"Flying F" Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the "Flying F" Observatory clear sky chart from 2005-11-06 to 2024-04-10.

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	4 7% 4 7% 6% 3 5% 5% 5% 7% 48%	83381
	Night	2 5% 3 5% 5% 3 4 5% 5% 8% 57%	85506
Transparency	Day	35% 3 9% 23% 22% 8%	83099
	Night	27% 3 11% 26% 25% 7%	85310
Seeing	Day	18% 21% 24% 21% 13% 3	14469
	Night	8% 11% 29% 32% 17% 2	24747

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	2 2 9% 7% 3 4 5% 7% 8% 54%	2697
	11th to 20th	Day	4 6% 5% 5% 3 4 4 6% 8% 55%	2860
	21st to end	Day	5% 4 8% 6% 3 4 5% 6% 8% 50%	3146
February	1st to 10th	Day	5% 4 10% 5% 3 4 4 5% 8% 53%	1710
	11th to 20th	Day	1 6% 3 6% 6% 2 5% 5% 6% 9% 51%	1759
	21st to end	Day	4 5% 10% 7% 3 4 5% 5% 9% 48%	1570
March	1st to 10th	Day	1 5% 7% 7% 7% 3 4 5% 5% 7% 50%	3353
	11th to 20th	Day	1 12% 8% 9% 5% 3 4 4 6% 7% 41%	3490
	21st to end	Day	1 12% 6% 10% 8% 5% 6% 5% 5% 6% 37%	3903
April	1st to 10th	Day	2 8% 3 6% 6% 3 6% 4 5% 8% 50%	2269
	11th to 20th	Day	2 11% 4 7% 6% 4 5% 5% 6% 7% 44%	2131
	21st to end	Day	3 8% 4 6% 7% 3 5% 5% 5% 7% 45%	2160
May	1st to 10th	Day	4 9% 3 8% 6% 3 7% 5% 5% 7% 44%	2217
	11th to 20th	Day	6% 10% 4 7% 7% 4 6% 5% 5% 8% 39%	2375
	21st to end	Day	6% 7% 2 6% 5% 3 5% 5% 6% 6% 50%	2724
June	1st to 10th	Day	5% 5% 2 4 5% 3 6% 6% 5% 8% 52%	2520
	11th to 20th	Day	4 4 2 4 5% 3 5% 5% 5% 6% 59%	2520
	21st to end	Day	4 5% 3 6% 6% 4 6% 6% 6% 6% 48%	2520
July	1st to 10th	Day	8% 7% 3 7% 8% 5% 7% 5% 6% 6% 38%	2520
	11th to 20th	Day	8% 7% 4 9% 9% 5% 7% 7% 6% 7% 33%	2389
	21st to end	Day	11% 8% 4 9% 9% 6% 8% 7% 7% 7% 24%	2545
August	1st to 10th	Day	13% 8% 4 8% 9% 5% 6% 5% 6% 6% 29%	2328
	11th to 20th	Day	9% 7% 4 7% 7% 4 7% 7% 6% 7% 35%	2179
	21st to end	Day	9% 8% 4 7% 8% 6% 5% 6% 6% 6% 35%	2376
September	1st to 10th	Day	8% 7% 3 7% 8% 4 5% 5% 6% 6% 40%	2160
	11th to 20th	Day	7% 6% 3 8% 6% 4 5% 5% 5% 6% 47%	2160
	21st to end	Day	6% 6% 3 5% 5% 3 4 4 4 5% 55%	1919
October	1st to 10th	Day	8% 9% 2 6% 5% 3 3 4 4 5% 52%	1800
	11th to 20th	Day	3 5% 1 3 3 2 3 3 4 4 69%	1800
	21st to end	Day	3 5% 3 5% 3 2 2 3 4 5% 64%	1980
November	1st to 10th	Day	1 4 2 3 3 2 2 4 3 7% 70%	1783
	11th to 20th	Day	1 3 2 2 3 2 3 4 4 6% 72%	1710
	21st to end	Day	4 3 5% 5% 2 4 4 4 7% 63%	1568
December	1st to 10th	Day	1 4 3 5% 5% 3 3 3 5% 8% 60%	1520
	11th to 20th	Day	4 3 4 5% 3 4 5% 6% 9% 56%	1926
	21st to end	Day	5% 3 6% 4 2 3 4 5% 8% 59%	2794
January	1st to 10th	Night	2 2 8% 9% 4 6% 6% 6% 7% 52%	4288
	11th to 20th	Night	3 3 9% 6% 3 5% 5% 5% 6% 56%	4110
	21st to end	Night	5% 4 7% 5% 3 4 5% 6% 9% 50%	4521
February	1st to 10th	Night	4 3 6% 5% 3 4 5% 4 7% 59%	2470
	11th to 20th	Night	3 2 5% 5% 3 4 5% 5% 7% 62%	2308
	21st to end	Night	3 4 6% 5% 3 5% 3 5% 8% 59%	1884
March	1st to 10th	Night	6% 3 6% 5% 2 4 5% 6% 8% 55%	3504
	11th to 20th	Night	1 9% 6% 11% 6% 3 4 5% 6% 8% 40%	3490
	21st to end	Night	1 9% 4 7% 6% 4 5% 4 5% 8% 47%	3747
April	1st to 10th	Night	1 5% 2 4 3 2 4 4 6% 7% 62%	1900
	11th to 20th	Night	1 7% 3 4 4 3 6% 4 6% 8% 53%	1777
	21st to end	Night	1 5% 3 3 4 2 4 5% 5% 7% 60%	1800
May	1st to 10th	Night	2 5% 3 4 5% 3 4 4 5% 8% 58%	1740
	11th to 20th	Night	4 7% 3 5% 4 3 3 4 5% 8% 53%	1516
	21st to end	Night	5% 4 1 3 4 2 4 4 5% 6% 61%	1552
June	1st to 10th	Night	2 2 1 2 2 2 4 4 6% 8% 66%	1440
	11th to 20th	Night	2 3 1 2 3 2 3 3 5% 6% 71%	1440
	21st to end	Night	2 3 2 3 3 2 5% 6% 6% 8% 61%	1440
July	1st to 10th	Night	4 5% 2 5% 6% 4 7% 6% 6% 10% 45%	1440
	11th to 20th	Night	3 4 2 3 4 3 5% 7% 8% 11% 50%	1567
	21st to end	Night	5% 6% 3 6% 6% 3 6% 7% 9% 12% 37%	1773
August	1st to 10th	Night	5% 3 2 6% 6% 3 6% 6% 9% 10% 44%	1611
	11th to 20th	Night	5% 5% 2 5% 5% 3 4 5% 9% 9% 48%	1719
	21st to end	Night	5% 5% 3 5% 5% 3 6% 6% 6% 10% 46%	1980
September	1st to 10th	Night	5% 5% 2 5% 6% 3 5% 6% 7% 9% 48%	1800
	11th to 20th	Night	5% 4 2 4 5% 3 5% 4 6% 8% 55%	1800
	21st to end	Night	4 3 1 4 3 2 2 3 5% 5% 66%	2037
October	1st to 10th	Night	6% 5% 2 5% 4 3 4 4 5% 6% 57%	2160
	11th to 20th	Night	2 3 1 2 2 2 3 3 4 7% 72%	2160
	21st to end	Night	2 5% 2 4 3 2 2 3 3 6% 68%	2376
November	1st to 10th	Night	1 3 2 2 2 1 3 4 4 7% 70%	2274
	11th to 20th	Night	2 1 2 2 1 3 3 4 7% 74%	2470
	21st to end	Night	1 5% 3 4 4 3 3 4 5% 6% 64%	2608
December	1st to 10th	Night	4 2 4 4 3 4 4 4 8% 63%	2660
	11th to 20th	Night	4 2 5% 4 2 4 5% 6% 9% 58%	3271
	21st to end	Night	5% 3 6% 5% 3 4 4 5% 7% 58%	4873

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	28% 2 14% 25% 26% 6%	2698
	11th to 20th	Day	29% 2 13% 26% 26% 4	2860
	21st to end	Day	36% 2 6% 28% 23% 5%	3146
February	1st to 10th	Day	30% 4 12% 26% 18% 10%	1710
	11th to 20th	Day	29% 4 7% 25% 26% 9%	1768
	21st to end	Day	35% 4 6% 20% 24% 11%	1570
March	1st to 10th	Day	34% 2 5% 26% 26% 8%	3353
	11th to 20th	Day	43% 2 6% 31% 16% 3	3490
	21st to end	Day	45% 2 8% 23% 19% 3	3903
April	1st to 10th	Day	32% 4 9% 23% 23% 9%	2269
	11th to 20th	Day	37% 3 8% 24% 22% 7%	2134
	21st to end	Day	37% 3 8% 29% 20% 3	2160
May	1st to 10th	Day	37% 3 9% 25% 23% 3	2217
	11th to 20th	Day	42% 4 10% 25% 16% 3	2379
	21st to end	Day	33% 4 7% 22% 26% 8%	2724
June	1st to 10th	Day	30% 3 9% 26% 22% 10%	2520
	11th to 20th	Day	24% 3 7% 19% 28% 19%	2520
	21st to end	Day	34% 4 6% 18% 24% 14%	2520
July	1st to 10th	Day	44% 6% 9% 14% 15% 12%	2451
	11th to 20th	Day	47% 6% 15% 16% 10% 5%	2317
	21st to end	Day	55% 8% 18% 11% 7% 1	2404
August	1st to 10th	Day	54% 6% 11% 10% 12% 6%	2313
	11th to 20th	Day	46% 5% 12% 16% 16% 6%	2179
	21st to end	Day	47% 5% 10% 19% 16% 3	2376
September	1st to 10th	Day	44% 4 9% 14% 20% 8%	2160
	11th to 20th	Day	39% 3 7% 18% 24% 9%	2160
	21st to end	Day	29% 3 5% 24% 32% 7%	1919
October	1st to 10th	Day	34% 2 6% 22% 24% 11%	1800
	11th to 20th	Day	21% 3 3 22% 39% 12%	1800
	21st to end	Day	23% 2 6% 28% 31% 9%	1980
November	1st to 10th	Day	16% 3 8% 27% 35% 11%	1783
	11th to 20th	Day	14% 2 8% 33% 33% 10%	1710
	21st to end	Day	22% 3 8% 26% 28% 13%	1568
December	1st to 10th	Day	24% 3 14% 28% 23% 8%	1520
	11th to 20th	Day	24% 5% 11% 28% 25% 6%	1924
	21st to end	Day	26% 3 8% 21% 25% 17%	2794
January	1st to 10th	Night	32% 2 8% 30% 24% 5%	4288
	11th to 20th	Night	25% 1 12% 27% 29% 5%	4110
	21st to end	Night	34% 2 6% 32% 21% 4	4521
February	1st to 10th	Night	25% 3 13% 26% 24% 9%	2470
	11th to 20th	Night	21% 3 9% 30% 28% 9%	2309
	21st to end	Night	26% 2 7% 25% 30% 10%	1884
March	1st to 10th	Night	27% 2 7% 25% 37% 3	3504
	11th to 20th	Night	44% 1 8% 29% 15% 3	3490
	21st to end	Night	36% 2 12% 27% 21% 2	3747
April	1st to 10th	Night	20% 5% 13% 28% 27% 7%	1900
	11th to 20th	Night	28% 2 10% 29% 26% 6%	1777
	21st to end	Night	24% 4 12% 36% 21% 4	1800
May	1st to 10th	Night	25% 3 11% 32% 24% 5%	1740
	11th to 20th	Night	32% 3 14% 27% 21% 2	1517
	21st to end	Night	24% 3 11% 29% 25% 8%	1552
June	1st to 10th	Night	18% 3 13% 27% 29% 10%	1440
	11th to 20th	Night	15% 3 6% 24% 32% 21%	1440
	21st to end	Night	21% 4 9% 22% 26% 18%	1440
July	1st to 10th	Night	36% 4 14% 14% 18% 14%	1400
	11th to 20th	Night	27% 8% 22% 22% 12% 9%	1516
	21st to end	Night	38% 12% 28% 15% 5% 2	1674
August	1st to 10th	Night	34% 9% 17% 17% 14% 9%	1602
	11th to 20th	Night	31% 5% 19% 19% 18% 8%	1719
	21st to end	Night	35% 6% 15% 22% 19% 4	1980
September	1st to 10th	Night	32% 5% 15% 18% 22% 8%	1800
	11th to 20th	Night	28% 4 11% 21% 27% 10%	1800
	21st to end	Night	20% 3 6% 31% 34% 6%	2037
October	1st to 10th	Night	30% 3 9% 20% 28% 11%	2160
	11th to 20th	Night	14% 3 6% 24% 41% 12%	2160
	21st to end	Night	19% 2 6% 34% 32% 7%	2376
November	1st to 10th	Night	14% 3 11% 32% 31% 9%	2274
	11th to 20th	Night	12% 3 9% 35% 33% 8%	2470
	21st to end	Night	22% 3 7% 28% 31% 10%	2608
December	1st to 10th	Night	21% 3 16% 27% 24% 8%	2660
	11th to 20th	Night	22% 5% 12% 27% 28% 6%	3272
	21st to end	Night	28% 3 8% 21% 26% 13%	4873

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	17% 17% 34% 20% 10% 1	270
	11th to 20th	Day	21% 23% 25% 24% 6% 1	270
	21st to end	Day	8% 22% 35% 25% 10% 1	297
February	1st to 10th	Day	22% 27% 31% 17% 2 1	270
	11th to 20th	Day	21% 29% 29% 16% 4 1	270
	21st to end	Day	31% 26% 24% 16% 2	225
March	1st to 10th	Day	27% 28% 26% 13% 5% 1	403
	11th to 20th	Day	24% 30% 25% 15% 5% 1	460
	21st to end	Day	33% 31% 26% 7% 3	506
April	1st to 10th	Day	26% 31% 26% 12% 3 1	457
	11th to 20th	Day	33% 36% 18% 8% 4	412
	21st to end	Day	32% 32% 21% 11% 3	420
May	1st to 10th	Day	25% 34% 25% 10% 5% 1	423
	11th to 20th	Day	18% 28% 26% 16% 9% 2	522
	21st to end	Day	21% 24% 21% 21% 12% 2	679
June	1st to 10th	Day	9% 21% 23% 26% 18% 3	630
	11th to 20th	Day	11% 23% 25% 23% 13% 4	630
	21st to end	Day	8% 20% 21% 23% 22% 6%	630
July	1st to 10th	Day	9% 9% 16% 31% 27% 7%	621
	11th to 20th	Day	11% 7% 19% 30% 26% 8%	490
	21st to end	Day	14% 8% 15% 31% 24% 8%	487
August	1st to 10th	Day	19% 9% 21% 28% 19% 5%	447
	11th to 20th	Day	14% 10% 22% 32% 18% 5%	437
	21st to end	Day	13% 9% 25% 28% 21% 4	495
September	1st to 10th	Day	12% 13% 25% 23% 22% 5%	450
	11th to 20th	Day	12% 22% 28% 22% 13% 2	450
	21st to end	Day	17% 16% 23% 20% 20% 3	334
October	1st to 10th	Day	19% 17% 23% 19% 17% 5%	270
	11th to 20th	Day	15% 21% 25% 20% 17% 2	270
	21st to end	Day	18% 24% 23% 20% 12% 3	297
November	1st to 10th	Day	21% 19% 23% 25% 10% 1	270
	11th to 20th	Day	14% 20% 27% 26% 10% 2	270
	21st to end	Day	16% 19% 30% 20% 13% 3	270
December	1st to 10th	Day	17% 20% 32% 18% 9% 3	270
	11th to 20th	Day	17% 19% 32% 20% 10% 1	270
	21st to end	Day	21% 22% 32% 19% 6% 1	297
January	1st to 10th	Night	6% 14% 35% 33% 10% 2	873
	11th to 20th	Night	9% 13% 35% 32% 10% 1	760
	21st to end	Night	5% 12% 39% 34% 9% 2	836
February	1st to 10th	Night	6% 15% 44% 29% 6% 1	760
	11th to 20th	Night	7% 13% 44% 28% 7%	744
	21st to end	Night	10% 15% 45% 27% 3	628
March	1st to 10th	Night	10% 21% 33% 29% 7%	760
	11th to 20th	Night	6% 13% 36% 32% 12% 1	760
	21st to end	Night	10% 16% 40% 30% 5%	793
April	1st to 10th	Night	11% 19% 37% 28% 5%	570
	11th to 20th	Night	13% 19% 35% 26% 8%	533
	21st to end	Night	9% 19% 35% 27% 10% 1	540
May	1st to 10th	Night	8% 13% 36% 31% 12% 1	540
	11th to 20th	Night	10% 11% 24% 37% 16% 2	531
	21st to end	Night	11% 15% 26% 30% 17% 2	584
June	1st to 10th	Night	5% 8% 23% 36% 26% 1	540
	11th to 20th	Night	5% 9% 29% 36% 19% 2	540
	21st to end	Night	3 8% 17% 39% 30% 2	540
July	1st to 10th	Night	5% 4 9% 37% 42% 4	525
	11th to 20th	Night	6% 2 6% 33% 47% 7%	522
	21st to end	Night	8% 2 3 26% 52% 8%	591
August	1st to 10th	Night	7% 3 6% 29% 48% 6%	537
	11th to 20th	Night	6% 2 9% 37% 41% 5%	534
	21st to end	Night	7% 4 11% 35% 39% 5%	594
September	1st to 10th	Night	6% 3 14% 38% 35% 4	540
	11th to 20th	Night	9% 4 17% 39% 28% 3	540
	21st to end	Night	6% 8% 17% 37% 27% 4	661
October	1st to 10th	Night	9% 9% 26% 36% 18% 2	720
	11th to 20th	Night	6% 8% 32% 36% 15% 3	720
	21st to end	Night	8% 12% 26% 34% 17% 3	792
November	1st to 10th	Night	6% 13% 29% 35% 14% 2	794
	11th to 20th	Night	8% 11% 36% 32% 11% 2	950
	21st to end	Night	9% 13% 32% 33% 12% 1	950
December	1st to 10th	Night	8% 14% 40% 29% 8% 1	950
	11th to 20th	Night	9% 17% 35% 29% 9% 1	950
	21st to end	Night	10% 13% 41% 29% 6% 1	1045

Page generated at 2024-04-07 07:28:16. Version ac07

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