Crest Airpark Astro-Shack
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crest Airpark Astro-Shack clear sky chart from 2005-11-06 to 2024-04-25.

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	22% 9% 4 7% 6% 3 5% 5% 5% 6% 29%	83756
	Night	24% 10% 3 7% 6% 3 4 4 5% 6% 28%	85366
Transparency	Day	57% 8% 11% 16% 7% 1	83477
	Night	58% 8% 10% 15% 7% 1	85225
Seeing	Day	27% 11% 20% 25% 14% 3	14216
	Night	31% 10% 15% 25% 17% 2	22782

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	38% 14% 4 8% 7% 3 4 3 4 4 11%	2539
	11th to 20th	Day	26% 10% 4 8% 6% 3 4 5% 4 6% 24%	2516
	21st to end	Day	42% 12% 4 8% 5% 3 3 4 4 5% 12%	2869
February	1st to 10th	Day	32% 11% 5% 7% 5% 3 5% 4 5% 7% 17%	1710
	11th to 20th	Day	32% 13% 4 7% 6% 4 3 4 3 6% 18%	1665
	21st to end	Day	28% 14% 5% 8% 7% 3 5% 3 4 3 20%	1489
March	1st to 10th	Day	18% 13% 5% 8% 8% 4 6% 5% 6% 6% 21%	3198
	11th to 20th	Day	22% 9% 4 6% 5% 3 4 5% 4 5% 34%	3490
	21st to end	Day	25% 14% 4 9% 6% 5% 6% 6% 5% 7% 15%	3965
April	1st to 10th	Day	27% 11% 4 9% 6% 4 6% 6% 6% 5% 16%	2280
	11th to 20th	Day	23% 10% 4 7% 7% 4 5% 5% 5% 6% 24%	2257
	21st to end	Day	21% 11% 4 10% 8% 4 5% 5% 5% 6% 21%	2435
May	1st to 10th	Day	19% 9% 3 7% 5% 4 6% 6% 4 7% 30%	2520
	11th to 20th	Day	18% 9% 4 7% 6% 3 6% 6% 6% 7% 27%	2477
	21st to end	Day	25% 10% 4 8% 6% 3 6% 5% 4 5% 23%	2723
June	1st to 10th	Day	22% 9% 3 7% 6% 4 5% 5% 6% 7% 25%	2520
	11th to 20th	Day	23% 10% 5% 8% 7% 4 6% 5% 5% 7% 20%	2685
	21st to end	Day	13% 7% 3 7% 7% 3 5% 4 5% 8% 39%	2700
July	1st to 10th	Day	12% 6% 2 5% 5% 3 4 4 5% 6% 50%	2700
	11th to 20th	Day	11% 6% 3 5% 4 3 4 3 4 7% 50%	2534
	21st to end	Day	8% 4 2 4 4 2 3 3 4 5% 61%	2741
August	1st to 10th	Day	10% 6% 2 4 3 3 3 4 4 8% 52%	2468
	11th to 20th	Day	8% 4 2 4 4 2 3 4 5% 8% 56%	2298
	21st to end	Day	12% 7% 3 6% 5% 3 4 5% 4 7% 44%	2456
September	1st to 10th	Day	10% 6% 2 5% 4 3 4 4 5% 6% 51%	2160
	11th to 20th	Day	15% 7% 3 6% 6% 3 4 5% 5% 7% 39%	2160
	21st to end	Day	19% 7% 3 6% 4 3 4 4 5% 8% 38%	1907
October	1st to 10th	Day	20% 8% 4 7% 6% 3 4 4 6% 7% 31%	1800
	11th to 20th	Day	26% 8% 3 6% 4 4 4 5% 5% 7% 28%	1800
	21st to end	Day	30% 8% 3 7% 6% 3 4 3 4 6% 24%	1868
November	1st to 10th	Day	33% 10% 4 6% 6% 3 5% 5% 4 5% 19%	1547
	11th to 20th	Day	32% 11% 3 7% 5% 3 4 4 4 5% 22%	1520
	21st to end	Day	32% 9% 4 8% 5% 3 4 4 5% 5% 21%	1520
December	1st to 10th	Day	29% 10% 3 6% 5% 3 5% 4 5% 6% 24%	1520
	11th to 20th	Day	33% 11% 3 6% 6% 4 4 5% 6% 6% 15%	1925
	21st to end	Day	27% 13% 5% 10% 8% 4 4 5% 4 4 16%	2794
January	1st to 10th	Night	38% 14% 4 8% 6% 4 5% 4 4 4 11%	4406
	11th to 20th	Night	28% 11% 4 6% 5% 2 3 4 5% 7% 24%	4382
	21st to end	Night	39% 10% 4 7% 6% 4 4 4 4 5% 14%	4786
February	1st to 10th	Night	32% 11% 4 8% 6% 3 5% 3 3 6% 18%	2470
	11th to 20th	Night	28% 12% 3 6% 7% 3 4 4 4 4 23%	2402
	21st to end	Night	30% 12% 3 7% 6% 2 4 5% 5% 5% 21%	1965
March	1st to 10th	Night	20% 14% 4 7% 7% 4 6% 5% 7% 7% 19%	3674
	11th to 20th	Night	21% 8% 3 5% 5% 3 4 4 4 7% 36%	3489
	21st to end	Night	30% 15% 4 8% 6% 3 5% 5% 5% 4 15%	3687
April	1st to 10th	Night	25% 10% 4 8% 7% 4 5% 7% 5% 7% 19%	1900
	11th to 20th	Night	20% 10% 4 7% 6% 3 5% 4 6% 6% 28%	1870
	21st to end	Night	21% 10% 3 8% 8% 4 6% 5% 5% 7% 23%	1623
May	1st to 10th	Night	18% 10% 3 8% 6% 4 4 4 6% 5% 32%	1440
	11th to 20th	Night	16% 8% 3 6% 6% 3 6% 6% 7% 8% 30%	1416
	21st to end	Night	18% 8% 3 9% 7% 3 5% 5% 5% 6% 29%	1552
June	1st to 10th	Night	17% 9% 4 8% 8% 3 6% 4 4 7% 31%	1440
	11th to 20th	Night	18% 10% 4 7% 7% 5% 6% 6% 5% 7% 26%	1270
	21st to end	Night	12% 6% 4 6% 4 3 4 4 5% 6% 46%	1260
July	1st to 10th	Night	8% 6% 3 5% 4 3 3 5% 5% 5% 53%	1260
	11th to 20th	Night	7% 6% 2 4 5% 3 3 4 3 5% 58%	1422
	21st to end	Night	6% 2 2 3 2 2 3 3 4 7% 66%	1576
August	1st to 10th	Night	7% 5% 1 4 4 2 3 3 5% 8% 58%	1469
	11th to 20th	Night	7% 4 2 3 4 2 3 3 3 7% 63%	1602
	21st to end	Night	10% 6% 2 5% 4 2 3 4 4 6% 53%	1899
September	1st to 10th	Night	11% 4 2 4 4 3 3 5% 5% 7% 54%	1800
	11th to 20th	Night	15% 7% 3 5% 4 3 5% 4 4 5% 43%	1800
	21st to end	Night	17% 7% 2 7% 5% 3 4 5% 4 6% 42%	2048
October	1st to 10th	Night	20% 7% 2 7% 6% 3 4 4 5% 6% 36%	2160
	11th to 20th	Night	25% 8% 3 6% 4 3 5% 4 5% 5% 32%	2160
	21st to end	Night	28% 8% 2 6% 4 2 4 4 5% 6% 30%	2487
November	1st to 10th	Night	33% 9% 3 7% 5% 3 4 4 5% 6% 21%	2529
	11th to 20th	Night	31% 9% 4 6% 7% 3 4 3 4 5% 24%	2660
	21st to end	Night	30% 10% 4 6% 5% 3 4 3 4 6% 23%	2660
December	1st to 10th	Night	29% 10% 4 6% 6% 3 4 4 4 5% 25%	2660
	11th to 20th	Night	30% 12% 4 7% 7% 3 4 5% 5% 4 18%	3280
	21st to end	Night	30% 12% 4 9% 9% 4 5% 4 4 5% 15%	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	76% 8% 5% 7% 3 1	2539
	11th to 20th	Day	61% 9% 9% 13% 6% 1	2540
	21st to end	Day	76% 6% 6% 8% 3 1	2869
February	1st to 10th	Day	69% 7% 10% 9% 4 1	1710
	11th to 20th	Day	68% 7% 8% 10% 6% 1	1674
	21st to end	Day	69% 7% 8% 11% 5%	1489
March	1st to 10th	Day	62% 10% 11% 12% 5%	3198
	11th to 20th	Day	52% 8% 10% 27% 2 1	3490
	21st to end	Day	69% 10% 10% 9% 1	3965
April	1st to 10th	Day	68% 11% 12% 8% 1	2280
	11th to 20th	Day	63% 8% 9% 13% 6% 1	2257
	21st to end	Day	67% 8% 9% 10% 4 1	2435
May	1st to 10th	Day	56% 10% 14% 15% 6%	2520
	11th to 20th	Day	55% 11% 16% 13% 5%	2480
	21st to end	Day	64% 9% 13% 13% 1	2724
June	1st to 10th	Day	60% 9% 15% 11% 5%	2520
	11th to 20th	Day	66% 9% 13% 10% 2	2685
	21st to end	Day	46% 8% 18% 18% 8% 2	2700
July	1st to 10th	Day	39% 10% 11% 24% 13% 2	2626
	11th to 20th	Day	36% 8% 10% 29% 16% 1	2458
	21st to end	Day	26% 6% 10% 37% 17% 4	2589
August	1st to 10th	Day	34% 8% 14% 28% 14% 3	2451
	11th to 20th	Day	28% 7% 18% 29% 14% 3	2298
	21st to end	Day	40% 8% 12% 30% 9% 1	2456
September	1st to 10th	Day	34% 7% 15% 26% 13% 5%	2160
	11th to 20th	Day	45% 9% 12% 18% 14% 3	2160
	21st to end	Day	47% 7% 15% 17% 11% 3	1907
October	1st to 10th	Day	52% 7% 11% 21% 7% 1	1800
	11th to 20th	Day	55% 7% 14% 17% 6% 1	1800
	21st to end	Day	62% 6% 10% 14% 9%	1868
November	1st to 10th	Day	68% 7% 9% 12% 4	1547
	11th to 20th	Day	67% 8% 7% 9% 7% 2	1520
	21st to end	Day	66% 6% 6% 11% 9% 2	1520
December	1st to 10th	Day	63% 8% 8% 13% 8% 1	1520
	11th to 20th	Day	68% 7% 11% 10% 4 1	1928
	21st to end	Day	69% 9% 9% 10% 3	2794
January	1st to 10th	Night	77% 7% 6% 6% 2 1	4406
	11th to 20th	Night	60% 9% 7% 16% 8% 1	4420
	21st to end	Night	73% 7% 7% 7% 5% 1	4786
February	1st to 10th	Night	69% 7% 9% 9% 5% 1	2470
	11th to 20th	Night	63% 9% 10% 9% 6% 2	2404
	21st to end	Night	66% 9% 8% 11% 5%	1965
March	1st to 10th	Night	61% 10% 9% 14% 5%	3674
	11th to 20th	Night	47% 10% 14% 25% 4 1	3490
	21st to end	Night	70% 11% 10% 9% 1	3687
April	1st to 10th	Night	66% 10% 12% 10% 2	1900
	11th to 20th	Night	58% 8% 12% 14% 7% 1	1870
	21st to end	Night	65% 9% 9% 11% 5% 1	1623
May	1st to 10th	Night	54% 9% 14% 15% 7% 1	1440
	11th to 20th	Night	53% 10% 17% 13% 6% 2	1416
	21st to end	Night	57% 12% 14% 15% 2	1552
June	1st to 10th	Night	58% 9% 15% 14% 5%	1440
	11th to 20th	Night	60% 9% 17% 12% 2	1270
	21st to end	Night	41% 8% 21% 21% 8% 2	1260
July	1st to 10th	Night	36% 10% 12% 24% 14% 4	1225
	11th to 20th	Night	33% 7% 10% 33% 17% 1	1375
	21st to end	Night	22% 7% 9% 37% 20% 5%	1488
August	1st to 10th	Night	26% 7% 14% 32% 18% 3	1461
	11th to 20th	Night	25% 7% 18% 32% 14% 4	1602
	21st to end	Night	35% 6% 14% 31% 12% 1	1899
September	1st to 10th	Night	32% 7% 15% 26% 15% 5%	1800
	11th to 20th	Night	45% 9% 9% 18% 14% 5%	1800
	21st to end	Night	45% 9% 10% 20% 12% 3	2048
October	1st to 10th	Night	49% 6% 13% 22% 8% 2	2160
	11th to 20th	Night	56% 6% 9% 19% 9% 1	2160
	21st to end	Night	56% 8% 9% 16% 11% 1	2487
November	1st to 10th	Night	66% 8% 10% 11% 4 1	2529
	11th to 20th	Night	66% 7% 8% 10% 6% 3	2660
	21st to end	Night	65% 7% 7% 11% 9% 1	2660
December	1st to 10th	Night	63% 7% 9% 12% 8% 1	2660
	11th to 20th	Night	68% 7% 10% 10% 4	3276
	21st to end	Night	70% 12% 6% 9% 3	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	39% 17% 18% 13% 9% 4	180
	11th to 20th	Day	36% 16% 16% 19% 9% 3	180
	21st to end	Day	41% 14% 18% 16% 8% 3	247
February	1st to 10th	Day	43% 11% 19% 17% 8% 2	370
	11th to 20th	Day	46% 13% 18% 15% 7% 1	365
	21st to end	Day	38% 17% 19% 21% 5%	343
March	1st to 10th	Day	32% 19% 22% 19% 8% 1	460
	11th to 20th	Day	32% 16% 20% 20% 9% 3	460
	21st to end	Day	37% 16% 22% 17% 8%	506
April	1st to 10th	Day	34% 17% 21% 16% 11% 1	460
	11th to 20th	Day	28% 20% 25% 17% 7% 3	452
	21st to end	Day	26% 18% 24% 22% 9% 1	437
May	1st to 10th	Day	22% 11% 25% 29% 11% 2	423
	11th to 20th	Day	30% 10% 23% 22% 13% 3	448
	21st to end	Day	30% 11% 21% 24% 11% 3	485
June	1st to 10th	Day	28% 10% 20% 24% 16% 3	450
	11th to 20th	Day	26% 14% 23% 24% 11% 2	615
	21st to end	Day	17% 8% 18% 34% 20% 3	630
July	1st to 10th	Day	16% 7% 16% 35% 24% 2	621
	11th to 20th	Day	12% 7% 20% 37% 20% 3	457
	21st to end	Day	8% 2 18% 40% 26% 6%	487
August	1st to 10th	Day	15% 6% 13% 34% 25% 8%	447
	11th to 20th	Day	8% 4 13% 37% 30% 8%	437
	21st to end	Day	16% 7% 22% 34% 16% 5%	495
September	1st to 10th	Day	16% 6% 23% 37% 14% 4	450
	11th to 20th	Day	21% 7% 18% 28% 22% 4	450
	21st to end	Day	20% 10% 22% 26% 19% 3	450
October	1st to 10th	Day	27% 10% 18% 23% 19% 3	450
	11th to 20th	Day	32% 9% 18% 22% 14% 5%	450
	21st to end	Day	35% 14% 18% 19% 9% 4	383
November	1st to 10th	Day	40% 12% 16% 19% 13%	210
	11th to 20th	Day	38% 17% 17% 9% 14% 4	180
	21st to end	Day	39% 11% 17% 15% 14% 4	180
December	1st to 10th	Day	46% 11% 16% 12% 10% 6%	180
	11th to 20th	Day	44% 11% 19% 18% 7% 2	180
	21st to end	Day	36% 15% 15% 21% 11% 2	198
January	1st to 10th	Night	45% 15% 18% 16% 6%	760
	11th to 20th	Night	39% 13% 17% 22% 9% 1	760
	21st to end	Night	38% 11% 18% 25% 7%	836
February	1st to 10th	Night	40% 11% 18% 23% 7% 1	760
	11th to 20th	Night	36% 12% 16% 27% 9% 1	744
	21st to end	Night	39% 13% 16% 22% 8% 1	628
March	1st to 10th	Night	33% 14% 18% 22% 11% 1	760
	11th to 20th	Night	34% 12% 18% 24% 11% 1	760
	21st to end	Night	37% 14% 15% 24% 8% 2	836
April	1st to 10th	Night	34% 12% 15% 25% 11% 2	760
	11th to 20th	Night	29% 10% 20% 27% 11% 2	742
	21st to end	Night	30% 16% 11% 30% 12% 1	513
May	1st to 10th	Night	24% 13% 13% 31% 19% 1	360
	11th to 20th	Night	23% 7% 12% 29% 26% 2	354
	21st to end	Night	24% 10% 13% 23% 26% 4	389
June	1st to 10th	Night	24% 10% 13% 28% 23% 2	360
	11th to 20th	Night	28% 11% 12% 27% 21% 1	360
	21st to end	Night	18% 4 12% 32% 31% 3	360
July	1st to 10th	Night	13% 8% 9% 31% 36% 4	350
	11th to 20th	Night	12% 5% 7% 35% 37% 4	348
	21st to end	Night	8% 5% 7% 29% 45% 6%	394
August	1st to 10th	Night	14% 3 7% 26% 43% 9%	395
	11th to 20th	Night	9% 2 7% 25% 44% 12%	534
	21st to end	Night	16% 6% 7% 26% 40% 5%	711
September	1st to 10th	Night	14% 5% 9% 38% 30% 5%	720
	11th to 20th	Night	20% 6% 10% 22% 35% 6%	720
	21st to end	Night	21% 6% 12% 33% 25% 3	720
October	1st to 10th	Night	26% 6% 13% 29% 25% 3	720
	11th to 20th	Night	29% 11% 12% 26% 18% 4	720
	21st to end	Night	33% 10% 16% 29% 10% 3	792
November	1st to 10th	Night	39% 10% 22% 21% 7%	740
	11th to 20th	Night	40% 11% 17% 24% 7% 1	760
	21st to end	Night	37% 11% 18% 25% 8%	760
December	1st to 10th	Night	32% 12% 21% 25% 9% 1	760
	11th to 20th	Night	43% 10% 20% 19% 7% 1	760
	21st to end	Night	48% 13% 16% 17% 4	836

Page generated at 2024-04-22 06:25:43. Version ac07

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