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 2025-09-19.

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	20% 9% 3 7% 5% 4 4 4 5% 6% 33%	131415
	Night	23% 10% 3 7% 5% 4 4 3 5% 6% 31%	126351
Transparency	Day	53% 6% 13% 18% 9% 2	131133
	Night	56% 6% 11% 17% 8% 1	126210
Seeing	Day	27% 11% 20% 25% 15% 3	16115
	Night	31% 10% 15% 26% 17% 2	24373

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	39% 13% 3 9% 6% 5% 4 3 4 5% 8%	3639
	11th to 20th	Day	19% 11% 3 9% 5% 5% 5% 4 5% 6% 28%	3616
	21st to end	Day	31% 9% 3 7% 3 3 3 3 4 4 30%	4121
February	1st to 10th	Day	30% 13% 4 8% 6% 4 4 3 5% 7% 17%	1800
	11th to 20th	Day	32% 14% 4 8% 5% 4 3 3 3 6% 18%	1755
	21st to end	Day	28% 15% 4 9% 6% 4 4 3 4 3 20%	1565
March	1st to 10th	Day	19% 14% 4 9% 6% 6% 6% 4 7% 7% 19%	4604
	11th to 20th	Day	21% 14% 4 9% 6% 5% 5% 4 4 4 25%	5000
	21st to end	Day	27% 13% 4 10% 6% 6% 6% 4 6% 6% 12%	5691
April	1st to 10th	Day	26% 13% 3 9% 5% 5% 5% 5% 6% 6% 16%	2400
	11th to 20th	Day	22% 11% 3 8% 6% 5% 5% 4 5% 6% 25%	2378
	21st to end	Day	20% 11% 4 10% 7% 6% 4 4 5% 6% 22%	2646
May	1st to 10th	Day	17% 7% 2 7% 4 4 5% 5% 5% 7% 37%	6320
	11th to 20th	Day	23% 11% 3 8% 5% 4 5% 4 5% 6% 26%	6277
	21st to end	Day	21% 10% 3 8% 4 5% 5% 4 5% 8% 28%	6903
June	1st to 10th	Day	21% 10% 3 7% 5% 5% 4 4 6% 7% 28%	2800
	11th to 20th	Day	21% 11% 4 9% 6% 6% 5% 4 6% 7% 21%	2984
	21st to end	Day	13% 7% 2 9% 6% 5% 5% 3 6% 7% 38%	3000
July	1st to 10th	Day	9% 4 1 4 3 3 3 3 4 5% 63%	6780
	11th to 20th	Day	6% 3 1 4 3 3 2 2 3 5% 69%	6348
	21st to end	Day	9% 4 2 5% 3 3 4 3 5% 6% 57%	6874
August	1st to 10th	Day	6% 4 2 5% 2 4 3 3 5% 7% 59%	4460
	11th to 20th	Day	12% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	4156
	21st to end	Day	18% 8% 2 7% 4 4 4 3 4 6% 41%	4448
September	1st to 10th	Day	10% 6% 2 6% 4 4 4 3 5% 6% 49%	2400
	11th to 20th	Day	15% 7% 3 7% 5% 4 4 4 6% 7% 38%	2377
	21st to end	Day	19% 7% 3 7% 4 4 4 3 5% 8% 37%	2012
October	1st to 10th	Day	18% 6% 2 7% 4 4 4 3 6% 10% 38%	3180
	11th to 20th	Day	29% 9% 3 7% 4 4 4 3 5% 6% 26%	3161
	21st to end	Day	29% 9% 3 9% 6% 5% 5% 3 5% 6% 21%	3241
November	1st to 10th	Day	32% 10% 4 7% 5% 5% 4 5% 4 5% 18%	1630
	11th to 20th	Day	32% 11% 3 9% 4 4 3 4 4 5% 21%	1600
	21st to end	Day	31% 10% 3 9% 5% 4 4 3 5% 5% 20%	1600
December	1st to 10th	Day	23% 8% 3 6% 5% 6% 5% 4 6% 7% 27%	2620
	11th to 20th	Day	33% 12% 3 8% 6% 6% 4 4 5% 5% 13%	3025
	21st to end	Day	33% 13% 4 10% 6% 5% 4 3 4 4 13%	4004
January	1st to 10th	Night	37% 14% 4 9% 6% 6% 5% 3 4 4 9%	6306
	11th to 20th	Night	20% 10% 3 7% 5% 4 4 3 5% 7% 31%	6282
	21st to end	Night	29% 9% 3 6% 5% 4 4 3 4 5% 30%	6837
February	1st to 10th	Night	31% 13% 3 9% 5% 5% 4 3 3 6% 19%	2600
	11th to 20th	Night	29% 13% 3 8% 5% 4 4 4 4 4 23%	2532
	21st to end	Night	30% 11% 3 8% 5% 3 4 4 5% 5% 21%	2065
March	1st to 10th	Night	20% 14% 3 8% 5% 5% 5% 4 7% 8% 21%	5288
	11th to 20th	Night	25% 10% 3 7% 4 4 4 3 5% 6% 28%	4999
	21st to end	Night	33% 13% 3 9% 5% 4 5% 4 5% 5% 13%	5283
April	1st to 10th	Night	24% 11% 4 9% 6% 5% 6% 5% 5% 7% 19%	2000
	11th to 20th	Night	20% 11% 3 8% 5% 5% 5% 4 6% 6% 29%	1969
	21st to end	Night	21% 10% 3 9% 7% 5% 5% 3 5% 7% 24%	1752
May	1st to 10th	Night	18% 9% 2 7% 4 4 4 3 4 5% 40%	3640
	11th to 20th	Night	20% 11% 3 8% 5% 5% 5% 4 6% 7% 26%	3616
	21st to end	Night	17% 12% 3 9% 5% 5% 5% 4 6% 7% 26%	3972
June	1st to 10th	Night	16% 9% 4 8% 6% 5% 5% 4 4 7% 33%	1600
	11th to 20th	Night	18% 10% 3 8% 6% 6% 5% 5% 6% 7% 27%	1410
	21st to end	Night	13% 7% 4 6% 4 4 3 4 5% 6% 44%	1400
July	1st to 10th	Night	7% 4 2 5% 3 3 3 2 3 4 63%	3180
	11th to 20th	Night	3 3 1 2 3 2 3 2 3 4 75%	3594
	21st to end	Night	9% 3 1 4 2 2 3 3 5% 7% 62%	3969
August	1st to 10th	Night	5% 4 1 4 3 3 2 2 4 6% 67%	2690
	11th to 20th	Night	14% 5% 2 7% 4 3 3 3 4 6% 48%	2902
	21st to end	Night	17% 6% 2 5% 3 3 4 3 4 6% 47%	3467
September	1st to 10th	Night	11% 4 2 5% 3 4 4 4 5% 7% 52%	2000
	11th to 20th	Night	15% 8% 3 7% 4 4 4 3 4 5% 42%	1980
	21st to end	Night	17% 7% 2 8% 4 4 4 3 4 6% 42%	2163
October	1st to 10th	Night	18% 6% 2 7% 4 3 4 4 5% 8% 41%	3800
	11th to 20th	Night	28% 8% 3 6% 3 5% 5% 3 5% 6% 29%	3777
	21st to end	Night	30% 10% 3 7% 4 4 4 3 5% 6% 24%	4320
November	1st to 10th	Night	33% 9% 3 8% 4 5% 4 3 5% 5% 21%	2666
	11th to 20th	Night	32% 10% 3 8% 6% 5% 4 3 4 5% 22%	2800
	21st to end	Night	30% 11% 4 7% 5% 4 4 3 5% 6% 22%	2800
December	1st to 10th	Night	22% 9% 3 6% 4 4 5% 5% 6% 7% 29%	4560
	11th to 20th	Night	34% 13% 4 9% 5% 4 4 4 5% 4 14%	5180
	21st to end	Night	33% 14% 4 10% 6% 5% 4 3 4 4 14%	6952

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	75% 6% 5% 10% 3	3639
	11th to 20th	Day	55% 6% 10% 19% 8% 1	3640
	21st to end	Day	59% 4 7% 16% 13% 1	4121
February	1st to 10th	Day	69% 7% 10% 9% 5% 1	1800
	11th to 20th	Day	69% 6% 8% 10% 6% 1	1764
	21st to end	Day	69% 6% 7% 12% 5%	1565
March	1st to 10th	Day	63% 7% 12% 11% 6%	4604
	11th to 20th	Day	63% 6% 9% 20% 2	5000
	21st to end	Day	71% 7% 12% 8% 1	5691
April	1st to 10th	Day	68% 10% 13% 8% 1	2400
	11th to 20th	Day	61% 8% 10% 14% 6% 1	2378
	21st to end	Day	66% 8% 11% 11% 4 1	2646
May	1st to 10th	Day	46% 8% 12% 24% 8%	6320
	11th to 20th	Day	57% 11% 15% 14% 2	6280
	21st to end	Day	55% 8% 21% 15% 2	6904
June	1st to 10th	Day	57% 9% 16% 14% 5%	2800
	11th to 20th	Day	64% 8% 13% 11% 3	2984
	21st to end	Day	47% 7% 18% 19% 8% 2	3000
July	1st to 10th	Day	27% 4 16% 23% 17% 12%	6706
	11th to 20th	Day	22% 3 11% 30% 31% 4	6272
	21st to end	Day	30% 3 20% 34% 12% 1	6681
August	1st to 10th	Day	26% 5% 11% 37% 19% 2	4443
	11th to 20th	Day	45% 4 19% 22% 8% 1	4195
	21st to end	Day	45% 4 11% 26% 12% 1	4447
September	1st to 10th	Day	35% 7% 16% 25% 13% 5%	2400
	11th to 20th	Day	46% 8% 13% 18% 13% 3	2377
	21st to end	Day	47% 7% 16% 17% 11% 2	2012
October	1st to 10th	Day	43% 5% 13% 31% 8%	3180
	11th to 20th	Day	59% 4 11% 16% 8% 1	3161
	21st to end	Day	66% 4 11% 10% 7% 2	3241
November	1st to 10th	Day	68% 7% 10% 11% 4	1630
	11th to 20th	Day	68% 8% 7% 8% 6% 2	1600
	21st to end	Day	66% 7% 7% 10% 8% 2	1600
December	1st to 10th	Day	53% 5% 7% 20% 14% 1	2620
	11th to 20th	Day	74% 5% 10% 9% 2	3028
	21st to end	Day	74% 6% 9% 8% 2	4004
January	1st to 10th	Night	75% 5% 7% 9% 3 1	6306
	11th to 20th	Night	51% 7% 11% 22% 9% 1	6320
	21st to end	Night	58% 5% 9% 17% 11% 1	6837
February	1st to 10th	Night	69% 6% 9% 9% 6% 1	2600
	11th to 20th	Night	63% 8% 10% 10% 7% 3	2534
	21st to end	Night	66% 8% 9% 12% 5%	2065
March	1st to 10th	Night	60% 7% 12% 14% 7%	5288
	11th to 20th	Night	58% 7% 12% 20% 3 1	5000
	21st to end	Night	72% 8% 11% 9%	5283
April	1st to 10th	Night	66% 10% 13% 10% 1	2000
	11th to 20th	Night	58% 7% 12% 14% 7% 1	1969
	21st to end	Night	64% 8% 10% 12% 5% 1	1752
May	1st to 10th	Night	48% 6% 13% 23% 10%	3637
	11th to 20th	Night	56% 10% 17% 14% 2 1	3616
	21st to end	Night	58% 11% 17% 13% 1	3972
June	1st to 10th	Night	55% 8% 15% 16% 5%	1600
	11th to 20th	Night	59% 8% 16% 14% 2	1410
	21st to end	Night	43% 7% 20% 20% 7% 2	1400
July	1st to 10th	Night	30% 5% 15% 21% 16% 13%	3145
	11th to 20th	Night	18% 3 12% 31% 35% 2	3547
	21st to end	Night	27% 4 20% 34% 13% 2	3857
August	1st to 10th	Night	21% 4 11% 41% 21% 2	2682
	11th to 20th	Night	42% 4 21% 21% 8% 3	2929
	21st to end	Night	42% 4 13% 29% 11% 1	3467
September	1st to 10th	Night	33% 7% 16% 25% 14% 5%	2000
	11th to 20th	Night	46% 8% 9% 19% 13% 5%	1980
	21st to end	Night	45% 9% 12% 20% 11% 3	2163
October	1st to 10th	Night	43% 4 15% 31% 6% 1	3800
	11th to 20th	Night	57% 3 11% 19% 8%	3777
	21st to end	Night	64% 5% 9% 14% 9%	4320
November	1st to 10th	Night	67% 8% 10% 11% 4	2666
	11th to 20th	Night	67% 7% 8% 10% 6% 3	2800
	21st to end	Night	65% 7% 7% 10% 8% 1	2800
December	1st to 10th	Night	53% 5% 8% 20% 13% 1	4560
	11th to 20th	Night	74% 5% 9% 10% 3	5176
	21st to end	Night	75% 8% 7% 8% 2	6952

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	41% 16% 17% 14% 9% 4	200
	11th to 20th	Day	34% 15% 16% 21% 11% 4	200
	21st to end	Day	39% 13% 18% 17% 9% 5%	272
February	1st to 10th	Day	41% 11% 20% 17% 8% 2	400
	11th to 20th	Day	46% 13% 19% 15% 7% 1	395
	21st to end	Day	38% 16% 19% 20% 5%	371
March	1st to 10th	Day	32% 18% 21% 20% 8% 1	500
	11th to 20th	Day	33% 16% 21% 19% 9% 2	500
	21st to end	Day	38% 15% 22% 17% 8%	550
April	1st to 10th	Day	34% 16% 21% 17% 11% 1	500
	11th to 20th	Day	27% 19% 25% 18% 8% 3	492
	21st to end	Day	26% 16% 23% 22% 10% 2	500
May	1st to 10th	Day	21% 11% 26% 28% 11% 2	503
	11th to 20th	Day	30% 11% 23% 20% 12% 3	528
	21st to end	Day	30% 10% 21% 23% 12% 3	573
June	1st to 10th	Day	26% 9% 20% 26% 16% 3	530
	11th to 20th	Day	26% 13% 23% 24% 11% 3	714
	21st to end	Day	18% 8% 17% 34% 20% 3	730
July	1st to 10th	Day	15% 6% 16% 36% 24% 3	721
	11th to 20th	Day	11% 7% 20% 37% 22% 4	538
	21st to end	Day	10% 3 17% 38% 26% 6%	575
August	1st to 10th	Day	14% 5% 13% 35% 26% 8%	527
	11th to 20th	Day	10% 4 14% 36% 28% 8%	517
	21st to end	Day	17% 7% 21% 32% 17% 7%	583
September	1st to 10th	Day	15% 6% 21% 37% 17% 4	530
	11th to 20th	Day	20% 7% 19% 29% 21% 5%	523
	21st to end	Day	20% 9% 23% 27% 19% 3	490
October	1st to 10th	Day	26% 10% 18% 23% 19% 3	490
	11th to 20th	Day	32% 9% 18% 21% 15% 4	490
	21st to end	Day	35% 14% 19% 19% 10% 4	420
November	1st to 10th	Day	40% 12% 16% 18% 14%	233
	11th to 20th	Day	38% 18% 20% 9% 13% 4	200
	21st to end	Day	39% 11% 16% 16% 14% 4	200
December	1st to 10th	Day	43% 10% 15% 13% 12% 8%	200
	11th to 20th	Day	46% 10% 20% 17% 7% 2	200
	21st to end	Day	40% 14% 15% 20% 10% 1	220
January	1st to 10th	Night	44% 15% 18% 17% 6%	800
	11th to 20th	Night	37% 13% 17% 24% 9% 1	800
	21st to end	Night	36% 10% 18% 26% 8% 1	880
February	1st to 10th	Night	39% 11% 19% 23% 7% 1	800
	11th to 20th	Night	37% 12% 15% 27% 9% 1	784
	21st to end	Night	40% 13% 16% 23% 7% 1	660
March	1st to 10th	Night	33% 13% 18% 23% 11% 1	800
	11th to 20th	Night	35% 12% 19% 24% 10% 1	800
	21st to end	Night	38% 14% 15% 24% 8% 1	880
April	1st to 10th	Night	34% 11% 16% 25% 12% 2	800
	11th to 20th	Night	29% 10% 20% 28% 11% 2	781
	21st to end	Night	30% 15% 11% 29% 14% 1	552
May	1st to 10th	Night	23% 12% 14% 31% 19% 1	400
	11th to 20th	Night	24% 7% 12% 30% 25% 2	394
	21st to end	Night	24% 10% 12% 24% 26% 3	433
June	1st to 10th	Night	23% 10% 13% 29% 24% 2	400
	11th to 20th	Night	28% 10% 13% 28% 20% 1	400
	21st to end	Night	20% 4 11% 31% 31% 3	400
July	1st to 10th	Night	13% 7% 9% 33% 34% 4	390
	11th to 20th	Night	11% 5% 7% 35% 39% 4	388
	21st to end	Night	9% 4 6% 30% 45% 6%	438
August	1st to 10th	Night	14% 2 6% 24% 45% 9%	440
	11th to 20th	Night	12% 2 7% 25% 42% 11%	594
	21st to end	Night	16% 5% 7% 27% 39% 5%	791
September	1st to 10th	Night	14% 5% 8% 36% 31% 6%	800
	11th to 20th	Night	21% 6% 10% 24% 34% 6%	792
	21st to end	Night	22% 6% 12% 32% 25% 3	760
October	1st to 10th	Night	25% 5% 13% 29% 24% 3	760
	11th to 20th	Night	30% 10% 12% 26% 18% 4	760
	21st to end	Night	34% 9% 16% 29% 10% 2	836
November	1st to 10th	Night	39% 10% 22% 21% 7%	780
	11th to 20th	Night	42% 11% 17% 23% 6% 1	800
	21st to end	Night	37% 11% 18% 26% 9%	800
December	1st to 10th	Night	32% 11% 21% 25% 11% 1	800
	11th to 20th	Night	43% 10% 21% 19% 6% 1	800
	21st to end	Night	49% 13% 17% 17% 4	880

Page generated at 2025-09-15 22:49:13. Version ac07

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