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 2024-12-09.

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	5% 5% 1 3 2 2 3 2 4 5% 67%	105197
	Night	6% 6% 2 3 2 2 3 2 4 5% 64%	103352
Transparency	Day	18% 6% 6% 18% 26% 25%	104949
	Night	19% 7% 6% 19% 26% 22%	103190
Seeing	Day	12% 11% 33% 30% 10% 4	15476
	Night	10% 4 16% 36% 29% 6%	25153

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	7% 7% 3 6% 4 4 6% 3 4 8% 46%	2539
	11th to 20th	Day	7% 6% 2 6% 5% 5% 5% 4 8% 9% 45%	2704
	21st to end	Day	11% 11% 2 6% 4 4 5% 4 7% 8% 37%	3212
February	1st to 10th	Day	12% 11% 3 4 3 2 3 2 5% 5% 52%	1900
	11th to 20th	Day	9% 11% 2 4 4 2 4 3 4 6% 50%	1850
	21st to end	Day	13% 13% 5% 5% 4 3 3 2 4 6% 43%	1570
March	1st to 10th	Day	12% 16% 4 7% 4 4 5% 3 4 6% 35%	3138
	11th to 20th	Day	4 7% 2 4 3 4 4 4 6% 10% 53%	3294
	21st to end	Day	8% 18% 3 7% 5% 4 4 3 5% 6% 37%	4165
April	1st to 10th	Day	8% 9% 2 5% 4 2 3 3 5% 7% 52%	2280
	11th to 20th	Day	8% 7% 2 4 2 2 3 3 5% 7% 55%	2249
	21st to end	Day	6% 7% 1 3 3 3 2 3 5% 6% 60%	2280
May	1st to 10th	Day	4 4 1 3 2 3 3 2 4 5% 69%	3945
	11th to 20th	Day	3 2 1 3 2 2 3 3 4 6% 72%	4071
	21st to end	Day	4 2 1 2 1 2 1 2 3 4 78%	4552
June	1st to 10th	Day	3 2 1 3 2 2 2 3 5% 7% 69%	2660
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 3 83%	2660
	21st to end	Day	1 2 1 2 1 2 2 2 2 86%	2660
July	1st to 10th	Day	1 1 1 1 1 1 1 2 2 89%	4420
	11th to 20th	Day	2 1 1 2 1 1 2 2 3 3 82%	4420
	21st to end	Day	1 2 1 1 1 1 1 2 2 4 83%	4473
August	1st to 10th	Day	2 1 1 1 2 2 2 3 3 84%	3783
	11th to 20th	Day	1 1 1 1 1 1 2 2 90%	3724
	21st to end	Day	1 1 1 1 1 2 2 90%	4180
September	1st to 10th	Day	2 1 1 1 2 2 2 3 5% 82%	2280
	11th to 20th	Day	1 1 1 1 2 2 2 2 4 85%	2176
	21st to end	Day	1 1 1 2 1 2 2 2 3 3 83%	2090
October	1st to 10th	Day	3 3 1 1 2 2 2 2 3 4 77%	3469
	11th to 20th	Day	2 2 1 3 3 2 3 2 3 3 77%	3161
	21st to end	Day	3 4 2 5% 2 3 3 3 4 6% 64%	3362
November	1st to 10th	Day	4 9% 2 3 3 2 3 2 4 7% 62%	1764
	11th to 20th	Day	6% 4 2 4 2 3 3 2 5% 6% 65%	1800
	21st to end	Day	8% 7% 2 4 3 3 3 4 5% 6% 56%	1800
December	1st to 10th	Day	7% 5% 2 4 4 3 4 2 6% 6% 56%	1782
	11th to 20th	Day	13% 10% 2 5% 5% 4 5% 3 5% 7% 41%	1990
	21st to end	Day	8% 11% 4 6% 3 5% 5% 4 6% 7% 40%	2794
January	1st to 10th	Night	9% 11% 3 6% 4 4 4 3 4 6% 46%	4406
	11th to 20th	Night	7% 9% 3 6% 4 4 5% 4 7% 8% 44%	4256
	21st to end	Night	14% 11% 3 5% 4 4 5% 4 6% 8% 38%	4455
February	1st to 10th	Night	11% 13% 3 5% 4 2 2 3 5% 5% 48%	2280
	11th to 20th	Night	9% 11% 2 3 2 3 3 2 5% 6% 55%	2218
	21st to end	Night	11% 12% 4 5% 3 3 4 2 4 5% 48%	1884
March	1st to 10th	Night	11% 16% 3 5% 3 3 5% 4 6% 7% 37%	3736
	11th to 20th	Night	6% 6% 2 4 3 4 4 3 5% 7% 55%	3681
	21st to end	Night	9% 15% 4 6% 4 3 4 3 5% 7% 41%	3488
April	1st to 10th	Night	9% 8% 2 5% 3 3 4 2 5% 6% 54%	1900
	11th to 20th	Night	7% 7% 2 3 3 3 3 3 4 6% 58%	1879
	21st to end	Night	5% 7% 1 3 2 2 3 2 3 6% 65%	1900
May	1st to 10th	Night	6% 6% 1 2 1 2 2 1 3 4 73%	3027
	11th to 20th	Night	3 2 1 2 2 1 2 1 3 5% 79%	2834
	21st to end	Night	4 2 1 1 1 1 1 1 2 3 81%	3028
June	1st to 10th	Night	4 3 1 3 2 2 2 3 4 5% 72%	1520
	11th to 20th	Night	1 1 1 1 1 1 2 2 2 4 84%	1520
	21st to end	Night	1 1 1 1 1 2 1 3 3 86%	1520
July	1st to 10th	Night	1 1 1 1 1 2 2 91%	2540
	11th to 20th	Night	1 1 1 1 1 1 2 2 3 4 84%	2540
	21st to end	Night	1 1 1 1 1 1 1 1 3 2 87%	3085
August	1st to 10th	Night	1 1 2 1 2 1 1 2 3 84%	3166
	11th to 20th	Night	1 1 1 1 3 91%	3126
	21st to end	Night	1 1 1 1 1 1 1 2 92%	3498
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 88%	1900
	11th to 20th	Night	1 1 1 2 1 1 1 2 3 2 85%	2004
	21st to end	Night	1 1 1 1 1 2 2 2 3 3 84%	2090
October	1st to 10th	Night	2 2 1 1 1 1 1 2 3 83%	3507
	11th to 20th	Night	2 2 1 2 2 2 3 3 4 3 77%	3777
	21st to end	Night	2 5% 1 3 2 2 2 2 3 4 73%	4201
November	1st to 10th	Night	5% 7% 2 4 3 2 3 3 4 6% 62%	2535
	11th to 20th	Night	5% 5% 1 4 3 2 3 3 5% 7% 62%	2600
	21st to end	Night	7% 7% 3 5% 3 3 3 3 5% 6% 54%	2600
December	1st to 10th	Night	8% 6% 2 6% 3 3 4 3 5% 6% 55%	2580
	11th to 20th	Night	15% 9% 2 5% 4 4 4 4 6% 7% 40%	3209
	21st to end	Night	8% 8% 3 8% 6% 5% 6% 4 6% 7% 38%	4862

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	22% 18% 10% 28% 16% 5%	2539
	11th to 20th	Day	26% 14% 9% 28% 14% 8%	2704
	21st to end	Day	36% 12% 9% 20% 16% 7%	3212
February	1st to 10th	Day	33% 5% 6% 19% 24% 12%	1900
	11th to 20th	Day	33% 6% 7% 18% 25% 12%	1860
	21st to end	Day	39% 8% 7% 21% 21% 3	1570
March	1st to 10th	Day	39% 15% 7% 16% 16% 7%	3138
	11th to 20th	Day	24% 10% 16% 29% 13% 8%	3294
	21st to end	Day	35% 16% 11% 22% 13% 3	4165
April	1st to 10th	Day	30% 7% 11% 27% 18% 7%	2280
	11th to 20th	Day	25% 7% 10% 28% 23% 8%	2252
	21st to end	Day	22% 6% 12% 34% 24% 3	2280
May	1st to 10th	Day	14% 7% 9% 34% 30% 7%	3945
	11th to 20th	Day	13% 5% 6% 30% 41% 6%	4074
	21st to end	Day	13% 3 5% 32% 44% 3	4552
June	1st to 10th	Day	14% 5% 9% 23% 35% 14%	2660
	11th to 20th	Day	8% 3 5% 15% 43% 26%	2660
	21st to end	Day	7% 2 3 9% 36% 43%	2660
July	1st to 10th	Day	5% 1 2 6% 16% 71%	4351
	11th to 20th	Day	10% 2 2 8% 20% 58%	4345
	21st to end	Day	8% 2 3 17% 26% 44%	4331
August	1st to 10th	Day	9% 1 2 7% 37% 44%	3770
	11th to 20th	Day	4 1 1 6% 28% 59%	3760
	21st to end	Day	4 1 1 9% 27% 58%	4179
September	1st to 10th	Day	8% 2 3 10% 32% 46%	2280
	11th to 20th	Day	7% 2 3 15% 40% 32%	2176
	21st to end	Day	9% 2 2 19% 36% 33%	2090
October	1st to 10th	Day	12% 2 3 11% 21% 52%	3469
	11th to 20th	Day	13% 2 2 17% 41% 25%	3161
	21st to end	Day	20% 3 3 12% 35% 28%	3362
November	1st to 10th	Day	21% 7% 5% 18% 29% 21%	1764
	11th to 20th	Day	20% 4 7% 20% 28% 21%	1800
	21st to end	Day	28% 5% 7% 14% 25% 22%	1800
December	1st to 10th	Day	25% 7% 7% 18% 24% 18%	1782
	11th to 20th	Day	39% 8% 9% 16% 16% 12%	1990
	21st to end	Day	37% 10% 7% 22% 17% 7%	2794
January	1st to 10th	Night	28% 16% 6% 24% 20% 6%	4406
	11th to 20th	Night	28% 16% 9% 26% 13% 9%	4256
	21st to end	Night	33% 15% 8% 20% 15% 9%	4455
February	1st to 10th	Night	37% 6% 5% 15% 23% 14%	2280
	11th to 20th	Night	29% 5% 7% 19% 26% 14%	2219
	21st to end	Night	37% 7% 8% 21% 22% 5%	1884
March	1st to 10th	Night	31% 17% 8% 20% 20% 5%	3736
	11th to 20th	Night	21% 11% 16% 29% 13% 9%	3681
	21st to end	Night	30% 17% 17% 22% 13% 2	3488
April	1st to 10th	Night	29% 7% 10% 28% 17% 8%	1900
	11th to 20th	Night	23% 7% 12% 29% 22% 7%	1879
	21st to end	Night	18% 8% 10% 40% 22% 3	1900
May	1st to 10th	Night	13% 7% 6% 36% 31% 7%	3027
	11th to 20th	Night	10% 2 5% 31% 47% 4	2835
	21st to end	Night	10% 4 6% 32% 45% 4	3028
June	1st to 10th	Night	15% 4 10% 22% 38% 11%	1520
	11th to 20th	Night	6% 3 7% 18% 41% 24%	1520
	21st to end	Night	6% 2 2 11% 40% 39%	1520
July	1st to 10th	Night	4 1 2 6% 18% 70%	2500
	11th to 20th	Night	7% 2 3 9% 20% 60%	2492
	21st to end	Night	7% 2 3 18% 24% 46%	2989
August	1st to 10th	Night	8% 1 2 10% 38% 41%	3156
	11th to 20th	Night	3 1 1 8% 25% 62%	3156
	21st to end	Night	4 1 1 10% 32% 53%	3498
September	1st to 10th	Night	6% 3 2 9% 34% 47%	1900
	11th to 20th	Night	8% 2 3 15% 43% 29%	2004
	21st to end	Night	7% 3 2 19% 35% 33%	2090
October	1st to 10th	Night	8% 2 3 11% 22% 54%	3507
	11th to 20th	Night	11% 3 2 14% 44% 26%	3777
	21st to end	Night	16% 2 2 12% 38% 30%	4201
November	1st to 10th	Night	21% 6% 6% 16% 30% 21%	2535
	11th to 20th	Night	20% 5% 7% 18% 25% 25%	2600
	21st to end	Night	29% 5% 7% 13% 25% 21%	2600
December	1st to 10th	Night	27% 7% 7% 17% 24% 18%	2580
	11th to 20th	Night	38% 10% 9% 16% 15% 12%	3209
	21st to end	Night	36% 14% 7% 21% 15% 7%	4862

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% 11% 29% 29% 3 1	180
	11th to 20th	Day	22% 10% 32% 25% 10% 2	279
	21st to end	Day	18% 12% 35% 26% 9%	427
February	1st to 10th	Day	21% 13% 33% 22% 9% 2	460
	11th to 20th	Day	20% 16% 33% 25% 5% 1	455
	21st to end	Day	25% 18% 33% 19% 5% 1	382
March	1st to 10th	Day	27% 15% 34% 19% 5%	460
	11th to 20th	Day	21% 19% 30% 22% 6% 2	460
	21st to end	Day	27% 19% 33% 16% 5%	506
April	1st to 10th	Day	21% 18% 28% 24% 8% 1	460
	11th to 20th	Day	23% 18% 31% 20% 7%	452
	21st to end	Day	16% 17% 30% 23% 9% 5%	460
May	1st to 10th	Day	19% 20% 29% 21% 8% 3	463
	11th to 20th	Day	13% 16% 32% 27% 8% 4	488
	21st to end	Day	18% 10% 30% 28% 9% 5%	529
June	1st to 10th	Day	6% 11% 35% 31% 11% 6%	490
	11th to 20th	Day	4 15% 37% 29% 9% 6%	490
	21st to end	Day	4 11% 35% 30% 13% 7%	490
July	1st to 10th	Day	2 5% 35% 37% 11% 10%	486
	11th to 20th	Day	2 2 26% 43% 14% 12%	484
	21st to end	Day	3 2 28% 41% 14% 11%	531
August	1st to 10th	Day	5% 6% 37% 31% 13% 9%	487
	11th to 20th	Day	3 5% 35% 37% 12% 9%	477
	21st to end	Day	2 4 32% 41% 14% 7%	539
September	1st to 10th	Day	2 5% 38% 37% 13% 4	490
	11th to 20th	Day	3 12% 39% 33% 11% 2	490
	21st to end	Day	5% 9% 36% 33% 15% 2	490
October	1st to 10th	Day	8% 11% 32% 36% 12% 1	490
	11th to 20th	Day	6% 11% 36% 35% 10% 2	490
	21st to end	Day	10% 9% 34% 31% 15% 1	489
November	1st to 10th	Day	11% 10% 24% 38% 14% 2	300
	11th to 20th	Day	11% 7% 32% 33% 15% 3	300
	21st to end	Day	16% 12% 25% 33% 12% 2	300
December	1st to 10th	Day	13% 11% 33% 34% 8% 1	294
	11th to 20th	Day	18% 8% 30% 29% 15%	210
	21st to end	Day	24% 14% 27% 26% 9%	198
January	1st to 10th	Night	19% 4 21% 33% 18% 5%	760
	11th to 20th	Night	11% 5% 23% 36% 19% 5%	760
	21st to end	Night	18% 4 25% 35% 16% 3	836
February	1st to 10th	Night	18% 4 22% 34% 16% 5%	760
	11th to 20th	Night	18% 4 20% 35% 18% 5%	744
	21st to end	Night	19% 6% 21% 36% 14% 3	628
March	1st to 10th	Night	18% 7% 21% 36% 15% 3	760
	11th to 20th	Night	16% 5% 17% 33% 24% 5%	760
	21st to end	Night	20% 7% 17% 36% 17% 3	836
April	1st to 10th	Night	15% 6% 19% 38% 21% 2	760
	11th to 20th	Night	12% 7% 18% 36% 23% 4	751
	21st to end	Night	13% 7% 18% 35% 22% 6%	760
May	1st to 10th	Night	11% 5% 21% 37% 24% 2	672
	11th to 20th	Night	7% 8% 15% 36% 30% 3	561
	21st to end	Night	12% 7% 17% 35% 27% 2	574
June	1st to 10th	Night	6% 2 11% 40% 37% 3	380
	11th to 20th	Night	2 1 11% 45% 36% 4	380
	21st to end	Night	1 1 8% 47% 41% 3	380
July	1st to 10th	Night	1 1 31% 59% 7%	370
	11th to 20th	Night	1 1 1 24% 65% 8%	368
	21st to end	Night	2 2 25% 58% 12%	603
August	1st to 10th	Night	2 1 6% 37% 47% 8%	756
	11th to 20th	Night	1 1 5% 34% 48% 12%	752
	21st to end	Night	2 4 31% 50% 13%	836
September	1st to 10th	Night	2 1 6% 32% 48% 12%	760
	11th to 20th	Night	1 1 9% 40% 40% 8%	760
	21st to end	Night	2 1 12% 38% 39% 8%	760
October	1st to 10th	Night	5% 1 11% 44% 34% 5%	760
	11th to 20th	Night	6% 2 13% 37% 34% 7%	760
	21st to end	Night	7% 3 14% 37% 30% 10%	836
November	1st to 10th	Night	12% 3 13% 38% 26% 8%	780
	11th to 20th	Night	8% 4 17% 41% 24% 6%	800
	21st to end	Night	11% 4 23% 38% 19% 4	800
December	1st to 10th	Night	12% 4 25% 37% 18% 3	794
	11th to 20th	Night	19% 4 23% 36% 14% 3	760
	21st to end	Night	18% 6% 24% 36% 13% 4	836

Page generated at 2024-12-06 00:54:47. Version ac07

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