Pine River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pine River Observatory clear sky chart from 2005-11-06 to 2026-03-03.

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	13% 11% 4 10% 6% 5% 5% 4 5% 7% 30%	132132
	Night	12% 11% 4 10% 6% 5% 5% 4 6% 7% 30%	129014
Transparency	Day	52% 5% 12% 19% 10% 1	135722
	Night	52% 5% 13% 19% 10% 1	133513
Seeing	Day	20% 20% 30% 19% 8% 3	16509
	Night	19% 18% 31% 22% 8% 1	25502

By Month

Percentage Cloud Cover NE (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	13% 12% 6% 18% 10% 6% 6% 5% 5% 5% 15%	4661
	11th to 20th	Day	7% 18% 8% 20% 11% 8% 6% 4 4 4 9%	5143
	21st to end	Day	11% 16% 6% 15% 9% 8% 8% 5% 6% 5% 12%	5780
February	1st to 10th	Day	11% 17% 4 14% 10% 6% 7% 4 5% 5% 17%	1890
	11th to 20th	Day	11% 13% 7% 15% 9% 6% 6% 4 5% 6% 18%	1843
	21st to end	Day	14% 16% 5% 12% 8% 4 6% 3 5% 5% 23%	1625
March	1st to 10th	Day	16% 11% 5% 11% 7% 5% 5% 3 4 6% 28%	4940
	11th to 20th	Day	9% 13% 5% 12% 6% 5% 5% 4 5% 7% 29%	4980
	21st to end	Day	14% 16% 5% 10% 5% 4 4 3 4 5% 31%	5465
April	1st to 10th	Day	15% 14% 4 9% 6% 5% 4 3 5% 6% 29%	2340
	11th to 20th	Day	17% 11% 3 6% 4 4 3 4 5% 6% 36%	2497
	21st to end	Day	18% 10% 4 7% 5% 4 4 3 5% 6% 34%	2600
May	1st to 10th	Day	16% 9% 3 7% 4 4 4 3 5% 8% 37%	5888
	11th to 20th	Day	15% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	6243
	21st to end	Day	17% 7% 2 7% 4 4 5% 4 5% 7% 39%	6949
June	1st to 10th	Day	15% 7% 2 6% 4 4 5% 4 7% 9% 36%	2800
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 7% 9% 41%	2954
	21st to end	Day	13% 6% 2 6% 5% 5% 5% 4 7% 8% 39%	3000
July	1st to 10th	Day	10% 6% 3 8% 6% 5% 5% 5% 7% 9% 38%	6819
	11th to 20th	Day	8% 5% 2 6% 5% 5% 5% 5% 6% 8% 45%	6392
	21st to end	Day	7% 4 2 6% 4 5% 5% 4 6% 9% 48%	6434
August	1st to 10th	Day	12% 7% 2 7% 4 4 5% 5% 7% 8% 38%	4234
	11th to 20th	Day	10% 8% 3 7% 5% 6% 6% 5% 8% 10% 34%	4174
	21st to end	Day	10% 5% 2 6% 4 5% 6% 4 7% 9% 42%	4549
September	1st to 10th	Day	14% 6% 3 7% 5% 5% 5% 4 5% 8% 39%	2400
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 3 6% 8% 45%	2246
	21st to end	Day	14% 7% 3 9% 6% 5% 5% 5% 6% 7% 34%	2181
October	1st to 10th	Day	17% 9% 3 7% 4 5% 5% 4 5% 7% 35%	2000
	11th to 20th	Day	15% 11% 4 9% 7% 6% 4 5% 6% 7% 26%	2000
	21st to end	Day	22% 17% 4 9% 5% 4 5% 4 5% 6% 20%	2200
November	1st to 10th	Day	11% 15% 5% 9% 7% 5% 4 4 5% 7% 28%	1751
	11th to 20th	Day	11% 15% 6% 11% 7% 6% 6% 5% 6% 6% 21%	1680
	21st to end	Day	14% 17% 7% 13% 8% 7% 6% 3 5% 7% 14%	1680
December	1st to 10th	Day	16% 20% 7% 16% 7% 6% 5% 4 6% 5% 8%	2680
	11th to 20th	Day	16% 20% 7% 13% 6% 5% 4 3 4 4 18%	3066
	21st to end	Day	22% 18% 7% 17% 7% 6% 4 3 4 3 10%	4048
January	1st to 10th	Night	12% 12% 5% 16% 11% 7% 5% 4 5% 6% 17%	8234
	11th to 20th	Night	8% 14% 7% 19% 12% 8% 6% 4 5% 5% 11%	7727
	21st to end	Night	9% 12% 6% 12% 10% 8% 8% 5% 6% 7% 17%	8401
February	1st to 10th	Night	11% 15% 4 12% 7% 6% 5% 5% 6% 6% 22%	2730
	11th to 20th	Night	9% 13% 6% 12% 7% 7% 5% 4 6% 7% 23%	2663
	21st to end	Night	11% 13% 4 11% 9% 6% 6% 5% 5% 7% 24%	2176
March	1st to 10th	Night	13% 10% 4 10% 7% 6% 5% 4 6% 7% 27%	4943
	11th to 20th	Night	8% 10% 4 9% 5% 5% 6% 5% 7% 8% 34%	4979
	21st to end	Night	16% 9% 4 9% 5% 5% 4 4 6% 6% 32%	5467
April	1st to 10th	Night	16% 13% 3 9% 5% 5% 5% 4 6% 7% 30%	2060
	11th to 20th	Night	15% 9% 2 8% 4 4 5% 3 4 7% 37%	1867
	21st to end	Night	13% 11% 3 9% 5% 5% 5% 4 5% 6% 35%	1800
May	1st to 10th	Night	17% 8% 2 6% 4 4 5% 4 5% 7% 38%	4053
	11th to 20th	Night	13% 6% 3 6% 4 4 4 4 6% 8% 43%	3649
	21st to end	Night	16% 6% 2 6% 4 3 3 4 5% 7% 45%	3926
June	1st to 10th	Night	12% 6% 2 7% 5% 4 4 4 6% 8% 43%	1600
	11th to 20th	Night	8% 5% 1 5% 5% 5% 4 4 8% 10% 45%	1440
	21st to end	Night	11% 6% 2 6% 4 4 4 3 6% 9% 45%	1400
July	1st to 10th	Night	6% 6% 3 6% 4 4 5% 4 6% 7% 49%	3160
	11th to 20th	Night	10% 4 1 4 4 4 4 4 5% 8% 52%	3553
	21st to end	Night	7% 5% 2 5% 4 4 4 4 6% 8% 52%	4415
August	1st to 10th	Night	8% 6% 2 6% 4 4 5% 4 5% 8% 49%	2915
	11th to 20th	Night	12% 5% 2 5% 4 4 4 3 5% 8% 50%	2875
	21st to end	Night	10% 5% 2 5% 4 4 4 4 5% 8% 49%	3314
September	1st to 10th	Night	9% 5% 2 6% 4 4 5% 4 6% 8% 48%	2000
	11th to 20th	Night	9% 4 2 5% 3 3 4 2 5% 7% 56%	2150
	21st to end	Night	16% 7% 3 7% 5% 4 4 3 4 6% 41%	2218
October	1st to 10th	Night	16% 7% 3 6% 4 5% 4 3 6% 7% 40%	2400
	11th to 20th	Night	17% 10% 3 7% 5% 4 5% 4 6% 6% 34%	2400
	21st to end	Night	19% 14% 3 8% 6% 4 5% 4 6% 5% 26%	2640
November	1st to 10th	Night	13% 10% 4 8% 5% 6% 5% 4 6% 6% 33%	2761
	11th to 20th	Night	13% 14% 5% 9% 5% 5% 5% 5% 5% 8% 26%	2940
	21st to end	Night	15% 15% 6% 10% 6% 5% 6% 4 6% 7% 19%	2940
December	1st to 10th	Night	14% 15% 7% 15% 7% 6% 7% 4 7% 5% 12%	4720
	11th to 20th	Night	11% 17% 7% 13% 7% 6% 5% 5% 6% 6% 18%	5348
	21st to end	Night	19% 21% 7% 16% 6% 5% 4 3 4 4 9%	7150

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	68% 5% 12% 11% 4	4662
	11th to 20th	Day	77% 6% 8% 6% 4	5177
	21st to end	Day	70% 6% 12% 8% 4	5780
February	1st to 10th	Day	70% 5% 7% 14% 4	1890
	11th to 20th	Day	66% 6% 9% 13% 5% 1	1852
	21st to end	Day	64% 4 9% 15% 7% 1	1625
March	1st to 10th	Day	58% 3 14% 13% 11%	4943
	11th to 20th	Day	54% 4 14% 20% 7% 2	4980
	21st to end	Day	55% 4 10% 19% 11% 2	5465
April	1st to 10th	Day	57% 4 10% 18% 10% 1	2340
	11th to 20th	Day	49% 4 9% 23% 14% 1	2497
	21st to end	Day	52% 5% 10% 19% 12% 2	2600
May	1st to 10th	Day	46% 5% 12% 19% 12% 5%	5897
	11th to 20th	Day	48% 6% 12% 16% 17% 2	6247
	21st to end	Day	45% 4 12% 20% 16% 3	6949
June	1st to 10th	Day	43% 6% 12% 22% 16% 1	2800
	11th to 20th	Day	39% 6% 13% 24% 16% 1	2954
	21st to end	Day	41% 6% 13% 25% 14% 1	3000
July	1st to 10th	Day	40% 7% 15% 22% 15% 1	6746
	11th to 20th	Day	34% 6% 12% 31% 16% 1	6316
	21st to end	Day	32% 7% 14% 31% 17% 1	6249
August	1st to 10th	Day	42% 6% 15% 25% 12% 1	4221
	11th to 20th	Day	43% 7% 16% 25% 9%	4213
	21st to end	Day	37% 7% 13% 33% 10% 1	4549
September	1st to 10th	Day	44% 6% 12% 27% 10% 2	2400
	11th to 20th	Day	38% 4 14% 30% 14%	2246
	21st to end	Day	48% 6% 12% 25% 8% 1	2181
October	1st to 10th	Day	44% 6% 12% 25% 12% 1	3260
	11th to 20th	Day	47% 6% 13% 20% 13%	3240
	21st to end	Day	61% 5% 13% 16% 6%	3538
November	1st to 10th	Day	56% 6% 12% 18% 7%	1751
	11th to 20th	Day	61% 6% 13% 13% 6% 1	1680
	21st to end	Day	69% 6% 12% 10% 2	1680
December	1st to 10th	Day	76% 6% 10% 6% 2	2680
	11th to 20th	Day	70% 7% 10% 8% 6%	3066
	21st to end	Day	79% 4 6% 7% 3	4048
January	1st to 10th	Night	65% 6% 14% 11% 3	8234
	11th to 20th	Night	72% 7% 9% 8% 3 1	7768
	21st to end	Night	60% 6% 13% 11% 9%	8401
February	1st to 10th	Night	61% 5% 12% 17% 5% 1	2730
	11th to 20th	Night	60% 6% 12% 16% 5%	2665
	21st to end	Night	59% 5% 13% 15% 8% 1	2176
March	1st to 10th	Night	54% 6% 13% 17% 9% 2	4953
	11th to 20th	Night	46% 5% 19% 20% 9% 1	4980
	21st to end	Night	51% 4 13% 19% 12% 2	5467
April	1st to 10th	Night	55% 4 9% 19% 13% 1	2060
	11th to 20th	Night	48% 4 9% 21% 16% 2	1867
	21st to end	Night	51% 4 11% 16% 16% 2	1800
May	1st to 10th	Night	46% 4 13% 15% 14% 8%	4060
	11th to 20th	Night	39% 6% 14% 24% 16% 2	3650
	21st to end	Night	40% 4 14% 25% 16% 2	3927
June	1st to 10th	Night	39% 5% 13% 23% 18% 2	1600
	11th to 20th	Night	34% 5% 16% 26% 19%	1440
	21st to end	Night	37% 5% 15% 27% 15% 1	1400
July	1st to 10th	Night	33% 5% 15% 27% 18% 2	3125
	11th to 20th	Night	30% 5% 12% 32% 19% 1	3507
	21st to end	Night	30% 6% 11% 34% 17% 2	4285
August	1st to 10th	Night	34% 4 15% 29% 16% 2	2904
	11th to 20th	Night	34% 5% 17% 29% 14% 1	2902
	21st to end	Night	33% 5% 15% 32% 13% 1	3314
September	1st to 10th	Night	32% 7% 17% 30% 13% 1	2000
	11th to 20th	Night	29% 4 14% 34% 19% 1	2150
	21st to end	Night	45% 4 14% 26% 11% 1	2218
October	1st to 10th	Night	36% 5% 11% 27% 20% 1	3920
	11th to 20th	Night	45% 5% 14% 22% 14% 1	3899
	21st to end	Night	48% 6% 16% 22% 8%	4252
November	1st to 10th	Night	51% 6% 13% 20% 9% 1	2761
	11th to 20th	Night	57% 6% 15% 14% 7% 1	2940
	21st to end	Night	63% 9% 14% 11% 2 1	2940
December	1st to 10th	Night	71% 7% 12% 8% 2	4720
	11th to 20th	Night	66% 6% 11% 10% 7%	5348
	21st to end	Night	78% 4 8% 7% 2	7150

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	21% 30% 31% 14% 3	220
	11th to 20th	Day	21% 35% 30% 10% 3 1	311
	21st to end	Day	25% 31% 31% 12% 1	363
February	1st to 10th	Day	28% 34% 28% 6% 4	330
	11th to 20th	Day	26% 32% 36% 5% 1	330
	21st to end	Day	34% 31% 30% 4	273
March	1st to 10th	Day	25% 27% 32% 13% 3	494
	11th to 20th	Day	24% 27% 33% 12% 4 1	500
	21st to end	Day	33% 22% 27% 14% 4	550
April	1st to 10th	Day	29% 23% 32% 11% 4	500
	11th to 20th	Day	33% 21% 24% 13% 7% 3	492
	21st to end	Day	30% 20% 30% 13% 6% 2	500
May	1st to 10th	Day	22% 19% 33% 17% 7% 2	503
	11th to 20th	Day	19% 17% 30% 22% 9% 3	527
	21st to end	Day	17% 16% 32% 22% 10% 3	573
June	1st to 10th	Day	18% 18% 30% 25% 8% 2	530
	11th to 20th	Day	13% 16% 33% 27% 9% 2	684
	21st to end	Day	17% 15% 36% 21% 8% 3	730
July	1st to 10th	Day	11% 11% 33% 28% 15% 3	721
	11th to 20th	Day	11% 13% 32% 25% 12% 6%	542
	21st to end	Day	8% 10% 37% 28% 11% 6%	576
August	1st to 10th	Day	8% 12% 28% 30% 16% 7%	526
	11th to 20th	Day	10% 9% 28% 26% 18% 8%	519
	21st to end	Day	15% 10% 28% 28% 14% 5%	583
September	1st to 10th	Day	15% 14% 26% 24% 14% 6%	530
	11th to 20th	Day	9% 11% 24% 25% 20% 12%	530
	21st to end	Day	16% 16% 25% 24% 15% 4	530
October	1st to 10th	Day	21% 17% 27% 19% 13% 4	530
	11th to 20th	Day	19% 27% 32% 16% 5% 1	530
	21st to end	Day	27% 28% 27% 15% 3	583
November	1st to 10th	Day	31% 25% 27% 14% 3 1	277
	11th to 20th	Day	26% 28% 32% 10% 3 1	220
	21st to end	Day	28% 25% 36% 11%	220
December	1st to 10th	Day	29% 27% 31% 13%	220
	11th to 20th	Day	35% 23% 29% 11% 3	220
	21st to end	Day	30% 30% 29% 8% 2	242
January	1st to 10th	Night	22% 29% 32% 14% 3	840
	11th to 20th	Night	24% 24% 30% 19% 2	840
	21st to end	Night	18% 20% 38% 19% 5%	924
February	1st to 10th	Night	20% 30% 32% 16% 1	840
	11th to 20th	Night	20% 25% 37% 15% 3	823
	21st to end	Night	23% 28% 32% 15% 2	692
March	1st to 10th	Night	21% 23% 36% 17% 3	809
	11th to 20th	Night	22% 24% 33% 16% 5%	800
	21st to end	Night	22% 20% 32% 21% 5%	880
April	1st to 10th	Night	24% 21% 35% 18% 2	800
	11th to 20th	Night	21% 20% 32% 19% 7% 1	683
	21st to end	Night	22% 18% 31% 23% 8%	600
May	1st to 10th	Night	18% 12% 28% 32% 9% 1	600
	11th to 20th	Night	18% 12% 33% 26% 10%	429
	21st to end	Night	12% 11% 31% 35% 11%	433
June	1st to 10th	Night	15% 10% 37% 30% 8% 1	400
	11th to 20th	Night	12% 10% 30% 38% 11%	400
	21st to end	Night	15% 8% 31% 32% 14% 1	400
July	1st to 10th	Night	6% 7% 27% 41% 19% 1	390
	11th to 20th	Night	10% 8% 30% 32% 18% 1	388
	21st to end	Night	9% 5% 32% 38% 16% 1	644
August	1st to 10th	Night	10% 5% 27% 35% 23% 2	597
	11th to 20th	Night	8% 6% 22% 39% 24% 2	594
	21st to end	Night	13% 8% 29% 30% 20% 1	712
September	1st to 10th	Night	11% 10% 28% 31% 17% 4	800
	11th to 20th	Night	12% 9% 25% 30% 20% 5%	800
	21st to end	Night	19% 12% 21% 28% 17% 4	800
October	1st to 10th	Night	18% 13% 31% 23% 14% 2	800
	11th to 20th	Night	23% 18% 31% 20% 7% 1	800
	21st to end	Night	26% 20% 31% 19% 3	880
November	1st to 10th	Night	23% 20% 32% 18% 7%	820
	11th to 20th	Night	24% 27% 27% 15% 6% 1	840
	21st to end	Night	25% 26% 31% 15% 3	840
December	1st to 10th	Night	24% 26% 32% 13% 3	840
	11th to 20th	Night	21% 27% 37% 12% 2	840
	21st to end	Night	30% 25% 30% 14% 2	924

Page generated at 2026-02-28 01:40:20. Version ac07

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