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 2024-01-16.

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	22% 12% 4 8% 6% 3 5% 4 5% 6% 26%	74480
	Night	19% 14% 4 8% 6% 3 4 4 4 5% 27%	75352
Transparency	Day	58% 10% 14% 12% 5% 1	74124
	Night	58% 10% 12% 12% 7% 1	75228
Seeing	Day	24% 7% 16% 23% 22% 8%	17263
	Night	22% 8% 18% 25% 20% 7%	21834

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% 13% 5% 8% 8% 3 4 4 5% 6% 29%	949
	11th to 20th	Day	18% 15% 7% 9% 5% 3 5% 4 4 6% 22%	1060
	21st to end	Day	19% 16% 4 8% 5% 3 5% 4 4 6% 24%	1278
February	1st to 10th	Day	16% 17% 5% 9% 6% 4 4 3 3 4 28%	1264
	11th to 20th	Day	23% 14% 4 11% 7% 3 5% 3 3 5% 20%	1436
	21st to end	Day	13% 13% 4 8% 7% 4 3 5% 5% 6% 32%	1332
March	1st to 10th	Day	15% 16% 4 8% 4 3 3 3 3 6% 35%	1745
	11th to 20th	Day	10% 13% 5% 8% 6% 3 5% 4 4 6% 37%	1915
	21st to end	Day	12% 17% 5% 8% 7% 3 4 5% 5% 5% 28%	2316
April	1st to 10th	Day	14% 16% 5% 10% 6% 3 6% 4 5% 4 27%	2203
	11th to 20th	Day	15% 14% 5% 8% 7% 5% 6% 4 4 4 28%	2439
	21st to end	Day	18% 15% 5% 9% 8% 4 4 4 5% 5% 24%	2520
May	1st to 10th	Day	20% 16% 5% 9% 6% 4 5% 4 5% 5% 21%	2751
	11th to 20th	Day	19% 12% 5% 7% 5% 3 5% 3 5% 5% 29%	2833
	21st to end	Day	23% 10% 4 6% 6% 3 5% 5% 6% 6% 27%	3122
June	1st to 10th	Day	22% 10% 5% 7% 5% 4 5% 5% 4 7% 26%	3145
	11th to 20th	Day	22% 10% 4 6% 5% 3 4 5% 5% 7% 29%	3240
	21st to end	Day	24% 10% 4 6% 5% 3 5% 5% 6% 7% 23%	3240
July	1st to 10th	Day	24% 10% 4 8% 6% 3 5% 5% 5% 7% 23%	3067
	11th to 20th	Day	23% 8% 4 6% 5% 3 5% 5% 5% 7% 29%	3006
	21st to end	Day	30% 8% 3 6% 5% 2 4 3 5% 7% 26%	3137
August	1st to 10th	Day	30% 7% 3 6% 6% 3 4 4 5% 6% 25%	2727
	11th to 20th	Day	31% 9% 4 6% 5% 3 4 4 4 5% 24%	2516
	21st to end	Day	28% 8% 3 7% 6% 3 5% 5% 4 6% 25%	2722
September	1st to 10th	Day	31% 10% 4 8% 7% 3 5% 5% 5% 5% 16%	2206
	11th to 20th	Day	34% 10% 4 5% 5% 3 4 4 5% 6% 20%	2160
	21st to end	Day	22% 11% 4 8% 7% 3 4 5% 5% 6% 26%	1905
October	1st to 10th	Day	32% 13% 4 6% 5% 2 4 3 4 5% 23%	1800
	11th to 20th	Day	23% 14% 6% 9% 8% 3 5% 4 4 5% 20%	1643
	21st to end	Day	19% 13% 3 8% 7% 4 5% 5% 4 5% 28%	1584
November	1st to 10th	Day	21% 13% 6% 8% 6% 4 5% 5% 5% 5% 22%	1368
	11th to 20th	Day	16% 10% 4 7% 6% 3 4 3 5% 7% 35%	1159
	21st to end	Day	19% 15% 5% 10% 6% 4 5% 5% 3 4 23%	1140
December	1st to 10th	Day	24% 16% 5% 8% 7% 4 4 4 3 3 20%	1032
	11th to 20th	Day	16% 17% 6% 10% 6% 4 4 3 4 4 26%	967
	21st to end	Day	13% 16% 5% 9% 11% 5% 5% 4 4 4 25%	1553
January	1st to 10th	Night	13% 13% 4 8% 8% 4 5% 4 5% 5% 30%	3217
	11th to 20th	Night	20% 18% 5% 10% 7% 3 4 4 4 4 19%	3025
	21st to end	Night	20% 17% 5% 8% 7% 4 4 4 4 5% 22%	3076
February	1st to 10th	Night	14% 15% 5% 9% 7% 3 5% 4 4 4 29%	2696
	11th to 20th	Night	21% 19% 6% 10% 7% 3 4 5% 4 5% 16%	2408
	21st to end	Night	14% 15% 4 8% 7% 4 4 4 4 5% 33%	1924
March	1st to 10th	Night	15% 18% 4 7% 5% 2 3 4 3 5% 36%	2215
	11th to 20th	Night	8% 12% 4 8% 8% 5% 6% 5% 5% 5% 34%	2042
	21st to end	Night	12% 16% 5% 8% 7% 3 5% 4 5% 5% 30%	2040
April	1st to 10th	Night	14% 18% 7% 7% 5% 3 4 3 4 6% 28%	1756
	11th to 20th	Night	14% 12% 4 7% 6% 3 6% 5% 5% 6% 31%	1471
	21st to end	Night	15% 15% 5% 8% 6% 3 5% 3 6% 6% 27%	1440
May	1st to 10th	Night	21% 13% 4 8% 7% 3 5% 5% 4 6% 25%	1208
	11th to 20th	Night	19% 14% 4 6% 5% 3 4 3 4 6% 32%	1062
	21st to end	Night	21% 10% 4 7% 3 3 4 5% 6% 6% 31%	1151
June	1st to 10th	Night	21% 9% 4 7% 8% 4 4 5% 4 5% 29%	810
	11th to 20th	Night	18% 10% 3 8% 6% 3 5% 5% 5% 7% 31%	720
	21st to end	Night	25% 7% 3 5% 5% 6% 6% 6% 5% 6% 25%	720
July	1st to 10th	Night	24% 13% 3 6% 6% 4 5% 4 6% 7% 23%	890
	11th to 20th	Night	24% 5% 3 5% 5% 4 5% 4 5% 9% 31%	954
	21st to end	Night	28% 7% 3 7% 5% 2 3 4 4 8% 29%	1182
August	1st to 10th	Night	30% 9% 4 6% 6% 4 4 4 4 5% 24%	1209
	11th to 20th	Night	29% 9% 3 7% 6% 4 4 4 4 6% 26%	1384
	21st to end	Night	27% 9% 2 6% 5% 3 3 3 5% 6% 29%	1633
September	1st to 10th	Night	32% 11% 4 8% 5% 3 3 3 4 6% 21%	1754
	11th to 20th	Night	31% 10% 4 7% 4 3 5% 4 4 5% 23%	1800
	21st to end	Night	26% 10% 4 8% 5% 2 3 4 4 5% 28%	2052
October	1st to 10th	Night	31% 12% 5% 6% 5% 2 4 4 4 4 23%	2160
	11th to 20th	Night	22% 14% 4 7% 8% 5% 5% 4 5% 5% 22%	2316
	21st to end	Night	22% 13% 5% 7% 7% 3 5% 4 3 5% 27%	2772
November	1st to 10th	Night	20% 14% 5% 8% 6% 3 4 3 4 5% 26%	2709
	11th to 20th	Night	15% 10% 4 7% 6% 3 5% 4 6% 5% 34%	3020
	21st to end	Night	19% 16% 5% 9% 5% 3 5% 3 5% 4 26%	3040
December	1st to 10th	Night	25% 15% 5% 8% 6% 3 4 4 4 4 22%	3141
	11th to 20th	Night	15% 16% 6% 9% 7% 4 5% 4 5% 6% 23%	4240
	21st to end	Night	13% 16% 5% 9% 9% 3 4 4 4 5% 28%	6115

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% 8% 9% 13% 10% 2	949
	11th to 20th	Day	62% 8% 12% 10% 7% 2	1060
	21st to end	Day	60% 11% 11% 6% 8% 3	1278
February	1st to 10th	Day	58% 11% 9% 11% 10% 2	1264
	11th to 20th	Day	64% 10% 9% 11% 5% 1	1443
	21st to end	Day	49% 12% 12% 16% 11% 1	1332
March	1st to 10th	Day	52% 8% 9% 13% 12% 5%	1745
	11th to 20th	Day	48% 7% 9% 17% 17% 2	1915
	21st to end	Day	57% 10% 11% 10% 9% 2	2316
April	1st to 10th	Day	59% 10% 12% 13% 5% 1	2203
	11th to 20th	Day	56% 9% 11% 15% 9%	2439
	21st to end	Day	57% 10% 13% 13% 6% 2	2520
May	1st to 10th	Day	63% 8% 14% 12% 3	2751
	11th to 20th	Day	53% 9% 13% 18% 7%	2836
	21st to end	Day	54% 10% 15% 18% 3	3123
June	1st to 10th	Day	56% 10% 18% 14% 2	3145
	11th to 20th	Day	53% 11% 20% 13% 2 1	3240
	21st to end	Day	58% 14% 20% 8%	3240
July	1st to 10th	Day	58% 14% 19% 9%	2983
	11th to 20th	Day	55% 10% 22% 12% 1	2913
	21st to end	Day	57% 13% 20% 10% 1	2963
August	1st to 10th	Day	58% 13% 20% 9% 1	2708
	11th to 20th	Day	62% 9% 16% 11% 2	2516
	21st to end	Day	60% 10% 14% 11% 4	2722
September	1st to 10th	Day	68% 12% 12% 6% 2	2206
	11th to 20th	Day	64% 8% 14% 12% 2	2160
	21st to end	Day	59% 10% 14% 14% 3	1905
October	1st to 10th	Day	63% 8% 12% 13% 4	1800
	11th to 20th	Day	64% 12% 9% 12% 3	1643
	21st to end	Day	56% 10% 11% 13% 9% 1	1584
November	1st to 10th	Day	61% 9% 10% 10% 7% 1	1368
	11th to 20th	Day	51% 11% 11% 19% 8% 1	1159
	21st to end	Day	62% 9% 8% 11% 7% 2	1140
December	1st to 10th	Day	66% 12% 7% 8% 6% 1	1032
	11th to 20th	Day	60% 10% 9% 13% 8%	970
	21st to end	Day	54% 13% 12% 10% 7% 4	1553
January	1st to 10th	Night	56% 10% 11% 10% 11% 2	3217
	11th to 20th	Night	67% 10% 8% 7% 6% 2	3025
	21st to end	Night	63% 8% 10% 9% 8% 2	3076
February	1st to 10th	Night	56% 10% 8% 12% 10% 4	2696
	11th to 20th	Night	69% 9% 8% 9% 5% 1	2412
	21st to end	Night	54% 8% 11% 15% 10% 2	1924
March	1st to 10th	Night	53% 6% 8% 15% 13% 5%	2215
	11th to 20th	Night	49% 7% 7% 18% 16% 3	2044
	21st to end	Night	54% 9% 13% 12% 9% 2	2040
April	1st to 10th	Night	57% 7% 12% 16% 7% 1	1756
	11th to 20th	Night	50% 10% 14% 18% 8%	1471
	21st to end	Night	56% 9% 12% 14% 8% 1	1440
May	1st to 10th	Night	59% 9% 12% 17% 3	1208
	11th to 20th	Night	53% 6% 11% 19% 10%	1063
	21st to end	Night	52% 10% 16% 20% 3	1151
June	1st to 10th	Night	53% 10% 21% 14% 1	810
	11th to 20th	Night	53% 8% 21% 15% 2 1	720
	21st to end	Night	55% 12% 26% 8%	720
July	1st to 10th	Night	57% 13% 20% 10%	865
	11th to 20th	Night	50% 12% 25% 12% 1	924
	21st to end	Night	54% 9% 26% 10% 1	1116
August	1st to 10th	Night	59% 11% 18% 11% 1	1203
	11th to 20th	Night	58% 10% 17% 14% 1	1384
	21st to end	Night	55% 10% 18% 13% 4	1633
September	1st to 10th	Night	65% 8% 16% 8% 3	1754
	11th to 20th	Night	64% 9% 14% 11% 2	1800
	21st to end	Night	59% 9% 13% 15% 4	2052
October	1st to 10th	Night	63% 9% 11% 12% 5%	2160
	11th to 20th	Night	64% 10% 12% 10% 4	2316
	21st to end	Night	59% 9% 12% 11% 8% 1	2772
November	1st to 10th	Night	60% 9% 11% 11% 8% 1	2709
	11th to 20th	Night	52% 10% 12% 19% 8%	3020
	21st to end	Night	60% 9% 10% 10% 9% 1	3040
December	1st to 10th	Night	64% 10% 11% 8% 7% 1	3141
	11th to 20th	Night	60% 11% 9% 13% 6%	4236
	21st to end	Night	53% 14% 12% 9% 7% 5%	6115

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	15% 11% 24% 29% 15% 8%	280
	11th to 20th	Day	17% 10% 21% 29% 18% 5%	271
	21st to end	Day	22% 8% 26% 29% 10% 5%	286
February	1st to 10th	Day	21% 7% 21% 29% 11% 10%	262
	11th to 20th	Day	24% 10% 29% 21% 14% 2	335
	21st to end	Day	19% 13% 30% 23% 13% 4	280
March	1st to 10th	Day	17% 10% 27% 19% 22% 5%	340
	11th to 20th	Day	12% 8% 21% 30% 20% 9%	455
	21st to end	Day	18% 7% 20% 30% 20% 5%	572
April	1st to 10th	Day	21% 9% 22% 24% 18% 5%	520
	11th to 20th	Day	19% 8% 12% 22% 29% 10%	570
	21st to end	Day	22% 5% 17% 24% 26% 6%	600
May	1st to 10th	Day	26% 9% 16% 25% 18% 6%	603
	11th to 20th	Day	23% 6% 18% 24% 25% 6%	625
	21st to end	Day	25% 3 13% 25% 25% 8%	691
June	1st to 10th	Day	21% 5% 12% 19% 27% 16%	810
	11th to 20th	Day	20% 4 9% 24% 29% 14%	810
	21st to end	Day	23% 4 9% 20% 33% 11%	810
July	1st to 10th	Day	24% 4 9% 18% 32% 12%	796
	11th to 20th	Day	25% 5% 10% 21% 30% 9%	738
	21st to end	Day	27% 3 9% 20% 26% 13%	684
August	1st to 10th	Day	30% 4 13% 25% 23% 6%	626
	11th to 20th	Day	28% 5% 17% 25% 20% 5%	615
	21st to end	Day	29% 5% 15% 23% 22% 6%	668
September	1st to 10th	Day	30% 7% 16% 21% 19% 7%	540
	11th to 20th	Day	34% 7% 11% 19% 21% 8%	540
	21st to end	Day	26% 7% 16% 21% 22% 8%	406
October	1st to 10th	Day	34% 8% 16% 21% 16% 5%	360
	11th to 20th	Day	28% 7% 17% 26% 18% 5%	360
	21st to end	Day	24% 9% 18% 25% 18% 6%	396
November	1st to 10th	Day	25% 9% 23% 21% 15% 7%	365
	11th to 20th	Day	20% 13% 24% 23% 18% 3	289
	21st to end	Day	25% 12% 20% 24% 16% 4	280
December	1st to 10th	Day	27% 6% 23% 26% 14% 5%	200
	11th to 20th	Day	30% 8% 26% 24% 7% 6%	90
	21st to end	Day	26% 10% 19% 26% 15% 5%	190
January	1st to 10th	Night	15% 9% 22% 32% 19% 3	940
	11th to 20th	Night	21% 12% 19% 29% 16% 4	853
	21st to end	Night	22% 7% 25% 27% 16% 3	880
February	1st to 10th	Night	19% 8% 23% 29% 17% 6%	800
	11th to 20th	Night	25% 9% 27% 25% 12% 2	744
	21st to end	Night	20% 11% 25% 24% 16% 4	510
March	1st to 10th	Night	19% 11% 24% 25% 16% 5%	620
	11th to 20th	Night	12% 7% 20% 32% 21% 7%	620
	21st to end	Night	15% 8% 16% 30% 21% 11%	620
April	1st to 10th	Night	19% 10% 18% 24% 20% 10%	540
	11th to 20th	Night	18% 5% 13% 21% 30% 13%	533
	21st to end	Night	17% 6% 13% 25% 28% 10%	540
May	1st to 10th	Night	19% 7% 11% 23% 29% 12%	406
	11th to 20th	Night	24% 4 10% 22% 30% 10%	354
	21st to end	Night	23% 4 7% 24% 33% 9%	389
June	1st to 10th	Night	20% 6% 7% 18% 31% 19%	270
	11th to 20th	Night	18% 6% 5% 21% 37% 14%	180
	21st to end	Night	23% 2 7% 17% 33% 19%	180
July	1st to 10th	Night	26% 5% 6% 15% 30% 19%	340
	11th to 20th	Night	25% 4 5% 19% 31% 16%	348
	21st to end	Night	26% 6% 9% 16% 25% 19%	394
August	1st to 10th	Night	29% 3 9% 24% 25% 9%	358
	11th to 20th	Night	29% 4 13% 24% 22% 9%	495
	21st to end	Night	28% 5% 9% 22% 26% 10%	594
September	1st to 10th	Night	31% 7% 14% 21% 21% 7%	540
	11th to 20th	Night	32% 4 12% 18% 22% 12%	540
	21st to end	Night	28% 7% 12% 23% 22% 10%	600
October	1st to 10th	Night	33% 7% 17% 24% 15% 3	630
	11th to 20th	Night	25% 5% 15% 24% 23% 9%	760
	21st to end	Night	25% 8% 19% 24% 19% 6%	891
November	1st to 10th	Night	23% 11% 20% 24% 17% 4	830
	11th to 20th	Night	19% 11% 25% 28% 15% 2	850
	21st to end	Night	23% 10% 22% 27% 15% 3	850
December	1st to 10th	Night	25% 9% 24% 26% 13% 3	861
	11th to 20th	Night	21% 9% 24% 29% 13% 4	940
	21st to end	Night	23% 12% 23% 24% 16% 3	1034

Page generated at 2024-01-13 15:28:28. Version ac07

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