Outlook
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Outlook 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	9% 8% 3 8% 6% 5% 5% 4 6% 8% 38%	141256
	Night	7% 9% 4 9% 6% 6% 6% 4 6% 7% 36%	139784
Transparency	Day	43% 6% 16% 25% 10% 1	140959
	Night	45% 5% 15% 23% 10% 1	139666
Seeing	Day	13% 9% 27% 29% 17% 5%	17991
	Night	12% 7% 31% 35% 14% 2	27285

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	7% 11% 5% 13% 10% 10% 6% 5% 6% 5% 24%	4125
	11th to 20th	Day	3 6% 3 11% 8% 8% 8% 6% 7% 9% 30%	4119
	21st to end	Day	5% 11% 4 11% 8% 7% 6% 4 7% 8% 28%	4889
February	1st to 10th	Day	7% 14% 5% 13% 7% 7% 7% 4 6% 7% 23%	1806
	11th to 20th	Day	7% 11% 5% 11% 8% 6% 5% 4 6% 7% 29%	1845
	21st to end	Day	4 11% 4 13% 10% 7% 7% 5% 6% 8% 24%	1579
March	1st to 10th	Day	6% 10% 4 12% 8% 6% 5% 4 6% 9% 30%	4600
	11th to 20th	Day	5% 13% 7% 17% 7% 5% 4 3 4 7% 29%	5109
	21st to end	Day	8% 12% 6% 13% 7% 5% 5% 4 6% 7% 29%	5848
April	1st to 10th	Day	6% 9% 4 8% 5% 6% 6% 5% 7% 8% 36%	2520
	11th to 20th	Day	10% 13% 4 11% 6% 5% 4 5% 6% 7% 29%	2601
	21st to end	Day	14% 11% 4 7% 5% 4 4 3 5% 7% 36%	2893
May	1st to 10th	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 42%	8224
	11th to 20th	Day	13% 8% 3 9% 6% 6% 6% 5% 8% 8% 28%	8191
	21st to end	Day	9% 6% 2 6% 5% 5% 5% 4 6% 8% 44%	9478
June	1st to 10th	Day	14% 7% 2 7% 5% 5% 4 4 7% 7% 38%	3307
	11th to 20th	Day	19% 6% 2 7% 5% 5% 5% 4 7% 8% 31%	3360
	21st to end	Day	12% 6% 2 6% 5% 5% 5% 4 8% 9% 39%	3356
July	1st to 10th	Day	6% 4 2 6% 5% 5% 5% 5% 7% 9% 47%	6781
	11th to 20th	Day	11% 5% 2 6% 4 4 5% 4 7% 9% 43%	6780
	21st to end	Day	6% 3 1 4 3 3 4 4 6% 9% 57%	7189
August	1st to 10th	Day	9% 5% 2 6% 4 4 5% 4 6% 7% 50%	4552
	11th to 20th	Day	7% 4 2 5% 4 4 4 5% 6% 10% 48%	4331
	21st to end	Day	11% 4 1 4 3 3 3 3 5% 7% 56%	4568
September	1st to 10th	Day	9% 4 2 6% 4 5% 5% 4 5% 7% 50%	2400
	11th to 20th	Day	13% 7% 2 5% 5% 4 4 4 6% 8% 42%	2400
	21st to end	Day	10% 4 2 5% 4 3 3 3 4 7% 54%	2120
October	1st to 10th	Day	8% 6% 2 6% 3 4 4 4 5% 9% 48%	3270
	11th to 20th	Day	6% 7% 2 6% 3 3 5% 4 8% 12% 43%	3228
	21st to end	Day	7% 9% 4 8% 5% 6% 6% 5% 6% 7% 39%	3097
November	1st to 10th	Day	13% 14% 5% 8% 6% 5% 4 4 5% 5% 32%	1648
	11th to 20th	Day	7% 13% 5% 13% 6% 6% 6% 4 5% 6% 28%	1680
	21st to end	Day	8% 13% 4 12% 7% 6% 5% 4 6% 7% 27%	1627
December	1st to 10th	Day	6% 12% 4 13% 9% 8% 7% 5% 5% 7% 25%	2123
	11th to 20th	Day	7% 12% 4 13% 9% 9% 7% 4 5% 6% 21%	2319
	21st to end	Day	3 7% 2 10% 9% 5% 5% 4 6% 7% 41%	3293
January	1st to 10th	Night	4 10% 5% 14% 9% 8% 7% 5% 6% 7% 25%	8768
	11th to 20th	Night	3 7% 4 12% 8% 9% 9% 6% 6% 8% 28%	8779
	21st to end	Night	5% 10% 4 12% 7% 6% 6% 4 7% 9% 30%	9296
February	1st to 10th	Night	7% 12% 5% 12% 7% 7% 6% 5% 6% 7% 25%	2834
	11th to 20th	Night	6% 11% 5% 11% 5% 6% 6% 6% 7% 7% 31%	2662
	21st to end	Night	3 9% 4 11% 8% 6% 7% 4 8% 9% 33%	2226
March	1st to 10th	Night	5% 9% 5% 12% 7% 6% 7% 4 7% 10% 28%	5481
	11th to 20th	Night	6% 11% 4 11% 8% 6% 6% 4 6% 8% 31%	5110
	21st to end	Night	9% 11% 5% 13% 6% 6% 6% 5% 6% 7% 26%	5358
April	1st to 10th	Night	7% 8% 3 7% 6% 5% 4 5% 6% 8% 42%	2100
	11th to 20th	Night	10% 12% 4 9% 6% 5% 5% 4 7% 6% 31%	1967
	21st to end	Night	10% 11% 3 7% 6% 6% 5% 4 6% 7% 35%	1726
May	1st to 10th	Night	13% 7% 3 6% 4 4 5% 4 5% 6% 45%	4724
	11th to 20th	Night	15% 11% 4 10% 5% 5% 5% 4 6% 7% 28%	4702
	21st to end	Night	10% 6% 2 6% 4 4 5% 4 7% 9% 42%	4686
June	1st to 10th	Night	11% 4 2 6% 5% 4 5% 5% 6% 9% 42%	1307
	11th to 20th	Night	17% 7% 1 5% 5% 6% 6% 5% 7% 7% 34%	1260
	21st to end	Night	11% 4 2 5% 4 4 5% 4 7% 9% 47%	1260
July	1st to 10th	Night	8% 4 2 5% 4 3 4 4 7% 10% 48%	3179
	11th to 20th	Night	6% 4 2 6% 4 4 6% 4 7% 9% 48%	3180
	21st to end	Night	5% 3 1 3 3 2 4 4 6% 8% 59%	3661
August	1st to 10th	Night	7% 4 2 5% 4 4 4 4 6% 7% 54%	2608
	11th to 20th	Night	4 3 2 5% 4 5% 5% 5% 7% 9% 50%	2726
	21st to end	Night	7% 4 2 4 3 3 4 4 6% 7% 55%	3341
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 5% 7% 52%	2000
	11th to 20th	Night	10% 6% 2 6% 3 4 4 4 5% 8% 47%	2000
	21st to end	Night	8% 6% 1 4 3 3 4 3 5% 8% 56%	2278
October	1st to 10th	Night	12% 7% 2 7% 4 4 4 3 5% 6% 46%	3920
	11th to 20th	Night	5% 5% 2 5% 4 4 5% 3 6% 7% 53%	3898
	21st to end	Night	8% 9% 3 7% 4 4 5% 4 6% 7% 43%	4690
November	1st to 10th	Night	13% 16% 4 8% 5% 4 5% 3 5% 6% 31%	2870
	11th to 20th	Night	6% 12% 5% 12% 6% 6% 5% 4 6% 7% 30%	2940
	21st to end	Night	7% 12% 5% 14% 6% 5% 5% 4 5% 7% 30%	2991
December	1st to 10th	Night	7% 14% 6% 14% 8% 8% 6% 4 5% 6% 22%	5276
	11th to 20th	Night	7% 13% 5% 12% 9% 9% 7% 5% 7% 7% 20%	6093
	21st to end	Night	3 6% 3 12% 8% 6% 5% 4 4 5% 44%	7887

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	60% 4 11% 17% 8%	4125
	11th to 20th	Day	48% 6% 15% 20% 10% 1	4140
	21st to end	Day	53% 5% 19% 16% 7%	4889
February	1st to 10th	Day	60% 5% 12% 16% 7%	1806
	11th to 20th	Day	52% 5% 13% 19% 10%	1854
	21st to end	Day	56% 5% 14% 18% 7%	1579
March	1st to 10th	Day	52% 5% 20% 17% 6%	4600
	11th to 20th	Day	55% 7% 15% 17% 5%	5110
	21st to end	Day	53% 7% 12% 23% 6%	5848
April	1st to 10th	Day	44% 8% 14% 24% 11%	2520
	11th to 20th	Day	52% 6% 15% 17% 9% 1	2601
	21st to end	Day	48% 5% 13% 25% 9% 1	2893
May	1st to 10th	Day	40% 3 11% 28% 16% 2	8224
	11th to 20th	Day	50% 6% 10% 23% 10%	8195
	21st to end	Day	36% 6% 13% 30% 13% 1	9478
June	1st to 10th	Day	42% 6% 14% 25% 11% 1	3307
	11th to 20th	Day	49% 7% 14% 22% 8% 1	3360
	21st to end	Day	39% 7% 20% 26% 7% 1	3356
July	1st to 10th	Day	30% 8% 23% 29% 10%	6707
	11th to 20th	Day	36% 6% 15% 35% 7%	6699
	21st to end	Day	24% 5% 21% 36% 13% 2	6986
August	1st to 10th	Day	33% 6% 20% 30% 10% 1	4536
	11th to 20th	Day	30% 6% 18% 37% 8%	4373
	21st to end	Day	29% 4 19% 34% 13% 1	4567
September	1st to 10th	Day	33% 5% 16% 29% 14% 3	2400
	11th to 20th	Day	40% 6% 16% 27% 9% 2	2400
	21st to end	Day	31% 4 15% 35% 14% 2	2120
October	1st to 10th	Day	33% 4 23% 29% 9% 1	3270
	11th to 20th	Day	33% 4 19% 34% 10%	3228
	21st to end	Day	44% 5% 17% 27% 6%	3097
November	1st to 10th	Day	54% 6% 14% 18% 7% 1	1648
	11th to 20th	Day	57% 7% 15% 17% 5%	1680
	21st to end	Day	56% 5% 17% 17% 4	1627
December	1st to 10th	Day	59% 8% 16% 12% 5%	2123
	11th to 20th	Day	63% 5% 20% 8% 4	2320
	21st to end	Day	43% 5% 12% 23% 14% 4	3293
January	1st to 10th	Night	57% 5% 14% 15% 8%	8769
	11th to 20th	Night	53% 5% 15% 16% 11% 1	8820
	21st to end	Night	51% 6% 19% 18% 7%	9296
February	1st to 10th	Night	56% 6% 13% 17% 8%	2834
	11th to 20th	Night	49% 5% 14% 19% 12% 1	2663
	21st to end	Night	45% 5% 16% 24% 10%	2226
March	1st to 10th	Night	50% 6% 20% 20% 5%	5481
	11th to 20th	Night	50% 7% 16% 19% 7%	5110
	21st to end	Night	54% 6% 10% 20% 9%	5358
April	1st to 10th	Night	40% 4 16% 25% 15% 1	2100
	11th to 20th	Night	50% 5% 12% 20% 10% 2	1967
	21st to end	Night	47% 6% 10% 25% 10% 1	1726
May	1st to 10th	Night	39% 5% 9% 27% 17% 3	4724
	11th to 20th	Night	54% 6% 9% 20% 11% 1	4702
	21st to end	Night	36% 6% 12% 29% 16% 1	4690
June	1st to 10th	Night	36% 7% 14% 29% 13% 1	1307
	11th to 20th	Night	46% 8% 14% 21% 11% 1	1260
	21st to end	Night	33% 7% 19% 28% 10% 1	1260
July	1st to 10th	Night	29% 7% 24% 30% 10%	3144
	11th to 20th	Night	31% 5% 15% 40% 9%	3138
	21st to end	Night	22% 5% 20% 38% 14% 2	3559
August	1st to 10th	Night	28% 5% 21% 31% 12% 2	2600
	11th to 20th	Night	27% 6% 19% 36% 12% 1	2750
	21st to end	Night	27% 5% 15% 34% 18% 1	3341
September	1st to 10th	Night	31% 4 13% 30% 15% 6%	2000
	11th to 20th	Night	34% 5% 16% 29% 12% 3	2000
	21st to end	Night	27% 5% 13% 33% 19% 3	2278
October	1st to 10th	Night	39% 3 17% 29% 11%	3920
	11th to 20th	Night	32% 4 13% 36% 14% 1	3898
	21st to end	Night	40% 4 14% 34% 8% 1	4690
November	1st to 10th	Night	55% 5% 13% 18% 8% 1	2870
	11th to 20th	Night	52% 7% 19% 16% 6%	2940
	21st to end	Night	53% 6% 17% 20% 3	2991
December	1st to 10th	Night	63% 7% 16% 11% 4	5276
	11th to 20th	Night	61% 7% 18% 11% 3	6091
	21st to end	Night	43% 4 10% 26% 13% 3	7887

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	13% 8% 29% 28% 16% 6%	220
	11th to 20th	Day	12% 12% 34% 26% 14% 2	220
	21st to end	Day	12% 14% 31% 29% 12% 2	308
February	1st to 10th	Day	14% 11% 34% 28% 11% 2	330
	11th to 20th	Day	11% 6% 33% 33% 13% 5%	330
	21st to end	Day	5% 8% 32% 37% 14% 4	273
March	1st to 10th	Day	12% 9% 32% 30% 15% 2	330
	11th to 20th	Day	10% 12% 30% 31% 13% 4	540
	21st to end	Day	14% 8% 29% 32% 15% 2	594
April	1st to 10th	Day	10% 14% 33% 27% 13% 3	540
	11th to 20th	Day	17% 15% 32% 23% 11% 2	532
	21st to end	Day	16% 11% 26% 32% 13% 2	703
May	1st to 10th	Day	15% 8% 25% 31% 16% 5%	753
	11th to 20th	Day	13% 9% 25% 31% 17% 6%	775
	21st to end	Day	14% 9% 23% 29% 18% 7%	844
June	1st to 10th	Day	14% 12% 27% 28% 16% 3	780
	11th to 20th	Day	19% 11% 27% 26% 13% 4	780
	21st to end	Day	15% 9% 19% 28% 22% 6%	780
July	1st to 10th	Day	8% 5% 21% 35% 24% 7%	722
	11th to 20th	Day	11% 6% 24% 30% 22% 7%	718
	21st to end	Day	8% 4 24% 29% 27% 8%	794
August	1st to 10th	Day	10% 5% 24% 29% 23% 9%	726
	11th to 20th	Day	11% 7% 19% 30% 27% 7%	628
	21st to end	Day	10% 7% 22% 31% 23% 7%	583
September	1st to 10th	Day	11% 8% 30% 28% 19% 4	530
	11th to 20th	Day	18% 9% 23% 31% 17% 2	530
	21st to end	Day	14% 9% 31% 31% 12% 3	400
October	1st to 10th	Day	18% 6% 26% 27% 18% 6%	330
	11th to 20th	Day	10% 10% 34% 28% 15% 2	330
	21st to end	Day	12% 14% 39% 23% 10% 2	363
November	1st to 10th	Day	18% 10% 32% 29% 9% 2	330
	11th to 20th	Day	15% 13% 33% 29% 9% 2	330
	21st to end	Day	8% 12% 36% 32% 9% 3	330
December	1st to 10th	Day	11% 8% 40% 28% 9% 4	253
	11th to 20th	Day	10% 12% 41% 30% 5% 1	220
	21st to end	Day	14% 4 36% 27% 15% 4	242
January	1st to 10th	Night	8% 10% 35% 36% 10% 1	1050
	11th to 20th	Night	10% 12% 38% 30% 9% 1	1050
	21st to end	Night	13% 9% 36% 32% 9% 1	1155
February	1st to 10th	Night	12% 7% 31% 36% 13% 2	944
	11th to 20th	Night	11% 8% 31% 36% 12% 2	824
	21st to end	Night	6% 6% 28% 36% 20% 4	692
March	1st to 10th	Night	10% 7% 31% 37% 13% 1	840
	11th to 20th	Night	9% 8% 35% 33% 13% 2	840
	21st to end	Night	14% 7% 29% 35% 13% 2	814
April	1st to 10th	Night	10% 7% 31% 37% 13% 1	630
	11th to 20th	Night	17% 8% 35% 30% 9% 1	623
	21st to end	Night	17% 10% 29% 33% 11%	630
May	1st to 10th	Night	14% 6% 26% 38% 15% 1	630
	11th to 20th	Night	14% 8% 28% 30% 17% 2	621
	21st to end	Night	19% 4 22% 36% 16% 3	516
June	1st to 10th	Night	13% 9% 28% 30% 19% 2	420
	11th to 20th	Night	18% 6% 22% 38% 15% 1	420
	21st to end	Night	13% 5% 20% 40% 20% 2	420
July	1st to 10th	Night	9% 4 17% 44% 25% 1	390
	11th to 20th	Night	11% 5% 26% 39% 18% 1	388
	21st to end	Night	5% 4 24% 42% 22% 3	519
August	1st to 10th	Night	7% 5% 21% 37% 26% 4	597
	11th to 20th	Night	7% 3 21% 41% 25% 2	594
	21st to end	Night	10% 5% 26% 36% 22% 1	660
September	1st to 10th	Night	11% 3 27% 40% 18% 1	600
	11th to 20th	Night	14% 5% 19% 44% 16% 1	600
	21st to end	Night	11% 6% 35% 36% 13%	748
October	1st to 10th	Night	18% 6% 28% 34% 14%	800
	11th to 20th	Night	10% 6% 36% 34% 12% 2	800
	21st to end	Night	16% 10% 36% 31% 8% 1	1090
November	1st to 10th	Night	21% 9% 32% 29% 8% 1	1025
	11th to 20th	Night	12% 9% 36% 31% 10% 2	1050
	21st to end	Night	13% 9% 38% 31% 8% 1	1050
December	1st to 10th	Night	13% 7% 38% 30% 11% 2	1050
	11th to 20th	Night	12% 11% 34% 31% 11% 1	1050
	21st to end	Night	10% 6% 33% 35% 13% 3	1155

Page generated at 2026-06-28 00:10:49. Version ac07

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