Crestview
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Crestview clear sky chart from 2005-11-06 to 2024-01-14.

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	10% 6% 3 6% 6% 4 5% 5% 6% 8% 41%	74800
	Night	10% 5% 2 5% 5% 3 4 5% 6% 8% 46%	74959
Transparency	Day	39% 6% 12% 18% 17% 8%	74534
	Night	35% 6% 13% 18% 19% 9%	74744
Seeing	Day	12% 9% 21% 24% 21% 14%	13540
	Night	12% 6% 21% 30% 25% 6%	23560

By Month

Percentage Cloud Cover SE (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	13% 7% 3 6% 5% 3 4 4 5% 7% 43%	1710
	11th to 20th	Day	12% 6% 2 4 4 2 4 4 4 7% 49%	1830
	21st to end	Day	16% 8% 3 6% 3 3 4 4 4 7% 43%	1980
February	1st to 10th	Day	16% 7% 3 5% 5% 3 4 4 5% 6% 43%	1800
	11th to 20th	Day	15% 5% 2 6% 4 3 4 4 5% 8% 44%	1748
	21st to end	Day	16% 7% 3 5% 5% 4 5% 5% 5% 6% 38%	1480
March	1st to 10th	Day	11% 4 2 5% 5% 3 4 5% 6% 7% 49%	1800
	11th to 20th	Day	12% 5% 3 5% 6% 3 5% 5% 6% 7% 43%	1916
	21st to end	Day	11% 5% 2 5% 5% 3 4 5% 5% 7% 47%	2241
April	1st to 10th	Day	13% 5% 2 5% 5% 2 4 4 5% 7% 46%	2160
	11th to 20th	Day	13% 5% 2 6% 5% 4 5% 4 4 7% 45%	2134
	21st to end	Day	7% 3 3 4 5% 3 4 4 5% 7% 56%	2160
May	1st to 10th	Day	7% 5% 2 4 4 3 5% 5% 7% 8% 51%	2222
	11th to 20th	Day	7% 5% 2 6% 7% 4 5% 6% 8% 9% 42%	2301
	21st to end	Day	6% 4 3 6% 7% 5% 7% 6% 6% 9% 41%	2531
June	1st to 10th	Day	8% 7% 4 9% 8% 5% 6% 7% 8% 10% 28%	2340
	11th to 20th	Day	5% 3 2 5% 6% 5% 8% 9% 9% 12% 36%	2340
	21st to end	Day	6% 5% 2 7% 8% 6% 9% 8% 9% 10% 30%	2340
July	1st to 10th	Day	8% 6% 4 8% 7% 6% 9% 9% 9% 11% 24%	2340
	11th to 20th	Day	8% 6% 4 7% 9% 5% 10% 9% 9% 11% 23%	2340
	21st to end	Day	6% 5% 3 8% 8% 5% 9% 8% 9% 11% 28%	2352
August	1st to 10th	Day	9% 4 3 6% 8% 6% 7% 8% 10% 12% 27%	2148
	11th to 20th	Day	10% 8% 3 8% 8% 5% 7% 9% 8% 9% 25%	2125
	21st to end	Day	11% 6% 4 9% 7% 5% 6% 6% 7% 8% 29%	2376
September	1st to 10th	Day	9% 7% 3 8% 8% 5% 6% 7% 7% 8% 32%	2084
	11th to 20th	Day	11% 7% 3 7% 7% 5% 5% 5% 5% 7% 36%	1980
	21st to end	Day	7% 5% 3 6% 6% 4 5% 6% 5% 6% 48%	1980
October	1st to 10th	Day	8% 5% 2 5% 5% 3 5% 4 5% 6% 51%	1980
	11th to 20th	Day	9% 3 2 3 4 2 4 3 5% 8% 57%	1980
	21st to end	Day	8% 4 2 5% 5% 3 3 3 4 6% 56%	2003
November	1st to 10th	Day	7% 5% 2 4 4 2 4 3 6% 7% 57%	1672
	11th to 20th	Day	9% 4 2 4 4 2 4 4 5% 8% 54%	1710
	21st to end	Day	13% 4 3 4 5% 3 4 5% 5% 6% 49%	1710
December	1st to 10th	Day	13% 5% 3 5% 5% 3 4 4 4 7% 47%	1710
	11th to 20th	Day	15% 8% 4 6% 5% 3 4 4 5% 5% 42%	2153
	21st to end	Day	18% 9% 3 6% 4 3 3 3 3 5% 42%	3124
January	1st to 10th	Night	14% 7% 3 5% 5% 3 5% 4 4 6% 46%	2451
	11th to 20th	Night	12% 7% 3 5% 4 2 4 4 6% 7% 47%	2203
	21st to end	Night	18% 6% 3 5% 4 3 4 4 4 5% 43%	2376
February	1st to 10th	Night	15% 6% 3 6% 5% 3 3 4 5% 6% 45%	2160
	11th to 20th	Night	18% 7% 2 4 4 2 3 3 4 6% 46%	2098
	21st to end	Night	16% 8% 2 6% 6% 3 4 4 5% 6% 40%	1776
March	1st to 10th	Night	11% 6% 2 5% 4 3 4 4 5% 7% 48%	2160
	11th to 20th	Night	11% 6% 3 5% 6% 3 4 5% 5% 8% 43%	2044
	21st to end	Night	10% 5% 2 4 5% 3 4 4 6% 8% 49%	2127
April	1st to 10th	Night	11% 7% 3 5% 5% 3 4 4 5% 8% 46%	1800
	11th to 20th	Night	13% 6% 2 5% 4 2 5% 4 5% 8% 46%	1775
	21st to end	Night	5% 3 2 3 4 3 5% 4 5% 7% 59%	1800
May	1st to 10th	Night	9% 3 2 3 3 3 5% 4 6% 7% 55%	1733
	11th to 20th	Night	5% 4 2 5% 5% 4 5% 6% 6% 10% 47%	1592
	21st to end	Night	5% 4 2 4 5% 3 4 5% 8% 12% 47%	1744
June	1st to 10th	Night	7% 4 3 6% 6% 4 6% 7% 8% 12% 37%	1620
	11th to 20th	Night	4 3 1 3 5% 4 6% 8% 10% 13% 43%	1620
	21st to end	Night	5% 3 3 5% 6% 3 6% 8% 8% 12% 40%	1620
July	1st to 10th	Night	5% 3 2 5% 6% 4 7% 8% 9% 13% 36%	1620
	11th to 20th	Night	5% 5% 2 4 6% 4 6% 7% 10% 14% 37%	1620
	21st to end	Night	3 2 3 4 5% 4 6% 9% 9% 14% 41%	1960
August	1st to 10th	Night	4 4 1 4 5% 3 6% 8% 10% 15% 41%	1790
	11th to 20th	Night	5% 4 2 6% 7% 5% 7% 8% 9% 13% 35%	1776
	21st to end	Night	8% 6% 3 7% 7% 5% 6% 6% 8% 11% 34%	1980
September	1st to 10th	Night	7% 5% 3 6% 5% 4 6% 7% 8% 12% 37%	1858
	11th to 20th	Night	9% 5% 2 5% 6% 4 5% 6% 7% 8% 43%	1980
	21st to end	Night	7% 5% 2 5% 5% 3 4 5% 5% 8% 51%	1980
October	1st to 10th	Night	6% 4 2 4 4 2 4 5% 7% 9% 53%	1980
	11th to 20th	Night	7% 5% 2 3 3 2 3 3 5% 7% 61%	1980
	21st to end	Night	10% 5% 2 4 4 2 3 5% 5% 5% 55%	2346
November	1st to 10th	Night	7% 5% 2 4 3 2 3 4 4 7% 59%	2406
	11th to 20th	Night	10% 4 2 4 4 3 3 3 5% 6% 55%	2470
	21st to end	Night	12% 6% 2 4 4 3 4 4 5% 7% 49%	2470
December	1st to 10th	Night	13% 6% 2 4 5% 2 4 4 5% 7% 46%	2470
	11th to 20th	Night	15% 6% 2 4 5% 2 4 4 4 6% 46%	3042
	21st to end	Night	17% 10% 3 5% 5% 2 3 4 4 5% 41%	4532

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	41% 3 6% 15% 25% 10%	1711
	11th to 20th	Day	34% 4 9% 18% 25% 10%	1830
	21st to end	Day	42% 3 5% 15% 23% 11%	1980
February	1st to 10th	Day	43% 3 7% 17% 20% 10%	1800
	11th to 20th	Day	39% 4 5% 18% 22% 12%	1758
	21st to end	Day	44% 6% 7% 17% 15% 11%	1480
March	1st to 10th	Day	34% 5% 7% 20% 22% 12%	1800
	11th to 20th	Day	39% 4 13% 16% 17% 10%	1916
	21st to end	Day	36% 5% 12% 19% 20% 9%	2241
April	1st to 10th	Day	37% 5% 10% 18% 20% 11%	2160
	11th to 20th	Day	39% 4 8% 19% 21% 10%	2134
	21st to end	Day	28% 4 10% 23% 25% 10%	2160
May	1st to 10th	Day	29% 5% 10% 22% 23% 10%	2222
	11th to 20th	Day	35% 7% 17% 19% 18% 4	2305
	21st to end	Day	37% 7% 14% 20% 19% 3	2531
June	1st to 10th	Day	47% 7% 15% 21% 8% 1	2340
	11th to 20th	Day	36% 9% 19% 25% 11% 1	2340
	21st to end	Day	43% 12% 19% 16% 9% 2	2340
July	1st to 10th	Day	46% 12% 23% 14% 4	2275
	11th to 20th	Day	48% 11% 23% 13% 4 1	2271
	21st to end	Day	43% 11% 22% 19% 5%	2220
August	1st to 10th	Day	43% 11% 23% 18% 4	2136
	11th to 20th	Day	48% 11% 22% 13% 6%	2125
	21st to end	Day	49% 10% 16% 15% 8% 2	2376
September	1st to 10th	Day	46% 9% 16% 14% 11% 5%	2084
	11th to 20th	Day	48% 6% 12% 15% 12% 7%	1980
	21st to end	Day	36% 6% 10% 18% 21% 9%	1980
October	1st to 10th	Day	33% 5% 9% 19% 20% 14%	1980
	11th to 20th	Day	26% 4 7% 22% 27% 14%	1980
	21st to end	Day	31% 3 4 14% 27% 20%	2003
November	1st to 10th	Day	27% 4 8% 19% 24% 17%	1672
	11th to 20th	Day	30% 3 7% 18% 28% 15%	1710
	21st to end	Day	35% 4 7% 20% 21% 13%	1710
December	1st to 10th	Day	38% 3 11% 18% 20% 10%	1710
	11th to 20th	Day	45% 2 5% 17% 20% 11%	2150
	21st to end	Day	46% 2 4 19% 22% 7%	3124
January	1st to 10th	Night	40% 4 6% 14% 24% 12%	2451
	11th to 20th	Night	36% 4 7% 17% 25% 11%	2203
	21st to end	Night	44% 3 5% 12% 25% 10%	2376
February	1st to 10th	Night	40% 2 6% 18% 21% 12%	2160
	11th to 20th	Night	41% 3 6% 14% 21% 15%	2099
	21st to end	Night	46% 4 7% 15% 16% 13%	1776
March	1st to 10th	Night	35% 4 9% 18% 22% 12%	2160
	11th to 20th	Night	38% 4 11% 19% 18% 10%	2044
	21st to end	Night	34% 4 11% 21% 20% 10%	2127
April	1st to 10th	Night	39% 4 11% 14% 20% 12%	1800
	11th to 20th	Night	37% 4 8% 20% 22% 9%	1775
	21st to end	Night	25% 3 10% 27% 25% 9%	1800
May	1st to 10th	Night	28% 3 14% 20% 26% 9%	1733
	11th to 20th	Night	31% 7% 19% 19% 20% 4	1593
	21st to end	Night	29% 7% 17% 25% 17% 5%	1745
June	1st to 10th	Night	36% 9% 19% 24% 11% 1	1620
	11th to 20th	Night	26% 12% 24% 25% 11% 2	1620
	21st to end	Night	33% 11% 27% 19% 10% 1	1620
July	1st to 10th	Night	34% 15% 26% 20% 5%	1575
	11th to 20th	Night	30% 15% 35% 15% 5%	1566
	21st to end	Night	27% 12% 35% 22% 4	1851
August	1st to 10th	Night	28% 13% 32% 22% 4 1	1778
	11th to 20th	Night	35% 13% 32% 15% 5%	1776
	21st to end	Night	41% 12% 19% 18% 8% 3	1980
September	1st to 10th	Night	36% 9% 23% 16% 11% 4	1858
	11th to 20th	Night	36% 9% 17% 18% 15% 5%	1980
	21st to end	Night	31% 7% 14% 19% 21% 8%	1980
October	1st to 10th	Night	27% 5% 11% 19% 23% 14%	1980
	11th to 20th	Night	24% 3 8% 21% 30% 14%	1980
	21st to end	Night	32% 3 4 16% 26% 18%	2346
November	1st to 10th	Night	26% 4 7% 19% 26% 18%	2406
	11th to 20th	Night	31% 3 5% 18% 28% 15%	2470
	21st to end	Night	35% 3 8% 18% 21% 14%	2470
December	1st to 10th	Night	38% 4 9% 19% 22% 8%	2470
	11th to 20th	Night	40% 3 7% 13% 24% 12%	3044
	21st to end	Night	47% 3 5% 19% 22% 5%	4532

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	19% 19% 39% 16% 6% 1	270
	11th to 20th	Day	12% 19% 36% 22% 9% 2	249
	21st to end	Day	20% 23% 41% 11% 5%	264
February	1st to 10th	Day	20% 28% 32% 16% 5%	240
	11th to 20th	Day	23% 21% 35% 19% 2	240
	21st to end	Day	13% 24% 45% 14% 4	198
March	1st to 10th	Day	12% 23% 43% 16% 5%	240
	11th to 20th	Day	17% 18% 33% 21% 9% 2	356
	21st to end	Day	15% 14% 35% 23% 11% 2	462
April	1st to 10th	Day	17% 16% 28% 25% 11% 2	420
	11th to 20th	Day	15% 15% 28% 26% 13% 2	412
	21st to end	Day	10% 10% 27% 31% 18% 4	420
May	1st to 10th	Day	10% 9% 24% 28% 21% 8%	423
	11th to 20th	Day	9% 4 20% 29% 23% 16%	447
	21st to end	Day	9% 2 16% 29% 23% 20%	485
June	1st to 10th	Day	12% 3 12% 30% 24% 19%	450
	11th to 20th	Day	8% 4 8% 26% 27% 26%	450
	21st to end	Day	7% 2 11% 23% 28% 29%	450
July	1st to 10th	Day	7% 2 5% 19% 29% 38%	445
	11th to 20th	Day	6% 2 4 17% 31% 41%	444
	21st to end	Day	5% 1 8% 18% 37% 30%	488
August	1st to 10th	Day	7% 4 19% 33% 37%	446
	11th to 20th	Day	10% 1 4 21% 32% 32%	439
	21st to end	Day	12% 3 7% 23% 31% 24%	495
September	1st to 10th	Day	10% 3 8% 23% 32% 24%	450
	11th to 20th	Day	15% 3 8% 29% 31% 13%	450
	21st to end	Day	10% 2 11% 30% 34% 14%	450
October	1st to 10th	Day	9% 4 23% 34% 24% 6%	450
	11th to 20th	Day	9% 4 20% 33% 26% 8%	450
	21st to end	Day	11% 10% 24% 32% 20% 4	410
November	1st to 10th	Day	15% 6% 26% 36% 14% 4	270
	11th to 20th	Day	11% 13% 35% 30% 10% 1	270
	21st to end	Day	14% 12% 36% 26% 11% 1	270
December	1st to 10th	Day	17% 16% 34% 21% 10% 2	270
	11th to 20th	Day	22% 15% 38% 20% 4 1	270
	21st to end	Day	27% 16% 27% 22% 7% 1	297
January	1st to 10th	Night	19% 11% 34% 29% 7% 1	760
	11th to 20th	Night	15% 12% 29% 34% 10%	735
	21st to end	Night	22% 11% 33% 28% 6%	792
February	1st to 10th	Night	17% 11% 32% 33% 6% 1	720
	11th to 20th	Night	18% 10% 36% 26% 9%	703
	21st to end	Night	19% 12% 36% 29% 4	592
March	1st to 10th	Night	14% 12% 33% 34% 8%	720
	11th to 20th	Night	13% 10% 34% 30% 12% 1	720
	21st to end	Night	12% 10% 32% 32% 13% 1	741
April	1st to 10th	Night	15% 11% 22% 39% 14% 1	540
	11th to 20th	Night	14% 7% 25% 34% 19% 1	533
	21st to end	Night	7% 6% 22% 42% 23% 1	540
May	1st to 10th	Night	10% 4 19% 41% 22% 4	540
	11th to 20th	Night	7% 3 14% 37% 34% 6%	531
	21st to end	Night	7% 2 10% 30% 44% 8%	584
June	1st to 10th	Night	9% 2 8% 29% 42% 10%	540
	11th to 20th	Night	4 3 6% 29% 45% 13%	540
	21st to end	Night	5% 2 6% 21% 49% 17%	540
July	1st to 10th	Night	6% 2 2 21% 47% 22%	525
	11th to 20th	Night	6% 1 3 15% 46% 29%	522
	21st to end	Night	3 1 2 20% 53% 21%	591
August	1st to 10th	Night	4 1 2 14% 50% 28%	537
	11th to 20th	Night	6% 1 2 15% 51% 25%	534
	21st to end	Night	9% 3 7% 20% 44% 18%	594
September	1st to 10th	Night	10% 2 5% 24% 42% 18%	598
	11th to 20th	Night	12% 2 10% 29% 40% 8%	720
	21st to end	Night	10% 2 11% 30% 39% 8%	720
October	1st to 10th	Night	8% 1 23% 37% 28% 3	720
	11th to 20th	Night	10% 3 19% 35% 29% 4	720
	21st to end	Night	12% 5% 22% 36% 23% 1	792
November	1st to 10th	Night	10% 6% 24% 38% 20% 2	740
	11th to 20th	Night	11% 8% 29% 37% 15% 1	760
	21st to end	Night	14% 6% 30% 35% 14% 1	760
December	1st to 10th	Night	17% 7% 29% 30% 16% 1	760
	11th to 20th	Night	17% 9% 29% 32% 13% 1	760
	21st to end	Night	23% 9% 28% 31% 9% 1	836

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