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 2024-01-14.

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% 10% 4 7% 6% 4 5% 5% 6% 7% 33%	74824
	Night	14% 12% 4 8% 6% 4 5% 5% 5% 6% 30%	74895
Transparency	Day	52% 4 14% 20% 9% 1	74516
	Night	55% 4 14% 18% 8% 1	74721
Seeing	Day	19% 9% 22% 28% 17% 5%	14365
	Night	22% 5% 17% 34% 19% 2	22994

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	22% 19% 6% 10% 6% 4 5% 5% 5% 6% 11%	1391
	11th to 20th	Day	17% 12% 6% 10% 8% 4 6% 7% 5% 7% 16%	1464
	21st to end	Day	15% 14% 6% 10% 8% 5% 6% 7% 6% 6% 17%	1584
February	1st to 10th	Day	15% 15% 6% 11% 8% 3 5% 6% 6% 4 21%	1442
	11th to 20th	Day	12% 16% 5% 10% 8% 4 6% 5% 5% 6% 23%	1575
	21st to end	Day	11% 16% 7% 9% 8% 4 6% 6% 6% 6% 21%	1473
March	1st to 10th	Day	12% 14% 6% 11% 8% 4 6% 6% 6% 6% 22%	1800
	11th to 20th	Day	13% 12% 6% 9% 7% 4 5% 5% 6% 7% 25%	1854
	21st to end	Day	13% 14% 4 8% 7% 5% 7% 6% 6% 8% 23%	2366
April	1st to 10th	Day	14% 15% 5% 8% 7% 5% 6% 5% 6% 7% 23%	2160
	11th to 20th	Day	13% 12% 4 8% 6% 5% 6% 5% 6% 6% 28%	2175
	21st to end	Day	13% 11% 4 8% 7% 4 7% 5% 6% 7% 27%	2453
May	1st to 10th	Day	14% 9% 4 7% 5% 4 6% 5% 6% 7% 32%	2520
	11th to 20th	Day	12% 7% 3 7% 7% 4 5% 6% 7% 8% 35%	2477
	21st to end	Day	17% 9% 3 7% 6% 3 6% 5% 6% 7% 32%	2822
June	1st to 10th	Day	19% 7% 3 7% 7% 4 6% 6% 6% 7% 28%	2726
	11th to 20th	Day	20% 9% 4 7% 7% 4 6% 5% 6% 7% 25%	2880
	21st to end	Day	11% 7% 3 6% 6% 4 4 5% 7% 8% 39%	2880
July	1st to 10th	Day	8% 5% 2 4 5% 3 5% 6% 6% 7% 48%	2840
	11th to 20th	Day	6% 4 2 5% 5% 3 5% 4 6% 8% 53%	2552
	21st to end	Day	4 2 1 3 4 2 3 4 5% 7% 64%	2741
August	1st to 10th	Day	5% 4 1 4 4 3 5% 4 5% 7% 57%	2507
	11th to 20th	Day	6% 4 1 4 4 2 4 5% 5% 7% 58%	2475
	21st to end	Day	9% 5% 2 5% 5% 4 4 6% 7% 8% 44%	2427
September	1st to 10th	Day	9% 5% 2 5% 5% 3 4 5% 6% 7% 51%	2160
	11th to 20th	Day	12% 6% 2 5% 5% 3 5% 5% 6% 9% 43%	2125
	21st to end	Day	15% 9% 3 5% 6% 3 5% 6% 5% 8% 35%	1980
October	1st to 10th	Day	14% 10% 3 6% 6% 3 5% 5% 6% 6% 36%	1805
	11th to 20th	Day	16% 11% 3 7% 4 3 5% 7% 6% 7% 32%	1722
	21st to end	Day	20% 10% 5% 7% 5% 3 4 5% 6% 6% 29%	1782
November	1st to 10th	Day	21% 14% 4 9% 7% 4 5% 6% 6% 5% 19%	1594
	11th to 20th	Day	18% 14% 6% 9% 7% 4 6% 5% 5% 6% 21%	1516
	21st to end	Day	18% 15% 5% 10% 9% 4 6% 6% 5% 7% 15%	1330
December	1st to 10th	Day	15% 15% 8% 12% 10% 3 5% 5% 5% 5% 17%	1330
	11th to 20th	Day	14% 18% 6% 12% 11% 6% 7% 5% 6% 4 12%	1682
	21st to end	Day	14% 16% 5% 10% 9% 5% 6% 5% 7% 6% 17%	2214
January	1st to 10th	Night	23% 19% 5% 8% 7% 4 4 4 6% 5% 14%	2784
	11th to 20th	Night	19% 16% 6% 12% 9% 4 5% 5% 4 7% 13%	2568
	21st to end	Night	14% 17% 6% 10% 7% 4 6% 5% 5% 5% 18%	2772
February	1st to 10th	Night	18% 17% 5% 9% 6% 4 5% 5% 5% 5% 20%	2516
	11th to 20th	Night	14% 18% 6% 9% 6% 3 4 4 4 6% 27%	2272
	21st to end	Night	12% 17% 6% 10% 7% 3 6% 4 5% 6% 25%	1782
March	1st to 10th	Night	15% 14% 5% 7% 7% 4 5% 4 5% 7% 26%	2160
	11th to 20th	Night	14% 12% 4 8% 7% 3 5% 6% 5% 7% 30%	2101
	21st to end	Night	11% 13% 4 8% 8% 4 5% 4 7% 8% 28%	1990
April	1st to 10th	Night	12% 11% 4 7% 6% 3 5% 7% 7% 8% 31%	1800
	11th to 20th	Night	12% 12% 4 7% 9% 4 7% 6% 5% 6% 27%	1736
	21st to end	Night	13% 10% 4 6% 4 5% 6% 6% 5% 7% 34%	1504
May	1st to 10th	Night	11% 11% 4 8% 6% 5% 5% 5% 6% 5% 34%	1440
	11th to 20th	Night	9% 7% 3 5% 7% 4 6% 5% 7% 10% 38%	1416
	21st to end	Night	15% 8% 3 6% 6% 4 4 5% 6% 6% 37%	1450
June	1st to 10th	Night	17% 8% 3 6% 6% 4 4 5% 6% 7% 32%	1229
	11th to 20th	Night	18% 8% 3 6% 7% 3 6% 6% 6% 7% 30%	1080
	21st to end	Night	8% 6% 4 6% 5% 4 6% 7% 7% 7% 41%	1080
July	1st to 10th	Night	8% 5% 2 5% 6% 2 4 4 6% 8% 50%	1117
	11th to 20th	Night	5% 4 2 3 4 2 4 4 6% 8% 57%	1404
	21st to end	Night	5% 2 1 2 3 2 3 5% 4 7% 66%	1576
August	1st to 10th	Night	4 2 2 4 4 2 4 5% 5% 8% 61%	1432
	11th to 20th	Night	4 3 1 3 4 2 4 4 5% 7% 64%	1424
	21st to end	Night	7% 4 2 4 4 3 4 5% 6% 7% 52%	1927
September	1st to 10th	Night	8% 5% 2 4 5% 3 5% 5% 6% 6% 52%	1800
	11th to 20th	Night	11% 6% 3 4 4 4 4 5% 6% 8% 47%	1834
	21st to end	Night	13% 7% 3 4 5% 3 5% 4 5% 8% 42%	1980
October	1st to 10th	Night	13% 8% 3 6% 5% 3 5% 5% 5% 6% 40%	2152
	11th to 20th	Night	18% 8% 4 7% 6% 3 4 4 5% 6% 35%	2237
	21st to end	Night	18% 10% 3 7% 5% 4 4 5% 5% 6% 32%	2574
November	1st to 10th	Night	24% 13% 4 7% 5% 3 5% 5% 6% 5% 22%	2485
	11th to 20th	Night	20% 14% 5% 9% 7% 4 4 5% 5% 4 23%	2660
	21st to end	Night	19% 16% 5% 9% 8% 3 5% 5% 6% 6% 18%	2833
December	1st to 10th	Night	18% 15% 6% 9% 7% 4 5% 5% 5% 6% 22%	2850
	11th to 20th	Night	16% 21% 7% 13% 10% 4 5% 4 4 4 11%	3510
	21st to end	Night	13% 18% 6% 10% 8% 5% 6% 6% 6% 6% 16%	5420

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	77% 5% 11% 5% 2	1391
	11th to 20th	Day	66% 8% 16% 8% 1 1	1464
	21st to end	Day	68% 5% 15% 10% 1 1	1584
February	1st to 10th	Day	66% 6% 14% 10% 4 1	1442
	11th to 20th	Day	63% 5% 15% 14% 3	1584
	21st to end	Day	65% 4 15% 14% 3	1473
March	1st to 10th	Day	64% 4 13% 14% 4 1	1800
	11th to 20th	Day	59% 3 13% 20% 5%	1854
	21st to end	Day	60% 3 18% 14% 4	2366
April	1st to 10th	Day	61% 5% 13% 17% 4	2160
	11th to 20th	Day	58% 3 12% 19% 7% 1	2175
	21st to end	Day	57% 4 12% 20% 7%	2453
May	1st to 10th	Day	51% 3 16% 20% 9% 1	2520
	11th to 20th	Day	48% 4 14% 25% 10%	2480
	21st to end	Day	53% 2 15% 22% 7% 1	2823
June	1st to 10th	Day	56% 3 10% 18% 10% 2	2726
	11th to 20th	Day	59% 4 11% 19% 7% 1	2880
	21st to end	Day	44% 3 15% 23% 13% 2	2880
July	1st to 10th	Day	36% 3 12% 26% 18% 5%	2763
	11th to 20th	Day	31% 3 14% 30% 18% 4	2475
	21st to end	Day	20% 3 12% 32% 28% 5%	2589
August	1st to 10th	Day	27% 4 14% 31% 20% 4	2490
	11th to 20th	Day	27% 4 16% 32% 19% 3	2475
	21st to end	Day	38% 3 15% 31% 12% 1	2427
September	1st to 10th	Day	33% 4 15% 34% 12% 3	2160
	11th to 20th	Day	40% 3 16% 26% 13% 2	2125
	21st to end	Day	48% 5% 20% 19% 8% 1	1980
October	1st to 10th	Day	49% 3 18% 25% 5%	1805
	11th to 20th	Day	52% 4 19% 21% 3	1722
	21st to end	Day	57% 4 19% 18% 3	1782
November	1st to 10th	Day	68% 5% 12% 13% 3	1594
	11th to 20th	Day	65% 7% 16% 10% 2 1	1516
	21st to end	Day	69% 6% 15% 8% 2	1330
December	1st to 10th	Day	69% 7% 10% 13% 1	1330
	11th to 20th	Day	75% 6% 12% 5% 2	1684
	21st to end	Day	68% 5% 14% 12% 1	2214
January	1st to 10th	Night	72% 4 13% 9% 3	2784
	11th to 20th	Night	71% 5% 16% 6% 2	2568
	21st to end	Night	67% 5% 15% 9% 2 1	2772
February	1st to 10th	Night	68% 4 12% 12% 4 1	2516
	11th to 20th	Night	61% 3 16% 17% 3	2274
	21st to end	Night	62% 3 14% 15% 6%	1782
March	1st to 10th	Night	60% 4 15% 14% 7% 1	2160
	11th to 20th	Night	55% 4 14% 20% 6% 1	2102
	21st to end	Night	55% 3 17% 20% 5%	1990
April	1st to 10th	Night	52% 5% 18% 19% 6%	1800
	11th to 20th	Night	56% 5% 12% 19% 7% 1	1736
	21st to end	Night	51% 3 13% 24% 9% 1	1504
May	1st to 10th	Night	52% 3 15% 20% 10% 1	1440
	11th to 20th	Night	41% 4 16% 30% 9% 1	1416
	21st to end	Night	46% 4 14% 24% 11%	1450
June	1st to 10th	Night	51% 3 11% 21% 10% 4	1229
	11th to 20th	Night	52% 4 11% 24% 9%	1080
	21st to end	Night	41% 4 18% 23% 12% 2	1080
July	1st to 10th	Night	34% 4 10% 27% 19% 6%	1085
	11th to 20th	Night	27% 5% 13% 31% 20% 4	1358
	21st to end	Night	19% 2 10% 32% 31% 6%	1488
August	1st to 10th	Night	24% 3 12% 29% 28% 5%	1424
	11th to 20th	Night	21% 4 12% 36% 24% 4	1424
	21st to end	Night	31% 3 13% 35% 17% 2	1927
September	1st to 10th	Night	33% 3 15% 29% 16% 4	1800
	11th to 20th	Night	38% 2 13% 26% 18% 3	1834
	21st to end	Night	42% 3 17% 26% 10% 2	1980
October	1st to 10th	Night	45% 4 17% 26% 8% 1	2152
	11th to 20th	Night	52% 3 16% 22% 7%	2237
	21st to end	Night	55% 3 18% 21% 3	2574
November	1st to 10th	Night	65% 6% 12% 13% 4	2485
	11th to 20th	Night	66% 4 13% 12% 4 1	2660
	21st to end	Night	67% 5% 16% 9% 3	2833
December	1st to 10th	Night	64% 4 16% 12% 3	2850
	11th to 20th	Night	78% 4 11% 6% 1	3507
	21st to end	Night	69% 4 16% 10% 2	5420

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	28% 8% 11% 28% 17% 8%	180
	11th to 20th	Day	23% 5% 17% 31% 17% 7%	166
	21st to end	Day	26% 3 20% 30% 16% 6%	176
February	1st to 10th	Day	31% 11% 28% 22% 6% 1	162
	11th to 20th	Day	24% 12% 22% 27% 13% 1	335
	21st to end	Day	17% 10% 25% 33% 13% 2	344
March	1st to 10th	Day	25% 16% 24% 22% 10% 3	420
	11th to 20th	Day	22% 11% 25% 23% 15% 4	420
	21st to end	Day	26% 11% 26% 18% 15% 3	462
April	1st to 10th	Day	28% 12% 24% 22% 11% 2	420
	11th to 20th	Day	24% 14% 25% 21% 12% 4	412
	21st to end	Day	20% 13% 27% 23% 12% 5%	420
May	1st to 10th	Day	17% 12% 28% 28% 12% 3	423
	11th to 20th	Day	18% 7% 23% 28% 17% 6%	448
	21st to end	Day	20% 8% 18% 26% 21% 6%	584
June	1st to 10th	Day	22% 9% 25% 29% 13% 4	656
	11th to 20th	Day	23% 9% 23% 27% 16% 3	810
	21st to end	Day	14% 7% 21% 30% 23% 4	810
July	1st to 10th	Day	12% 7% 18% 34% 24% 5%	758
	11th to 20th	Day	6% 11% 24% 34% 20% 5%	474
	21st to end	Day	5% 7% 22% 32% 26% 8%	487
August	1st to 10th	Day	9% 4 20% 34% 22% 11%	447
	11th to 20th	Day	7% 7% 22% 32% 21% 11%	437
	21st to end	Day	13% 7% 21% 30% 20% 9%	495
September	1st to 10th	Day	14% 9% 24% 30% 20% 5%	450
	11th to 20th	Day	18% 6% 20% 28% 24% 4	450
	21st to end	Day	22% 9% 22% 25% 16% 5%	450
October	1st to 10th	Day	22% 6% 20% 26% 19% 7%	450
	11th to 20th	Day	25% 6% 21% 25% 19% 5%	372
	21st to end	Day	31% 6% 21% 26% 14% 3	297
November	1st to 10th	Day	28% 6% 24% 25% 16% 2	232
	11th to 20th	Day	29% 7% 18% 22% 18% 4	180
	21st to end	Day	28% 4 16% 29% 15% 9%	180
December	1st to 10th	Day	27% 6% 9% 27% 21% 9%	180
	11th to 20th	Day	28% 3 24% 24% 16% 5%	180
	21st to end	Day	24% 4 16% 37% 16% 3	198
January	1st to 10th	Night	35% 6% 19% 26% 11% 2	850
	11th to 20th	Night	28% 6% 19% 32% 14% 2	734
	21st to end	Night	24% 6% 20% 32% 16% 2	792
February	1st to 10th	Night	30% 5% 19% 32% 13% 1	720
	11th to 20th	Night	27% 6% 16% 36% 15% 1	704
	21st to end	Night	20% 6% 17% 32% 21% 3	592
March	1st to 10th	Night	25% 8% 19% 29% 17% 2	720
	11th to 20th	Night	21% 7% 23% 32% 15% 1	720
	21st to end	Night	20% 6% 22% 32% 17% 3	792
April	1st to 10th	Night	20% 9% 17% 34% 19% 2	720
	11th to 20th	Night	21% 7% 20% 34% 17% 1	668
	21st to end	Night	18% 7% 22% 34% 17% 1	424
May	1st to 10th	Night	19% 6% 15% 36% 23% 1	360
	11th to 20th	Night	12% 5% 16% 42% 21% 4	354
	21st to end	Night	22% 2 14% 32% 29% 2	389
June	1st to 10th	Night	21% 5% 18% 37% 16% 2	360
	11th to 20th	Night	23% 6% 15% 33% 21% 2	360
	21st to end	Night	12% 7% 17% 37% 25% 3	360
July	1st to 10th	Night	11% 3 11% 36% 37% 1	350
	11th to 20th	Night	8% 4 15% 37% 34% 3	348
	21st to end	Night	6% 2 9% 42% 38% 3	394
August	1st to 10th	Night	6% 2 11% 32% 43% 6%	358
	11th to 20th	Night	5% 3 8% 41% 37% 6%	356
	21st to end	Night	10% 3 12% 40% 33% 3	739
September	1st to 10th	Night	12% 3 13% 38% 30% 4	720
	11th to 20th	Night	15% 4 12% 29% 34% 7%	720
	21st to end	Night	18% 5% 15% 38% 21% 3	720
October	1st to 10th	Night	18% 3 13% 39% 25% 3	720
	11th to 20th	Night	23% 4 16% 32% 22% 2	720
	21st to end	Night	26% 5% 19% 33% 15% 3	792
November	1st to 10th	Night	32% 6% 16% 37% 8% 1	740
	11th to 20th	Night	31% 7% 21% 26% 12% 2	760
	21st to end	Night	28% 6% 18% 33% 13% 3	933
December	1st to 10th	Night	25% 5% 17% 35% 15% 3	950
	11th to 20th	Night	29% 6% 18% 35% 11% 1	950
	21st to end	Night	31% 4 20% 34% 9% 1	1105

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