Deerlodge Park Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Deerlodge Park Campground clear sky chart from 2005-11-06 to 2025-03-27.

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	3 6% 2 6% 4 4 5% 5% 7% 9% 50%	113170
	Night	4 7% 2 6% 5% 5% 5% 5% 7% 8% 46%	115060
Transparency	Day	28% 7% 12% 23% 19% 11%	112926
	Night	33% 7% 13% 23% 17% 8%	114894
Seeing	Day	6% 10% 24% 33% 21% 6%	15947
	Night	6% 5% 19% 46% 22% 2	26234

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	2 8% 4 9% 6% 7% 9% 8% 8% 10% 30%	3799
	11th to 20th	Day	1 7% 3 9% 7% 7% 7% 7% 8% 10% 35%	4100
	21st to end	Day	2 9% 4 11% 7% 8% 6% 5% 8% 8% 30%	4510
February	1st to 10th	Day	3 9% 4 8% 6% 6% 6% 4 7% 10% 38%	1800
	11th to 20th	Day	4 11% 3 7% 4 5% 6% 6% 8% 11% 36%	1755
	21st to end	Day	2 7% 4 7% 5% 4 6% 4 7% 9% 44%	1618
March	1st to 10th	Day	2 10% 3 8% 5% 5% 6% 5% 7% 9% 40%	3554
	11th to 20th	Day	2 9% 3 5% 4 4 7% 5% 9% 11% 40%	3600
	21st to end	Day	4 10% 3 7% 6% 6% 6% 6% 10% 12% 29%	3892
April	1st to 10th	Day	5% 8% 2 6% 5% 4 5% 4 6% 9% 44%	2264
	11th to 20th	Day	4 9% 3 7% 5% 5% 6% 4 6% 9% 42%	2251
	21st to end	Day	5% 7% 2 6% 4 4 5% 5% 6% 11% 43%	2370
May	1st to 10th	Day	6% 10% 3 8% 6% 6% 7% 5% 7% 8% 34%	4110
	11th to 20th	Day	3 3 1 4 3 4 5% 5% 9% 11% 50%	4219
	21st to end	Day	6% 4 2 4 4 4 5% 4 6% 8% 54%	4825
June	1st to 10th	Day	3 3 1 3 3 4 3 4 6% 11% 58%	2660
	11th to 20th	Day	3 3 1 3 3 3 4 3 6% 8% 63%	2660
	21st to end	Day	2 2 1 3 3 3 4 3 6% 8% 67%	2660
July	1st to 10th	Day	2 1 2 2 2 3 2 5% 6% 74%	4430
	11th to 20th	Day	3 2 1 3 3 5% 6% 6% 9% 11% 50%	4244
	21st to end	Day	2 2 1 4 3 4 4 4 6% 8% 60%	4454
August	1st to 10th	Day	3 2 1 4 4 4 5% 5% 8% 9% 55%	4092
	11th to 20th	Day	2 2 1 4 3 3 4 4 7% 10% 60%	4028
	21st to end	Day	2 2 1 4 3 3 4 3 6% 7% 64%	4213
September	1st to 10th	Day	4 2 1 2 2 2 3 3 5% 8% 67%	2280
	11th to 20th	Day	2 2 1 4 3 3 4 3 6% 7% 65%	2214
	21st to end	Day	4 3 1 4 2 2 2 2 3 6% 70%	2036
October	1st to 10th	Day	4 3 1 2 2 2 2 2 4 5% 73%	3170
	11th to 20th	Day	4 3 1 4 3 3 4 3 6% 10% 58%	3150
	21st to end	Day	5% 6% 2 4 3 4 4 3 5% 6% 58%	3438
November	1st to 10th	Day	4 5% 2 7% 3 3 4 3 6% 8% 53%	1899
	11th to 20th	Day	4 6% 2 5% 3 4 3 3 7% 9% 54%	1625
	21st to end	Day	3 6% 3 7% 5% 5% 4 5% 6% 7% 49%	1600
December	1st to 10th	Day	3 5% 2 6% 4 5% 6% 5% 6% 8% 50%	2620
	11th to 20th	Day	2 6% 3 6% 5% 5% 7% 6% 9% 10% 40%	3026
	21st to end	Day	4 12% 4 11% 6% 7% 7% 7% 9% 11% 22%	4004
January	1st to 10th	Night	2 8% 4 10% 8% 7% 8% 7% 8% 10% 28%	6208
	11th to 20th	Night	2 9% 3 10% 6% 6% 8% 7% 10% 10% 30%	5880
	21st to end	Night	3 11% 4 12% 8% 8% 7% 5% 7% 7% 29%	6468
February	1st to 10th	Night	3 8% 3 7% 5% 5% 5% 5% 7% 10% 41%	2600
	11th to 20th	Night	3 11% 3 9% 6% 4 5% 5% 6% 8% 39%	2532
	21st to end	Night	2 8% 3 9% 5% 4 4 4 7% 8% 44%	2008
March	1st to 10th	Night	3 10% 3 7% 4 4 5% 4 8% 10% 41%	3540
	11th to 20th	Night	4 8% 3 6% 5% 6% 6% 5% 8% 10% 40%	3600
	21st to end	Night	7% 13% 4 9% 6% 6% 6% 4 8% 9% 28%	3899
April	1st to 10th	Night	6% 9% 3 5% 5% 4 5% 4 6% 10% 42%	1915
	11th to 20th	Night	8% 8% 3 7% 4 5% 5% 5% 7% 8% 40%	1877
	21st to end	Night	6% 7% 3 6% 5% 6% 5% 5% 7% 9% 41%	1806
May	1st to 10th	Night	9% 8% 2 6% 5% 4 5% 4 8% 8% 40%	2860
	11th to 20th	Night	5% 5% 2 6% 5% 5% 5% 5% 7% 9% 46%	2685
	21st to end	Night	8% 5% 2 4 4 4 3 3 6% 7% 52%	2762
June	1st to 10th	Night	3 4 2 5% 4 4 5% 4 5% 8% 57%	1520
	11th to 20th	Night	4 4 1 4 4 4 4 3 5% 6% 59%	1520
	21st to end	Night	3 2 1 3 4 4 5% 3 5% 7% 63%	1520
July	1st to 10th	Night	3 2 1 3 3 3 3 4 5% 7% 67%	2540
	11th to 20th	Night	2 3 1 5% 5% 5% 5% 5% 9% 12% 47%	2722
	21st to end	Night	2 2 1 4 4 4 4 4 6% 9% 60%	3109
August	1st to 10th	Night	2 3 1 3 3 4 5% 4 8% 9% 57%	2847
	11th to 20th	Night	2 4 2 5% 4 5% 5% 5% 7% 8% 55%	2811
	21st to end	Night	2 2 1 4 4 4 5% 4 6% 8% 60%	3452
September	1st to 10th	Night	4 3 1 3 3 3 3 3 5% 6% 67%	1900
	11th to 20th	Night	5% 4 1 4 4 4 3 2 5% 6% 62%	1962
	21st to end	Night	4 3 1 4 3 2 3 2 3 6% 70%	2143
October	1st to 10th	Night	4 3 1 3 2 2 3 2 4 4 74%	3800
	11th to 20th	Night	5% 4 1 3 3 3 3 3 6% 9% 60%	3778
	21st to end	Night	5% 7% 2 4 3 3 4 3 5% 8% 58%	4120
November	1st to 10th	Night	5% 6% 2 5% 4 3 4 4 6% 8% 52%	2379
	11th to 20th	Night	3 5% 2 4 4 4 4 4 6% 8% 55%	2772
	21st to end	Night	3 7% 3 6% 5% 4 5% 3 6% 9% 49%	2800
December	1st to 10th	Night	3 9% 2 4 4 4 5% 5% 6% 7% 51%	4570
	11th to 20th	Night	3 6% 3 6% 5% 5% 7% 7% 8% 10% 40%	5181
	21st to end	Night	4 10% 4 10% 7% 7% 7% 6% 9% 9% 26%	6974

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	42% 11% 20% 16% 11%	3800
	11th to 20th	Day	36% 10% 18% 22% 12% 2	4100
	21st to end	Day	45% 7% 17% 17% 13% 1	4510
February	1st to 10th	Day	40% 10% 18% 21% 10% 2	1800
	11th to 20th	Day	41% 7% 17% 24% 9% 1	1764
	21st to end	Day	34% 8% 14% 28% 14% 2	1618
March	1st to 10th	Day	35% 11% 11% 29% 12% 2	3554
	11th to 20th	Day	32% 9% 21% 27% 11% 1	3600
	21st to end	Day	40% 12% 14% 24% 8% 2	3892
April	1st to 10th	Day	33% 7% 13% 24% 17% 5%	2264
	11th to 20th	Day	35% 7% 11% 24% 19% 4	2254
	21st to end	Day	32% 7% 12% 27% 20% 2	2370
May	1st to 10th	Day	38% 9% 10% 20% 19% 4	4110
	11th to 20th	Day	20% 8% 11% 34% 22% 5%	4223
	21st to end	Day	24% 6% 8% 29% 29% 5%	4825
June	1st to 10th	Day	19% 5% 10% 25% 26% 14%	2660
	11th to 20th	Day	18% 4 7% 15% 30% 26%	2660
	21st to end	Day	15% 3 6% 14% 30% 32%	2660
July	1st to 10th	Day	11% 3 5% 10% 23% 48%	4361
	11th to 20th	Day	20% 5% 9% 16% 25% 25%	4170
	21st to end	Day	18% 6% 8% 15% 20% 33%	4314
August	1st to 10th	Day	21% 6% 10% 24% 19% 19%	4078
	11th to 20th	Day	19% 6% 9% 22% 27% 17%	4067
	21st to end	Day	19% 5% 8% 19% 25% 25%	4212
September	1st to 10th	Day	15% 4 8% 18% 27% 28%	2280
	11th to 20th	Day	17% 5% 9% 21% 28% 19%	2214
	21st to end	Day	17% 2 5% 23% 39% 14%	2036
October	1st to 10th	Day	16% 2 8% 19% 32% 24%	3170
	11th to 20th	Day	22% 3 10% 33% 28% 4	3150
	21st to end	Day	26% 4 10% 38% 19% 3	3438
November	1st to 10th	Day	28% 6% 12% 31% 22% 2	1899
	11th to 20th	Day	27% 5% 18% 33% 16% 1	1625
	21st to end	Day	31% 8% 16% 30% 15% 1	1600
December	1st to 10th	Day	29% 7% 17% 39% 8%	2620
	11th to 20th	Day	33% 10% 25% 25% 6%	3024
	21st to end	Day	49% 10% 16% 17% 8%	4004
January	1st to 10th	Night	46% 9% 17% 18% 8% 1	6208
	11th to 20th	Night	42% 9% 17% 21% 11% 1	5880
	21st to end	Night	52% 7% 13% 15% 12% 1	6468
February	1st to 10th	Night	37% 11% 19% 23% 10% 2	2600
	11th to 20th	Night	40% 7% 15% 24% 13% 1	2533
	21st to end	Night	36% 7% 15% 26% 14% 2	2008
March	1st to 10th	Night	35% 8% 10% 31% 15% 1	3540
	11th to 20th	Night	34% 7% 20% 26% 11% 2	3600
	21st to end	Night	47% 10% 14% 22% 6% 1	3899
April	1st to 10th	Night	35% 7% 12% 23% 17% 6%	1915
	11th to 20th	Night	38% 6% 12% 21% 20% 4	1877
	21st to end	Night	37% 7% 10% 24% 20% 3	1806
May	1st to 10th	Night	36% 8% 10% 17% 25% 4	2860
	11th to 20th	Night	28% 9% 13% 27% 17% 7%	2686
	21st to end	Night	28% 6% 7% 26% 28% 4	2762
June	1st to 10th	Night	23% 6% 11% 22% 23% 15%	1520
	11th to 20th	Night	25% 5% 6% 13% 25% 26%	1520
	21st to end	Night	18% 4 6% 12% 25% 34%	1520
July	1st to 10th	Night	16% 4 5% 10% 20% 44%	2500
	11th to 20th	Night	24% 5% 10% 19% 22% 21%	2673
	21st to end	Night	20% 4 10% 16% 25% 26%	3011
August	1st to 10th	Night	19% 5% 11% 26% 16% 21%	2838
	11th to 20th	Night	25% 6% 13% 17% 21% 17%	2838
	21st to end	Night	22% 5% 9% 17% 24% 24%	3452
September	1st to 10th	Night	18% 4 7% 18% 25% 28%	1900
	11th to 20th	Night	23% 5% 9% 19% 24% 20%	1962
	21st to end	Night	18% 3 5% 18% 38% 18%	2143
October	1st to 10th	Night	16% 3 5% 15% 38% 23%	3800
	11th to 20th	Night	21% 4 10% 27% 31% 6%	3778
	21st to end	Night	25% 4 10% 35% 22% 3	4120
November	1st to 10th	Night	29% 5% 12% 27% 24% 3	2379
	11th to 20th	Night	26% 6% 15% 34% 18% 2	2772
	21st to end	Night	32% 5% 14% 31% 17% 2	2800
December	1st to 10th	Night	29% 8% 16% 36% 11%	4570
	11th to 20th	Night	36% 9% 21% 29% 5%	5182
	21st to end	Night	50% 9% 12% 19% 9%	6974

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	7% 10% 24% 37% 19% 3	300
	11th to 20th	Day	4 8% 22% 47% 15% 3	300
	21st to end	Day	6% 7% 20% 45% 18% 4	330
February	1st to 10th	Day	4 13% 30% 44% 7% 2	300
	11th to 20th	Day	7% 11% 31% 39% 11% 1	300
	21st to end	Day	5% 12% 27% 42% 13% 1	264
March	1st to 10th	Day	7% 13% 29% 34% 16% 2	500
	11th to 20th	Day	8% 11% 31% 34% 14% 3	500
	21st to end	Day	10% 15% 33% 31% 11% 1	531
April	1st to 10th	Day	7% 13% 27% 33% 17% 3	460
	11th to 20th	Day	10% 18% 32% 27% 12% 1	452
	21st to end	Day	8% 17% 28% 27% 17% 3	460
May	1st to 10th	Day	10% 13% 33% 29% 12% 3	463
	11th to 20th	Day	8% 9% 25% 29% 22% 6%	571
	21st to end	Day	7% 11% 22% 33% 22% 5%	734
June	1st to 10th	Day	4 8% 19% 32% 29% 7%	680
	11th to 20th	Day	5% 11% 26% 32% 21% 4	680
	21st to end	Day	3 9% 23% 35% 25% 4	680
July	1st to 10th	Day	2 3 17% 34% 35% 8%	671
	11th to 20th	Day	2 3 18% 34% 31% 11%	561
	21st to end	Day	2 4 18% 32% 32% 12%	531
August	1st to 10th	Day	2 4 22% 38% 24% 10%	487
	11th to 20th	Day	3 5% 23% 32% 27% 11%	477
	21st to end	Day	2 6% 20% 31% 28% 13%	539
September	1st to 10th	Day	5% 6% 20% 25% 27% 17%	490
	11th to 20th	Day	3 10% 29% 30% 19% 9%	490
	21st to end	Day	7% 12% 17% 25% 30% 9%	436
October	1st to 10th	Day	10% 8% 15% 26% 25% 16%	300
	11th to 20th	Day	5% 13% 22% 29% 23% 8%	300
	21st to end	Day	10% 10% 27% 33% 18% 2	330
November	1st to 10th	Day	11% 14% 22% 30% 17% 5%	300
	11th to 20th	Day	6% 12% 26% 36% 15% 5%	300
	21st to end	Day	6% 9% 25% 38% 20% 3	300
December	1st to 10th	Day	8% 8% 20% 39% 18% 7%	300
	11th to 20th	Day	4 4 24% 50% 16% 2	300
	21st to end	Day	8% 10% 26% 38% 15% 3	330
January	1st to 10th	Night	8% 4 21% 48% 17% 2	946
	11th to 20th	Night	6% 3 22% 51% 15% 3	800
	21st to end	Night	9% 4 21% 50% 13% 2	880
February	1st to 10th	Night	6% 5% 26% 51% 10% 2	800
	11th to 20th	Night	8% 5% 26% 51% 10%	784
	21st to end	Night	5% 8% 27% 52% 8% 1	660
March	1st to 10th	Night	8% 6% 22% 47% 16% 1	800
	11th to 20th	Night	6% 5% 18% 54% 16% 1	800
	21st to end	Night	9% 5% 25% 46% 14%	862
April	1st to 10th	Night	8% 10% 26% 43% 12%	585
	11th to 20th	Night	10% 11% 23% 42% 13% 1	563
	21st to end	Night	8% 10% 26% 35% 19% 2	570
May	1st to 10th	Night	12% 7% 23% 38% 19% 2	570
	11th to 20th	Night	5% 5% 16% 44% 27% 3	561
	21st to end	Night	9% 7% 20% 38% 23% 3	617
June	1st to 10th	Night	4 7% 16% 40% 31% 2	570
	11th to 20th	Night	5% 5% 24% 44% 20% 1	570
	21st to end	Night	2 3 15% 47% 32% 1	570
July	1st to 10th	Night	5% 1 12% 39% 42% 2	555
	11th to 20th	Night	2 4 8% 43% 40% 3	552
	21st to end	Night	2 1 7% 38% 48% 4	624
August	1st to 10th	Night	3 1 7% 48% 40% 2	567
	11th to 20th	Night	3 2 8% 47% 37% 2	564
	21st to end	Night	4 1 9% 40% 42% 4	627
September	1st to 10th	Night	4 2 9% 44% 35% 5%	570
	11th to 20th	Night	5% 2 13% 43% 32% 4	632
	21st to end	Night	5% 3 16% 38% 32% 6%	760
October	1st to 10th	Night	7% 4 15% 44% 28% 3	760
	11th to 20th	Night	5% 5% 19% 46% 24% 2	760
	21st to end	Night	8% 6% 19% 43% 23% 2	836
November	1st to 10th	Night	8% 4 20% 45% 22% 1	819
	11th to 20th	Night	5% 6% 26% 47% 15% 1	1000
	21st to end	Night	5% 7% 21% 49% 17% 1	1000
December	1st to 10th	Night	8% 4 20% 52% 15% 1	1000
	11th to 20th	Night	10% 4 23% 50% 13% 1	1000
	21st to end	Night	9% 10% 23% 46% 11% 2	1100

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