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 2025-02-25.

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	8% 9% 3 8% 6% 5% 6% 4 6% 8% 36%	111818
	Night	7% 10% 4 9% 6% 6% 6% 5% 7% 8% 32%	115498
Transparency	Day	43% 9% 16% 19% 10% 3	111574
	Night	45% 10% 17% 18% 8% 1	115388
Seeing	Day	16% 14% 24% 25% 16% 6%	15734
	Night	14% 10% 23% 34% 18% 3	24336

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% 18% 5% 15% 8% 6% 7% 4 6% 7% 14%	3179
	11th to 20th	Day	6% 11% 3 8% 6% 6% 7% 6% 10% 11% 25%	3449
	21st to end	Day	8% 14% 5% 11% 7% 6% 6% 6% 8% 7% 22%	4004
February	1st to 10th	Day	9% 15% 5% 13% 8% 7% 6% 4 6% 7% 21%	1675
	11th to 20th	Day	4 14% 5% 10% 7% 7% 6% 5% 8% 7% 26%	1755
	21st to end	Day	6% 14% 5% 14% 8% 6% 7% 6% 6% 6% 21%	1549
March	1st to 10th	Day	6% 15% 5% 13% 7% 6% 6% 5% 6% 7% 25%	3138
	11th to 20th	Day	3 9% 3 8% 7% 6% 7% 5% 8% 7% 37%	3391
	21st to end	Day	8% 13% 5% 11% 7% 6% 6% 5% 7% 8% 26%	4070
April	1st to 10th	Day	8% 12% 4 11% 7% 7% 7% 6% 8% 7% 24%	2280
	11th to 20th	Day	9% 12% 4 10% 6% 5% 5% 5% 7% 8% 29%	2252
	21st to end	Day	9% 12% 4 9% 6% 5% 6% 6% 7% 8% 28%	2644
May	1st to 10th	Day	7% 9% 3 7% 6% 5% 5% 5% 6% 8% 39%	4420
	11th to 20th	Day	6% 7% 3 9% 6% 6% 5% 5% 8% 12% 32%	4377
	21st to end	Day	13% 12% 4 10% 6% 6% 6% 4 7% 7% 25%	4813
June	1st to 10th	Day	14% 8% 3 8% 5% 5% 6% 4 6% 6% 33%	2932
	11th to 20th	Day	14% 9% 3 7% 7% 5% 5% 5% 6% 7% 32%	3040
	21st to end	Day	8% 6% 2 7% 5% 5% 6% 4 6% 7% 43%	3015
July	1st to 10th	Day	4 4 1 5% 3 4 3 3 5% 6% 63%	4740
	11th to 20th	Day	3 2 1 3 2 3 3 3 4 5% 72%	4648
	21st to end	Day	5% 3 1 4 3 3 4 3 5% 7% 63%	4790
August	1st to 10th	Day	2 2 1 3 3 4 4 4 6% 9% 61%	4401
	11th to 20th	Day	3 4 1 5% 5% 6% 5% 5% 7% 8% 51%	4247
	21st to end	Day	8% 4 2 5% 4 5% 6% 4 7% 9% 47%	4287
September	1st to 10th	Day	8% 5% 2 7% 4 4 4 3 5% 7% 51%	2280
	11th to 20th	Day	11% 6% 2 7% 5% 5% 4 4 5% 7% 42%	2280
	21st to end	Day	12% 7% 3 8% 5% 4 5% 5% 7% 8% 36%	2036
October	1st to 10th	Day	10% 7% 3 8% 5% 5% 5% 4 6% 7% 40%	3180
	11th to 20th	Day	14% 12% 3 8% 5% 5% 4 3 6% 8% 32%	3110
	21st to end	Day	11% 10% 3 10% 6% 6% 7% 4 6% 7% 28%	3101
November	1st to 10th	Day	15% 14% 5% 9% 6% 6% 7% 4 5% 6% 24%	1618
	11th to 20th	Day	10% 13% 4 10% 6% 6% 6% 4 6% 8% 26%	1600
	21st to end	Day	10% 17% 4 9% 8% 6% 7% 4 6% 8% 21%	1540
December	1st to 10th	Day	5% 11% 4 12% 9% 8% 10% 6% 7% 7% 21%	2290
	11th to 20th	Day	7% 14% 6% 14% 9% 8% 8% 5% 7% 6% 17%	2437
	21st to end	Day	7% 13% 6% 12% 9% 10% 9% 6% 7% 7% 15%	3250
January	1st to 10th	Night	8% 18% 6% 15% 9% 9% 8% 4 5% 6% 11%	6766
	11th to 20th	Night	6% 12% 4 11% 7% 6% 6% 5% 11% 10% 22%	6447
	21st to end	Night	8% 13% 5% 11% 8% 7% 6% 5% 8% 12% 17%	6952
February	1st to 10th	Night	9% 18% 6% 12% 8% 5% 5% 4 5% 6% 22%	2723
	11th to 20th	Night	4 13% 5% 11% 7% 6% 6% 4 7% 8% 30%	2532
	21st to end	Night	5% 13% 5% 14% 8% 6% 6% 4 7% 7% 24%	1998
March	1st to 10th	Night	4 12% 4 10% 7% 6% 7% 6% 7% 9% 27%	3736
	11th to 20th	Night	4 9% 2 6% 4 5% 5% 5% 7% 10% 43%	3587
	21st to end	Night	7% 12% 4 9% 6% 6% 6% 6% 7% 7% 31%	3583
April	1st to 10th	Night	6% 12% 3 7% 7% 7% 5% 6% 6% 7% 34%	1900
	11th to 20th	Night	7% 10% 3 8% 6% 5% 6% 6% 8% 7% 35%	1879
	21st to end	Night	5% 10% 3 7% 5% 6% 5% 5% 7% 9% 39%	1533
May	1st to 10th	Night	6% 9% 3 8% 6% 5% 4 3 5% 7% 43%	2540
	11th to 20th	Night	5% 7% 3 7% 5% 5% 6% 4 8% 10% 39%	2516
	21st to end	Night	7% 8% 4 10% 6% 6% 7% 5% 7% 7% 33%	2762
June	1st to 10th	Night	10% 8% 2 6% 6% 5% 7% 4 8% 9% 35%	1244
	11th to 20th	Night	8% 6% 3 7% 5% 6% 6% 6% 8% 10% 35%	1140
	21st to end	Night	5% 5% 2 6% 5% 4 4 4 7% 8% 50%	1160
July	1st to 10th	Night	3 3 2 5% 3 3 4 4 5% 7% 61%	2220
	11th to 20th	Night	3 2 1 2 2 2 2 3 4 6% 73%	2311
	21st to end	Night	3 2 1 3 2 3 4 4 5% 6% 67%	2762
August	1st to 10th	Night	2 2 1 3 3 4 5% 4 7% 8% 61%	2529
	11th to 20th	Night	3 2 1 5% 4 5% 5% 4 6% 9% 55%	2581
	21st to end	Night	7% 5% 2 5% 4 4 5% 5% 7% 10% 47%	3388
September	1st to 10th	Night	6% 3 1 4 4 4 4 3 5% 7% 58%	1900
	11th to 20th	Night	8% 5% 2 5% 4 4 4 3 7% 8% 49%	1900
	21st to end	Night	9% 7% 3 7% 5% 4 4 4 6% 8% 43%	2139
October	1st to 10th	Night	8% 8% 3 7% 5% 5% 6% 4 5% 7% 44%	3800
	11th to 20th	Night	15% 9% 3 7% 5% 4 5% 6% 7% 7% 33%	3825
	21st to end	Night	10% 11% 3 9% 5% 6% 6% 6% 6% 6% 32%	4457
November	1st to 10th	Night	14% 15% 4 9% 6% 5% 6% 4 6% 6% 24%	2678
	11th to 20th	Night	12% 12% 4 9% 7% 6% 6% 5% 7% 6% 24%	2800
	21st to end	Night	10% 17% 4 11% 7% 6% 6% 5% 6% 7% 21%	2836
December	1st to 10th	Night	7% 10% 3 9% 7% 7% 10% 6% 9% 8% 24%	4890
	11th to 20th	Night	9% 16% 6% 15% 9% 7% 6% 5% 6% 5% 15%	5750
	21st to end	Night	7% 13% 5% 14% 8% 8% 8% 6% 7% 6% 17%	7734

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	64% 11% 14% 9% 1	3179
	11th to 20th	Day	43% 14% 23% 14% 2 3	3473
	21st to end	Day	52% 13% 17% 13% 4	4004
February	1st to 10th	Day	59% 10% 10% 12% 7% 1	1675
	11th to 20th	Day	52% 12% 15% 14% 7%	1764
	21st to end	Day	58% 9% 15% 13% 4	1549
March	1st to 10th	Day	55% 10% 11% 17% 7%	3138
	11th to 20th	Day	39% 10% 20% 24% 6%	3391
	21st to end	Day	54% 10% 16% 11% 8%	4070
April	1st to 10th	Day	55% 10% 15% 17% 4	2280
	11th to 20th	Day	50% 9% 13% 16% 10% 1	2252
	21st to end	Day	52% 7% 16% 16% 9% 1	2644
May	1st to 10th	Day	42% 6% 15% 25% 11% 1	4420
	11th to 20th	Day	41% 11% 20% 21% 7%	4380
	21st to end	Day	56% 9% 16% 15% 4 1	4814
June	1st to 10th	Day	49% 8% 14% 17% 9% 4	2932
	11th to 20th	Day	50% 8% 13% 20% 7% 1	3040
	21st to end	Day	39% 7% 17% 22% 13% 2	3015
July	1st to 10th	Day	22% 6% 10% 20% 26% 16%	4666
	11th to 20th	Day	15% 4 10% 25% 30% 15%	4567
	21st to end	Day	20% 5% 15% 30% 21% 9%	4639
August	1st to 10th	Day	17% 7% 13% 30% 28% 5%	4384
	11th to 20th	Day	27% 9% 24% 26% 11% 2	4289
	21st to end	Day	31% 8% 20% 28% 11% 1	4286
September	1st to 10th	Day	32% 7% 16% 26% 16% 4	2280
	11th to 20th	Day	40% 7% 13% 23% 14% 3	2280
	21st to end	Day	42% 10% 19% 19% 8% 2	2036
October	1st to 10th	Day	41% 8% 19% 26% 6%	3180
	11th to 20th	Day	49% 7% 13% 25% 5%	3110
	21st to end	Day	49% 12% 19% 18% 3	3101
November	1st to 10th	Day	59% 9% 15% 14% 3	1618
	11th to 20th	Day	54% 11% 17% 14% 5%	1600
	21st to end	Day	57% 12% 13% 13% 4	1540
December	1st to 10th	Day	54% 14% 18% 12% 2	2290
	11th to 20th	Day	59% 14% 12% 10% 4	2438
	21st to end	Day	60% 14% 15% 10% 1	3250
January	1st to 10th	Night	67% 12% 12% 8% 2	6766
	11th to 20th	Night	48% 12% 20% 13% 4 4	6485
	21st to end	Night	51% 15% 18% 14% 2	6952
February	1st to 10th	Night	61% 8% 13% 12% 6% 1	2723
	11th to 20th	Night	49% 9% 18% 16% 7%	2534
	21st to end	Night	55% 10% 13% 16% 6%	1998
March	1st to 10th	Night	47% 11% 15% 20% 8%	3736
	11th to 20th	Night	31% 10% 22% 29% 8%	3588
	21st to end	Night	49% 11% 16% 16% 9%	3583
April	1st to 10th	Night	46% 10% 22% 18% 5%	1900
	11th to 20th	Night	43% 10% 18% 20% 10%	1879
	21st to end	Night	39% 11% 20% 21% 9%	1533
May	1st to 10th	Night	40% 8% 14% 26% 12% 1	2540
	11th to 20th	Night	34% 13% 21% 26% 6%	2516
	21st to end	Night	45% 12% 21% 16% 5%	2762
June	1st to 10th	Night	41% 10% 17% 21% 8% 3	1244
	11th to 20th	Night	41% 9% 21% 21% 9%	1140
	21st to end	Night	31% 7% 23% 24% 13% 2	1160
July	1st to 10th	Night	21% 7% 12% 26% 19% 15%	2185
	11th to 20th	Night	13% 5% 11% 30% 34% 7%	2269
	21st to end	Night	17% 6% 16% 30% 17% 14%	2674
August	1st to 10th	Night	17% 8% 14% 27% 30% 4	2521
	11th to 20th	Night	22% 9% 28% 26% 11% 3	2605
	21st to end	Night	29% 9% 23% 26% 12% 1	3388
September	1st to 10th	Night	25% 7% 17% 31% 16% 3	1900
	11th to 20th	Night	33% 7% 17% 22% 16% 4	1900
	21st to end	Night	38% 8% 21% 19% 11% 2	2139
October	1st to 10th	Night	38% 7% 21% 27% 6%	3800
	11th to 20th	Night	46% 7% 17% 25% 5%	3825
	21st to end	Night	46% 8% 20% 21% 4	4457
November	1st to 10th	Night	57% 9% 14% 14% 5%	2678
	11th to 20th	Night	54% 12% 15% 13% 5% 1	2800
	21st to end	Night	58% 11% 15% 12% 4	2836
December	1st to 10th	Night	47% 14% 21% 14% 3	4890
	11th to 20th	Night	65% 11% 13% 8% 3	5748
	21st to end	Night	56% 13% 15% 14% 3	7734

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% 14% 14% 32% 14% 9%	200
	11th to 20th	Day	13% 9% 17% 36% 23% 4	200
	21st to end	Day	15% 9% 21% 35% 17% 4	220
February	1st to 10th	Day	20% 15% 27% 24% 11% 4	275
	11th to 20th	Day	15% 15% 26% 25% 14% 4	395
	21st to end	Day	20% 19% 23% 24% 12% 4	369
March	1st to 10th	Day	22% 18% 22% 22% 13% 2	460
	11th to 20th	Day	18% 19% 25% 16% 15% 7%	460
	21st to end	Day	19% 23% 25% 16% 13% 4	506
April	1st to 10th	Day	21% 22% 25% 20% 9% 3	460
	11th to 20th	Day	19% 23% 21% 21% 11% 6%	452
	21st to end	Day	23% 16% 28% 17% 11% 4	460
May	1st to 10th	Day	16% 16% 26% 25% 13% 4	463
	11th to 20th	Day	16% 12% 22% 26% 18% 6%	488
	21st to end	Day	17% 13% 26% 24% 14% 6%	529
June	1st to 10th	Day	18% 17% 29% 21% 13% 2	762
	11th to 20th	Day	20% 16% 24% 23% 14% 3	870
	21st to end	Day	13% 13% 23% 27% 18% 7%	845
July	1st to 10th	Day	10% 14% 27% 28% 16% 5%	671
	11th to 20th	Day	8% 15% 27% 28% 17% 6%	615
	21st to end	Day	6% 8% 26% 29% 22% 8%	531
August	1st to 10th	Day	7% 6% 24% 28% 25% 11%	487
	11th to 20th	Day	8% 8% 23% 29% 22% 11%	477
	21st to end	Day	12% 11% 26% 25% 17% 9%	539
September	1st to 10th	Day	12% 12% 22% 24% 21% 10%	490
	11th to 20th	Day	15% 12% 22% 25% 19% 7%	490
	21st to end	Day	19% 13% 24% 23% 14% 6%	490
October	1st to 10th	Day	22% 11% 23% 20% 12% 12%	490
	11th to 20th	Day	24% 16% 15% 21% 18% 7%	464
	21st to end	Day	23% 12% 22% 28% 10% 5%	330
November	1st to 10th	Day	23% 10% 21% 30% 12% 3	226
	11th to 20th	Day	23% 15% 20% 23% 13% 8%	200
	21st to end	Day	20% 9% 23% 25% 17% 8%	200
December	1st to 10th	Day	15% 6% 16% 30% 22% 12%	200
	11th to 20th	Day	18% 12% 21% 30% 14% 7%	200
	21st to end	Day	14% 6% 21% 40% 15% 4	220
January	1st to 10th	Night	23% 10% 23% 30% 12% 2	900
	11th to 20th	Night	15% 9% 23% 37% 14% 2	836
	21st to end	Night	13% 9% 25% 36% 14% 3	880
February	1st to 10th	Night	18% 10% 24% 34% 11% 3	800
	11th to 20th	Night	11% 7% 25% 39% 16% 2	784
	21st to end	Night	13% 11% 23% 32% 20% 2	646
March	1st to 10th	Night	14% 11% 25% 29% 18% 2	760
	11th to 20th	Night	13% 16% 25% 28% 16% 2	760
	21st to end	Night	14% 13% 25% 29% 16% 3	836
April	1st to 10th	Night	13% 12% 20% 35% 18% 2	760
	11th to 20th	Night	11% 13% 26% 30% 18% 2	751
	21st to end	Night	11% 13% 23% 38% 13% 3	393
May	1st to 10th	Night	12% 12% 22% 37% 15% 3	380
	11th to 20th	Night	7% 8% 22% 34% 26% 2	374
	21st to end	Night	12% 7% 25% 33% 21% 2	411
June	1st to 10th	Night	13% 10% 28% 35% 12% 2	380
	11th to 20th	Night	12% 9% 30% 32% 16% 2	380
	21st to end	Night	7% 8% 27% 36% 19% 3	380
July	1st to 10th	Night	7% 6% 23% 41% 22% 1	370
	11th to 20th	Night	5% 7% 25% 40% 22% 1	368
	21st to end	Night	3 3 25% 39% 26% 4	416
August	1st to 10th	Night	3 3 14% 38% 37% 4	378
	11th to 20th	Night	5% 3 17% 37% 35% 4	421
	21st to end	Night	8% 6% 20% 35% 28% 3	765
September	1st to 10th	Night	8% 7% 18% 35% 26% 6%	760
	11th to 20th	Night	10% 6% 17% 28% 31% 8%	760
	21st to end	Night	13% 11% 21% 31% 20% 4	760
October	1st to 10th	Night	14% 7% 18% 35% 21% 4	760
	11th to 20th	Night	19% 10% 19% 29% 19% 3	760
	21st to end	Night	19% 12% 23% 31% 14% 3	836
November	1st to 10th	Night	23% 10% 20% 37% 9% 1	780
	11th to 20th	Night	20% 12% 28% 26% 13% 1	800
	21st to end	Night	18% 11% 23% 32% 13% 3	836
December	1st to 10th	Night	13% 8% 24% 36% 17% 3	1000
	11th to 20th	Night	17% 11% 26% 33% 12% 1	1045
	21st to end	Night	17% 10% 25% 36% 11% 1	1110

Page generated at 2025-02-22 03:51:38. Version ac07

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