Harrington Lodge Silver Star Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Harrington Lodge Silver Star Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	10% 10% 3 8% 5% 5% 5% 4 6% 7% 35%	131439
	Night	11% 13% 4 9% 5% 5% 5% 4 6% 6% 32%	128563
Transparency	Day	49% 4 15% 22% 9% 2	131155
	Night	53% 4 15% 19% 8% 1	128424
Seeing	Day	19% 9% 22% 27% 17% 5%	16968
	Night	21% 6% 17% 34% 19% 2	25479

By Month

Percentage Cloud Cover NW (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% 22% 7% 17% 7% 6% 6% 4 5% 5% 9%	3342
	11th to 20th	Day	9% 12% 4 11% 6% 5% 7% 7% 8% 9% 22%	3616
	21st to end	Day	11% 15% 5% 11% 8% 6% 6% 5% 6% 6% 20%	4004
February	1st to 10th	Day	15% 16% 5% 13% 5% 5% 5% 5% 6% 4 20%	1603
	11th to 20th	Day	11% 17% 5% 10% 6% 6% 5% 4 5% 6% 25%	1755
	21st to end	Day	10% 19% 6% 10% 7% 5% 6% 5% 7% 5% 20%	1642
March	1st to 10th	Day	8% 14% 5% 12% 6% 6% 6% 5% 8% 7% 23%	4518
	11th to 20th	Day	6% 13% 5% 10% 6% 5% 5% 4 6% 7% 35%	4705
	21st to end	Day	12% 15% 4 10% 6% 6% 6% 4 6% 7% 23%	5959
April	1st to 10th	Day	13% 15% 4 9% 6% 7% 5% 5% 7% 7% 23%	2400
	11th to 20th	Day	12% 13% 4 9% 6% 6% 5% 5% 6% 6% 29%	2421
	21st to end	Day	12% 12% 4 9% 6% 6% 6% 4 6% 7% 27%	2727
May	1st to 10th	Day	9% 10% 3 8% 4 5% 5% 3 5% 7% 41%	6320
	11th to 20th	Day	12% 11% 4 9% 6% 6% 6% 5% 7% 8% 25%	6277
	21st to end	Day	13% 10% 3 9% 5% 5% 5% 4 6% 8% 31%	7170
June	1st to 10th	Day	17% 8% 3 8% 6% 6% 5% 5% 6% 7% 30%	3030
	11th to 20th	Day	18% 10% 4 9% 6% 6% 5% 4 6% 7% 25%	3200
	21st to end	Day	11% 7% 3 7% 5% 5% 4 5% 7% 8% 38%	3200
July	1st to 10th	Day	5% 3 2 5% 3 3 4 4 5% 7% 60%	7116
	11th to 20th	Day	5% 3 1 4 3 3 4 3 4 7% 63%	6394
	21st to end	Day	4 4 1 4 4 3 4 4 7% 9% 56%	6874
August	1st to 10th	Day	3 3 1 4 3 4 5% 4 6% 7% 60%	4541
	11th to 20th	Day	4 4 2 6% 4 4 5% 4 6% 9% 52%	4470
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 7% 46%	4391
September	1st to 10th	Day	8% 4 2 5% 4 4 4 4 6% 7% 52%	2400
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 6% 9% 44%	2361
	21st to end	Day	14% 9% 3 8% 4 4 5% 4 6% 7% 36%	2200
October	1st to 10th	Day	12% 10% 3 10% 5% 4 4 4 6% 7% 36%	3285
	11th to 20th	Day	19% 12% 4 7% 3 4 3 4 5% 5% 33%	3109
	21st to end	Day	13% 10% 5% 10% 4 5% 4 4 7% 7% 30%	3200
November	1st to 10th	Day	20% 15% 4 10% 6% 5% 5% 5% 5% 5% 19%	1764
	11th to 20th	Day	17% 16% 5% 9% 6% 6% 5% 4 5% 6% 20%	1675
	21st to end	Day	17% 18% 4 11% 7% 6% 6% 4 5% 7% 14%	1470
December	1st to 10th	Day	11% 14% 5% 11% 7% 5% 5% 4 6% 7% 25%	2360
	11th to 20th	Day	12% 20% 7% 14% 8% 7% 6% 4 5% 5% 12%	2712
	21st to end	Day	11% 18% 5% 12% 7% 7% 5% 4 7% 7% 17%	3228
January	1st to 10th	Night	16% 24% 7% 11% 6% 5% 5% 4 6% 5% 11%	6649
	11th to 20th	Night	10% 13% 4 12% 7% 6% 7% 5% 6% 8% 23%	6282
	21st to end	Night	12% 17% 5% 11% 6% 5% 5% 4 5% 6% 24%	6952
February	1st to 10th	Night	17% 18% 5% 11% 6% 6% 4 4 5% 5% 20%	2795
	11th to 20th	Night	12% 19% 5% 9% 5% 4 4 3 5% 6% 29%	2532
	21st to end	Night	11% 19% 5% 11% 6% 4 6% 3 5% 6% 24%	1987
March	1st to 10th	Night	9% 13% 5% 9% 6% 5% 5% 4 7% 8% 28%	5376
	11th to 20th	Night	7% 14% 4 9% 6% 4 5% 4 5% 6% 35%	5290
	21st to end	Night	10% 14% 4 10% 7% 7% 6% 5% 7% 7% 24%	5016
April	1st to 10th	Night	12% 11% 4 9% 6% 5% 5% 5% 7% 8% 29%	2000
	11th to 20th	Night	11% 13% 4 9% 7% 6% 6% 5% 5% 6% 29%	1930
	21st to end	Night	12% 11% 3 7% 4 7% 5% 4 6% 6% 35%	1670
May	1st to 10th	Night	6% 10% 4 10% 6% 6% 5% 3 5% 6% 40%	3640
	11th to 20th	Night	10% 10% 4 9% 6% 6% 6% 4 6% 8% 32%	3616
	21st to end	Night	10% 7% 3 8% 5% 5% 5% 5% 6% 7% 39%	3702
June	1st to 10th	Night	16% 8% 2 7% 6% 5% 5% 4 6% 8% 33%	1365
	11th to 20th	Night	17% 8% 3 7% 5% 4 7% 4 6% 7% 31%	1200
	21st to end	Night	8% 7% 3 6% 5% 6% 5% 5% 7% 7% 40%	1200
July	1st to 10th	Night	6% 5% 2 6% 4 4 4 3 5% 6% 54%	2827
	11th to 20th	Night	4 4 2 5% 3 3 3 3 5% 6% 63%	3562
	21st to end	Night	6% 4 2 4 3 3 4 4 5% 7% 58%	3969
August	1st to 10th	Night	3 2 1 4 3 3 5% 5% 8% 8% 57%	2609
	11th to 20th	Night	4 4 2 6% 5% 4 4 4 7% 9% 50%	2577
	21st to end	Night	9% 7% 2 5% 3 4 4 4 6% 7% 48%	3524
September	1st to 10th	Night	7% 4 2 5% 3 5% 4 4 6% 7% 54%	2000
	11th to 20th	Night	10% 6% 2 5% 3 5% 4 3 6% 7% 48%	2038
	21st to end	Night	13% 8% 3 6% 5% 4 4 3 5% 7% 43%	2200
October	1st to 10th	Night	10% 10% 3 9% 4 4 5% 3 5% 5% 41%	3912
	11th to 20th	Night	22% 8% 3 6% 3 3 3 3 5% 7% 37%	4043
	21st to end	Night	14% 12% 4 9% 5% 4 3 3 5% 6% 35%	4600
November	1st to 10th	Night	22% 15% 4 8% 4 5% 5% 4 6% 6% 22%	2754
	11th to 20th	Night	20% 16% 5% 11% 6% 5% 4 4 5% 4 22%	2940
	21st to end	Night	17% 18% 5% 10% 7% 5% 5% 4 6% 6% 18%	3132
December	1st to 10th	Night	13% 12% 4 9% 5% 5% 5% 4 6% 9% 30%	5040
	11th to 20th	Night	15% 23% 7% 14% 8% 5% 4 3 4 4 13%	5700
	21st to end	Night	10% 20% 6% 13% 6% 5% 5% 4 6% 6% 17%	7934

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	80% 3 9% 7% 1	3342
	11th to 20th	Day	57% 9% 22% 9% 2 2	3640
	21st to end	Day	67% 5% 14% 10% 3	4004
February	1st to 10th	Day	65% 6% 12% 10% 5% 1	1603
	11th to 20th	Day	61% 5% 14% 15% 4 1	1764
	21st to end	Day	65% 4 15% 14% 3	1642
March	1st to 10th	Day	61% 4 9% 20% 6%	4518
	11th to 20th	Day	48% 4 15% 28% 5%	4705
	21st to end	Day	61% 3 11% 18% 6%	5959
April	1st to 10th	Day	60% 4 13% 18% 4	2400
	11th to 20th	Day	56% 3 12% 20% 8% 1	2421
	21st to end	Day	56% 4 12% 21% 7%	2727
May	1st to 10th	Day	44% 3 8% 29% 15% 1	6320
	11th to 20th	Day	56% 3 12% 23% 6%	6280
	21st to end	Day	51% 3 17% 24% 4	7171
June	1st to 10th	Day	54% 4 10% 19% 11% 2	3030
	11th to 20th	Day	58% 4 10% 20% 7% 1	3200
	21st to end	Day	45% 3 15% 22% 13% 2	3200
July	1st to 10th	Day	25% 4 12% 27% 23% 9%	7039
	11th to 20th	Day	24% 3 15% 29% 21% 8%	6317
	21st to end	Day	25% 3 20% 32% 15% 5%	6681
August	1st to 10th	Day	23% 4 10% 40% 21% 3	4524
	11th to 20th	Day	30% 3 25% 29% 10% 2	4512
	21st to end	Day	37% 4 19% 30% 9% 1	4390
September	1st to 10th	Day	32% 4 15% 34% 13% 3	2400
	11th to 20th	Day	39% 3 16% 28% 13% 1	2361
	21st to end	Day	47% 5% 21% 19% 8% 1	2200
October	1st to 10th	Day	48% 5% 21% 22% 4	3285
	11th to 20th	Day	53% 4 13% 27% 3	3109
	21st to end	Day	54% 5% 21% 17% 2	3200
November	1st to 10th	Day	68% 5% 12% 13% 3	1764
	11th to 20th	Day	66% 7% 16% 9% 2 1	1675
	21st to end	Day	70% 6% 14% 8% 2	1470
December	1st to 10th	Day	60% 7% 21% 12% 1	2360
	11th to 20th	Day	74% 5% 13% 7% 1	2714
	21st to end	Day	66% 4 16% 13% 1	3228
January	1st to 10th	Night	76% 2 13% 6% 2	6649
	11th to 20th	Night	59% 9% 18% 10% 4	6320
	21st to end	Night	65% 4 16% 13% 2	6952
February	1st to 10th	Night	68% 5% 11% 11% 5% 1	2795
	11th to 20th	Night	59% 3 15% 17% 5% 1	2534
	21st to end	Night	63% 3 14% 14% 6%	1987
March	1st to 10th	Night	55% 3 11% 25% 7%	5376
	11th to 20th	Night	49% 5% 16% 22% 7%	5291
	21st to end	Night	59% 4 11% 19% 7%	5016
April	1st to 10th	Night	53% 5% 17% 19% 6%	2000
	11th to 20th	Night	55% 5% 11% 21% 8% 1	1930
	21st to end	Night	50% 3 12% 25% 9% 1	1670
May	1st to 10th	Night	45% 3 7% 25% 18%	3637
	11th to 20th	Night	51% 3 13% 27% 6%	3616
	21st to end	Night	46% 3 16% 28% 7%	3702
June	1st to 10th	Night	49% 3 11% 21% 12% 3	1365
	11th to 20th	Night	52% 4 10% 24% 10%	1200
	21st to end	Night	42% 5% 18% 23% 11% 2	1200
July	1st to 10th	Night	31% 4 10% 21% 21% 13%	2795
	11th to 20th	Night	25% 3 14% 26% 24% 8%	3516
	21st to end	Night	26% 3 14% 34% 16% 7%	3857
August	1st to 10th	Night	23% 4 8% 36% 25% 3	2601
	11th to 20th	Night	34% 3 17% 30% 14% 2	2601
	21st to end	Night	37% 2 19% 28% 12% 2	3524
September	1st to 10th	Night	31% 3 14% 30% 18% 3	2000
	11th to 20th	Night	36% 3 13% 28% 17% 3	2038
	21st to end	Night	42% 3 17% 26% 10% 1	2200
October	1st to 10th	Night	46% 3 19% 25% 7%	3912
	11th to 20th	Night	49% 4 14% 27% 7%	4043
	21st to end	Night	52% 4 18% 23% 3	4600
November	1st to 10th	Night	65% 6% 12% 13% 4	2754
	11th to 20th	Night	67% 4 13% 12% 4	2940
	21st to end	Night	68% 5% 16% 9% 3	3132
December	1st to 10th	Night	53% 6% 25% 14% 2	5040
	11th to 20th	Night	77% 3 12% 6% 1	5697
	21st to end	Night	68% 4 15% 12% 2	7934

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	26% 9% 14% 27% 17% 7%	202
	11th to 20th	Day	23% 5% 19% 32% 16% 6%	200
	21st to end	Day	24% 3 20% 32% 16% 5%	220
February	1st to 10th	Day	29% 11% 28% 21% 9% 3	203
	11th to 20th	Day	22% 10% 24% 29% 13% 3	395
	21st to end	Day	19% 11% 25% 31% 13% 2	411
March	1st to 10th	Day	24% 15% 24% 23% 12% 3	500
	11th to 20th	Day	21% 11% 25% 23% 16% 4	500
	21st to end	Day	27% 11% 24% 19% 16% 3	550
April	1st to 10th	Day	27% 13% 25% 22% 10% 2	500
	11th to 20th	Day	24% 15% 25% 22% 12% 3	492
	21st to end	Day	19% 12% 26% 24% 13% 6%	500
May	1st to 10th	Day	16% 12% 29% 27% 13% 3	503
	11th to 20th	Day	20% 7% 22% 29% 17% 6%	528
	21st to end	Day	19% 9% 20% 27% 20% 6%	684
June	1st to 10th	Day	21% 8% 25% 29% 13% 3	760
	11th to 20th	Day	22% 9% 23% 27% 15% 4	930
	21st to end	Day	14% 7% 21% 30% 23% 4	930
July	1st to 10th	Day	11% 7% 19% 34% 24% 5%	872
	11th to 20th	Day	6% 10% 25% 33% 20% 6%	557
	21st to end	Day	6% 7% 22% 31% 26% 8%	575
August	1st to 10th	Day	9% 5% 20% 32% 23% 12%	527
	11th to 20th	Day	8% 8% 22% 30% 20% 12%	517
	21st to end	Day	12% 8% 20% 29% 21% 10%	583
September	1st to 10th	Day	12% 8% 21% 28% 23% 9%	530
	11th to 20th	Day	16% 7% 20% 28% 24% 6%	530
	21st to end	Day	23% 10% 24% 24% 15% 4	530
October	1st to 10th	Day	20% 7% 22% 27% 18% 6%	530
	11th to 20th	Day	25% 6% 21% 24% 19% 5%	442
	21st to end	Day	29% 7% 24% 25% 12% 2	363
November	1st to 10th	Day	28% 8% 25% 23% 14% 1	282
	11th to 20th	Day	29% 9% 20% 21% 16% 5%	220
	21st to end	Day	25% 6% 20% 29% 13% 8%	220
December	1st to 10th	Day	27% 7% 10% 27% 20% 9%	220
	11th to 20th	Day	31% 6% 23% 22% 14% 4	220
	21st to end	Day	21% 7% 18% 33% 18% 3	242
January	1st to 10th	Night	34% 7% 19% 27% 12% 2	903
	11th to 20th	Night	26% 6% 20% 33% 14% 2	800
	21st to end	Night	24% 6% 21% 33% 15% 2	880
February	1st to 10th	Night	29% 6% 19% 32% 13% 1	800
	11th to 20th	Night	25% 5% 16% 37% 15% 1	784
	21st to end	Night	21% 7% 17% 32% 20% 3	660
March	1st to 10th	Night	24% 7% 20% 30% 18% 2	800
	11th to 20th	Night	20% 8% 23% 33% 16% 1	800
	21st to end	Night	20% 6% 21% 33% 17% 3	880
April	1st to 10th	Night	20% 9% 19% 34% 18% 2	800
	11th to 20th	Night	21% 7% 21% 33% 17% 1	742
	21st to end	Night	17% 9% 21% 34% 18% 1	470
May	1st to 10th	Night	18% 7% 16% 34% 23% 1	400
	11th to 20th	Night	13% 5% 17% 42% 20% 3	394
	21st to end	Night	21% 3 15% 31% 28% 2	433
June	1st to 10th	Night	20% 6% 18% 39% 16% 2	400
	11th to 20th	Night	22% 7% 16% 33% 21% 2	400
	21st to end	Night	13% 7% 16% 38% 24% 3	400
July	1st to 10th	Night	11% 4 12% 35% 37% 2	390
	11th to 20th	Night	7% 4 15% 37% 34% 3	388
	21st to end	Night	6% 3 10% 40% 37% 3	438
August	1st to 10th	Night	6% 2 11% 31% 43% 6%	398
	11th to 20th	Night	5% 4 10% 39% 36% 6%	396
	21st to end	Night	10% 3 11% 39% 33% 3	822
September	1st to 10th	Night	11% 3 12% 37% 32% 6%	800
	11th to 20th	Night	15% 4 11% 30% 35% 6%	800
	21st to end	Night	17% 6% 17% 38% 20% 3	800
October	1st to 10th	Night	17% 4 13% 39% 24% 2	800
	11th to 20th	Night	23% 5% 17% 32% 21% 2	800
	21st to end	Night	25% 6% 20% 33% 14% 3	880
November	1st to 10th	Night	30% 7% 16% 38% 8%	820
	11th to 20th	Night	30% 8% 21% 27% 12% 2	840
	21st to end	Night	27% 6% 18% 34% 12% 3	1032
December	1st to 10th	Night	25% 6% 17% 34% 14% 3	1050
	11th to 20th	Night	30% 6% 18% 33% 11% 1	1050
	21st to end	Night	29% 6% 20% 34% 10% 1	1229

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