Parkfield
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Parkfield clear sky chart from 2005-11-06 to 2025-11-18.

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 2 2 3 2 4 5% 71%	134989
	Night	4 3 1 4 3 3 3 2 4 5% 68%	132827
Transparency	Day	17% 3 6% 18% 29% 27%	130018
	Night	20% 3 7% 18% 26% 25%	128787
Seeing	Day	7% 6% 20% 32% 25% 10%	16857
	Night	7% 3 11% 35% 35% 9%	26385

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% 5% 2 4 3 3 4 3 5% 6% 61%	3775
	11th to 20th	Day	5% 4 2 6% 4 4 4 4 4 5% 59%	4100
	21st to end	Day	9% 7% 2 6% 4 4 5% 4 5% 7% 46%	4510
February	1st to 10th	Day	13% 7% 2 4 3 3 4 4 4 6% 51%	1870
	11th to 20th	Day	7% 6% 3 5% 4 4 4 4 5% 7% 51%	1950
	21st to end	Day	10% 8% 2 5% 4 3 4 4 5% 7% 47%	1650
March	1st to 10th	Day	8% 7% 3 8% 5% 5% 6% 5% 6% 7% 40%	4601
	11th to 20th	Day	6% 7% 3 5% 4 4 4 3 5% 6% 54%	5000
	21st to end	Day	5% 7% 3 7% 5% 6% 5% 5% 6% 8% 43%	5749
April	1st to 10th	Day	7% 7% 2 5% 4 3 3 3 5% 8% 55%	2400
	11th to 20th	Day	5% 5% 2 4 4 3 4 3 5% 7% 58%	2369
	21st to end	Day	4 3 1 3 3 4 4 3 5% 6% 63%	2400
May	1st to 10th	Day	2 3 1 3 2 2 2 2 3 5% 77%	5440
	11th to 20th	Day	1 1 1 2 2 2 2 4 5% 79%	5742
	21st to end	Day	1 1 2 1 1 2 1 3 5% 82%	6902
June	1st to 10th	Day	2 2 1 2 2 2 2 3 5% 7% 72%	2800
	11th to 20th	Day	1 1 1 1 1 1 1 2 4 88%	2800
	21st to end	Day	1 1 1 1 1 2 2 3 88%	2800
July	1st to 10th	Day	1 1 2 95%	6319
	11th to 20th	Day	1 1 1 1 1 1 1 2 2 88%	6060
	21st to end	Day	1 1 1 1 1 1 3 4 87%	6402
August	1st to 10th	Day	1 1 1 1 1 1 1 2 3 89%	5531
	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 3 89%	2400
	11th to 20th	Day	2 1 2 2 2 2 2 2 3 82%	2386
	21st to end	Day	1 2 1 2 2 1 3 2 4 4 78%	2200
October	1st to 10th	Day	1 1 1 2 2 2 2 3 4 5% 76%	3295
	11th to 20th	Day	1 2 1 3 2 2 3 2 4 4 77%	3261
	21st to end	Day	2 4 2 4 2 2 3 3 5% 6% 67%	3558
November	1st to 10th	Day	3 3 1 5% 3 3 3 4 5% 7% 62%	1939
	11th to 20th	Day	6% 5% 2 4 3 3 4 3 5% 7% 59%	1863
	21st to end	Day	6% 5% 2 4 4 4 4 4 5% 6% 57%	1800
December	1st to 10th	Day	4 5% 3 6% 4 3 4 4 5% 7% 56%	2737
	11th to 20th	Day	11% 8% 3 6% 4 3 4 4 6% 7% 45%	3028
	21st to end	Day	8% 7% 2 6% 5% 5% 5% 4 8% 11% 39%	4004
January	1st to 10th	Night	5% 6% 2 5% 3 3 3 3 5% 8% 57%	6160
	11th to 20th	Night	6% 5% 2 6% 3 3 3 3 4 6% 58%	5880
	21st to end	Night	9% 6% 2 6% 5% 4 4 4 5% 7% 49%	6468
February	1st to 10th	Night	11% 6% 2 5% 3 4 4 3 5% 5% 52%	2529
	11th to 20th	Night	6% 5% 2 4 3 3 4 3 5% 8% 56%	2338
	21st to end	Night	7% 6% 3 5% 4 3 3 2 4 6% 56%	1980
March	1st to 10th	Night	7% 9% 4 8% 5% 5% 5% 3 5% 8% 42%	5288
	11th to 20th	Night	5% 5% 3 6% 3 3 4 3 4 6% 58%	5000
	21st to end	Night	9% 7% 3 6% 4 4 3 3 5% 6% 49%	5226
April	1st to 10th	Night	4 4 2 5% 3 3 4 3 5% 6% 61%	2000
	11th to 20th	Night	3 3 1 5% 3 3 3 3 3 6% 67%	1979
	21st to end	Night	2 2 1 2 3 3 4 4 5% 6% 68%	2000
May	1st to 10th	Night	1 1 2 1 1 2 2 3 5% 82%	4560
	11th to 20th	Night	1 1 1 1 1 2 2 4 6% 81%	4153
	21st to end	Night	1 1 1 1 1 1 1 2 3 89%	3972
June	1st to 10th	Night	2 2 1 2 2 2 2 3 4 5% 77%	1600
	11th to 20th	Night	1 1 1 1 2 2 3 88%	1600
	21st to end	Night	1 1 1 2 3 91%	1600
July	1st to 10th	Night	1 1 1 95%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 92%	3906
	21st to end	Night	1 1 1 1 1 1 1 4 5% 85%	4472
August	1st to 10th	Night	1 1 1 1 1 1 2 2 90%	4277
	11th to 20th	Night	1 1 1 2 94%	4506
	21st to end	Night	1 1 1 1 1 2 3 90%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 2 2 89%	2000
	11th to 20th	Night	2 2 2 1 1 1 1 3 3 84%	2012
	21st to end	Night	1 1 1 2 2 2 2 2 2 4 82%	2200
October	1st to 10th	Night	2 1 2 2 1 2 1 3 4 81%	3888
	11th to 20th	Night	1 2 1 2 2 2 2 2 3 4 79%	3897
	21st to end	Night	3 3 1 3 2 2 2 2 3 5% 74%	4253
November	1st to 10th	Night	2 3 1 4 3 3 3 2 5% 6% 69%	2578
	11th to 20th	Night	5% 4 2 5% 3 3 3 3 5% 6% 62%	2691
	21st to end	Night	5% 5% 2 5% 4 3 4 4 6% 7% 55%	2600
December	1st to 10th	Night	5% 4 2 4 3 4 5% 3 5% 7% 58%	4431
	11th to 20th	Night	12% 8% 3 5% 4 4 5% 4 7% 8% 41%	5176
	21st to end	Night	8% 7% 3 8% 6% 5% 6% 5% 7% 10% 36%	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	22% 5% 14% 31% 19% 9%	3775
	11th to 20th	Day	28% 3 8% 14% 22% 25%	4100
	21st to end	Day	35% 5% 10% 13% 23% 14%	4510
February	1st to 10th	Day	34% 4 6% 20% 23% 13%	1870
	11th to 20th	Day	32% 5% 8% 22% 24% 9%	1960
	21st to end	Day	36% 5% 9% 21% 23% 7%	1650
March	1st to 10th	Day	36% 8% 11% 17% 23% 5%	4601
	11th to 20th	Day	30% 4 9% 33% 16% 7%	5000
	21st to end	Day	34% 7% 12% 26% 18% 3	5749
April	1st to 10th	Day	28% 4 11% 26% 22% 9%	2400
	11th to 20th	Day	25% 5% 9% 28% 24% 9%	2372
	21st to end	Day	21% 4 9% 29% 29% 8%	2400
May	1st to 10th	Day	12% 2 6% 24% 37% 19%	5440
	11th to 20th	Day	8% 2 6% 29% 40% 14%	5745
	21st to end	Day	8% 2 4 26% 50% 10%	6904
June	1st to 10th	Day	13% 2 9% 21% 37% 18%	2800
	11th to 20th	Day	5% 1 4 14% 42% 33%	2800
	21st to end	Day	6% 1 2 9% 33% 49%	2800
July	1st to 10th	Day	2 1 4 22% 72%	6251
	11th to 20th	Day	6% 1 1 3 23% 65%	5986
	21st to end	Day	4 2 1 13% 35% 44%	6217
August	1st to 10th	Day	7% 1 1 8% 35% 47%	4026
	11th to 20th	Day	3 1 7% 29% 60%	3880
	21st to end	Day	5% 1 1 11% 26% 58%	4311
September	1st to 10th	Day	4 2 2 11% 31% 50%	2400
	11th to 20th	Day	9% 2 2 18% 42% 27%	2386
	21st to end	Day	10% 3 2 17% 38% 30%	2200
October	1st to 10th	Day	11% 2 3 12% 23% 49%	3295
	11th to 20th	Day	13% 2 5% 20% 33% 27%	3261
	21st to end	Day	18% 2 3 14% 35% 27%	3558
November	1st to 10th	Day	20% 4 8% 20% 30% 18%	1939
	11th to 20th	Day	25% 4 10% 21% 26% 14%	1863
	21st to end	Day	27% 3 7% 18% 26% 19%	1800
December	1st to 10th	Day	28% 3 6% 15% 29% 18%	2737
	11th to 20th	Day	38% 4 10% 18% 22% 9%	3028
	21st to end	Day	36% 6% 16% 25% 12% 5%	4004
January	1st to 10th	Night	25% 5% 13% 27% 22% 8%	6160
	11th to 20th	Night	27% 4 10% 16% 24% 21%	5880
	21st to end	Night	34% 4 9% 16% 22% 15%	6468
February	1st to 10th	Night	34% 4 7% 19% 23% 13%	2529
	11th to 20th	Night	26% 4 9% 23% 27% 10%	2339
	21st to end	Night	29% 4 8% 24% 27% 8%	1980
March	1st to 10th	Night	38% 5% 10% 20% 22% 5%	5288
	11th to 20th	Night	26% 5% 12% 31% 18% 8%	5000
	21st to end	Night	34% 5% 14% 24% 18% 4	5226
April	1st to 10th	Night	23% 4 14% 28% 20% 11%	2000
	11th to 20th	Night	19% 4 12% 27% 27% 11%	1979
	21st to end	Night	16% 4 10% 29% 31% 9%	2000
May	1st to 10th	Night	8% 2 9% 32% 31% 18%	4557
	11th to 20th	Night	6% 1 8% 26% 41% 18%	4154
	21st to end	Night	5% 1 5% 24% 46% 20%	3972
June	1st to 10th	Night	11% 2 9% 21% 37% 20%	1600
	11th to 20th	Night	5% 1 4 15% 40% 36%	1600
	21st to end	Night	4 1 1 9% 34% 51%	1600
July	1st to 10th	Night	2 3 18% 77%	3600
	11th to 20th	Night	4 1 1 3 19% 73%	3857
	21st to end	Night	4 4 1 12% 31% 48%	4345
August	1st to 10th	Night	6% 1 1 10% 28% 54%	3111
	11th to 20th	Night	3 1 1 4 26% 66%	3256
	21st to end	Night	4 1 1 7% 27% 60%	3608
September	1st to 10th	Night	5% 2 2 8% 27% 56%	2000
	11th to 20th	Night	8% 1 2 15% 36% 37%	2012
	21st to end	Night	8% 2 2 16% 39% 32%	2200
October	1st to 10th	Night	9% 2 3 11% 22% 53%	3888
	11th to 20th	Night	12% 1 4 19% 38% 25%	3897
	21st to end	Night	15% 1 2 14% 41% 26%	4253
November	1st to 10th	Night	17% 3 6% 21% 31% 21%	2578
	11th to 20th	Night	22% 3 10% 21% 27% 17%	2691
	21st to end	Night	27% 4 9% 17% 27% 17%	2600
December	1st to 10th	Night	26% 3 6% 16% 31% 19%	4431
	11th to 20th	Night	39% 4 12% 18% 17% 10%	5176
	21st to end	Night	42% 6% 15% 23% 11% 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% 8% 31% 27% 12% 3	258
	11th to 20th	Day	14% 7% 27% 33% 17% 3	400
	21st to end	Day	12% 7% 27% 32% 20% 3	440
February	1st to 10th	Day	18% 11% 25% 27% 16% 4	435
	11th to 20th	Day	13% 12% 27% 31% 16% 3	495
	21st to end	Day	15% 11% 27% 33% 13% 2	414
March	1st to 10th	Day	16% 14% 26% 29% 15% 1	500
	11th to 20th	Day	16% 10% 26% 27% 17% 3	500
	21st to end	Day	15% 16% 24% 27% 15% 3	550
April	1st to 10th	Day	12% 10% 24% 27% 20% 7%	500
	11th to 20th	Day	9% 13% 24% 28% 20% 6%	492
	21st to end	Day	4 9% 27% 33% 17% 9%	500
May	1st to 10th	Day	7% 7% 26% 35% 18% 7%	503
	11th to 20th	Day	4 10% 22% 32% 24% 9%	528
	21st to end	Day	5% 9% 19% 31% 23% 12%	573
June	1st to 10th	Day	2 6% 17% 36% 25% 14%	530
	11th to 20th	Day	1 5% 19% 36% 29% 9%	530
	21st to end	Day	1 2 18% 33% 29% 17%	530
July	1st to 10th	Day	1 1 13% 38% 29% 17%	526
	11th to 20th	Day	2 8% 34% 33% 24%	524
	21st to end	Day	1 1 10% 32% 35% 21%	575
August	1st to 10th	Day	1 2 15% 37% 28% 17%	527
	11th to 20th	Day	1 1 12% 32% 33% 21%	517
	21st to end	Day	1 1 8% 32% 34% 23%	583
September	1st to 10th	Day	1 2 14% 29% 34% 21%	530
	11th to 20th	Day	3 3 16% 32% 33% 12%	530
	21st to end	Day	2 4 14% 33% 37% 10%	530
October	1st to 10th	Day	2 5% 18% 35% 31% 9%	530
	11th to 20th	Day	4 5% 20% 32% 30% 9%	530
	21st to end	Day	5% 4 19% 33% 31% 8%	583
November	1st to 10th	Day	5% 5% 17% 33% 33% 6%	415
	11th to 20th	Day	9% 6% 19% 38% 21% 7%	321
	21st to end	Day	8% 5% 25% 37% 21% 4	300
December	1st to 10th	Day	13% 4 25% 34% 18% 5%	238
	11th to 20th	Day	11% 9% 26% 30% 20% 6%	200
	21st to end	Day	16% 9% 26% 31% 14% 4	220
January	1st to 10th	Night	16% 3 11% 39% 24% 7%	800
	11th to 20th	Night	9% 3 12% 42% 28% 7%	800
	21st to end	Night	13% 5% 11% 40% 26% 6%	880
February	1st to 10th	Night	16% 5% 12% 35% 26% 7%	800
	11th to 20th	Night	12% 4 15% 36% 27% 7%	784
	21st to end	Night	12% 6% 14% 46% 19% 3	660
March	1st to 10th	Night	15% 6% 15% 37% 23% 5%	800
	11th to 20th	Night	11% 4 16% 37% 27% 6%	800
	21st to end	Night	11% 8% 16% 35% 26% 5%	880
April	1st to 10th	Night	5% 8% 15% 40% 28% 4	800
	11th to 20th	Night	5% 7% 18% 34% 30% 6%	791
	21st to end	Night	4 6% 19% 35% 29% 8%	800
May	1st to 10th	Night	3 4 14% 42% 29% 8%	800
	11th to 20th	Night	3 5% 16% 37% 32% 6%	632
	21st to end	Night	3 5% 12% 38% 36% 6%	433
June	1st to 10th	Night	3 2 11% 37% 43% 4	400
	11th to 20th	Night	1 2 12% 42% 40% 5%	400
	21st to end	Night	1 1 9% 34% 50% 7%	400
July	1st to 10th	Night	1 2 29% 58% 10%	390
	11th to 20th	Night	1 1 21% 57% 20%	497
	21st to end	Night	1 1 1 17% 58% 21%	657
August	1st to 10th	Night	2 1 5% 27% 51% 15%	701
	11th to 20th	Night	1 1 5% 24% 58% 13%	792
	21st to end	Night	1 3 22% 56% 18%	880
September	1st to 10th	Night	1 2 4 24% 54% 16%	800
	11th to 20th	Night	3 2 6% 32% 44% 14%	800
	21st to end	Night	1 2 9% 29% 47% 13%	800
October	1st to 10th	Night	3 3 6% 37% 39% 12%	800
	11th to 20th	Night	6% 2 7% 37% 38% 11%	800
	21st to end	Night	5% 2 7% 35% 38% 13%	880
November	1st to 10th	Night	4 3 12% 35% 36% 11%	820
	11th to 20th	Night	7% 2 10% 41% 33% 7%	828
	21st to end	Night	7% 3 11% 41% 30% 9%	800
December	1st to 10th	Night	11% 3 10% 40% 30% 5%	800
	11th to 20th	Night	16% 4 9% 43% 24% 5%	800
	21st to end	Night	13% 6% 15% 40% 21% 5%	880

Page generated at 2025-11-14 21:55:59. Version ac07

Copyright © 2025 Attilla Danko.