Icefog Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Icefog Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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	13% 10% 4 9% 7% 4 6% 6% 6% 7% 28%	74254
	Night	9% 12% 6% 10% 8% 4 6% 5% 5% 7% 28%	75584
Transparency	Day	52% 10% 17% 16% 5%	73849
	Night	54% 9% 14% 16% 7% 1	75508
Seeing	Day	15% 5% 16% 27% 26% 11%	17424
	Night	13% 4 15% 32% 28% 8%	21944

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	5% 9% 5% 11% 9% 3 6% 3 4 6% 40%	532
	11th to 20th	Day	6% 12% 8% 11% 10% 6% 6% 5% 7% 7% 25%	744
	21st to end	Day	5% 12% 7% 10% 8% 4 7% 6% 6% 8% 27%	971
February	1st to 10th	Day	3 12% 6% 10% 6% 3 4 6% 5% 4 41%	1080
	11th to 20th	Day	4 13% 6% 15% 8% 5% 6% 7% 6% 8% 23%	1319
	21st to end	Day	4 18% 7% 10% 8% 4 5% 6% 5% 6% 27%	1184
March	1st to 10th	Day	4 13% 7% 12% 8% 4 5% 5% 6% 7% 30%	1752
	11th to 20th	Day	3 10% 5% 8% 7% 4 7% 5% 6% 6% 39%	1836
	21st to end	Day	5% 9% 6% 9% 7% 4 5% 5% 6% 6% 38%	2371
April	1st to 10th	Day	6% 14% 7% 9% 7% 5% 5% 6% 6% 7% 26%	2300
	11th to 20th	Day	5% 9% 4 8% 7% 3 5% 5% 5% 7% 40%	2488
	21st to end	Day	6% 7% 3 7% 8% 5% 6% 5% 7% 7% 39%	2744
May	1st to 10th	Day	6% 10% 4 9% 9% 4 7% 7% 6% 7% 28%	2938
	11th to 20th	Day	7% 8% 3 9% 8% 4 6% 5% 6% 8% 36%	3090
	21st to end	Day	12% 8% 3 7% 7% 4 6% 7% 7% 9% 30%	3603
June	1st to 10th	Day	13% 7% 4 9% 8% 5% 7% 7% 6% 8% 27%	3541
	11th to 20th	Day	13% 8% 4 8% 7% 4 6% 6% 8% 8% 29%	3600
	21st to end	Day	16% 7% 3 6% 7% 4 6% 5% 7% 10% 29%	3600
July	1st to 10th	Day	14% 6% 3 6% 7% 5% 7% 6% 8% 8% 30%	3600
	11th to 20th	Day	21% 9% 4 8% 8% 4 6% 6% 7% 7% 20%	3320
	21st to end	Day	19% 7% 4 8% 6% 4 7% 6% 7% 8% 23%	3511
August	1st to 10th	Day	24% 10% 4 8% 7% 4 5% 6% 5% 6% 20%	2887
	11th to 20th	Day	22% 9% 3 8% 7% 4 5% 5% 7% 7% 22%	2760
	21st to end	Day	22% 11% 4 8% 7% 4 5% 6% 5% 7% 21%	2772
September	1st to 10th	Day	20% 11% 4 7% 6% 4 6% 5% 6% 7% 25%	2346
	11th to 20th	Day	22% 12% 5% 9% 7% 3 6% 5% 5% 6% 20%	2127
	21st to end	Day	19% 14% 5% 9% 7% 3 4 5% 6% 4 25%	1956
October	1st to 10th	Day	16% 17% 6% 9% 8% 4 4 5% 5% 6% 20%	1702
	11th to 20th	Day	11% 18% 6% 11% 8% 4 4 5% 5% 4 25%	1584
	21st to end	Day	11% 13% 5% 11% 8% 4 5% 5% 7% 7% 23%	1406
November	1st to 10th	Day	9% 14% 6% 12% 7% 4 5% 6% 6% 6% 25%	1150
	11th to 20th	Day	9% 11% 7% 13% 11% 5% 3 4 3 5% 28%	950
	21st to end	Day	11% 14% 5% 11% 8% 6% 4 5% 5% 5% 26%	704
December	1st to 10th	Day	13% 14% 6% 9% 5% 3 6% 5% 6% 8% 25%	570
	11th to 20th	Day	3 18% 9% 11% 10% 4 7% 4 5% 4 25%	512
	21st to end	Day	3 11% 6% 11% 7% 4 7% 7% 7% 7% 30%	704
January	1st to 10th	Night	4 10% 5% 9% 7% 3 6% 6% 6% 7% 36%	3649
	11th to 20th	Night	6% 13% 6% 10% 8% 5% 6% 5% 6% 7% 28%	3360
	21st to end	Night	5% 11% 6% 10% 9% 4 7% 6% 6% 8% 29%	3384
February	1st to 10th	Night	3 12% 6% 12% 7% 3 4 3 4 7% 40%	2880
	11th to 20th	Night	5% 12% 5% 10% 8% 5% 6% 6% 7% 8% 28%	2528
	21st to end	Night	5% 15% 9% 11% 8% 4 5% 5% 5% 7% 27%	2072
March	1st to 10th	Night	4 14% 7% 11% 8% 5% 6% 5% 4 5% 31%	2206
	11th to 20th	Night	4 9% 4 9% 7% 4 6% 5% 4 6% 42%	2122
	21st to end	Night	7% 10% 5% 7% 5% 4 6% 5% 5% 5% 41%	1983
April	1st to 10th	Night	6% 13% 6% 10% 7% 5% 6% 7% 6% 6% 28%	1657
	11th to 20th	Night	6% 7% 3 8% 8% 5% 6% 6% 6% 6% 39%	1421
	21st to end	Night	7% 8% 3 7% 7% 4 6% 5% 7% 7% 39%	1213
May	1st to 10th	Night	8% 9% 4 7% 9% 5% 7% 8% 7% 9% 28%	1022
	11th to 20th	Night	6% 6% 3 7% 7% 4 6% 7% 6% 8% 39%	803
	21st to end	Night	13% 7% 3 6% 8% 4 5% 6% 5% 10% 32%	672
June	1st to 10th	Night	9% 9% 3 7% 10% 4 7% 6% 9% 11% 24%	418
	11th to 20th	Night	12% 8% 4 8% 8% 4 7% 5% 5% 12% 26%	360
	21st to end	Night	14% 7% 1 9% 7% 3 7% 9% 8% 10% 26%	360
July	1st to 10th	Night	10% 8% 4 7% 5% 3 6% 9% 8% 11% 29%	360
	11th to 20th	Night	22% 11% 5% 6% 6% 4 5% 8% 5% 8% 20%	639
	21st to end	Night	17% 9% 4 9% 7% 4 7% 7% 6% 8% 25%	806
August	1st to 10th	Night	24% 10% 4 9% 8% 5% 6% 5% 6% 6% 18%	1051
	11th to 20th	Night	23% 10% 4 8% 7% 7% 6% 6% 5% 7% 19%	1138
	21st to end	Night	26% 9% 4 6% 8% 3 5% 6% 5% 5% 24%	1584
September	1st to 10th	Night	17% 10% 4 8% 6% 5% 6% 5% 6% 7% 26%	1613
	11th to 20th	Night	19% 12% 5% 8% 7% 5% 6% 5% 6% 6% 22%	1833
	21st to end	Night	18% 13% 4 7% 6% 4 4 6% 5% 6% 26%	2002
October	1st to 10th	Night	15% 17% 5% 9% 6% 4 5% 5% 6% 6% 20%	2258
	11th to 20th	Night	10% 14% 6% 10% 7% 3 5% 5% 5% 7% 28%	2376
	21st to end	Night	9% 15% 6% 12% 8% 4 5% 5% 5% 7% 24%	2950
November	1st to 10th	Night	10% 17% 5% 11% 7% 3 6% 5% 5% 5% 26%	2928
	11th to 20th	Night	9% 13% 7% 12% 9% 4 5% 5% 4 6% 26%	3230
	21st to end	Night	9% 13% 6% 12% 8% 4 6% 5% 6% 6% 26%	3454
December	1st to 10th	Night	9% 14% 6% 11% 7% 4 6% 5% 6% 7% 26%	3610
	11th to 20th	Night	5% 18% 8% 14% 9% 5% 6% 5% 5% 5% 19%	4679
	21st to end	Night	4 11% 6% 11% 9% 5% 6% 6% 6% 7% 29%	6963

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	46% 8% 10% 23% 10% 3	532
	11th to 20th	Day	56% 6% 15% 14% 9% 1	744
	21st to end	Day	55% 6% 13% 16% 8% 1	971
February	1st to 10th	Day	45% 6% 7% 19% 19% 4	1080
	11th to 20th	Day	57% 8% 11% 16% 8%	1326
	21st to end	Day	56% 7% 11% 15% 10% 1	1184
March	1st to 10th	Day	52% 7% 15% 16% 8% 2	1752
	11th to 20th	Day	43% 6% 9% 26% 13% 2	1836
	21st to end	Day	43% 9% 18% 14% 14% 3	2371
April	1st to 10th	Day	54% 7% 15% 17% 7% 1	2300
	11th to 20th	Day	42% 8% 16% 25% 8% 1	2488
	21st to end	Day	41% 8% 15% 27% 9%	2744
May	1st to 10th	Day	51% 8% 15% 20% 6%	2938
	11th to 20th	Day	43% 9% 13% 26% 9%	3093
	21st to end	Day	45% 9% 19% 20% 7%	3604
June	1st to 10th	Day	51% 11% 18% 17% 3	3541
	11th to 20th	Day	49% 11% 18% 19% 3	3600
	21st to end	Day	49% 12% 21% 16% 2	3600
July	1st to 10th	Day	48% 12% 22% 15% 3	3501
	11th to 20th	Day	59% 13% 17% 11%	3216
	21st to end	Day	54% 14% 22% 9%	3316
August	1st to 10th	Day	62% 11% 19% 7%	2867
	11th to 20th	Day	58% 13% 20% 9%	2760
	21st to end	Day	61% 11% 19% 8% 1	2772
September	1st to 10th	Day	57% 11% 20% 11% 1	2346
	11th to 20th	Day	62% 10% 16% 11%	2127
	21st to end	Day	61% 9% 13% 13% 3	1956
October	1st to 10th	Day	64% 9% 14% 9% 3	1702
	11th to 20th	Day	61% 9% 15% 11% 3	1584
	21st to end	Day	56% 11% 17% 14% 1	1406
November	1st to 10th	Day	57% 9% 17% 12% 5%	1150
	11th to 20th	Day	59% 8% 13% 16% 4	950
	21st to end	Day	58% 8% 12% 16% 6%	704
December	1st to 10th	Day	55% 10% 14% 14% 5% 2	570
	11th to 20th	Day	60% 7% 13% 16% 4	514
	21st to end	Day	44% 14% 15% 17% 9% 1	704
January	1st to 10th	Night	44% 9% 15% 19% 10% 3	3649
	11th to 20th	Night	53% 7% 12% 19% 8%	3360
	21st to end	Night	52% 7% 14% 17% 9% 1	3384
February	1st to 10th	Night	47% 4 8% 16% 20% 5%	2880
	11th to 20th	Night	50% 9% 13% 20% 8%	2532
	21st to end	Night	58% 6% 12% 14% 9% 1	2072
March	1st to 10th	Night	54% 6% 11% 17% 9% 3	2206
	11th to 20th	Night	43% 6% 9% 25% 14% 2	2124
	21st to end	Night	44% 8% 15% 15% 16% 2	1983
April	1st to 10th	Night	52% 9% 14% 18% 6% 1	1657
	11th to 20th	Night	42% 9% 20% 21% 7% 1	1421
	21st to end	Night	40% 6% 16% 28% 9%	1213
May	1st to 10th	Night	47% 12% 13% 23% 4	1022
	11th to 20th	Night	39% 9% 19% 24% 8%	803
	21st to end	Night	47% 10% 13% 23% 8%	672
June	1st to 10th	Night	49% 12% 18% 18% 3	418
	11th to 20th	Night	53% 11% 15% 18% 4	360
	21st to end	Night	50% 12% 21% 15% 1	360
July	1st to 10th	Night	47% 15% 22% 13% 3	350
	11th to 20th	Night	60% 12% 16% 11% 1	620
	21st to end	Night	53% 13% 22% 11%	761
August	1st to 10th	Night	65% 9% 16% 10%	1046
	11th to 20th	Night	63% 12% 14% 11%	1138
	21st to end	Night	62% 11% 17% 9% 1	1584
September	1st to 10th	Night	55% 10% 21% 12% 2	1613
	11th to 20th	Night	61% 9% 15% 14% 1	1833
	21st to end	Night	58% 10% 13% 15% 3	2002
October	1st to 10th	Night	63% 10% 15% 9% 3	2258
	11th to 20th	Night	55% 11% 19% 12% 3	2376
	21st to end	Night	59% 9% 17% 12% 3	2950
November	1st to 10th	Night	58% 8% 14% 15% 3 1	2928
	11th to 20th	Night	60% 8% 14% 15% 3	3230
	21st to end	Night	57% 9% 12% 16% 6%	3454
December	1st to 10th	Night	56% 9% 15% 14% 6% 1	3610
	11th to 20th	Night	64% 8% 11% 13% 4	4676
	21st to end	Night	48% 9% 15% 16% 11% 1	6963

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	6% 3 14% 46% 26% 6%	90
	11th to 20th	Day	7% 14% 37% 37% 5%	86
	21st to end	Day	9% 4 12% 34% 26% 15%	181
February	1st to 10th	Day	6% 7% 14% 29% 26% 18%	260
	11th to 20th	Day	8% 6% 20% 28% 26% 12%	311
	21st to end	Day	10% 7% 20% 36% 21% 7%	280
March	1st to 10th	Day	7% 3 21% 36% 24% 9%	340
	11th to 20th	Day	9% 5% 20% 31% 24% 12%	340
	21st to end	Day	9% 6% 21% 29% 27% 9%	567
April	1st to 10th	Day	10% 9% 23% 30% 22% 6%	574
	11th to 20th	Day	8% 5% 22% 27% 29% 8%	590
	21st to end	Day	7% 4 15% 33% 31% 10%	600
May	1st to 10th	Day	11% 4 19% 30% 27% 8%	603
	11th to 20th	Day	8% 7% 21% 30% 26% 8%	705
	21st to end	Day	14% 8% 16% 31% 24% 8%	978
June	1st to 10th	Day	11% 5% 17% 25% 28% 15%	990
	11th to 20th	Day	13% 4 14% 22% 32% 15%	990
	21st to end	Day	15% 3 10% 25% 32% 15%	990
July	1st to 10th	Day	14% 3 11% 25% 36% 11%	971
	11th to 20th	Day	18% 5% 13% 25% 25% 14%	856
	21st to end	Day	18% 3 12% 24% 25% 18%	863
August	1st to 10th	Day	25% 4 16% 22% 23% 10%	626
	11th to 20th	Day	23% 6% 15% 26% 23% 7%	615
	21st to end	Day	27% 6% 14% 22% 22% 10%	693
September	1st to 10th	Day	23% 7% 14% 20% 24% 12%	617
	11th to 20th	Day	27% 8% 14% 25% 17% 9%	507
	21st to end	Day	25% 8% 13% 23% 19% 13%	360
October	1st to 10th	Day	23% 9% 18% 20% 19% 11%	360
	11th to 20th	Day	16% 5% 19% 19% 28% 14%	360
	21st to end	Day	16% 5% 12% 21% 31% 16%	396
November	1st to 10th	Day	17% 5% 12% 27% 26% 13%	266
	11th to 20th	Day	11% 3 12% 29% 26% 19%	90
	21st to end	Day	17% 2 11% 29% 36% 6%	90
December	1st to 10th	Day	21% 4 16% 33% 19% 7%	90
	11th to 20th	Day	9% 6% 23% 34% 20% 8%	90
	21st to end	Day	6% 10% 18% 34% 24% 7%	99
January	1st to 10th	Night	7% 2 15% 36% 29% 12%	1102
	11th to 20th	Night	10% 4 16% 39% 25% 7%	920
	21st to end	Night	8% 3 16% 39% 26% 7%	930
February	1st to 10th	Night	6% 5% 18% 33% 28% 11%	800
	11th to 20th	Night	7% 3 17% 40% 27% 5%	784
	21st to end	Night	9% 6% 17% 40% 25% 4	658
March	1st to 10th	Night	8% 3 18% 39% 27% 3	638
	11th to 20th	Night	9% 3 16% 38% 30% 5%	604
	21st to end	Night	10% 3 18% 34% 26% 9%	594
April	1st to 10th	Night	10% 5% 19% 36% 26% 4	540
	11th to 20th	Night	8% 3 17% 37% 30% 4	533
	21st to end	Night	9% 2 12% 31% 40% 6%	493
May	1st to 10th	Night	10% 2 15% 29% 37% 7%	302
	11th to 20th	Night	6% 5% 18% 37% 33% 2	177
	21st to end	Night	16% 7% 8% 33% 30% 6%	195
June	1st to 10th	Night	11% 3 16% 24% 38% 8%	180
	11th to 20th	Night	12% 3 14% 29% 32% 9%	180
	21st to end	Night	15% 2 5% 27% 42% 9%	180
July	1st to 10th	Night	11% 3 12% 27% 41% 6%	175
	11th to 20th	Night	20% 5% 11% 26% 30% 8%	174
	21st to end	Night	19% 2 10% 27% 35% 8%	197
August	1st to 10th	Night	28% 5% 8% 21% 32% 5%	335
	11th to 20th	Night	23% 4 12% 26% 28% 6%	424
	21st to end	Night	29% 4 8% 21% 27% 11%	594
September	1st to 10th	Night	22% 4 12% 22% 30% 9%	540
	11th to 20th	Night	22% 4 14% 28% 29% 4	540
	21st to end	Night	24% 4 17% 24% 26% 5%	551
October	1st to 10th	Night	21% 7% 17% 27% 24% 4	728
	11th to 20th	Night	14% 4 16% 30% 25% 11%	810
	21st to end	Night	13% 4 11% 35% 30% 7%	891
November	1st to 10th	Night	17% 5% 15% 32% 24% 7%	830
	11th to 20th	Night	15% 3 13% 29% 28% 12%	850
	21st to end	Night	14% 2 15% 30% 28% 11%	992
December	1st to 10th	Night	13% 5% 16% 34% 23% 9%	1130
	11th to 20th	Night	11% 4 19% 30% 28% 9%	1130
	21st to end	Night	9% 5% 14% 34% 29% 10%	1243

Page generated at 2024-01-14 05:55:02. Version ac07

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