	10% 14% 23% 31% 21% 2	680
July	1st to 10th	Day	5% 10% 27% 30% 25% 3	671
	11th to 20th	Day	7% 14% 29% 32% 17% 2	548
	21st to end	Day	4 10% 31% 34% 19% 2	531
August	1st to 10th	Day	6% 12% 28% 31% 18% 5%	487
	11th to 20th	Day	7% 9% 25% 32% 21% 6%	477
	21st to end	Day	8% 11% 27% 32% 18% 4	539
September	1st to 10th	Day	8% 13% 24% 26% 23% 5%	490
	11th to 20th	Day	12% 13% 24% 27% 19% 5%	490
	21st to end	Day	16% 14% 20% 26% 20% 4	490
October	1st to 10th	Day	18% 8% 22% 33% 16% 3	443
	11th to 20th	Day	19% 10% 22% 28% 14% 7%	300
	21st to end	Day	20% 11% 26% 33% 7% 2	330
November	1st to 10th	Day	24% 13% 22% 33% 8%	282
	11th to 20th	Day	21% 8% 25% 33% 12% 1	270
	21st to end	Day	14% 9% 20% 43% 13% 1	240
December	1st to 10th	Day	23% 8% 25% 26% 13% 4	180
	11th to 20th	Day	19% 10% 28% 32% 9% 1	180
	21st to end	Day	15% 10% 28% 33% 11% 3	198
January	1st to 10th	Night	19% 8% 23% 36% 12% 1	898
	11th to 20th	Night	17% 9% 25% 35% 12% 2	760
	21st to end	Night	16% 7% 24% 41% 12% 1	836
February	1st to 10th	Night	21% 9% 29% 31% 8% 1	760
	11th to 20th	Night	17% 9% 28% 35% 9% 1	744
	21st to end	Night	14% 11% 28% 34% 13% 1	628
March	1st to 10th	Night	13% 7% 28% 40% 11% 1	760
	11th to 20th	Night	13% 9% 25% 38% 15%	760
	21st to end	Night	17% 8% 24% 39% 12% 1	836
April	1st to 10th	Night	15% 9% 23% 38% 13% 1	760
	11th to 20th	Night	15% 11% 25% 38% 12%	563
	21st to end	Night	15% 9% 22% 38% 16% 1	570
May	1st to 10th	Night	15% 9% 23% 34% 19%	570
	11th to 20th	Night	11% 6% 18% 38% 25% 2	468
	21st to end	Night	18% 6% 17% 27% 31% 1	411
June	1st to 10th	Night	17% 6% 15% 36% 22% 4	380
	11th to 20th	Night	19% 9% 18% 37% 17% 1	380
	21st to end	Night	7% 3 16% 41% 32% 1	380
July	1st to 10th	Night	5% 1 9% 51% 34% 1	370
	11th to 20th	Night	4 2 11% 57% 26%	368
	21st to end	Night	3 1 9% 54% 31% 1	416
August	1st to 10th	Night	4 2 12% 49% 32% 1	484
	11th to 20th	Night	4 3 11% 47% 33% 2	564
	21st to end	Night	7% 4 13% 47% 27% 1	627
September	1st to 10th	Night	9% 1 15% 44% 28% 3	736
	11th to 20th	Night	12% 2 12% 38% 34% 2	760
	21st to end	Night	14% 6% 15% 39% 23% 3	760
October	1st to 10th	Night	13% 6% 17% 42% 20% 1	760
	11th to 20th	Night	17% 4 15% 43% 19% 3	760
	21st to end	Night	19% 7% 21% 37% 14% 1	836
November	1st to 10th	Night	22% 6% 22% 40% 10%	760
	11th to 20th	Night	22% 9% 23% 36% 9% 1	884
	21st to end	Night	13% 7% 24% 43% 12%	950
December	1st to 10th	Night	17% 8% 24% 37% 12% 2	950
	11th to 20th	Night	16% 7% 28% 39% 9%	950
	21st to end	Night	18% 10% 28% 35% 9% 1	1045

Page generated at 2024-11-03 00:11:09. Version ac07

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