Grants Pass
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Grants Pass clear sky chart from 2005-11-06 to 2025-08-05.

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	10% 8% 3 6% 4 4 4 3 4 6% 49%	129936
	Night	13% 9% 3 7% 4 4 4 3 4 6% 44%	126993
Transparency	Day	35% 6% 11% 22% 18% 8%	129646
	Night	39% 7% 13% 22% 14% 6%	126798
Seeing	Day	14% 11% 23% 26% 19% 7%	15880
	Night	15% 5% 14% 34% 28% 4	24885

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	25% 16% 5% 12% 7% 5% 4 3 5% 5% 13%	3639
	11th to 20th	Day	21% 11% 3 9% 5% 4 4 3 4 4 32%	3934
	21st to end	Day	22% 9% 3 6% 4 3 3 3 4 7% 36%	4510
February	1st to 10th	Day	16% 13% 4 10% 6% 6% 5% 5% 7% 6% 22%	1800
	11th to 20th	Day	16% 14% 4 10% 6% 5% 4 4 5% 7% 26%	1755
	21st to end	Day	16% 17% 5% 10% 6% 4 4 3 5% 5% 24%	1581
March	1st to 10th	Day	15% 15% 5% 10% 6% 4 5% 3 6% 7% 25%	4900
	11th to 20th	Day	17% 15% 4 8% 5% 5% 4 3 4 5% 30%	5000
	21st to end	Day	17% 14% 4 10% 6% 5% 5% 4 6% 7% 21%	5515
April	1st to 10th	Day	14% 12% 5% 10% 7% 5% 5% 4 5% 7% 25%	2400
	11th to 20th	Day	15% 12% 4 8% 5% 4 4 3 5% 7% 33%	2369
	21st to end	Day	11% 10% 3 8% 5% 4 4 4 6% 8% 38%	2545
May	1st to 10th	Day	9% 7% 2 6% 3 4 4 4 5% 6% 51%	5897
	11th to 20th	Day	6% 5% 2 6% 4 4 5% 4 6% 7% 52%	6277
	21st to end	Day	6% 4 2 4 3 3 3 3 5% 7% 60%	6902
June	1st to 10th	Day	10% 7% 2 6% 4 4 3 3 5% 8% 48%	2800
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 3 5% 6% 56%	2800
	21st to end	Day	4 3 1 3 2 2 3 2 4 5% 69%	2800
July	1st to 10th	Day	1 1 1 1 1 1 1 1 2 3 86%	6319
	11th to 20th	Day	1 1 1 1 1 1 2 1 2 3 85%	6320
	21st to end	Day	1 1 1 1 1 1 1 3 3 85%	6475
August	1st to 10th	Day	2 2 1 3 2 2 2 2 3 4 77%	4144
	11th to 20th	Day	2 2 1 3 2 2 3 2 3 5% 75%	4026
	21st to end	Day	2 2 1 4 2 2 2 2 3 4 76%	4252
September	1st to 10th	Day	2 3 1 2 2 2 3 2 3 6% 74%	2280
	11th to 20th	Day	5% 4 2 5% 3 3 4 3 5% 7% 58%	2237
	21st to end	Day	7% 4 2 5% 3 3 3 3 5% 8% 58%	2024
October	1st to 10th	Day	5% 4 1 5% 3 3 3 2 3 5% 66%	3180
	11th to 20th	Day	8% 8% 3 7% 5% 4 5% 4 6% 9% 42%	3161
	21st to end	Day	13% 10% 3 8% 5% 5% 5% 4 6% 8% 33%	3448
November	1st to 10th	Day	19% 11% 5% 10% 6% 5% 6% 3 5% 6% 24%	1794
	11th to 20th	Day	18% 13% 4 11% 6% 5% 5% 4 6% 8% 19%	1600
	21st to end	Day	16% 13% 4 11% 6% 6% 5% 4 4 6% 25%	1600
December	1st to 10th	Day	11% 7% 4 8% 6% 5% 4 4 6% 8% 38%	2620
	11th to 20th	Day	27% 14% 4 12% 7% 6% 5% 3 5% 5% 11%	3028
	21st to end	Day	26% 19% 6% 15% 8% 6% 4 3 3 4 7%	4004
January	1st to 10th	Night	29% 15% 4 10% 6% 5% 5% 3 5% 5% 14%	6306
	11th to 20th	Night	19% 11% 4 9% 4 5% 3 3 4 5% 33%	6037
	21st to end	Night	25% 10% 3 6% 3 3 3 2 4 4 37%	6468
February	1st to 10th	Night	15% 14% 5% 8% 5% 4 5% 4 5% 7% 28%	2600
	11th to 20th	Night	18% 13% 5% 8% 4 4 4 3 5% 6% 29%	2532
	21st to end	Night	14% 15% 4 8% 4 4 5% 3 5% 7% 30%	2047
March	1st to 10th	Night	17% 16% 4 9% 5% 4 4 4 6% 7% 24%	4990
	11th to 20th	Night	14% 14% 4 9% 6% 4 4 3 4 5% 34%	5000
	21st to end	Night	16% 14% 5% 11% 6% 5% 5% 4 5% 6% 22%	5458
April	1st to 10th	Night	14% 15% 3 8% 6% 5% 6% 3 5% 6% 29%	2000
	11th to 20th	Night	11% 13% 3 8% 5% 3 4 4 4 6% 40%	1979
	21st to end	Night	12% 9% 3 7% 4 4 4 5% 6% 7% 39%	1850
May	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 5% 6% 54%	4082
	11th to 20th	Night	6% 6% 2 6% 4 4 4 3 4 7% 53%	3616
	21st to end	Night	6% 4 1 4 3 3 3 2 4 7% 63%	3972
June	1st to 10th	Night	10% 6% 2 4 4 4 4 3 5% 6% 51%	1600
	11th to 20th	Night	6% 4 1 3 3 3 4 3 5% 6% 62%	1600
	21st to end	Night	3 3 1 2 2 2 3 2 2 4 76%	1600
July	1st to 10th	Night	2 1 1 1 1 1 2 2 3 4 80%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 1 2 2 88%	3640
	21st to end	Night	2 2 1 1 1 1 2 2 3 3 83%	4378
August	1st to 10th	Night	1 1 1 2 2 2 2 2 3 4 80%	2884
	11th to 20th	Night	1 2 1 2 1 2 3 2 4 6% 77%	2812
	21st to end	Night	3 2 1 3 2 2 2 2 3 3 77%	3422
September	1st to 10th	Night	2 1 1 2 1 2 2 1 4 4 81%	1900
	11th to 20th	Night	4 3 1 3 3 3 3 3 5% 6% 67%	1939
	21st to end	Night	7% 4 2 4 3 3 3 3 4 6% 62%	2156
October	1st to 10th	Night	4 3 2 4 2 2 2 2 3 4 72%	3800
	11th to 20th	Night	8% 6% 2 6% 4 4 3 3 6% 7% 51%	3777
	21st to end	Night	13% 11% 4 9% 5% 5% 5% 4 6% 6% 33%	4121
November	1st to 10th	Night	18% 10% 4 8% 7% 5% 4 3 4 6% 30%	2499
	11th to 20th	Night	19% 11% 4 9% 6% 6% 5% 4 6% 7% 23%	2800
	21st to end	Night	17% 10% 3 8% 5% 4 5% 3 5% 7% 33%	2800
December	1st to 10th	Night	11% 8% 3 7% 5% 4 4 4 5% 7% 43%	4560
	11th to 20th	Night	25% 17% 5% 11% 6% 5% 5% 3 4 5% 14%	5176
	21st to end	Night	25% 15% 4 11% 7% 5% 5% 3 4 5% 15%	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	65% 12% 8% 11% 3	3639
	11th to 20th	Day	51% 7% 9% 22% 9% 2	3934
	21st to end	Day	45% 8% 8% 13% 15% 11%	4510
February	1st to 10th	Day	55% 11% 14% 13% 7% 1	1800
	11th to 20th	Day	52% 12% 12% 16% 6% 2	1764
	21st to end	Day	57% 11% 10% 14% 7% 1	1581
March	1st to 10th	Day	54% 7% 13% 20% 6%	4900
	11th to 20th	Day	52% 8% 11% 14% 15%	5000
	21st to end	Day	54% 11% 15% 16% 3	5515
April	1st to 10th	Day	55% 9% 13% 15% 6% 1	2400
	11th to 20th	Day	49% 8% 16% 14% 9% 4	2372
	21st to end	Day	42% 8% 18% 19% 11% 1	2545
May	1st to 10th	Day	31% 7% 11% 26% 22% 4	5897
	11th to 20th	Day	28% 7% 14% 29% 19% 3	6280
	21st to end	Day	23% 7% 21% 38% 12%	6904
June	1st to 10th	Day	35% 7% 15% 30% 13% 1	2800
	11th to 20th	Day	28% 6% 14% 33% 17% 2	2800
	21st to end	Day	19% 3 12% 34% 25% 7%	2800
July	1st to 10th	Day	7% 2 6% 24% 30% 32%	6251
	11th to 20th	Day	8% 1 5% 14% 34% 38%	6245
	21st to end	Day	8% 1 5% 33% 38% 14%	6288
August	1st to 10th	Day	13% 2 6% 21% 39% 19%	4129
	11th to 20th	Day	12% 3 8% 35% 31% 12%	4065
	21st to end	Day	14% 3 7% 31% 34% 10%	4251
September	1st to 10th	Day	12% 4 6% 25% 33% 20%	2280
	11th to 20th	Day	23% 6% 13% 26% 23% 8%	2237
	21st to end	Day	24% 6% 10% 27% 22% 11%	2024
October	1st to 10th	Day	21% 6% 10% 18% 25% 22%	3180
	11th to 20th	Day	35% 6% 18% 24% 14% 3	3161
	21st to end	Day	43% 7% 12% 19% 16% 3	3448
November	1st to 10th	Day	55% 10% 12% 12% 10% 1	1794
	11th to 20th	Day	56% 10% 13% 11% 7% 3	1600
	21st to end	Day	53% 12% 10% 9% 12% 4	1600
December	1st to 10th	Day	40% 6% 11% 20% 19% 3	2620
	11th to 20th	Day	68% 11% 9% 8% 4	3028
	21st to end	Day	73% 13% 6% 6% 2	4004
January	1st to 10th	Night	66% 10% 9% 11% 2 1	6306
	11th to 20th	Night	50% 8% 9% 22% 8% 2	6037
	21st to end	Night	49% 6% 7% 13% 15% 11%	6468
February	1st to 10th	Night	51% 10% 15% 15% 8% 1	2600
	11th to 20th	Night	52% 9% 13% 18% 7% 1	2534
	21st to end	Night	48% 12% 16% 16% 6% 2	2047
March	1st to 10th	Night	53% 7% 18% 16% 5%	4990
	11th to 20th	Night	46% 9% 12% 20% 11% 2	5000
	21st to end	Night	55% 13% 17% 13% 2	5458
April	1st to 10th	Night	53% 8% 17% 16% 6%	2000
	11th to 20th	Night	43% 10% 18% 19% 8% 3	1979
	21st to end	Night	40% 10% 21% 22% 6% 1	1850
May	1st to 10th	Night	28% 8% 15% 28% 21% 1	4079
	11th to 20th	Night	29% 7% 18% 34% 10% 1	3616
	21st to end	Night	23% 6% 31% 35% 6%	3972
June	1st to 10th	Night	34% 7% 18% 33% 8%	1600
	11th to 20th	Night	24% 6% 19% 35% 14% 1	1600
	21st to end	Night	15% 4 15% 41% 21% 5%	1600
July	1st to 10th	Night	10% 2 7% 29% 24% 29%	3600
	11th to 20th	Night	6% 1 3 18% 37% 35%	3592
	21st to end	Night	8% 1 6% 41% 33% 11%	4254
August	1st to 10th	Night	10% 2 7% 24% 46% 10%	2875
	11th to 20th	Night	10% 3 13% 39% 25% 10%	2839
	21st to end	Night	13% 3 8% 33% 35% 7%	3422
September	1st to 10th	Night	9% 2 7% 30% 34% 17%	1900
	11th to 20th	Night	18% 5% 16% 32% 22% 6%	1939
	21st to end	Night	23% 5% 12% 27% 21% 12%	2156
October	1st to 10th	Night	18% 4 10% 21% 28% 18%	3800
	11th to 20th	Night	31% 6% 17% 31% 12% 3	3777
	21st to end	Night	47% 7% 11% 19% 11% 4	4121
November	1st to 10th	Night	52% 8% 14% 12% 11% 2	2499
	11th to 20th	Night	56% 9% 14% 12% 8% 2	2800
	21st to end	Night	48% 9% 13% 14% 12% 4	2800
December	1st to 10th	Night	39% 7% 11% 22% 20% 2	4560
	11th to 20th	Night	67% 9% 11% 10% 3	5176
	21st to end	Night	62% 14% 11% 10% 3 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	33% 13% 20% 18% 12% 5%	200
	11th to 20th	Day	27% 7% 15% 24% 15% 12%	325
	21st to end	Day	22% 9% 18% 22% 21% 9%	440
February	1st to 10th	Day	20% 12% 18% 25% 22% 4	400
	11th to 20th	Day	29% 11% 21% 21% 13% 5%	395
	21st to end	Day	26% 14% 18% 25% 13% 3	380
March	1st to 10th	Day	26% 16% 23% 21% 11% 3	500
	11th to 20th	Day	22% 14% 21% 22% 17% 4	500
	21st to end	Day	24% 18% 20% 23% 14% 1	550
April	1st to 10th	Day	22% 15% 26% 23% 11% 3	500
	11th to 20th	Day	18% 18% 27% 21% 12% 4	492
	21st to end	Day	16% 17% 28% 22% 13% 5%	500
May	1st to 10th	Day	16% 15% 27% 21% 16% 5%	503
	11th to 20th	Day	17% 15% 25% 22% 16% 6%	528
	21st to end	Day	13% 12% 26% 26% 16% 7%	573
June	1st to 10th	Day	12% 12% 26% 25% 17% 7%	530
	11th to 20th	Day	10% 17% 33% 24% 12% 5%	530
	21st to end	Day	4 9% 28% 32% 18% 8%	530
July	1st to 10th	Day	3 8% 26% 37% 18% 8%	526
	11th to 20th	Day	2 6% 30% 35% 19% 8%	524
	21st to end	Day	1 4 25% 37% 23% 10%	575
August	1st to 10th	Day	3 5% 24% 34% 24% 10%	504
	11th to 20th	Day	1 8% 22% 32% 25% 12%	477
	21st to end	Day	5% 6% 23% 30% 26% 10%	539
September	1st to 10th	Day	4 6% 21% 30% 28% 11%	490
	11th to 20th	Day	9% 7% 23% 29% 25% 9%	490
	21st to end	Day	8% 9% 20% 29% 25% 9%	490
October	1st to 10th	Day	11% 9% 18% 26% 24% 12%	490
	11th to 20th	Day	12% 9% 18% 22% 27% 11%	490
	21st to end	Day	19% 10% 19% 24% 17% 11%	539
November	1st to 10th	Day	17% 12% 17% 29% 18% 8%	350
	11th to 20th	Day	19% 10% 17% 24% 22% 9%	200
	21st to end	Day	19% 7% 16% 28% 22% 10%	200
December	1st to 10th	Day	17% 8% 12% 28% 22% 13%	200
	11th to 20th	Day	29% 6% 20% 20% 20% 6%	200
	21st to end	Day	28% 11% 20% 20% 17% 3	220
January	1st to 10th	Night	23% 9% 17% 34% 15% 3	800
	11th to 20th	Night	20% 7% 17% 32% 20% 5%	800
	21st to end	Night	22% 5% 13% 33% 23% 4	880
February	1st to 10th	Night	20% 7% 16% 35% 22% 2	800
	11th to 20th	Night	21% 7% 17% 34% 20% 2	784
	21st to end	Night	19% 9% 18% 36% 17% 1	660
March	1st to 10th	Night	23% 10% 19% 31% 16% 2	800
	11th to 20th	Night	20% 8% 16% 34% 21% 2	800
	21st to end	Night	20% 9% 22% 31% 18%	880
April	1st to 10th	Night	18% 10% 21% 31% 18% 2	800
	11th to 20th	Night	15% 10% 19% 32% 21% 3	791
	21st to end	Night	16% 6% 16% 32% 28% 2	650
May	1st to 10th	Night	11% 7% 14% 37% 29% 3	595
	11th to 20th	Night	9% 7% 15% 33% 34% 3	394
	21st to end	Night	9% 4 17% 35% 31% 4	433
June	1st to 10th	Night	10% 4 13% 35% 36% 3	400
	11th to 20th	Night	7% 5% 15% 42% 30% 2	400
	21st to end	Night	5% 2 10% 37% 45% 2	400
July	1st to 10th	Night	2 1 8% 35% 52% 2	390
	11th to 20th	Night	2 1 7% 43% 45% 2	388
	21st to end	Night	2 1 4 29% 55% 9%	615
August	1st to 10th	Night	2 1 4 29% 53% 11%	579
	11th to 20th	Night	2 1 4 28% 56% 10%	564
	21st to end	Night	3 1 11% 34% 44% 7%	786
September	1st to 10th	Night	2 2 12% 31% 48% 5%	760
	11th to 20th	Night	4 2 13% 29% 42% 9%	760
	21st to end	Night	8% 4 10% 34% 36% 9%	760
October	1st to 10th	Night	9% 2 13% 36% 34% 6%	760
	11th to 20th	Night	12% 3 10% 36% 34% 6%	760
	21st to end	Night	15% 4 13% 34% 27% 7%	836
November	1st to 10th	Night	19% 6% 13% 36% 22% 4	780
	11th to 20th	Night	21% 6% 16% 35% 20% 2	800
	21st to end	Night	19% 5% 14% 36% 24% 2	800
December	1st to 10th	Night	19% 5% 12% 37% 23% 4	800
	11th to 20th	Night	24% 8% 14% 34% 19% 2	800
	21st to end	Night	27% 8% 20% 32% 11% 2	880

Page generated at 2025-08-01 22:32:26. Version ac07

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