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 2024-11-10.

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% 3 8% 5% 5% 4 4 5% 6% 35%	105606
	Night	18% 10% 3 8% 5% 4 4 3 5% 6% 32%	102153
Transparency	Day	26% 48% 9% 11% 5% 1	105360
	Night	29% 49% 8% 10% 4 1	102045
Seeing	Day	21% 9% 19% 26% 20% 7%	15236
	Night	25% 9% 17% 25% 20% 4	23532

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% 18% 6% 12% 7% 6% 5% 3 5% 4 12%	2219
	11th to 20th	Day	20% 11% 4 9% 5% 5% 5% 4 7% 7% 21%	2387
	21st to end	Day	23% 17% 5% 11% 8% 6% 6% 4 5% 5% 11%	2866
February	1st to 10th	Day	22% 14% 5% 10% 6% 5% 5% 5% 6% 6% 17%	1710
	11th to 20th	Day	20% 14% 4 9% 6% 5% 5% 5% 5% 6% 21%	1665
	21st to end	Day	18% 13% 5% 9% 6% 6% 5% 5% 5% 5% 23%	1458
March	1st to 10th	Day	14% 11% 3 10% 8% 6% 7% 5% 7% 8% 21%	3228
	11th to 20th	Day	16% 9% 2 6% 4 5% 5% 4 5% 6% 37%	3490
	21st to end	Day	18% 10% 4 11% 7% 7% 6% 4 6% 6% 21%	3938
April	1st to 10th	Day	19% 12% 4 9% 5% 6% 6% 5% 6% 6% 22%	2280
	11th to 20th	Day	19% 11% 3 7% 6% 5% 5% 5% 6% 6% 28%	2300
	21st to end	Day	19% 9% 3 8% 6% 5% 5% 4 6% 6% 28%	2513
May	1st to 10th	Day	17% 8% 2 5% 4 4 4 3 5% 6% 42%	4420
	11th to 20th	Day	14% 6% 2 6% 4 4 5% 4 6% 8% 41%	4377
	21st to end	Day	27% 9% 3 8% 5% 5% 4 4 4 6% 25%	4813
June	1st to 10th	Day	20% 8% 3 7% 4 4 4 4 6% 6% 34%	2779
	11th to 20th	Day	17% 9% 3 8% 6% 5% 6% 4 6% 7% 29%	2850
	21st to end	Day	12% 7% 2 6% 5% 4 4 4 7% 7% 42%	2850
July	1st to 10th	Day	6% 4 1 4 2 3 2 2 4 4 68%	4740
	11th to 20th	Day	6% 3 1 3 3 2 3 3 4 5% 67%	4648
	21st to end	Day	11% 6% 2 4 3 3 2 3 3 5% 57%	4790
August	1st to 10th	Day	5% 3 1 4 2 3 3 3 5% 7% 63%	4323
	11th to 20th	Day	9% 8% 3 7% 4 4 4 3 5% 7% 45%	4026
	21st to end	Day	13% 8% 3 7% 4 4 3 3 3 5% 46%	4368
September	1st to 10th	Day	10% 5% 2 5% 3 4 4 2 5% 8% 52%	2280
	11th to 20th	Day	12% 8% 2 8% 5% 4 5% 4 4 6% 41%	2280
	21st to end	Day	14% 7% 3 8% 4 4 5% 4 5% 7% 39%	2003
October	1st to 10th	Day	13% 7% 3 8% 6% 6% 6% 5% 7% 9% 31%	3180
	11th to 20th	Day	21% 13% 4 10% 5% 4 4 3 5% 6% 25%	3161
	21st to end	Day	17% 12% 5% 13% 7% 6% 5% 4 5% 6% 20%	3261
November	1st to 10th	Day	25% 12% 5% 9% 6% 5% 5% 4 5% 6% 18%	1574
	11th to 20th	Day	24% 11% 4 9% 6% 5% 4 3 4 6% 23%	1520
	21st to end	Day	25% 11% 3 10% 6% 5% 5% 3 6% 7% 19%	1520
December	1st to 10th	Day	17% 16% 3 9% 7% 5% 5% 3 5% 7% 22%	1520
	11th to 20th	Day	18% 16% 5% 14% 7% 7% 5% 4 6% 5% 13%	1827
	21st to end	Day	18% 18% 6% 13% 7% 6% 5% 4 5% 5% 14%	2442
January	1st to 10th	Night	23% 17% 5% 11% 8% 6% 6% 3 5% 5% 13%	4726
	11th to 20th	Night	22% 12% 3 7% 5% 4 4 4 7% 7% 26%	4509
	21st to end	Night	26% 13% 4 10% 6% 6% 5% 4 5% 6% 14%	4791
February	1st to 10th	Night	23% 14% 4 9% 5% 4 5% 4 5% 6% 21%	2470
	11th to 20th	Night	19% 13% 3 11% 7% 5% 5% 3 4 4 25%	2402
	21st to end	Night	19% 15% 3 8% 6% 4 4 4 5% 6% 24%	1995
March	1st to 10th	Night	14% 13% 4 11% 7% 7% 7% 5% 6% 6% 19%	3643
	11th to 20th	Night	13% 10% 2 6% 5% 4 4 4 6% 6% 41%	3489
	21st to end	Night	23% 14% 4 10% 6% 5% 5% 4 5% 5% 19%	3715
April	1st to 10th	Night	21% 12% 3 9% 7% 4 5% 5% 6% 7% 21%	1900
	11th to 20th	Night	19% 11% 3 7% 6% 5% 5% 4 5% 6% 30%	1828
	21st to end	Night	21% 10% 3 7% 6% 6% 4 4 7% 7% 26%	1667
May	1st to 10th	Night	16% 7% 2 7% 4 4 3 3 4 5% 45%	2540
	11th to 20th	Night	15% 5% 3 6% 4 4 3 3 5% 6% 45%	2516
	21st to end	Night	26% 9% 4 8% 4 4 4 3 5% 6% 26%	2762
June	1st to 10th	Night	22% 7% 3 7% 5% 4 4 4 6% 6% 32%	1397
	11th to 20th	Night	23% 9% 4 9% 5% 4 4 3 6% 6% 28%	1330
	21st to end	Night	13% 6% 2 6% 5% 5% 5% 3 6% 6% 45%	1330
July	1st to 10th	Night	10% 4 1 4 2 2 2 2 3 3 67%	2220
	11th to 20th	Night	5% 2 1 2 2 2 1 2 3 5% 74%	2311
	21st to end	Night	14% 4 1 4 4 3 3 3 5% 5% 54%	2762
August	1st to 10th	Night	5% 3 1 3 3 3 3 3 4 5% 67%	2608
	11th to 20th	Night	12% 6% 3 7% 4 3 4 2 4 6% 49%	2812
	21st to end	Night	15% 6% 2 6% 3 3 4 3 4 5% 50%	3303
September	1st to 10th	Night	10% 4 3 5% 4 3 3 3 4 6% 56%	1900
	11th to 20th	Night	15% 8% 3 6% 4 4 4 4 5% 7% 41%	1900
	21st to end	Night	14% 7% 3 7% 3 4 4 3 5% 6% 44%	2175
October	1st to 10th	Night	13% 6% 3 8% 5% 4 4 4 6% 8% 39%	3800
	11th to 20th	Night	21% 10% 3 7% 4 4 4 3 5% 6% 32%	3777
	21st to end	Night	20% 11% 4 10% 6% 5% 5% 3 5% 6% 26%	4301
November	1st to 10th	Night	26% 10% 3 8% 5% 5% 5% 4 5% 6% 24%	2706
	11th to 20th	Night	21% 13% 5% 8% 6% 5% 4 4 4 5% 24%	2660
	21st to end	Night	21% 14% 4 8% 6% 6% 5% 3 5% 6% 22%	2660
December	1st to 10th	Night	21% 13% 4 9% 7% 4 4 3 5% 5% 25%	2660
	11th to 20th	Night	21% 14% 6% 12% 6% 5% 5% 4 5% 6% 16%	3374
	21st to end	Night	22% 17% 4 11% 6% 6% 5% 4 5% 5% 15%	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% 42% 5% 5% 1	2219
	11th to 20th	Day	34% 41% 12% 11% 2	2411
	21st to end	Day	48% 45% 4 3	2866
February	1st to 10th	Day	25% 67% 3 3 2 1	1710
	11th to 20th	Day	27% 65% 3 3 2	1674
	21st to end	Day	22% 66% 5% 4 3	1458
March	1st to 10th	Day	30% 46% 12% 8% 3	3228
	11th to 20th	Day	23% 43% 12% 21% 1	3490
	21st to end	Day	35% 47% 11% 7% 1	3938
April	1st to 10th	Day	22% 67% 6% 5%	2280
	11th to 20th	Day	19% 66% 6% 6% 2 1	2300
	21st to end	Day	20% 66% 5% 6% 2	2513
May	1st to 10th	Day	23% 43% 10% 16% 8% 1	4420
	11th to 20th	Day	21% 45% 18% 13% 3	4380
	21st to end	Day	36% 45% 13% 5% 1	4814
June	1st to 10th	Day	15% 67% 9% 7% 3	2779
	11th to 20th	Day	17% 66% 7% 7% 3	2850
	21st to end	Day	15% 64% 9% 9% 2	2850
July	1st to 10th	Day	10% 36% 4 17% 21% 12%	4666
	11th to 20th	Day	8% 37% 5% 21% 27% 2	4567
	21st to end	Day	21% 37% 16% 19% 7%	4639
August	1st to 10th	Day	11% 38% 8% 29% 14% 1	4306
	11th to 20th	Day	27% 40% 15% 14% 4 1	4065
	21st to end	Day	29% 37% 8% 18% 7%	4367
September	1st to 10th	Day	17% 61% 9% 7% 5% 1	2280
	11th to 20th	Day	20% 61% 7% 5% 6%	2280
	21st to end	Day	19% 61% 8% 8% 4	2003
October	1st to 10th	Day	29% 41% 14% 14% 2	3180
	11th to 20th	Day	42% 37% 8% 9% 4	3161
	21st to end	Day	42% 39% 8% 7% 4	3261
November	1st to 10th	Day	30% 58% 7% 4 1	1574
	11th to 20th	Day	23% 61% 6% 5% 3 2	1520
	21st to end	Day	24% 60% 4 6% 4	1520
December	1st to 10th	Day	26% 60% 2 8% 3	1520
	11th to 20th	Day	39% 50% 5% 4 1	1829
	21st to end	Day	47% 41% 8% 3 1	2442
January	1st to 10th	Night	45% 42% 6% 4 2	4726
	11th to 20th	Night	33% 39% 11% 14% 2	4547
	21st to end	Night	47% 45% 5% 3 1	4791
February	1st to 10th	Night	24% 66% 4 3 3 1	2470
	11th to 20th	Night	26% 64% 4 4 1 1	2404
	21st to end	Night	22% 65% 5% 6% 2	1995
March	1st to 10th	Night	37% 47% 7% 6% 3	3643
	11th to 20th	Night	18% 45% 14% 22% 1 1	3490
	21st to end	Night	40% 45% 8% 6% 1	3715
April	1st to 10th	Night	21% 66% 7% 5% 1	1900
	11th to 20th	Night	20% 66% 5% 6% 2 1	1828
	21st to end	Night	22% 66% 5% 5% 2	1667
May	1st to 10th	Night	20% 43% 8% 19% 9% 1	2540
	11th to 20th	Night	19% 44% 19% 13% 4	2516
	21st to end	Night	34% 49% 11% 5% 1	2762
June	1st to 10th	Night	17% 66% 9% 7% 2	1397
	11th to 20th	Night	19% 65% 6% 7% 2	1330
	21st to end	Night	16% 64% 10% 8% 2	1330
July	1st to 10th	Night	12% 36% 5% 18% 18% 12%	2185
	11th to 20th	Night	7% 35% 5% 20% 32% 1	2269
	21st to end	Night	22% 38% 11% 18% 10%	2674
August	1st to 10th	Night	9% 38% 8% 29% 14% 1	2600
	11th to 20th	Night	28% 39% 16% 13% 4 1	2839
	21st to end	Night	27% 38% 9% 18% 7%	3303
September	1st to 10th	Night	16% 62% 8% 8% 6% 1	1900
	11th to 20th	Night	21% 61% 5% 6% 6% 1	1900
	21st to end	Night	18% 61% 6% 11% 3	2175
October	1st to 10th	Night	27% 39% 15% 17% 2	3800
	11th to 20th	Night	36% 39% 9% 13% 3	3777
	21st to end	Night	41% 39% 9% 7% 4	4301
November	1st to 10th	Night	29% 57% 7% 6% 1	2706
	11th to 20th	Night	25% 61% 4 5% 3 2	2660
	21st to end	Night	25% 61% 4 5% 5% 1	2660
December	1st to 10th	Night	26% 61% 3 6% 3	2660
	11th to 20th	Night	36% 53% 5% 3 2	3371
	21st to end	Night	43% 44% 6% 6% 2	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	32% 13% 24% 17% 11% 3	180
	11th to 20th	Day	27% 16% 26% 15% 14% 2	180
	21st to end	Day	39% 10% 19% 20% 9% 2	244
February	1st to 10th	Day	35% 14% 20% 19% 11% 1	370
	11th to 20th	Day	36% 9% 21% 21% 10% 1	365
	21st to end	Day	28% 17% 21% 21% 11% 2	330
March	1st to 10th	Day	26% 13% 23% 23% 12% 2	460
	11th to 20th	Day	25% 14% 16% 23% 15% 7%	460
	21st to end	Day	29% 10% 25% 20% 13% 3	506
April	1st to 10th	Day	26% 15% 18% 23% 13% 4	460
	11th to 20th	Day	21% 13% 26% 22% 10% 7%	452
	21st to end	Day	22% 11% 22% 26% 16% 3	460
May	1st to 10th	Day	14% 9% 20% 33% 19% 5%	463
	11th to 20th	Day	18% 6% 15% 30% 19% 11%	488
	21st to end	Day	21% 6% 13% 30% 20% 10%	529
June	1st to 10th	Day	19% 7% 22% 29% 19% 5%	609
	11th to 20th	Day	18% 8% 23% 29% 18% 4	680
	21st to end	Day	12% 5% 18% 33% 24% 8%	680
July	1st to 10th	Day	10% 4 17% 32% 28% 10%	671
	11th to 20th	Day	8% 5% 15% 30% 32% 11%	615
	21st to end	Day	8% 3 10% 31% 34% 14%	531
August	1st to 10th	Day	8% 2 9% 28% 37% 15%	487
	11th to 20th	Day	6% 2 10% 34% 32% 16%	477
	21st to end	Day	12% 5% 15% 33% 26% 9%	539
September	1st to 10th	Day	15% 3 15% 34% 28% 6%	490
	11th to 20th	Day	16% 6% 16% 27% 28% 6%	490
	21st to end	Day	21% 7% 20% 26% 23% 5%	490
October	1st to 10th	Day	21% 8% 21% 21% 21% 8%	490
	11th to 20th	Day	27% 10% 19% 19% 17% 7%	490
	21st to end	Day	29% 13% 22% 19% 13% 4	427
November	1st to 10th	Day	40% 12% 18% 19% 10%	205
	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	32% 13% 14% 20% 19% 2	795
	21st to end	Night	32% 10% 18% 21% 16% 3	836
February	1st to 10th	Night	31% 12% 19% 22% 12% 3	760
	11th to 20th	Night	27% 11% 19% 25% 17% 1	744
	21st to end	Night	28% 13% 19% 24% 14% 3	628
March	1st to 10th	Night	26% 13% 21% 23% 14% 2	760
	11th to 20th	Night	27% 14% 18% 23% 15% 3	760
	21st to end	Night	28% 12% 21% 26% 11% 2	836
April	1st to 10th	Night	27% 8% 19% 26% 17% 2	760
	11th to 20th	Night	23% 8% 22% 27% 16% 4	700
	21st to end	Night	25% 8% 21% 29% 14% 3	527
May	1st to 10th	Night	19% 6% 19% 32% 21% 4	380
	11th to 20th	Night	18% 4 16% 27% 32% 3	374
	21st to end	Night	24% 6% 14% 28% 23% 5%	411
June	1st to 10th	Night	23% 5% 19% 33% 18% 2	380
	11th to 20th	Night	24% 7% 20% 27% 19% 3	380
	21st to end	Night	17% 4 12% 36% 30% 2	380
July	1st to 10th	Night	12% 3 12% 34% 35% 4	370
	11th to 20th	Night	9% 3 14% 32% 39% 3	368
	21st to end	Night	7% 3 12% 33% 41% 5%	416
August	1st to 10th	Night	12% 2 7% 25% 46% 8%	418
	11th to 20th	Night	9% 1 7% 27% 44% 13%	564
	21st to end	Night	13% 4 12% 30% 37% 4	719
September	1st to 10th	Night	12% 3 8% 36% 34% 7%	760
	11th to 20th	Night	17% 5% 13% 22% 31% 12%	760
	21st to end	Night	17% 6% 17% 27% 27% 6%	760
October	1st to 10th	Night	18% 7% 16% 27% 25% 8%	760
	11th to 20th	Night	24% 10% 16% 22% 22% 6%	760
	21st to end	Night	28% 9% 19% 26% 15% 4	836
November	1st to 10th	Night	33% 11% 20% 24% 13%	778
	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 2024-11-07 03:55:50. Version ac07

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