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 2024-11-12.

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	11% 10% 3 8% 5% 5% 5% 4 6% 7% 35%	105771
	Night	13% 13% 4 9% 5% 5% 5% 4 5% 6% 32%	101967
Transparency	Day	49% 4 14% 22% 9% 2	105529
	Night	54% 4 14% 19% 8% 1	101855
Seeing	Day	19% 9% 22% 28% 18% 5%	15553
	Night	22% 5% 17% 34% 19% 2	23958

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	16% 23% 7% 15% 7% 6% 6% 4 4 4 8%	2320
	11th to 20th	Day	13% 17% 5% 11% 6% 5% 6% 7% 5% 6% 19%	2516
	21st to end	Day	14% 16% 5% 12% 8% 8% 6% 6% 6% 6% 12%	2794
February	1st to 10th	Day	16% 17% 5% 13% 5% 4 5% 5% 5% 4 21%	1522
	11th to 20th	Day	11% 17% 5% 10% 7% 6% 5% 4 5% 6% 25%	1665
	21st to end	Day	10% 19% 6% 10% 7% 5% 6% 5% 6% 5% 21%	1562
March	1st to 10th	Day	9% 16% 6% 13% 7% 6% 5% 5% 7% 6% 21%	3138
	11th to 20th	Day	8% 9% 4 8% 5% 5% 4 3 6% 7% 42%	3286
	21st to end	Day	10% 15% 4 10% 7% 6% 6% 4 6% 7% 26%	4155
April	1st to 10th	Day	13% 16% 4 9% 6% 6% 5% 5% 7% 6% 23%	2280
	11th to 20th	Day	12% 13% 4 9% 6% 6% 5% 5% 6% 6% 29%	2298
	21st to end	Day	13% 13% 4 9% 6% 6% 6% 4 6% 7% 26%	2590
May	1st to 10th	Day	10% 8% 3 8% 5% 6% 6% 4 7% 8% 36%	4420
	11th to 20th	Day	11% 8% 4 8% 5% 6% 5% 5% 7% 9% 32%	4377
	21st to end	Day	16% 12% 4 10% 6% 5% 5% 4 6% 7% 24%	4996
June	1st to 10th	Day	18% 8% 3 9% 6% 6% 5% 5% 6% 7% 28%	2878
	11th to 20th	Day	19% 10% 4 8% 6% 6% 5% 4 6% 7% 25%	3040
	21st to end	Day	11% 7% 3 7% 5% 5% 4 4 7% 8% 38%	3040
July	1st to 10th	Day	5% 3 2 4 3 3 4 4 5% 6% 61%	4978
	11th to 20th	Day	3 2 1 4 3 3 3 3 4 6% 69%	4466
	21st to end	Day	4 3 1 4 3 3 4 3 6% 8% 59%	4790
August	1st to 10th	Day	3 3 1 4 3 4 5% 4 6% 7% 62%	4401
	11th to 20th	Day	4 4 1 5% 4 4 5% 4 6% 9% 52%	4330
	21st to end	Day	9% 5% 2 6% 4 4 5% 4 6% 7% 46%	4257
September	1st to 10th	Day	8% 5% 2 6% 4 4 4 4 6% 7% 51%	2280
	11th to 20th	Day	12% 6% 2 6% 4 5% 5% 4 6% 9% 42%	2243
	21st to end	Day	14% 9% 2 7% 5% 5% 5% 4 6% 8% 35%	2090
October	1st to 10th	Day	12% 10% 3 10% 5% 4 4 4 5% 7% 36%	3185
	11th to 20th	Day	19% 12% 4 7% 3 4 3 4 5% 5% 33%	3014
	21st to end	Day	13% 10% 5% 10% 4 5% 4 4 7% 7% 30%	3101
November	1st to 10th	Day	20% 15% 4 10% 6% 5% 5% 5% 5% 5% 19%	1679
	11th to 20th	Day	18% 15% 5% 9% 7% 6% 5% 4 5% 6% 21%	1524
	21st to end	Day	18% 17% 5% 11% 7% 6% 5% 4 5% 7% 15%	1330
December	1st to 10th	Day	15% 17% 7% 13% 8% 5% 4 4 6% 5% 17%	1330
	11th to 20th	Day	14% 19% 6% 14% 9% 7% 6% 4 6% 4 11%	1682
	21st to end	Day	14% 16% 5% 12% 8% 7% 5% 4 7% 6% 17%	2214
January	1st to 10th	Night	19% 25% 6% 11% 6% 5% 4 3 5% 4 11%	4648
	11th to 20th	Night	14% 18% 6% 12% 6% 5% 6% 4 4 6% 18%	4382
	21st to end	Night	15% 20% 6% 13% 7% 6% 6% 4 5% 5% 13%	4862
February	1st to 10th	Night	18% 18% 5% 11% 6% 6% 4 4 5% 5% 19%	2656
	11th to 20th	Night	13% 19% 5% 9% 5% 4 4 3 5% 6% 28%	2402
	21st to end	Night	11% 19% 5% 11% 6% 4 6% 3 5% 6% 24%	1891
March	1st to 10th	Night	10% 14% 5% 10% 6% 5% 6% 4 7% 8% 26%	3736
	11th to 20th	Night	9% 10% 3 7% 4 4 4 4 5% 7% 44%	3689
	21st to end	Night	10% 14% 4 10% 7% 6% 5% 4 6% 7% 29%	3498
April	1st to 10th	Night	12% 12% 3 8% 6% 4 5% 5% 7% 8% 30%	1900
	11th to 20th	Night	11% 13% 4 9% 7% 6% 6% 5% 5% 6% 28%	1833
	21st to end	Night	13% 12% 3 7% 4 7% 5% 5% 6% 6% 33%	1587
May	1st to 10th	Night	7% 9% 4 10% 7% 7% 6% 4 5% 6% 35%	2540
	11th to 20th	Night	10% 7% 3 7% 5% 5% 6% 4 7% 9% 36%	2516
	21st to end	Night	13% 9% 4 9% 6% 6% 6% 5% 6% 6% 31%	2576
June	1st to 10th	Night	17% 8% 2 7% 6% 5% 5% 4 6% 8% 33%	1297
	11th to 20th	Night	17% 8% 3 7% 5% 4 7% 4 6% 7% 30%	1140
	21st to end	Night	8% 7% 3 6% 5% 6% 6% 5% 8% 7% 39%	1140
July	1st to 10th	Night	6% 5% 2 6% 4 3 4 3 5% 6% 55%	1979
	11th to 20th	Night	3 3 2 4 2 3 3 2 4 5% 69%	2490
	21st to end	Night	4 4 2 3 3 3 4 4 5% 7% 62%	2762
August	1st to 10th	Night	2 2 1 4 3 3 5% 4 8% 8% 58%	2529
	11th to 20th	Night	4 4 2 6% 5% 4 4 4 7% 9% 51%	2497
	21st to end	Night	9% 7% 2 6% 4 4 4 4 6% 7% 48%	3417
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 6% 53%	1900
	11th to 20th	Night	10% 6% 2 5% 3 5% 4 4 6% 7% 47%	1936
	21st to end	Night	13% 8% 3 5% 5% 4 4 3 5% 7% 42%	2090
October	1st to 10th	Night	10% 10% 4 9% 5% 4 4 3 5% 5% 41%	3792
	11th to 20th	Night	22% 8% 3 6% 3 3 3 3 5% 7% 36%	3918
	21st to end	Night	14% 12% 4 9% 5% 4 3 3 5% 6% 34%	4457
November	1st to 10th	Night	23% 14% 4 8% 4 5% 5% 4 6% 5% 22%	2620
	11th to 20th	Night	20% 16% 4 10% 5% 5% 4 4 5% 4 22%	2674
	21st to end	Night	18% 17% 5% 9% 7% 5% 5% 4 6% 6% 18%	2833
December	1st to 10th	Night	17% 16% 5% 10% 6% 5% 5% 3 5% 5% 22%	2850
	11th to 20th	Night	16% 22% 7% 14% 9% 5% 5% 3 4 4 11%	3510
	21st to end	Night	12% 19% 5% 12% 7% 6% 6% 5% 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	82% 3 9% 5% 1	2320
	11th to 20th	Day	64% 6% 17% 9% 2 2	2540
	21st to end	Day	73% 5% 15% 6% 1	2794
February	1st to 10th	Day	67% 5% 13% 10% 4 1	1522
	11th to 20th	Day	62% 4 15% 14% 5% 1	1674
	21st to end	Day	65% 4 14% 14% 3	1562
March	1st to 10th	Day	64% 3 8% 20% 4 1	3138
	11th to 20th	Day	44% 2 20% 30% 4	3286
	21st to end	Day	59% 2 14% 18% 6%	4155
April	1st to 10th	Day	61% 5% 13% 17% 4	2280
	11th to 20th	Day	57% 3 12% 19% 8% 1	2298
	21st to end	Day	58% 4 11% 20% 7%	2590
May	1st to 10th	Day	48% 2 11% 26% 13% 1	4420
	11th to 20th	Day	50% 2 12% 27% 9%	4380
	21st to end	Day	61% 1 13% 18% 5%	4997
June	1st to 10th	Day	56% 3 10% 18% 10% 2	2878
	11th to 20th	Day	59% 4 10% 20% 7% 1	3040
	21st to end	Day	44% 3 14% 23% 14% 2	3040
July	1st to 10th	Day	26% 3 8% 25% 26% 12%	4901
	11th to 20th	Day	19% 2 8% 29% 30% 11%	4389
	21st to end	Day	23% 4 13% 31% 21% 7%	4639
August	1st to 10th	Day	21% 4 10% 40% 22% 3	4384
	11th to 20th	Day	29% 3 25% 29% 11% 2	4372
	21st to end	Day	38% 4 20% 30% 8% 1	4256
September	1st to 10th	Day	33% 4 14% 33% 12% 3	2280
	11th to 20th	Day	40% 3 16% 26% 13% 1	2243
	21st to end	Day	47% 5% 21% 19% 8% 1	2090
October	1st to 10th	Day	48% 5% 20% 22% 4	3185
	11th to 20th	Day	53% 4 13% 27% 3	3014
	21st to end	Day	54% 4 21% 17% 2	3101
November	1st to 10th	Day	68% 5% 12% 12% 3	1679
	11th to 20th	Day	65% 7% 15% 10% 2 1	1524
	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	77% 3 11% 7% 2	4648
	11th to 20th	Night	68% 5% 14% 9% 3 1	4420
	21st to end	Night	75% 4 13% 6% 1	4862
February	1st to 10th	Night	69% 4 11% 11% 4 1	2656
	11th to 20th	Night	59% 3 15% 17% 5% 1	2404
	21st to end	Night	64% 3 14% 14% 6%	1891
March	1st to 10th	Night	57% 2 10% 22% 8%	3736
	11th to 20th	Night	43% 2 21% 27% 6%	3690
	21st to end	Night	57% 2 12% 21% 8%	3498
April	1st to 10th	Night	53% 5% 18% 18% 6%	1900
	11th to 20th	Night	56% 5% 11% 20% 7% 1	1833
	21st to end	Night	52% 3 12% 23% 9% 1	1587
May	1st to 10th	Night	51% 2 9% 23% 14%	2540
	11th to 20th	Night	44% 2 14% 32% 8%	2516
	21st to end	Night	55% 2 14% 23% 7%	2576
June	1st to 10th	Night	50% 3 11% 21% 11% 4	1297
	11th to 20th	Night	52% 4 10% 24% 9%	1140
	21st to end	Night	42% 5% 17% 23% 11% 2	1140
July	1st to 10th	Night	30% 4 6% 21% 24% 15%	1947
	11th to 20th	Night	19% 4 7% 26% 33% 11%	2444
	21st to end	Night	23% 3 9% 34% 21% 10%	2674
August	1st to 10th	Night	21% 4 8% 37% 26% 3	2521
	11th to 20th	Night	33% 3 18% 31% 14% 2	2521
	21st to end	Night	37% 2 19% 29% 11% 1	3417
September	1st to 10th	Night	32% 3 14% 31% 17% 4	1900
	11th to 20th	Night	38% 3 13% 27% 17% 3	1936
	21st to end	Night	42% 3 18% 25% 10% 1	2090
October	1st to 10th	Night	47% 3 18% 25% 7%	3792
	11th to 20th	Night	49% 4 14% 27% 6%	3918
	21st to end	Night	52% 4 18% 24% 3	4457
November	1st to 10th	Night	65% 6% 12% 13% 4	2620
	11th to 20th	Night	66% 4 13% 12% 4 1	2674
	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	24% 4 18% 31% 17% 7%	180
	21st to end	Day	26% 3 19% 31% 16% 5%	198
February	1st to 10th	Day	32% 11% 27% 21% 8% 1	182
	11th to 20th	Day	23% 11% 24% 26% 14% 3	365
	21st to end	Day	20% 10% 23% 32% 13% 2	379
March	1st to 10th	Day	24% 15% 23% 23% 12% 3	460
	11th to 20th	Day	21% 11% 24% 24% 16% 4	460
	21st to end	Day	26% 10% 25% 19% 17% 3	506
April	1st to 10th	Day	28% 13% 24% 23% 10% 2	460
	11th to 20th	Day	24% 14% 24% 22% 12% 4	452
	21st to end	Day	20% 13% 26% 24% 13% 5%	460
May	1st to 10th	Day	16% 12% 29% 27% 13% 3	463
	11th to 20th	Day	18% 7% 23% 29% 17% 6%	488
	21st to end	Day	19% 9% 19% 26% 20% 6%	634
June	1st to 10th	Day	22% 8% 25% 29% 13% 3	708
	11th to 20th	Day	23% 9% 23% 26% 16% 3	870
	21st to end	Day	14% 7% 22% 30% 23% 4	870
July	1st to 10th	Day	12% 6% 19% 34% 24% 5%	815
	11th to 20th	Day	5% 10% 24% 33% 21% 6%	515
	21st to end	Day	5% 7% 22% 32% 25% 8%	531
August	1st to 10th	Day	8% 5% 20% 33% 23% 11%	487
	11th to 20th	Day	8% 7% 21% 30% 21% 13%	477
	21st to end	Day	13% 8% 21% 30% 20% 8%	539
September	1st to 10th	Day	13% 8% 22% 29% 21% 6%	490
	11th to 20th	Day	17% 7% 20% 28% 24% 5%	490
	21st to end	Day	22% 10% 23% 24% 16% 5%	490
October	1st to 10th	Day	21% 7% 21% 26% 18% 7%	490
	11th to 20th	Day	26% 6% 20% 25% 19% 5%	407
	21st to end	Day	30% 6% 23% 25% 13% 3	330
November	1st to 10th	Day	27% 8% 23% 25% 15% 2	257
	11th to 20th	Day	30% 8% 18% 22% 18% 4	182
	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	27% 5% 19% 33% 14% 2	760
	21st to end	Night	25% 5% 20% 32% 15% 2	836
February	1st to 10th	Night	30% 5% 18% 32% 13% 1	760
	11th to 20th	Night	26% 5% 16% 36% 15% 1	744
	21st to end	Night	21% 7% 17% 32% 21% 3	628
March	1st to 10th	Night	24% 7% 20% 29% 18% 2	760
	11th to 20th	Night	21% 7% 22% 33% 16% 1	760
	21st to end	Night	20% 6% 21% 33% 17% 3	836
April	1st to 10th	Night	20% 9% 18% 34% 18% 2	760
	11th to 20th	Night	21% 6% 21% 34% 17% 1	705
	21st to end	Night	18% 8% 22% 34% 17% 1	447
May	1st to 10th	Night	18% 7% 15% 35% 23% 1	380
	11th to 20th	Night	13% 5% 16% 42% 20% 3	374
	21st to end	Night	21% 3 15% 31% 28% 2	411
June	1st to 10th	Night	21% 6% 18% 38% 16% 2	380
	11th to 20th	Night	22% 6% 16% 33% 21% 2	380
	21st to end	Night	12% 7% 16% 37% 24% 3	380
July	1st to 10th	Night	11% 4 12% 35% 37% 2	370
	11th to 20th	Night	7% 4 15% 38% 33% 3	368
	21st to end	Night	6% 3 10% 42% 37% 3	416
August	1st to 10th	Night	6% 2 11% 32% 43% 7%	378
	11th to 20th	Night	5% 3 9% 39% 38% 7%	376
	21st to end	Night	11% 3 12% 39% 32% 3	781
September	1st to 10th	Night	11% 3 12% 38% 31% 4	760
	11th to 20th	Night	15% 4 11% 30% 34% 7%	760
	21st to end	Night	18% 5% 16% 38% 21% 3	760
October	1st to 10th	Night	18% 4 13% 39% 24% 2	760
	11th to 20th	Night	23% 4 16% 32% 22% 2	760
	21st to end	Night	26% 5% 19% 33% 14% 3	836
November	1st to 10th	Night	32% 6% 16% 38% 8% 1	780
	11th to 20th	Night	30% 7% 21% 26% 12% 2	764
	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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