Homer
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Homer clear sky chart from 2005-11-06 to 2026-04-17.

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	20% 14% 4 9% 5% 5% 5% 3 5% 6% 24%	134904
	Night	18% 16% 5% 10% 6% 5% 4 3 4 5% 25%	136128
Transparency	Day	59% 9% 14% 12% 5% 1	134563
	Night	59% 9% 11% 12% 7% 2	136051
Seeing	Day	24% 7% 16% 23% 22% 8%	20274
	Night	22% 8% 18% 25% 20% 7%	24830

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	15% 19% 5% 10% 7% 5% 4 3 4 5% 25%	2957
	11th to 20th	Day	17% 15% 5% 10% 6% 4 4 3 4 5% 26%	3383
	21st to end	Day	17% 15% 4 8% 5% 6% 6% 3 3 4 29%	4154
February	1st to 10th	Day	15% 17% 4 10% 6% 5% 4 3 3 5% 28%	1475
	11th to 20th	Day	22% 17% 4 12% 6% 4 4 3 4 4 21%	1683
	21st to end	Day	12% 13% 3 9% 5% 5% 4 4 5% 6% 33%	1557
March	1st to 10th	Day	11% 23% 5% 10% 4 3 3 2 3 5% 30%	4436
	11th to 20th	Day	9% 17% 6% 12% 7% 5% 5% 4 5% 6% 22%	4937
	21st to end	Day	15% 18% 5% 12% 6% 5% 5% 3 4 5% 21%	5954
April	1st to 10th	Day	12% 18% 5% 11% 5% 5% 5% 3 5% 4 27%	2571
	11th to 20th	Day	16% 16% 4 10% 6% 5% 5% 3 4 4 27%	2797
	21st to end	Day	17% 19% 4 10% 6% 5% 4 3 4 5% 23%	2800
May	1st to 10th	Day	20% 21% 5% 11% 7% 5% 4 3 4 4 15%	6971
	11th to 20th	Day	19% 15% 4 9% 5% 5% 4 3 4 6% 27%	7213
	21st to end	Day	23% 12% 4 9% 5% 5% 4 4 6% 7% 21%	7968
June	1st to 10th	Day	22% 13% 4 8% 5% 5% 4 3 4 7% 24%	3495
	11th to 20th	Day	20% 10% 3 7% 5% 4 4 4 5% 7% 31%	3600
	21st to end	Day	23% 12% 4 8% 5% 5% 5% 4 6% 7% 22%	3600
July	1st to 10th	Day	24% 12% 5% 10% 5% 4 4 4 5% 6% 22%	7727
	11th to 20th	Day	26% 11% 4 8% 5% 5% 5% 3 5% 7% 20%	7568
	21st to end	Day	23% 7% 3 7% 5% 5% 5% 3 5% 7% 29%	7899
August	1st to 10th	Day	30% 8% 3 7% 5% 4 4 3 5% 7% 23%	4956
	11th to 20th	Day	28% 8% 3 6% 3 4 5% 3 4 5% 29%	4557
	21st to end	Day	28% 10% 3 8% 4 4 5% 4 5% 6% 24%	4943
September	1st to 10th	Day	32% 11% 3 10% 6% 4 5% 4 5% 5% 15%	2450
	11th to 20th	Day	33% 11% 3 6% 4 4 4 3 5% 6% 20%	2400
	21st to end	Day	21% 12% 4 10% 6% 4 4 3 5% 6% 25%	2115
October	1st to 10th	Day	22% 12% 4 11% 5% 5% 7% 4 6% 6% 18%	3260
	11th to 20th	Day	16% 11% 4 8% 6% 4 5% 3 5% 6% 33%	2948
	21st to end	Day	19% 15% 3 8% 4 4 4 3 3 5% 32%	2831
November	1st to 10th	Day	20% 15% 5% 9% 5% 5% 5% 4 5% 5% 22%	1514
	11th to 20th	Day	15% 11% 4 8% 6% 4 4 2 5% 7% 34%	1281
	21st to end	Day	18% 15% 5% 10% 6% 5% 5% 5% 4 4 25%	1260
December	1st to 10th	Day	21% 19% 6% 11% 7% 6% 5% 4 4 4 14%	1810
	11th to 20th	Day	15% 21% 7% 12% 5% 5% 4 2 3 3 21%	1557
	21st to end	Day	10% 16% 5% 12% 10% 6% 4 3 4 4 26%	2277
January	1st to 10th	Night	15% 17% 5% 11% 7% 6% 4 3 4 3 25%	9998
	11th to 20th	Night	21% 18% 5% 10% 6% 4 3 2 3 3 26%	9549
	21st to end	Night	17% 15% 4 9% 6% 6% 5% 3 4 4 28%	10044
February	1st to 10th	Night	13% 16% 4 10% 6% 4 5% 3 5% 5% 28%	3145
	11th to 20th	Night	20% 20% 5% 11% 6% 4 4 3 4 5% 17%	2821
	21st to end	Night	13% 14% 3 9% 6% 5% 4 3 4 5% 34%	2249
March	1st to 10th	Night	11% 20% 6% 11% 5% 4 4 3 4 5% 29%	5638
	11th to 20th	Night	6% 16% 5% 14% 7% 7% 7% 5% 6% 6% 23%	5240
	21st to end	Night	13% 20% 5% 12% 7% 5% 5% 4 5% 5% 20%	5219
April	1st to 10th	Night	14% 19% 6% 8% 5% 4 4 3 4 6% 27%	2048
	11th to 20th	Night	13% 15% 4 9% 5% 5% 5% 4 5% 6% 30%	1686
	21st to end	Night	15% 18% 5% 9% 6% 5% 3 3 6% 5% 26%	1600
May	1st to 10th	Night	19% 19% 5% 13% 6% 4 5% 3 4 5% 16%	3008
	11th to 20th	Night	18% 17% 5% 9% 5% 4 3 3 4 5% 28%	2702
	21st to end	Night	18% 14% 5% 11% 5% 5% 5% 4 6% 6% 22%	2929
June	1st to 10th	Night	22% 11% 4 8% 6% 4 4 3 4 5% 27%	900
	11th to 20th	Night	16% 10% 2 8% 5% 5% 5% 4 5% 7% 33%	800
	21st to end	Night	23% 9% 3 7% 5% 7% 6% 4 5% 6% 25%	800
July	1st to 10th	Night	25% 12% 4 8% 5% 5% 6% 3 6% 6% 20%	2270
	11th to 20th	Night	24% 13% 5% 10% 5% 6% 5% 2 4 5% 21%	2412
	21st to end	Night	23% 7% 3 7% 4 5% 4 4 5% 8% 30%	2968
August	1st to 10th	Night	28% 8% 3 8% 6% 5% 6% 4 5% 4 23%	2201
	11th to 20th	Night	26% 7% 2 6% 4 4 4 3 4 6% 34%	2501
	21st to end	Night	25% 10% 3 7% 4 4 4 3 5% 5% 30%	2962
September	1st to 10th	Night	33% 12% 4 9% 4 4 3 2 4 5% 19%	1950
	11th to 20th	Night	31% 11% 4 8% 4 4 5% 3 4 5% 22%	2000
	21st to end	Night	25% 11% 4 9% 4 4 4 3 4 5% 27%	2282
October	1st to 10th	Night	22% 11% 4 10% 7% 6% 5% 4 5% 5% 21%	3920
	11th to 20th	Night	17% 11% 3 7% 5% 5% 5% 3 4 5% 35%	4197
	21st to end	Night	18% 15% 4 8% 5% 4 4 2 3 4 33%	4970
November	1st to 10th	Night	19% 15% 5% 10% 5% 4 4 2 4 5% 25%	3003
	11th to 20th	Night	14% 11% 4 8% 5% 5% 5% 3 6% 5% 34%	3338
	21st to end	Night	18% 17% 4 10% 5% 4 4 3 5% 4 27%	3360
December	1st to 10th	Night	24% 20% 6% 11% 6% 4 4 2 4 4 15%	5589
	11th to 20th	Night	15% 21% 7% 11% 6% 5% 4 3 5% 5% 18%	6880
	21st to end	Night	10% 17% 6% 12% 8% 5% 4 3 4 5% 25%	8949

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	57% 7% 9% 11% 13% 4	2958
	11th to 20th	Day	59% 7% 11% 11% 11% 1	3401
	21st to end	Day	60% 8% 9% 8% 13% 2	4155
February	1st to 10th	Day	56% 12% 10% 12% 9% 2	1475
	11th to 20th	Day	63% 10% 9% 11% 6% 1	1690
	21st to end	Day	48% 11% 11% 16% 12% 2	1557
March	1st to 10th	Day	57% 7% 6% 9% 16% 4	4436
	11th to 20th	Day	55% 10% 7% 17% 10% 1	4937
	21st to end	Day	59% 11% 11% 12% 6% 1	5954
April	1st to 10th	Day	58% 10% 12% 14% 5% 1	2571
	11th to 20th	Day	57% 9% 11% 15% 8%	2797
	21st to end	Day	59% 9% 12% 13% 5% 2	2800
May	1st to 10th	Day	67% 7% 11% 13% 2	6971
	11th to 20th	Day	57% 10% 13% 16% 5%	7216
	21st to end	Day	59% 10% 16% 13% 1	7969
June	1st to 10th	Day	58% 10% 17% 14% 2	3495
	11th to 20th	Day	50% 11% 22% 15% 2 1	3600
	21st to end	Day	59% 13% 20% 8%	3600
July	1st to 10th	Day	61% 11% 21% 6%	7643
	11th to 20th	Day	63% 10% 19% 8%	7475
	21st to end	Day	53% 9% 25% 12%	7678
August	1st to 10th	Day	59% 10% 20% 10% 1	4937
	11th to 20th	Day	56% 8% 20% 15% 2	4600
	21st to end	Day	60% 8% 16% 12% 4	4942
September	1st to 10th	Day	69% 11% 11% 6% 2	2450
	11th to 20th	Day	64% 8% 14% 12% 2	2400
	21st to end	Day	60% 10% 14% 14% 3	2115
October	1st to 10th	Day	64% 8% 14% 12% 3	3260
	11th to 20th	Day	52% 10% 12% 17% 8% 1	2948
	21st to end	Day	54% 7% 10% 21% 7% 1	2831
November	1st to 10th	Day	62% 9% 10% 11% 7% 1	1514
	11th to 20th	Day	51% 10% 10% 20% 8%	1281
	21st to end	Day	60% 9% 8% 13% 8% 2	1260
December	1st to 10th	Day	71% 9% 7% 7% 4 1	1810
	11th to 20th	Day	66% 9% 10% 9% 6% 1	1560
	21st to end	Day	56% 11% 11% 14% 5% 3	2277
January	1st to 10th	Night	60% 7% 9% 8% 11% 5%	9998
	11th to 20th	Night	63% 6% 7% 11% 12% 1	9594
	21st to end	Night	59% 8% 10% 8% 10% 4	10044
February	1st to 10th	Night	54% 11% 9% 14% 9% 3	3145
	11th to 20th	Night	67% 9% 8% 9% 6% 1	2825
	21st to end	Night	52% 8% 10% 15% 10% 4	2249
March	1st to 10th	Night	57% 8% 7% 12% 11% 5%	5638
	11th to 20th	Night	54% 10% 8% 14% 12% 1	5242
	21st to end	Night	61% 9% 10% 12% 7% 1	5219
April	1st to 10th	Night	57% 7% 11% 16% 7% 1	2048
	11th to 20th	Night	52% 10% 14% 17% 8%	1686
	21st to end	Night	57% 8% 12% 14% 7% 1	1600
May	1st to 10th	Night	68% 8% 9% 14% 2	3005
	11th to 20th	Night	57% 7% 10% 21% 6%	2703
	21st to end	Night	58% 12% 18% 11% 1	2929
June	1st to 10th	Night	56% 10% 20% 13% 1	900
	11th to 20th	Night	50% 8% 23% 16% 2 1	800
	21st to end	Night	55% 11% 26% 7%	800
July	1st to 10th	Night	62% 10% 22% 5%	2245
	11th to 20th	Night	64% 11% 19% 6%	2382
	21st to end	Night	52% 7% 29% 11%	2884
August	1st to 10th	Night	61% 10% 17% 12% 1	2195
	11th to 20th	Night	50% 8% 23% 18% 1	2524
	21st to end	Night	56% 9% 16% 16% 3	2962
September	1st to 10th	Night	67% 8% 15% 7% 2	1950
	11th to 20th	Night	65% 8% 14% 11% 2	2000
	21st to end	Night	59% 8% 14% 15% 4	2282
October	1st to 10th	Night	64% 8% 10% 15% 3	3920
	11th to 20th	Night	52% 9% 14% 14% 10% 1	4197
	21st to end	Night	57% 6% 9% 18% 9% 1	4970
November	1st to 10th	Night	61% 9% 10% 12% 8% 1	3003
	11th to 20th	Night	51% 10% 11% 19% 8% 1	3338
	21st to end	Night	59% 9% 10% 12% 9% 1	3360
December	1st to 10th	Night	71% 7% 9% 7% 5% 1	5589
	11th to 20th	Night	66% 10% 9% 9% 5% 1	6876
	21st to end	Night	57% 12% 11% 11% 5% 4	8949

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	16% 10% 25% 28% 15% 7%	320
	11th to 20th	Day	18% 10% 22% 27% 19% 4	320
	21st to end	Day	24% 10% 25% 26% 11% 5%	352
February	1st to 10th	Day	20% 7% 20% 29% 12% 12%	323
	11th to 20th	Day	24% 13% 27% 21% 13% 2	425
	21st to end	Day	17% 12% 30% 23% 13% 4	355
March	1st to 10th	Day	17% 12% 25% 22% 20% 4	430
	11th to 20th	Day	12% 7% 19% 32% 22% 9%	565
	21st to end	Day	15% 7% 19% 28% 23% 7%	704
April	1st to 10th	Day	21% 9% 21% 25% 18% 7%	640
	11th to 20th	Day	20% 9% 14% 23% 26% 9%	694
	21st to end	Day	22% 6% 16% 24% 25% 7%	700
May	1st to 10th	Day	25% 9% 16% 25% 18% 6%	703
	11th to 20th	Day	23% 7% 17% 23% 24% 5%	725
	21st to end	Day	24% 5% 14% 25% 25% 8%	803
June	1st to 10th	Day	22% 7% 13% 18% 25% 14%	930
	11th to 20th	Day	18% 4 10% 25% 29% 14%	930
	21st to end	Day	22% 5% 9% 21% 32% 11%	930
July	1st to 10th	Day	25% 5% 10% 20% 30% 11%	916
	11th to 20th	Day	26% 5% 11% 21% 28% 9%	851
	21st to end	Day	26% 4 11% 22% 25% 12%	794
August	1st to 10th	Day	30% 4 13% 25% 22% 6%	726
	11th to 20th	Day	28% 6% 17% 25% 19% 6%	715
	21st to end	Day	30% 6% 15% 22% 20% 6%	772
September	1st to 10th	Day	32% 7% 17% 21% 17% 7%	620
	11th to 20th	Day	34% 8% 11% 19% 21% 7%	620
	21st to end	Day	26% 8% 15% 22% 22% 8%	470
October	1st to 10th	Day	34% 9% 16% 20% 15% 6%	420
	11th to 20th	Day	27% 7% 17% 26% 19% 5%	420
	21st to end	Day	24% 10% 16% 25% 18% 6%	462
November	1st to 10th	Day	26% 8% 21% 23% 16% 6%	425
	11th to 20th	Day	18% 12% 23% 24% 19% 3	331
	21st to end	Day	24% 10% 19% 24% 19% 4	320
December	1st to 10th	Day	26% 7% 22% 26% 15% 4	231
	11th to 20th	Day	30% 8% 25% 25% 7% 5%	110
	21st to end	Day	24% 9% 19% 27% 14% 6%	222
January	1st to 10th	Night	16% 8% 22% 32% 19% 3	1060
	11th to 20th	Night	23% 12% 19% 29% 15% 3	977
	21st to end	Night	23% 9% 24% 26% 15% 3	1045
February	1st to 10th	Night	17% 8% 22% 29% 17% 6%	950
	11th to 20th	Night	23% 11% 27% 25% 11% 2	887
	21st to end	Night	19% 12% 26% 24% 15% 4	610
March	1st to 10th	Night	17% 12% 23% 27% 16% 5%	740
	11th to 20th	Night	11% 7% 19% 32% 22% 8%	740
	21st to end	Night	14% 7% 15% 30% 22% 11%	728
April	1st to 10th	Night	19% 10% 17% 24% 20% 10%	630
	11th to 20th	Night	18% 6% 14% 23% 27% 11%	611
	21st to end	Night	18% 7% 13% 24% 28% 11%	600
May	1st to 10th	Night	19% 8% 11% 23% 28% 11%	450
	11th to 20th	Night	24% 4 10% 23% 29% 10%	394
	21st to end	Night	22% 5% 8% 24% 32% 9%	433
June	1st to 10th	Night	22% 7% 8% 17% 30% 17%	300
	11th to 20th	Night	16% 6% 5% 20% 39% 15%	200
	21st to end	Night	22% 2 6% 18% 34% 19%	200
July	1st to 10th	Night	26% 5% 6% 17% 29% 17%	380
	11th to 20th	Night	25% 5% 5% 20% 29% 15%	388
	21st to end	Night	25% 6% 9% 16% 26% 18%	438
August	1st to 10th	Night	30% 3 9% 24% 25% 9%	398
	11th to 20th	Night	29% 4 13% 24% 22% 9%	551
	21st to end	Night	29% 5% 9% 23% 24% 10%	660
September	1st to 10th	Night	33% 7% 14% 20% 20% 6%	600
	11th to 20th	Night	33% 5% 12% 19% 21% 11%	600
	21st to end	Night	27% 7% 11% 23% 23% 10%	674
October	1st to 10th	Night	32% 8% 17% 23% 16% 4	710
	11th to 20th	Night	25% 6% 15% 25% 22% 8%	855
	21st to end	Night	25% 8% 19% 23% 18% 6%	1001
November	1st to 10th	Night	23% 12% 19% 24% 17% 4	930
	11th to 20th	Night	19% 10% 25% 28% 16% 2	950
	21st to end	Night	22% 10% 22% 28% 16% 3	950
December	1st to 10th	Night	26% 10% 24% 25% 12% 3	964
	11th to 20th	Night	21% 11% 24% 28% 13% 3	1060
	21st to end	Night	22% 13% 22% 24% 15% 3	1166

Page generated at 2026-04-13 22:44:26. Version ac07

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