Fresno
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Fresno clear sky chart from 2005-11-06 to 2025-10-19.

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	5% 3 1 3 2 2 2 2 3 5% 71%	134890
	Night	6% 3 1 4 2 3 3 2 4 5% 67%	132261
Transparency	Day	18% 4 8% 17% 26% 27%	129928
	Night	20% 5% 9% 19% 25% 22%	128212
Seeing	Day	6% 5% 16% 30% 29% 15%	16589
	Night	7% 4 20% 39% 26% 5%	26066

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	8% 8% 3 9% 7% 6% 4 4 5% 7% 39%	3639
	11th to 20th	Day	7% 7% 2 6% 4 4 4 3 4 5% 53%	3990
	21st to end	Day	12% 7% 3 6% 5% 5% 5% 4 5% 7% 42%	4510
February	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 5% 6% 48%	1895
	11th to 20th	Day	10% 6% 2 4 4 3 4 4 5% 7% 52%	1950
	21st to end	Day	13% 5% 2 5% 5% 3 4 4 4 6% 48%	1650
March	1st to 10th	Day	12% 5% 2 7% 4 4 5% 4 6% 9% 42%	4518
	11th to 20th	Day	10% 4 2 6% 4 3 3 3 5% 7% 54%	4946
	21st to end	Day	11% 5% 2 4 3 3 4 4 5% 8% 51%	5835
April	1st to 10th	Day	8% 4 2 4 3 2 3 3 4 6% 61%	2400
	11th to 20th	Day	6% 4 1 3 3 3 3 3 5% 6% 63%	2369
	21st to end	Day	4 3 1 3 3 2 3 3 4 6% 68%	2400
May	1st to 10th	Day	3 2 1 2 1 1 1 1 2 3 81%	5520
	11th to 20th	Day	1 1 1 1 1 1 2 3 4 84%	5857
	21st to end	Day	1 1 1 1 1 1 1 2 3 86%	6902
June	1st to 10th	Day	2 1 1 2 2 2 1 2 4 5% 77%	2800
	11th to 20th	Day	1 1 1 1 1 1 1 1 3 90%	2800
	21st to end	Day	1 1 1 1 1 2 2 2 88%	2800
July	1st to 10th	Day	1 1 2 94%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 89%	6320
	21st to end	Day	1 1 1 1 1 1 2 4 88%	6445
August	1st to 10th	Day	1 1 1 1 1 1 1 1 2 90%	5488
	11th to 20th	Day	1 1 1 95%	5364
	21st to end	Day	1 1 1 1 1 1 1 2 3 88%	5984
September	1st to 10th	Day	1 1 1 1 1 1 1 2 2 89%	2400
	11th to 20th	Day	2 1 1 2 1 1 2 1 2 3 84%	2353
	21st to end	Day	1 1 1 1 1 1 2 2 3 4 83%	2200
October	1st to 10th	Day	1 1 2 1 2 2 2 3 4 81%	3386
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 79%	3242
	21st to end	Day	2 2 1 3 3 3 3 3 4 6% 70%	3448
November	1st to 10th	Day	5% 2 1 3 4 2 4 3 5% 7% 63%	1769
	11th to 20th	Day	8% 4 2 3 4 3 4 3 5% 7% 58%	1800
	21st to end	Day	8% 6% 2 5% 4 3 3 3 5% 7% 53%	1800
December	1st to 10th	Day	6% 6% 3 8% 5% 6% 5% 4 6% 7% 43%	2759
	11th to 20th	Day	13% 7% 3 8% 7% 6% 5% 5% 6% 8% 32%	3028
	21st to end	Day	14% 11% 4 11% 7% 5% 5% 4 6% 7% 25%	4004
January	1st to 10th	Night	10% 6% 3 7% 4 5% 4 3 5% 7% 47%	6306
	11th to 20th	Night	10% 5% 2 6% 3 4 3 3 4 5% 55%	5969
	21st to end	Night	13% 6% 2 7% 4 4 4 2 5% 6% 47%	6468
February	1st to 10th	Night	13% 6% 2 4 3 3 3 3 4 6% 53%	2503
	11th to 20th	Night	10% 4 1 4 2 2 3 3 5% 7% 58%	2338
	21st to end	Night	12% 4 1 4 3 3 3 2 4 6% 56%	1980
March	1st to 10th	Night	11% 5% 2 6% 4 4 4 4 6% 7% 46%	5376
	11th to 20th	Night	8% 4 2 6% 4 4 4 3 5% 6% 54%	5051
	21st to end	Night	15% 6% 2 5% 3 3 3 3 4 6% 51%	5138
April	1st to 10th	Night	8% 4 2 4 3 3 3 3 4 6% 62%	2000
	11th to 20th	Night	5% 3 1 4 3 3 2 3 3 6% 68%	1979
	21st to end	Night	4 3 1 2 2 3 3 3 4 6% 70%	2000
May	1st to 10th	Night	3 1 1 2 1 1 2 2 3 4 80%	4473
	11th to 20th	Night	2 1 2 1 1 1 2 2 4 85%	4039
	21st to end	Night	1 1 1 1 1 1 1 1 2 90%	3972
June	1st to 10th	Night	3 2 1 2 2 2 2 2 3 4 78%	1600
	11th to 20th	Night	1 1 1 1 1 1 2 3 89%	1600
	21st to end	Night	1 1 1 1 1 1 2 2 91%	1600
July	1st to 10th	Night	1 1 1 2 95%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 2 89%	3640
	21st to end	Night	1 1 1 1 2 1 2 3 89%	4421
August	1st to 10th	Night	1 1 1 1 1 1 1 2 2 90%	4322
	11th to 20th	Night	1 1 1 1 1 94%	4506
	21st to end	Night	1 1 1 1 1 1 1 2 3 87%	5015
September	1st to 10th	Night	1 1 1 1 1 2 2 90%	2000
	11th to 20th	Night	2 1 2 1 1 2 1 2 3 85%	2045
	21st to end	Night	1 1 1 1 1 1 2 2 3 3 84%	2200
October	1st to 10th	Night	1 1 1 1 1 1 2 2 2 4 84%	3809
	11th to 20th	Night	2 1 1 2 1 2 2 2 3 4 81%	3873
	21st to end	Night	3 2 1 3 1 2 2 1 3 4 79%	4121
November	1st to 10th	Night	5% 4 1 4 2 2 2 2 4 6% 67%	2527
	11th to 20th	Night	5% 3 1 3 2 3 3 2 4 7% 65%	2600
	21st to end	Night	9% 4 1 5% 3 2 3 3 5% 7% 58%	2600
December	1st to 10th	Night	6% 4 2 5% 4 6% 5% 4 6% 7% 51%	4422
	11th to 20th	Night	14% 5% 2 6% 5% 5% 5% 4 7% 10% 37%	5176
	21st to end	Night	11% 8% 3 10% 7% 6% 6% 4 6% 8% 31%	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	38% 12% 20% 16% 13% 1	3639
	11th to 20th	Day	33% 8% 10% 14% 23% 12%	3990
	21st to end	Day	39% 9% 11% 14% 24% 3	4510
February	1st to 10th	Day	34% 8% 13% 25% 16% 5%	1895
	11th to 20th	Day	32% 6% 13% 24% 19% 5%	1960
	21st to end	Day	35% 7% 13% 26% 16% 2	1650
March	1st to 10th	Day	35% 9% 16% 19% 19% 3	4518
	11th to 20th	Day	29% 6% 16% 29% 13% 7%	4946
	21st to end	Day	29% 8% 14% 31% 15% 3	5835
April	1st to 10th	Day	25% 4 12% 29% 22% 8%	2400
	11th to 20th	Day	22% 5% 12% 26% 25% 10%	2372
	21st to end	Day	17% 5% 10% 31% 29% 8%	2400
May	1st to 10th	Day	12% 2 6% 23% 39% 19%	5520
	11th to 20th	Day	7% 2 5% 27% 42% 16%	5860
	21st to end	Day	7% 2 4 22% 46% 20%	6904
June	1st to 10th	Day	11% 3 9% 21% 33% 24%	2800
	11th to 20th	Day	4 1 4 13% 37% 41%	2800
	21st to end	Day	6% 1 2 8% 26% 57%	2800
July	1st to 10th	Day	2 1 3 14% 79%	6251
	11th to 20th	Day	5% 1 2 3 14% 75%	6245
	21st to end	Day	4 1 2 10% 34% 50%	6259
August	1st to 10th	Day	7% 1 2 5% 27% 59%	3994
	11th to 20th	Day	3 1 1 5% 25% 66%	3880
	21st to end	Day	5% 1 1 7% 29% 57%	4311
September	1st to 10th	Day	5% 1 4 7% 29% 54%	2400
	11th to 20th	Day	7% 2 4 17% 38% 31%	2353
	21st to end	Day	8% 1 4 17% 39% 31%	2200
October	1st to 10th	Day	9% 2 4 13% 25% 47%	3386
	11th to 20th	Day	11% 2 6% 23% 39% 19%	3242
	21st to end	Day	15% 3 6% 19% 37% 19%	3448
November	1st to 10th	Day	21% 6% 11% 26% 27% 9%	1769
	11th to 20th	Day	25% 7% 15% 26% 23% 4	1800
	21st to end	Day	30% 6% 10% 25% 22% 7%	1800
December	1st to 10th	Day	34% 8% 12% 22% 19% 4	2759
	11th to 20th	Day	45% 9% 12% 20% 12% 2	3028
	21st to end	Day	54% 11% 15% 13% 6% 1	4004
January	1st to 10th	Night	33% 10% 19% 23% 14% 1	6306
	11th to 20th	Night	29% 8% 12% 15% 27% 9%	5969
	21st to end	Night	35% 7% 10% 21% 21% 5%	6468
February	1st to 10th	Night	32% 5% 11% 25% 19% 7%	2503
	11th to 20th	Night	26% 5% 12% 28% 23% 6%	2339
	21st to end	Night	28% 5% 14% 29% 19% 5%	1980
March	1st to 10th	Night	34% 8% 13% 21% 22% 3	5376
	11th to 20th	Night	29% 6% 15% 28% 16% 6%	5051
	21st to end	Night	34% 6% 14% 27% 15% 3	5138
April	1st to 10th	Night	24% 4 12% 30% 22% 9%	2000
	11th to 20th	Night	19% 4 11% 29% 27% 10%	1979
	21st to end	Night	16% 4 12% 29% 33% 6%	2000
May	1st to 10th	Night	10% 3 8% 28% 36% 16%	4470
	11th to 20th	Night	7% 2 4 25% 47% 15%	4040
	21st to end	Night	6% 1 3 20% 54% 16%	3972
June	1st to 10th	Night	12% 3 7% 22% 34% 23%	1600
	11th to 20th	Night	5% 2 4 13% 36% 41%	1600
	21st to end	Night	4 1 2 7% 26% 61%	1600
July	1st to 10th	Night	2 1 2 13% 82%	3600
	11th to 20th	Night	5% 1 2 3 12% 77%	3592
	21st to end	Night	4 1 2 8% 35% 50%	4296
August	1st to 10th	Night	7% 2 5% 23% 63%	3144
	11th to 20th	Night	3 1 2 3 20% 71%	3256
	21st to end	Night	5% 1 6% 23% 64%	3608
September	1st to 10th	Night	5% 2 2 7% 26% 59%	2000
	11th to 20th	Night	8% 2 2 14% 39% 35%	2045
	21st to end	Night	8% 1 3 15% 36% 37%	2200
October	1st to 10th	Night	8% 2 3 10% 23% 54%	3809
	11th to 20th	Night	9% 2 5% 22% 40% 22%	3873
	21st to end	Night	12% 1 4 19% 42% 22%	4121
November	1st to 10th	Night	19% 4 10% 25% 27% 15%	2527
	11th to 20th	Night	18% 6% 12% 26% 28% 9%	2600
	21st to end	Night	26% 5% 10% 24% 27% 8%	2600
December	1st to 10th	Night	26% 8% 14% 26% 18% 7%	4422
	11th to 20th	Night	39% 9% 17% 18% 15% 2	5176
	21st to end	Night	45% 13% 17% 18% 6% 1	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	25% 5% 14% 30% 19% 9%	200
	11th to 20th	Day	14% 5% 14% 28% 24% 16%	355
	21st to end	Day	14% 3 14% 24% 31% 14%	440
February	1st to 10th	Day	13% 6% 16% 25% 24% 16%	447
	11th to 20th	Day	12% 7% 17% 32% 21% 12%	495
	21st to end	Day	11% 6% 21% 32% 23% 7%	414
March	1st to 10th	Day	13% 7% 20% 30% 23% 7%	500
	11th to 20th	Day	13% 8% 23% 25% 20% 10%	500
	21st to end	Day	13% 10% 25% 27% 17% 8%	550
April	1st to 10th	Day	10% 9% 25% 26% 17% 12%	500
	11th to 20th	Day	8% 11% 24% 30% 19% 8%	492
	21st to end	Day	3 11% 24% 29% 19% 13%	500
May	1st to 10th	Day	5% 8% 26% 33% 20% 9%	503
	11th to 20th	Day	3 7% 25% 33% 25% 7%	528
	21st to end	Day	5% 6% 19% 32% 29% 10%	573
June	1st to 10th	Day	1 3 20% 33% 28% 14%	530
	11th to 20th	Day	2 4 20% 34% 30% 11%	530
	21st to end	Day	1 2 12% 35% 35% 16%	530
July	1st to 10th	Day	1 1 8% 32% 41% 17%	526
	11th to 20th	Day	1 3 27% 44% 25%	524
	21st to end	Day	1 4 29% 46% 19%	575
August	1st to 10th	Day	3 1 10% 35% 36% 16%	527
	11th to 20th	Day	1 9% 34% 38% 18%	517
	21st to end	Day	1 1 8% 29% 40% 21%	583
September	1st to 10th	Day	1 1 9% 32% 37% 20%	530
	11th to 20th	Day	2 3 17% 35% 30% 14%	530
	21st to end	Day	1 2 15% 27% 37% 17%	530
October	1st to 10th	Day	2 3 15% 29% 31% 20%	530
	11th to 20th	Day	3 5% 14% 27% 31% 20%	523
	21st to end	Day	4 4 13% 24% 34% 20%	539
November	1st to 10th	Day	6% 4 12% 22% 33% 24%	305
	11th to 20th	Day	6% 5% 9% 27% 34% 19%	300
	21st to end	Day	11% 3 10% 30% 29% 17%	300
December	1st to 10th	Day	12% 2 11% 32% 28% 15%	243
	11th to 20th	Day	11% 7% 12% 31% 23% 18%	200
	21st to end	Day	18% 6% 16% 27% 25% 8%	220
January	1st to 10th	Night	17% 2 12% 35% 26% 8%	800
	11th to 20th	Night	11% 2 9% 40% 32% 6%	800
	21st to end	Night	16% 2 11% 36% 30% 5%	880
February	1st to 10th	Night	14% 3 13% 37% 27% 7%	800
	11th to 20th	Night	11% 5% 15% 35% 30% 5%	784
	21st to end	Night	12% 3 16% 41% 24% 3	660
March	1st to 10th	Night	12% 5% 19% 39% 23% 2	800
	11th to 20th	Night	11% 5% 21% 36% 23% 4	800
	21st to end	Night	12% 7% 25% 35% 19% 1	880
April	1st to 10th	Night	9% 8% 30% 30% 21% 3	800
	11th to 20th	Night	5% 10% 33% 31% 19% 2	791
	21st to end	Night	4 10% 33% 31% 20% 4	800
May	1st to 10th	Night	4 7% 37% 32% 18% 2	765
	11th to 20th	Night	4 8% 39% 40% 10%	582
	21st to end	Night	4 8% 38% 43% 7%	433
June	1st to 10th	Night	3 8% 43% 39% 7% 1	400
	11th to 20th	Night	1 6% 43% 41% 9%	400
	21st to end	Night	2 4 39% 45% 11%	400
July	1st to 10th	Night	1 34% 52% 12%	390
	11th to 20th	Night	3 22% 61% 13% 1	388
	21st to end	Night	1 19% 51% 26% 3	632
August	1st to 10th	Night	3 1 24% 48% 21% 2	721
	11th to 20th	Night	1 1 21% 49% 26% 3	792
	21st to end	Night	1 1 14% 44% 36% 3	880
September	1st to 10th	Night	1 1 15% 44% 36% 4	800
	11th to 20th	Night	2 2 26% 39% 26% 5%	800
	21st to end	Night	2 2 17% 36% 37% 6%	800
October	1st to 10th	Night	3 3 16% 37% 34% 7%	800
	11th to 20th	Night	4 3 14% 34% 37% 9%	792
	21st to end	Night	4 2 12% 31% 37% 13%	836
November	1st to 10th	Night	7% 2 10% 33% 38% 10%	780
	11th to 20th	Night	6% 2 9% 41% 35% 8%	800
	21st to end	Night	9% 3 11% 38% 33% 7%	800
December	1st to 10th	Night	12% 3 9% 40% 31% 6%	800
	11th to 20th	Night	15% 2 8% 42% 27% 6%	800
	21st to end	Night	16% 3 12% 43% 22% 3	880

Page generated at 2025-10-15 22:50:29. Version ac07

Copyright © 2025 Attilla Danko.