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 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	9% 8% 3 8% 6% 5% 5% 4 6% 8% 38%	111525
	Night	7% 8% 4 9% 6% 6% 6% 4 6% 7% 37%	115743
Transparency	Day	43% 6% 17% 25% 9% 1	111273
	Night	45% 6% 16% 23% 9% 1	115641
Seeing	Day	13% 9% 27% 29% 17% 5%	16077
	Night	12% 7% 31% 35% 14% 2	25594

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	6% 12% 5% 12% 9% 9% 6% 6% 6% 5% 24%	3179
	11th to 20th	Day	3 7% 4 11% 7% 8% 8% 6% 7% 8% 31%	3159
	21st to end	Day	6% 12% 4 10% 6% 7% 6% 4 7% 8% 31%	3774
February	1st to 10th	Day	7% 14% 5% 13% 7% 7% 7% 4 6% 7% 22%	1720
	11th to 20th	Day	7% 11% 5% 11% 8% 6% 5% 4 6% 7% 29%	1755
	21st to end	Day	4 11% 4 12% 10% 7% 7% 5% 6% 9% 24%	1469
March	1st to 10th	Day	7% 12% 5% 11% 9% 7% 6% 4 5% 6% 28%	3130
	11th to 20th	Day	5% 12% 6% 11% 6% 4 4 4 5% 9% 36%	3489
	21st to end	Day	6% 9% 6% 12% 8% 5% 5% 4 6% 8% 30%	3996
April	1st to 10th	Day	6% 10% 4 7% 5% 6% 6% 6% 7% 7% 36%	2280
	11th to 20th	Day	10% 13% 5% 10% 6% 5% 4 5% 6% 7% 28%	2351
	21st to end	Day	15% 11% 4 7% 5% 5% 4 3 5% 7% 34%	2617
May	1st to 10th	Day	21% 10% 2 5% 4 4 4 4 5% 7% 32%	4430
	11th to 20th	Day	7% 6% 2 8% 6% 7% 7% 5% 8% 9% 34%	4388
	21st to end	Day	13% 8% 3 8% 5% 5% 6% 4 7% 8% 32%	5068
June	1st to 10th	Day	14% 7% 2 7% 4 5% 4 4 7% 7% 39%	2992
	11th to 20th	Day	20% 6% 2 7% 5% 5% 5% 4 6% 8% 31%	3040
	21st to end	Day	11% 6% 2 5% 5% 5% 5% 5% 8% 9% 40%	3036
July	1st to 10th	Day	5% 4 1 6% 5% 5% 6% 5% 8% 10% 45%	4740
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 7% 9% 48%	4740
	21st to end	Day	4 3 1 4 3 3 4 3 6% 8% 61%	5002
August	1st to 10th	Day	8% 5% 2 6% 4 4 5% 4 6% 7% 50%	4412
	11th to 20th	Day	8% 4 2 5% 4 4 4 4 6% 9% 48%	4196
	21st to end	Day	11% 4 1 4 3 3 3 3 5% 7% 55%	4428
September	1st to 10th	Day	9% 4 2 5% 4 5% 5% 4 5% 7% 49%	2280
	11th to 20th	Day	14% 8% 2 5% 5% 4 4 4 6% 7% 42%	2280
	21st to end	Day	10% 5% 2 5% 4 4 4 3 5% 8% 53%	2015
October	1st to 10th	Day	9% 6% 2 6% 3 3 4 4 5% 9% 48%	3170
	11th to 20th	Day	5% 7% 2 6% 3 3 5% 4 8% 12% 43%	3129
	21st to end	Day	7% 9% 4 8% 5% 6% 6% 5% 6% 7% 39%	3001
November	1st to 10th	Day	13% 15% 4 8% 6% 5% 4 4 5% 4 32%	1568
	11th to 20th	Day	7% 13% 5% 14% 7% 6% 6% 4 5% 6% 27%	1600
	21st to end	Day	9% 13% 5% 12% 7% 6% 5% 4 6% 7% 27%	1550
December	1st to 10th	Day	5% 12% 4 13% 9% 8% 7% 5% 5% 7% 25%	2060
	11th to 20th	Day	7% 12% 4 13% 9% 9% 7% 4 5% 6% 22%	2259
	21st to end	Day	3 7% 2 10% 9% 5% 5% 4 6% 7% 41%	3222
January	1st to 10th	Night	3 9% 5% 13% 9% 9% 8% 6% 7% 7% 25%	6766
	11th to 20th	Night	4 8% 4 13% 9% 10% 10% 6% 6% 7% 24%	6739
	21st to end	Night	6% 10% 4 11% 6% 6% 6% 4 6% 8% 32%	7180
February	1st to 10th	Night	7% 12% 5% 12% 7% 7% 6% 6% 6% 7% 25%	2699
	11th to 20th	Night	5% 11% 5% 11% 6% 6% 6% 6% 7% 7% 31%	2532
	21st to end	Night	3 9% 4 11% 7% 6% 7% 4 8% 9% 33%	2078
March	1st to 10th	Night	6% 11% 4 12% 7% 6% 7% 4 7% 9% 27%	3721
	11th to 20th	Night	4 9% 4 9% 6% 6% 5% 4 7% 9% 35%	3490
	21st to end	Night	6% 7% 5% 12% 7% 6% 7% 6% 7% 9% 28%	3651
April	1st to 10th	Night	6% 8% 3 7% 6% 5% 4 5% 6% 8% 42%	1900
	11th to 20th	Night	10% 12% 4 9% 6% 5% 5% 4 7% 7% 31%	1778
	21st to end	Night	10% 11% 4 7% 6% 6% 5% 4 6% 6% 35%	1562
May	1st to 10th	Night	21% 10% 4 7% 3 3 4 3 5% 6% 34%	2540
	11th to 20th	Night	12% 7% 3 8% 5% 5% 5% 4 6% 7% 36%	2518
	21st to end	Night	15% 7% 3 6% 5% 5% 5% 4 6% 7% 37%	2494
June	1st to 10th	Night	11% 4 2 6% 5% 4 5% 4 7% 9% 42%	1183
	11th to 20th	Night	18% 6% 1 5% 6% 6% 6% 4 7% 7% 35%	1140
	21st to end	Night	10% 4 2 4 4 4 5% 4 7% 9% 48%	1140
July	1st to 10th	Night	7% 4 2 5% 4 4 5% 5% 8% 11% 45%	2219
	11th to 20th	Night	5% 3 1 5% 3 4 4 4 6% 10% 56%	2220
	21st to end	Night	2 2 1 3 2 3 3 4 6% 8% 67%	2553
August	1st to 10th	Night	7% 3 2 5% 4 4 4 4 6% 7% 55%	2528
	11th to 20th	Night	5% 3 2 5% 4 5% 5% 5% 7% 9% 51%	2642
	21st to end	Night	7% 4 2 4 3 3 4 4 6% 7% 55%	3239
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 6% 7% 51%	1900
	11th to 20th	Night	11% 7% 2 6% 3 4 4 4 5% 8% 47%	1900
	21st to end	Night	8% 6% 2 5% 3 3 4 3 5% 8% 54%	2163
October	1st to 10th	Night	12% 8% 2 7% 4 4 4 3 5% 6% 46%	3800
	11th to 20th	Night	5% 5% 2 6% 4 4 5% 3 5% 7% 53%	3778
	21st to end	Night	8% 9% 3 7% 4 4 5% 4 6% 7% 43%	4544
November	1st to 10th	Night	13% 16% 4 8% 5% 4 5% 3 5% 6% 31%	2730
	11th to 20th	Night	6% 12% 5% 13% 6% 6% 5% 4 6% 7% 29%	2800
	21st to end	Night	7% 12% 5% 14% 6% 5% 5% 4 5% 7% 30%	2848
December	1st to 10th	Night	7% 14% 6% 14% 8% 7% 6% 4 5% 6% 22%	5119
	11th to 20th	Night	7% 13% 5% 12% 9% 9% 6% 5% 7% 7% 20%	5933
	21st to end	Night	3 6% 3 12% 8% 6% 5% 3 4 5% 45%	7716

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	59% 5% 13% 18% 6%	3179
	11th to 20th	Day	49% 6% 14% 20% 10% 1	3180
	21st to end	Day	50% 5% 23% 17% 4	3774
February	1st to 10th	Day	60% 5% 12% 16% 7%	1720
	11th to 20th	Day	53% 5% 14% 18% 10% 1	1764
	21st to end	Day	55% 5% 14% 17% 8%	1469
March	1st to 10th	Day	56% 5% 16% 16% 7%	3130
	11th to 20th	Day	46% 9% 19% 18% 7%	3490
	21st to end	Day	49% 9% 14% 22% 6%	3996
April	1st to 10th	Day	43% 8% 14% 24% 11%	2280
	11th to 20th	Day	53% 6% 14% 17% 8% 1	2351
	21st to end	Day	49% 5% 14% 23% 8% 1	2617
May	1st to 10th	Day	50% 4 16% 22% 8% 1	4430
	11th to 20th	Day	42% 8% 13% 25% 11% 1	4392
	21st to end	Day	46% 8% 16% 21% 8% 1	5068
June	1st to 10th	Day	42% 6% 14% 25% 11% 1	2992
	11th to 20th	Day	49% 7% 13% 21% 8% 1	3040
	21st to end	Day	37% 8% 21% 26% 8% 1	3036
July	1st to 10th	Day	30% 9% 23% 28% 9%	4666
	11th to 20th	Day	31% 7% 16% 36% 10%	4659
	21st to end	Day	21% 5% 17% 39% 16% 2	4844
August	1st to 10th	Day	33% 6% 20% 31% 10% 1	4396
	11th to 20th	Day	30% 6% 17% 37% 8%	4238
	21st to end	Day	30% 4 19% 34% 12%	4427
September	1st to 10th	Day	33% 5% 17% 27% 14% 3	2280
	11th to 20th	Day	40% 7% 15% 27% 10% 2	2280
	21st to end	Day	32% 4 15% 34% 13% 2	2015
October	1st to 10th	Day	34% 4 23% 29% 9% 1	3170
	11th to 20th	Day	33% 4 19% 34% 10%	3129
	21st to end	Day	44% 5% 17% 28% 6%	3001
November	1st to 10th	Day	55% 6% 14% 18% 7%	1568
	11th to 20th	Day	57% 7% 15% 17% 5%	1600
	21st to end	Day	56% 5% 17% 17% 4	1550
December	1st to 10th	Day	59% 8% 16% 12% 5%	2060
	11th to 20th	Day	63% 5% 20% 8% 4	2260
	21st to end	Day	42% 5% 12% 23% 14% 4	3222
January	1st to 10th	Night	55% 6% 16% 17% 5%	6766
	11th to 20th	Night	58% 5% 13% 14% 10% 1	6780
	21st to end	Night	49% 6% 22% 19% 3	7180
February	1st to 10th	Night	56% 6% 12% 17% 8%	2699
	11th to 20th	Night	49% 5% 15% 18% 12% 1	2533
	21st to end	Night	45% 5% 16% 24% 10%	2078
March	1st to 10th	Night	52% 5% 17% 21% 5%	3721
	11th to 20th	Night	43% 8% 20% 20% 8%	3490
	21st to end	Night	47% 8% 13% 21% 10%	3651
April	1st to 10th	Night	39% 4 16% 25% 15% 1	1900
	11th to 20th	Night	51% 5% 12% 20% 10% 3	1778
	21st to end	Night	47% 6% 11% 24% 10% 2	1562
May	1st to 10th	Night	49% 7% 12% 23% 9% 1	2540
	11th to 20th	Night	43% 8% 10% 21% 17% 1	2518
	21st to end	Night	43% 8% 14% 26% 9%	2494
June	1st to 10th	Night	36% 7% 14% 29% 12% 1	1183
	11th to 20th	Night	46% 8% 14% 20% 12% 1	1140
	21st to end	Night	31% 7% 20% 29% 11% 2	1140
July	1st to 10th	Night	29% 8% 24% 29% 9%	2184
	11th to 20th	Night	25% 5% 14% 44% 12%	2178
	21st to end	Night	15% 4 15% 46% 16% 2	2472
August	1st to 10th	Night	27% 6% 21% 32% 12% 2	2520
	11th to 20th	Night	26% 6% 18% 36% 12% 1	2666
	21st to end	Night	27% 5% 15% 34% 17% 1	3239
September	1st to 10th	Night	32% 5% 14% 28% 16% 6%	1900
	11th to 20th	Night	35% 5% 15% 29% 13% 3	1900
	21st to end	Night	29% 5% 13% 32% 19% 3	2163
October	1st to 10th	Night	40% 3 17% 29% 11%	3800
	11th to 20th	Night	32% 3 13% 37% 14% 1	3778
	21st to end	Night	40% 4 14% 34% 7% 1	4544
November	1st to 10th	Night	55% 5% 13% 18% 8% 1	2730
	11th to 20th	Night	53% 7% 18% 16% 5%	2800
	21st to end	Night	53% 6% 18% 19% 3	2848
December	1st to 10th	Night	62% 7% 16% 11% 4	5119
	11th to 20th	Night	61% 7% 18% 11% 3	5931
	21st to end	Night	43% 4 10% 27% 13% 4	7716

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% 9% 27% 29% 17% 7%	200
	11th to 20th	Day	12% 11% 33% 28% 16% 2	200
	21st to end	Day	13% 13% 32% 29% 12% 2	280
February	1st to 10th	Day	15% 11% 33% 28% 11% 2	300
	11th to 20th	Day	10% 6% 34% 32% 13% 5%	300
	21st to end	Day	5% 7% 28% 39% 16% 5%	237
March	1st to 10th	Day	12% 11% 31% 28% 15% 3	270
	11th to 20th	Day	11% 10% 30% 32% 13% 5%	460
	21st to end	Day	13% 7% 28% 32% 17% 2	506
April	1st to 10th	Day	10% 15% 32% 27% 13% 4	460
	11th to 20th	Day	17% 14% 31% 23% 12% 2	452
	21st to end	Day	16% 11% 27% 32% 12% 2	607
May	1st to 10th	Day	16% 7% 25% 28% 18% 6%	653
	11th to 20th	Day	9% 8% 25% 33% 18% 7%	675
	21st to end	Day	15% 9% 22% 27% 18% 8%	734
June	1st to 10th	Day	13% 11% 26% 29% 17% 3	680
	11th to 20th	Day	20% 12% 27% 25% 13% 5%	680
	21st to end	Day	13% 9% 20% 29% 23% 6%	680
July	1st to 10th	Day	7% 5% 22% 35% 24% 7%	671
	11th to 20th	Day	10% 6% 25% 30% 22% 7%	668
	21st to end	Day	8% 5% 24% 29% 27% 8%	739
August	1st to 10th	Day	9% 4 25% 29% 23% 9%	676
	11th to 20th	Day	11% 7% 19% 29% 28% 7%	583
	21st to end	Day	11% 7% 23% 31% 23% 6%	539
September	1st to 10th	Day	12% 8% 30% 29% 18% 4	490
	11th to 20th	Day	19% 9% 24% 31% 16% 2	490
	21st to end	Day	15% 9% 32% 29% 12% 3	367
October	1st to 10th	Day	18% 5% 26% 26% 19% 6%	300
	11th to 20th	Day	9% 10% 34% 28% 16% 3	300
	21st to end	Day	11% 13% 38% 24% 11% 2	330
November	1st to 10th	Day	18% 9% 32% 30% 9% 3	300
	11th to 20th	Day	15% 12% 33% 28% 10% 2	300
	21st to end	Day	9% 13% 36% 31% 8% 3	300
December	1st to 10th	Day	10% 7% 39% 30% 10% 4	230
	11th to 20th	Day	10% 11% 41% 32% 6% 2	200
	21st to end	Day	14% 3 34% 28% 16% 4	220
January	1st to 10th	Night	8% 10% 34% 36% 11% 2	1000
	11th to 20th	Night	10% 11% 38% 31% 10% 1	1000
	21st to end	Night	13% 9% 36% 32% 9% 1	1100
February	1st to 10th	Night	12% 6% 31% 36% 13% 2	899
	11th to 20th	Night	11% 8% 31% 36% 12% 2	784
	21st to end	Night	6% 5% 28% 36% 21% 4	646
March	1st to 10th	Night	10% 7% 31% 37% 14% 2	760
	11th to 20th	Night	9% 8% 35% 34% 14% 2	760
	21st to end	Night	13% 7% 28% 37% 13% 2	736
April	1st to 10th	Night	9% 7% 32% 36% 13% 1	570
	11th to 20th	Night	17% 8% 33% 31% 10% 1	563
	21st to end	Night	17% 10% 28% 34% 10%	570
May	1st to 10th	Night	15% 6% 25% 37% 16% 1	570
	11th to 20th	Night	11% 8% 29% 31% 19% 2	561
	21st to end	Night	20% 4 20% 36% 16% 4	466
June	1st to 10th	Night	13% 9% 26% 31% 18% 2	380
	11th to 20th	Night	19% 6% 22% 37% 15% 1	380
	21st to end	Night	11% 6% 20% 41% 21% 2	380
July	1st to 10th	Night	8% 4 18% 44% 25% 1	370
	11th to 20th	Night	10% 5% 26% 39% 18% 1	368
	21st to end	Night	5% 4 25% 41% 23% 3	493
August	1st to 10th	Night	6% 5% 22% 37% 26% 4	567
	11th to 20th	Night	7% 3 20% 41% 26% 2	564
	21st to end	Night	10% 4 26% 36% 21% 1	627
September	1st to 10th	Night	11% 3 28% 40% 18% 1	570
	11th to 20th	Night	15% 5% 19% 44% 16% 1	570
	21st to end	Night	12% 6% 34% 35% 13%	710
October	1st to 10th	Night	19% 5% 27% 34% 14%	760
	11th to 20th	Night	10% 6% 35% 34% 12% 2	760
	21st to end	Night	16% 9% 35% 31% 8% 1	1035
November	1st to 10th	Night	21% 9% 31% 30% 8% 1	975
	11th to 20th	Night	12% 9% 35% 32% 11% 2	1000
	21st to end	Night	13% 9% 38% 31% 8% 1	1000
December	1st to 10th	Night	13% 6% 37% 30% 12% 2	1000
	11th to 20th	Night	12% 10% 34% 32% 11% 1	1000
	21st to end	Night	10% 6% 32% 35% 14% 3	1100

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