Pisony Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pisony Ranch clear sky chart from 2005-11-06 to 2025-03-12.

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	6% 8% 3 7% 5% 5% 5% 4 7% 9% 42%	112268
	Night	4 8% 3 8% 5% 4 5% 4 7% 9% 44%	115385
Transparency	Day	35% 7% 17% 25% 13% 3	112021
	Night	35% 7% 18% 25% 12% 2	115278
Seeing	Day	21% 20% 27% 20% 10% 2	15617
	Night	16% 17% 27% 26% 12% 2	24958

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	1 8% 4 13% 7% 6% 4 4 7% 10% 35%	3179
	11th to 20th	Day	1 7% 4 11% 7% 8% 7% 5% 8% 9% 35%	3428
	21st to end	Day	1 5% 2 7% 4 4 5% 5% 7% 10% 49%	4004
February	1st to 10th	Day	2 9% 4 10% 7% 7% 7% 4 7% 10% 33%	1615
	11th to 20th	Day	2 11% 4 11% 6% 5% 6% 5% 7% 10% 33%	1755
	21st to end	Day	1 9% 4 13% 7% 5% 7% 4 8% 9% 34%	1649
March	1st to 10th	Day	1 7% 4 10% 6% 5% 5% 4 7% 10% 42%	3238
	11th to 20th	Day	3 10% 3 5% 4 4 5% 4 7% 9% 46%	3457
	21st to end	Day	5% 18% 7% 12% 5% 4 4 4 6% 8% 26%	3885
April	1st to 10th	Day	5% 14% 3 10% 6% 6% 5% 5% 8% 8% 30%	2304
	11th to 20th	Day	8% 15% 5% 10% 6% 4 5% 5% 7% 8% 29%	2440
	21st to end	Day	10% 14% 5% 8% 5% 4 5% 5% 6% 7% 33%	2470
May	1st to 10th	Day	13% 18% 5% 9% 6% 5% 5% 4 5% 5% 25%	4194
	11th to 20th	Day	9% 9% 2 8% 5% 6% 6% 5% 8% 9% 31%	4648
	21st to end	Day	15% 9% 3 6% 5% 6% 6% 5% 8% 11% 27%	5161
June	1st to 10th	Day	13% 10% 3 8% 6% 6% 6% 5% 7% 7% 31%	2850
	11th to 20th	Day	17% 8% 3 8% 6% 6% 6% 5% 7% 7% 28%	2850
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 9% 44%	2850
July	1st to 10th	Day	5% 4 2 5% 4 4 5% 4 7% 9% 52%	4740
	11th to 20th	Day	4 2 1 3 3 4 4 4 7% 8% 60%	4740
	21st to end	Day	3 2 1 3 2 4 4 4 5% 8% 65%	4863
August	1st to 10th	Day	12% 5% 2 5% 4 4 4 4 7% 8% 45%	4401
	11th to 20th	Day	7% 3 2 3 3 4 4 4 7% 9% 55%	4029
	21st to end	Day	6% 4 1 4 3 3 4 3 6% 7% 58%	4521
September	1st to 10th	Day	12% 5% 2 4 3 3 4 3 6% 7% 50%	2320
	11th to 20th	Day	11% 7% 2 4 4 3 5% 3 7% 9% 46%	2090
	21st to end	Day	9% 8% 2 4 3 3 4 3 6% 8% 50%	2090
October	1st to 10th	Day	6% 8% 3 5% 4 3 4 4 5% 8% 50%	3378
	11th to 20th	Day	3 6% 2 6% 4 4 5% 5% 6% 10% 49%	2918
	21st to end	Day	5% 8% 2 7% 4 4 5% 3 7% 10% 46%	3101
November	1st to 10th	Day	5% 11% 4 7% 5% 5% 4 5% 8% 8% 38%	1700
	11th to 20th	Day	2 7% 3 6% 4 4 5% 5% 9% 9% 45%	1570
	21st to end	Day	3 10% 3 10% 6% 4 4 4 7% 9% 40%	1400
December	1st to 10th	Day	1 6% 3 7% 3 4 4 4 6% 11% 51%	2290
	11th to 20th	Day	2 7% 3 10% 5% 4 5% 5% 7% 10% 42%	2642
	21st to end	Day	1 7% 4 8% 6% 5% 5% 4 7% 11% 42%	3498
January	1st to 10th	Night	2 8% 5% 12% 7% 5% 5% 5% 8% 8% 34%	6766
	11th to 20th	Night	1 6% 3 10% 7% 6% 6% 6% 7% 9% 39%	6512
	21st to end	Night	1 7% 3 8% 4 5% 5% 5% 7% 10% 45%	6952
February	1st to 10th	Night	2 11% 4 10% 8% 5% 5% 5% 6% 9% 35%	2784
	11th to 20th	Night	1 11% 4 10% 6% 6% 5% 4 7% 10% 36%	2532
	21st to end	Night	1 7% 4 12% 6% 6% 6% 5% 6% 8% 38%	1980
March	1st to 10th	Night	1 6% 3 13% 8% 6% 7% 5% 7% 9% 36%	3856
	11th to 20th	Night	3 7% 3 7% 4 4 5% 3 6% 8% 49%	3549
	21st to end	Night	6% 18% 7% 13% 5% 4 4 4 6% 7% 25%	3767
April	1st to 10th	Night	8% 11% 4 9% 5% 5% 4 4 6% 8% 37%	1875
	11th to 20th	Night	7% 11% 3 9% 4 3 4 4 7% 9% 37%	1691
	21st to end	Night	6% 12% 5% 7% 5% 5% 5% 4 6% 8% 37%	1710
May	1st to 10th	Night	11% 15% 4 8% 5% 4 5% 4 5% 6% 32%	2769
	11th to 20th	Night	7% 7% 2 6% 4 5% 5% 4 9% 11% 39%	2245
	21st to end	Night	13% 9% 3 8% 5% 6% 6% 4 6% 8% 33%	2414
June	1st to 10th	Night	11% 7% 3 6% 5% 4 6% 4 7% 9% 38%	1330
	11th to 20th	Night	16% 8% 2 6% 3 5% 6% 5% 5% 8% 34%	1330
	21st to end	Night	5% 4 1 4 4 4 5% 5% 7% 9% 52%	1330
July	1st to 10th	Night	4 3 2 4 3 4 4 4 7% 8% 57%	2220
	11th to 20th	Night	3 3 1 3 3 3 4 2 5% 7% 65%	2220
	21st to end	Night	3 2 1 3 2 2 3 3 4 5% 71%	2686
August	1st to 10th	Night	13% 6% 2 5% 3 3 3 2 5% 6% 52%	2529
	11th to 20th	Night	5% 4 1 4 4 4 5% 6% 7% 10% 50%	2808
	21st to end	Night	5% 3 1 4 3 3 4 4 6% 8% 58%	3146
September	1st to 10th	Night	9% 4 2 4 3 3 3 2 4 7% 57%	1857
	11th to 20th	Night	11% 7% 1 4 2 2 3 3 7% 8% 51%	2090
	21st to end	Night	9% 6% 2 5% 3 3 4 3 5% 9% 51%	2090
October	1st to 10th	Night	6% 6% 2 4 3 2 3 3 5% 7% 58%	3597
	11th to 20th	Night	3 4 1 3 2 4 4 3 8% 12% 55%	3993
	21st to end	Night	3 6% 3 6% 3 4 4 4 6% 9% 51%	4457
November	1st to 10th	Night	4 11% 4 8% 5% 4 5% 5% 6% 8% 40%	2577
	11th to 20th	Night	1 7% 3 6% 5% 4 5% 5% 8% 11% 45%	2825
	21st to end	Night	3 9% 4 9% 5% 5% 4 4 7% 11% 40%	3000
December	1st to 10th	Night	2 6% 3 8% 4 4 4 5% 7% 11% 46%	4890
	11th to 20th	Night	2 8% 4 10% 6% 5% 5% 6% 8% 10% 35%	5550
	21st to end	Night	1 10% 5% 10% 6% 5% 5% 4 7% 8% 39%	7458

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	43% 7% 16% 21% 11% 2	3179
	11th to 20th	Day	43% 6% 17% 18% 12% 3	3452
	21st to end	Day	28% 7% 21% 31% 12% 1	4004
February	1st to 10th	Day	43% 9% 18% 19% 9% 2	1615
	11th to 20th	Day	42% 9% 19% 20% 8% 2	1764
	21st to end	Day	42% 8% 16% 22% 9% 2	1649
March	1st to 10th	Day	33% 9% 17% 22% 17% 2	3238
	11th to 20th	Day	30% 9% 26% 27% 8% 1	3458
	21st to end	Day	52% 9% 16% 17% 6%	3885
April	1st to 10th	Day	44% 10% 18% 20% 7%	2304
	11th to 20th	Day	47% 9% 15% 20% 8% 1	2440
	21st to end	Day	47% 8% 16% 20% 8% 1	2470
May	1st to 10th	Day	56% 7% 11% 20% 5%	4194
	11th to 20th	Day	39% 11% 16% 25% 7%	4652
	21st to end	Day	42% 12% 19% 17% 9%	5162
June	1st to 10th	Day	47% 9% 14% 19% 9% 1	2850
	11th to 20th	Day	51% 8% 12% 18% 11% 1	2850
	21st to end	Day	32% 9% 16% 26% 14% 2	2850
July	1st to 10th	Day	26% 6% 11% 28% 21% 8%	4666
	11th to 20th	Day	21% 4 11% 32% 23% 9%	4659
	21st to end	Day	17% 4 8% 28% 27% 16%	4709
August	1st to 10th	Day	33% 5% 15% 25% 17% 5%	4384
	11th to 20th	Day	25% 4 21% 36% 13% 2	4068
	21st to end	Day	23% 5% 12% 41% 17% 2	4520
September	1st to 10th	Day	31% 6% 12% 27% 18% 6%	2320
	11th to 20th	Day	32% 6% 14% 29% 16% 3	2090
	21st to end	Day	31% 7% 17% 31% 13% 2	2090
October	1st to 10th	Day	31% 5% 18% 34% 11% 1	3378
	11th to 20th	Day	29% 5% 23% 26% 15% 1	2918
	21st to end	Day	32% 5% 19% 28% 12% 3	3101
November	1st to 10th	Day	39% 11% 17% 22% 10% 1	1700
	11th to 20th	Day	30% 13% 22% 24% 10% 1	1570
	21st to end	Day	40% 8% 24% 18% 8% 2	1400
December	1st to 10th	Day	28% 7% 30% 26% 8% 1	2290
	11th to 20th	Day	36% 8% 28% 21% 6%	2644
	21st to end	Day	35% 7% 17% 25% 14% 2	3498
January	1st to 10th	Night	43% 10% 16% 23% 7% 1	6766
	11th to 20th	Night	41% 6% 17% 20% 11% 5%	6550
	21st to end	Night	31% 8% 22% 26% 13% 1	6952
February	1st to 10th	Night	45% 8% 15% 19% 11% 2	2784
	11th to 20th	Night	41% 9% 20% 21% 8% 1	2533
	21st to end	Night	42% 8% 15% 24% 10% 2	1980
March	1st to 10th	Night	38% 11% 17% 21% 13% 1	3856
	11th to 20th	Night	28% 10% 25% 27% 9% 1	3549
	21st to end	Night	54% 9% 15% 17% 4 1	3767
April	1st to 10th	Night	42% 9% 17% 21% 9% 1	1875
	11th to 20th	Night	41% 8% 16% 28% 7%	1691
	21st to end	Night	42% 9% 14% 26% 8% 1	1710
May	1st to 10th	Night	50% 8% 14% 23% 6%	2769
	11th to 20th	Night	31% 10% 17% 33% 9%	2245
	21st to end	Night	44% 11% 19% 16% 9% 1	2414
June	1st to 10th	Night	39% 8% 18% 24% 9% 1	1330
	11th to 20th	Night	44% 9% 17% 19% 11% 1	1330
	21st to end	Night	24% 9% 20% 30% 16% 2	1330
July	1st to 10th	Night	23% 4 18% 28% 19% 8%	2185
	11th to 20th	Night	19% 4 14% 31% 23% 10%	2178
	21st to end	Night	17% 3 8% 30% 27% 16%	2601
August	1st to 10th	Night	33% 4 14% 25% 20% 4	2521
	11th to 20th	Night	28% 4 22% 30% 14% 2	2835
	21st to end	Night	23% 3 13% 39% 20% 2	3146
September	1st to 10th	Night	26% 5% 15% 32% 16% 6%	1857
	11th to 20th	Night	29% 6% 17% 29% 16% 3	2090
	21st to end	Night	30% 7% 18% 28% 14% 3	2090
October	1st to 10th	Night	26% 4 14% 33% 22% 1	3597
	11th to 20th	Night	21% 5% 23% 29% 19% 2	3993
	21st to end	Night	30% 6% 17% 37% 9%	4457
November	1st to 10th	Night	40% 10% 19% 20% 10% 1	2577
	11th to 20th	Night	30% 12% 22% 24% 12% 1	2825
	21st to end	Night	37% 10% 22% 19% 10% 3	3000
December	1st to 10th	Night	32% 6% 28% 22% 10% 2	4890
	11th to 20th	Night	40% 10% 24% 19% 7%	5547
	21st to end	Night	40% 7% 18% 21% 12% 3	7458

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	20% 23% 30% 17% 6% 7%	200
	11th to 20th	Day	21% 16% 32% 23% 7% 2	200
	21st to end	Day	18% 29% 36% 9% 6% 2	220
February	1st to 10th	Day	20% 21% 39% 14% 4 1	207
	11th to 20th	Day	14% 20% 36% 22% 6% 1	300
	21st to end	Day	24% 25% 33% 13% 5% 1	413
March	1st to 10th	Day	23% 27% 28% 15% 5% 2	500
	11th to 20th	Day	22% 24% 26% 18% 10% 2	465
	21st to end	Day	27% 27% 24% 15% 6% 2	506
April	1st to 10th	Day	23% 25% 31% 16% 4	460
	11th to 20th	Day	24% 23% 29% 16% 6% 2	452
	21st to end	Day	28% 22% 25% 16% 7% 2	460
May	1st to 10th	Day	24% 18% 25% 19% 11% 3	463
	11th to 20th	Day	26% 14% 21% 22% 12% 4	642
	21st to end	Day	27% 13% 20% 24% 14% 3	734
June	1st to 10th	Day	22% 21% 23% 22% 10% 2	680
	11th to 20th	Day	28% 20% 21% 20% 9% 2	680
	21st to end	Day	13% 14% 28% 25% 15% 4	680
July	1st to 10th	Day	11% 14% 26% 28% 18% 3	671
	11th to 20th	Day	13% 16% 27% 27% 15% 2	668
	21st to end	Day	8% 15% 34% 27% 13% 3	578
August	1st to 10th	Day	14% 16% 27% 29% 10% 4	487
	11th to 20th	Day	9% 12% 35% 26% 12% 5%	477
	21st to end	Day	13% 19% 33% 22% 10% 2	539
September	1st to 10th	Day	19% 21% 25% 21% 10% 3	490
	11th to 20th	Day	21% 16% 30% 21% 11% 2	490
	21st to end	Day	29% 22% 27% 14% 6% 2	490
October	1st to 10th	Day	22% 21% 28% 17% 9% 2	430
	11th to 20th	Day	24% 20% 24% 19% 11% 2	300
	21st to end	Day	28% 22% 27% 15% 6% 2	330
November	1st to 10th	Day	27% 28% 22% 18% 4 1	300
	11th to 20th	Day	31% 25% 29% 11% 4	285
	21st to end	Day	27% 23% 25% 14% 7% 5%	200
December	1st to 10th	Day	23% 26% 24% 17% 9% 2	200
	11th to 20th	Day	25% 22% 33% 16% 4 1	200
	21st to end	Day	19% 20% 34% 15% 10% 2	220
January	1st to 10th	Night	20% 22% 31% 21% 5% 1	1000
	11th to 20th	Night	13% 23% 37% 21% 5% 1	900
	21st to end	Night	11% 26% 33% 21% 7% 1	880
February	1st to 10th	Night	15% 17% 34% 22% 10% 3	800
	11th to 20th	Night	15% 16% 33% 29% 7% 1	784
	21st to end	Night	14% 16% 33% 23% 12% 1	660
March	1st to 10th	Night	13% 19% 35% 22% 10% 1	800
	11th to 20th	Night	16% 19% 28% 26% 10% 1	766
	21st to end	Night	18% 16% 23% 31% 9% 2	836
April	1st to 10th	Night	16% 19% 28% 24% 11% 2	735
	11th to 20th	Night	15% 22% 25% 25% 12% 1	563
	21st to end	Night	17% 17% 28% 26% 11% 1	570
May	1st to 10th	Night	21% 13% 22% 27% 16% 1	518
	11th to 20th	Night	19% 8% 18% 28% 24% 3	374
	21st to end	Night	25% 8% 17% 29% 19% 2	411
June	1st to 10th	Night	20% 14% 21% 29% 14% 3	380
	11th to 20th	Night	24% 13% 22% 24% 16% 1	380
	21st to end	Night	9% 11% 20% 38% 21% 1	380
July	1st to 10th	Night	9% 8% 17% 38% 28%	370
	11th to 20th	Night	8% 7% 20% 45% 20% 1	368
	21st to end	Night	8% 7% 18% 42% 24% 2	416
August	1st to 10th	Night	9% 6% 13% 40% 29% 2	378
	11th to 20th	Night	9% 6% 20% 36% 25% 3	561
	21st to end	Night	12% 10% 23% 35% 18% 2	627
September	1st to 10th	Night	14% 9% 18% 33% 22% 4	703
	11th to 20th	Night	17% 10% 20% 29% 19% 5%	760
	21st to end	Night	18% 15% 27% 23% 14% 3	760
October	1st to 10th	Night	21% 12% 20% 32% 14% 2	760
	11th to 20th	Night	16% 19% 23% 28% 14% 1	760
	21st to end	Night	17% 23% 29% 23% 7% 2	836
November	1st to 10th	Night	20% 24% 27% 22% 5% 1	822
	11th to 20th	Night	22% 27% 30% 18% 3 1	1000
	21st to end	Night	16% 22% 36% 18% 7% 1	1000
December	1st to 10th	Night	14% 22% 31% 24% 8% 1	1000
	11th to 20th	Night	15% 22% 36% 22% 5% 1	1000
	21st to end	Night	16% 23% 32% 22% 7% 1	1100

Page generated at 2025-03-09 06:08:44. Version ac07

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