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 2024-12-24.

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% 13% 4 9% 5% 4 4 3 5% 6% 25%	106586
	Night	19% 15% 4 9% 5% 5% 4 3 4 5% 28%	102156
Transparency	Day	58% 10% 14% 12% 4 1	106291
	Night	57% 10% 12% 13% 7% 2	102100
Seeing	Day	24% 7% 16% 23% 22% 8%	18583
	Night	22% 8% 18% 25% 20% 7%	23013

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	18% 18% 5% 11% 7% 4 4 3 4 4 22%	1589
	11th to 20th	Day	17% 13% 5% 7% 4 3 3 2 4 6% 36%	1795
	21st to end	Day	13% 12% 3 6% 5% 6% 6% 3 3 4 38%	2245
February	1st to 10th	Day	16% 18% 5% 10% 6% 5% 3 3 3 5% 27%	1334
	11th to 20th	Day	23% 16% 4 12% 6% 4 4 3 4 5% 20%	1518
	21st to end	Day	12% 14% 3 9% 5% 4 4 4 5% 6% 32%	1413
March	1st to 10th	Day	11% 20% 5% 9% 3 3 3 2 3 5% 36%	3021
	11th to 20th	Day	10% 15% 5% 11% 6% 5% 5% 5% 5% 6% 27%	3373
	21st to end	Day	20% 22% 5% 10% 5% 4 4 3 3 4 19%	4063
April	1st to 10th	Day	13% 18% 4 11% 5% 5% 5% 3 5% 4 27%	2326
	11th to 20th	Day	15% 15% 5% 9% 6% 6% 5% 3 4 4 28%	2577
	21st to end	Day	17% 18% 4 10% 6% 5% 4 4 4 5% 23%	2660
May	1st to 10th	Day	24% 22% 5% 11% 6% 5% 4 3 4 3 13%	4861
	11th to 20th	Day	18% 14% 4 8% 4 4 4 3 5% 6% 30%	5023
	21st to end	Day	27% 12% 4 9% 5% 4 4 3 5% 6% 21%	5545
June	1st to 10th	Day	22% 12% 4 8% 5% 5% 4 3 4 7% 24%	3320
	11th to 20th	Day	21% 10% 3 7% 5% 4 4 3 5% 7% 29%	3420
	21st to end	Day	23% 11% 4 7% 5% 5% 5% 4 7% 7% 22%	3420
July	1st to 10th	Day	26% 11% 4 9% 5% 5% 5% 4 6% 6% 20%	5397
	11th to 20th	Day	28% 10% 4 8% 5% 5% 5% 4 5% 7% 21%	5280
	21st to end	Day	25% 8% 3 7% 4 4 5% 3 6% 7% 29%	5499
August	1st to 10th	Day	30% 8% 3 7% 5% 4 4 3 5% 7% 24%	4804
	11th to 20th	Day	29% 9% 3 6% 4 4 5% 3 4 5% 29%	4415
	21st to end	Day	28% 10% 3 8% 4 4 5% 4 5% 6% 24%	4792
September	1st to 10th	Day	31% 11% 3 10% 6% 4 5% 4 5% 5% 15%	2328
	11th to 20th	Day	33% 10% 3 6% 4 4 4 3 5% 6% 21%	2280
	21st to end	Day	22% 12% 3 9% 6% 4 4 3 5% 6% 26%	2010
October	1st to 10th	Day	22% 12% 4 11% 5% 5% 7% 5% 6% 6% 18%	3160
	11th to 20th	Day	16% 10% 4 8% 6% 4 5% 4 5% 6% 33%	2857
	21st to end	Day	19% 15% 3 8% 4 4 4 3 3 5% 33%	2743
November	1st to 10th	Day	21% 15% 5% 9% 5% 5% 5% 4 5% 5% 22%	1441
	11th to 20th	Day	15% 11% 4 8% 6% 4 4 2 5% 7% 35%	1220
	21st to end	Day	18% 15% 5% 10% 6% 6% 5% 4 4 4 25%	1200
December	1st to 10th	Day	23% 18% 4 9% 7% 6% 4 4 4 3 19%	1085
	11th to 20th	Day	15% 18% 6% 11% 5% 5% 4 2 4 4 25%	1007
	21st to end	Day	13% 17% 5% 10% 10% 6% 4 3 4 4 25%	1565
January	1st to 10th	Night	18% 19% 5% 10% 7% 5% 4 4 4 4 20%	5377
	11th to 20th	Night	20% 17% 4 8% 4 3 2 2 3 3 34%	5113
	21st to end	Night	13% 13% 3 7% 5% 5% 4 3 4 5% 37%	5420
February	1st to 10th	Night	14% 17% 5% 10% 6% 4 5% 3 4 4 29%	2846
	11th to 20th	Night	21% 20% 5% 11% 6% 4 4 3 4 5% 17%	2546
	21st to end	Night	14% 15% 3 9% 6% 4 4 3 4 5% 33%	2041
March	1st to 10th	Night	12% 16% 4 9% 4 4 3 4 4 5% 36%	3833
	11th to 20th	Night	8% 15% 5% 12% 6% 6% 6% 4 5% 5% 27%	3584
	21st to end	Night	18% 23% 5% 9% 5% 4 4 3 4 4 19%	3568
April	1st to 10th	Night	14% 19% 5% 8% 5% 5% 4 3 4 6% 28%	1853
	11th to 20th	Night	14% 14% 4 9% 5% 5% 5% 4 5% 6% 30%	1553
	21st to end	Night	14% 17% 5% 9% 5% 5% 3 3 6% 6% 27%	1520
May	1st to 10th	Night	22% 20% 5% 12% 6% 4 4 3 3 5% 17%	2108
	11th to 20th	Night	15% 18% 4 7% 5% 4 3 3 5% 5% 32%	1882
	21st to end	Night	20% 12% 4 9% 5% 6% 5% 4 6% 5% 24%	2040
June	1st to 10th	Night	21% 11% 4 8% 6% 4 4 3 4 5% 28%	855
	11th to 20th	Night	17% 10% 2 9% 5% 5% 5% 4 5% 7% 31%	760
	21st to end	Night	23% 8% 3 7% 4 7% 6% 4 5% 6% 26%	760
July	1st to 10th	Night	28% 14% 4 8% 6% 5% 5% 2 5% 5% 18%	1580
	11th to 20th	Night	28% 11% 4 8% 4 5% 4 2 4 5% 25%	1683
	21st to end	Night	26% 6% 3 6% 4 4 3 3 5% 8% 31%	2066
August	1st to 10th	Night	28% 8% 3 8% 6% 5% 6% 4 4 5% 23%	2133
	11th to 20th	Night	26% 7% 2 6% 4 5% 4 3 4 6% 34%	2423
	21st to end	Night	24% 10% 3 7% 4 4 4 3 5% 5% 30%	2871
September	1st to 10th	Night	32% 12% 4 9% 4 4 3 3 4 6% 20%	1852
	11th to 20th	Night	31% 10% 4 8% 3 4 4 3 4 5% 23%	1900
	21st to end	Night	26% 11% 4 9% 4 3 4 3 4 5% 27%	2167
October	1st to 10th	Night	21% 11% 4 10% 7% 6% 5% 4 5% 5% 21%	3800
	11th to 20th	Night	16% 11% 3 7% 5% 5% 5% 3 4 5% 35%	4068
	21st to end	Night	18% 15% 4 8% 5% 4 4 2 3 4 33%	4816
November	1st to 10th	Night	20% 15% 5% 10% 5% 4 4 2 4 5% 25%	2856
	11th to 20th	Night	15% 10% 3 8% 5% 5% 5% 3 6% 5% 35%	3179
	21st to end	Night	17% 16% 4 10% 5% 4 4 3 5% 4 27%	3200
December	1st to 10th	Night	25% 17% 5% 9% 5% 4 4 3 4 4 21%	3308
	11th to 20th	Night	14% 19% 5% 10% 6% 5% 4 4 5% 5% 22%	4420
	21st to end	Night	13% 17% 5% 10% 8% 4 3 3 4 5% 28%	6175

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% 10% 11% 11% 8% 1	1589
	11th to 20th	Day	48% 9% 11% 15% 15% 2	1813
	21st to end	Day	50% 13% 11% 8% 14% 4	2245
February	1st to 10th	Day	57% 11% 9% 11% 9% 2	1334
	11th to 20th	Day	64% 10% 9% 11% 6% 1	1525
	21st to end	Day	48% 12% 12% 16% 12% 1	1413
March	1st to 10th	Day	51% 9% 8% 12% 14% 5%	3021
	11th to 20th	Day	50% 12% 9% 17% 11% 1	3373
	21st to end	Day	60% 13% 12% 8% 6% 1	4063
April	1st to 10th	Day	58% 10% 12% 13% 5% 1	2326
	11th to 20th	Day	56% 9% 11% 15% 8%	2577
	21st to end	Day	57% 10% 13% 13% 5% 2	2660
May	1st to 10th	Day	72% 8% 10% 8% 2	4861
	11th to 20th	Day	50% 12% 13% 20% 5%	5026
	21st to end	Day	60% 11% 14% 13% 2	5546
June	1st to 10th	Day	58% 10% 17% 13% 1	3320
	11th to 20th	Day	52% 11% 21% 14% 2 1	3420
	21st to end	Day	58% 13% 21% 8%	3420
July	1st to 10th	Day	62% 13% 20% 6%	5313
	11th to 20th	Day	63% 9% 18% 10%	5187
	21st to end	Day	54% 10% 22% 14%	5326
August	1st to 10th	Day	59% 10% 20% 11% 1	4785
	11th to 20th	Day	56% 8% 20% 15% 1	4458
	21st to end	Day	60% 8% 16% 12% 4	4791
September	1st to 10th	Day	68% 12% 12% 6% 2	2328
	11th to 20th	Day	64% 8% 14% 13% 2	2280
	21st to end	Day	59% 10% 14% 14% 3	2010
October	1st to 10th	Day	64% 8% 14% 12% 2	3160
	11th to 20th	Day	52% 10% 12% 17% 9% 1	2857
	21st to end	Day	53% 7% 10% 22% 7% 1	2743
November	1st to 10th	Day	62% 9% 11% 10% 7% 1	1441
	11th to 20th	Day	51% 11% 11% 20% 8%	1220
	21st to end	Day	60% 9% 8% 12% 9% 2	1200
December	1st to 10th	Day	67% 11% 7% 8% 6% 1	1085
	11th to 20th	Day	61% 10% 9% 13% 7%	1010
	21st to end	Day	54% 13% 12% 10% 7% 4	1565
January	1st to 10th	Night	60% 10% 12% 10% 7% 1	5377
	11th to 20th	Night	55% 8% 8% 13% 14% 2	5158
	21st to end	Night	48% 12% 13% 9% 12% 6%	5420
February	1st to 10th	Night	55% 11% 9% 12% 9% 4	2846
	11th to 20th	Night	67% 9% 9% 9% 5% 1	2550
	21st to end	Night	53% 8% 10% 15% 11% 2	2041
March	1st to 10th	Night	50% 11% 8% 14% 10% 7%	3833
	11th to 20th	Night	51% 11% 9% 16% 12% 2	3586
	21st to end	Night	61% 11% 12% 8% 6% 1	3568
April	1st to 10th	Night	56% 8% 11% 16% 8% 1	1853
	11th to 20th	Night	51% 10% 14% 17% 8%	1553
	21st to end	Night	55% 9% 13% 15% 8% 1	1520
May	1st to 10th	Night	69% 8% 9% 12% 3	2108
	11th to 20th	Night	51% 8% 11% 24% 6%	1883
	21st to end	Night	56% 14% 15% 13% 2	2040
June	1st to 10th	Night	54% 11% 21% 13% 1	855
	11th to 20th	Night	52% 8% 22% 15% 2 1	760
	21st to end	Night	54% 11% 26% 8%	760
July	1st to 10th	Night	65% 11% 18% 6%	1555
	11th to 20th	Night	61% 10% 20% 8% 1	1653
	21st to end	Night	52% 7% 29% 12% 1	2000
August	1st to 10th	Night	61% 9% 17% 12% 1	2127
	11th to 20th	Night	50% 9% 23% 18% 1	2446
	21st to end	Night	55% 10% 16% 16% 3	2871
September	1st to 10th	Night	66% 8% 16% 8% 3	1852
	11th to 20th	Night	64% 8% 14% 12% 2	1900
	21st to end	Night	59% 9% 13% 15% 4	2167
October	1st to 10th	Night	64% 8% 10% 15% 3	3800
	11th to 20th	Night	52% 9% 14% 14% 11% 1	4068
	21st to end	Night	56% 6% 9% 19% 9% 1	4816
November	1st to 10th	Night	61% 9% 10% 11% 7% 1	2856
	11th to 20th	Night	51% 10% 11% 20% 8% 1	3179
	21st to end	Night	58% 9% 10% 12% 10% 1	3200
December	1st to 10th	Night	65% 9% 10% 8% 7% 1	3308
	11th to 20th	Night	61% 11% 9% 13% 6%	4416
	21st to end	Night	54% 13% 12% 9% 7% 5%	6175

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	16% 11% 21% 28% 19% 5%	280
	21st to end	Day	21% 10% 26% 28% 11% 5%	308
February	1st to 10th	Day	21% 7% 21% 30% 11% 9%	282
	11th to 20th	Day	24% 12% 29% 20% 13% 2	365
	21st to end	Day	18% 13% 31% 22% 12% 4	307
March	1st to 10th	Day	17% 12% 26% 19% 21% 5%	370
	11th to 20th	Day	13% 8% 21% 30% 21% 9%	492
	21st to end	Day	17% 8% 21% 28% 21% 5%	616
April	1st to 10th	Day	20% 9% 22% 26% 19% 5%	560
	11th to 20th	Day	18% 9% 14% 22% 28% 10%	618
	21st to end	Day	20% 6% 16% 24% 26% 8%	650
May	1st to 10th	Day	26% 9% 17% 25% 18% 6%	653
	11th to 20th	Day	22% 7% 17% 23% 25% 5%	675
	21st to end	Day	24% 4 14% 25% 24% 8%	747
June	1st to 10th	Day	21% 7% 12% 19% 26% 15%	870
	11th to 20th	Day	19% 4 10% 25% 29% 14%	870
	21st to end	Day	22% 4 9% 21% 33% 11%	870
July	1st to 10th	Day	25% 4 9% 20% 31% 11%	856
	11th to 20th	Day	27% 5% 10% 21% 29% 9%	794
	21st to end	Day	27% 4 10% 21% 25% 12%	739
August	1st to 10th	Day	30% 4 13% 25% 23% 6%	676
	11th to 20th	Day	29% 6% 17% 24% 19% 5%	665
	21st to end	Day	30% 6% 15% 23% 21% 6%	720
September	1st to 10th	Day	31% 7% 17% 21% 18% 7%	580
	11th to 20th	Day	34% 8% 11% 19% 20% 7%	580
	21st to end	Day	27% 7% 15% 21% 22% 8%	438
October	1st to 10th	Day	33% 8% 16% 21% 16% 7%	390
	11th to 20th	Day	27% 7% 17% 25% 19% 5%	390
	21st to end	Day	24% 9% 18% 26% 17% 6%	429
November	1st to 10th	Day	26% 9% 22% 22% 15% 6%	395
	11th to 20th	Day	19% 13% 23% 25% 17% 3	310
	21st to end	Day	23% 11% 19% 24% 18% 4	300
December	1st to 10th	Day	26% 7% 22% 26% 14% 5%	215
	11th to 20th	Day	32% 8% 25% 24% 6% 5%	100
	21st to end	Day	27% 10% 19% 25% 15% 5%	193
January	1st to 10th	Night	15% 9% 22% 32% 19% 3	940
	11th to 20th	Night	21% 12% 19% 29% 15% 3	873
	21st to end	Night	21% 8% 25% 27% 16% 2	935
February	1st to 10th	Night	18% 8% 23% 30% 16% 5%	850
	11th to 20th	Night	24% 10% 28% 25% 11% 2	792
	21st to end	Night	20% 11% 27% 23% 15% 3	546
March	1st to 10th	Night	18% 12% 23% 25% 16% 5%	660
	11th to 20th	Night	12% 8% 20% 31% 21% 7%	660
	21st to end	Night	15% 8% 16% 29% 20% 11%	656
April	1st to 10th	Night	18% 9% 18% 24% 20% 9%	570
	11th to 20th	Night	18% 6% 14% 21% 29% 12%	563
	21st to end	Night	17% 6% 13% 25% 29% 11%	570
May	1st to 10th	Night	20% 7% 11% 22% 29% 11%	428
	11th to 20th	Night	23% 5% 10% 22% 30% 10%	374
	21st to end	Night	23% 5% 8% 24% 32% 9%	411
June	1st to 10th	Night	20% 7% 7% 17% 31% 18%	285
	11th to 20th	Night	17% 6% 5% 21% 38% 13%	190
	21st to end	Night	22% 2 6% 17% 34% 18%	190
July	1st to 10th	Night	26% 5% 6% 16% 29% 18%	360
	11th to 20th	Night	26% 4 6% 19% 29% 16%	368
	21st to end	Night	26% 6% 9% 15% 25% 19%	416
August	1st to 10th	Night	29% 3 9% 24% 25% 9%	378
	11th to 20th	Night	29% 4 13% 23% 22% 9%	523
	21st to end	Night	28% 5% 9% 23% 25% 10%	627
September	1st to 10th	Night	32% 7% 14% 20% 21% 6%	570
	11th to 20th	Night	32% 4 12% 19% 21% 11%	570
	21st to end	Night	28% 7% 11% 22% 22% 10%	637
October	1st to 10th	Night	31% 8% 16% 24% 17% 5%	670
	11th to 20th	Night	24% 6% 15% 24% 22% 8%	808
	21st to end	Night	25% 8% 19% 24% 18% 6%	946
November	1st to 10th	Night	24% 12% 20% 24% 16% 4	880
	11th to 20th	Night	19% 10% 26% 28% 15% 2	900
	21st to end	Night	22% 10% 22% 28% 16% 3	900
December	1st to 10th	Night	26% 9% 24% 25% 12% 3	913
	11th to 20th	Night	22% 10% 24% 28% 13% 3	1000
	21st to end	Night	23% 13% 23% 23% 15% 3	1054

Page generated at 2024-12-21 00:13:46. Version ac07

Copyright © 2024 Attilla Danko.