Navajo Flats
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Navajo Flats clear sky chart from 2005-11-06 to 2025-04-11.

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	3 3 1 3 3 3 3 3 4 6% 68%	117352
	Night	3 4 1 4 3 3 3 3 4 6% 65%	119829
Transparency	Day	18% 2 6% 19% 28% 27%	117106
	Night	21% 3 7% 18% 26% 25%	119664
Seeing	Day	6% 9% 23% 33% 23% 7%	16049
	Night	6% 4 12% 36% 35% 7%	25748

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	5% 4 2 5% 3 3 4 4 5% 7% 59%	3805
	11th to 20th	Day	5% 6% 2 4 3 3 4 3 4 6% 61%	4100
	21st to end	Day	7% 7% 2 7% 3 4 4 4 6% 8% 47%	4510
February	1st to 10th	Day	10% 7% 2 4 4 3 3 3 4 6% 53%	1901
	11th to 20th	Day	6% 6% 2 5% 5% 4 4 4 6% 8% 49%	1950
	21st to end	Day	8% 8% 2 7% 4 3 4 4 5% 6% 49%	1650
March	1st to 10th	Day	10% 7% 3 6% 4 5% 5% 5% 6% 7% 42%	4594
	11th to 20th	Day	4 5% 2 5% 4 4 5% 4 5% 7% 55%	5000
	21st to end	Day	4 6% 2 7% 5% 5% 6% 5% 7% 9% 45%	5779
April	1st to 10th	Day	6% 5% 2 4 4 4 4 3 5% 7% 56%	2400
	11th to 20th	Day	5% 4 1 4 3 3 4 4 5% 8% 59%	2251
	21st to end	Day	3 3 1 3 3 3 3 3 5% 7% 66%	2280
May	1st to 10th	Day	2 2 1 3 2 2 2 2 4 5% 77%	3800
	11th to 20th	Day	1 1 1 1 2 2 2 2 4 5% 79%	3947
	21st to end	Day	1 1 2 2 2 2 2 3 5% 81%	4778
June	1st to 10th	Day	2 2 1 2 2 2 2 3 5% 7% 72%	2660
	11th to 20th	Day	1 1 1 1 1 2 2 3 88%	2660
	21st to end	Day	1 1 2 1 1 1 2 2 87%	2660
July	1st to 10th	Day	1 1 1 1 1 2 2 92%	4420
	11th to 20th	Day	1 1 1 1 1 2 2 2 2 4 83%	4207
	21st to end	Day	1 1 1 1 1 1 2 1 2 4 86%	4455
August	1st to 10th	Day	1 1 1 1 1 2 1 3 4 86%	3875
	11th to 20th	Day	1 1 1 2 93%	3724
	21st to end	Day	1 1 1 1 1 2 2 91%	4180
September	1st to 10th	Day	1 1 1 1 1 1 1 3 4 87%	2280
	11th to 20th	Day	1 1 2 1 2 2 2 2 4 84%	2258
	21st to end	Day	1 1 2 2 2 2 2 4 5% 81%	2090
October	1st to 10th	Day	1 1 2 2 2 2 3 3 6% 78%	3225
	11th to 20th	Day	1 1 1 3 2 2 3 2 3 4 78%	3161
	21st to end	Day	2 3 1 4 3 3 3 3 4 7% 67%	3448
November	1st to 10th	Day	4 4 1 4 3 2 3 2 5% 7% 65%	1850
	11th to 20th	Day	3 3 1 4 3 4 4 4 4 6% 64%	1800
	21st to end	Day	6% 4 2 5% 3 4 4 4 6% 7% 56%	1800
December	1st to 10th	Day	3 4 3 5% 4 5% 4 4 5% 8% 57%	2822
	11th to 20th	Day	7% 6% 3 6% 4 4 5% 5% 7% 8% 45%	3028
	21st to end	Day	8% 7% 2 6% 5% 4 5% 5% 7% 10% 40%	4004
January	1st to 10th	Night	5% 7% 2 6% 3 3 4 3 5% 7% 55%	6132
	11th to 20th	Night	4 6% 2 5% 3 3 3 3 4 6% 60%	5880
	21st to end	Night	8% 9% 2 5% 4 4 4 4 5% 7% 47%	6468
February	1st to 10th	Night	7% 6% 3 5% 3 4 4 3 5% 6% 54%	2496
	11th to 20th	Night	5% 4 2 5% 4 4 5% 4 5% 8% 55%	2338
	21st to end	Night	6% 6% 2 5% 4 5% 4 3 4 6% 57%	1980
March	1st to 10th	Night	5% 9% 3 7% 5% 5% 6% 4 7% 8% 40%	5298
	11th to 20th	Night	4 5% 2 6% 4 4 4 4 6% 6% 56%	5000
	21st to end	Night	6% 6% 3 7% 5% 4 4 4 6% 7% 48%	5194
April	1st to 10th	Night	4 4 2 4 4 3 4 4 5% 8% 60%	2000
	11th to 20th	Night	4 4 1 3 3 3 2 3 5% 5% 67%	1883
	21st to end	Night	3 3 1 3 3 2 4 4 4 7% 67%	1900
May	1st to 10th	Night	1 3 1 2 1 2 1 2 3 4 80%	3180
	11th to 20th	Night	1 1 1 2 3 3 3 4 7% 76%	2947
	21st to end	Night	1 1 1 1 2 2 2 5% 6% 79%	2794
June	1st to 10th	Night	1 1 2 2 1 2 2 5% 6% 77%	1520
	11th to 20th	Night	1 1 2 1 1 2 5% 87%	1520
	21st to end	Night	1 1 1 1 1 2 3 89%	1520
July	1st to 10th	Night	1 1 1 1 2 93%	2540
	11th to 20th	Night	1 1 1 1 1 1 2 4 87%	2754
	21st to end	Night	1 1 1 1 1 2 2 3 87%	3109
August	1st to 10th	Night	1 1 1 1 1 2 1 2 3 86%	3071
	11th to 20th	Night	1 1 1 1 1 1 3 92%	3126
	21st to end	Night	1 1 1 1 1 1 2 92%	3498
September	1st to 10th	Night	1 1 1 1 2 1 2 4 86%	1900
	11th to 20th	Night	1 1 2 1 2 2 2 2 4 84%	1920
	21st to end	Night	1 2 2 1 2 2 2 4 84%	2090
October	1st to 10th	Night	1 1 1 1 1 1 2 4 4 82%	3738
	11th to 20th	Night	1 2 1 2 2 2 3 2 3 4 78%	3777
	21st to end	Night	1 3 1 4 2 3 2 2 4 5% 73%	4121
November	1st to 10th	Night	2 3 1 4 2 2 3 3 4 6% 68%	2447
	11th to 20th	Night	2 3 1 5% 3 3 3 3 5% 6% 65%	2600
	21st to end	Night	4 5% 2 5% 4 4 4 5% 6% 8% 53%	2600
December	1st to 10th	Night	4 4 1 3 4 4 5% 3 5% 8% 58%	4360
	11th to 20th	Night	7% 6% 3 7% 5% 5% 5% 5% 7% 8% 42%	5176
	21st to end	Night	7% 7% 3 9% 6% 6% 6% 5% 7% 10% 34%	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	24% 3 9% 33% 20% 10%	3805
	11th to 20th	Day	27% 2 7% 16% 22% 27%	4100
	21st to end	Day	35% 3 7% 16% 21% 18%	4510
February	1st to 10th	Day	33% 3 5% 19% 24% 16%	1901
	11th to 20th	Day	32% 4 7% 23% 24% 10%	1960
	21st to end	Day	36% 3 8% 20% 26% 7%	1650
March	1st to 10th	Day	39% 4 11% 17% 24% 5%	4594
	11th to 20th	Day	27% 5% 11% 33% 17% 8%	5000
	21st to end	Day	34% 5% 10% 30% 18% 3	5779
April	1st to 10th	Day	28% 4 10% 26% 23% 9%	2400
	11th to 20th	Day	24% 2 11% 28% 26% 10%	2254
	21st to end	Day	19% 3 8% 30% 31% 8%	2280
May	1st to 10th	Day	12% 2 7% 22% 36% 20%	3800
	11th to 20th	Day	10% 2 3 24% 43% 18%	3950
	21st to end	Day	9% 2 5% 32% 44% 8%	4778
June	1st to 10th	Day	14% 2 9% 21% 36% 18%	2660
	11th to 20th	Day	5% 1 4 15% 42% 32%	2660
	21st to end	Day	7% 1 2 8% 34% 49%	2660
July	1st to 10th	Day	3 1 1 4 17% 75%	4351
	11th to 20th	Day	9% 1 2 6% 18% 64%	4134
	21st to end	Day	6% 2 2 11% 28% 52%	4315
August	1st to 10th	Day	6% 1 1 7% 36% 48%	3860
	11th to 20th	Day	3 1 6% 30% 61%	3760
	21st to end	Day	4 1 1 10% 28% 57%	4179
September	1st to 10th	Day	5% 1 2 8% 31% 52%	2280
	11th to 20th	Day	8% 1 1 17% 43% 30%	2258
	21st to end	Day	9% 1 1 17% 40% 31%	2090
October	1st to 10th	Day	10% 2 3 14% 22% 50%	3225
	11th to 20th	Day	12% 3 4 20% 39% 23%	3161
	21st to end	Day	17% 3 3 12% 36% 28%	3448
November	1st to 10th	Day	20% 2 7% 22% 28% 21%	1850
	11th to 20th	Day	22% 3 9% 22% 26% 19%	1800
	21st to end	Day	27% 4 7% 16% 24% 22%	1800
December	1st to 10th	Day	26% 3 5% 17% 27% 22%	2822
	11th to 20th	Day	34% 5% 10% 18% 21% 11%	3028
	21st to end	Day	37% 4 12% 28% 15% 4	4004
January	1st to 10th	Night	29% 2 11% 28% 23% 8%	6132
	11th to 20th	Night	27% 2 7% 19% 23% 22%	5880
	21st to end	Night	36% 2 7% 18% 21% 16%	6468
February	1st to 10th	Night	30% 4 7% 18% 25% 15%	2496
	11th to 20th	Night	27% 4 8% 23% 27% 11%	2339
	21st to end	Night	30% 3 7% 24% 28% 8%	1980
March	1st to 10th	Night	38% 5% 8% 20% 24% 4	5298
	11th to 20th	Night	28% 5% 12% 30% 18% 7%	5000
	21st to end	Night	35% 4 14% 26% 18% 3	5194
April	1st to 10th	Night	23% 5% 14% 27% 21% 11%	2000
	11th to 20th	Night	20% 2 11% 28% 30% 9%	1883
	21st to end	Night	17% 4 10% 28% 33% 9%	1900
May	1st to 10th	Night	10% 2 7% 28% 29% 24%	3180
	11th to 20th	Night	11% 3 3 22% 39% 22%	2948
	21st to end	Night	10% 2 4 27% 42% 14%	2794
June	1st to 10th	Night	10% 2 9% 20% 35% 22%	1520
	11th to 20th	Night	6% 1 4 14% 38% 37%	1520
	21st to end	Night	4 1 2 7% 31% 55%	1520
July	1st to 10th	Night	2 1 5% 14% 78%	2500
	11th to 20th	Night	5% 1 1 6% 15% 72%	2704
	21st to end	Night	5% 2 1 5% 30% 57%	3011
August	1st to 10th	Night	6% 1 1 8% 28% 55%	3062
	11th to 20th	Night	3 1 4 25% 67%	3156
	21st to end	Night	3 1 2 5% 27% 61%	3498
September	1st to 10th	Night	7% 1 2 6% 27% 58%	1900
	11th to 20th	Night	9% 2 2 12% 38% 38%	1920
	21st to end	Night	7% 2 1 15% 42% 34%	2090
October	1st to 10th	Night	8% 1 3 12% 24% 53%	3738
	11th to 20th	Night	11% 3 3 20% 37% 26%	3777
	21st to end	Night	16% 2 2 14% 39% 28%	4121
November	1st to 10th	Night	18% 3 5% 22% 28% 23%	2447
	11th to 20th	Night	20% 3 9% 22% 26% 21%	2600
	21st to end	Night	27% 4 8% 17% 24% 19%	2600
December	1st to 10th	Night	24% 4 5% 16% 33% 18%	4360
	11th to 20th	Night	37% 5% 12% 18% 17% 11%	5176
	21st to end	Night	43% 4 13% 23% 13% 4	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	19% 14% 33% 24% 9% 1	275
	11th to 20th	Day	13% 15% 29% 28% 12% 3	400
	21st to end	Day	13% 13% 33% 24% 15% 2	440
February	1st to 10th	Day	14% 16% 28% 28% 12% 3	451
	11th to 20th	Day	12% 17% 30% 28% 12% 2	495
	21st to end	Day	12% 18% 33% 26% 9% 2	414
March	1st to 10th	Day	18% 16% 32% 25% 9%	500
	11th to 20th	Day	15% 15% 29% 29% 11% 1	500
	21st to end	Day	13% 18% 32% 26% 10% 2	550
April	1st to 10th	Day	12% 12% 30% 27% 17% 2	500
	11th to 20th	Day	9% 13% 32% 27% 16% 3	453
	21st to end	Day	4 12% 32% 30% 17% 5%	460
May	1st to 10th	Day	8% 10% 30% 31% 16% 5%	463
	11th to 20th	Day	2 9% 28% 33% 22% 6%	488
	21st to end	Day	3 12% 22% 34% 21% 7%	529
June	1st to 10th	Day	3 5% 20% 36% 26% 9%	490
	11th to 20th	Day	1 6% 22% 39% 24% 9%	490
	21st to end	Day	1 3 15% 36% 29% 16%	490
July	1st to 10th	Day	1 10% 39% 35% 15%	486
	11th to 20th	Day	1 1 8% 35% 35% 20%	484
	21st to end	Day	1 7% 34% 38% 19%	531
August	1st to 10th	Day	2 1 14% 38% 30% 16%	487
	11th to 20th	Day	1 1 9% 38% 34% 17%	477
	21st to end	Day	1 1 8% 34% 41% 15%	539
September	1st to 10th	Day	1 3 11% 37% 35% 13%	490
	11th to 20th	Day	2 4 17% 40% 31% 6%	490
	21st to end	Day	5% 17% 39% 32% 7%	490
October	1st to 10th	Day	2 6% 23% 37% 29% 4	490
	11th to 20th	Day	2 8% 23% 36% 26% 5%	490
	21st to end	Day	3 7% 23% 35% 27% 5%	539
November	1st to 10th	Day	5% 9% 24% 31% 27% 4	386
	11th to 20th	Day	5% 8% 28% 36% 20% 3	300
	21st to end	Day	11% 8% 25% 32% 20% 3	300
December	1st to 10th	Day	6% 12% 27% 38% 14% 3	262
	11th to 20th	Day	11% 14% 27% 27% 18% 5%	200
	21st to end	Day	15% 14% 32% 25% 10% 4	220
January	1st to 10th	Night	13% 6% 18% 36% 21% 6%	800
	11th to 20th	Night	9% 3 18% 43% 22% 5%	800
	21st to end	Night	12% 4 17% 42% 20% 4	880
February	1st to 10th	Night	13% 8% 14% 39% 23% 4	800
	11th to 20th	Night	8% 8% 17% 39% 23% 5%	784
	21st to end	Night	11% 8% 18% 44% 16% 3	660
March	1st to 10th	Night	10% 8% 18% 43% 19% 3	800
	11th to 20th	Night	9% 5% 16% 39% 26% 5%	800
	21st to end	Night	9% 9% 19% 37% 24% 3	880
April	1st to 10th	Night	7% 6% 16% 43% 25% 3	800
	11th to 20th	Night	7% 7% 19% 33% 30% 4	753
	21st to end	Night	4 6% 17% 37% 29% 7%	760
May	1st to 10th	Night	3 4 14% 40% 32% 7%	760
	11th to 20th	Night	2 4 13% 36% 39% 6%	635
	21st to end	Night	2 5% 11% 37% 38% 8%	430
June	1st to 10th	Night	2 3 7% 35% 48% 4	380
	11th to 20th	Night	8% 34% 50% 7%	380
	21st to end	Night	1 1 4 29% 57% 8%	380
July	1st to 10th	Night	1 20% 70% 9%	370
	11th to 20th	Night	1 12% 64% 22%	489
	21st to end	Night	1 1 12% 61% 24%	624
August	1st to 10th	Night	1 2 23% 58% 15%	699
	11th to 20th	Night	1 21% 63% 13%	752
	21st to end	Night	1 1 19% 63% 17%	836
September	1st to 10th	Night	1 1 4 24% 58% 13%	760
	11th to 20th	Night	1 1 5% 36% 46% 10%	760
	21st to end	Night	1 1 7% 33% 50% 9%	760
October	1st to 10th	Night	3 1 7% 40% 42% 7%	760
	11th to 20th	Night	4 2 9% 40% 38% 7%	760
	21st to end	Night	4 2 10% 41% 35% 9%	836
November	1st to 10th	Night	4 4 14% 37% 33% 8%	780
	11th to 20th	Night	4 3 14% 47% 26% 6%	800
	21st to end	Night	6% 5% 17% 43% 25% 6%	800
December	1st to 10th	Night	10% 5% 15% 41% 25% 4	800
	11th to 20th	Night	12% 4 17% 44% 20% 3	800
	21st to end	Night	12% 7% 20% 42% 17% 3	880

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