Pine Flat Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pine Flat Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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	4 5% 1 3 2 2 3 2 4 5% 68%	139730
	Night	5% 6% 2 4 2 2 3 2 4 5% 65%	139603
Transparency	Day	18% 4 5% 18% 28% 26%	134806
	Night	20% 5% 6% 18% 28% 22%	135501
Seeing	Day	12% 12% 33% 29% 10% 4	17185
	Night	10% 4 17% 36% 28% 5%	26927

By Month

Percentage Cloud Cover SW (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	9% 5% 3 6% 4 3 5% 3 5% 8% 49%	4722
	11th to 20th	Day	4 3 1 4 3 3 3 3 5% 7% 65%	5072
	21st to end	Day	6% 7% 2 6% 4 4 4 3 6% 8% 50%	5979
February	1st to 10th	Day	11% 11% 3 4 2 2 3 2 5% 5% 52%	2100
	11th to 20th	Day	9% 11% 3 4 4 3 4 3 4 7% 48%	2050
	21st to end	Day	12% 12% 4 4 4 3 3 2 4 7% 46%	1730
March	1st to 10th	Day	11% 16% 5% 7% 4 4 4 3 4 6% 37%	4618
	11th to 20th	Day	7% 10% 2 4 3 4 3 4 6% 9% 48%	4829
	21st to end	Day	8% 14% 3 7% 4 4 4 3 5% 7% 42%	6101
April	1st to 10th	Day	8% 9% 2 5% 4 2 3 3 5% 7% 53%	2413
	11th to 20th	Day	8% 7% 2 4 3 2 3 3 5% 8% 55%	2369
	21st to end	Day	5% 8% 1 3 3 3 2 3 5% 7% 59%	2400
May	1st to 10th	Day	3 4 2 4 2 3 3 2 4 5% 68%	5650
	11th to 20th	Day	3 3 1 3 2 2 3 2 3 5% 72%	5841
	21st to end	Day	3 2 1 2 1 2 2 2 3 5% 79%	6524
June	1st to 10th	Day	3 2 1 3 2 2 2 3 5% 7% 70%	2800
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 3 84%	2800
	21st to end	Day	1 2 1 2 1 2 1 2 2 86%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 92%	6319
	11th to 20th	Day	1 1 1 1 1 2 1 2 3 86%	6320
	21st to end	Day	1 1 1 1 1 1 1 2 4 87%	6420
August	1st to 10th	Day	1 1 2 2 2 2 2 3 4 83%	5346
	11th to 20th	Day	1 1 1 1 2 93%	5364
	21st to end	Day	1 1 2 2 2 2 2 2 3 85%	5984
September	1st to 10th	Day	2 1 1 1 2 2 2 3 4 82%	2400
	11th to 20th	Day	1 1 1 1 1 2 2 2 2 4 84%	2290
	21st to end	Day	1 1 1 2 1 2 2 2 3 3 82%	2200
October	1st to 10th	Day	3 3 1 1 2 2 2 2 3 4 77%	3578
	11th to 20th	Day	2 2 1 3 3 2 3 2 3 3 76%	3261
	21st to end	Day	3 4 2 5% 2 3 3 3 4 6% 64%	3469
November	1st to 10th	Day	4 8% 2 3 2 2 3 2 4 7% 63%	1854
	11th to 20th	Day	6% 5% 2 4 2 3 3 2 5% 6% 62%	1890
	21st to end	Day	8% 6% 2 4 3 3 4 4 5% 6% 56%	1890
December	1st to 10th	Day	4 4 2 3 3 3 4 3 5% 5% 63%	3040
	11th to 20th	Day	10% 8% 2 4 3 3 4 4 5% 7% 50%	3215
	21st to end	Day	9% 9% 3 5% 3 5% 5% 4 7% 8% 43%	4092
January	1st to 10th	Night	9% 10% 3 6% 4 3 3 3 4 6% 49%	8172
	11th to 20th	Night	4 5% 2 3 2 2 3 3 5% 6% 65%	7900
	21st to end	Night	8% 8% 3 6% 4 4 4 3 5% 6% 49%	8227
February	1st to 10th	Night	11% 13% 3 5% 4 2 2 3 5% 5% 48%	2520
	11th to 20th	Night	9% 11% 3 4 2 3 4 3 5% 6% 52%	2458
	21st to end	Night	10% 11% 4 5% 3 3 4 2 4 5% 50%	2076
March	1st to 10th	Night	8% 17% 4 7% 4 3 5% 3 5% 6% 39%	5496
	11th to 20th	Night	6% 9% 3 5% 4 4 5% 4 5% 7% 50%	5385
	21st to end	Night	7% 12% 3 6% 4 4 5% 4 5% 8% 43%	5116
April	1st to 10th	Night	8% 8% 2 5% 3 3 4 2 5% 6% 54%	2010
	11th to 20th	Night	6% 8% 2 3 3 3 3 2 4 6% 58%	1979
	21st to end	Night	5% 8% 2 3 3 2 2 2 3 6% 64%	2000
May	1st to 10th	Night	5% 6% 1 3 2 2 2 2 3 4 70%	4337
	11th to 20th	Night	3 3 1 2 1 2 1 1 3 5% 78%	4074
	21st to end	Night	3 1 1 1 1 1 1 1 2 3 84%	4350
June	1st to 10th	Night	4 3 1 3 2 2 2 2 4 5% 73%	1600
	11th to 20th	Night	1 1 1 1 1 1 2 2 2 5% 84%	1600
	21st to end	Night	1 1 1 1 1 2 1 3 3 87%	1600
July	1st to 10th	Night	1 1 1 1 2 93%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 88%	3640
	21st to end	Night	1 1 1 1 1 1 1 2 3 88%	4448
August	1st to 10th	Night	1 1 1 1 1 2 1 2 4 85%	4486
	11th to 20th	Night	1 1 1 1 2 94%	4506
	21st to end	Night	1 1 1 1 2 2 2 3 86%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 88%	2000
	11th to 20th	Night	1 1 1 2 1 1 1 2 3 2 84%	2110
	21st to end	Night	1 2 1 1 1 2 2 2 3 3 83%	2200
October	1st to 10th	Night	2 2 1 1 1 1 1 2 3 83%	3617
	11th to 20th	Night	2 2 1 2 2 2 3 3 4 3 77%	3897
	21st to end	Night	2 5% 1 4 2 2 2 2 3 4 73%	4336
November	1st to 10th	Night	5% 6% 2 3 3 2 3 2 4 6% 63%	2665
	11th to 20th	Night	5% 5% 2 4 3 2 3 3 5% 7% 60%	2730
	21st to end	Night	7% 7% 2 5% 3 3 3 3 5% 6% 56%	2730
December	1st to 10th	Night	5% 4 2 4 3 3 3 3 5% 6% 63%	4370
	11th to 20th	Night	10% 6% 2 5% 4 4 4 4 7% 9% 46%	5207
	21st to end	Night	6% 7% 3 8% 6% 6% 7% 5% 8% 10% 35%	7106

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	25% 10% 7% 28% 20% 9%	4723
	11th to 20th	Day	16% 7% 5% 15% 19% 37%	5072
	21st to end	Day	29% 6% 5% 14% 30% 16%	5979
February	1st to 10th	Day	33% 5% 6% 18% 25% 13%	2100
	11th to 20th	Day	34% 5% 7% 19% 24% 11%	2060
	21st to end	Day	37% 7% 8% 21% 22% 5%	1730
March	1st to 10th	Day	41% 10% 5% 15% 19% 11%	4618
	11th to 20th	Day	30% 7% 13% 30% 14% 7%	4829
	21st to end	Day	33% 11% 10% 24% 16% 5%	6101
April	1st to 10th	Day	30% 7% 11% 27% 19% 7%	2413
	11th to 20th	Day	25% 7% 10% 27% 24% 8%	2372
	21st to end	Day	22% 6% 11% 34% 23% 3	2400
May	1st to 10th	Day	17% 5% 9% 30% 32% 8%	5650
	11th to 20th	Day	14% 3 5% 30% 43% 5%	5844
	21st to end	Day	10% 2 4 25% 51% 7%	6525
June	1st to 10th	Day	14% 5% 9% 23% 35% 14%	2800
	11th to 20th	Day	7% 3 5% 15% 43% 28%	2800
	21st to end	Day	7% 2 3 9% 36% 44%	2800
July	1st to 10th	Day	3 1 1 4 18% 73%	6251
	11th to 20th	Day	8% 1 2 6% 26% 57%	6245
	21st to end	Day	6% 1 2 13% 36% 43%	6234
August	1st to 10th	Day	9% 1 2 7% 36% 45%	3890
	11th to 20th	Day	4 1 1 6% 28% 59%	3880
	21st to end	Day	5% 1 1 9% 27% 56%	4311
September	1st to 10th	Day	8% 2 3 11% 32% 44%	2400
	11th to 20th	Day	8% 2 3 15% 41% 31%	2290
	21st to end	Day	9% 2 2 19% 34% 33%	2200
October	1st to 10th	Day	12% 2 3 11% 21% 52%	3578
	11th to 20th	Day	13% 2 2 16% 41% 25%	3261
	21st to end	Day	19% 3 3 12% 36% 28%	3469
November	1st to 10th	Day	20% 7% 4 19% 28% 22%	1854
	11th to 20th	Day	23% 3 7% 20% 27% 20%	1890
	21st to end	Day	28% 4 7% 15% 25% 21%	1890
December	1st to 10th	Day	22% 4 4 17% 30% 23%	3040
	11th to 20th	Day	31% 5% 8% 19% 25% 10%	3215
	21st to end	Day	34% 7% 9% 24% 18% 8%	4092
January	1st to 10th	Night	30% 9% 6% 23% 21% 11%	8172
	11th to 20th	Night	16% 8% 5% 14% 25% 31%	7900
	21st to end	Night	30% 8% 4 12% 29% 17%	8227
February	1st to 10th	Night	36% 5% 5% 15% 23% 15%	2520
	11th to 20th	Night	31% 5% 7% 20% 24% 13%	2459
	21st to end	Night	34% 6% 8% 22% 23% 7%	2076
March	1st to 10th	Night	37% 11% 6% 16% 23% 7%	5496
	11th to 20th	Night	28% 8% 12% 32% 13% 7%	5385
	21st to end	Night	31% 11% 19% 19% 17% 3	5116
April	1st to 10th	Night	29% 7% 10% 28% 17% 8%	2010
	11th to 20th	Night	24% 7% 11% 28% 23% 7%	1979
	21st to end	Night	19% 7% 10% 39% 22% 3	2000
May	1st to 10th	Night	17% 5% 7% 35% 31% 5%	4334
	11th to 20th	Night	12% 2 5% 37% 42% 3	4075
	21st to end	Night	8% 2 4 30% 51% 5%	4350
June	1st to 10th	Night	14% 3 10% 23% 39% 11%	1600
	11th to 20th	Night	6% 3 7% 18% 40% 26%	1600
	21st to end	Night	6% 2 2 11% 39% 40%	1600
July	1st to 10th	Night	3 1 1 4 21% 71%	3600
	11th to 20th	Night	5% 1 2 7% 28% 56%	3592
	21st to end	Night	6% 1 2 13% 39% 38%	4322
August	1st to 10th	Night	8% 1 2 10% 38% 41%	3256
	11th to 20th	Night	3 1 1 8% 26% 61%	3256
	21st to end	Night	5% 1 1 10% 32% 52%	3608
September	1st to 10th	Night	6% 2 2 10% 34% 45%	2000
	11th to 20th	Night	9% 2 3 15% 43% 28%	2110
	21st to end	Night	8% 2 3 20% 35% 33%	2200
October	1st to 10th	Night	9% 2 3 11% 22% 53%	3617
	11th to 20th	Night	11% 3 2 14% 43% 27%	3897
	21st to end	Night	16% 2 2 12% 38% 30%	4336
November	1st to 10th	Night	20% 6% 6% 16% 31% 22%	2665
	11th to 20th	Night	22% 4 7% 18% 25% 24%	2730
	21st to end	Night	28% 5% 7% 14% 26% 21%	2730
December	1st to 10th	Night	21% 4 4 18% 31% 22%	4370
	11th to 20th	Night	29% 6% 9% 21% 21% 13%	5207
	21st to end	Night	33% 10% 12% 22% 18% 6%	7106

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	27% 12% 29% 28% 4	220
	11th to 20th	Day	19% 11% 33% 25% 10% 2	331
	21st to end	Day	16% 13% 36% 26% 9%	498
February	1st to 10th	Day	20% 16% 33% 21% 8% 2	540
	11th to 20th	Day	24% 17% 32% 22% 4 1	535
	21st to end	Day	22% 19% 35% 19% 5%	446
March	1st to 10th	Day	27% 18% 33% 18% 4	540
	11th to 20th	Day	21% 19% 30% 23% 6% 1	540
	21st to end	Day	26% 19% 32% 17% 5%	594
April	1st to 10th	Day	20% 19% 29% 23% 9% 1	505
	11th to 20th	Day	23% 18% 32% 20% 7%	492
	21st to end	Day	16% 17% 32% 22% 9% 4	500
May	1st to 10th	Day	19% 21% 28% 21% 8% 3	503
	11th to 20th	Day	13% 16% 32% 26% 8% 4	528
	21st to end	Day	17% 11% 31% 28% 8% 5%	573
June	1st to 10th	Day	5% 12% 36% 30% 12% 5%	530
	11th to 20th	Day	4 15% 38% 28% 9% 6%	530
	21st to end	Day	5% 13% 35% 29% 13% 7%	530
July	1st to 10th	Day	2 6% 36% 35% 11% 10%	526
	11th to 20th	Day	2 2 27% 43% 14% 12%	524
	21st to end	Day	3 3 29% 41% 13% 11%	575
August	1st to 10th	Day	4 7% 37% 30% 13% 8%	527
	11th to 20th	Day	3 5% 35% 37% 12% 9%	517
	21st to end	Day	2 4 33% 39% 15% 7%	583
September	1st to 10th	Day	2 6% 39% 36% 13% 4	530
	11th to 20th	Day	5% 12% 38% 33% 11% 2	530
	21st to end	Day	5% 11% 37% 32% 14% 2	530
October	1st to 10th	Day	8% 12% 33% 35% 11% 1	530
	11th to 20th	Day	7% 11% 35% 34% 10% 2	530
	21st to end	Day	9% 9% 34% 31% 15% 1	530
November	1st to 10th	Day	11% 10% 25% 39% 13% 2	330
	11th to 20th	Day	14% 8% 31% 31% 13% 2	330
	21st to end	Day	15% 12% 26% 33% 12% 2	330
December	1st to 10th	Day	12% 12% 35% 34% 8% 1	330
	11th to 20th	Day	16% 9% 29% 31% 14% 1	256
	21st to end	Day	26% 15% 29% 22% 7%	242
January	1st to 10th	Night	19% 5% 23% 32% 16% 4	840
	11th to 20th	Night	10% 5% 27% 36% 18% 5%	840
	21st to end	Night	17% 4 26% 35% 15% 3	924
February	1st to 10th	Night	18% 5% 24% 34% 15% 4	840
	11th to 20th	Night	19% 5% 22% 33% 16% 4	824
	21st to end	Night	18% 7% 23% 37% 13% 2	692
March	1st to 10th	Night	17% 8% 22% 36% 14% 3	840
	11th to 20th	Night	15% 5% 17% 34% 23% 5%	840
	21st to end	Night	19% 7% 17% 37% 18% 2	924
April	1st to 10th	Night	15% 6% 19% 38% 20% 2	804
	11th to 20th	Night	12% 7% 19% 37% 22% 3	791
	21st to end	Night	13% 7% 18% 35% 22% 6%	800
May	1st to 10th	Night	10% 5% 21% 36% 25% 2	707
	11th to 20th	Night	8% 8% 16% 36% 29% 3	591
	21st to end	Night	11% 7% 17% 36% 26% 2	604
June	1st to 10th	Night	6% 2 11% 42% 37% 3	400
	11th to 20th	Night	2 1 12% 46% 35% 4	400
	21st to end	Night	1 1 8% 47% 40% 3	400
July	1st to 10th	Night	1 2 34% 56% 7%	390
	11th to 20th	Night	1 1 1 24% 66% 7%	388
	21st to end	Night	2 3 26% 57% 11%	636
August	1st to 10th	Night	2 1 7% 38% 45% 7%	796
	11th to 20th	Night	1 1 5% 35% 47% 12%	792
	21st to end	Night	2 1 4 31% 50% 13%	880
September	1st to 10th	Night	2 1 7% 33% 47% 12%	800
	11th to 20th	Night	2 1 10% 40% 40% 8%	800
	21st to end	Night	2 2 13% 38% 37% 8%	800
October	1st to 10th	Night	5% 2 13% 43% 32% 5%	800
	11th to 20th	Night	6% 3 14% 37% 33% 7%	800
	21st to end	Night	6% 3 15% 38% 29% 9%	880
November	1st to 10th	Night	11% 3 14% 39% 25% 7%	820
	11th to 20th	Night	9% 5% 18% 40% 23% 5%	840
	21st to end	Night	11% 4 23% 39% 18% 4	840
December	1st to 10th	Night	11% 5% 26% 37% 18% 3	840
	11th to 20th	Night	18% 4 24% 38% 14% 3	840
	21st to end	Night	18% 7% 26% 35% 12% 3	924

Page generated at 2026-03-29 23:18:40. Version ac07

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