Quilchena Ranch
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Quilchena Ranch clear sky chart from 2005-11-06 to 2026-07-01.

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	7% 9% 3 8% 6% 5% 6% 5% 7% 8% 37%	141299
	Night	7% 10% 4 9% 6% 6% 6% 5% 7% 8% 33%	139736
Transparency	Day	42% 9% 16% 21% 10% 2	141014
	Night	44% 10% 18% 19% 8% 1	139603
Seeing	Day	16% 14% 24% 25% 15% 6%	17596
	Night	14% 10% 23% 34% 17% 2	25969

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	9% 19% 5% 14% 7% 6% 7% 4 6% 7% 16%	4125
	11th to 20th	Day	6% 11% 3 9% 5% 5% 6% 5% 10% 10% 30%	4493
	21st to end	Day	7% 13% 5% 11% 7% 6% 6% 6% 9% 8% 23%	5186
February	1st to 10th	Day	9% 15% 5% 12% 8% 7% 6% 4 6% 7% 21%	1759
	11th to 20th	Day	4 14% 5% 10% 7% 7% 6% 5% 8% 7% 27%	1845
	21st to end	Day	6% 14% 5% 13% 8% 7% 7% 7% 6% 6% 21%	1665
March	1st to 10th	Day	6% 12% 4 11% 6% 7% 6% 6% 7% 7% 28%	4618
	11th to 20th	Day	3 9% 3 10% 7% 7% 7% 6% 8% 8% 32%	4969
	21st to end	Day	8% 13% 4 10% 6% 6% 6% 5% 7% 8% 26%	5964
April	1st to 10th	Day	8% 11% 4 10% 7% 7% 7% 6% 9% 8% 25%	2520
	11th to 20th	Day	8% 11% 3 10% 6% 5% 5% 5% 7% 8% 30%	2492
	21st to end	Day	8% 11% 4 9% 6% 5% 6% 6% 6% 8% 31%	2923
May	1st to 10th	Day	5% 9% 3 7% 5% 5% 4 4 5% 8% 46%	8195
	11th to 20th	Day	7% 8% 3 9% 6% 6% 7% 6% 9% 11% 28%	8160
	21st to end	Day	10% 9% 3 8% 5% 5% 5% 5% 7% 9% 33%	8993
June	1st to 10th	Day	13% 8% 3 8% 5% 5% 6% 4 7% 6% 35%	3240
	11th to 20th	Day	13% 8% 3 7% 7% 5% 5% 4 6% 7% 34%	3360
	21st to end	Day	8% 6% 2 7% 5% 6% 6% 4 7% 7% 42%	3332
July	1st to 10th	Day	3 4 1 5% 3 4 4 4 5% 7% 60%	6781
	11th to 20th	Day	4 2 1 3 2 3 3 3 4 6% 67%	6646
	21st to end	Day	4 3 1 5% 3 3 4 3 5% 8% 61%	6874
August	1st to 10th	Day	3 2 1 3 3 4 5% 4 6% 9% 60%	4541
	11th to 20th	Day	3 4 2 5% 5% 6% 5% 5% 6% 8% 50%	4384
	21st to end	Day	8% 4 2 5% 4 5% 5% 4 6% 9% 47%	4423
September	1st to 10th	Day	7% 5% 2 6% 4 4 4 3 5% 8% 52%	2400
	11th to 20th	Day	11% 6% 2 7% 5% 5% 4 4 5% 7% 44%	2400
	21st to end	Day	12% 7% 3 8% 5% 4 5% 5% 7% 8% 37%	2142
October	1st to 10th	Day	10% 7% 3 8% 5% 5% 5% 5% 6% 7% 40%	3280
	11th to 20th	Day	14% 12% 3 8% 5% 5% 4 3 6% 8% 32%	3208
	21st to end	Day	10% 10% 4 10% 6% 6% 7% 4 6% 7% 28%	3200
November	1st to 10th	Day	15% 14% 5% 9% 6% 6% 7% 4 5% 6% 23%	1700
	11th to 20th	Day	10% 13% 4 11% 6% 6% 6% 4 6% 8% 25%	1680
	21st to end	Day	10% 16% 4 10% 8% 6% 7% 4 6% 8% 21%	1617
December	1st to 10th	Day	6% 11% 4 12% 9% 8% 9% 6% 7% 7% 20%	2360
	11th to 20th	Day	7% 14% 6% 14% 9% 8% 8% 5% 6% 6% 17%	2502
	21st to end	Day	7% 13% 6% 12% 9% 10% 9% 6% 7% 7% 15%	3322
January	1st to 10th	Night	7% 18% 6% 15% 9% 9% 8% 5% 6% 6% 11%	8770
	11th to 20th	Night	7% 11% 4 10% 6% 5% 7% 6% 13% 9% 23%	8389
	21st to end	Night	7% 12% 5% 11% 7% 6% 7% 5% 9% 13% 19%	8994
February	1st to 10th	Night	8% 17% 6% 12% 8% 6% 5% 4 5% 6% 22%	2859
	11th to 20th	Night	4 13% 5% 11% 6% 6% 6% 4 7% 8% 30%	2662
	21st to end	Night	5% 12% 5% 13% 9% 6% 6% 4 7% 7% 24%	2140
March	1st to 10th	Night	4 10% 4 10% 6% 6% 7% 6% 9% 9% 29%	5496
	11th to 20th	Night	3 9% 3 9% 5% 6% 6% 5% 7% 10% 36%	5249
	21st to end	Night	7% 12% 4 10% 6% 6% 6% 6% 8% 7% 26%	5253
April	1st to 10th	Night	6% 11% 3 8% 6% 7% 5% 6% 6% 7% 34%	2100
	11th to 20th	Night	7% 9% 3 8% 6% 5% 6% 6% 8% 7% 35%	2079
	21st to end	Night	5% 9% 3 7% 5% 6% 5% 4 7% 8% 41%	1694
May	1st to 10th	Night	4 6% 2 7% 5% 5% 6% 4 6% 6% 50%	4724
	11th to 20th	Night	4 7% 3 8% 5% 6% 6% 5% 9% 12% 36%	4700
	21st to end	Night	6% 6% 3 7% 5% 5% 6% 5% 7% 9% 40%	5178
June	1st to 10th	Night	10% 7% 1 6% 6% 5% 6% 5% 8% 10% 36%	1375
	11th to 20th	Night	8% 6% 3 7% 5% 5% 6% 5% 7% 10% 37%	1260
	21st to end	Night	5% 6% 2 5% 5% 5% 5% 4 6% 8% 49%	1282
July	1st to 10th	Night	3 3 2 4 3 3 4 4 6% 8% 59%	3180
	11th to 20th	Night	3 2 1 3 2 2 3 3 4 6% 70%	3313
	21st to end	Night	3 2 1 4 3 4 4 4 5% 7% 63%	3969
August	1st to 10th	Night	2 2 1 4 3 4 5% 4 7% 8% 60%	2609
	11th to 20th	Night	3 2 2 5% 5% 5% 5% 4 6% 9% 54%	2664
	21st to end	Night	6% 5% 2 5% 4 4 5% 5% 6% 9% 48%	3494
September	1st to 10th	Night	6% 3 1 4 4 4 4 4 5% 7% 58%	2000
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 6% 8% 50%	2000
	21st to end	Night	9% 7% 3 6% 5% 5% 4 4 6% 8% 43%	2253
October	1st to 10th	Night	8% 8% 3 7% 5% 5% 6% 4 5% 7% 44%	3920
	11th to 20th	Night	15% 9% 3 7% 5% 4 5% 5% 7% 7% 33%	3947
	21st to end	Night	10% 11% 3 10% 5% 6% 6% 6% 6% 6% 32%	4600
November	1st to 10th	Night	14% 15% 4 10% 6% 5% 6% 4 7% 6% 24%	2815
	11th to 20th	Night	12% 12% 4 10% 7% 6% 6% 5% 7% 6% 24%	2940
	21st to end	Night	10% 16% 4 11% 7% 6% 6% 5% 6% 8% 21%	2978
December	1st to 10th	Night	7% 10% 3 9% 7% 7% 10% 6% 8% 8% 23%	5040
	11th to 20th	Night	9% 16% 6% 15% 9% 7% 6% 5% 6% 5% 14%	5905
	21st to end	Night	7% 13% 5% 14% 8% 8% 8% 6% 7% 6% 17%	7905

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	63% 11% 13% 11% 1	4125
	11th to 20th	Day	40% 13% 24% 18% 3 3	4517
	21st to end	Day	51% 13% 16% 16% 3	5187
February	1st to 10th	Day	60% 10% 10% 12% 7% 1	1759
	11th to 20th	Day	51% 11% 15% 14% 7%	1854
	21st to end	Day	58% 9% 15% 13% 5% 1	1665
March	1st to 10th	Day	49% 10% 13% 17% 10%	4618
	11th to 20th	Day	42% 10% 17% 23% 8%	4969
	21st to end	Day	52% 9% 15% 15% 9%	5964
April	1st to 10th	Day	53% 10% 15% 18% 4	2520
	11th to 20th	Day	49% 9% 14% 18% 10% 2	2492
	21st to end	Day	49% 7% 16% 17% 10% 1	2923
May	1st to 10th	Day	36% 5% 13% 32% 13% 1	8195
	11th to 20th	Day	44% 12% 18% 20% 6%	8163
	21st to end	Day	45% 8% 18% 24% 4 1	8994
June	1st to 10th	Day	47% 8% 14% 18% 10% 4	3240
	11th to 20th	Day	48% 8% 13% 21% 9% 1	3360
	21st to end	Day	39% 7% 16% 22% 13% 2	3332
July	1st to 10th	Day	23% 6% 13% 23% 22% 13%	6707
	11th to 20th	Day	18% 5% 15% 26% 24% 11%	6565
	21st to end	Day	20% 6% 18% 32% 18% 6%	6681
August	1st to 10th	Day	18% 7% 13% 30% 27% 5%	4524
	11th to 20th	Day	27% 9% 24% 27% 11% 2	4426
	21st to end	Day	31% 8% 20% 28% 12% 2	4422
September	1st to 10th	Day	31% 6% 16% 26% 17% 3	2400
	11th to 20th	Day	39% 6% 13% 24% 15% 3	2400
	21st to end	Day	41% 10% 20% 19% 8% 2	2142
October	1st to 10th	Day	40% 8% 19% 26% 6%	3280
	11th to 20th	Day	50% 7% 13% 25% 5%	3208
	21st to end	Day	49% 12% 19% 17% 3	3200
November	1st to 10th	Day	59% 9% 15% 14% 3	1700
	11th to 20th	Day	55% 10% 17% 13% 5%	1680
	21st to end	Day	57% 12% 13% 13% 4	1617
December	1st to 10th	Day	55% 14% 18% 12% 2	2360
	11th to 20th	Day	59% 14% 12% 10% 4	2503
	21st to end	Day	60% 14% 14% 11% 1	3322
January	1st to 10th	Night	66% 12% 13% 8% 2	8770
	11th to 20th	Night	44% 12% 22% 15% 5% 3	8427
	21st to end	Night	49% 14% 18% 18% 2	8994
February	1st to 10th	Night	60% 8% 13% 12% 6% 1	2859
	11th to 20th	Night	49% 9% 17% 16% 8%	2664
	21st to end	Night	55% 10% 13% 16% 6%	2140
March	1st to 10th	Night	42% 11% 18% 21% 7%	5496
	11th to 20th	Night	37% 9% 19% 24% 11%	5250
	21st to end	Night	52% 10% 14% 16% 8%	5253
April	1st to 10th	Night	45% 10% 22% 18% 4	2100
	11th to 20th	Night	42% 10% 19% 20% 9%	2079
	21st to end	Night	38% 10% 20% 21% 10%	1694
May	1st to 10th	Night	32% 7% 13% 33% 15%	4721
	11th to 20th	Night	35% 12% 22% 26% 5%	4700
	21st to end	Night	38% 10% 21% 26% 5%	5182
June	1st to 10th	Night	39% 10% 17% 21% 10% 3	1375
	11th to 20th	Night	39% 9% 20% 22% 10%	1260
	21st to end	Night	32% 7% 22% 24% 13% 2	1282
July	1st to 10th	Night	22% 7% 18% 23% 19% 11%	3145
	11th to 20th	Night	15% 6% 20% 28% 27% 5%	3271
	21st to end	Night	19% 7% 20% 31% 14% 10%	3857
August	1st to 10th	Night	18% 8% 14% 27% 29% 4	2601
	11th to 20th	Night	23% 9% 28% 26% 11% 3	2688
	21st to end	Night	28% 9% 23% 26% 13% 2	3494
September	1st to 10th	Night	24% 7% 17% 31% 17% 3	2000
	11th to 20th	Night	32% 7% 17% 23% 16% 4	2000
	21st to end	Night	38% 8% 21% 20% 11% 2	2253
October	1st to 10th	Night	38% 7% 22% 27% 6%	3920
	11th to 20th	Night	46% 7% 17% 25% 6%	3947
	21st to end	Night	46% 9% 20% 21% 4	4600
November	1st to 10th	Night	56% 10% 14% 14% 6%	2815
	11th to 20th	Night	54% 13% 15% 12% 5% 1	2940
	21st to end	Night	58% 11% 16% 12% 4	2978
December	1st to 10th	Night	48% 15% 21% 14% 3	5040
	11th to 20th	Night	65% 11% 13% 8% 3	5903
	21st to end	Night	56% 13% 15% 14% 3	7905

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	18% 15% 14% 32% 13% 8%	220
	11th to 20th	Day	13% 9% 16% 35% 24% 4	220
	21st to end	Day	14% 9% 20% 34% 19% 4	242
February	1st to 10th	Day	19% 15% 26% 25% 11% 3	299
	11th to 20th	Day	14% 16% 26% 25% 15% 4	425
	21st to end	Day	21% 18% 22% 24% 12% 3	413
March	1st to 10th	Day	22% 18% 21% 24% 13% 2	540
	11th to 20th	Day	21% 19% 24% 16% 14% 6%	540
	21st to end	Day	21% 24% 23% 16% 12% 4	594
April	1st to 10th	Day	19% 21% 26% 20% 10% 4	540
	11th to 20th	Day	18% 23% 22% 21% 11% 6%	532
	21st to end	Day	22% 15% 28% 18% 13% 5%	540
May	1st to 10th	Day	15% 15% 27% 24% 15% 3	543
	11th to 20th	Day	16% 13% 22% 26% 17% 6%	568
	21st to end	Day	18% 14% 26% 23% 13% 5%	617
June	1st to 10th	Day	17% 17% 29% 22% 13% 3	870
	11th to 20th	Day	19% 17% 25% 23% 14% 3	990
	21st to end	Day	12% 13% 24% 27% 18% 6%	962
July	1st to 10th	Day	10% 15% 28% 27% 16% 5%	722
	11th to 20th	Day	8% 14% 27% 28% 17% 5%	662
	21st to end	Day	6% 8% 26% 29% 22% 9%	575
August	1st to 10th	Day	7% 6% 24% 28% 25% 10%	527
	11th to 20th	Day	8% 9% 24% 28% 21% 10%	517
	21st to end	Day	11% 10% 24% 26% 17% 11%	583
September	1st to 10th	Day	11% 11% 20% 24% 21% 13%	530
	11th to 20th	Day	14% 12% 22% 25% 19% 8%	530
	21st to end	Day	20% 14% 24% 23% 14% 5%	530
October	1st to 10th	Day	21% 12% 23% 20% 12% 12%	530
	11th to 20th	Day	24% 17% 15% 20% 18% 6%	502
	21st to end	Day	24% 13% 22% 26% 10% 5%	363
November	1st to 10th	Day	25% 10% 21% 30% 11% 3	248
	11th to 20th	Day	22% 14% 20% 25% 12% 7%	220
	21st to end	Day	20% 9% 23% 26% 15% 7%	220
December	1st to 10th	Day	17% 8% 15% 29% 20% 10%	220
	11th to 20th	Day	21% 13% 20% 27% 12% 6%	220
	21st to end	Day	14% 7% 21% 40% 14% 3	242
January	1st to 10th	Night	23% 10% 24% 30% 11% 2	950
	11th to 20th	Night	15% 9% 22% 38% 14% 2	879
	21st to end	Night	12% 9% 24% 37% 15% 3	924
February	1st to 10th	Night	18% 10% 24% 35% 11% 3	840
	11th to 20th	Night	11% 7% 25% 40% 16% 2	824
	21st to end	Night	13% 11% 24% 31% 19% 1	692
March	1st to 10th	Night	15% 12% 25% 29% 18% 2	840
	11th to 20th	Night	15% 16% 25% 28% 15% 2	840
	21st to end	Night	15% 14% 25% 28% 15% 3	924
April	1st to 10th	Night	13% 12% 20% 35% 18% 2	840
	11th to 20th	Night	12% 14% 26% 29% 18% 1	831
	21st to end	Night	10% 14% 22% 38% 13% 3	434
May	1st to 10th	Night	11% 12% 22% 39% 14% 3	420
	11th to 20th	Night	7% 9% 24% 34% 24% 2	414
	21st to end	Night	12% 8% 24% 34% 21% 2	455
June	1st to 10th	Night	12% 11% 29% 35% 12% 2	420
	11th to 20th	Night	11% 10% 30% 32% 15% 2	420
	21st to end	Night	7% 7% 27% 36% 20% 3	420
July	1st to 10th	Night	7% 7% 23% 41% 22% 1	390
	11th to 20th	Night	5% 7% 25% 40% 21% 1	388
	21st to end	Night	3 4 24% 38% 27% 4	438
August	1st to 10th	Night	3 4 15% 39% 35% 4	398
	11th to 20th	Night	5% 3 17% 37% 34% 4	444
	21st to end	Night	8% 6% 20% 35% 29% 3	805
September	1st to 10th	Night	7% 7% 17% 36% 26% 7%	800
	11th to 20th	Night	10% 6% 16% 29% 32% 7%	800
	21st to end	Night	14% 12% 21% 32% 19% 3	800
October	1st to 10th	Night	14% 7% 18% 37% 21% 4	800
	11th to 20th	Night	19% 10% 20% 30% 19% 3	800
	21st to end	Night	19% 12% 22% 31% 13% 3	880
November	1st to 10th	Night	22% 11% 21% 36% 8% 1	820
	11th to 20th	Night	20% 12% 28% 27% 13% 1	840
	21st to end	Night	17% 11% 23% 33% 12% 3	878
December	1st to 10th	Night	14% 8% 24% 35% 16% 3	1050
	11th to 20th	Night	19% 12% 26% 31% 11% 1	1100
	21st to end	Night	16% 10% 25% 37% 11% 1	1171

Page generated at 2026-06-27 23:10:45. Version ac07

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