Tinyblue Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tinyblue Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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	16% 9% 4 7% 6% 4 5% 5% 5% 7% 33%	74814
	Night	19% 10% 4 7% 6% 3 5% 4 5% 6% 31%	74929
Transparency	Day	34% 41% 11% 10% 4 1	74505
	Night	35% 41% 9% 10% 4 1	74756
Seeing	Day	21% 8% 18% 26% 20% 7%	14070
	Night	25% 9% 17% 25% 21% 4	22553

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	23% 15% 6% 12% 6% 4 5% 4 5% 4 17%	1329
	11th to 20th	Day	20% 11% 5% 9% 8% 5% 6% 5% 6% 7% 18%	1381
	21st to end	Day	22% 14% 5% 8% 8% 4 7% 5% 5% 5% 16%	1628
February	1st to 10th	Day	22% 14% 5% 8% 6% 4 6% 6% 5% 6% 17%	1620
	11th to 20th	Day	20% 13% 5% 8% 7% 3 5% 6% 5% 5% 22%	1575
	21st to end	Day	18% 13% 4 8% 7% 4 6% 6% 5% 5% 23%	1374
March	1st to 10th	Day	19% 12% 4 8% 7% 4 7% 6% 6% 7% 21%	1851
	11th to 20th	Day	21% 11% 4 7% 6% 5% 4 6% 5% 7% 25%	1980
	21st to end	Day	17% 10% 5% 10% 8% 5% 6% 6% 6% 6% 20%	2240
April	1st to 10th	Day	19% 10% 4 8% 6% 4 6% 6% 6% 7% 22%	2160
	11th to 20th	Day	20% 9% 4 7% 7% 4 6% 6% 6% 6% 26%	2177
	21st to end	Day	18% 9% 3 7% 7% 4 6% 5% 6% 7% 29%	2380
May	1st to 10th	Day	14% 7% 3 6% 6% 3 6% 5% 6% 8% 36%	2520
	11th to 20th	Day	15% 8% 3 7% 5% 4 5% 6% 6% 8% 34%	2477
	21st to end	Day	21% 8% 4 6% 7% 3 4 5% 4 7% 32%	2723
June	1st to 10th	Day	20% 7% 3 6% 5% 3 4 5% 5% 6% 35%	2632
	11th to 20th	Day	17% 9% 3 7% 7% 3 6% 5% 6% 7% 29%	2700
	21st to end	Day	11% 6% 2 5% 5% 3 5% 5% 6% 8% 43%	2700
July	1st to 10th	Day	10% 6% 2 5% 4 3 4 3 5% 6% 53%	2700
	11th to 20th	Day	10% 4 2 4 4 3 4 4 4 7% 54%	2650
	21st to end	Day	8% 4 2 2 3 2 2 4 3 6% 63%	2741
August	1st to 10th	Day	9% 4 2 4 3 3 4 4 5% 7% 56%	2468
	11th to 20th	Day	7% 4 1 4 4 2 3 4 5% 8% 57%	2298
	21st to end	Day	10% 6% 2 5% 4 3 4 5% 4 7% 49%	2486
September	1st to 10th	Day	10% 5% 2 4 4 3 4 3 4 8% 53%	2160
	11th to 20th	Day	12% 7% 3 7% 6% 3 5% 5% 4 6% 43%	2160
	21st to end	Day	15% 7% 3 7% 5% 3 5% 5% 4 7% 39%	1899
October	1st to 10th	Day	17% 8% 4 7% 6% 3 6% 5% 5% 8% 32%	1800
	11th to 20th	Day	18% 10% 5% 9% 7% 3 4 5% 5% 7% 27%	1800
	21st to end	Day	21% 12% 5% 7% 7% 3 5% 5% 5% 7% 24%	1874
November	1st to 10th	Day	26% 11% 5% 8% 7% 4 5% 5% 5% 6% 19%	1502
	11th to 20th	Day	24% 10% 5% 8% 7% 4 4 4 4 6% 23%	1520
	21st to end	Day	26% 10% 4 8% 7% 4 5% 5% 6% 8% 19%	1520
December	1st to 10th	Day	18% 14% 5% 9% 8% 4 5% 4 4 7% 23%	1520
	11th to 20th	Day	18% 15% 6% 13% 8% 5% 6% 5% 6% 5% 13%	1827
	21st to end	Day	18% 17% 6% 12% 9% 5% 5% 5% 5% 5% 14%	2442
January	1st to 10th	Night	25% 12% 5% 8% 8% 4 6% 4 5% 6% 18%	2836
	11th to 20th	Night	23% 14% 3 7% 6% 4 6% 6% 5% 6% 21%	2621
	21st to end	Night	24% 11% 4 8% 6% 4 6% 5% 5% 7% 20%	2727
February	1st to 10th	Night	24% 13% 4 8% 6% 4 5% 4 5% 5% 22%	2340
	11th to 20th	Night	20% 12% 4 9% 9% 4 5% 4 4 5% 26%	2272
	21st to end	Night	20% 13% 4 7% 7% 4 4 5% 5% 6% 25%	1881
March	1st to 10th	Night	20% 10% 4 7% 6% 4 7% 5% 5% 6% 26%	2106
	11th to 20th	Night	21% 12% 4 6% 6% 4 5% 5% 5% 6% 25%	1979
	21st to end	Night	21% 13% 4 8% 7% 4 5% 5% 6% 6% 21%	2116
April	1st to 10th	Night	21% 11% 4 8% 7% 3 5% 7% 6% 7% 22%	1800
	11th to 20th	Night	19% 11% 4 6% 6% 4 6% 5% 5% 6% 29%	1731
	21st to end	Night	21% 9% 3 6% 6% 4 5% 5% 7% 7% 28%	1580
May	1st to 10th	Night	18% 6% 3 6% 5% 3 4 4 5% 7% 39%	1440
	11th to 20th	Night	17% 6% 4 6% 5% 3 4 5% 6% 8% 37%	1416
	21st to end	Night	22% 8% 4 7% 5% 3 5% 5% 5% 6% 31%	1552
June	1st to 10th	Night	21% 6% 5% 6% 6% 4 4 5% 5% 6% 32%	1324
	11th to 20th	Night	23% 8% 5% 7% 6% 3 5% 3 6% 6% 28%	1260
	21st to end	Night	12% 5% 2 5% 5% 3 5% 4 5% 7% 46%	1260
July	1st to 10th	Night	13% 5% 1 5% 4 2 3 3 4 5% 56%	1260
	11th to 20th	Night	9% 3 2 4 3 2 3 2 4 7% 61%	1309
	21st to end	Night	9% 3 1 3 3 2 3 3 4 5% 65%	1576
August	1st to 10th	Night	9% 4 2 4 3 2 4 3 5% 5% 60%	1469
	11th to 20th	Night	7% 3 2 3 3 1 2 3 4 7% 64%	1602
	21st to end	Night	9% 4 2 4 4 3 4 4 5% 7% 54%	1869
September	1st to 10th	Night	10% 4 3 4 4 2 3 3 4 6% 56%	1800
	11th to 20th	Night	15% 6% 3 5% 4 3 4 5% 5% 7% 42%	1800
	21st to end	Night	14% 7% 3 6% 4 3 4 4 5% 6% 44%	2060
October	1st to 10th	Night	14% 7% 3 8% 7% 3 4 4 4 6% 40%	2160
	11th to 20th	Night	18% 8% 3 6% 5% 4 5% 5% 5% 6% 36%	2160
	21st to end	Night	20% 9% 3 6% 6% 3 5% 4 5% 6% 33%	2481
November	1st to 10th	Night	26% 9% 3 6% 6% 4 5% 5% 5% 6% 25%	2574
	11th to 20th	Night	22% 11% 6% 7% 7% 4 5% 5% 4 5% 25%	2660
	21st to end	Night	22% 12% 5% 7% 7% 4 5% 4 5% 6% 22%	2660
December	1st to 10th	Night	21% 11% 5% 8% 8% 3 5% 5% 4 5% 25%	2660
	11th to 20th	Night	21% 14% 6% 11% 7% 4 5% 5% 4 6% 17%	3374
	21st to end	Night	22% 16% 5% 10% 8% 4 5% 5% 5% 5% 16%	5214

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	46% 44% 4 5% 1	1329
	11th to 20th	Day	41% 46% 6% 5% 1 1	1381
	21st to end	Day	44% 42% 7% 4 2	1628
February	1st to 10th	Day	43% 42% 8% 5% 2	1620
	11th to 20th	Day	39% 42% 9% 6% 4	1584
	21st to end	Day	41% 43% 7% 6% 3	1374
March	1st to 10th	Day	42% 41% 10% 5% 2	1851
	11th to 20th	Day	40% 42% 8% 8% 2	1980
	21st to end	Day	43% 41% 9% 8%	2240
April	1st to 10th	Day	39% 42% 12% 6% 1	2160
	11th to 20th	Day	38% 40% 7% 9% 5% 1	2177
	21st to end	Day	36% 42% 10% 8% 4 1	2380
May	1st to 10th	Day	32% 41% 13% 11% 3	2520
	11th to 20th	Day	30% 41% 13% 13% 5%	2480
	21st to end	Day	38% 40% 12% 9% 2	2724
June	1st to 10th	Day	36% 39% 13% 7% 3 1	2632
	11th to 20th	Day	37% 41% 14% 7% 1	2700
	21st to end	Day	26% 41% 16% 11% 5% 1	2700
July	1st to 10th	Day	19% 41% 13% 18% 7% 2	2626
	11th to 20th	Day	20% 40% 12% 20% 8% 1	2569
	21st to end	Day	15% 39% 12% 22% 10% 2	2589
August	1st to 10th	Day	21% 40% 15% 18% 6%	2451
	11th to 20th	Day	17% 38% 15% 18% 8% 3	2298
	21st to end	Day	22% 40% 14% 18% 6% 1	2486
September	1st to 10th	Day	17% 39% 13% 18% 10% 3	2160
	11th to 20th	Day	26% 39% 11% 13% 10% 1	2160
	21st to end	Day	30% 42% 10% 11% 5% 1	1899
October	1st to 10th	Day	33% 40% 10% 12% 5%	1800
	11th to 20th	Day	35% 41% 12% 9% 2 1	1800
	21st to end	Day	40% 41% 7% 7% 5%	1874
November	1st to 10th	Day	41% 44% 7% 4 3	1502
	11th to 20th	Day	39% 44% 8% 5% 3	1520
	21st to end	Day	41% 44% 6% 6% 2	1520
December	1st to 10th	Day	39% 46% 6% 6% 3	1520
	11th to 20th	Day	51% 37% 7% 5% 1	1829
	21st to end	Day	54% 31% 10% 4 1	2442
January	1st to 10th	Night	44% 44% 5% 5% 1	2836
	11th to 20th	Night	40% 46% 6% 5% 2 1	2621
	21st to end	Night	41% 42% 7% 7% 3 1	2727
February	1st to 10th	Night	42% 41% 8% 7% 2	2340
	11th to 20th	Night	37% 42% 9% 7% 5%	2274
	21st to end	Night	40% 40% 9% 8% 3	1881
March	1st to 10th	Night	38% 41% 10% 9% 2	2106
	11th to 20th	Night	41% 41% 8% 7% 2	1980
	21st to end	Night	42% 41% 9% 7% 1	2116
April	1st to 10th	Night	40% 42% 9% 6% 2	1800
	11th to 20th	Night	35% 40% 10% 8% 6% 1	1731
	21st to end	Night	36% 41% 10% 8% 5% 1	1580
May	1st to 10th	Night	32% 42% 10% 12% 5%	1440
	11th to 20th	Night	28% 41% 14% 11% 5% 1	1416
	21st to end	Night	39% 41% 8% 10% 2	1552
June	1st to 10th	Night	37% 40% 11% 7% 3 2	1324
	11th to 20th	Night	38% 41% 14% 7% 1	1260
	21st to end	Night	24% 41% 16% 12% 5% 3	1260
July	1st to 10th	Night	20% 39% 11% 19% 7% 3	1225
	11th to 20th	Night	15% 40% 13% 23% 9% 1	1267
	21st to end	Night	13% 40% 10% 18% 15% 4	1488
August	1st to 10th	Night	18% 39% 13% 19% 8% 2	1461
	11th to 20th	Night	14% 38% 13% 18% 14% 3	1602
	21st to end	Night	20% 40% 13% 18% 8% 1	1869
September	1st to 10th	Night	15% 39% 10% 21% 10% 4	1800
	11th to 20th	Night	25% 40% 8% 12% 12% 3	1800
	21st to end	Night	26% 40% 10% 17% 7% 1	2060
October	1st to 10th	Night	30% 39% 9% 14% 7%	2160
	11th to 20th	Night	29% 41% 13% 13% 4	2160
	21st to end	Night	32% 41% 10% 11% 5%	2481
November	1st to 10th	Night	37% 46% 8% 6% 3 1	2574
	11th to 20th	Night	39% 44% 9% 6% 2	2660
	21st to end	Night	40% 44% 8% 6% 2	2660
December	1st to 10th	Night	38% 44% 9% 6% 3	2660
	11th to 20th	Night	46% 40% 8% 4 1	3371
	21st to end	Night	52% 34% 7% 6% 1	5214

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	33% 13% 24% 17% 10% 3	180
	11th to 20th	Day	27% 16% 29% 12% 13% 2	164
	21st to end	Day	40% 9% 17% 21% 10% 2	220
February	1st to 10th	Day	36% 14% 20% 17% 11% 1	340
	11th to 20th	Day	38% 10% 21% 21% 10% 1	335
	21st to end	Day	27% 16% 22% 21% 12% 2	300
March	1st to 10th	Day	27% 12% 24% 24% 11% 2	420
	11th to 20th	Day	27% 15% 15% 22% 15% 6%	420
	21st to end	Day	29% 11% 24% 19% 13% 3	462
April	1st to 10th	Day	26% 14% 20% 23% 13% 5%	420
	11th to 20th	Day	23% 13% 24% 22% 10% 8%	412
	21st to end	Day	22% 10% 22% 27% 15% 3	420
May	1st to 10th	Day	14% 9% 20% 33% 20% 4	423
	11th to 20th	Day	20% 6% 15% 29% 19% 11%	448
	21st to end	Day	19% 5% 14% 31% 21% 11%	485
June	1st to 10th	Day	19% 6% 22% 28% 19% 5%	562
	11th to 20th	Day	18% 7% 22% 30% 19% 4	630
	21st to end	Day	12% 5% 17% 34% 25% 8%	630
July	1st to 10th	Day	10% 5% 15% 31% 29% 10%	621
	11th to 20th	Day	9% 5% 15% 29% 31% 11%	568
	21st to end	Day	7% 3 8% 31% 36% 15%	487
August	1st to 10th	Day	9% 2 9% 27% 37% 16%	447
	11th to 20th	Day	6% 1 9% 35% 33% 16%	437
	21st to end	Day	11% 4 15% 34% 26% 9%	495
September	1st to 10th	Day	15% 3 16% 34% 27% 5%	450
	11th to 20th	Day	15% 6% 16% 27% 30% 7%	450
	21st to end	Day	20% 6% 20% 26% 23% 5%	450
October	1st to 10th	Day	22% 7% 20% 21% 21% 9%	450
	11th to 20th	Day	26% 10% 20% 20% 18% 8%	450
	21st to end	Day	31% 13% 21% 18% 14% 4	389
November	1st to 10th	Day	42% 11% 18% 19% 10% 1	187
	11th to 20th	Day	34% 9% 24% 12% 14% 7%	180
	21st to end	Day	33% 13% 21% 15% 7% 10%	180
December	1st to 10th	Day	32% 13% 22% 12% 13% 8%	180
	11th to 20th	Day	35% 17% 25% 16% 6% 1	180
	21st to end	Day	31% 16% 26% 18% 7% 2	198
January	1st to 10th	Night	34% 12% 22% 18% 12% 3	850
	11th to 20th	Night	33% 13% 13% 20% 18% 2	761
	21st to end	Night	31% 9% 18% 22% 17% 3	792
February	1st to 10th	Night	32% 12% 19% 22% 13% 3	720
	11th to 20th	Night	28% 11% 19% 25% 16% 1	704
	21st to end	Night	28% 11% 20% 24% 14% 3	592
March	1st to 10th	Night	27% 13% 20% 23% 15% 2	720
	11th to 20th	Night	29% 14% 18% 23% 14% 3	720
	21st to end	Night	28% 12% 20% 26% 11% 2	792
April	1st to 10th	Night	27% 8% 19% 27% 16% 3	720
	11th to 20th	Night	24% 8% 22% 26% 16% 4	663
	21st to end	Night	25% 7% 21% 30% 14% 3	500
May	1st to 10th	Night	19% 6% 18% 32% 21% 4	360
	11th to 20th	Night	19% 3 15% 27% 33% 3	354
	21st to end	Night	23% 5% 14% 28% 24% 5%	389
June	1st to 10th	Night	23% 5% 19% 33% 18% 2	360
	11th to 20th	Night	24% 7% 19% 28% 19% 3	360
	21st to end	Night	15% 4 11% 36% 31% 2	360
July	1st to 10th	Night	13% 3 11% 33% 36% 4	350
	11th to 20th	Night	9% 3 14% 31% 40% 3	348
	21st to end	Night	7% 3 11% 33% 42% 5%	394
August	1st to 10th	Night	12% 2 7% 24% 47% 8%	395
	11th to 20th	Night	7% 1 7% 27% 45% 13%	534
	21st to end	Night	12% 4 12% 30% 37% 5%	681
September	1st to 10th	Night	12% 3 8% 37% 33% 7%	720
	11th to 20th	Night	17% 4 13% 22% 32% 12%	720
	21st to end	Night	18% 6% 17% 27% 26% 6%	720
October	1st to 10th	Night	18% 7% 15% 26% 26% 8%	720
	11th to 20th	Night	24% 9% 17% 21% 23% 6%	720
	21st to end	Night	27% 9% 18% 26% 16% 4	792
November	1st to 10th	Night	32% 11% 19% 25% 13%	740
	11th to 20th	Night	33% 9% 21% 21% 13% 4	760
	21st to end	Night	32% 10% 19% 20% 15% 5%	760
December	1st to 10th	Night	29% 11% 16% 24% 17% 3	760
	11th to 20th	Night	35% 12% 21% 19% 12% 2	787
	21st to end	Night	37% 13% 22% 18% 9% 1	935

Page generated at 2024-01-09 22:25:00. Version ac07

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